Characterization of Confined Liquid Jet Injected into Oscillating Air Crossflow

Abstract

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. Phaseaveraged 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.

Response of spray number density and evaporation rate to velocity oscillations

“…During an instability cycle, different droplet concentration were seen, leading to heat release rate oscillations. In a recent, similar experimental study by Bodoc et al 18 the formation of an alternating dense and diluted zones of two-phase flow was observed downstream of the multipoint jet-in-crossflow injector.…”

Dynamics of a spray formed by laminar liquid jet in modulated crossflow

“…The Weber number is different for water tests and engine conditions (~2260 versus ~160, respectively) but, following the regime maps of Wu et al (1997) and Sallam et al (2004), for both values of We the atomization process corresponds to the shear break-up regime. The characterization of the acoustical field, of the air crossflow in the absence of the liquid phase and the liquid jet trajectory were the main concerns of another publication (Bodoc et al, 2018). Within this paper the focus is on the spray behavior analysis using the Phase Doppler Anemometry (PDA) technique.…”

A new efficient momentum preserving Level-Set/VOF method for high density and momentum ratio incompressible two-phase flows

“…However, still important discrepancies exist between literature correlations. For this reason, the present work attempts a comparison with the particular experience of Bodoc et al [39], where the liquid jet trajectories have been evaluated for several values of q, obtained by varying the liquid injection velocity. The aim of this test is not to fully investigate the atomization up to the droplet formation, but rather to focus on the capability of the proposed scheme to reproduce the complex momentum exchange between gas and liquid in a high density ratio (10 3 ) and strong shearing (u g /u l ≈ 60) configuration.…”