Cross-Spectral Analysis of the Pressure in a Mach 0.85 Turbulent Jet

Measurements of the near-field pressure in an unheatedMach 0.85 round jet were performed simultaneously with far-field acoustic pressure measurements at Syracuse University’s Skytop Anechoic Chamber facility to directly quantify the strength and frequency content of the propagating portion of the jet’s near-field pressure. The largest contributions were determined to be at the lower wave numbers commonly associated with hydrodynamic pressure fluctuations. This indicates that large low-frequency hydrodynamic fluctuations are obscuring a significant source of acoustic fluctuations in the jet and dictates that care must be taken when using single point measurements of nearfield pressure spectral decay to differentiate between acoustic (propagating) and hydrodynamic (nonpropagating) fluctuations.