EFFECTS ON MOMENTUM THICKNESS AND DENSITY RATIO FOR SIDE-JET FORMATION IN ROUND JETS WITH VARIABLE-DENSITY

If the mass density of an issuing gas is sufficiently lower than that of the ambient gas, radial ejections of the jet gas may be generated near the nozzle exit. These radial ejections are referred to as side jets. The parameters for side-jet formation have been reported to be the density ratio of the jet gas and the ambient gas and the momentum thickness at the nozzle exit. In the present experimental study, gases with variable density were discharged into still air. Two round nozzles having different area contraction ratios were used in order to vary the momentum thickness. The momentum thicknesses were obtained after the velocity profiles at the nozzle exit were measured by a hot-wire probe and a hot-wire concentration probe for jets with various density ratios and issuing velocities. The existence of side jets was confirmed by flow visualization of the jets using a laser sheet. The domain for side-jet formation is illustrated using the non-dimensional momentum thickness and the density ratio.