Control of afterbody vortices from a slanted-base cylinder using sweeping jets

Abstract

In this paper, a sweeping jet is applied to control the afterbody vortices behind a slanted-base cylinder for the first time at Reynolds numbers from 87 000 to 200 000. The control effects are examined using stereo particle image velocimetry and surface pressure measurements with the jet momentum coefficient (Cμ) varying from 0.056 to 0.893. It is found that the sweeping jet results in increasingly diffused and larger afterbody vortices as Cμ increases. While an increase in Cμ up to 0.167 leads to a reduction in the circulation of the afterbody vortices and their earlier detachment from the slanted base, a further increase in Cμ introduces additional vorticity into the afterbody vortices leading to higher vortex strength, which could be detrimental to the control purpose. The interaction mechanism of sweeping jets lies in that turbulence is injected into the afterbody vortices as the sweeping jet intersects with these vortices and this subsequently causes diffusion of velocity gradient in the vortices, which weakens their strength. As the sweeping jet spreads itself sideways, while it propagates downstream along the endplate, it pushes the afterbody vortices upward and to the side. The impact of the sweeping jet has resulted in the dominant vortex wandering frequency of the afterbody vortex being locked to that of the sweeping jet. This also causes the afterbody vortices detach themselves from the endplate earlier resulting in a shorter low-pressure footprint on the surface.