Experiments on unsteady vortex flowfield of typical rotor airfoils under dynamic stall conditions

A new experiment for airfoil dynamic stall is conducted by employing the advanced particle image velocimetry (PIV) technology in an open-return wind tunnel. The aim of this experimental investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex (LEV) of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack (AoA) of airfoil can obviously influence the dynamic stall characteristics of airfoil, and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the convection velocity of LEV is estimated in this measurement, and the results demonstrate that the influence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil. (C) 2016 Chinese Society of Aeronautics and Astronautics. Published by Elsevier Ltd.