Experimental analysis of friction drag reduction by spanwise traveling surface waves

In times of globalization, the international transport is gaining more and more importance. Thus, the responsible dealing with energy, especially in the transport sector, is indispensable. One promising way to reduce the energy consumption of aircrafts is to minimize the friction drag via modification of the near-wall flow field by active or passive means. In this study, the effectiveness of an active drag control method for turbulent boundary layers based on spanwise traveling transversal surface waves is investigated experimentally. The experimental setup consists of a flat plate equipped with an insert to generate the wave motion by an electromagnetic actuator system. Particle-image velocimetry (PIV) and micro-particle-tracking velocimetry (μ-PTV) are applied to determine the influence of the Reynolds number, the wave amplitude, and of an adverse pressure gradient (APG) on the drag reduction. Phase-averaged PIV measurements above the actuated surface provide insight into the underlying flow phenomena.