Control of dynamic stall using zero-net-mass-flux oscillatory jets

Recently, the zero-net-mass-flux oscillatory jets or synthetic jets have proven to be a promising tool for controlling various separated flows. The objective of the present study is to explore the applicability of synthetic jets for attaining lift enhancement of a pitching airfoil suffering from dynamic stall. For this purpose, numerical simulations of flow over a sinusoidally pitching NACA0015 airfoil are conducted at the chord Reynolds number of 90,000. The uncontrolled flow in this case shows mild stall and is dominated by a series of small shear-layer vortices from leading-edge separation, where synthetic jets actuated at the $12\%$ chord downstream location from the leading edge lead to mean lift enhancement. At a higher Reynolds number of $3 \times 10^5$, unsteady RANS employing the $v^2$--$f$ model predicts deep stall with the generation of a large-scale leading-edge vortex. In this case, synthetic jets are deficient in controlling the grossly moving separation and necessitate a more sophisticated actuation algorithm. Results from an ongoing large-eddy simulation at $\textrm{Re}=3 \times 10^5$ and the predictive capability of URANS in synthetic-jet control applications will also be discussed.