Control of shock-induced flow separation using elliptical air-jet vortex generators*

Flow separation, induced by strong shock waves interacting with a boundary layer, is harmful to many aerospace applications. An established technique to control the flow is by using air-jet vortex generators (AJVGs). Here, streamwise vortices are generated by injecting steady air-jets into the crossflow, which redistribute the boundary-layer momentum, thereby improving their resistance to separation. The effectiveness of AJVGs depends on a number of parameters. An encouraging parameter is the jet-orifice shape, which affects the topology and dynamics of the jet-induced vortices and consequently the control effectiveness. In this study, we investigate the potential of AJVGs with elliptical jet-orifices in controlling a 24^o ramp-induced interaction at M_e= 2.52 and Re_θ = 8225.

A circular orifice and two elliptical orifices with aspect ratios of 0.5 & 2 were studied, all with the same hydraulic diameter. Oil-flow visualizations and PIV were used as flow diagnostics. Jet injection via elliptical AJVGs generate streamwise vortices that are wider and penetrate deeper into the flow. The ensuing improvement in momentum transfer results in a 25% reduction in separation length for elliptical AJVGs, in comparison to only a 17% reduction for the circular case.