Analysis of noise produced by jet impact near the trailing edge of a flat plate

Abstract

The sound field produced by the interaction of a subsonic cold gas jet with the trailing edge of a large flat plate is analyzed. The jet issuing from a 2-in.-diameter convergent nozzle impacted the plate seven nozzle diameters downstream from the nozzle exit and one diameter from the plate's trailing edge. The plane of the plate intersected the nozzle axis at 60°. Data analysis was performed to obtain a better understanding of the dominant noise source and the mechanism governing the peak frequency of the broad-band spectra. Results indicate that noise from the plate emanates from two principal sources: first, the impact of the jet on the plate and, second, the flow over the plate's trailing edge. Above a jet Mach number of 0.5, the dominant noise as detected on the impingement side of the plate results from the jet impact (eighth power of the velocity dependence) rather than a trailing edge disturbance (fifth or sixth power of the velocity dependence), which is generally assumed dominant. Also, the frequency of the peak SPL may be governed by a feedback phenomenon, resulting in periodic formation and shedding of ring vortices from the nozzle.