Exploration on the mechanism for noise mitigation using fluidic injection for a supersonic rectangular jet

Supersonic jet noise is known to negatively impact personnel health and aircraft structural health. Laboratory experiments have demonstrated that secondary fluidic injection is effective at reducing supersonic jet noise in rectangular jets. However, the mechanism for this noise mitigation is not well established. Large eddy simulations of a supersonic rectangular jet (AR=2) at overexpanded condition (NPR = 3) with and without injection using CharLES were examined to identify the effect of the fluidic injection on both the flow field and the far-field acoustics. The simulations were validated against experimental measurements conducted by collaborators at Univ. Cincinnati. The fluidic injection significantly modifies the flow field, and the shock structures present within the nozzle, which are inaccessible in experiments. The shock cell structure (strength of the shock cells and their spatial scale) are modified with the fluidic injection, contributing to the observed noise reduction. The initial shear layer is significantly thickened by turbulence generated from injection. SPOD analysis is used to study the impact of fluidic injection on Kelvin-Helmholtz wave and guided jet mode. This work is sponsored by the Office of Naval Research and compute resources are provided by the NSF ACCESS program.