Mixing Characteristics of Multijet Modified by Cyclic Perturbation(<Special Issue>Jets, Wakes and Separated Flows)

The effect of cyclic perturbation on the mixing performance of millimeter-sized multiple air jets was investigated using flow visualization, hot-wire anemometry and laser Doppler anemometry techniques. Two types of external perturbation method were used, i.e., adding an acoustic sound and applying a pulsating flow to the jet. External acoustic sounds were found to be an additional dominant factor for the jet mixing, and in the multiple-jet case, the main jet located in the middle between the two same-sized jets was split into two, entrained into the neighboringjets, and eventually merged into one developed flow. For the pulsating-jet case, depending on the phase in one cycle, the jet flow condition alternately changed between laminar and turbulent. This affected the time-mean values of the jet flow profile. An adverse change in the mixing performance at the locations near the nozzle and far downstream was obtained between the pulsating- and steady-jet cases.