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The reduction of pollutant emissions is currently a major concern in the aerospace sector. Among the proposed solutions, lean combustion appears as an effective technology to reduce the environmental impact. However, this type of technology may also favour the appearance of combustion instabilities. These instabilities, resulting from a thermo-acoustic coupling, can lead to irreversible damage to the combustion chambers.
Experimental studies previously conducted at ONERA on a multipoint injector (Apeloig 2013) highlighted the importance of atomization on the instabilities loop. Indeed, the fuel vapour concentration near the injection zone has been shown to fluctuate in accordance with the imposed acoustic perturbation. The driving mechanism would then result from a flapping motion of the liquid jets in the multiple injection points, induced by the gas flow oscillations. This would in turn affect the characteristic convective timescales of the fuel, in the form of a spray or even of thin liquid films on the duct walls.
In order to characterize this interaction, this work focuses on the unsteady simulation of a round liquid jet in the presence of a transverse gas flow in a rectangular section duct. Following an experimental study (Desclaux 2018), the multi-scale numerical approach for multi-phase flows (Blanchard 2014), implemented in the ONERA CEDRE code, has been tested in presence of an imposed acoustic perturbation. This approach consists of the coupling of three models: a multi-fluid model, based on the Navier-Stokes equations for compressible fluids, able to capture the largest scales of the liquid column atomization; a dispersed phase approach, used for describing the spray created by the atomization of the jet; and a “Shallow Water” approach for films. The coupling of these approaches is provided by dedicated atomization and impact models, which ensure liquid transfer between the three models.
Simulation results show that the multi-fluid solver is able to correctly capture the largest scales of the liquid jet. The liquid jet trajectories have been found to match the experimental data for several air-liquid velocity ratios. Moreover, the jet was found to dynamically respond to the imposed acoustic perturbation. As the liquid is transferred to the dispersed phase solver, the jet motion deeply affects the spray formation and behaviour. Good agreement was found on the particle resulting mean velocity. An important wall deposition has been detected for particular jet positions as well.
The proposed approach has proven a promising tool for further investigation of atomization effect on combustion instabilities.
