Towards a hybrid model for cavitation inception

Cavitating flows consist of a wide range of resolvable scales as well as micro-scale bubbles that are unresolvable. These micro bubbles serve as cavitation nuclei, and thus play an important role in the resulting dynamics. In this work, a hybrid model is developed that is based on an interface capturing scheme that includes phase change for the resolvable scales, and a stochastic sub-grid bubbles model. In this work, we focus on inter-scale transfer from the sub-grid to resolved scale as this is relevant to cavitation inception. To this end, we recast the gas phase into both resolvable and sub-grid scales, and their respective equations are coupled using source terms. Following Denefle et al. (2015, Comput. Fluids), we propose a source term that depends on the volume fraction of the sub-grid scale and is activated when this volume fraction exceeds a threshold. The hybrid model is implemented in our in-house multi-component flow code, using a five-equation multiphase model. As a proof of concept, the hybrid model is tested by simulating acoustic pulses impinging on an initially sub-grid bubble cluster and comparing the results with fully resolved simulations of the same problem.