Role of nozzle-exit boundary layer in producing jet noise

Abstract

Often the measurements from different jet noise studies, which are thought to have been acquired at or corrected to identical jet conditions, do not match when compared to each other. This study looks at the nozzle-exit boundary layer as a possible factor for these differences. The nozzle-exit boundary layer state can easily be changed depending on the design of the jet-facility or the nozzle. To this end, jet noise measurements and nozzle-exit velocity profile measurements were acquired for nozzles where the nozzle-exit boundary state was changed either by using different types of nozzles, ASME nozzles versus conical nozzles, or extensions were added to the nozzles straight section. It is shown that as the laminar boundary layer transitions to turbulent, the high-frequency jet noise is reduced. In addition, development of a novel empirical correction for these effects was attempted.