Increased Turbulent Jet Mixing Rates Obtained by Self-Excited Acoustic Oscillations

Abstract

A new device, capable of greatly increasing subsonic jet mixing rates, has been discovered. This device, which we have named the “whistler nozzle,” consists of a convergent nozzle section, a constant area section, and a step change to an exit section with a larger constant area. The exit section excites a standing acoustic wave in the constant area section, in a way similar to the action of an organ pipe. The result of this resonance is a loud pure tone and a greatly increased rate of jet mixing. The increased mixing rates appear related to the acoustically stimulated vortex shedding character (large scale structure or superturbulence) observed by Crow and Champagne [1] in their pioneering study of jets excited by a loudspeaker, and others utilizing upstream valves and pistons, except that the whistler nozzle is self-excited. The standing wave and the resulting increased mixing rates occur for a wide range of exit plane configurations and jet parameters.