Separation control with elliptical air-jet vortex generators

Abstract

AbstractThe flow organisation of air-jet vortex generators (AJVGs) of elliptical cross sections and their control effectiveness on a$$24^{\circ }$$24∘-compression-ramp-induced shock-wave/boundary-layer interaction was analysed on the basis of experiments at$$M_{\infty } = 2.52$$M∞=2.52and$$Re_{\theta _c} = 8225$$Reθc=8225. We investigated a circular orifice and two elliptical orifices of aspect ratios 0.5 and 2; all characterised by the same hydraulic diameter. Measurements of separation lengths from oil-flow visualisation and PIV reveal that elliptical AJVGs achieve a$$25\%$$25%reduction in total separation length, which constitutes a strong improvement over the$$17\%$$17%reduction achieved with the commonly used circular AJVGs. The jet-induced structures from elliptical AJVGs penetrate on average$$25\%$$25%farther into the boundary layer. However, the lateral spread is limited to a maximum value equal to the inter-jet spacing in the control array, which highlights the onset of jet/jet interactions between adjacent jets in the array. A consequence of these interactions is better flow entrainment for the elliptical cases, as observed in the mean boundary-layer velocity profiles and an improved turbulent mixing (indicated by an increase in Reynolds-shear-stress magnitude).