Elimination of shock associated noise in supersonic jets by destructive wave interference

Paper i proceeding, 2018

A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied resulting in unique acoustic behavior and flow field modifications. For most conditions the acoustics are relatively unaffected or increased, but for very specific conditions noise was drastically decreased. For optimized conditions the shock noise was completely eliminated and in other cases a jet instability was generated that significantly decreased high frequency noise. Measurements of the velocity field indicated that shock interaction due to shocks from the injection jet interact with the primary jet shocks, and significantly reduce the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with LES, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of OASPL of -7 dB at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction, destructive interference of the shock structure in the jet is reported.