Experimental study on the stability and breakup of a planar liquid sheet under a standing wave acoustic field

When combustion instability occurs - in addition to periodic change in the nozzle flow rate caused by pressure oscillation - the instability of the liquid sheet is also affected by pressure oscillation, reflected mainly in oscillation of the internal parameters of the fluid. In this work, the parametric instability of a liquid sheet under a standing wave acoustic field was studied theoretically, and the influence of acoustic parameters on the instability of a liquid sheet was analyzed. It was found that sinuous and varicose modes were coupled in the subharmonic region. Atomization characteristics of slit nozzles under a standing wave acoustic field were studied experimentally; the effects of acoustic pressure and injector position were analyzed with respect to the acoustic field on atomization characteristics and the characteristics of nozzles in the critical state. It was found that under the same acoustic pressure, the effect of the acoustic field at the velocity antinode (VAN) was stronger than the effect at the acoustic intensity antinode (IAN), and there was little effect at the acoustic pressure antinode. There was also a critical value of acoustic pressure: when the pressure threshold was exceeded, Faraday waves were motivated at VAN and IAN. An interesting phenomenon is that the frequency of the surface wave is the same as the acoustic frequency, but the Faraday wave was found to be subharmonic rather than harmonic. The effect of flow rate on atomization characteristics was analyzed. The wavelength of the Faraday wave and breakup length of the liquid sheet were well in accord with the theoretical wavelength calculated in the analysis of liquid sheet instability.