Influence of actuation parameters of multi-DBD plasma actuators on the static and dynamic behaviour of an airfoil in unsteady flow

The purpose of this paper is to perform a numerical study regarding the implementation of dielectric barrier discharge plasma micro-actuators for load alleviation on a NACA 23012 oscillating blade in a freestream flow. The work aims to evaluate the feasibility of using multiple dielectric barrier discharge (multi-DBD PAs) plasma actuators as a novel approach for load alleviation and stability control of airfoils in unsteady flow. A 6-actuators configuration, positioned at the trailing edge, is designed and tested. In this configuration, half of the actuators operate on the suction surface and the others on the pressure surface. In particular, the actuators located on the suction surface reduce the airfoil lift force if the induced body force is in a direction that is opposite of the main flow, because they lead to a slight and local increment of pressure on the surface. Instead, when actuators produce a body force aligned with the streamwise direction, they lead to a slight reduction of pressure, increasing lift. Contrarily, the actuators located on the pressure surface increase the lift, if the induced body force is in the direction opposite of the flow and reduce the lift in the opposite case. The effects of plasma actuators on the flow are incorporated into Navier-Stokes equations as a body force vector into the momentum equation. Different switching on/off laws of the actuators have been are compared, in order to reduce the loads amplitude of the airfoil, and to increase the stability of the blade response to the flow, and thus, alleviating fatigue phenomena on the blade and enhancing its aeroelastic stability. The effect of the phase of the plasma actuators switching law was evaluated for different pitching oscillation reduced frequencies, ranging from 0.1 to 0.5. The results underline the capability of DBD-PAs to control and reduce unsteady loads on an oscillating airfoil, improving also the airfoil stability if the phase of the actuation force is optimized for each pitching oscillation reduced frequency. (C) 2019 Elsevier Masson SAS. All rights reserved.