Unsteady Aerodynamics Prediction of Low-Reynolds-Number Airfoils

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In a rarefied atmosphere, for instance, at an ultra-high altitude, the Reynolds number based on flight velocity and airfoil's length scale is lowered significantly. Besides, the flight velocity is usually far greater than that of hobby model planes, flying near ground surface; therefore, the Mach number becomes relatively high, although it is still subsonic. In this study, we would experimentally reproduce the coupling between acoustic and hydrodynamic disturbances, using wind-tunnel facilities. A model airfoil is placed in a rarefied flow, achieved in a low-pressure wind-tunnel. The frequency characteristics obtained in the experiments agree well with our numerical analysis, which strongly suggests the existence of acoustic-hydrodynamic coupling at low Reynolds number.