Control of Traveling Crossflow Vortices Using Plasma Actuators

Abstract

It has been shown recently by direct numerical simulations that plasma actuators can be used to delay laminar-turbulent transition caused by steady crossflow vortices (CFVs) in three-dimensional boundary layers on swept aerodynamic surfaces. In the current work the applicability of such actuators to control transition caused by traveling CFVs is explored by two techniques. In the first technique, named upstream flow deformation, the actuators are used to excite steady CFV control modes. The resulting narrow spaced control CFVs induce a beneficial mean-flow distortion and weaken the primary crossflow instability, yielding delayed transition. In the second technique, the direct attenuation of nonlinear traveling CFVs, the actuators are positioned more downstream, where the traveling CFVs have already established. The localized unsteady forcing against the direction of the crossflow is then aimed at attenuating the amplitude of the traveling CFVs by directly tackling the three-dimensional nonlinear disturbance state. With both techniques transition can be delayed, however with a significantly higher efficiency for the method of upstream flow deformation.