An experimental study of the effects of pitch-pivot-point location on the propulsion performance of a pitching airfoil |
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| Institution: | 1. Center for Aerodynamics, School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai 200240, China;2. Department of Aerospace Engineering, Iowa State University, Ames, IA 50010, USA;3. The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;1. Swinburne University of Technology, Hawthorn, Victoria 3122, Australia;2. Université de Toulouse; INP; IMFT (Institut de Mécanique des Fluides de Toulouse), Allée Camille Soula, F-31400 Toulouse, France;3. CNRS; IMFT, F-31400 Toulouse, France;4. Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Melbourne, Victoria 3800, Australia;1. Department of Aerodynamics, Nanjing University of Aeronautics and Astronautics Yudao Street 29, Nanjing, Jiangsu 210016, China;2. School of Engineering and Information Technology, University of New South Wales Canberra, ACT 2600, Australia;3. Aerodynamics Development Department, AVIC Aerodynamics Research Institute Yangshan Street 1, Shenyang, Liaoning 110034, China;1. School of Energy and Power Engineering, Xi''an Jiaotong University, Xi''an, Shaanxi Province, 710049, China;2. Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi''an Jiaotong University, Xi''an, Shaanxi Province, 710049, China;3. Engineering Simulation and Aerospace Computing(ESAC), School of Mechanical Engineering, Northwestern Polytechnical University, P. O. Box 552, Xi''an, Shaanxi Province, 710072, China;1. University of Shanghai for Science and Technology, Shanghai, 200093, China;2. Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer, Shanghai, 200093, China;3. Marine Design and Research Institute of China, Shanghai, 200011, China |
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| Abstract: | An experimental investigation was conducted to characterize the evolution of the unsteady vortex structures in the wake of a pitching airfoil with the pitch-pivot-point moving from 0.16C to 0.52C (C is the chord length of the airfoil). The experimental study was conducted in a low-speed wind tunnel with a symmetric NACA0012 airfoil model in pitching motion under different pitching kinematics (i.e., reduced frequency k=3.8–13.2). A high-resolution particle image velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the characteristics of the wake flow and the resultant propulsion performance of the pitching airfoil. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged velocity distributions in the wake flow, “phase-locked” PIV measurements were also performed to elucidate further details about the behavior of the unsteady vortex structures. Both the vorticity–moment theorem and the integral momentum theorem were used to evaluate the effects of the pitch-pivot-point location on the propulsion performance of the pitching airfoil. It was found that the pitch-pivot-point would affect the evolution of the unsteady wake vortices and resultant propulsion performance of the pitching airfoil greatly. Moving the pitch-pivot-point of the pitching airfoil can be considered as adding a plunging motion to the original pitching motion. With the pitch-pivot-point moving forward (or backward), the added plunging motion would make the airfoil trailing edge moving in the same (or opposite) direction as of the original pitching motion, which resulted in the generated wake vortices and resultant thrust enhanced (or weakened) by the added plunging motion. |
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| Keywords: | Micro-Air-Vehicles (MAVs) Unsteady Aerodynamics Pitching Airfoil Pitch-pivot-point Location PIV |
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