Transversal surface wave control by gain switching iterative learning improving research on active turbulent flow control

Active turbulent flow control for friction drag reduction at high Reynolds numbers (Re > 104) on transportation systems such as airplanes is investigated. The drag reduction is based on transversal surface waves effecting the turbulent boundary layer. For this wave parameter studies are performed in subsonic wind tunnel experiments using an in house developed electromagnetic actuation system for flexible generation of sinusoidal surface waves with amplitudes between 50 and 500 μm. To ensure an amplitude accuracy better than 5% and a real-time parameter switching we evaluated a gain switching iterative learning control for the transversal surface waves. This approach enables efficient and reliable wind tunnel experiments investigating active turbulent flow control.