Assessing the role of surface tension force to the simulation of sub-grid scale interaction of turbulence and cavitation under realistic diesel injection conditions

With the ever increasing operating pressures of modern fuel injectors, the spray formation processes are increasingly influenced by the inception and development of cavitation inside the injector orifices and nozzle. The turbulent effects that contribute to the jet formation and subsequent break-up processes are enhanced by the growth and destructive collapse of cavitation bubbles. Turbulent effects generated by cavitation are resisted by viscosity and surface tension forces formed at the interface between the two phases. Sub-grid scale LES turbulence models are largely viscosity based and only assume flows in single phase. In the current work a systematic variation of the turbulence models and their constants were performed to investigate the influence of surface tension on the cavitation cloud topology as well as on the interaction of cavitation and turbulence. The objective is to extend our understanding of the shortcomings of the assumptions made in current SGS turbulence models and highlight the necessary modifications needed to consider high-velocity two-phase flows of direct fuel injectors. An OpenFOAM based solver (cavitatingFoam) was modified to account for interfacial phenomena such as surface tension. Results are compared with published data for a single injector nozzle and a sensitivity analysis is performed based on the fluid properties. Interaction between the cavitation layer and the near-wall was also investigated, where flow characteristics and grid refinement of the near-wall grid were adjusted to observe any transitional effects.