Numerical investigation on streamwise vortex generation by plasma actuator

Abstract

To clarify vortex formation and development, numerical simulations of a streamwise vortex generation by a dielectric-barrier-discharge plasma actuator were performed. The simulations are set based on the experiment by Jukes and Choi [“Dielectric-barrier-discharge vortex generators: Characterisation and optimisation for flow separation control,” Exp. Fluids 52, 329 (2012)], which is a laminar boundary-layer flow with a plasma actuator aligned to the freestream direction ( x). The input momentum by the plasma actuator varies in the low (CaseL), medium (CaseM), and high (CaseH) cases. The streamwise vortex distributions for CaseL and CaseM are similar, and the vortex developments qualitatively agree with the experimental result. In these cases, the single streamwise vortex with the negative x-vorticity is mainly generated by the plasma actuator. For CaseH, however, the generated vortex is made up of both the main streamwise vortex with negative x-vorticity and the helical vortices with positive x-vorticity surrounding the main vortex. These encircling vortices twist the main vortex. Scaling the vortex characteristics, as proposed by Jukes and Choi [“On the formation of streamwise vortices by plasma vortex generators,” J. Fluid Mech. 733, 370 (2013)], demonstrates that the vortex characteristics can be scaled for simulation results. The streamline visualization clarifies the streamwise vortex formation by the induced flow from the plasma actuator and entrainment of the freestream flow to the streamwise vortex. The transient behavior of the streamwise vortex formation is examined for CaseM and CaseH. CaseM and CaseH have distinct transient behavior in the formation of the main streamwise vortex and the surrounding vortices.