Characterization of Confined Liquid Jet Injected into Oscillating Air Crossflow

The aim of this work is to study the role of the liquid phase in the thermo-acoustic coupling that leads to combustion instabilities. In multipoint injection systems, the liquid fuel is injected through orifices as jets which are destabilized by the high-speed air flowing in a transverse direction. This paper is focused on the effect of an acoustic excitation imposed on the air flow on the various liquid features observed in actual fuel injection systems. This concerns the initial jet trajectory, its breakup, the formation and transport of the resulting spray, the liquid film formation on walls and its final atomization at the outlet of the injection system. Experimental investigations were performed on a simplified geometry designed to reproduce these main phenomena. Phase-averaged processing of the experimental data is used to analyze the relationship between the acoustic excitation and the liquid phase behavior. In particular, the phase delays imposed by the various processes involved are analyzed. The processing of high-speed video recordings reveals harmonic oscillation of the liquid column which periodically breaks into a spray structure or impacts the opposite wall, forming a liquid film. Using PDA measurements, it is shown that the resulting two-phase flow consists of alternating dense and diluted zones transported by the air flow. At the end of the channel, the liquid film flowing on the wall opposite the liquid jet is periodically atomized through the oscillating shear forces imposed by the air flow.