RESEARCH ARTICLE Stall control at high angle of attack with plasma sheet actuators

Abstract We analyzed the modifications of the air-flow around an NACA 0015 airfoil when the flow was perturbed with electrohydrodynamic forces. The actuation was produced with a plasma sheet device (PSD) consisting in two bare electrodes flush moun-ted on the surface of the wing profile operated to obtain a discharge contouring the body in the inter-electrode space. We analyze the influence of different parameters of the actuation (frequency, input power, electrodes position) on the aerodynamic performance of the airfoil, basing our study on measurements of the surface pressure distribution and of the flow fields with particle image velocimetry technique. The experiments indicated that at moderate Reynolds numbers (150,000 < Re < 333,000) and at high angles of attack, steady or periodic actuations enabled large improvement of the lift and drag/lift aerodynamic coefficients by reattaching the flow along the extra-dos. However, to attain the same results steady actuations required larger power consumption. When exciting the flow with a moderate value of non-dimensional power coefficient (ratio of electric power flow with the kinetic power flow), a frequency of excitation produced a peak on the coefficients that evaluate the airfoil performance. This peak in terms of a non-dimensional frequency was close to 0.4 and can be associated to an optimal frequency of excita-tion. However, our work indicates that this peak is not constant for all stalled flow conditions and should be analyzed considering scale factors that take into account the ratio of the length where the forcing acts and the cord length. List of symbols b electrode length in the span direction c cord length fexc frequency of excitation of the actuator l curvilinear coordinate in the tangential direction of the surface x axis coincident with the airfoil cord (being x = 0 the leading edge position) Cl momentum addition coefficient CW power addition coefficien