Numerical Investigation of Plasma Actuator Configurations for Flow Separation Control at Multiple Angles of Attack

Abstract

The primary objective of this study was to analyze the effectiveness of aerodynamic plasma actuators as a means of active flow control over a low speed airfoil at multiple angles of attack each corresponding to two different flow separation mechanisms (i.e., laminar separation bubble and turbulent flow separation at stall conditions). Detailed parametric studies based on steady and unsteady Navier-Stokes simulations were performed for a NACA 0012 airfoil at a chord Reynolds number of 10 5 . In particular, parametric studies were performed to investigate the influence of the number, the location, the imposed body force magnitude and steady vs. unsteady operation of the plasma actuators on the flow control effectiveness. First, the effectiveness of plasma actuators was studied when applied to the airfoil at a relatively low angle of attack, which involved the development of a laminar separation bubble (LSB). Next, the effectiveness of plasma actuators was analyzed at a high angle of attack where the stall of the airfoil occurs with a fully turbulent flow assumption. The results show that plasma actuators can provide significant improvement in aerodynamic performance for the flow conditions and geometry considered in this study. For LSB control, as much as a 50% improvement in the lift to drag ratio was observed. Results also show that the same improvement can be achieved using an unsteady or multiple actuators, which can require as much as 75% less time averaged body force compared to a single, steady actuator. For the stalled airfoil case, significant recovery in aerodynamic performance was observed for a single, steady actuator. However this was achieved using a voltage input eight times higher than what was used for LSB control. For the stall conditions considered in this study, unsteady and multiple actuator configurations do not provide the same enhancement as a single, steady actuator, which may be due to the nature of the flow separation (turbulent, trailing edge separation). The results of both cases show that the optimum location for the effectiveness of a plasma actuator would be just upstream of the separation location, which implies the usefulness of multiple actuator systems for flow control over a range of operating conditions.