Passive flow control of a stalled airfoil using a microcylinder

The effect of passive flow control using a microcylinder near the leading edge of a stalled airfoil (NACA 0012) at a Reynolds number of 6 × 106 is investigated through a computational study. Detailed parametric analyses for the microcylinder are carried out based on Reynolds averaged Navier-Stokes (RANS) calculations in order to determine the optimal control parameters. Computations using delayed detached eddy simulation (DDES) for the controlled and uncontrolled cases are supplemented to capture the transient vortical structures in the massive separation region and further verify the numerical results from RANS. It is found that the total aerodynamic forces of the entire system are highly sensitive to the spacing between the surfaces of the airfoil and the microcylinder. When a superior set of control parameters is adopted, significant enhancement of lift coefficient and lift-to-drag ratio can be achieved after stall, accompanying a pronounced decrease of drag coefficient. Both RANS and DDES results indicate that the heavy stall can be effectively delayed and the extent of large separation region on the airfoil suction surface can also be diminished by such a little control device. A physical analysis of the flow fields is performed to illustrate the mechanisms of flow control for the improvement of airfoil aerodynamic performance.