Optimization of microjet control for supersonic impinging jet*

Supersonic impinging jets tend to experience resonance and generate a highly unsteady flowfield. In Short Take-Off and Vertical Landing (STOVL) applications, these highly unsteady jets produce loud noise and cause severe lift-loss. Therefore, a control method to reduce the jet resonance is required to improve the safety and efficiency of STOVL aircraft. Microjet injection into a round impinging jet is studied in this work as a method for reducing impinging jet resonance where the effectiveness of microjet control varies with impingement distance. In the present study, optimization of microjet control on a supersonic round jet (Mach 1.5) is performed by using a Genetic Algorithm to minimize jet noise at selected impingement distances. Sixteen internal microjets in the diverging section of the supersonic nozzle and sixteen external microjets at the lip of the nozzle are installed to reduce jet resonance, and an automated experimental optimization procedure is implemented to find the best actuator locations to reduce jet noise. The effectiveness of the optimization is examined with the help of schlieren flow visualization and acoustics measurements.