Observations of a sweeping jet actuator for flow separation control of a backward-facing ramp

Abstract

Flow separation control of a sweeping jet actuator in a backward-facing ramp was studied using two-dimensional and stereoscopic particle-image velocimetry. The actuator was operated at a single supply rate pertaining to a jet velocity of 7.3 m/s and positioned at the streamwise location of 0.8 and 3.7 boundary layer thickness upstream of the separating edge. Three wind tunnel reference velocities corresponding to Reynolds numbers based on the boundary layer thickness of Re δ = 2400, 5200, and 9800 (jet-to-reference velocity ratios of 1, 0.5, and 0.3) were investigated, and the control effectiveness was assessed based on the size of the separation bubble. For all three Reynolds numbers, positioning the actuator nearer to the separating edge offered poorer flow separation control for measurement planes near the jet centerline. This was attributed to the upwash effect of the jet which directed high momentum fluid away from the wall leading to lower levels of entrainment, and the formation of a localized low-pressure region that coincided with the sharp change in ramp geometry leading to stronger adverse pressure gradients and lower streamwise velocities that were more likely to undergo flow reversal. At high jet-to-reference velocity ratios, the effect was accentuated, and a secondary separation bubble was observed. When the actuator was positioned further upstream, the primary streamwise vortices produced by the sweeping jet lifted away from the wall, and secondary flow structures induced near the wall contributed to higher levels of near-wall entrainment and improved flow control along the jet centerline. In contrast, for measurement planes far from the jet centerline, positioning the actuator nearer the separating edge was preferable. This was attributed to milder decay of the primary streamwise vortices, leading to stronger downwash effect and higher entrainment levels that were able to affect a wider spanwise area.

More information

Identifiers

ORCID for Desmond Lim: orcid.org/0000-0001-6191-6803

Catalogue record

Export record

Altmetrics