Numerical investigation of the breakup behavior of an oscillating two-phase jet

Abstract

Low emission combustion is critically influenced by fuel-air mixing quality. In the case of liquid fuels, atomization of the injected liquid is a vital component. Compared to standard injector nozzles, a spatially oscillating jet, as produced by a fluidic oscillator, has shown superior performance. To better understand and control breakup mechanisms of turbulent oscillating two-phase jets, numerical investigations are conducted for a jet with liquid Reynolds number Rel = 8701 and liquid Weber number Wel = 4759. Simulations are performed using a volume of fluid method. No explicit turbulence modeling is incorporated, but numerical viscosity of the discretization acts as an implicit subgrid scale model. Octree discretization in space in combination with adaptive mesh refinement allows for high-resolution interface capturing while allowing for moderate usage of computational resources. Two grid resolutions and refinement criteria are used to investigate the influence of spatial resolution and resolved turbulence on jet breakup. Inlet boundary conditions for the two-phase simulations are obtained from preceding single-phase, unsteady Reynolds-averaged Navier-Stokes simulations of a fluidic oscillator. The highest grid resolution shows an accurate representation of surface-tension- and inertia-induced breakup mechanisms, and turbulence effects along the interface appear sufficiently resolved. Besides Kelvin-Helmholtz instabilities, Rayleigh-Taylor instabilities, induced from jet oscillation, are observed. Superposition of these characterizes jet degradation and leads to early breakup. For validation, data from preceding flow experiments of a fluidic oscillator are used to compare droplet sizes and spatial development of the jet. Good agreement is found for all relevant properties.