Numerical Investigation of Supersonic Jet Noise Suppression via Downstream Micro jet Fluidic Injection

摘要

In the present research, a computational investigation in support of our previous experimental study of using a downstream microjet fluidic injection (DMFI) technique to suppress supersonic jet noise is carried out The jet noise reduction scheme utilizes a microjet tube placed downstream and along the centerline of a converging-diverging nozzle, with a design Mach number of 1.5 with air as both the injection and primary gas mediums. Previous experimental studies of the problem on an underexpanded jet have suggested that the presence of a microjet tube alone in the jet plume alters the shock cell structure and weakens shock intensity, effectively attenuating both broadband shock-associated and screech tones. The present study aims to expand upon previous experimental work to gain a better understanding of the influence of various designs and operational parameters on the effectiveness of the scheme as a practical means to reduce supersonic jet noise. The scheme involves perpendicular injection into a supersonic jet using a cylindrical tube equipped with four equally-spaced injection ports. The effects of injection mass flow, as well as the axial location of the injection ports are investigated. The flow simulations are carried out by applying Detached Eddy Simulation (DES); while jet noise predictions are performed using Ffowcs Williams Hawldngs (FWH) acoustic model for compressible flow on the computational domain. The results of this investigation further validate the findings of our previous experimental study on effectiveness of the DMFI scheme to eliminate discrete tones in the noise spectra by mere placement of the microjet tube in the jet plume. The broadband shock-associated noise is affected by weakening of the shock cell strength, reducing shock cell spacing and faster decay of the primary jet core. Downstream microjet fluidic injection is also shown to result in modification of the jet shear layer by enhancing jet mixing, hence attenuating mixing tones in the far-field.