Capability of the Present Cavitating and Turbulence Models for Confined Flow Simulations

Abstract

Cavitating flow is a complex phenomenon closely related with turbulent and multiphase flows with mass transfer between the liquid and gaseous phases. This flow is affected by several factors as surrounding pressure, the local state of the turbulence, the non-condensable dissolved gases concentration and others. For studying this kind of flow several numerical models were developed and they are available in commercial and in-house software. A numerical model for cavitating flows involves a multiphase model, including a mass transfer submodel, and a turbulence model. Inside a commercial or an in-house numerical code there are several options and possible combinations of these models. To select the most suitable combination from this broad offer is not an easy task. This task involves also several decisions concerning a lot of calibration parameters that must to be defined in advance. The default values for these parameters are related to simple flow conditions, i.e., simple geometries and flows without any detachment. Under cavitation conditions these conditions are not the common situation. This work deals with the enhancement of some previous results obtained over simple geometries as orifices (injectors) with circular transversal sections. The model combinations that offered better results earlier are now studied more carefully. This study implies a detailed tuning of the production/dissipation coefficients of turbulence energy present in the turbulence models, and other parameters related to the cavitation state of the flow. It is known that these parameters have a strong influence over the numerical results obtained, both in terms of stability and accuracy. Also, a detailed comparison between mixture and volume of fluid models for modeling the multiphase flow was performed. The numerical results obtained were compared against experimental data for pressure, velocity and vapor fraction. In this work it is demonstrated that it is necessary to perform a careful calibration of both the turbulence and the cavitation models used, because there is a very close relation between the turbulence state of the flow, and the cavitation inception condition. A suitable calibration work allows us to diminish the mesh size (number of cells) saving a lot of computational resources too.