Abstract: To investigate flow field structures of a round jet controlled by acoustic excitation, large eddy simulation (LES) was performed to calculate a round jet (Re=2 020) under phase-locked global acoustic excitation. The control effects on the velocity and vorticity fields were described in various perspectives, and the frequency selectivity of jet response was analyzed. The preferred model frequency of unmodulated jet agreed well with the experiments. The mean and root mean square (RMS) velocity, probability density functions (PDF), skewness, kurtosis and momentum thickness were used to explore the modification of velocity fluctuation and mixing properties. Vortical structures were illustrated by Q criterion and instantaneous vorticity. The key vortex structure in the modulated cases was identified as Hills sphere vortex. It is concluded that acoustic excitation can effectively control the flow field. Especially when the modulation frequency is near the preferred mode, a small amount of modulation energy input can cause significant change in flow structures.

Key words: acoustic excitation, free jet, large eddy simulation, fluid control, the Hills sphere vortex