Effect of Nozzle-Exit Boundary Layer on Jet Noise

Abstract

A number of jet noise experiments have been performed over the years in different facilities and the measured lossless spectra do not always match. Some of the researchers have suggested this discrepancy is associated with rig noise. Another school of thought is that this discrepancy could be due to differing nozzle-exit boundary layers. One of the criticized datasets is the Tanna database, which was acquired at the Lockheed Georgia anechoic jetfacility, now operated by Georgia Tech Research Institute (GTRI), where the current authors work. In this paper, this rig noise contamination claim is examined by operating the facility at conditions and for nozzle geometries that would enhance upstream noise if it were dominant. The facility was found to produce jet mixing noise free of rig noise. A muffler installed upstream of the jet nozzle also showed that rig noise was nonexistent. Jet noise was acquired from two types of nozzles: ASME and conical. Boundary layer characteristics of both nozzle types were acquired and compared. It was found that a jet exhaust from an ASME nozzle produced more noise compared to a nozzle with a developed nozzle-exit boundary layer and that increase may be responsible for the effect that was blamed to be the result of contamination in some published studies.