Interaction between a vortex generator and a synthetic jet in a crossflow

Abstract

The interaction of a combined vortex generator and a finite-span synthetic jet, i.e., a hybrid actuator, with a zero pressure gradient laminar boundary layer over a flat plate was explored experimentally using Stereoscopic Particle Image Velocimetry (SPIV). The free stream velocity was U∞ = 10 m/s corresponding to a Reynolds number based on the local boundary layer thickness Reδ ≈ 2000. The synthetic jet was activated at multiple blowing ratios, and the vortex generator (placed either upstream or downstream of the synthetic jet) had a height of 1.6 times the local boundary layer thickness. When exposed to the crossflow, the pitched and skewed synthetic jet and vortex generator independently produced a single streamwise vortex in the far field. However, when the combined synthetic jet and vortex generator were placed together on the flat plate, the two streamwise vortices, associated with the two devices, did not combine. When the vortex generator was upstream of the synthetic jet, the jet pushed the vortex generator’s vortex upward into the free stream. When the vortex generator was placed downstream of the synthetic jet, the vortex associated with it was completely destroyed. Although the presence of the vortex generator did not impact the added enstrophy from the synthetic jet, it resulted in higher velocities near the surface when the vortex generator was upstream of the synthetic jet. It was shown that placing the vortex generator upstream of the synthetic jet was imperative for the performance of the hybrid actuator.