Breakup of swirling liquid sheet in the presence of acoustically perturbed gas jet*

We aim to investigate the effects of acoustically perturbed gas jet on the near orifice breakup of swirling, annular liquid sheet. The gas jet has a tendency to respond to the combustor acoustic field generated from the unsteady heat release, which in turn creates unsteady atomization responsible for heat release rate, thereby forming two-way coupling. Present experiments focus on these unsteady effects with the help of upstream acoustic excitation up to 2000 Hz. The interaction between the swirling liquid sheet and the gas jet perturbations was studied using time-resolved shadowgraphy followed by the POD analysis. The steady spray starts pulsating periodically in the presence of forcing, and this triggered pulsation picks up the forcing frequency as the dominant pulsation frequency at lower frequencies (<1000 Hz). The self-pulsation regime, common in the coaxial atomizers, however, has a different response to the acoustics. Apart from revealing various large scale modes, the unsteady dynamics show the existence of two dominant frequencies viz. self-pulsation frequency and the forcing frequency. When the forcing frequency is close to the pulsation frequency, the lock-in occurs resulting from the extraction of forcing energy by the self-pulsation phenomenon.