A New Unsteady Model for Dense Cloud Cavitation

Abstract

A new unsteady, cavitation model for dense cloud cavitation is presented wherein the phase change process (bubble growth/collapse) is coupled to the acoustic propagation in a multi-phase fluid. This cavitation model predicts the number density and radius of bubbles in vapor clouds by tracking both the aggregate surface area and volume fraction of the cloud. Hence, formulations for the dynamics of individual bubbles (e.g. Rayleigh-Plesset equation) may be integrated within the macroscopic context of a dense vapor cloud i.e. a cloud that occupies a significant fraction of available volume and contains numerous bubbles. This formulation has been implemented within the CRUNCH CFD, which has a compressible “real” fluid formulation, a multi-element, unstructured grid framework, and has been validated extensively for liquid rocket turbopump inducers. Rigorous validation of the formulation is presented for various cases including unsteady simulations of a cavitating NACA0015 airfoil where the frequency of pressure fluctuations and time-averaged mean cavity lengths were compared with experimental data. The model also provides the spatial and temporal history of the bubble size distribution in the vapor clouds that are shed, an important physical parameter that is difficult to measure experimentally and is a significant advancement in the modeling of dense cloud cavitation.