@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{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} }