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Experiments were carried out to assess the influence of spanwise spacing between adjacent orifices of an air-jet vortex-generator (AJVG) array on their separation-control effectiveness. The array was applied to a 24° compression-ramp-induced shock-wave / turbulent boundary-layer interaction at $$M_{\infty } = 2.52$$ M ∞ = 2.52 and $$Re_{\theta } = 8225$$ R e θ = 8225 . Three spanwise oriented AJVG arrays of small, intermediate, and large jet spacings were studied. Their influence on the mean-flow organisation and turbulence quantities was assessed using flow visualisations and planar particle image velocimetry across multiple measurement planes. The streamwise vortices induced by the AJVGs incited different control effects depending on the degree of interaction between adjacent vortices. The array with intermediate spacing achieved the most favourable effects with reductions in separation length and area of about $$25\%$$ 25 % and $$52\%$$ 52 % , respectively. This reduction was brought about by the formation of stable, interacting streamwise-elongated coherent vortices downstream of jet injection and the associated entrainment of high-momentum fluid. The smallest jet spacing incites vortex interactions to adverse strength, breaking up the coherent structures and even increasing separation. The AJVGs with the largest spacing display characteristics similar to single jets in crossflow, with only a local modification of the separation region. Turbulent quantities are amplified both by the jets and the separation-inducing shock; AJVG control reduces the amplification across the shock-wave/boundary-layer interaction and the intermediate jet spacing is most effective also here.

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The 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 ∞ = 2.52 and $$Re_{\theta _c} = 8225$$ R e θ c = 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).