ID 99

Experimental investigations of acoustically excited liquid sheet

 

Abstract:

Acoustic oscillations in the liquid rocket engine combustion chamber interact with the process of sheet breakup and spray formation and may lead to oscillatory atomization and unsteady heat release resulting in combustion instability. It is hence essential to study the effect of the acoustic field on the liquid sheet breakup for effectively controlling instabilities. Preliminary results of acoustic forcing on the liquid sheet formed by the oblique impingement of two liquid jets are presented in the context of liquid rocket engines. The glycerol-water and water alone sheets are excited by the external acoustic field. Effects of sound pressure level (50-120 dB) and excitation frequency (100-1000 Hz) on the sheet breakup process are investigated. It was observed that the smooth sheet starts violent flapping in the presence of the acoustic field. The water sheet is found to respond to discrete excitation frequencies; however, the glycerol-water sheet responds continuously over a range of frequencies and the upper limit of the range was seen to increase with the increase in Weber number. As excitation frequency increases, the number of waves on the sheet surface increases. Shadowgraphic sheet visualization from the side view revealed an increase in wave amplitude due to flapping and the amplitude was found to reduce as the excitation frequency increases. For all frequencies, wave amplitude shows significant response only at a certain minimum sound pressure level and this pressure increases as the excitation frequency increases. The frequency of waves on the sheet closely matches with the excitation frequency.