@article{garcia_kim_vinod_sahoo_wax_kim_fang_narayanaswamy_wu_jiang_2024, title={Carbon nanofibers/liquid metal composites for high temperature laser ultrasound}, volume={138}, ISSN={["1874-9968"]}, url={https://doi.org/10.1016/j.ultras.2024.107245}, DOI={10.1016/j.ultras.2024.107245}, abstractNote={As the demand for clean energy becomes greater worldwide, there will also be an increasing demand for next generation nuclear power plants that incorporate advanced sensors and monitoring equipment. A major challenge posed by nuclear power plants is that, during normal operation, the reactor compartment is subjected to high operating temperatures and radiation flux. Diagnostic sensors monitoring such structures are also subject to temperatures reaching hundreds of degrees Celsius, which puts them at risk for heat degradation. In this work, the ability of carbon nanofibers to work in conjunction with a liquid metal as a photoacoustic transmitter was demonstrated at high temperatures. Fields metal, a Bi-In-Sn eutectic, and gallium are compared as acoustic mediums. Fields metal was shown experimentally to have superior performance over gallium and other reference cases. Under stimulation from a low fluence 6 ns pulse laser at 6 mJ/cm2 with 532 nm green light, the Fields metal transducer transmitted a 200 kHz longitudinal wave with amplitude >5.5 times that generated by a gallium transducer at 300 °C. Each high temperature test was conducted from a hot to cold progression, beginning as high as 300 °C, and then cooling down to 100 °C. Each test shows increasing signal amplitude of the liquid metal transducers as temperature decreases. Carbon nanofibers show a strong improvement over previously used candle-soot nanoparticles in both their ability to produce strong acoustic signals and absorb higher laser fluences up to 12 mJ/cm2.}, journal={ULTRASONICS}, author={Garcia, Nicholas and Kim, Howuk and Vinod, Kaushik and Sahoo, Abinash and Wax, Michael and Kim, Taeyang and Fang, Tiegang and Narayanaswamy, Venkat and Wu, Huaiyu and Jiang, Xiaoning}, year={2024}, month={Mar} }
 @article{varigonda_serafim_freydin_dowell_narayanaswamy_2024, title={Two-dimensional pressure field imaging of an elastic panel executing post-flutter oscillations}, volume={125}, ISSN={["1095-8622"]}, DOI={10.1016/j.jfluidstructs.2023.104056}, abstractNote={Two dimensional pressure field was acquired at 10 kHz to study the post flutter oscillations of a thin elastic panel placed beneath a Mach 2.5 turbulent boundary layer. The panel was made of aluminum and is secured to the mounting fixture using a collection of rivets, which resulted in a boundary condition that was between both ideally clamped and pinned boundaries. Direct comparison of the mean and unsteady pressure fields were made for the panel executing post flutter oscillations and oscillations away from the flutter boundary. Whereas the mean pressure fields were largely similar during and away from post-flutter oscillations, the unsteady pressure fields showed a significant increase in the pr.m.s. during post flutter oscillations. The spectral content of the pressure oscillations and panel oscillations revealed that the tonal aeroelastic frequency dominate the post flutter oscillations. This tonal frequency was determined to lie at the close vicinity of the (2,1) panel elastic mode. The r.m.s. panel deflection field during post flutter oscillations were also reconstructed from the unsteady pressure fields and the reconstructed panel deflection also corresponded to the (2,1) elastic mode.Further coherence and cross-correlation analyses provided insights into possible mechanisms that control the transition of the panel oscillations away from the flutter boundary. The analyses suggest that the transition away from the flutter boundary is possibly initiated by the decoherence of the organized pressure field during the post flutter region by the turbulent boundary layer.}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, author={Varigonda, Santosh V. and Serafim, Luisa P. and Freydin, Maxim and Dowell, Earl. H. and Narayanaswamy, Venkateswaran}, year={2024}, month={Mar} }
 @article{walz_narayanaswamy_2023, title={Dual separation control and drag mitigation in high speed flows using viscoelastic materials}, volume={35}, url={http://dx.doi.org/10.1063/5.0141572}, DOI={10.1063/5.0141572}, abstractNote={Boundary layer separation and friction drag form key delimiting phenomena that subvert the aerial platforms from achieving greater efficiency and accessing wider operation envelope. Both these phenomena are significantly aggravated in supersonic platforms due to the interactions between shock waves with the boundary layer that develops over the vehicle surface and within the engines. The present work demonstrates a new paradigm that leverages the native or programmable material properties of the aerostructures to engender simultaneous reduction in the separation scales and mitigation of skin friction drag. As a first step toward realizing this paradigm, the present work demonstrates, for the first time, the simultaneous skin friction drag mitigation in a Mach 2.5 boundary layer and control of shock induced boundary layer separation, both using viscoelastic implants placed under the flow. It is experimentally demonstrated that the appropriately chosen viscoelastic materials can simultaneously reduce the skin friction coefficient at the measurement location by 11% and mitigate the size of a large-scale separated flow by up to 28%. The reported performance matches the current generation flow effectors in both separation scale and skin friction mitigation. The present study opens a new application space for soft/programmable materials in high speed aerial vehicles.}, number={3}, journal={Physics of Fluids}, publisher={AIP Publishing}, author={Walz, James and Narayanaswamy, Venkat}, year={2023}, month={Mar}, pages={031704} }
 @article{varigonda_narayanaswamy_2023, title={Fluid structure interactions generated by an oblique shock impinging on a thin elastic panel}, volume={119}, ISSN={["1095-8622"]}, url={http://dx.doi.org/10.1016/j.jfluidstructs.2023.103890}, DOI={10.1016/j.jfluidstructs.2023.103890}, abstractNote={The flow structure coupling generated by an impinging shock boundary layer interactions (SBLI) flowfield over a rectangular panel is investigated. The impinging oblique shock is generated by an 8° shock generator placed incident to a Mach 2.5 flow. The shock strength is large enough to generate a mean separation that is nearly two-dimensional over the panel span. The panel is configured such that the panel oscillation amplitude is much smaller than the panel and incoming boundary layer thicknesses. This resulted in a weak coupling between the flowfield and structural response, and forms a relatively simpler configuration to study. Two multivariate measurement campaigns are performed to capture the mean and dynamic flowfield and panel response. The first campaign simultaneously measures the 2D panel surface pressure field, panel center-span deflection, and off-body velocity field at 10 Hz. The second campaign measures simultaneously the 2D panel surface pressure field and panel strain at two mid-span locations at 10 kHz. The acquisition rate is sufficient to resolve at least the first seven panel elastic models. These measurements provide comprehensive information about the fluid structure interaction (FSI) phenomenon from both aerodynamics and structural dynamics perspectives. Summarily, with the weak flow/structure interactions implemented in this study, there is no change in the mean separation size. However, the pressure fluctuations beneath the SBLI unit exhibit discrete elevations in the vicinity of different panel resonance mode frequencies. The greatest elevation pressure PSD occurs at the panel modes that overlaps with the separation bubble pulsation frequency band. Detailed coherence maps at and away from panel elastic modes and conditional statistics reveal critical insights into the mechanisms that cause the strengthening of the pressure fluctuations due to flow/structure coupling. It was found that the acoustic forcing by the cavity resonance has an important contribution to the dynamics of the surface pressure and panel oscillations.}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, publisher={Elsevier BV}, author={Varigonda, S. V. and Narayanaswamy, V.}, year={2023}, month={May} }
 @article{jenquin_johnson_narayanaswamy_2023, title={Investigations of shock-boundary layer interaction dynamics using high-bandwidth pressure field imaging}, volume={961}, ISSN={["1469-7645"]}, url={http://dx.doi.org/10.1017/jfm.2023.168}, DOI={10.1017/jfm.2023.168}, abstractNote={The large-scale pulsations of shock-induced separation with length scale that significantly exceeds the incoming boundary layer thickness are investigated. The shock–boundary layer interaction (SBLI) unit is generated by an inward-turning axisymmetric compression ramp at an inflow Mach number of 2.5. A substantial region surrounding the centre azimuth exhibited mean and dynamic flow features that are consistent with two-dimensional separation. Two-dimensional highly resolved maps of surface pressure field are obtained using fast-response pressure-sensitive paint fluorescence imaging at 40 kHz repetition rate. The measurement domain covered significant regions of the incoming boundary layer through the relaxing boundary layer downstream of the reattachment as well as over 25 boundary layer thicknesses in the azimuthal direction. These measurements provide new insights into the spanwise coupling of the SBLI unit in addition to its inherent dynamics. The power spectral density (PSD) of the centreline pressure exhibits very good agreement with theoretical models and complementary measurements using fast-response pressure transducers, which served to validate the pressure field measurements. Detailed examination of the PSD reveals strong agreement with the literature, which includes the peak Strouhal number of the separation and reattachment shock motions as well as the downward frequency shift along the separation bubble. Furthermore, the pressure fluctuation maps reveal streamwise-elongated structures just downstream of the ramp leading edge that persist well downstream of the reattachment. A time sequence of conditional average pressure fluctuation maps is constructed surrounding isolated pressure excursions in the intermittent region. This sequence, along with two-point cross correlation analysis, provides critical information about the flow processes that drive the separation bubble pulsations in the SBLI units with large separation scales. Overall, the imbalance in the mass within the separation bubble appears to be the critical mechanism that drives the separation bubble pulsations. Furthermore, the pressure perturbations originating at azimuthally offset locations are also observed to influence the separation bubble dynamics.}, journal={JOURNAL OF FLUID MECHANICS}, publisher={Cambridge University Press (CUP)}, author={Jenquin, Chase and Johnson, Ethan C. and Narayanaswamy, Venkat}, year={2023}, month={Apr} }
 @article{sahoo_narayanaswamy_lyons_2023, title={Quenching measurements of Kr 5p[3/2](2) <- <- 4p(61)S(0) electronic transition using absorption spectra}, volume={62}, ISSN={["2155-3165"]}, url={http://dx.doi.org/10.1364/ao.475382}, DOI={10.1364/AO.475382}, abstractNote={Quenching rate is an important parameter to include in fluorescence
					measurements that are aimed at quantifying the thermochemical field of
					a reacting flow. Traditionally, the quenching measurements were
					obtained at low pressures using the direct measurements of quenching
					times followed by a linear scaling to the desired pressure. This
					approach, however, cannot account for the possible deviation from the
					linear pressure scaling at elevated pressures due to three and
					multi-body collisions. Furthermore, the best accuracy on the quenching
					rate is obtained with ultra-short pulse lasers that are typically not
					readily available. This study offsets these limitations by
					demonstrating a new approach for making direct quenching measurements
					at atmospheric conditions and using nanosecond lasers. The quenching
					measurements are demonstrated in a krypton-perturber system, and the 
      
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     two-photon electronic transition is
					accessed. A theoretical construct is presented that relates the
					absorption spectral parameters and the integrated fluorescence signal
					to the quenching rate, referenced to a given species and conditions.
					Using this formulation, the relative quenching rates for different
					perturber species, namely, air, 
      
	
	  
	    
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    , are reported as measured at 1 atm
					and 300 K. As such, the present technique is limited to the
					measurement of the relative quenching rate, unlike the previous
					studies where absolute quenching rates are measured. Nonetheless, when
					the reference quenching rate is independently measured, the relative
					quenching rates can be converted to absolute values.}, number={6}, journal={APPLIED OPTICS}, publisher={Optica Publishing Group}, author={Sahoo, Abinash and Narayanaswamy, Venkateswaran and Lyons, Kevin M.}, year={2023}, month={Feb}, pages={110–117} }
 @inproceedings{jenquin_johnson_narayanaswamy_2022, title={Effects of Pressure Sensitive Paint on the Dynamics of Half-Inlet Shock Dynamics}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85122673493&partnerID=MN8TOARS}, DOI={10.2514/6.2022-0068}, abstractNote={This study examined the pressure dynamics within the shock boundary layer interaction (SBLI) region of a steel half-isolator model. The steel model featured a 3D-printed microramp vortex generator (VG) and a compression ramp mounted on the steel half-isolator. The trailing edge of the VG was placed 50mm upstream of the compression ramp's leading edge. On top of this model, both thick and thin coats of homebrew, fast-response pressure sensitive paint (PSP) was applied. The fast-response PSP, imaged at 40kHz, allowed pressure fluctuations to be seen as the boundary layer interacted with the shock structure and with the high-momentum flow from the VG. Using a profilometry analysis, the height of the paint off the model was able to be quantified. The pressure data from the PSP was analyzed around the area of the SBLI, giving insight into how the thickness of the PSP affected the pressure dynamics in the SBLI region. The root mean square results indicate that the thickness of the paint serves to change the location of the shock impingement on the boundary layer.}, booktitle={AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022}, author={Jenquin, C. and Johnson, E. and Narayanaswamy, V.}, year={2022}, pages={1–13} }
 @article{johnson_jenquin_mccready_narayanaswamy_edwards_2022, title={Experimental Investigations of the Hypersonic Stream-Traced Performance Inlet at Subdesign Mach Number}, volume={61}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144482289&partnerID=MN8TOARS}, DOI={10.2514/1.J062113}, abstractNote={ Stream-traced inlets offer superior compression efficiency for scramjet engines and are strong prospects for practical application. However, only limited experimental information is available on the subdesign performance of these inlets. In this study, the operation of a stream-traced truncated-Busemann inlet with a design point of Mach 5.5 and a physical contraction ratio of [Formula: see text] is experimentally investigated in a Mach 4.0 flow. Several nonintrusive flow measurement techniques are employed to provide a thorough understanding of the intricate flowfield within these inlets at various operation conditions. The measurements include surface pressure, mean streak-line patterns, off-body velocity fields, and qualitative gas density fields. Together, these datasets provided a unique understanding of the flow evolution and load distribution within the inlet and isolator with and without application of an external backpressure. The facility effects on the inlet operation are also explored. Without appropriate boundary-layer conditioning, the wind-tunnel starting shock could not be swallowed by the inlet; this is termed a “failed start” operation. During the failed start operation the inlet flowfield and surface pressure field, even without external backpressure, exhibited strong similarities with an unstarted inlet. The failed start operation enabled a unique lens to the flowfield in the unstarted inlet throat that could not be otherwise obtained due to optical constraints. }, number={1}, journal={AIAA JOURNAL}, author={Johnson, Ethan and Jenquin, Chase and McCready, Jonathan and Narayanaswamy, Venkat and Edwards, Jack}, year={2022}, month={Sep} }
 @inproceedings{johnson_jenquin_narayanaswamy_2022, title={Experimental Studies of Unstart Shock Dynamics within a Streamtraced Scramjet Inlet}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135380742&partnerID=MN8TOARS}, DOI={10.2514/6.2022-3478}, abstractNote={Streamtraced inlets offer unparalleled inlet efficiencies for hypersonic air breathing propulsion engines, but experimentally investigating these complex three-dimensional compression systems has proven to be a challenging task. Traditional pressure transducers can be difficult to mount to perfectly contoured geometries and simply cannot provide a holistic understanding of the three-dimensional flow field produced by these inlets. This effort address these concerns by implementing a sprayable dynamic pressure-sensitive paint to select interior regions of a streamtraced inlet. The use of this paint allows for a more complete understanding of the flow evolution within the scramjet inlet by producing time-accurate surface pressure fields at the painted areas. For this experimental study, this paint is used to examine the shock dynamics within a started inlet and during inlet unstart. Power spectral density analyses of the attached boundary layers within the isolator of the started inlet reveal energies that agree strongly with those measured within two-dimensional inlet/isolators, while cross-coherence studies of the unstarted inlet reveal a strong linear coupling between the separated inflow at the intake and the flow entrained within the isolator.}, booktitle={AIAA AVIATION 2022 Forum}, author={Johnson, E. and Jenquin, C. and Narayanaswamy, V.}, year={2022} }
 @article{narayanaswamy_varigonda_2022, title={Fluid Structure Interactions Generated by an Oblique Shock Impinging on a Thin Elastic Panel}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85145488659&partnerID=MN8TOARS}, journal={SSRN}, author={Narayanaswamy, V. and Varigonda, S.V.}, year={2022} }
 @inproceedings{walz_narayanaswamy_2022, title={Investigations of Shock Boundary Layer Interactions Over a Soft Material for Separated Control}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85122765351&partnerID=MN8TOARS}, DOI={10.2514/6.2022-0605}, abstractNote={Integration of novel materials to high speed platforms holds the key to widening the vehicle operating envelope as well as enhancing their efficiency. Supersonic inlets can particularly benefit from new materials that can both help sustain a stable shock train during sub-design Mach number operation as well as not consume significant acreage that are seldom available in these sub-systems. This work explores the application of soft materials for the purpose of separation control within an inlet at sub-design operation. A rectangular channel that was open from the top (called half-inlet in this work) allowed for the boundary layers to develop along the walls and junctures, as is the case with planar inlets. A compression ramp placed at the aft end of the half-inlet generated a shock induced separation, which is a primary delimiter of the inlet performance. The half-inlet was placed in a Mach 2.5 inflow and two compression ramps, 20º and 24º, provided two different separation strengths for a parametric investigation. The material of choice was a polyurethane rubber that was embedded on the half-inlet floor over which the shock induced separation was introduced. Two different shore hardnesses (20A and 60A) were chosen for this exploration and the thickness of the rubber implant was fixed at 4 mm. The resulting separated flow was measured using a variety of data acquisition techniques that include surface streakline visualization, pressure-sensitive paint (PSP), and particle image velocimetry (PIV). Comparisons were made between the half-inlets without and with the rubber implant to quantify the separation response. The underlying mechanisms that cause the observed modifications to the separated flow is also discussed.}, booktitle={AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022}, author={Walz, J. and Narayanaswamy, V.}, year={2022} }
 @inproceedings{deboskey_kessler_johnson_bojko_sahoo_narayanaswamy_lyons_2022, title={Investigations of the Transition Between Conventional and Distributed Regime in Turbulent Jet Flames}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85123613832&partnerID=MN8TOARS}, DOI={10.2514/6.2022-2089}, abstractNote={Turbulent combustion of jet flames in a vitiated coflow was investigated across a range of jet Reynolds numbers. The studies revealed a transition from conventional autoignition combustion to a regime of moderate or intense low-oxygen dilution (MILD) combustion, which is commonly characterized by a nearly invisible flame. Typically, MILD combustion is achieved under conditions where the oxidizer has a high temperature and low oxygen content. Although substantial literature is available on conventional and MILD combustion, the boundaries of transition between the two regimes and the underlying driving mechanisms remain largely unknown. At North Carolina State University (NCSU), experimental investigations were performed in their Jet In Vitiated Co Flow Burner (JIVCFB) to explore the transition between conventional autoignition combustion and fully MILD flames. The Naval Research Laboratory (NRL) is performing accompanying simulations of these MILD experiments with their in-house JENRE® Multiphysics Framework. The experimental work primarily uses CH* chemiluminescence to image fully MILD methane flames in the NCSU JIVCFB. Due to the underlying complexity of MILD combustion, a series of counterflow flame cases were performed at various experimental conditions to better understand the link between kinetics, mixing, and strain at the transitional MILD conditions. These calculations were first performed in a series of premixed and non-premixed flames available in the literature to ensure the accuracy of the kinetics models. With the adequate evaluation of the accuracy of the models, they are employed to predict the species distribution of the NCSU’s MILD flame setting. The initial set of calculations provided in this work primarily focused on laminar strained flame calculations. Subsequently, preliminary modeling aimed to capture the fine fluid dynamic scales is presented to capture some of the fluid dynamic structures seen in experiments.}, booktitle={AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022}, author={Deboskey, R. and Kessler, D. and Johnson, R.F. and Bojko, B. and Sahoo, A. and Narayanaswamy, V. and Lyons, K.M.}, year={2022} }
 @inproceedings{johnson_jenquin_mccready_narayanaswamy_edwards_2022, title={Mach 4 Performance of a Hypersonic Streamtraced Inlet Part 1: Experimental Investigations}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85122760827&partnerID=MN8TOARS}, DOI={10.2514/6.2022-0065}, abstractNote={Streamtraced inlets offer unparalleled efficiencies for scramjet engines, but limited experimental information is available on the sub-design performance of these inlets. In this study, the operation of a streamtraced half-Busemann inlet with a design point of Mach 5.5 and a contraction ratio of 3:1 is experimentally studied in a Mach 4.0 flow. Several non-intrusive flow measurement techniques are employed to provide a thorough understanding of the intricate flow field within these inlets at various operation conditions. These include the surface pressure and mean streakline patterns as well as off body velocity fields as well as semi-quantitative fields. Together, these datasets provided a unique understanding of the flow evolution and load distribution within the inlet at various operational phases that include tare condition without back pressuring as well as back pressure operation until unstart. The facility effects on the inlet operation is also explored where it was found that without boundary layer conditioning the wind tunnel starting shock could not be swallowed by the inlet. However, this "fails to start” operation enabled a unique lens to the flowfield in the unstarted inlet throat that was not possible with back pressure due to optical access restraints.}, booktitle={AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022}, author={Johnson, E. and Jenquin, C. and McCready, J. and Narayanaswamy, V. and Edwards, J.}, year={2022} }
 @inproceedings{mccready_hoppe_johnson_edwards_narayanaswamy_2022, title={Mach 4 Performance of a Hypersonic Streamtraced Inlet – Part 2: Computational Results}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85122577117&partnerID=MN8TOARS}, DOI={10.2514/6.2022-0066}, abstractNote={Reynolds-averaged Navier-Stokes simulations (RANS) at Mach 4 operation of a design Mach 5.5 inward-turning, streamtraced inlet tested in NCSU’s supersonic wind tunnel are presented. Computational predictions for an inlet geometry with squared-off leading edges indicate that the inlet unstarts, in accord with experimental observations. Comparisons between solutions obtained using an immersed-boundary (IB) method and those obtained on unstructured, body-fitted grids show small differences, but overall, the predictive capability of the IB approach is on par with conventional CFD methods. Simulations of a model with half-rounded leading edges show a started solution if a free-stream initialization is used but indicate that the inlet fails to start if the effects of the blowdown process in NCSU’s wind tunnel are modeled. Without boundary layer control, the experimental inlet model fails to start for all geometries tested. Comparisons with available PIV, planar laser scattering, and wall-pressure measurements indicate that the RANS approach based on Menter BSL and SST turbulence models adequately captures the structure of the streamtraced inlet flow fields under started and unstarted conditions.}, booktitle={AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022}, author={McCready, J.T. and Hoppe, C.A. and Johnson, E.C. and Edwards, J.R. and Narayanaswamy, V.}, year={2022} }
 @article{sahoo_ramachandran_narayanaswamy_lyons_2022, title={Mixture fraction measurement in turbulent non-premixed MILD jet flame using Rayleigh scattering}, volume={61}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127193360&partnerID=MN8TOARS}, DOI={10.1364/AO.444109}, abstractNote={Turbulent combustion of jet flames in a hot diluted coflow of
					combustion products is conducive to the transition from conventional
					flamelet combustion to a regime of moderate or intense low oxygen
					dilution (MILD) combustion, which is commonly characterized by a very
					low emission and noise. MILD combustion is also characterized by
					distributed combustion where the net heat release is positive across
					the entire combustion domain. The turbulence/chemistry interactions in
					this regime that determine the flame structure, local temperature, and
					species distribution critically depend on the mixture fraction and
					scalar dissipation fields. However, there are no experimental tools to
					measure the mixture fraction field in a distributed (MILD) combustion
					regime. The present work offsets this limitation by demonstrating a
					Rayleigh scattering-based approach to measure mixture fraction in a
					turbulent ethylene MILD combustion zone. 1D counterflow flame
					simulations enabled mapping the locally calibrated Rayleigh scattering
					fields to mixture fractions in the fuel-rich regions. This approach
					also shows very low sensitivity to the local temperature and
					composition. Overall, the results provide compelling evidence that the
					distributed heat release does not significantly impact the turbulent
					processes of the flow-field for the conditions examined. The
					measurement uncertainty from this approach and its extension to more
					complex fuels are also discussed. The present technique is limited to
					mildly turbulent, fully MILD/distributed flame with representative
					scalar dissipation rates.}, number={9}, journal={Applied Optics}, author={Sahoo, Abinash and Ramachandran, Aravind and Narayanaswamy, Venkateswaran and Lyons, Kevin M.}, year={2022}, pages={2338–2351} }
 @inproceedings{acharya_hartman_narayanaswamy_2022, title={Multi-fidelity Reduced-Dimensional Modeling for Shock-fin Interaction}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135379771&partnerID=MN8TOARS}, DOI={10.2514/6.2022-3479}, abstractNote={Development of reduced-dimensional and reduced-order model simplifies a high-dimensional system by reducing the degrees of freedom, keeping only those that are important to model the nonlinear, multi-scale phenomena of interest. The research presented in this paper show a methodology for developing a reduced-dimensional and reduced-order model from a set of high-fidelity experimental data by a combination of unsupervised clustering methods and semi-supervised polynomial regression methods. The reduced-order model developed by this method is utilized to predict the pressure field for shock-boundary layer interaction phenomena occurring during the interaction of supersonic freestream flow over a cylinder with the double-fins mounted on the cylinder. Selections of certain regions of flow can be made to characterize how well the clustering algorithm reduces the order of the original data, while still capturing the most relevant physics. Statistical analysis of the training data enables uncertainty estimations of the reduced-order model developed in this work. Future work on this topic will include validation of the model as well as application for supersonic jet and fin interactions.}, booktitle={AIAA AVIATION 2022 Forum}, author={Acharya, R. and Hartman, K. and Narayanaswamy, V.}, year={2022} }
 @article{freydin_dowell_varigonda_narayanaswamy_2022, title={Response of a plate with piezoelectric elements to turbulent pressure fluctuation in supersonic flow}, volume={114}, ISSN={["1095-8622"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135818767&partnerID=MN8TOARS}, DOI={10.1016/j.jfluidstructs.2022.103696}, abstractNote={The aeroelastic response of a plate with supersonic freestream flow on one side and a shallow cavity on the other to turbulent pressure fluctuations is investigated computationally and experimentally. An empirical model is developed for the pressure fluctuations in a turbulent boundary layer that accounts for spatial and spectral variations in the pressure field. Supersonic wind tunnel tests were conducted in a Mach 2.5 flow with and without an impinging shock at the plate surface. In both cases the boundary layer was turbulent. The impinging shock creates shock-wave boundary-layer interaction, which alters the characteristics of the pressure fluctuations. Pressure-sensitive paint was used to measure the unsteady pressure on the surface of a rigid plate and characterize the pressure field (local mean, rms, and the spatial coherence length) and piezoelectric patches were used as sensors to measure the response of an elastic plate. The extracted pressure parameters were used to simulate the fluid–structure response and correlate with experiments. The computed pressure perturbation due to plate motion is found to be small relative to the natural pressure fluctuation for the fluid/structural configuration studied. Computed and measured power spectra of the piezoelectric element voltage show good agreement over a wide range of structural natural frequencies. Aeroelastic response sensitivity to pressure fluctuation coherence length was also investigated computationally. It is found that with small fluid elements, which represent small-scale uncorrelated noise, the structural response is relatively small because the excitation is filtered by the plate dynamics. Experimental results suggest that the effective excitation spatial scale is on the order of the boundary layer thickness.}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, author={Freydin, Maxim and Dowell, Earl H. and Varigonda, Santosh Vaibhav and Narayanaswamy, Venkateswaran}, year={2022}, month={Oct} }
 @inproceedings{sahoo_deboskey_narayanaswamy_lyons_2021, title={2D Velocity Field Measurement of Conventional and Distributed Regime Turbulent Jet Flame using Particle Image Velocimetry}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85126766360&partnerID=MN8TOARS}, DOI={10.2514/6.2021-3626}, booktitle={AIAA Propulsion and Energy Forum, 2021}, author={Sahoo, A. and Deboskey, R. and Narayanaswamy, V. and Lyons, K.}, year={2021} }
 @inproceedings{peltier_rice_johnson_narayanaswamy_sellers_2021, title={Effects of three-dimensional pressure gradients on high-speed turbulent boundary layers}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85100309661&partnerID=MN8TOARS}, booktitle={AIAA Scitech 2021 Forum}, author={Peltier, S.J. and Rice, B.E. and Johnson, E. and Narayanaswamy, V. and Sellers, M.E.}, year={2021}, pages={1–15} }
 @inproceedings{boles_thomas_salazar_edwards_narayanaswamy_mccready_2021, title={Flow distortion computational modeling and design optimization for supersonic inlet}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85100313851&partnerID=MN8TOARS}, booktitle={AIAA Scitech 2021 Forum}, author={Boles, J. and Thomas, C. and Salazar, G. and Edwards, J. and Narayanaswamy, V. and McCready, J.}, year={2021}, pages={1–21} }
 @inproceedings{varigonda_jenquin_narayanaswamy_2021, title={Impact of Panel Vibrations on the Dynamic Field Properties in Supersonic ow}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85123884035&partnerID=MN8TOARS}, DOI={10.2514/6.2021-2926}, abstractNote={Following the investigations into the FSI of a thin compliant plate in supersonic flows in our earlier efforts, the behavior of the dynamic surface quantities are presented in this work. This paper studies the variation in the power spectral densities (PSDs) of the surface pressure and panel deflection strains impacted by the flow/structure coupling between a panel executing small amplitude vibrations subjected to an incoming supersonic flow. Parameters explored to study the variation in the dynamic quantities include the flow Mach number, dynamic pressure, introduction of a shock wave boundary layer-interaction (SBLI), and forcing the panel vibrations at different frequencies. As an important feature of this paper, a synchronous measurement of panel surface pressure and displacement strains are presented. Together, they help understand the dynamic flow response to the vibrating structure and the panel's response to the unsteady and turbulent flow. Platinum based fast response pressure sensitive paints (PSPs) were used to measure the surface pressure over the panel at 10 kHz. Simultaneously, piezoelectric sensors placed at key locations, were used to measure displacement strains. These piezoelectric sensors were also employed to force the panel vibrations at different frequencies in a separate experimental campaign.}, booktitle={AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2021}, author={Varigonda, S.V. and Jenquin, C. and Narayanaswamy, V.}, year={2021} }
 @article{leonard_narayanaswamy_2021, title={Investigation of shock dynamics in an axisymmetric inlet/isolator with attached boundary layers}, volume={908}, ISSN={["1469-7645"]}, url={https://doi.org/10.1017/jfm.2020.899}, DOI={10.1017/jfm.2020.899}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Leonard, Michael D. and Narayanaswamy, V.}, year={2021}, month={Feb} }
 @article{varigonda_narayanaswamy_2021, title={Methodology to image the panel surface pressure power spectra in weakly coupled fluid/structure interactions}, volume={62}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85117895242&partnerID=MN8TOARS}, DOI={10.1007/s00348-021-03314-4}, number={11}, journal={EXPERIMENTS IN FLUIDS}, author={Varigonda, S. V. and Narayanaswamy, V.}, year={2021}, month={Nov} }
 @article{freydin_levin_dowell_varigonda_narayanaswamy_2021, title={Natural Frequencies of a Heated Plate: Theory and Experiment (Sept, 10.2514/1.J059660, 2020)}, volume={59}, ISSN={["1533-385X"]}, DOI={10.2514/1.J059660.c1}, abstractNote={Free AccessArticle UpdatesCorrection: Natural Frequencies of a Heated Plate: Theory and ExperimentCorrections for this articleNatural Frequencies of a Heated Plate: Theory and ExperimentMaxim Freydin, Dani Levin, Earl H. Dowell, Santosh Vaibhav Varigonda and Venkateswaran NarayanaswamyMaxim Freydin https://orcid.org/0000-0001-5146-0216 Duke University, Durham, North Carolina 27708Search for more papers by this author, Dani Levin Duke University, Durham, North Carolina 27708Search for more papers by this author, Earl H. Dowell Duke University, Durham, North Carolina 27708Search for more papers by this author, Santosh Vaibhav Varigonda North Carolina State University, Raleigh, North Carolina 27695Search for more papers by this author and Venkateswaran Narayanaswamy North Carolina State University, Raleigh, North Carolina 27695Search for more papers by this authorPublished Online:7 May 2021https://doi.org/10.2514/1.J059660.c1SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail AboutCorrection NoticeThis correction pertains to the numerical values of the non-dimensional in-plane edge stiffness presented in the results section in the original article when it was first published online [https://doi.org/10.2514/1.J059660]. The error originates in an erroneous mathematical definition made in a separate paper [6] in which the structural plate model with elastic in-plane boundaries was derived. The error resulted in a respective error in the numerical code. The effect of that error on the results in this article is that all numerical values of the non-dimensional in-plane edge stiffness stated throughout the paper need to be multiplied by a factor of two. For example, the calibrated non-dimensional in-plane edge stiffness in Section IV was found to be 0.5, which means the correct value is 1. Specific affected figures are Fig. 5, 6, and 7. References [6] Freydin M., Dowell E. H. and , “Nonlinear Theoretical Aeroelastic Model of a Plate: Free to Fixed In-Plane Boundaries,” AIAA Journal, Vol. 59, No. 2, 2021. https://doi.org/10.2514/1.J059551 Google Scholar Previous article FiguresReferencesRelatedDetailsRelated articlesNatural Frequencies of a Heated Plate: Theory and Experiment2 Sep 2020AIAA Journal What's Popular Volume 59, Number 6June 2021 Crossmark TopicsContinuum MechanicsMaterials and Structural MechanicsSolid MechanicsStructural Mechanics KeywordsPlate TheoryPDF Received16 April 2021Accepted16 April 2021Published online7 May 2021}, number={6}, journal={AIAA JOURNAL}, author={Freydin, Maxim and Levin, Dani and Dowell, Earl H. and Varigonda, Santosh Vaibhav and Narayanaswamy, Venkateswaran}, year={2021}, month={May}, pages={AU2–AU2} }
 @inproceedings{anand bharadwaj_baskaran_ghosh_narayanaswamy_2021, title={Numerical investigation of passive flow control using permeable and wavy walls in oblique shock-wave/boundary-layer interaction}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85100304482&partnerID=MN8TOARS}, booktitle={AIAA Scitech 2021 Forum}, author={Anand Bharadwaj, S. and Baskaran, S.P. and Ghosh, S. and Narayanaswamy, V.}, year={2021}, pages={1–14} }
 @inproceedings{pickles_balachandra_mettu_subbareddy_narayanaswamy_vasile_despirito_2020, title={Computational modeling of fin induced shock wave/turbulent boundary layer interactions over an axisymmetric surface}, volume={1 PartF}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85091933493&partnerID=MN8TOARS}, DOI={10.2514/6.2020-1332}, booktitle={AIAA Scitech 2020 Forum}, author={Pickles, J.D. and Balachandra and Mettu, R. and Subbareddy, P.K. and Narayanaswamy, V. and Vasile, J.D. and Despirito, J.}, year={2020}, pages={1–13} }
 @article{pickles_narayanaswamy_2020, title={Control of Fin Shock Induced Flow Separation Using Vortex Generators}, volume={58}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85095110597&partnerID=MN8TOARS}, DOI={10.2514/1.J059624}, abstractNote={This work demonstrates the control of the shock-induced separated flow generated by a sharp fin placed on a cylindrical surface (fin-on-cylinder shock-wave/boundary-layer interaction) with an incid...}, number={11}, journal={AIAA JOURNAL}, author={Pickles, Joshua D. and Narayanaswamy, Venkateswaran}, year={2020}, month={Nov}, pages={4794–4806} }
 @article{sahoo_zelenak_narayanaswamy_2020, title={Erratum: Temperature dependence of collisional broadening and shift for the Kr 4p6S10 → 5p[3/2]2 electronic transition (Applied Optics (2020) 59 (1438–1446) DOI: 10.1364/AO.380102)}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082706874&partnerID=MN8TOARS}, DOI={10.1364/AO.390320}, abstractNote={This publisher’s note corrects the author listing in Appl. Opt.
					59, 1438 (2020)APOPAI0003-693510.1364/AO.380102.}, number={7}, journal={Applied Optics}, author={Sahoo, A. and Zelenak, D. and Narayanaswamy, V.}, year={2020}, pages={2085} }
 @article{pickles_narayanaswamy_2020, title={Investigation of Surface Curvature Effects on Unseparated Fin Shock-Wave/Boundary-Layer Interactions}, volume={58}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85081178443&partnerID=MN8TOARS}, DOI={10.2514/1.J058596}, abstractNote={The effect of three-dimensional (3-D) relief from surface curvature on a shock/boundary-layer interaction (SBLI) is investigated by mounting a sharp fin on a cylindrical surface. The test article c...}, number={2}, journal={AIAA JOURNAL}, author={Pickles, Joshua D. and Narayanaswamy, Venkateswaran}, year={2020}, month={Feb}, pages={770–778} }
 @inproceedings{varigonda_narayanaswamy_boxx_2020, title={Investigations of fsi generated by an impinging sbli on a thin panel using multivariate imaging of flow/structural properties}, volume={1 PartF}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092787745&partnerID=MN8TOARS}, DOI={10.2514/6.2020-3001}, abstractNote={This work presents the "first response" of an impinging shock boundary layer interactions (SBLI) flowfield to a thin panel executing small amplitude elastic oscillations (oscillation amplitude much smaller than the incoming boundary layer thickness), which provide crucial understanding of the genesis of the macro-scale flow response with larger amplitude vibrations and ultimately to feedback coupling between flow and structures. The oblique shock was generated by an 8 degree wedge placed incident to a Mach 2.5 flow. The shock strength was large enough to generate a mean separation which was nearly two-dimensional over the panel span. As a critical component of this research, the first ever simultaneous multivariate measurements of panel surface pressure, panel center-span deflection, and off-body velocity field are also presented. Together, these measurements provide comprehensive information on the FSI phenomenon from both aerodynamics and structural dynamics perspectives. Summarily, at the low amplitude panel vibrations, there is no change in the mean separation size, which was confirmed by multiple measurements. Interestingly, the separation shock oscillations appear to pick up some of the panel resonance modes frequencies. Detailed cross-coherence maps at and away from panel modes as well as conditional maps of panel surface pressure reveal further information about how the shock motions can eventual result in macro-scale response.}, booktitle={AIAA AVIATION 2020 FORUM}, author={Varigonda, S.V. and Narayanaswamy, V. and Boxx, I.}, year={2020} }
 @inproceedings{sahoo_narayanaswamy_ramachandran_lyons_2020, title={Mixture fraction imaging of distributed regime turbulent jet flame using rayleigh scattering}, volume={1 PartF}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092613746&partnerID=MN8TOARS}, DOI={10.2514/6.2020-3238}, abstractNote={Turbulent combustion of jet flames in a hot diluted co-flow of combustion products is conducive for transition from conventional flamelet combustion to a regime of Moderate or Intense Low-oxygen Dilution (MILD) combustion, which is commonly characterized by very low emission and noise. The MILD combustion is also characterized by distributed combustion where the net heat release is positive across the entire combustion domain. The turbulence/chemistry interactions in this regime that determines the flame structure, local temperature and species distribution critical depend on the mixture fraction and scalar dissipation fields. As such there are no experimental tools to measure the mixture fraction field in distributed (MILD) combustion regime. The present work offsets this limitation and demonstrates a Rayleigh scattering based approach in a turbulent ethylene MILD combustion. 1-D counterflow flame simulations enabled mapping the local calibrated Rayleigh scattering field to mixture fraction in fuel-rich regions. This approach also shows very little sensitivity to the local temperature and composition. The mean and RMS of the mixture fraction exhibit almost identical profiles as non-reacting jets after density ratio correction. Further, the probability density function of the mixture fraction at various radial locations closely adhered to a Beta−distribution that is also obeyed by non-reacting jets.}, booktitle={AIAA AVIATION 2020 FORUM}, author={Sahoo, A. and Narayanaswamy, V. and Ramachandran, A. and Lyons, K.}, year={2020} }
 @article{freydin_levin_dowell_varigonda_narayanaswamy_2020, title={Natural Frequencies of a Heated Plate: Theory and Experiment}, volume={58}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85095131109&partnerID=MN8TOARS}, DOI={10.2514/1.J059660}, abstractNote={No AccessTechnical NotesNatural Frequencies of a Heated Plate: Theory and ExperimentCorrections for this articleCorrection: Natural Frequencies of a Heated Plate: Theory and ExperimentMaxim Freydin, Dani Levin, Earl H. Dowell, Santosh Vaibhav Varigonda and Venkateswaran NarayanaswamyMaxim FreydinDuke University, Durham, North Carolina 27708*Graduate Research Assistant, Department of Mechanical Engineering and Materials Science. Student Member AIAA.Search for more papers by this author, Dani LevinDuke University, Durham, North Carolina 27708*Graduate Research Assistant, Department of Mechanical Engineering and Materials Science. Student Member AIAA.Search for more papers by this author, Earl H. DowellDuke University, Durham, North Carolina 27708†William Holland Hall Professor, Department of Mechanical Engineering and Materials Science. Honorary Fellow AIAA.Search for more papers by this author, Santosh Vaibhav VarigondaNorth Carolina State University, Raleigh, North Carolina 27695‡Graduate Research Assistant, Department of Mechanical and Aerospace Engineering.Search for more papers by this author and Venkateswaran NarayanaswamyNorth Carolina State University, Raleigh, North Carolina 27695§Associate Professor, Department of Mechanical and Aerospace Engineering. Senior Member AIAA.Search for more papers by this authorPublished Online:2 Sep 2020https://doi.org/10.2514/1.J059660SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Whalen T. J., Schöneich A. G., Laurence S. J., Sullivan B. T., Bodony D. J., Freydin M., Dowell E. H. and Buck G. M., “Hypersonic Fluid–Structure Interactions in Compression Corner Shock-Wave/Boundary-Layer Interaction,” AIAA Journal, Vol. XX, No. XX, July 2020, pp. XX. https://doi.org/10.2514/1.J059152 Google Scholar[2] Freydin M., Dowell E. H., Whalen T. J. and Laurence S. J., “A Theoretical Computational Model of a Plate in Hypersonic Flow,” Journal of Fluids and Structures, Vol. 93, Feb. 2020, Paper 102858. https://doi.org/10.1016/j.jfluidstructs.2019.102858 CrossrefGoogle Scholar[3] Spottswood S. M., Beberniss T. J., Eason T. G., Perez R. A., Donbar J. M., Ehrhardt D. A. and Riley Z. B., “Exploring the Response of a Thin, Flexible Panel to Shock-Turbulent Boundary-Layer Interactions,” Journal of Sound and Vibration, Vol. 443, March 2019, pp. 74–89. https://doi.org/10.1016/j.jsv.2018.11.035 CrossrefGoogle Scholar[4] Santos Silva A. C., Sebastian C. M., Lambros J. and Patterson E. A., “High Temperature Modal Analysis of a Non-Uniformly Heated Rectangular Plate: Experiments and Simulations,” Journal of Sound and Vibration, Vol. 443, March 2019, pp. 397–410. https://doi.org/10.1016/j.jsv.2018.11.041 CrossrefGoogle Scholar[5] Ehrhardt D. A. and Virgin L. N., “Experiments on the Thermal Post-Buckling of Panels, Including Localized Heating,” Journal of Sound and Vibration, Vol. 439, Jan. 2019, pp. 300–309. https://doi.org/10.1016/j.jsv.2018.08.043 CrossrefGoogle Scholar[6] Freydin M. and Dowell E. H., “Nonlinear Theoretical Aeroelastic Model of a Plate: Free to Fixed In-Plane Boundaries,” AIAA Journal (under review). Google Scholar[7] Freydin M. and Dowell E. H., “Nonlinear Theoretical/Computational Model of a Plate in Hypersonic Flow with Arbitrary In-Plane Stiffness at the Boundaries,” Second International Symposium on Flutter and Its Application, May 2020, pp. 196–205, https://www.ladhyx.polytechnique.fr/isfa2020/proceedings.html. Google Scholar[8] Dowell E. H. and Voss H. M., “The Effect of a Cavity on Panel Vibration,” AIAA Journal, Vol. 1, No. 2, 1963, pp. 476–477. https://doi.org/10.2514/3.1568 LinkGoogle Scholar[9] Dowell E. H., Aeroelasticity of Plates and Shells, Springer, Berlin, 1974, pp. 48–49. Google Scholar Previous article Next article FiguresReferencesRelatedDetailsCited byHypersonic Fluid–Structure Interaction on a Cone–Slice–Ramp GeometryAnshuman Pandey, Katya M. Casper, Steven J. Beresh, Rajkumar Bhakta and Russell Spillers12 February 2023 | AIAA Journal, Vol. 0, No. 0Response of a plate with piezoelectric elements to turbulent pressure fluctuation in supersonic flowJournal of Fluids and Structures, Vol. 114Demonstration of Internal-Digital Image Correlation (Internal-DIC) for Fluid-Structure Interaction Measurements in a Hypersonic Wind TunnelAnshuman Pandey, Bryan E. Schmidt and Katya M. Casper20 June 2022An Experimental and Computational Correlation Study for Fluid-Thermal-Structural Interaction of a Control Surface in Hypersonic FlowAravinth Sadagopan, Daning Huang, Adam Jirasek, Jürgen Seidel, Anshuman Pandey and Katya M. Casper29 December 2021Fluid/Structural/Thermal/Dynamics Interaction (FSTDI) in Hypersonic Flow16 October 2021Supersonic Aerothermoelastic Experiments of Aerospace StructuresS. Michael Spottswood, Benjamin P. Smarslok, Ricardo A. Perez, Timothy J. Beberniss, Benjamin J. Hagen, Zachary B. Riley, Kirk R. Brouwer and David A. Ehrhardt6 October 2021 | AIAA Journal, Vol. 59, No. 12Methodology to image the panel surface pressure power spectra in weakly coupled fluid/structure interactions28 October 2021 | Experiments in Fluids, Vol. 62, No. 11Impact of Panel Vibrations on the Dynamic Field Properties in Supersonic flowSantosh Vaibhav Varigonda, Chase Jenquin and Venkateswaran Narayanaswamy28 July 2021Fully Coupled Nonlinear Aerothermoelastic Computational Model of a Plate in Hypersonic FlowMaxim Freydin and Earl H. Dowell14 June 2021 | AIAA Journal, Vol. 59, No. 7Hypersonic Fluid-Structure Interaction on the Control Surface of a Slender ConeAnshuman Pandey and Katya M. Casper4 January 2021Fluid-Thermal-Structural Interactions in Ramp-Induced Shock-Wave Boundary-Layer Interactions at Mach 6Antonio Giovanni Schöneich, Thomas J. Whalen, Stuart J. Laurence, Bryson T. Sullivan, Daniel J. Bodony, Maxim Freydin, Earl H. Dowell, Larson J. Stacey and Gregory M. Buck4 January 2021Related articlesCorrection: Natural Frequencies of a Heated Plate: Theory and Experiment7 May 2021AIAA Journal What's Popular Volume 58, Number 11November 2020Supplemental Materials CrossmarkInformationCopyright © 2020 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the eISSN 1533-385X to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp. TopicsAerodynamicsAeronautical EngineeringAeronauticsAerothermodynamicsComputational Fluid DynamicsFinite Element MethodFlow RegimesFluid DynamicsFluid MechanicsFluid Structure InteractionNumerical AnalysisThermodynamicsThermophysics and Heat TransferWind Tunnels KeywordsStatic PressurePlate TheoryHypersonic Wind TunnelsFinite Element ModelingThermal StressesAerodynamic ForceMaterial PropertiesData AcquisitionFSIStructural ModelingAcknowledgmentsThis work was supported in part by a U.S. Air Force Office of Scientific Research grant with Jaimie Tiley as the Program Director. The authors would like to thank Jaimie Tiley and Ivett Leyva for their encouragement and guidance.PDF Received3 April 2020Accepted4 August 2020Published online2 September 2020}, number={11}, journal={AIAA JOURNAL}, author={Freydin, Maxim and Levin, Dani and Dowell, Earl H. and Varigonda, Santosh Vaibhav and Narayanaswamy, Venkateswaran}, year={2020}, month={Nov}, pages={4969–4973} }
 @inproceedings{ramachandran_chauhan_narayanaswamy_lyons_johnson_2020, title={On the transition of autoignitive jet flames to mild combustion}, volume={1 PartF}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092417190&partnerID=MN8TOARS}, DOI={10.2514/6.2020-1842}, abstractNote={Turbulent combustion of jet flames in a vitiated coflow has been studied across a range of jet Reynolds numbers for a propane jet and an ethylene-propane jet. The studies revealed a transition from conventional autoignitive combustion to a regime of Moderate or Intense Low-oxygen Dilution (MILD) combustion, which is commonly characterized by an invisible flame. The flames studied here are luminous at low jet velocities and become MILD at higher jet velocities. Planar Laser-Induced Fluorescence (PLIF) of formaldehyde (CH_2 O), a key intermediate species in hydrocarbon combustion, is combined with CH*-chemiluminescence imaging and Rayleigh scattering to investigate the phenomena. The transition to MILD combustion is accompanied by a broadening of the formaldehyde region, indicating delayed consumption of formaldehyde and hence a broader low-temperature reaction zone. As the transition is approached, the appearance of holes in the chemiluminescent front is also observed. Close matches between the location and structure of these holes with regions of formaldehyde in the flame are illustrated, along with the observed tendency of formaldehyde to extend into local extinctions in a non-MILD split flame. These regions are proposed to be signatures that precede the transition to a fully MILD flame. Scalar dissipation rates measured in the split flame and compared against kinetic simulations of MILD flames suggests the possible inception of MILD combustion through the ignition of relatively rich mixtures. The transition to MILD combustion with the formation of formaldehyde in the locally extinguished pockets is linked to previous studies on reaction zone weakening, leading to the hypothesis of MILD combustion serving as an alternative flame stabilization mechanism, when local turbulence-chemistry interactions inhibit autoignition.}, booktitle={AIAA Scitech 2020 Forum}, author={Ramachandran, A. and Chauhan, A. and Narayanaswamy, V. and Lyons, K.M. and Johnson, R.}, year={2020} }
 @article{sahoo_zelenak_narayanaswamy_2020, title={Pressure scaling of the collisional broadening parameters of Kr 4p(6)S(0)(1) ->-> 5p [3/2](2) transition}, volume={59}, ISSN={["2155-3165"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85091807687&partnerID=MN8TOARS}, DOI={10.1364/AO.394932}, abstractNote={Pressure scaling of collisional broadening parameters of krypton
					(absorber) 
      
	4
	
	  
	    p
	    6
	  
	
	
	  S
	  0
	  1
	
	→→
	5
	p
	
	  [
	  3
	  
	    /
	  
	  2
	  
	    ]
	    2
	  
	
      
     transition centered at 107.3 nm in
					the presence of nitrogen 
      
	
	  
	    
	      N
	    
	    2
	  
	
      
     (perturber) is investigated. The
					absorption spectrum in the vicinity of the transition is obtained from
					the two-photon excitation scan of krypton in the presence of the
					perturber at different prescribed pressures varying from a few torrs
					to 10 atm. The absorption spectra reveal noticeable asymmetry at
					atmospheric pressure, and the asymmetry becomes increasingly
					pronounced with pressure; however, the absorption spectra at
					sub-atmospheric pressures tested are symmetric. The absorption spectra
					are fitted with synthetic asymmetric Voigt profiles across all
					pressures, wherein the asymmetry parameter is varied to capture the
					asymmetry at different pressures. The collisional
					shift (
      
	
	  
	    δ
	    C
	  
	
      
    ), the symmetric equivalent
					collisional full width at half maximum (
      
	
	  
	    w
	    
	      C
	      ,
	      0
	    
	  
	
      
    ), and the asymmetry parameter (
      
	a
      
    ) are determined from the synthetic
					fits at various pressures. All the parameters are observed to vary
					linearly with pressure over the entire range of the pressure values
					tested. The mechanisms that cause the asymmetry in the absorption
					spectra are also discussed.}, number={26}, journal={APPLIED OPTICS}, publisher={The Optical Society}, author={Sahoo, Abinash and Zelenak, Dominic and Narayanaswamy, Venkateswaran}, year={2020}, month={Sep}, pages={7760–7769} }
 @article{sahoo_zelenak_narayanaswamy_2020, title={Temperature dependence of collisional broadening and shift for the Kr 4p<sup>6</sup>S<sup>1</sup><sub>0</sub> → 5p[3/2]<sub>2</sub> electronic transition}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85079400837&partnerID=MN8TOARS}, DOI={10.1364/AO.380102}, abstractNote={Temperature scaling of collisional broadening parameters for krypton
					(absorber) 
      
	4
	
	  
	    p
	    6
	  
	
	
	  S
	  0
	  1
	
	→
	5
	p
	
	  [
	  3
	  
	    /
	  
	  2
	  
	    ]
	    2
	  
	
      
     electronic transition centered at
					107.3 nm in the presence of major combustion species (perturber) is
					investigated. The absorption spectrum in the vicinity of the
					transition is obtained from the fluorescence due to the two-photon
					excitation scan of krypton. Krypton was added in small amounts to
					major combustion species such as 
      
	
	  
	    
	      C
	      H
	    
	    4
	  
	
      
    , 
      
	
	  
	    
	      C
	      O
	    
	    2
	  
	
      
    , 
      
	
	  
	    
	      N
	    
	    2
	  
	
      
    , and air, which then heated to
					elevated temperatures when flowed through a set of heated coils. In a
					separate experimental campaign, laminar premixed flat flame product
					mixtures of methane combustion were employed to extend the
					investigations to higher temperature ranges relevant to combustion.
					Collisional full width half maximum (FWHM) (
      
	
	  
	    w
	    C
	  
	
      
    ) and shift (
      
	
	  
	    δ
	    C
	  
	
      
    ) were computed from the absorption
					spectrum by synthetically fitting Voigt profiles to the excitation
					scans, and their corresponding temperature scaling was determined by
					fitting power-law temperature dependencies to the 
      
	
	  
	    w
	    C
	  
	
      
     and 
      
	
	  
	    δ
	    C
	  
	
      
     data for each perturber species. The
					temperature exponents of 
      
	
	  
	    w
	    C
	  
	
      
     and 
      
	
	  
	    δ
	    C
	  
	
      
     for all considered combustion species
					(perturbers) were 
      
	−
	
	  0.73
	
      
     and 
      
	−
	
	  0.6
	
      
    , respectively. Whereas the
					temperature exponents of 
      
	
	  
	    w
	    C
	  
	
      
     are closer to the value (
      
	−
	
	  0.7
	
      
    ) predicted by the dispersive
					interaction collision theory, the corresponding exponents of 
      
	
	  
	    δ
	    C
	  
	
      
     are in between the dispersive
					interaction theory and the kinetic theory of hard-sphere collisions.
					Comparison with existing literature on broadening parameters of NO,
					OH, and CO laser-induced fluorescence spectra reveal interesting
					contributions from non-dispersive interactions on the temperature
					exponent.}, number={5}, journal={Applied Optics}, author={Sahoo, Abinash and Zelenak, Dominic and Narayanaswamy, Venkateswaran}, year={2020}, pages={1438–1446} }
 @inproceedings{sahoo_narayanaswamy_2019, title={2D temperature field measurement in a sooting flame using the 2-line Kr plif thermometry technique}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85079363435&partnerID=MN8TOARS}, DOI={10.2514/6.2019-3289}, booktitle={AIAA Aviation 2019 Forum}, author={Sahoo, A. and Narayanaswamy, V.}, year={2019}, pages={1–15} }
 @inproceedings{pickles_narayanaswamy_2019, title={Achieving high maneuverability and precision in munitions using non-linear flow interactions}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85086429466&partnerID=MN8TOARS}, booktitle={Proceedings - 31st International Symposium on Ballistics, BALLISTICS 2019}, author={Pickles, J.D. and Narayanaswamy, V.}, year={2019}, pages={848–859} }
 @article{zelenak_narayanaswamy_2019, title={Demonstration of a two-line Kr PLIF thermometry technique for gaseous combustion applications}, volume={44}, ISSN={["1539-4794"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85059987939&partnerID=MN8TOARS}, DOI={10.1364/OL.44.000367}, abstractNote={Experiments were performed to demonstrate a dual-wavelength excitation krypton planar laser-induced fluorescence (Kr PLIF)-based 2D temperature imaging technique in a laminar non-sooting CH4/N2 diffusion flame. The technique exploits the thermochemical dependence of the overlap integral arising from Kr absorption and excitation laser spectra to yield the temperature without the need to know the local mixture composition. The choice of the two excitation wavelengths is made using the knowledge of the fuel mixture and pressure. The two excitation wavelengths lie within the same 4p6S01→→5p[32]2 transition, and their selection is informed such that the resulting Kr PLIF signal ratio depends primarily on the temperature and negligibly on local composition. Mean temperature fields show excellent agreement when compared to Fluent simulations across different regions of the combustion domain, while the single-shot temperature field exhibits slightly degraded accuracy. Overall, the technique provides very similar figures of merit compared to conventional composition-dependent thermometry approaches and showcases a promising scope for application in complex reacting flows.}, number={2}, journal={OPTICS LETTERS}, author={Zelenak, Dominic and Narayanaswamy, Venkateswaran}, year={2019}, month={Jan}, pages={367–370} }
 @article{funderburk_narayanaswamy_2019, title={Experimental Investigation of Microramp Control of an Axisymmetric Shock/Boundary-Layer Interaction}, volume={57}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85070370366&partnerID=MN8TOARS}, DOI={10.2514/1.J057846}, abstractNote={Mitigation of shock-induced boundary-layer separation using vortex generators (VGs) is an emerging flow control approach in planar inlet geometries. In the present work, an experimental campaign is...}, number={8}, journal={AIAA JOURNAL}, author={Funderburk, Morgan L. and Narayanaswamy, Venkateswaran}, year={2019}, month={Aug}, pages={3379–3394} }
 @article{funderburk_narayanaswamy_2019, title={Investigation of Negative Surface Curvature Effects in Axisymmetric Shock/Boundary-Layer Interaction}, volume={57}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85067429803&partnerID=MN8TOARS}, DOI={10.2514/1.J057275}, abstractNote={The shock/boundary-layer interactions (SBLIs) generated by a negatively curved compression ramp are investigated. The ramp was mounted to the inner surface of a semicircular hollow cylinder, along ...}, number={4}, journal={AIAA JOURNAL}, author={Funderburk, Morgan L. and Narayanaswamy, Venkateswaran}, year={2019}, month={Apr}, pages={1594–1607} }
 @inproceedings{varigonda_narayanaswamy_2019, title={Investigation of shock wave induced flow separation over a flexible panel in supersonic flows}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092757958&partnerID=MN8TOARS}, DOI={10.2514/6.2019-3543}, booktitle={AIAA Aviation 2019 Forum}, author={Varigonda, S.V. and Narayanaswamy, V.}, year={2019}, pages={1–11} }
 @article{ramachandran_narayanaswamy_lyons_2019, title={Observations on the Role of Auto-Ignition in Flame Stabilization in Turbulent Non-Premixed Jet Flames in Vitiated Coflow}, volume={141}, ISSN={["1528-8919"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062721393&partnerID=MN8TOARS}, DOI={10.1115/1.4042807}, abstractNote={Turbulent combustion of non-premixed jets issuing into a vitiated coflow is studied at coflow temperatures that do not significantly exceed the fuel auto-ignition temperatures, with the objective of observing the global features of lifted flames in this operating temperature regime and the role played by auto-ignition in flame stabilization. Three distinct modes of flame base motions are identified, which include a fluctuating lifted flame base (mode A), avalanche downstream motion of the flame base (mode B), and the formation and propagation of auto-ignition kernels (mode C). Reducing the confinement length of the hot coflow serves to highlight the role of auto-ignition in flame stabilization when the flame is subjected to destabilization by ambient air entrainment. The influence of auto-ignition is further assessed by computing ignition delay times for homogeneous CH4/air mixtures using chemical kinetic simulations and comparing them against the flow transit time corresponding to mean flame liftoff height of the bulk flame base. It is inferred from these studies that while auto-ignition is an active flame stabilization mechanism in this regime, the effect of turbulence may be crucial in determining the importance of auto-ignition toward stabilizing the flame at the conditions studied. An experimental investigation of auto-ignition characteristics at various jet Reynolds numbers reveals that turbulence appears to have a suppressing effect on the active role of auto-ignition in flame stabilization.}, number={6}, journal={JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, author={Ramachandran, Aravind and Narayanaswamy, Venkateswaran and Lyons, Kevin M.}, year={2019}, month={Jun} }
 @article{pickles_mettu_subbareddy_narayanaswamy_2019, title={On the mean structure of sharp-fin-induced shock wave/turbulent boundary layer interactions over a cylindrical surface}, volume={865}, ISSN={["1469-7645"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85061720934&partnerID=MN8TOARS}, DOI={10.1017/jfm.2019.53}, abstractNote={Interactions between an oblique shock wave generated by a sharp fin placed on a cylindrical surface and the incoming boundary layer are investigated to unravel the mean features of the resulting shock/boundary layer interaction (SBLI) unit. This fin-on-cylinder SBLI unit has several unique features caused by the three-dimensional (3-D) relief offered by the cylindrical surface that noticeably alter the shock structure. Complementary experimental and computational studies are made to delineate both the surface and off-body flow features of the fin-on-cylinder SBLI unit and to obtain a detailed understanding of the mechanisms that dictate the mean flow and wall pressure features of the SBLI unit. Results show that the fin-on-cylinder SBLI exhibits substantial deviation from quasi-conical symmetry that is observed in planar fin SBLI. Furthermore, the separated flow growth rate appears to decrease with downstream distance and the separation size is consistently smaller than the planar fin SBLI with the same inflow and fin configurations. The causes for the observed diminution of the separated flow and its downstream growth rate were investigated in the light of changes caused by the cylinder curvature on the inviscid as well as separation shock. It was found that the inviscid shock gets progressively weakened in the region close to the triple point with downstream distance due to the 3-D relief effect from cylinder curvature. This weakening of the inviscid shock feeds into the separation shock, which is also independently impacted by the 3-D relief, to result in the observed modifications in the fin-on-cylinder SBLI unit.}, journal={JOURNAL OF FLUID MECHANICS}, author={Pickles, J. D. and Mettu, B. R. and Subbareddy, P. K. and Narayanaswamy, V.}, year={2019}, month={Apr}, pages={212–246} }
 @article{funderburk_narayanaswamy_2019, title={Spectral signal quality of fast pressure sensitive paint measurements in turbulent shock-wave/boundary layer interactions}, volume={60}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85073063330&partnerID=MN8TOARS}, DOI={10.1007/s00348-019-2799-x}, number={10}, journal={EXPERIMENTS IN FLUIDS}, author={Funderburk, Morgan L. and Narayanaswamy, Venkateswaran}, year={2019}, month={Oct} }
 @article{sahoo_narayanaswamy_2019, title={Two-dimensional temperature field imaging in laminar sooting flames using a two-line Kr PLIF approach}, volume={125}, ISSN={["1432-0649"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85070822897&partnerID=MN8TOARS}, DOI={10.1007/s00340-019-7280-2}, number={9}, journal={APPLIED PHYSICS B-LASERS AND OPTICS}, publisher={Springer Science and Business Media LLC}, author={Sahoo, Abinash and Narayanaswamy, Venkateswaran}, year={2019}, month={Sep} }
 @inproceedings{pham_gianikos_narayanaswamy_2018, title={Compression ramp induced shock wave/turbulent boundary layer interactions on a compliant material}, volume={56}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85141619302&partnerID=MN8TOARS}, DOI={10.2514/6.2018-0095}, number={7}, booktitle={AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018}, author={Pham, H.T. and Gianikos, Z.N. and Narayanaswamy, Venkat}, year={2018}, pages={2925–2929} }
 @article{pham_gianikos_narayanaswamy_2018, title={Compression ramp induced shock-wave/turbulent boundary-layer interactions on a compliant material}, volume={56}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85049150866&partnerID=MN8TOARS}, DOI={10.2514/1.J056652}, abstractNote={PHA. M, HARRY TOÀN. Compression Ramp Induced Shock Wave/Turbulent Boundary Layer Interactions on a Compliant Material. (Under the direction of Dr. Venkateswaran Narayanaswamy.). An investigation into the potential use of soft compliant materials towards unsteady shock load mitigation is made. Compression ramps with different angles are used to generate shock waves impinging on the surface of the compliant layer embedded on a rigid flat plate in a Mach 2.5 flow. A urethane rubber material is chosen as the candidate compliant material for its well characterized material properties and ease of fabrication. Shock boundary layer interactions and fluid structure interactions are analyzed through oil-pigment surface streakline visualization and high-speed pressure transducer measurements. Reductions in the mean separation size are observed by embedding the compliant layer compared to without it. Furthermore, significant reduction in the energy content of the low frequency shock oscillations over the intermittent region was also observed by embedding a compliant layer on the rigid plate. © Copyright 2018 by Harry Toàn Pha.m}, number={7}, journal={AIAA Journal}, author={Pham, H.T. and Gianikos, Z.N. and Narayanaswamy, V.}, year={2018}, pages={2925–2929} }
 @inproceedings{funderburk_narayanaswamy_2018, title={Experimental investigation of microramp vortex generator application upstream of an axisymmetric shock boundary layer interaction}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85066477317&partnerID=MN8TOARS}, DOI={10.2514/6.2018-4937}, booktitle={2018 Joint Propulsion Conference}, author={Funderburk, M.L. and Narayanaswamy, V.}, year={2018} }
 @inproceedings{pickles_mettu_subbareddy_narayanaswamy_2018, title={Fin-generated shock wave/turbulent boundary layer interactions on a cylindrical surface with a distorted incoming boundary layer}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85051295265&partnerID=MN8TOARS}, DOI={10.2514/6.2018-3396}, booktitle={2018 Fluid Dynamics Conference}, author={Pickles, J.D. and Mettu, B.R. and Subbareddy, P.K. and Narayanaswamy, V.}, year={2018} }
 @article{pickles_mettu_subbareddy_narayanaswamy_2018, title={Gas density field imaging in shock dominated flows using planar laser scattering}, volume={59}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85048239189&partnerID=MN8TOARS}, DOI={10.1007/s00348-018-2562-8}, number={7}, journal={EXPERIMENTS IN FLUIDS}, author={Pickles, Joshua D. and Mettu, Balachandra R. and Subbareddy, Pramod K. and Narayanaswamy, Venkateswaran}, year={2018}, month={Jul} }
 @inproceedings{leonard_narayanaswamy_2018, title={Investigations of flowfield and dynamics in an axisymmetric isolator}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85141620734&partnerID=MN8TOARS}, DOI={10.2514/6.2018-1611}, booktitle={AIAA Aerospace Sciences Meeting, 2018}, author={Leonard, M.D. and Narayanaswamy, V.}, year={2018} }
 @inproceedings{narayanaswamy_zelenak_2018, title={Two-line Kr PLIF technique for composition independent temperature imaging in gaseous combustion}, volume={Part F103-LACSEA 2018}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85051279797&partnerID=MN8TOARS}, DOI={10.1364/LACSEA.2018.LTu3C.2}, abstractNote={A two-line Kr PLIF based thermometry technique will be presented for application in gaseous combustion. The technique uses the spectral line broadening of the krypton seeded into the fuel stream to provide 2D temperature field.}, booktitle={Optics InfoBase Conference Papers}, author={Narayanaswamy, V. and Zelenak, D.}, year={2018} }
 @article{zelenak_narayanaswamy_2017, title={Composition-independent mean temperature measurements in laminar diffusion flames using spectral lineshape information}, volume={58}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85029953501&partnerID=MN8TOARS}, DOI={10.1007/s00348-017-2430-y}, number={10}, journal={EXPERIMENTS IN FLUIDS}, author={Zelenak, D. and Narayanaswamy, V.}, year={2017}, month={Oct} }
 @inproceedings{funderburk_narayanaswamy_2017, title={Experimental investigation of shock boundary layer interactions in axisymmetric isolator geometries}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85088202935&partnerID=MN8TOARS}, DOI={10.2514/6.2017-5052}, booktitle={53rd AIAA/SAE/ASEE Joint Propulsion Conference, 2017}, author={Funderburk, M.L. and Narayanaswamy, V.}, year={2017} }
 @inproceedings{lam_pickles_narayanaswamy_carter_kimmel_2017, title={High-speed schlieren and 10-Hz Kr PLIF for the new AFRL mach-6 Ludwieg tube hypersonic wind tunnel}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85017211937&partnerID=MN8TOARS}, DOI={10.2514/6.2017-0550}, booktitle={AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting}, author={Lam, K.-Y. and Pickles, J.D. and Narayanaswamy, V. and Carter, C.D. and Kimmel, R.L.}, year={2017} }
 @inproceedings{ley_narayanaswamy_2017, title={Parametric study of forced ignition in laminar and turbulent methane jets}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85088061673&partnerID=MN8TOARS}, DOI={10.2514/6.2017-4770}, booktitle={53rd AIAA/SAE/ASEE Joint Propulsion Conference, 2017}, author={Ley, K. and Narayanaswamy, V.}, year={2017} }
 @inproceedings{pickles_mettu_subbareddy_narayanaswamy_2017, title={Sharp-fin induced shock wave/turbulent boundary layer interactions in an axisymmetric configuration}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85081176764&partnerID=MN8TOARS}, DOI={10.2514/6.2017-4314}, booktitle={47th AIAA Fluid Dynamics Conference, 2017}, author={Pickles, J.D. and Mettu, B.R. and Subbareddy, P.K. and Narayanaswamy, V.}, year={2017} }
 @article{zelenak_sealy_narayanaswamy_2016, title={Collisional broadening of Kr (4p(6) S-0(1) -> -> 5p [3/2](2)) transition with combustion species as collision partners}, volume={174}, journal={Journal of Quantitative Spectroscopy & Radiative Transfer}, author={Zelenak, D. and Sealy, W. and Narayanaswamy, V.}, year={2016}, pages={28–38} }
 @article{zelenak_sealy_narayanaswamy_2016, title={Collisional broadening of Kr (4p6S01→→5p[32]2) transition with combustion species as collision partners}, volume={174}, ISSN={0022-4073}, url={http://dx.doi.org/10.1016/J.JQSRT.2016.01.017}, DOI={10.1016/J.JQSRT.2016.01.017}, abstractNote={Abstract Collisional broadening of krypton 4 p 6 S 0 1 → → 5 p [ 3 2 ] 2 transition centered at 107.3 nm caused by common combustion species is investigated in this work. The present work investigates the compositional and thermodynamic dependencies of the collisional parameters between collision partners with similar electronic energy level gaps. In this situation, the classical expression of dispersive energy during collisions cannot be simplified to obtain closed form equations for the collisional parameters. The broadening parameters, namely collisional full width at half maximum (wc) and collisional shift (δc) are obtained through a two-photon excitation scan of krypton (Kr) present in a mixture containing krypton and the collision partner at 295 K and 101 kPa. The compositional scaling of wc and δc are compared with scaling at situations corresponding to both large and small perturber electronic energy level gaps as compared to the absorber’s electronic energy level gap. In the Kr PLIF system, wc scaling corresponds to a situation where the perturber electronic energy level gap is significantly larger than absorber energy level gap, whereas δc scaling corresponds to when the absorber electronic energy level gap is significantly larger than the perturber electronic energy level gap. Further, contributions from non-dispersive forces are computed to be significantly smaller than dispersive forces, which results to the observed tight scaling. The observed compositional scaling is shown to be consistent with a different collisional partner system (NO as the absorber and combustion species as perturbers), indicating that the scaling obtained with the krypton system is general to situations with perturbers and absorbers having similar electronic energy level spacing.}, journal={Journal of Quantitative Spectroscopy and Radiative Transfer}, publisher={Elsevier BV}, author={Zelenak, Dominic and Sealy, William and Narayanaswamy, Venkateswaran}, year={2016}, month={May}, pages={28–38} }
 @article{funderburk_narayanaswamy_2016, title={Experimental investigation of primary and corner shock boundary layer interactions at mild back pressure ratios}, volume={28}, ISSN={["1089-7666"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84983745346&partnerID=MN8TOARS}, DOI={10.1063/1.4960963}, abstractNote={Unstart of rectangular inlets occurs as a result of interactions between shock-induced separation units along the floor/ceiling, corner, and sidewalls. While a significant body of literature exists regarding the individual flow interactions at the inlet floor/ceiling (called primary separation) and sidewalls, limited efforts have focused on the mean and dynamic features of the corner separation. Experiments are conducted to investigate primary and corner shock boundary layer interactions (SBLI) with the objectives of elucidating the flow interactions that occur in the corner, and characterizing the interaction between the corner and primary separation units at mild back pressure ratios. Surface streakline flow visualization and high-frequency wall static pressure measurements are performed along the centerline and corner regions of shock-induced flow separation generated by a 12° compression ramp in a Mach 2.5 flow. Sidewall fences that extend upstream of the leading edge of the flat plate generate corner separation of adequate size to determine the mean flow structures, characterize the unsteady motions, and investigate the mechanisms that drive the unsteadiness of primary and corner SBLI. Results show that the corner and primary SBLI units differ fundamentally in both their mean and unsteady features and their response to upstream and downstream flow perturbations. These observations suggest that the two behave as independent units at this relatively low shock-induced back pressure ratio.}, number={8}, journal={PHYSICS OF FLUIDS}, author={Funderburk, M. and Narayanaswamy, V.}, year={2016}, month={Aug} }
 @inproceedings{funderburk_narayanaswamy_2016, title={Experimental investigation of shock boundary layer interactions to unravel inlet unstart physics}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84980347810&partnerID=MN8TOARS}, booktitle={46th AIAA Fluid Dynamics Conference}, author={Funderburk, M.L. and Narayanaswamy, V.}, year={2016} }
 @inproceedings{pickles_subbareddy_narayanaswamy_2016, title={Sharp-fin induced shock wave/turbulent boundary layer interactions in an axisymmetric configuration}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85088071146&partnerID=MN8TOARS}, DOI={10.2514/6.2016-3340}, booktitle={46th AIAA Fluid Dynamics Conference}, author={Pickles, J.D. and Subbareddy, P.K. and Narayanaswamy, V.}, year={2016} }
 @inproceedings{zelenak_sealy_narayanaswamy_2015, title={Composition-independent temperature and pressure measurements using lineshape information}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84960517327&partnerID=MN8TOARS}, booktitle={46th AIAA Plasmadynamics and Lasers Conference}, author={Zelenak, D. and Sealy, W. and Narayanaswamy, V.}, year={2015} }
 @inproceedings{hegde_funderburk_hill_narayanaswamy_2015, title={Experimental investigation into shock induced corner boundary layer separation}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85086951086&partnerID=MN8TOARS}, DOI={10.2514/6.2015-2934}, booktitle={45th AIAA Fluid Dynamics Conference}, author={Hegde, A. and Funderburk, M. and Hill, J. and Narayanaswamy, V.}, year={2015} }
 @inproceedings{ramachandran_tyler_patel_narayanaswamy_lyons_2015, title={Global features of flame stabilization in turbulent non-premixed jet flames in vitiated coflow}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84960469252&partnerID=MN8TOARS}, DOI={10.2514/6.2015-2313}, booktitle={45th AIAA Fluid Dynamics Conference}, author={Ramachandran, A. and Tyler, D.A. and Patel, P.K. and Narayanaswamy, V. and Lyons, K.M.}, year={2015}, pages={1–13} }
 @inproceedings{characterization of the nasa langley arc heated scramjet test facility using no plif_2014, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85078067828&partnerID=MN8TOARS}, DOI={10.2514/6.2014-2652}, abstractNote={The nitric oxide planar laser-induced fluorescence (NO PLIF) imaging was used to characterize the air flow of the NASA Langley Arc Heated Scramjet Test Facility (AHSTF) configured with a Mach 6 nozzle. The arc raises the enthalpy of the test gas in AHSTF, producing nitric oxide. Nitric oxide persists as the temperature drops through the nozzle into the test section. NO PLIF was used to qualitatively visualize the flowfield at different experimental conditions, measure the temperature of the gas flow exiting the facility nozzle, and visualize the wave structure downstream of the nozzle at different operating conditions. Uniformity and repeatability of the nozzle flow were assessed. Expansion and compression waves on the free-jet shear layer as the nozzle flow expands into the test section were visualized. The main purpose of these experiments was to assess the uniformity of the NO in the freestream gas for planned experiments, in which NO PLIF will be used for qualitative fuel-mole-fraction sensitive imaging. The shot-to-shot fluctuations in the PLIF signal, caused by variations in the overall laser intensity as well as NO concentration and temperature variations in the flow was 20-25% of the mean signal, as determined by taking the standard deviation of a set of images obtained at constant conditions and dividing by the mean. The fluctuations within individual images, caused by laser sheet spatial variations as well as NO concentration and temperature variations in the flow, were about 28% of the mean in images, determined by taking standard deviation within individual images, dividing by the mean in the same image and averaged over the set of images. Applying an averaged laser sheet intensity correction reduced the within-image intensity fluctuations to about 10% suggesting that the NO concentration is uniform to within 10%. There was no significant difference in flow uniformity between the low and high enthalpy settings. While not strictly quantitative, the temperature maps show qualitative agreement with the computations of the flow.}, booktitle={AIAA AVIATION 2014 - 30th AIAA Aerodynamic Measurement Technology and Ground Testing Conference}, year={2014} }
 @article{clemens_narayanaswamy_2014, title={Low-Frequency Unsteadiness of Shock Wave/Turbulent Boundary Layer Interactions}, volume={46}, ISSN={["0066-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84891810972&partnerID=MN8TOARS}, DOI={10.1146/annurev-fluid-010313-141346}, abstractNote={ Shock wave/boundary layer interactions occur in a wide range of supersonic internal and external flows, and often these interactions are associated with turbulent boundary layer separation. The resulting separated flow is associated with large-scale, low-frequency unsteadiness whose cause has been the subject of much attention and debate. In particular, some researchers have concluded that the source of low-frequency motions is in the upstream boundary layer, whereas others have argued for a downstream instability as the driving mechanism. Owing to substantial recent activity, we are close to developing a comprehensive understanding, albeit only in simplified flow configurations. A plausible model is that the interaction responds as a dynamical system that is forced by external disturbances. The low-frequency dynamics seem to be adequately described by a recently proposed shear layer entrainment-recharge mechanism. Upstream boundary layer fluctuations seem to be an important source of disturbances, but the evidence suggests that their impact is reduced with increasing size of the separated flow. }, journal={ANNUAL REVIEW OF FLUID MECHANICS, VOL 46}, author={Clemens, Noel T. and Narayanaswamy, Venkateswaran}, year={2014}, pages={469–492} }
 @article{gampert_narayanaswamy_schaefer_peters_2013, title={Conditional statistics of the turbulent/non-turbulent interface in a jet flow}, volume={731}, ISSN={0022-1120 1469-7645}, url={http://dx.doi.org/10.1017/JFM.2013.327}, DOI={10.1017/JFM.2013.327}, abstractNote={Abstract}, journal={Journal of Fluid Mechanics}, publisher={Cambridge University Press (CUP)}, author={Gampert, Markus and Narayanaswamy, Venkat and Schaefer, Philip and Peters, Norbert}, year={2013}, month={Aug}, pages={615–638} }
 @article{gampert_schaefer_narayanaswamy_peters_2013, title={Gradient trajectory analysis in a Jet flow for turbulent combustion modelling}, volume={14}, ISSN={1468-5248}, url={http://dx.doi.org/10.1080/14685248.2012.747688}, DOI={10.1080/14685248.2012.747688}, abstractNote={Based on planar high-speed Rayleigh scattering measurements of the mixture fraction Z of propane discharging from a turbulent round jet into co-flowing carbon dioxide at nozzle-based Reynolds numbers Re 0 = 3000–8600, we use scalar gradient trajectories to investigate the local structure of the turbulent scalar field with a focus on the scalar turbulent/non-turbulent interface. The latter is located between the fully turbulent part of the jet and the outer flow. Using scalar gradient trajectories, we partition the turbulent scalar field into these three regions according to an approach developed by Mellado et al. (J.P. Mellado, L. Wang, and N. Peters, Gradient trajectory analysis of a scalar field with external intermittency, J. Fluid Mech. 626 (2009), pp. 333–365.). Based on these different regions, we investigate in a next step zonal statistics of the scalar probability density function (pdf) P(Z) as well as the scalar difference along the trajectory ΔZ and its mean scalar value Zm , where the latter two quantities are used to parameterize the scalar profile along gradient trajectories. We show that the scalar pdf P(Z) can be reconstructed from zonal gradient trajectory statistics of the joint pdf P(Zm , ΔZ). Furthermore, on the one hand we relate our results for the scalar turbulent/non-turbulent interface to the findings made in other experimental and numerical studies of the turbulent/non-turbulent interface, and on the other hand discuss them in the context of the flamelet approach and the modelling of pdfs in turbulent non-premixed combustion. Finally, we compare the zonal statistics for P(Z) with the composite model of Effelsberg and Peters (E. Effelsberg and N. Peters, A composite model for the conserved scalar pdf, Combust. Flame 50 (1983), pp. 351–360) and observe a very good qualitative and quantitative agreement.}, number={1}, journal={Journal of Turbulence}, publisher={Informa UK Limited}, author={Gampert, M. and Schaefer, P. and Narayanaswamy, V. and Peters, N.}, year={2013}, month={Jan}, pages={147–164} }
 @article{gampert_narayanaswamy_peters_2013, title={Scalar gradient trajectory measurements using high-frequency cinematographic planar Rayleigh scattering}, volume={54}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84886400214&partnerID=MN8TOARS}, DOI={10.1007/s00348-013-1621-4}, number={12}, journal={EXPERIMENTS IN FLUIDS}, author={Gampert, Markus and Narayanaswamy, Venkat and Peters, Norbert}, year={2013}, month={Dec} }
 @article{narayanaswamy_clemens_2013, title={Simultaneous LII and PIV measurements in the soot formation region of turbulent non-premixed jet flames}, volume={34}, ISSN={["1873-2704"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84877691505&partnerID=MN8TOARS}, DOI={10.1016/j.proci.2012.06.018}, abstractNote={An experimental study was performed to investigate the soot–turbulence interaction in the soot-formation region of turbulent non-premixed co-flowing ethylene/N2 jet flames. Simultaneous velocity and soot volume-fraction (fv) fields were obtained using two-component particle image velocimetry and laser-induced incandescence, respectively. Measurements were made for jet exit Reynolds numbers between 8500 and 12,300, and the measurement location was 10 jet diameters downstream, near the beginning of the yellow luminous region where soot is first formed. In agreement with previous studies, the peak mean fv in the production region is inversely related to the bulk strain rate. The simultaneous data show that soot is formed to the inside of the stoichiometric surface (inferred from stoichiometric velocity), but the formation region moves outside to regions of lower velocity and strain rate as the bulk strain rate is increased. Soot structures form in low strain rate regions, but their upstream edge is seen to become stretched out and aligned at a preferred angle (near 45 degrees) owing to alignment with the instantaneous principal extensive strain rate. Statistical analysis shows that the soot exists, on average, in fluid with axial velocity of about 3 m/s and strain rate of 700 s−1, regardless of the jet exit velocity. The radial profiles of the covariance between fv and radial velocity are consistent with a model where the soot is formed at a preferred radial location (near the reaction zone) and then is transported by turbulent fluctuations to regions of lower fv.}, number={1}, journal={PROCEEDINGS OF THE COMBUSTION INSTITUTE}, author={Narayanaswamy, V. and Clemens, N. T.}, year={2013}, pages={1455–1463} }
 @article{narayanaswamy_raja_clemens_2012, title={Control of a shock/boundary-layer interaction by using a pulsed-plasma jet actuator}, volume={50}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84555178897&partnerID=MN8TOARS}, DOI={10.2514/1.J051246}, abstractNote={S HOCK wave/boundary-layer interactions (SWBLIs) are a common feature of supersonic/hypersonic flight, and the unsteadiness of strongly separated interactions can lead to rapid fatigue of structural panels as well as inlet instability and unstart. To mitigate these problems, there is interest in developing techniques for controlling the separatedflowunsteadiness by using both passive and active control techniques. Previous SWBLI control work has focused on reducing the size of the separated flow and/or shifting the frequency of the interaction unsteadiness to a band that does not coincide with the resonant frequency of structural panels. A detailed survey of the variousmeans used for controlling SWBLI until the late 1980s is given in [1]. Recently, plasma-based actuators have been used by researchers for active control of SWBLI, since these actuators have several inherent desirable features such as high bandwidth and no moving parts. For example, previous researchers have used surface-mounted arc discharges [2] and glow discharges with external magnetic fields [3,4] to achieve control of reflected SWBLI. Wang et al. [5] used surface-mounted arc discharges with external magnetic fields and demonstrated the weakening of the separation shock strength in front of a compression ramp. Recently, arc discharges have been employed by Grossman et al. [6] and subsequent researchers [7–11] to generate a pulsed synthetic jet, which they termed a spark jet. The spark-jet design was modified by Narayanaswamy et al. [12] to extend the pulsing frequency to the kilohertz range. They termed the actuator a pulsed-plasma jet since the term spark implies a thermal discharge, which was not the case at the pressures used in their study (and in the current work). Narayanaswamy et al. [12] performed a detailed parametric study of the velocity and temperature characteristics of the pulsed-plasma jets. They reported a jet-exit velocity of about 300 m=s and a bulk gas temperature in the range 600–1000 K for the range of discharge currents tested. The same pulsed-plasma-jet array actuator is used in the present work to control the separation shock of a SWBLI generated by a compression ramp in a Mach 3 flow.}, number={1}, journal={AIAA Journal}, author={Narayanaswamy, V. and Raja, L.L. and Clemens, N.T.}, year={2012}, pages={246–249} }
 @article{narayanaswamy_raja_clemens_2012, title={Control of unsteadiness of a shock wave/turbulent boundary layer interaction by using a pulsed-plasma-jet actuator}, volume={24}, ISSN={1070-6631 1089-7666}, url={http://dx.doi.org/10.1063/1.4731292}, DOI={10.1063/1.4731292}, abstractNote={A pulsed-plasma jet actuator is used to control the unsteady motion of the separation shock of a shock wave/boundary layer interaction formed by a compression ramp in a Mach 3 flow. The actuator is based on a plasma-generated synthetic jet and is configured as an array of three jets that can be injected normal to the cross-flow, pitched, or pitched and skewed. The typical peak jet exit velocity of the actuators is about 300 m/s and the pulsing frequencies are a few kilohertz. A study of the interaction between the pulsed-plasma jets and the shock/boundary layer interaction was performed in a time-resolved manner using 10 kHz schlieren imaging. When the actuator, pulsed at StL ≈ 0.04 (f = 2 kHz), was injected into the upstream boundary layer, the separation shock responded to the plasma jet by executing a rapid upstream motion followed by a gradual downstream recovery motion. Schlieren movies of the interaction showed that the separation shock unsteadiness was locked to the pulsing frequency of the actuator, with amplitude of about one boundary layer thickness. Wall-pressure measurements made under the intermittent region showed about a 30% decrease in the overall magnitude of the pressure fluctuations in the low-frequency band associated with unsteady large-scale motion of the separated flow. Furthermore, by increasing the pulsing frequency to 3.3 kHz, the amplitude of the separation shock oscillation was reduced to less than half the boundary layer thickness. Investigation into the effect of the actuator location on the shock wave/boundary layer interaction (SWBLI) showed qualitatively and quantitatively that the actuator placed upstream of the separation shock caused significant modification to the SWBLI unsteadiness, whereas injection from inside the separation bubble did not cause a noticeable effect.}, number={7}, journal={Physics of Fluids}, publisher={AIP Publishing}, author={Narayanaswamy, Venkateswaran and Raja, Laxminarayan L. and Clemens, Noel T.}, year={2012}, month={Jul}, pages={076101} }
 @article{narayanaswamy_burns_clemens_2011, title={Kr-PLIF for scalar imaging in supersonic flows}, volume={36}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80455129888&partnerID=MN8TOARS}, DOI={10.1364/OL.36.004185}, abstractNote={Experiments were performed to explore the use of two-photon planar laser-induced fluorescence (PLIF) of krypton gas for applications of scalar imaging in supersonic flows. Experiments were performed in an underexpanded jet of krypton, which exhibited a wide range of conditions, from subsonic to hypersonic. Excellent signal-to-noise ratios were obtained, showing the technique is suitable for single-shot imaging. The data were used to infer the distribution of gas density and temperature by correcting the fluorescence signal for quenching effects and using isentropic relations. The centerline variation of the density and temperature from the experiments agree very well with those predicted with an empirical correlation and a CFD simulation (FLUENT). Overall, the high signal levels and quantifiable measurements indicate that Kr-PLIF could be an effective scalar marker for use in supersonic and hypersonic flow applications.}, number={21}, journal={Optics Letters}, author={Narayanaswamy, V. and Burns, R. and Clemens, N.T.}, year={2011}, pages={4185–4187} }
 @article{narayanaswamy_clemens_raja_2011, title={Method for acquiring pressure measurements in presence of plasma-induced interference for supersonic flow control applications}, volume={22}, ISSN={0957-0233 1361-6501}, url={http://dx.doi.org/10.1088/0957-0233/22/12/125107}, DOI={10.1088/0957-0233/22/12/125107}, abstractNote={The operation of pulsed-plasma actuators for flow control is often associated with the presence of charged species in the flow and severe electromagnetic interference with external circuitry. These effects can lead to time-resolved transducer pressure measurements that are contaminated with electromagnetic interference effects or even transducer damage due to the interaction with charged species. A new technique is developed that enables high-bandwidth pressure measurements to be made in the presence of such rapidly switched plasma actuators. The technique is applied for the specific configuration of a pulsed-plasma jet actuator (spark jet) that is used to control the unsteadiness of a shock wave/boundary layer interaction generated by a compression ramp in a Mach 3 flow. The critical component of the technique involves using a pulsed-ground electrode to drain the charged species from the plasma jet before they reach the pressure transducer. The pulsed-ground electrode was shown to drain charged species into the pulsed ground prior to interacting with the transducer, which made it possible to make measurements without damaging the transducer. The resulting signals were still contaminated by electromagnetic interference spikes and so a data-processing technique was used to remove the artifacts and recover a largely uncontaminated power spectrum. The signal processing scheme used interpolation schemes previously developed for laser Doppler velocimetry applications. The data-processing procedure is demonstrated with a benchmark case in which the electromagnetic interference was isolated from the pulsed-plasma jet actuation effect. It is shown that the data-processing procedure removed the contamination from the electromagnetic interference at all frequencies but for the pulsing frequency and its higher harmonics.}, number={12}, journal={Measurement Science and Technology}, publisher={IOP Publishing}, author={Narayanaswamy, Venkateswaran and Clemens, Noel T and Raja, Laxminarayan L}, year={2011}, month={Nov}, pages={125107} }
 @article{hsu_narayanaswamy_clemens_frank_2011, title={Mixture fraction imaging in turbulent non-premixed flames with two-photon LIF of krypton}, volume={33}, ISSN={1540-7489}, url={http://dx.doi.org/10.1016/j.proci.2010.06.051}, DOI={10.1016/j.proci.2010.06.051}, abstractNote={The use of a noble gas as an inert tracer for mixing studies in combustion systems is investigated. Simultaneous two-photon laser-induced fluorescence (LIF) of krypton and Rayleigh scattering are used for imaging measurements of mixture fraction and temperature in turbulent non-premixed jet flames. The turbulent flames investigated in this study include a piloted CH4/air flame (Sandia flame D) and a CH4/H2/N2 flame (DLR-B flame). These flames are well-documented in the literature and enable an evaluation of krypton as a tracer in different fuel mixtures with varying degrees of differential diffusion. Krypton is excited from the ground state to the 5p[3/2]2 state using 215 nm laser radiation, and the fluorescence decay to the metastable state, 5s[3/2]2, is detected at 760 nm. Single-shot krypton LIF and Rayleigh scattering images are analyzed in an iterative routine to determine mixture fraction and temperature. Measurements of the temperature- and species-dependent quenching rates for Kr-LIF are incorporated into this routine. The resulting average radial profiles of mixture fraction and temperature for both flames agree well with previously published measurements. The use of a noble gas as a chemically inert tracer has potential applications for mixing studies in a broad range of combustion environments.}, number={1}, journal={Proceedings of the Combustion Institute}, publisher={Elsevier BV}, author={Hsu, A.G. and Narayanaswamy, V. and Clemens, N.T. and Frank, J.H.}, year={2011}, pages={759–766} }
 @inproceedings{guo_zhao_song_combs_narayanaswamy_clemens_chen_li_zou_jiang_2011, title={Upconverting nanophosphors for high temperature applications}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-81455133723&partnerID=MN8TOARS}, booktitle={Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011}, author={Guo, X. and Zhao, H. and Song, H. and Combs, C. and Narayanaswamy, V. and Clemens, N. and Chen, X. and Li, K.K. and Zou, Y.K. and Jiang, H.}, year={2011}, pages={429–432} }
 @article{narayanaswamy_raja_clemens_2010, title={Characterization of a high-frequency pulsed-plasma jet actuator for supersonic flow control}, volume={48}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-76949095393&partnerID=MN8TOARS}, DOI={10.2514/1.41352}, abstractNote={thepulsed-plasmajet,thejetisinjectednormallyintoaMach3crossflowandthepenetrationdistanceismeasuredby using schlieren imaging. These measurements show that the jet penetrates 1.5 boundary-layer thicknesses into the crossflow andthe jet-to-crossflowmomentum fluxratioisestimated to be0.6.Aseries of experiments wasconducted to determine the characteristics of the pulsed-plasma jet issuing into stagnant air at a pressure of 35 torr. These resultsshowthattypicaljetvelocitiesofabout250 m=scanbeinducedwithdischargeenergiesofabout30mJperjet. Furthermore, the maximum pulsing frequency was found to be about 5 kHz, because above this frequency the jet beginstomisfire.Themisfiringappearstobeduetothe finitetimeittakesforthecavitytoberechargedwithambient air between discharge pulses. The velocity at the exit of the jet is found to be primarily dependent on the discharge current and independent of other discharge parameters such as cavity volume and orifice diameter. Temperature measurementsaremadeusingopticalemissionspectroscopyandrevealthepresenceofconsiderablenonequilibrium between rotational and vibrational modes. The gas heating efficiency was found to be 10% and this parameter is shown to have a direct effect on the plasma jet velocity. These results indicate that the pulsed-plasma jet creates a sufficiently strong flow perturbation that holds great promise as a supersonic flow actuator.}, number={2}, journal={AIAA Journal}, author={Narayanaswamy, V. and Raja, L.L. and Clemens, N.T.}, year={2010}, pages={297–305} }
 @inproceedings{narayanaswamy_clemens_raja_2010, title={Investigation of a pulsed-plasma jet for shock / boundary layer control}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78649810322&partnerID=MN8TOARS}, booktitle={48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition}, author={Narayanaswamy, V. and Clemens, N.T. and Raja, L.L.}, year={2010} }
 @inproceedings{lochman_murphree_narayanaswamy_clemens_2010, title={PLIF imaging of naphthalene-ablation products in a Mach 5 turbulent boundary layer}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84877723148&partnerID=MN8TOARS}, DOI={10.2514/6.2010-4346}, abstractNote={A new technique is currently under development that uses planar laser-induced fluorescence (PLIF) imaging of sublimated naphthalene to image the transport of ablation products in a hypersonic boundary layer. The primary motivation for this work is to understand scalar transport in hypersonic boundary layers and to develop a database for validation of computational models. The naphthalene is molded into a rectangular insert that is mounted flush with the floor of a Mach 5 wind tunnel. The distribution of naphthalene in the boundary layer is imaged by using PLIF, where the laser excitation is at 266 nm and the fluorescence is collected in the range of 320 to 380 nm. To investigate the use of naphthalene PLIF as a quantitative diagnostic technique, a series of experiments is conducted to determine the linearity of the fluorescence signal with laser fluence, as well as the temperature and pressure dependencies of the signal. The naphthalene fluorescence at 297 K is determined to be linear for laser fluence that is less than about 200 J/m 2 . The temperature dependence of the naphthalene fluorescence signal is found at atmospheric pressure over the temperature range of 297K to 525K. A monotonic increase in the fluorescence is observed with increasing temperature. Naphthalene fluorescence lifetime measurements were also made in pure-air and nitrogen environments at 300 K over the range 3.3 kPa to 101.3 kPa. The results in air show the expected Stern-Volmer behavior with decreasing lifetimes at increasing pressure, whereas nitrogen exhibits the opposite trend. Preliminary PLIF images of the sublimated naphthalene are acquired in a Mach 5 turbulent boundary layer. Relatively low signal-to-noise-ratio images were obtained at a stagnation temperature of 345 K, but much higher quality images were obtained at a stagnation temperature of 375 K. Our results indicate that PLIF of sublimating naphthalene may be an effective tool for studying scalar transport in hypersonic flows.}, booktitle={27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference 2010}, author={Lochman, B.J. and Murphree, Z.R. and Narayanaswamy, V. and Clemens, N.T.}, year={2010} }
 @inproceedings{clemens_narayanaswamy_2009, title={Shock/turbulent boundary layer interactions: Review of recent work on sources of unsteadiness}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78349243684&partnerID=MN8TOARS}, booktitle={39th AIAA Fluid Dynamics Conference}, author={Clemens, N.T. and Narayanaswamy, V.}, year={2009} }
 @inproceedings{narayanaswamy_shin_clemens_raja_2008, title={Investigation of plasma-generated jets for supersonic flow control}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78149451744&partnerID=MN8TOARS}, DOI={10.2514/6.2008-285}, booktitle={46th AIAA Aerospace Sciences Meeting and Exhibit}, author={Narayanaswamy, V. and Shin, J. and Clemens, N.T. and Raja, L.L.}, year={2008} }
 @inproceedings{shin_narayanaswamy_raja_clemens_2007, title={Characteristics of a plasma actuator in Mach 3 flow}, volume={14}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34250798514&partnerID=MN8TOARS}, booktitle={Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting}, author={Shin, J. and Narayanaswamy, V. and Raja, L.L. and Clemens, N.T.}, year={2007}, pages={9665–9675} }
 @article{shin_narayanaswamy_raja_clemens_2007, title={Characterization of a direct-current glow discharge plasma actuator in low-pressure supersonic flow}, volume={45}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34547583158&partnerID=MN8TOARS}, DOI={10.2514/1.27197}, abstractNote={DOI: 10.2514/1.27197 An experimental study of a direct-current, nonequilibrium glow plasma discharge in the presence of a Mach 2.85 supersonic flow is presented. The discharge is generated with pinlike electrodes flush-mounted on a plane surface with sustaining currents between 25 to 300 mA. In the presence of a supersonic flow, two distinct discharge modes (diffuse and constricted) are observed depending on the flow and discharge operating conditions. The effect of the dischargeonthe flow(“plasmaactuation”)ischaracterizedbytheappearanceofaweakshockwaveinthevicinityof the discharge. The shock is observed at low powers (10 W) for the diffuse discharge mode but is absent for the higher power (100 W) constricted mode. High-speed laser schlieren imaging suggests that plasma actuation is rapid as it occurs on a time scale that is less than 220 s. Rotational (gas) and vibrational temperature within the dischargeareestimatedbyemissionspectralline fitsofN2 andN 2 rovibronicbandsnear365–395nm.Theelectronic temperatures are estimated by using the Boltzmann plot method for Fe(I) atomic lines. Rotational temperatures are found to be high (1500 K) in the absence of a flow but drop sharply (500 K) in the presence of a supersonic flow for both the diffuse and constricted discharge modes. The vibrational and electronic temperatures are measured to be about 3000 K and 1.25 eV, respectively, and these temperatures are the same with and without flow. The gas temperature spatial profiles above the cathode surface are similar for the diffuse and constricted modes indicating that dilatational effects due to gas heating are similar. However, complete absence of flow actuation as indicated visually by the shock indicates that electrostatic forces may also play an important role in high-speed plasma-flow actuation phenomena. Analytical estimates using cathode sheath theory indicate thation pressure within sheath can besignificant,resulting ingascompressionwithin sheathandacorrespondingexpansionaboveit. Theexpansion,in turn, may fully negate the dilatational effect in the constricted case resulting in an apparent absence of forcing in the constricted case.}, number={7}, journal={AIAA Journal}, author={Shin, J. and Narayanaswamy, V. and Raja, L.L. and Clemens, N.T.}, year={2007}, pages={1596–1605} }
 @inproceedings{shin_narayanaswamy_raja_clemens_2006, title={Generation of plasma induced flow actuation by DC glow-like discharge in a supersonic flow}, volume={3}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34250751149&partnerID=MN8TOARS}, DOI={10.2514/6.2006-169}, abstractNote={Plasma induced ∞ow fleld modiflcation is studied experimentally using non-equilibrium DC surface discharge in a Mach 3 supersonic ∞ow. An array of small pin electrodes (` = 3=32") is used in streamwise plasma discharge conflguration. The schlieren imaging shows that an oblique shock can be obtained with a volumetric glow discharge on the cathode with a relatively low current (as low as 50 mA). The actuation is found to be immediate with a time scale less than 222 „s whenever there is a noticeable volumetric glow region on the cathode in both cathode upstream and cathode downstream cases. With a laser schlieren, three identiflable modes are observed and the selected modes which have a volumetric glow on top of the cathode can give an actuation while the other mode does not show any noticeable efiect. The conditions to get an appropriate mode are dependent mostly on the stagnation pressure. Increasing the current gives a preference to have a constricted plasma while a pressure decrease gives a volumetric glow.}, booktitle={Collection of Technical Papers - 44th AIAA Aerospace Sciences Meeting}, author={Shin, J. and Narayanaswamy, V. and Raja, L.L. and Clemens, N.}, year={2006}, pages={2042–2051} }