An analysis of nonlinear response of free circular jets to acoustic excitation

Acoustic excitation is an effective means of flow and combustion control. To investigate the modulation effects of acoustic excitation on the circular jet, large eddy simulation was adopted to calculate the circular jet (Re=2020) submitted to acoustic modulation with different frequencies. The nonlinear response of the flow field to acoustic excitation was studied. The analysis of vorticity field and Q criterion demonstrate that the response of the flow field structure is dependent on the excitation frequency. The analysis of transfer function and decomposition of fluctuating velocity reveal that the propagation of perturbation wave has three modes: convective mode, mixed acoustic-convective mode and acoustic mode, which agrees well with the experimental results. The spatial distributions of power spectrum density (PSD) of velocity display the redistribution of turbulent energy in the frequency space. It is shown that the response of jets to excitation reflects the flow structures and is closely related to the propagation mode of the perturbations. When the excitation frequency is near the preferred frequency of the jet, the perturbations propagate in a convective mode, while the flow structures and energy distribution in frequency space exhibit a significant change.