Influence of the turbulence modeling on the simulation of unsteady cavitating flows

Abstract

The present work is focused on the analysis of cloud cavitation, i.e. high-speed unsteady liquid /vapor flows characterized by periodical large-scale shedding. The study relies on the numerical modeling of cavitating flows with a homogeneous approach coupled with the Reynolds-Averaged Navier-Stokes (RANS) framework. A new algorithm based on an implicit fractional step method is used to solve the time-dependent mass, momentum and transport equation for the void fraction. It is combined with an original treatment of the cavitation source term, which enables to maintain the void fraction within its physical range [0 1] throughout the calculation. No artificial numerical limitation is applied, so the overall mass conservation of the method is not deteriorated. The influence of the turbulence modeling on the results is investigated by applying a k-ε RNG and a k-ω SST model with and without the modification of the turbulent viscosity proposed by Reboud et al.[1,2]. Cavitation on a 2D Venturi type section and a NACA hydrofoil are both considered. The present work confirms the capability of the modified k-ε RNG and k-ω SST models to reproduce the main features of cloud cavitation. The role of the transport of principal turbulent shear stress in the mechanism of flow unsteadiness is discussed, as well as the validity of the Bradshaw's assumption for adverse pressure gradient. The benefit and the limitations of the modification of the turbulent viscosity are shown: while it enables to reproduce the main features of the flow behavior, significant discrepancies in the local shear stress are still found.