Experimental and numerical investigation of fast control surface deflections

The development of load alleviation for an aircraft requires an accurate and efficient prediction of gust and maneuver loads. In the design of an aircraft the prediction of these unsteady loads has become crucial for the ideal alleviation of gust loads. A database for unsteady aerodynamic responses is however very cost expensive and time consuming to generate, in an experiment and with numerical simulations. An efficient tool for the computation of aerodynamic responses is the linear frequency domain solver, which allows the prediction of amplitude and phase shift of any periodic oscillation of body or flow in the frequency domain. The unsteady response allows a fast and efficient prediction for any arbitrary unsteady change of in example a control surface deflection or a gust speed. The validation of the linear frequency domain solver for unsteady aerodynamics is crucial, so that its prediction quality is ensured. A wind tunnel experiment was set up, which focused on fast control surface deflections and analyzed the capabilities and accuracy of the method. The experiment was accompanied by two- and three-dimensional URANS simulations, which allow a more detailed comparison and help to increase the understanding of the flow physics. For higher frequencies of the control surface oscillation, the adjusting position of the stagnation point on the leading edge lags behind the actual control surface position as if it were in a quasi-steady state. This leads to a phase lag between motion and resulting force and a lower lift response amplitude.