Jet installation noise reduction using porous treatments

Abstract

The possibility of jet-installation noise reduction has been experimentally demonstrated using a flat-plate fitted with flow permeable metal foam fitted at the trailing-edge. Tests were conducted for single-stream cold subsonic jets with a round nozzle adjacent to a flat-plate for a wide range of flow velocities (M=0.3−0.9) in an anechoic chamber. Thorough investigations of the far-field noise for various polar angles were carried out to demonstrate the regions with noise reduction. Four porous trailing-edges were tested with various increasing permeability and surface roughness. Far-field results showed substantial noise reduction for the installed configuration fitted with porous trailing-edges. Overall sound pressure level scaling with velocity demonstrates that trailing-edge scattering noise is reduced by the application of from porous trailing-edge. Detailed analysis using coherence and correlations of the far-field results are also presented to gain a better understanding of the effects of different porous materials. The effect of plate distance was also investigated and the results showed tonal characteristics for cases with high surface roughness. Overall, a thorough experimental study is provided for understanding the jet installation noise reduction mechanism using porous trailing-edges.