Aerodynamic Gust Response in High Angles of Attack

Abstract

The paper presents Navier-Stokes turbulent simulations of gust responses of a rigid airfoil and of a rigid wing configuration about high mean angles of attack, close to stall, in Reynolds numbers in the order of one million. Responses show that flow separation associated with high angles of attack significantly affect the lift build-up dynamics. Airfoil sharp-edge gust response about high mean angle of attack does not resemble the Kussner function. It involves an initial sharp rise of the lift, which overshoots the steady state value. The maximum lift force that develop in response to a one-minus-cosine gust about high mean angle of attack can be either higher or lower than the response about zero mean angle of attack, depending on the gust gradient length. For short gusts, a dynamic stall effect is observed, where the maximum lift response is higher than that computed about small mean angles of attack, while for longer gusts the maximum lift response is smaller. For the rigid HALE wing case, the lift that develop in response to a one-minus-cosine gust about high mean angle of attack is lower than the response about low mean angles of attack. Since the gust response about high angles of attack does not scale linearly, convolution with sharp-edge gust response does not serve well for prediction of the gust response, and full simulation is required for accurate estimation of the gust loads.