Influence and Mechanism of Coflow Jet Airfoil Parameters in Subsonic Flow

Many studies have focused on the application and mechanism of coflow jet (CFJ) flow control technique in incompressible flow. However, the influence of CFJ parameters in subsonic flow is still uncertain. Five major CFJ airfoil parameters are investigated for their influence and mechanism on lift enhancement, flow separation control, and aerodynamic efficiency at Mach numbers 0.3 and 0.5 in this study. Two optimized CFJ airfoils are then designed to achieve better overall performance, and are compared with a baseline CFJ airfoil. An improved computational model using an actuator disk boundary is applied to simplify the iteration process in numerical simulation. The results show that the interaction between the jet flow and supersonic region on the upper surface is the prominent factor for CFJ airfoils in subsonic flow, and the proper injection location should be downstream of the normal shock wave to prevent interaction, increase maximum lift, and delay stall. Moderate injection orifice size and proper jet momentum coefficient are recommended to balance the energy consumption and aerodynamic performance at high angles of attack. A control strategy that varies the jet momentum coefficient for different angles may achieve high aerodynamic efficiency as much as possible. A relatively front suction location can suppress flow separation more efficiently, and larger suction orifice is better for reducing energy consumption. The optimized CFJ airfoils have much better overall performance than the baseline CFJ airfoil. The enhancement of maximum lift increases to more than 30% and the stall is delayed by 3° with high jet momentum coefficient. The energy consumption is largely reduced, and the maximum corrected lift-to-drag ratio increases by 61% and 28% at Mach numbers 0.3 and 0.5, respectively. Also, the optimized CFJ airfoils can provide higher lift than the baseline airfoil with the same aerodynamic efficiency.