Experimental and Numerical Characterization of a Liquid Jet Injected into Air Crossflow with Acoustic Forcing

Abstract

The current work presents a study on spray dynamics in aeronautical injectors. More particularly, the experimental characterization of a liquid jet in an oscillating gaseous cross flow (LJIOGCF) atomization is presented and compared to numerical simulations. The experimental setup consists of a water jet transversally injected into an oscillating subsonic air flow at ambient conditions. In a first step, a cross-comparison is performed in order to validate the numerical model and the tools used to quantitatively analyze the experimental data in the case of steady air flows. In a second step, the air flow is submitted to longitudinal acoustic waves using a pneumatic loudspeaker. A detailed database, representative of the actual dynamics of LJIOGCF configurations, is obtained using both experiments and numerical simulations. Visualizations with a back lighting approach are employed to characterize the liquid jet close to the injection location while phase doppler anemometry is used to determine the characteristics of the crossflow and the spray in terms of droplet size, velocity and concentration. Phase-averaging is performed to characterize the response of the liquid jet, the air velocity field and the spray oscillations during the excitation cycle. The numerical simulation relies on a multi-scale large eddy simulation approach. This method couples a multi-fluid solver for the liquid jet main body with a dispersed phase solver for the atomized spray. The acoustic perturbation is imposed as a fluctuating air inflow condition. The experimental results show that the acoustic forcing induces a flapping motion of the liquid jet. As a consequence, velocity and concentration waves travelling downstream the liquid jet appear. Coupling phenomena between the crossflow, the atomization of the liquid jet and the transport of droplets are observed, revealing different wave transport velocities. It further appears that spray dynamics are both driven by liquid column and crossflow oscillations. The numerical simulation is able to capture the global flapping dynamics of the liquid jet’s main body. More quantitative comparisons show a very good agreement between simulation and experiments regarding the jet trajectories over the entire excitation cycle. Numerical droplet average velocities are also in good agreement with experiments. Finally, the numerical simulation partly reproduces the coupling between acoustics and spray dynamics observed in the experiments.