Large Eddy Simulation of Liquid-Jet Primary Breakup in Air Crossflow

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A robust two-phase-flow large-eddy-simulation methodology is applied to simulate the primary breakup of an axisymmetric liquid jet injected into an air crossflow at atmospheric pressure. The coupled level-set and volume-of-fluid method is implemented for accurate interface tracking. To deal with high liquid/gas density ratio, an extrapolated liquid-velocity field is created and used for momentum-equation discretization in the vicinity of the interface. Based on the local level-set value, sharp jumps in fluid density and viscosity are assumed across the interface. By simulating the nonturbulent inflow of a liquid jet into a nonturbulent gaseous crossflow, regular surface waves are observed in the large-eddy-simulation predictions on the upstream side of the liquid jet, with the wavelength agreeing well with experimental measurements. The predicted wavelength decreases as the gaseous Weber number increases, implying that the surface waves arise from a Rayleigh–Taylor-type instability. The simulated velocity field shows that, as the instability grows, gaseous vortices develop in the wave troughs, further enhancing the breakup of the liquid core. The turbulent inflow of a liquid jet into a turbulent gas crossflow is also simulated, and the effect of turbulent eddies on the liquid-jet primary breakup is examined. The rescaling/recycling method for large-eddy-simulation inlet-condition generation is implemented to generate realistic (i.e., physically correlated) turbulent inflows. It is found that it is the liquid rather than the gaseous turbulence that determines the initial liquid-jet instability and interface characteristics; further downstream, the turbulent liquid jet disintegrates more chaotically than the nonturbulent jet due to strong aerodynamic and turbulence effects. When appropriate turbulent inflows are specified, the liquid-jet penetration into the air crossflow (and the subsequent spread of the spray) is correctly predicted by the current large-eddy-simulation methodology, which displays good numerical robustness and accuracy for high liquid/gas density-ratio two-phase systems.