Virtual wall oscillations forced by a dbd plasma actuator operating under beat frequency – a concept for turbulent drag reduction

Abstract

A modified concept for generating DBD-based virtual spanwise wall oscillations is introduced in continuation of earlier efforts by Hehner et al. (2019) ["Stokes-layer formation under absence of moving parts – A novel oscillatory plasma actuator design for turbulent drag reduc-tion", Phys. Fluids 31, 051701]. Four groups of a multi-electrode actuator array are operated at interfering high-voltage signals to achieve an oscillating discharge intensity at 50 Hz beat frequency. The resulting velocity fields have been recorded with time-resolved planar high-speed particle image velocimetry so as to analyse the induced flow topology and wall-normal velocity profiles. A direct comparison of the results to Hehner et al. (2019) has indicated favourable effects of the new concept in terms of flow topology (i.e improved spanwise flow homogeneity, velocity magnitude increase and reduced lift-off), which renders the new operation concept of the actuator array particularly promising for Stokes-layer-like flow formations and, consequently, for turbulent drag reduction over a range of Reynolds numbers.