Noise of Swirling Exhaust Jets

Noise and flow characteristics of model swirling jets were measured. A swirling jet from a plug-nozzle generated a strong vortex flow and a broadband noise higher than that of a nonswirling jet. Exit guide vanes were found to be able to decrease the swirl and the noise simultaneously. A swirling jet with a nonswirling jet core flow was tested. The nonswirling core flow prevented the formation of strong vortex and kept the swirling jet noise at a relatively lower level. Noise attenuation for this flow only occurred at small angles from jet axis. The noise increase of the swirling jet over the nonswirling jet was found to depend on swirl angle, pressure ratio, and total temperature of the jet.