Control of salient flow features in the wake of a \(25^{\circ }\) Ahmed model using microjets

Flow control, employing linear arrays of discrete microjets, is applied to the rear of a \(25^{\circ }\) Ahmed model. The locations of the arrays are selected to test the effectiveness of microjet control at directly manipulating the various features found in typical flow fields generated by ground vehicles. Parametric sweeps are conducted to investigate the flow response as a function of the jet velocity and momentum. The effect and efficiency of the control are quantified through aerodynamic force measurements, while local modifications are investigated via pressure measurements on the rear surfaces of the model. The change in the pressure distribution reveals each control’s effects on a targeted flow structure and highlights the complex interaction between the salient flow features found in the wake of the Ahmed model. The strategies tested reveal a balance between the closed separation and longitudinal vortices which form above the rear slant surface, with beneficial modifications to one structure (in terms of drag reduction) often complimented by a detrimental contribution by the other. Areas of pressure recovery on the surface of the model are observed for each control technique and the changes to the aerodynamic forces are quantified. Microjets proved most effective when utilized for separation control producing a maximum change to the coefficients of drag and lift of \(-\,10.6\%\) and \(-\,18\%\) of the baseline values, respectively. Control techniques targeting other flow structures such as the C-pillar vortices and trailing wake proved less effective, producing a maximum reduction in drag and lift of \(-\,0.9\%\) and \(-\,6\%\).