Measuring/Suppressing Vortex Shedding from a Confluent Nozzle’s Core-Nozzle Lip

The noise produced by subsonic, internally mixed air jets from a model-scale, axisymmetric nozzle was shown to contain “lip noise” related to vortex shedding from the core-nozzle lip, despite the core-nozzle lip being reasonably thin. The lip noise grew stronger with increased core-stream temperature for a given jet Mach number and was less prominent above the broadband jet noise as the jet Mach number was increased. The lip noise’s frequency was found to scale with the bypass stream’s velocity at the core-nozzle lip and the core-nozzle lip thickness—pointing to unexplained differences in the characteristic frequency of lip noise/vortex shedding from similar nozzles in prior works. A modified nozzle configuration allowed optical access to the core nozzle’s wake, and time-resolved schlieren flow visualizations ([Formula: see text] frames per second) and particle-image velocimetry data were obtained. Modal analyses of these flow measurements via the proper orthogonal decomposition and its spectral variant established a link between the observed noise and the underlying vortex shedding. A boundary-layer trip was shown to suppress the vortex shedding—although, it sometimes led to a different, high-frequency noise.