Dynamics and Response to Control of Single and Dual Supersonic Impinging Jets

Abstract

An impinging jet produces a highly unsteady flowfield which results in very high noise levels, harmful structural vibrations, and significant loss of lift and stability in applications such as the short takeoff and vertical landing aircraft. An understanding of the flowfield and implementation of an effective flow control technique are necessary to reduce these adverse effects. The presence of multiple impinging jets leads to the generation of a fountain flow, which further adds to the complexity of the flowfield dynamics. In the present study, flowfields of a single supersonic round jet (Mach 1.5) and dual impinging jets (consisting of a Mach 1.5 supersonic jet and an additional sonic jet) are explored. A microjet-based control method is applied to attenuate flow unsteadiness by modifying shear layer instability characteristics of the supersonic jet. Passive and active influence of the microjet hardware on acoustics are examined over a range of impingement distances (2.25D–10D) with a fine resolution (D/16) to obtain detailed resonance characteristics. Based on the resonance tone behavior as a function of impingement distances, detailed flowfield characteristics at certain impingement distances are investigated with the help of schlieren visualization, near-field acoustics, and unsteady surface pressure measurements. The effectiveness of the microjet flow control method in reducing noise is also evaluated in the flowfield of single and dual impinging jets. For single and dual impinging jets configuration, relative to their respective baseline cases, the microjet control on dual impinging jets shows better noise attenuation of overall sound pressure level within short impingement distances ().