Open-loop control of the flow past and forces on a two-dimensional elliptical-nosed body

Simulations are conducted on an elliptical-nosed, square-backed cylinder in the presence of a moving ground plane. Open-loop active flow control is applied to the body in the form of zero-net-mass-flux combined injection and suction near the top trailing edge. Both steady and periodic control are used, and their effects on the aerodynamic forces on the body and wake flow are examined. Steady control is shown to deflect the separating shear layer and reduce the wake width, subsequently reducing the drag. The effect of periodic control is shown to be sensitive to the control frequency–different frequencies can either enhance or inhibit the formation of large-scale coherent structures in the wake. Notably, all five actuation cases tested resulted in a drag reduction over the natural flow case except when the frequency matched the wake shedding frequency. A drag reduction of tilde 25 ∼ 25 ${\sim}25$ % occurred for the highest control frequency tested ( italic St equals italic fH slash upper U Subscript normal infinity Baseline equals 5 St = fH / U ∞ = 5 $\textit{St}= \textit{fH} /U_\infty=5$ , with f f $f$ the forcing frequency, upper H H $H$ the body height, and upper U Subscript normal infinity U ∞ $U_\infty$ the free-stream velocity) for a non-dimensional momentum coefficient of 0.006.