The interactions of a circular synthetic jet with a turbulent crossflow

Abstract

The three-dimensional flow of a circular synthetic jet interacting with a turbulent crossflow is investigated with unsteady Reynold-Averaged Navier–Stokes simulations. The effects of jet momentum are examined using three blowing ratios (CB=0.32, 0.67, and 1.10) at constant actuation frequency (f=300 Hz), approach crossflow Reynolds number, Reθ=900, and boundary layer thickness, δ/d=7.25, where d is the jet diameter. The results showed that the expelled jet is accompanied by a reverse flow region on the downstream side which undergoes alternating expansion and contraction during the jet cycle. The size of the reverse flow region and depth of penetration increased with increasing jet momentum. For the low momentum jet, the expelled flow structure evolved into a hairpin vortex which significantly enhanced the wall shear stress in the spanwise direction and near the jet exit. The higher momentum jets, on the other hand, exhibited strong vortex loops around the expelled jet column that transitioned into trailing vortex pairs and a tilted vortex ring further downstream. Along the wall, both horseshoe vortex upstream of the jet exit and tertiary vortices downstream were found attached to the wall. The strong tertiary vortices promoted downwash of fluids which significantly enhanced the wall shear stress along the symmetry plane for the medium and high momentum jets. The impact of the tertiary vortices increased with the jet momentum, offering greater potential for flow separation control.