Performance Efficient Jet Noise Reduction for Supersonic Nozzles

Abstract

The variable area, round, axisymmetric, supersonic exhaust nozzle for high performance military aircraft represents a remarkable technological achievement. These variable exhaust nozzles (VEN) utilize conic contraction and expansion sections and provide a simple mechanical means to control the throat-to-exhaust area ratio as a function of throttle input while maintaining structural and thermal integrity. Despite this admirable design, the result is a jet that unavoidably includes shockwaves both inside the nozzle and in the exhaust. The sharp throat radius provides the potential for flow separation which is exacerbated by shock-boundary-layer interactions within the nozzle resulting in reduced pressure recovery on the wall which translates into reduced thrust. A novel design, patented by Dr. John M. Seiner, is shown to eliminate shocks by altering the contour of the VEN seals. This results in the elimination of shock noise in the far-field spectra. The shape of the contoured seals provides the added benefit of generating streamwise vorticity which is evident in the reduction in mixing noise in the far-field spectra. Particle image velocimetry data is presented to demonstrate the enhanced mixing that is generated. Experimental evidence obtained at both model scale and full-scale demonstrates the ability to obtain 2–5 dB noise reduction with an optimized contoured seal design.