Investigating the Influence of DBD Plasma Actuators on Skin Friction

Abstract

The main driver of developments in the wind energy sector is not the absolute maximization of energy capture, but the reduction of the Cost of Energy (CoE). More and more research is carried out to investigate control of the air flow to reduce fatigue loads, structural requirements, and apply novel control strategies to ultimately reduce this important CoE. Plasma actuators have been the subject of an increasing amount of research in recent years in the field of Active Flow Control (AFC). Of particular interest to the present study is the alternating current Dielectric Barrier Discharge (DBD) plasma actuator, which is widely used due to the low mass, low power consumption, fast response time, absence of moving parts and large actuation bandwidth. Successful applications of the technique include postponement and control of flow separation, transition delay by Tollmien-Schlichting wave cancellation, stream-wise vortex generation and the control of dynamic stall on oscillating airfoils. To fully take advantage of the potential performance increase DBD actuators can offer, its effect should be accounted for as early as possible in the aerodynamic design phase. Previous work at TU Delft incorporated the DBD plasma body force in the integral boundary layer formulations. In the light of discrepancies between the existing model and experimental observations, attention is focused on the skin friction. An experimental campaign was designed and conducted at the open jet facility to acquire high resolution PIV of the turbulent boundary layer during various states of boundary layer development, for both actuated and non-actuated cases. The velocity fields were post-processed to obtain the variation in skin friction induced by the DBD plasma. Major conclusion from the observations is the fact that the increase in skin friction due to actuation occurs downstream of the actual plasma body force region, and extents for approximately 2.6 body force lengths. A semi-elliptical fit is employed to model the variation in skin friction due to DBD plasma actuation dCf . The steps to be taken to implement the dCf in a numerical boundary layer solver are investigated. The work includes a first approach in Matlab, to pave the way for future work to include the skin friction correction in rapid-analysis, viscous-inviscid panel codes based on integral boundary layer formulation such as Rfoil.