@article{reed_naik_abney_herbert_fine_vadlamannati_morris_taylor_muglia_granlund_et al._2024, title={Experimental Validation of an Iterative Learning-Based Flight Trajectory Optimizer for an Underwater Kite}, url={https://doi.org/10.1109/TCST.2024.3359891}, DOI={10.1109/TCST.2024.3359891}, abstractNote={In this work, we present an iterative learning strategy and experimental validation thereof for optimizing the flight trajectory of an underwater kite. The methodology is adapted to two different power generation configurations. The iterative learning algorithm consists of two main steps, which are executed at each iteration. In the first step, a meta-model is updated using a recursive least squares (RLS) estimate to capture an economic performance index as a function of a set of basis parameters that define the flight trajectory. The second step is an iterative learning update using information from past cycles to update basis parameters at future cycles using a gradient ascent formulation. This algorithm was experimentally validated on a scaled experimental prototype underwater kite system towed behind a test vessel in Lake Norman, North Carolina. Using our experimental system and algorithm, we were able to increase the kite’s mechanical power generation by an average of 24.4% across the tests performed.}, journal={IEEE Transactions on Control Systems Technology}, author={Reed, James and Naik, Kartik and Abney, Andrew and Herbert, Dillon and Fine, Jacob and Vadlamannati, Ashwin and Morris, James and Taylor, Trip and Muglia, Michael and Granlund, Kenneth and et al.}, year={2024} }
 @article{elfering_metoyer_chatterjee_mazzoleni_bryant_granlund_2023, title={Blade element momentum theory for a skewed coaxial turbine}, volume={269}, ISSN={["1873-5258"]}, url={https://doi.org/10.1016/j.oceaneng.2022.113555}, DOI={10.1016/j.oceaneng.2022.113555}, abstractNote={A coaxial turbine under skew with significant rotor spacing has the potential for increased power output compared to a flow-aligned turbine due to a portion of the downstream rotor experiencing freestream velocity, referred to as a fresh flow region. A lab-scale prototype was designed and built to investigate the skew-to-power relationship of a coaxial turbine system as it compared to a blade element momentum theory model with multiple, sheared streamtubes representing the downstream rotor fresh flow region. The inclusion of the downstream rotor fresh flow region in the theoretical analysis is compared to the experimental data. The results support that the torque and power performance of the downstream rotor and overall skewed coaxial turbine system are predicted more accurately.}, journal={OCEAN ENGINEERING}, author={Elfering, Kelsey and Metoyer, Rodney and Chatterjee, Punnag and Mazzoleni, Andre and Bryant, Matthew and Granlund, Kenneth}, year={2023}, month={Feb} }
 @article{hassan_bryant_mazzoleni_ramaprabhu_granlund_2022, title={Analytical wake model for coaxial dual-rotor turbines}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, DOI={10.1109/OCEANS47191.2022.9977241}, abstractNote={This work develops and validates a novel analytical wake model for coaxial dual-rotor turbines. With the diameters, and axial induction factors of the upstream and downstream rotors, and the freestream velocity, the proposed model estimates the wake velocity deficit in the near- and far-wake of the coaxial turbine. It is developed by utilizing the Bernoulli principle along the streamlines that pass through the near- and far-wake control volumes and the conservation laws for mass and momentum. This simple model can be used to calculate the velocity distribution in the wake using just one parameter. The wake prediction is contrasted with CFD results for various flow conditions to find good agreements between them. The novel wake model can be useful for solving the turbine farm layout optimization problem that involve dual-rotor configurations for the power generators.}, journal={2022 OCEANS HAMPTON ROADS}, author={Hassan, Mehedi and Bryant, Matthew and Mazzoleni, Andre and Ramaprabhu, Praveen and Granlund, Kenneth}, year={2022} }
 @article{abney_reed_naik_bryant_herbert_leonard_vadlamannati_mook_beknalkar_alvarez_et al._2022, title={Autonomous Closed-Loop Experimental Characterization and Dynamic Model Validation of a Scaled Underwater Kite}, volume={144}, ISSN={["1528-9028"]}, DOI={10.1115/1.4054141}, abstractNote={
 This paper presents the closed-loop experimental framework and dynamic model validation for a 1/12-scale underwater kite design. The pool-based tow testing framework described herein, which involves a fully actuated, closed-loop controlled kite and flexible tether, significantly expands upon the capabilities of any previously developed open-source framework for experimental underwater kite characterization. Specifically, the framework has allowed for the validation of three closed-loop flight control strategies, along with a critical comparison between dynamic model predictions and experimental results. In this paper, we provide a detailed presentation of the experimental tow system and kite setup, describe the control algorithms implemented and tested, and quantify the level of agreement between our multi-degree-of-freedom kite dynamic model and experimental data. We also present a sensitivity analysis that helps to identify the most influential parameters to kite performance and further explain remaining mismatches between the model and data.}, number={7}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Abney, Andrew and Reed, James and Naik, Kartik and Bryant, Samuel and Herbert, Dillon and Leonard, Zak and Vadlamannati, Ashwin and Mook, Mariah and Beknalkar, Sumedh and Alvarez, Miguel and et al.}, year={2022}, month={Jul} }
 @article{williams_bryant_agrawal_mazzoleni_granlund_ramaprabhu_bryant_2022, title={Characterization of the Steady-State Operating Conditions of Tethered Coaxial Turbines}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, url={http://dx.doi.org/10.1109/oceans47191.2022.9977052}, DOI={10.1109/OCEANS47191.2022.9977052}, abstractNote={Tethered coaxial turbines (TCTs) may be a feasible configuration to extract hydrokinetic energy from the Gulf Stream’s flow. A TCT consists of two rotors attached to the halves of a rotary generator, which is moored to a mounting point via a tether. Flow causes the rotors to counter-rotate which induce power within the generator. The TCT’s steady-state operating domain and power extraction is determined by the intersection of the hydrodynamic operating domain of the rotors and electromechanic operating domain of the generator. As a result, the TCT’s operating point can be selected with an electrical load resistance, skew angle, and flow speed. Previous analytical methods for evaluating dual rotor devices have assumed ideal rotor, flow, and generator characteristics to simplify the quantification of power extraction. The proposed hydrodynamic analysis modifies traditional blade-element momentum theory (BEMT) to accept nonuniform inflow into the rotor, via a radially and azimuthally discretized BEMT method (RAD-BEMT). RAD-BEMT is leveraged alongside a momentum theory wake development factor to determine the response of the back rotor within the nonuniform wake of the front rotor. The back rotor response is determined by minimizing the difference in mass continuity and rotor torques. Our electromechanical analysis considers an AC generator, and the effects of voltage rectification, system resistance, and capacitance on the TCT’s power extraction capabilities. A case study was performed to demonstrate the ability of torque and mass continuity minimization to locate a hydrodynamic operating point, for axial and skew flow conditions. Additionally, power extraction capabilities, load resistance selection, and the qualitative effects of skew on the minimization domain are discussed.}, journal={2022 OCEANS HAMPTON ROADS}, publisher={IEEE}, author={Williams, Vinson Oliver and Bryant, Samuel and Agrawal, Saurabh and Mazzoleni, Andre P. and Granlund, Kenneth and Ramaprabhu, Praveen and Bryant, Matthew}, year={2022} }
 @article{agrawal_williams_tong_hassan_muglia_bryant_granlund_ramaprabhu_mazzoleni_2022, title={Demonstration of a Towed Coaxial Turbine Subscale Prototype for Hydrokinetic Energy Harvesting in Skew}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, url={http://dx.doi.org/10.1109/oceans47191.2022.9977395}, DOI={10.1109/OCEANS47191.2022.9977395}, abstractNote={The immense potential for ocean current energy harvesting is being actively explored by researchers, exhibiting the importance of the marine hydrokinetic industry. This paper presents a towed dual rotor coaxial turbine prototype built to demonstrate the ability of tethered, underwater, hydrokinetic devices to harvest energy from ocean currents. A sub-scale test article was developed to measure fluid power conversion and serve as a platform for operational feasibility in open-water testing. Tow testing of this article was done in the freshwaters of Lake Norman in North Carolina at three tow speeds: 1 m/s, 1.25 m/s and 1.5 m/s. Preliminary results demonstrate the ability to extract power, system robustness, waterproofing capabilities, and illuminates the nuances and non-linearities unique to the tethered coaxial turbine system.}, journal={2022 OCEANS HAMPTON ROADS}, publisher={IEEE}, author={Agrawal, Saurabh and Williams, Vinson Oliver and Tong, Xinyang and Hassan, Mehedi and Muglia, Mike and Bryant, Matthew and Granlund, Kenneth and Ramaprabhu, Praveen and Mazzoleni, Andre P.}, year={2022} }
 @article{elfering_narsipur_granlund_2022, title={High streamwise airfoil oscillations at constant low and high incidence angles}, volume={34}, ISSN={["1089-7666"]}, url={https://doi.org/10.1063/5.0097570}, DOI={10.1063/5.0097570}, abstractNote={Ratios of streamwise airfoil oscillations to the freestream velocity above 30% have not been well investigated in the literature for a reduced frequency range relevant to unsteady applications. A known departure from the experimental correlation to analytical theory for lower magnitudes of this ratio, known as surge amplitude, motivates a parameter study for constant freestream, at constant low- and high-incidence angles, to understand the circulatory lift dependence on angle of attack, Reynolds number, surge amplitude, and reduced frequency in comparison with theory and higher-order computations. To better understand the increased deviation between theory and experiment with increasing velocity fluctuation, a detailed study of surge amplitude of 0.5 is investigated. The experiment for comparison was a free-surface water tunnel with a NACA (National Advisory Committee for Aeronautics) 0018 airfoil oscillated in the streamwise direction. Force measurements, normalized by instantaneous dynamic pressure, reveal that unsteady lift is dependent on Reynolds number and reduced frequency in both attached and fully separated conditions. In separated conditions, mean and fluctuating lift show a dependency on reduced frequency for larger velocity fluctuations than a relative surge amplitude of 10%. Two-dimensional computations were found to agree well with experimental data for Reynolds number 75 k, low incidence cases, and for high incidence with reduced frequencies less than 0.15, where a fully separated upper surface boundary layer condition occurred. Agreement between computations and experiments was not favorable for reduced frequencies above 0.15 for high incidence cases, where partial upper surface boundary layer reattachment is predicted.}, number={8}, journal={PHYSICS OF FLUIDS}, author={Elfering, Kelsey and Narsipur, Shreyas and Granlund, Kenneth}, year={2022}, month={Aug} }
 @article{aleman_gopalarathnam_granlund_2022, title={Novel Surface Flow-Reversal Sensor Applied to Detection of Airfoil Stall}, volume={5}, ISSN={["1533-3868"]}, url={https://doi.org/10.2514/1.C036732}, DOI={10.2514/1.C036732}, abstractNote={No AccessEngineering NotesNovel Surface Flow-Reversal Sensor Applied to Detection of Airfoil StallMaria A. Aleman, Ashok Gopalarathnam and Kenneth GranlundMaria A. Aleman https://orcid.org/0000-0001-5538-0299North Carolina State University, Raleigh, North Carolina 27695*Ph.D. Candidate, Department of Mechanical and Aerospace Engineering; . Student Member AIAA.Search for more papers by this author, Ashok Gopalarathnam https://orcid.org/0000-0002-1119-7887North Carolina State University, Raleigh, North Carolina 27695†Professor, Department of Mechanical and Aerospace Engineering; . Associate Fellow AIAA.Search for more papers by this author and Kenneth Granlund https://orcid.org/0000-0002-0108-8038North Carolina State University, Raleigh, North Carolina 27695‡Assistant Professor, Department of Mechanical and Aerospace Engineering; . Associate Fellow AIAA.Search for more papers by this authorPublished Online:15 May 2022https://doi.org/10.2514/1.C036732SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Komerath N. M., Liou S. G., Schwartz R. J. and Kim J. 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Google Scholar Previous article Next article FiguresReferencesRelatedDetails What's Popular Volume 59, Number 5September 2022 CrossmarkInformationCopyright © 2022 by Maria A. Aleman, Ashok Gopalarathnam, and Kenneth Granlund. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the eISSN 1533-3868 to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp. TopicsAerodynamic PerformanceAerodynamicsAeronautical EngineeringAeronauticsAviationAviation SafetyAvionicsFlight TestGuidance, Navigation, and Control SystemsPressure SensorsSensorsSkin FrictionTransducersTurbulenceWind Tunnels KeywordsFlow SensorsAirfoilWind Tunnel TestsLift CoefficientBoundary Layer SeparationAdverse Pressure GradientAerodynamic CharacteristicsTwo Dimensional FlowShear StressStatic PressurePDF Received28 October 2021Accepted4 April 2022Published online15 May 2022}, journal={JOURNAL OF AIRCRAFT}, publisher={American Institute of Aeronautics and Astronautics (AIAA)}, author={Aleman, Maria A. and Gopalarathnam, Ashok and Granlund, Kenneth}, year={2022}, month={May} }
 @article{gothard_granlund_2022, title={Store Separation Trajectory Clusters from Machine Learning}, volume={59}, ISSN={["1533-3868"]}, DOI={10.2514/1.C036261}, abstractNote={Store separation of a generic, thin-finned, missile through a continuously oscillating shear layer into subsonic flow was conducted experimentally through 100 drop tests to identify potential group...}, number={1}, journal={JOURNAL OF AIRCRAFT}, author={Gothard, William D. and Granlund, Kenneth O.}, year={2022}, pages={117–125} }
 @article{turpin_granlund_hayashi_sakaue_2021, title={Back-imaging of polymer-ceramic pressure-sensitive paint}, volume={32}, ISSN={["1361-6501"]}, url={https://doi.org/10.1088/1361-6501/ac0a0f}, DOI={10.1088/1361-6501/ac0a0f}, abstractNote={The feasibility of back-imaging polymer-ceramic pressure-sensitive paint (PC-PSP) was investigated, with supersonic flow over a rectangular cavity being the test subject. A PC-PSP formulation in which the luminophore was fully-integrated into the binding layer created a PSP which luminesced from the top and bottom of the layer. This PSP was applied to a clear acrylic plate serving as the cavity ceiling. Two identical high-speed cameras imaged the paint; one viewed the top of the PSP layer (front-imaging) whereas the other viewed the bottom of the layer (back-imaging). The temporal, time-averaged, and spectral response measured by each camera were functionally identical. Specifically, the two data were found to be 90% correlated in time at zero delay. The minor differences can be attributed to random noise and the fact that the cameras viewed through two different materials (one through acrylic and the other through optically-polished glass). These results illustrate that back-imaging is a promising method for overcoming the optical access constraints of conventional PSP imaging techniques.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, publisher={IOP Publishing}, author={Turpin, Aaron M. and Granlund, Kenneth O. and Hayashi, Tatsunori and Sakaue, Hirotaka}, year={2021}, month={Oct} }
 @article{weisler_waghela_granlund_bryant_2021, title={Finite wing lift during water-to-air transition}, volume={6}, ISSN={["2469-990X"]}, url={https://doi.org/10.1103/PhysRevFluids.6.054002}, DOI={10.1103/PhysRevFluids.6.054002}, abstractNote={We report the experimental investigation of lift generation by an initially submerged aspect ratio 4 wing that translates through the water-air interface. Many animals, such as flying fish and diving seabirds, use wings or fins to produce lift forces as they transit the water-air interface, and cross-domain underwater-aerial vehicles were recently demonstrated, but lift production of a wing egressing from water had not yet been quantified. Our results show that the lift history is markedly different for low egress velocities versus high egress velocities, with low velocities exhibiting a large oscillation in lift coefficient and high velocities exhibiting a more linear lift attenuation.}, number={5}, journal={PHYSICAL REVIEW FLUIDS}, publisher={American Physical Society (APS)}, author={Weisler, W. A. and Waghela, R. and Granlund, K. and Bryant, M.}, year={2021}, month={May} }
 @article{turpin_speth_sherer_granlund_2021, title={Low-frequency, spanwise oscillation in a finite-width cavity at Mach 1.5}, volume={33}, ISSN={["1089-7666"]}, url={https://doi.org/10.1063/5.0053682}, DOI={10.1063/5.0053682}, abstractNote={A joint experimental–computational program examined low-frequency, spanwise oscillations in supersonic flow over a finite-width cavity. Lowpass-filtered rear wall surface pressure revealed that shear layer impingement was most often biased to one side of the wall, switching sides at a frequency two orders of magnitude below resonance. Therefore, a bifurcation into two spanwise-asymmetric, mirrored, quasi-steady states could be defined. The states were described by biased impingement/ejection near the rear wall, asymmetry of the shear layer, and centrifugal inner-cavity flow. Resonance amplitudes were also found to be spatially modulated by the low-frequency flow switching. A yawed inflow was found to force one of the asymmetric states.}, number={7}, journal={PHYSICS OF FLUIDS}, author={Turpin, Aaron M. and Speth, Rachelle L. and Sherer, Scott E. and Granlund, Kenneth O.}, year={2021}, month={Jul} }
 @article{metoyer_chatterjee_elfering_bryant_granlund_mazzoleni_2021, title={Modeling, simulation, and equilibrium analysis of tethered coaxial dual-rotor ocean current turbines}, volume={243}, ISSN={["1879-2227"]}, DOI={10.1016/j.enconman.2021.113929}, abstractNote={Tethered multirotor axial flow turbines have been proposed to overcome the many challenges associated with extracting ocean current energy where deep waters render seabed mounting strategies infeasible. However, flexible systems are inherently more susceptible to perturbation than fixed systems. The effects of flow misalignment on the hydrokinetic energy conversion of multirotor coaxial turbines have been investigated recently; however, the spatial dynamics and equilibrium behaviors of tethered coaxial turbines have not been well characterized, limiting the ability of designers to explicitly tailor the device behavior. In this work, a computational model of a dual-rotor coaxial turbine is presented, and the model is employed to explore the equilibrium behavior of the turbine with variations in parameters. A complete characterization of the hydrostatic state of the system and a comparative study of representative tethered turbine simulation cases is also presented. Two important findings are presented. First, that a positively buoyant dual-rotor turbine that is anchored to a surface-dwelling platform can operate where the turbine is located at some desired depth below the surface. Second, that more than one turbine system may be anchored to a single point while maintaining the desired orientation and position of each turbine to avoid collision and maximize energy production. The results and methods presented in this paper may be used to inform application-specific coaxial turbine design and to develop additional targeted empirical and simulation studies.}, journal={ENERGY CONVERSION AND MANAGEMENT}, author={Metoyer, Rodney and Chatterjee, Punnag and Elfering, Kelsey and Bryant, Matthew and Granlund, Kenneth and Mazzoleni, Andre}, year={2021}, month={Sep} }
 @article{turpin_granlund_hayashi_sakaue_2021, title={Supersonic cavity flow with a downstream-sliding door}, volume={62}, ISSN={["1432-1114"]}, DOI={10.1007/s00348-021-03338-w}, number={12}, journal={EXPERIMENTS IN FLUIDS}, author={Turpin, Aaron M. and Granlund, Kenneth O. and Hayashi, Tatsunori and Sakaue, Hirotaka}, year={2021}, month={Dec} }
 @article{metoyer_chatterjee_elfering_bryant_granlund_mazzoleni_2020, title={Experimental analysis of dual coaxial turbines in skew}, volume={215}, url={https://doi.org/10.1016/j.oceaneng.2020.107877}, DOI={10.1016/j.oceaneng.2020.107877}, abstractNote={Ocean currents are a potentially reliable source of renewable energy, but the complications associated with deploying current energy conversion (CEC) devices in deep water make harvesting that energy a challenge. One promising approach is to use tethered axial-flow CECs composed of one or more pairs of coaxial counter-rotating turbines. However, a dual-rotor system moored in unsteady water by a flexible tether is likely to experience a condition, called skew, where the axis of rotation is not aligned with the direction of flow. A lab-scale turbine was constructed to investigate the effect of skew on fluid power conversion of a coaxial CEC. A semi-empirical model of the power conversion was developed for comparing the results to a recently published analytical model. It was found that the analytical model represents the data better than a simple ad hoc modification to previous models that is often used to estimate the power dynamics. Additionally, the results support the existence of a physical phenomenon – captured by the recent model but not represented in the ad hoc modification – in which the downstream rotor of a coaxial pair is partially within the wake and partially out of the wake of the upstream rotor.}, journal={Ocean Engineering}, publisher={Elsevier BV}, author={Metoyer, Rodney and Chatterjee, Punnag and Elfering, Kelsey and Bryant, Matthew and Granlund, Kenneth and Mazzoleni, Andre}, year={2020}, month={Nov}, pages={107877} }
 @article{jacuzzi_granlund_2020, title={Heaving Inverted Wing in Extreme Ground Effect}, volume={142}, ISSN={["1528-901X"]}, DOI={10.1115/1.4047804}, abstractNote={
 An inverted single element was subjected to a sinusoidal heaving motion in both free flight and extreme ground effect, with the ground-effect simulations oscillating in various states of interaction with the peak lift ride height of the wing. Peak negative lift during the heaving cycle was greater than the static values at the same ground clearances, time, and ensemble averaging showed an overall reduction in the lift coefficient of 10–22%. An analytical model combining potential flow lift predictions and a new variation of the Goman–Khrabrov state-space model predicts the lift behavior of the wing-in-ground effect based on reduced frequency and ground clearance.}, number={11}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Jacuzzi, Eric and Granlund, Kenneth}, year={2020}, month={Nov} }
 @article{siddiqui_naik_cobb_granlund_vermillion_2020, title={Lab-Scale, Closed-Loop Experimental Characterization, Model Refinement, and Validation of a Hydrokinetic Energy-Harvesting Ocean Kite}, volume={142}, ISSN={["1528-9028"]}, DOI={10.1115/1.4047825}, abstractNote={
 This paper presents a study wherein we experimentally characterize the dynamics and control system of a lab-scale ocean kite, and then refine, validate, and extrapolate this model for use in a full-scale system. Ocean kite systems, which harvest tidal and ocean current resources through high-efficiency cross-current motion, enable energy extraction with an order of magnitude less material (and cost) than stationary systems with the same rated power output. However, an ocean kite represents a nascent technology that is characterized by relatively complex dynamics and requires sophisticated control algorithms. In order to characterize the dynamics and control of ocean kite systems rapidly, at a relatively low cost, the authors have developed a lab-scale, closed-loop prototyping environment for characterizing tethered systems, whereby 3D printed systems are tethered and flown in a water channel environment. While this system has been shown to be capable of yielding similar dynamic characteristics to some full-scale systems, there are also fundamental limitations to the geometric scales and flow speeds within the water channel environment, making many other real-world scenarios impossible to replicate from the standpoint of dynamic similarity. To address these scenarios, we show how the lab-scale framework is used to refine and validate a scalable dynamic model of a tethered system, which can then be extrapolated to full-scale operation. In this work, we present an extensive case study of this model refinement, validation, and extrapolation on an ocean kite system intended for operation in the Gulf Stream or similar current environments.}, number={11}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Siddiqui, Ayaz and Naik, Kartik and Cobb, Mitchell and Granlund, Kenneth and Vermillion, Chris}, year={2020}, month={Nov} }
 @article{elfering_granlund_2020, title={Lift Equivalence and Cancellation for Airfoil Surge-Pitch-Plunge Oscillations}, volume={58}, ISSN={["1533-385X"]}, DOI={10.2514/1.J059068}, abstractNote={A NACA 0018 airfoil in freestream velocity is oscillated in longitudinal, transverse, and angle-of-attack directions with respect to the freestream velocity, known as surge, plunge, and pitch. The ...}, number={11}, journal={AIAA JOURNAL}, author={Elfering, Kelsey H. and Granlund, Kenneth O.}, year={2020}, month={Nov}, pages={4629–4643} }
 @article{turpin_chin_granlund_2020, title={Supersonic Cavity Flow Subjected to Continuous and Transient Leading-Edge Blowing}, volume={58}, ISSN={["1533-385X"]}, DOI={10.2514/1.J059267}, abstractNote={A rectangular cavity (L/D=5.67) with Mach 1.5 freestream was subjected to a large temporal variation in leading-edge blowing in order to experimentally investigate the effect on aerodynamic and aer...}, number={10}, journal={AIAA JOURNAL}, author={Turpin, Aaron M. and Chin, Daniel and Granlund, Kenneth}, year={2020}, month={Oct}, pages={4415–4425} }
 @article{chin_turpin_granlund_2020, title={Time-Dependent Aerodynamic Loads on Single and Tandem Stores in a Supersonic Cavity}, volume={57}, ISSN={["1533-3868"]}, DOI={10.2514/1.C035749}, abstractNote={To understand time-dependent aerodynamic loads on single and tandem (fore/aft) slender cylinders translated out into the supersonic freestream from a cavity at Mach 1.5, the normal force and pitchi...}, number={4}, journal={JOURNAL OF AIRCRAFT}, author={Chin, Daniel and Turpin, Aaron and Granlund, Kenneth}, year={2020}, pages={702–714} }
 @article{khatri_chatterjee_metoyer_mazzoleni_bryant_granlund_2019, title={Dual-Actuator Disc Theory for Turbines in Yaw}, volume={57}, ISSN={["1533-385X"]}, DOI={10.2514/1.J057740}, abstractNote={No AccessTechnical NotesDual-Actuator Disc Theory for Turbines in YawDheepak N. Khatri, Punnag Chatterjee, Rodney Metoyer, Andre P. Mazzoleni, Matthew Bryant and Kenneth O. GranlundDheepak N. KhatriNorth Carolina State University, Raleigh, North Carolina 27695*Graduate Research Assistant, Department of Mechanical and Aerospace Engineering.Search for more papers by this author, Punnag ChatterjeeNorth Carolina State University, Raleigh, North Carolina 27695*Graduate Research Assistant, Department of Mechanical and Aerospace Engineering.Search for more papers by this author, Rodney MetoyerNorth Carolina State University, Raleigh, North Carolina 27695*Graduate Research Assistant, Department of Mechanical and Aerospace Engineering.Search for more papers by this author, Andre P. MazzoleniNorth Carolina State University, Raleigh, North Carolina 27695†Associate Professor, Department of Mechanical and Aerospace Engineering. Associate Fellow AIAA.Search for more papers by this author, Matthew BryantNorth Carolina State University, Raleigh, North Carolina 27695‡Assistant Professor, Department of Mechanical and Aerospace Engineering.Search for more papers by this author and Kenneth O. GranlundNorth Carolina State University, Raleigh, North Carolina 27695§Assistant Professor, Department of Mechanical and Aerospace Engineering. Senior Member AIAA.Search for more papers by this authorPublished Online:23 Jan 2019https://doi.org/10.2514/1.J057740SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Betz A., “Das Maximum der theoretisch möglichen Ausnützung des Windes durch Windmotoren,” Zeitschrift für das gesamte Turbinenwesen, 1920, pp. 26, 307–309. Google Scholar[2] Newman B. G., “Actuator Disc Theory for Vertical Wind Turbines,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 15, Nos. 1–3, 1983, pp. 347–355. doi:https://doi.org/10.1016/0167-6105(83)90204-0 JWEAD6 0167-6105 CrossrefGoogle Scholar[3] Rosenberg A., Selvaraj S. and Sharma A., “A Novel Dual-Rotor Turbine for Increased Wind Energy Capture,” Journal of Physics: Conference Series, Vol. 524, 2014, Paper 012078. doi:https://doi.org/10.1088/1742-6596/524/1/012078 JPCSDZ 1742-6588 CrossrefGoogle Scholar[4] Adams Z. and Chen J., “Flux-Line Theory: A Novel Analytical Model for Cycloturbines,” AIAA Journal, Vol. 55, No. 11, 2017, pp. 3851–3867. doi:https://doi.org/10.2514/1.J055804 AIAJAH 0001-1452 LinkGoogle Scholar[5] Anderson M., “Horizontal Axis Wind Turbines in Yaw,” Proceedings of the First British Wind Energy Association (BWEA) Wind Energy Workshop, 1979, pp. 57–67, http://adsabs.harvard.edu/abs/1979wien.work...57A. Google Scholar[6] Grant I., Parkin P. and Wang X., “Optical Vortex Tracking Studies of a Horizontal Axis Wind Turbine in Yaw Using Laser-Sheet, Flow Visualization,” Experiments in Fluids, Vol. 23, No. 6, 1997, pp. 513–519. doi:https://doi.org/10.1007/s003480050142 EXFLDU 0723-4864 CrossrefGoogle Scholar[7] Newman B. G., “Multiple Actuator Disc Theory for Wind Turbines,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 24, No. 3, 1986, pp. 215–225. doi:https://doi.org/10.1016/0167-6105(86)90023-1 JWEAD6 0167-6105 CrossrefGoogle Scholar[8] Howland M., Bossuyt J., Martinez-Tossas L., Meyers J. and Meneveau C., “Wake Structure in Actuator Disk Models of Wind Turbines in Yaw Under Uniform Inflow Conditions,” Journal of Renewable and Sustainable Energy, Vol. 8, No. 4, 2016, Paper 043301. doi:https://doi.org/10.1063/1.4955091 CrossrefGoogle Scholar Previous article Next article FiguresReferencesRelatedDetailsCited byPool-Based Tow System for Testing Tethered Hydrokinetic Devices Being Developed to Harvest Energy From Ocean CurrentsMarine Technology Society Journal, Vol. 57, No. 1Blade element momentum theory for a skewed coaxial turbineOcean Engineering, Vol. 269Closed-Loop-Flight-Based Combined Geometric and Structural Wing Design optimization Framework for a Marine Hydrokinetic Energy KiteDemonstration of a Towed Coaxial Turbine Subscale Prototype for Hydrokinetic Energy Harvesting in SkewCharacterization of the Steady-State Operating Conditions of Tethered Coaxial TurbinesIncreased Energy Conversion with a Horizontal Axis Turbine in TranslationModeling, simulation, and equilibrium analysis of tethered coaxial dual-rotor ocean current turbinesEnergy Conversion and Management, Vol. 243Experimental analysis of dual coaxial turbines in skewOcean Engineering, Vol. 215 What's Popular Volume 57, Number 5May 2019 CrossmarkInformationCopyright © 2018 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 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 EngineeringAeronauticsConservation of Momentum EquationsEnergyEnergy FormsEnergy Forms, Production and ConversionEquations of Fluid DynamicsFlow RegimesFluid DynamicsFluid Flow PropertiesTurbinesTurbomachineryWind EngineeringWind Turbine KeywordsTurbinesYawConservation of MassHorizontal Axis TurbineFree Stream VelocityConservation EquationsTwo Dimensional FlowNavier Stokes EquationsKinetic EnergyFluid DensityAcknowledgmentsThis work was funded by a grant from the North Carolina Coastal Studies Institute. The authors would like to thank undergraduate research assistants Tyler Farr and Kyle Weiner for their contributions to these results.PDF Received27 August 2018Accepted2 December 2018Published online23 January 2019}, number={5}, journal={AIAA JOURNAL}, author={Khatri, Dheepak N. and Chatterjee, Punnag and Metoyer, Rodney and Mazzoleni, Andre P. and Bryant, Matthew and Granlund, Kenneth O.}, year={2019}, month={May}, pages={2204–2208} }
 @article{jacuzzi_granlund_2019, title={Passive flow control for drag reduction in vehicle platoons}, volume={189}, ISSN={["1872-8197"]}, DOI={10.1016/j.jweia.2019.03.001}, abstractNote={The use of passive ducting from the vehicle nose out of the front wheel opening was studied as a method of modifying the wake profile of a NASCAR Xfinity Series race vehicle to influence its effect on the drag of a trailing vehicle. Utilizing a fixed inlet area due to geometric constraints, exit angle, height and exit/inlet area ratio were explored using multi-vehicle Computational Fluid Dynamics (CFD) simulations and wind tunnel validation. Results indicate that appropriately positioned ducts reduce trailing car drag throughout the range of vehicle spacing studied; most significantly, it reduces the drag peak for the trailing car at approximately 1/4 to 1/2 car length spacing. Increased exit area is shown to enhance drag reduction for the trailing car at all vehicle spacings. Increasing exit angle closer to perpendicular to the direction of travel was shown to be effective as well, even being capable of eliminating the drag peak for the trailing car. Aerodynamic efficiency was increased over the non-ducted baseline configuration with the duct exit angle nearer to the direction of travel, while it was negatively impacted with the duct exit angle perpendicular to the direction of travel. Wind tunnel testing confirmed that aerodynamic efficiency improvement was due to an increase in negative lift under the car, while Kiel probe measurements validated the shape and positioning of the wake changes caused by the ducts.}, journal={JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS}, author={Jacuzzi, Eric and Granlund, Kenneth}, year={2019}, month={Jun}, pages={104–117} }
 @article{chin_granlund_maatz_schmit_reeder_2019, title={Stochastic Store Trajectory of Ice Models from a Cavity into Supersonic Flow}, volume={56}, ISSN={["1533-3868"]}, DOI={10.2514/1.C035104}, abstractNote={Store separation of prolate spheroid ice models with fins from a 4.5∶1 length-to-depth cavity into Mach=2.22 freestream was conducted experimentally to statistically investigate the existence of a ...}, number={4}, journal={JOURNAL OF AIRCRAFT}, author={Chin, Daniel and Granlund, Kenneth and Maatz, Ian and Schmit, Ryan F. and Reeder, Mark F.}, year={2019}, pages={1313–1319} }
 @article{ramesh_granlund_ol_gopalarathnam_edwards_2018, title={Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows}, volume={32}, ISSN={["1432-2250"]}, DOI={10.1007/s00162-017-0442-0}, abstractNote={A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements.}, number={2}, journal={THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS}, author={Ramesh, Kiran and Granlund, Kenneth and Ol, Michael V. and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2018}, month={Apr}, pages={109–136} }
 @article{stevens_babinsky_manar_mancini_jones_nakata_phillips_bomphrey_gozukara_granlund_et al._2017, title={Experiments and Computations on the Lift of Accelerating Flat Plates at Incidence}, volume={55}, ISSN={["1533-385X"]}, DOI={10.2514/1.j055323}, abstractNote={R. J. Bomphrey and N. Phillips were supported by the Engineering and Physical Sciences Research Council (EP/H004025/1 to R. J. Bomphrey). R. J. Bomphrey and T. Nakata were supported by the Biotechnology and Biological Sciences Research Council (BB/J001244/1 to R. J. Bomphrey).}, number={10}, journal={AIAA JOURNAL}, author={Stevens, P. R. R. J. and Babinsky, H. and Manar, F. and Mancini, P. and Jones, A. R. and Nakata, T. and Phillips, N. and Bomphrey, R. J. and Gozukara, A. C. and Granlund, K. O. and et al.}, year={2017}, month={Oct}, pages={3255–3265} }
 @article{granlund k._l._2016, title={Non-linearity of apparent mass for multi-element bodies}, volume={54}, number={2}, journal={AIAA Journal}, author={Granlund K., Ol M. and L., Bernal}, year={2016}, pages={771–776} }
 @article{granlund_ol_jones_2016, title={Streamwise Oscillation of Airfoils into Reverse Flow}, volume={54}, ISSN={["1533-385X"]}, DOI={10.2514/1.j054674}, abstractNote={A NACA 0012 airfoil is oscillated in streamwise direction in a constant freestream and at a fixed incidence angle such that reverse flow occurs cyclically. Force measurements reveal that lift is close to unsteady theory while advancing into the freestream, if the angle of attack permits attached flow. Lift is augmented at large angles of attack, where the flow is separated under steady conditions, and does not become appreciatively negative in flow reversal for either attached or separated flow, contrary to one unsteady theory but supported by another. Dye flow visualization reveals a coherent vortical structure upstream of the leading edge before flow reversal, which is believed to attenuate negative lift.}, number={5}, journal={AIAA JOURNAL}, author={Granlund, Kenneth O. and Ol, Michael V. and Jones, Anya R.}, year={2016}, month={May}, pages={1628–1636} }
 @article{mancini_manar_granlund_ol_jones_2015, title={Unsteady aerodynamic characteristics of a translating rigid wing at low Reynolds number}, volume={27}, ISSN={1070-6631 1089-7666}, url={http://dx.doi.org/10.1063/1.4936396}, DOI={10.1063/1.4936396}, abstractNote={Rectilinearly surging wings are investigated under several different velocity profiles and incidence angles. The primary wing studied here was an aspect ratio 4 rectangular flat plate. Studies on acceleration distance, ranging from 0.125c to 6c, and incidence angles 5°–45° were performed to obtain a better understanding of the force and moment histories during an extended surge motion over several chord-lengths of travel. Flow visualization and particle image velocimetry were performed to show the flow structures responsible for variations in force and moment coefficients. It was determined that the formation and subsequent shedding of a leading edge vortex correspond to oscillations in force coefficients for wings at high angle of attack. Comparing unsteady lift results to static force measurements, it was determined that for cases with large flow separation, even after 14 chords traveled at a constant velocity, the unsteady forces do not converge to the fully developed values. Forces were then broken up into circulatory and non-circulatory components to identify individual contributors to lift. Although it was observed that the “fast” and “slow” cases produced nearly identical vortex trajectories, circulation measurements confirmed that the faster acceleration case generates more vorticity in the form of a tighter, more coherent vortex and produces significantly more circulation than the slower acceleration case, which is consistent with the difference in force production.}, number={12}, journal={Physics of Fluids}, publisher={AIP Publishing}, author={Mancini, Peter and Manar, Field and Granlund, Kenneth and Ol, Michael V. and Jones, Anya R.}, year={2015}, month={Dec}, pages={123102} }
 @article{mancini p._f._granlund_ol_2015, title={Unsteady aerodynamic characteristics of a translating rigid wing at low Reynolds number}, volume={27}, number={123102}, journal={Physics of Fluids (Woodbury, N.Y.)}, author={Mancini P., Manar and F., A Jones A. and Granlund, K. and Ol, M.}, year={2015} }
 @article{mancini p._granlund_ol_2015, title={Unsteady aerodynamic response of a rapidly started flexible wing}, volume={7}, number={2}, journal={International Journal of Micro Air Vehicles}, author={Mancini P., A Jones A. and Granlund, K. and Ol, M.}, year={2015}, pages={147–158} }
 @article{granlund_monnier_ol_williams_2014, title={Airfoil longitudinal gust response in separated vs. attached flows}, volume={26}, ISSN={1070-6631 1089-7666}, url={http://dx.doi.org/10.1063/1.4864338}, DOI={10.1063/1.4864338}, abstractNote={Airfoil aerodynamic loads are expected to have quasi-steady, linear dependence on the history of input disturbances, provided that small-amplitude bounds are observed. We explore this assertion for the problem of periodic sinusoidal streamwise gusts, by comparing experiments on nominally 2D airfoils in temporally sinusoidal modulation of freestream speed in a wind tunnel vs. sinusoidal displacement of the airfoil in constant freestream in a water tunnel. In the wind tunnel, there is a streamwise unsteady pressure gradient causing a buoyancy force, while in the water tunnel one must subtract the inertial load of the test article. Both experiments have an added-mass contribution to aerodynamic force. Within measurement resolution, lift and drag, fluctuating and mean, were in good agreement between the two facilities. For incidence angle below static stall, small-disturbance theory was found to be in good agreement with measured lift history, regardless of oscillation frequency. The circulatory component of fluctuating drag was found to be independent of oscillation frequency. For larger incidence angles, there is marked departure between the measured lift history and that predicted from Greenberg's formula. Flow visualization shows coupling between bluff-body shedding and motion-induced shedding, identifiable with lift cancellation or augmentation, depending on the reduced frequency. Isolating the buoyancy effect in the wind tunnel and dynamic tares in the water tunnel, and theoretical calculation of apparent-mass in both cases, we arrive at good agreement in measured circulatory contribution between the two experiments whether the flow is attached or separated substantiating the linear superposition of the various constituents to total lift and drag, and supporting the idea that aerodynamic gust response can legitimately be studied in a steady freestream by oscillating the test article.}, number={2}, journal={Physics of Fluids}, publisher={AIP Publishing}, author={Granlund, K. and Monnier, B. and Ol, M. and Williams, D.}, year={2014}, month={Feb}, pages={027103} }
 @article{granlund_monnier_m._williams_2014, title={Airfoil longitudinal gust response in separated vs. attached flows}, volume={26}, number={027103}, journal={Physics of Fluids (Woodbury, N.Y.)}, author={Granlund, K. and Monnier, B. Ol and M. and Williams, D.}, year={2014} }
 @article{ramesh_gopalarathnam_granlund_ol_edwards_2014, title={Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding}, volume={751}, ISSN={0022-1120 1469-7645}, url={http://dx.doi.org/10.1017/jfm.2014.297}, DOI={10.1017/jfm.2014.297}, abstractNote={Abstract}, journal={Journal of Fluid Mechanics}, publisher={Cambridge University Press (CUP)}, author={Ramesh, Kiran and Gopalarathnam, Ashok and Granlund, Kenneth and Ol, Michael V. and Edwards, Jack R.}, year={2014}, month={Jun}, pages={500–538} }
 @article{schlueter_jones_granlund_oi_2014, title={Effect of Root Cutout on Force Coefficients of Rotating Wings}, volume={52}, ISSN={["1533-385X"]}, DOI={10.2514/1.j052821}, abstractNote={b = wingspan, m c = wing chord, m Re = Reynolds number, Vref; maxc∕v rr = wing root radius or root cutout rt = wing tip radius, m r75 = radius to reference plane, axis-relative method, m r75 = radius to reference plane, root-relative method, m s = distance travelled at wing reference plane, m s∕c = stroke-to-chord ratio S = wing area, m Vref; max = maximum local velocity at reference plane, m · s −1 Vroot = local velocity at wing root, m · s −1 V tip = local velocity at wing tip, m · s −1}, number={6}, journal={AIAA JOURNAL}, author={Schlueter, Kristy L. and Jones, Anya R. and Granlund, Kenneth and Oi, Michael}, year={2014}, month={Jun}, pages={1322–1325} }
 @article{granlund_ol_bernal_2014, title={Free-to-Pivot Flat Plates in Hover for Reynolds Numbers 14 to 21,200}, volume={52}, ISSN={["1533-385X"]}, DOI={10.2514/1.j053169}, abstractNote={A = motion translation amplitude b = plate span; 275 mm CN = motion-parallel force coefficient (N∕0.5ρbcUref) CP = motion-parallel power coefficient (∫ 10CN t∕T U t∕T ∕Uref) CT = motion-normal force (thrust) coefficient CZ = plate-normal force coefficient c = plate chord; 50 mm f = translation frequency h0 = nondimensional translation amplitude; A∕c Re = Reynolds number based on maximum velocity (A2πfc∕ν) St = Strouhal number (fc∕A2πf) t∕T = phase of plate leading edge imposed motion; 0 ≤ t∕T ≤ 1 Uref = maximum translation velocity}, number={9}, journal={AIAA JOURNAL}, author={Granlund, Kenneth O. and Ol, Michael V. and Bernal, Luis P.}, year={2014}, month={Sep}, pages={2083–2086} }
 @article{jantzen_taira_granlund_ol_2014, title={Vortex dynamics around pitching plates}, volume={26}, ISSN={1070-6631 1089-7666}, url={http://dx.doi.org/10.1063/1.4879035}, DOI={10.1063/1.4879035}, abstractNote={Vortex dynamics of wakes generated by rectangular aspect-ratio 2 and 4 and two-dimensional pitching flat plates in free stream are examined with direct numerical simulation and water tunnel experiments. Evolution of wake vortices comprised of tip, leading-edge, and trailing-edge vortices is compared with force history for a range of pitch rates. The plate pivots about its leading edge with reduced frequency from π/8 to π/48, which corresponds to pitching over 1 to 6 chord lengths of travel. Computations have reasonable agreement with experiments, despite large differences in Reynolds number. Computations show that the tip effects are confined initially near the wing tips, but begin to strongly affect the leading-edge vortex as the motion of the plate proceeds, with concomitant effects on lift and drag history. Scaling relations based on reduced frequency are shown to collapse aerodynamic force history for the various pitch rates.}, number={5}, journal={Physics of Fluids}, publisher={AIP Publishing}, author={Jantzen, Ryan T. and Taira, Kunihiko and Granlund, Kenneth O. and Ol, Michael V.}, year={2014}, month={May}, pages={053606} }
 @article{jantzen r._granlund k._m._2014, title={Vortex dynamics around pitching plates}, volume={26}, number={053606}, journal={Physics of Fluids (Woodbury, N.Y.)}, author={Jantzen R., Taira K. and Granlund K. and M., Ol}, year={2014} }
 @article{ramesh_gopalarathnam_edwards_ol_granlund_2013, title={An unsteady airfoil theory applied to pitching motions validated against experiment and computation}, volume={27}, ISSN={0935-4964 1432-2250}, url={http://dx.doi.org/10.1007/s00162-012-0292-8}, DOI={10.1007/s00162-012-0292-8}, number={6}, journal={Theoretical and Computational Fluid Dynamics}, publisher={Springer Science and Business Media LLC}, author={Ramesh, Kiran and Gopalarathnam, Ashok and Edwards, Jack R. and Ol, Michael V. and Granlund, Kenneth}, year={2013}, month={Jan}, pages={843–864} }
 @article{granlund_ol_bernal_2013, title={Experiments on free-to-pivot hover motions of flat plates}, volume={40}, journal={Journal of Fluids and Structures}, author={Granlund, K. and Ol, M. and Bernal, L.}, year={2013}, pages={337–355} }
 @article{granlund_ol_bernal_2013, title={Unsteady pitching flat plates}, volume={733}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2013.444}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Granlund, Kenneth O. and Ol, Michael V. and Bernal, Luis P.}, year={2013}, month={Oct} }
 @article{baik_bernal_granlund_ol_2012, title={Unsteady force generation and vortex dynamics of pitching and plunging aerofoils}, volume={709}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2012.318}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Baik, Yeon Sik and Bernal, Luis P. and Granlund, Kenneth and Ol, Michael V.}, year={2012}, month={Oct}, pages={37–68} }
 @article{mcgowan_granlund_ol_gopalarathnam_edwards_2011, title={Investigations of Lift-Based Pitch-Plunge Equivalence for Airfoils at Low Reynolds Numbers}, volume={49}, ISSN={["0001-1452"]}, DOI={10.2514/1.j050924}, abstractNote={The limits of linear superposition in two-dimensional high-rate low-Reynolds-number aerodynamics are examined by comparing the lift-coefficient history and flowfield evolution for airfoils undergoing harmonic motions in pure pitch, pure plunge, and pitch―plunge combinations. Using quasi-steady airfoil theory and Theodorsen's formula as predictive tools, pitching motions are sought that produce lift histories identical to those of prescribed plunging motions. It follows that a suitable phasing of pitch and plunge in a combined motion should identically produce zero lift, canceling either the circulatory contribution (with quasi-steady theory) or the combination of circulatory and noncirculatory contributions (with Theodorsen's formula). Lift history is measured experimentally in a water tunnel using a force balance and is compared with two-dimensional Reynolds-averaged Navier―Stokes computations and Theodorsen's theory; computed vorticity contours are compared with dye injection in the water tunnel. Theodorsen's method evinces considerable, and perhaps surprising, resilience in finding pitch-to-plunge equivalence of lift-coefficient―time history, despite its present application to cases in which its mathematical assumptions are demonstrably violated. A combination of pitch and plunge motions can be found such that net lift coefficient is nearly identically zero for arbitrarily high reduced frequency, provided that amplitude is small. Conversely, cancellation is possible at large motion amplitude, provided that reduced frequency is moderate. The product of Strouhal number and nondimensional amplitude is therefore suggested as the upper bound for when superposition and linear predictions remain valid in massively unsteady two-dimensional problems.}, number={7}, journal={AIAA JOURNAL}, author={McGowan, Gregory Z. and Granlund, Kenneth and Ol, Michael V. and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2011}, month={Jul}, pages={1511–1524} }