MIXING CHARACTERISTICS OF MULTI-JETS MODIFIED BY CYCLIC PERTURBATION(Multiple Jet)

Abstract

Cyclic perturbation effect on mixing performance of millimeter-sized multiple air jets was investigated using flow visualization, hot wire aneinometry and laser Doppler anemometry techniques. Two types of external perturbation method were used, i.e. adding an acoustic sound and applying a pulsatile flow to the jet itself. External acoustic sounds (St〜0.35) were found to be an additional dominant factor for the jet mixing. Furthermore, the main jet located in the middle between the two same-sized jets was split into two, entrained into the neighboring jets, and eventually merged into one developed-flow, much quicker than the case without the sound. For the pulsatile jet case, depending on the phase in one cycle, a jet flow condition alternately changed between laminar and turbulent. This affected the time-mean values of the jet flow profile. An adverse change of the mixing performance at the location near the nozzle and far downstream was obtained between the pulsatile jet and steady jet cases, namely a better mixing performance was obtained by the pulsatile jet case near the nozzle and vice versa.