Active noise control of supersonic impinging jets using a physical model

Supersonic impinging jets produce a highly unsteady flowfield leading to a noisy environment with high dynamic pressure loads on nearby surfaces. In prior work, it was demonstrated that microjet injection along the circumference of the main jet nozzle directly into the shear layer of the main jet disrupts the feedback loop inherent in high-speed impinging jet flows, thereby significantly reducing the adverse effects produced. The microjet action was due to steady blowing whose flow rate was either uniform along the circumference or varied using the eigenmode of the flow. While these methods yielded some successes, uniform reduction of all operating conditions was not obtained. In order to obtain an improved reduction of the unsteadiness, a new model of the impinging jet flow field is suggested in this paper based on a collision model of two identical vortices. The introduction of the microjet appears to cause a weakening of this vortical structure and leading to noise reduction. The vortical structure seems to be destroyed effectively when the microjet injection is pulsed, thereby leading to uniform suppression of impinging jet noise.