Over the years, there have been numerous studies on determining subsonic jet noise source locations, typically plotted as Strouhal number as a function of distance from the nozzle exit. A comparison of the results of various studies yields a spread of about two nozzle diameters in measured source location. This work examines how nozzle geometry could be a potential cause of observed differences in different studies in subsonic jet noise source location. ASME and conical nozzles of nominally the same diameter are compared using source location, schlieren flow visualization, and velocity profile measurements. ASME nozzles, which are designed to have thinner nozzle exit boundary layers, have noise source distributions that are 0.25 to 2 diameters upstream of their conical counterparts. The thinner nozzle exit boundary layers of the ASME nozzles results in faster growth of turbulent structures in the mixing layer. Because the size of these structures is inversely proportional to the frequency of noise produced by the structures, this faster growth results in the upstream shift seen in the source location.
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