A dual scale LES model for interface dynamics

While significant progress has been made in the past decade to predict atomization using detailed numerical simulations, these come at significant computational cost since the range of scales that must be resolved exceeds those of a single phase turbulent flow significantly. A switch to a Large Eddy Simulation (LES) approach would be desirable, however, the underlying assumption of LES methods that the dynamics of the unresolved sub-filter scale can be inferred from the resolved scales is questionable when atomization occurs. Similar to viscosity in single-phase flows, surface tension scales with the inverse of a length-scale, but unlike viscosity, it can act to either dissipate surface corrugations preventing breakup, giving rise to the Hinze scale, or enhance surface corrugations due to the Rayleigh-Plateau instability, resulting in breakup. Which process is dominant on the sub-filter scale seems to depend entirely on the sub-filter interfacial geometry, i.e., if the interface is in the shape of ligaments, the surface tension can lead to breakup, whereas in other cases, surface-tension forces can inhibit breakup. Unfortunately, the sub-filter geometry cannot be inferred from the filtered interfacial geometry alone. LES approaches going beyond the traditional single-phase cascade hypothesis may be required for two-phase flows with atomization. 

In this presentation, a dual scale LES modeling approach will be discussed that can handle the dual nature of surface tension on the sub-filter scale. The model maintains a fully resolved realization of the phase interface, shifting the modeling task to reconstructing the fully resolved interfacial advection velocity from the filter-scale velocity, taking the effects of sub-filter surface tension, turbulent eddies, and shear into account. Results showing the viability of the dual-scale LES approach in canonical test cases will be discussed.