Reproduction of the cavitating flows patterns in several nozzles geometries by using calibrated turbulence and cavitation models

Abstract

Cavitating flow is a complex phenomenon 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 effects. To study this kind of flow, several numerical models have been developed and they are now available in commercial and in-house software. A numerical model for cavitating flows involves a multiphase model, including both mass transfer and turbulence submodels. Inside of a commercial or an in-house numerical code there are several options and possible combinations of these submodels. A selection of the more suitable combination from this broad offer is a difficult task, involving then a subsequent careful calibration of the models selected, due to the fact that the default values for the calibration parameters that have these submodels, 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 that allow to say that it is possible to capture several cavitating flows characteristics, improving a ‘standard’ numerical (i.e., without any calibration) simulation by means of a detailed tuning of the production/dissipation coefficients present in the equations of the Eddy Viscosity Models for turbulence, and other parameters related to the two-phase state of the flow. The numerical results obtained were compared against experimental data for pressure, velocity and the structure of the two-phase cavity. It is demonstrated that a careful calibration of both the turbulence and the cavitation submodels used is of paramount importance, because there is a very close relation between the turbulence state of the flow and the cavitation inception/developing conditions. A suitable calibration work allows also diminish the mesh size, saving a lot of computational resources or the use of more sophisticated strategies for turbulence simulations (e.g., Large Eddy Simulations). Those are very expensive in terms of the necessary computational resources required. A more general conclusions than obtained in previous works are presented, because results for other different nozzles configurations were obtained.