Effects of Jet Density and Exit Velocity Distribution on the Relationship between Preferred Frequency and Jet Diffusion

Abstract

This report aims to clarify the relationship between the preferred frequency and jet diffusion. The disturbance frequency used to control mixing, based on the preferred frequency of a flow in the initial area of the jet column mode, is often selected to enhance the diffusion of the jet flow. In the diffusive mixing enhancement of gaseous fuel and air, the properties of the jet flow and the surrounding gas differ. Thus, for the jet flow, air, CO 2 , and He were used. Three types of nozzle, convergent, orifice and pipe were used. First, the laser light sheet technique was used to visualize the cross section of the jet flow. The distance from the nozzle to the position at which the vortex rings form increases with the density ratio. The fluctuation velocity of the jet flow was measured with a hot-wire anemometer and PIV to investigate the preferred frequency and determine the Strouhal number. The Strouhal number was found not to depend on the Reynolds number and remain at an almost constant value. These findings elucidate the effects of the jet density and exit velocity distribution on the relationship between the preferred frequency and jet diffusion.