Understanding the effect of external acoustic forcing on impinging jet atomisation used in liquid rocket combustors
Due to the simple design, better atomisation and mixing characteristics, the impinging jet configuration has been a preferred injection system for storable liquid propellant rocket engines. The major problem associated with liquid propellant rocket engines using the impinging jet injector configuration is combustion instability. Acoustic oscillations in the combustion chamber affects the process atomisation leading to oscillatory sheet breakup and spray formation. This further causes unsteady heat release favorable for sustaining the combustion instability. Therefore, understanding the effect of acoustic field on the liquid sheet atomisation is essential for effectively controlling instabilities.
Experiments are being carried out to study the liquid sheet atomisation process in the presence of controlled external acoustic field. The effects of acoustic frequency and sound pressure level on sheet characteristics are studied using high speed imaging technique.
■ External acoustic excitations changed the smooth sheet to violently flapping sheet resulting in the reduction in sheet breakup length and sheet width.
■ Amplified waves due to external oscillations leads to the formation of droplet clusters, which lead to sharp and unsteady heat release pattern.
■ Existence of coherence between the external excitation frequency and frequency of amplified waves on the surface of liquid sheet is observed.