Primary Atomization of a Liquid Jet in Crossflow

Abstract

We present a visualization of the primary atomization of a turbulent liquid jet injected into a turbulent gaseous cross-stream. Detailed numerical simulation results were obtained using the Refined Level Set Grid (RLSG) method, coupled to a finite volume, balanced force, incompressible LES/DNS flow solver (M. Herrmann, J. Comput. Phys., 227, 2008). The liquid jet is injected into a Re=740,000 compressed air cross stream with momentum flux ratio 6.6, Weber number 330, Reynolds number 14,000, and density ratio 10. The simulation takes the details of the injector geometry (C. Brown & V. McDonell, ILASS Americas, 2006) into account. Grid resolution in the primary atomization region is a constant 32 grid points per injector diameter in the flow solver, and 64 grid points per injector diameter in the level set solver, resulting in grid sizes of 21 million control volumes for the flow solver and a theoretical maximum of 840 million nodes for the level set solver. We employ a hybrid Eulerian/Lagrangian approach for the liquid in that broken off, small, nearly spherical liquid drops tracked by the Eulerian level set approach are transferred into Lagrangian point particles to capture the evolution of the liquid spray downstream of the primary atomization region (M. Herrmann, J. Comput. Phys., 2010). The simulation results clearly show the simultaneous presence of two distinct breakup modes. While the main column of the jet is subject to a wavy instability mode, resulting in the formation of bags that break under the influence of the cross stream flow at the end of the liquid core, ligaments are formed on the sides of the jet near the injector exit that stretch and break. The flow in the wake of the bending liquid jet is characterized by strong turbulence. Comparison of the simulation results to experimental data show that mean jet penetration is in excellent agreement to experimental correlations and drop size distributions converge under grid refinement (M. Herrmann, J. Eng. Gas Turb. Power, 132(2), 2010).