Load Control for Unsteady Gusts with Control Surfaces using the Linear Frequency Domain

Abstract

A method is presented, that is able to mitigate gust loads on an airfoil induced by an incoming gust velocity field. It thereby computes the lift coefficient response to a specified arbitrary gust velocity profile and predicts the required time-accurate control surface deflection. The method uses the linear frequency domain solver to predict frequency responses for the gust and control surface derivative of the lift coefficient efficiently. The frequency responses are computed and then subsequently filled as samples into a surrogate model. For a new flight condition the surrogate model predicts the frequency response by mere interpolation. Because the aerodynamic response on the gust and the behavior of the control surface are known, the aerodynamic lift response and the required flap deflection for alleviation can both be predicted from a given gust velocity field. The method is thereby able to predict the aerodynamic response and a time-accurate deflection for any flight condition in the design space within milliseconds. Results of the method are shown and analyzed on a 2D profile of a transonic airfoil with an implemented plain flap. The parameter studies were made in low speed with variation of Mach number, Reynolds number, angle of attack, flap chord size and initial flap deflection. In comparison to unsteady Reynoldsaveraged Navier-Stokes computations, the presented method can predict the aerodynamic responses with the same accuracy and it saves more than 6 orders of magnitude in computation time. Using the linear frequency domain solver it is also able to predict the arising unsteady aerodynamic behavior and still cover the viscous effects in the flow.