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Active Control of Flow Over an Oscillating NACA 0012 Airfoil

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Active Control of Flow over an Oscillating NACA 0012 Airfoil Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By David Armando Castañeda Vergara, M.S., B.S. Graduate Program in Aeronautical and Astronautical Engineering The Ohio State University 2020 Dissertation Committee: Dr. Mo Samimy, Advisor Dr. Datta Gaitonde Dr. Jim Gregory Dr. Miguel Visbal Dr. Nathan Webb c Copyright by David Armando Castañeda Vergara 2020 Abstract Dynamic stall (DS) is a time-dependent flow separation and stall phenomenon that occurs due to unsteady motion of a lifting surface. When the motion is sufficiently rapid, the flow can remain attached well beyond the static stall angle of attack. The eventual stall and dynamic stall vortex formation, convection, and shedding processes introduce large unsteady aerodynamic loads (lift, drag, and moment) which are undesirable. Dynamic stall occurs in many applications, including rotorcraft, micro aerial vehicles (MAVs), and wind turbines. This phenomenon typically occurs in rotorcraft applications over the rotor at high forward flight speeds or during maneuvers with high load factors. The primary adverse characteristic of dynamic stall is the onset of high torsional and vibrational loads on the rotor due to the associated unsteady aerodynamic forces. Nanosecond Dielectric Barrier Discharge (NS-DBD) actuators are flow control devices which can excite natural instabilities in the flow. These actuators have demonstrated the ability to delay or mitigate dynamic stall. To study the effect of an NS-DBD actuator on DS, a preliminary proof-of-concept experiment was conducted. This experiment examined the control of DS over a NACA 0015 airfoil; however, the setup had significant limitations. The NS-DBD showed significant promise as a means of reducing the unsteady loads associated with dynamic stall, despite limitations of the proof-of-concept experiment. The limitations/issues with the preliminary set up were rectified by designing an upgraded experimental setup for examining dynamic stall flow control using NS-DBD plasma actuators on a NACA 0012 airfoil. The upgrade ii included installing a modular, vertically-mounted airfoil driven by a direct-drive servomotor in combination with a multi-axis force and torque transducer, all of which was controlled by a real-time data acquisition device. In addition, the airfoil (in the proof-of-concept experiment) imposed a high tunnel blockage when at large angles of attack. This issue was ameliorated by reducing the airfoil chord length and aspect ratio. End plates were added to prevent tip vortex formation and to reduce tunnel sidewall interference. Baseline data were obtained using the upgraded setup. Force and moment data from the load cell were acquired for all cases to obtain aerodynamic loading data. The results showed significantly lower uncertainty levels when compared with the data obtained from the previous setup due to the increased repeatability of the airfoil motion and the direct measurement of aerodynamic forces (which includes the effect of any potential flow three- dimensionality). After baseline experiments, a series of flow control tests on dynamic stall were performed using NS-DBD plasma actuator installed at the leading edge of the NACA 0012 airfoil. A combination of three chord-based Reynolds numbers (300,000, 500,000, and 700,000) with reduced frequencies from 0.025 to 0.075 was used. Two excitation schemes were used: continuous excitation (excitation at a given frequency continuously throughout multiple oscillation cycles, as typically done in the literature) and a new method: Excitation in Parts of the Oscillating Cycle (EPOC). EPOC is excitation over a selected portion of the oscillating cycle or a variation of the excitation in the oscillation cycle. From load cell and PIV results, it is concluded that continuous excitation for deep and light stall produces significant changes in lift, drag, and moment during the oscillating cycle. Excited cases exhibit a reduction in lift hysteresis, peak drag, and negative damping compared with baseline due to the effects of excitation-triggered coherent structures. Results for light and deep dynamic stall using iii EPOC control showed that it is possible to improve a particular benefit (e.g. reduction in lift hysteresis, negative damping or drag ) with targeted control and the use of a particular excitation timing during the oscillating cycle. Different EPOC schemes can be used for different situations depending on the application requirements. iv Dedicated to my family and all my good friends! v Acknowledgments Dr. Samimy, I express my gratitude to you for your guidance and patience during all these years and for showing me that in science, we must be humans first and then scientists. Dr. Nathan Webb, thanks for sharing all your experience and knowledge in the field of experimental fluid dynamics and for the support as a friend outside the laboratory routine. For Achal Singhal, thank you for helping me with this project and for your honest feedback in the last years. Nicole Whiting, I am grateful for your dedication and your contribution to this project. Thank you for being an example of a good team worker! Josh Gueth, thanks for being the master of the tools and for your help during all the stages of this project. My highest appreciation to Jeffrey Barton and Dr. Matthew McCrink for your help with the NS pulser. I also want to thank to Benjamin Egelhoff for your collaboration and efficiency making the components for the experimental set up. To all the labmates who have shared your time with me, I am all gratitude. Finally, Colciencias, Fulbright, and the Ohio State University thanks for the support all these years. vi Vita December 2008 . B.S. Aeronautical Engineering Universidad de San Buenaventura Bogota, Colombia March 2011 . M.S. Mechanical Engineering Universidad Nacional de Colombia Bogota, Colombia 2012-2013 . .Lecturer Universidad de San Buenaventura Bogota, Colombia 2013-2018 . .Fulbright Fellow The Ohio State University Columbus, Ohio, USA 2018-present . .Graduate Research Associate The Ohio State University Columbus, Ohio, USA Publications Conference Publications David Castañeda, Nicole Whiting, Nathan Webb, and Mo Samimy. Design and Character- ization of an Experimental Setup for Active Control of Dynamic Stall over a NACA 0012 Airfoil In AIAA Aviation 2019 Forum, AIAA 2019-3212, doi:10.2514/6.2019-3212. June 2019. Nicole Whiting, David Castañeda, Nathan Webb, and Mo Samimy. Control of Dynamic Stall over a NACA 0012 Airfoil Using NS-DBD Plasma Actuators In AIAA SciTech 2020 Forum, AIAA-2020-1568. January 2020. vii Achal Singhal, David Castañeda, Nathan Webb, and Mo Samimy. Unsteady Flow Separa- tion Control over a NACA 0015 using NS-DBD Plasma Actuators In 55th AIAA Aerospace Sciences Meeting,AIAA 2017-1687, doi:10.2514/6.2017-1687. Jan 2017. Archival Publications David Castañeda, Nicole Whiting, Nathan Webb, and Mo Samimy. Design, validation of a facility and its preliminary results for light dynamic stall flow control. In Experiments in Fluids, will be submitted in 2020 . David Castañeda, Nathan Webb, and Mo Samimy. Strategies for flow control in deep dynamic stall using plasma actuators. In Physics of Fluids , will be submitted in 2020. Achal Singhal, David Castañeda, Nathan Webb, and Mo Samimy. Control of dynamic stall over a NACA 0015 airfoil using plasma actuators In AIAA Journal, doi:10.2514/1.J056071. Sep 2017. Theses David Castañeda. Design and Construction of a Windpump System Based on a Bioinspired Rotor (In Spanish). Universidad Nacional de Colombia, Bogota, Colombia, Dec 2010. David Castañeda et al. Detailed design of a Supersonic wind tunnel for its implementation at the University of San Buenaventura (In Spanish). Universidad de San Buenaventura, Bogota, Colombia, Dec 2007. Fields of Study Major Field: Aeronautical and Astronautical Engineering Studies in: Aerodynamics, Experimental Techniques, Flow Control, Fluid Mechanics, Optical Diagnostics, Turbulence viii Table of Contents Page Abstract . ii Dedication . .v Acknowledgments . vi Vita ........................................... vii List of Tables . xii List of Figures . xiv 1. Introduction . .1 1.1 Thesis Overview . .3 2. Background and Related Work . .4 2.1 Static Stall . .8 2.2 Comparison between Thin and Thick Airfoils . 12 2.3 Flow Characteristics over an Oscillating Airfoil . 15 2.4 Flow Characteristics of Dynamic Stall . 17 2.4.1 Parameters that influence Dynamic Stall . 22 2.4.2 Aerodynamic Damping . 23 2.5 Flow Control in Dynamic Stall . 25 2.5.1 Initial Work in Dynamic Stall Flow Control at GDTL . 28 3. Redesigned Experimental Setup . 34 3.1 Redesigned Experimental Set up Components . 36 3.1.1 Subsonic Wind Tunnel Facility . 36 ix 3.1.2 Airfoil Model . 38 3.1.3 Plasma Actuator . 41 3.1.4 Load Cell Transducer . 43 3.1.5 Direct Drive Servomotor . 44 3.1.6 Data Acquisition System . 45 3.2 Particle Image Velocimetry (PIV) . 47 3.3 Experimental set up capabilities . 51 4. Baseline Static and Dynamic Experiments . 52 4.1 Discussion of Motion profile, End Plates, and Aspect ratio effects . 53 4.1.1 Motion Profile . 53 4.1.2 End plates effects . 54 4.1.3 Aspect ratio influence . 56 4.2 Static Baseline . 58 4.3 Dynamic Baseline . 61 4.3.1 Filtering process . 61 4.3.2 Dynamic Stall Results . 65 4.4 Effect of plasma actuator installation . 71 5. Excitation Results and Discussion . 74 5.1 Light Dynamic Stall Regime . 76 5.1.1 Baseline Results for Light Dynamic Stall Cases . 77 5.1.2 Continuous Excitation in Light DS Cases . 79 5.1.3 EPOC in Light DS Cases . 89 5.1.4 PIV results in Light Dynamic Stall regime . 102 5.2 Deep Dynamic Stall Regime . 113 5.2.1 Continuous Excitation in Deep DS Cases . 113 5.2.2 EPOC in Deep DS Cases . 123 5.2.3 PIV results in Deep DS regime .
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