Development of algorithm based on the fractional time step for the simulation of cavitation.

Abstract

Cavitation is one of the most demanding physical phenomena influencing the performance of hydraulic machines. It is therefore important to predict correctly its inception and development appearance, and quantify the performance losses associated with it. The objective of the simulations is to predict the instabilities associated with the presence of cavitation. The aim of this work is to develop a semi-compressible cavitating algorithm based on the fractional step method in Code_saturne. An implicit solver, based on a transport equation of void fraction coupled with the Navier-Stokes equations is proposed. Specific treatment of cavitation source terms provides physical values of the void fraction (between 0 and 1) without any numerical limitation. The influence of the turbulence models is also studied. To do this, several turbulence models are tested and compared. The instabilities due to three-dimensional effects are particularly analyzed. This work allows obtaining a numerical tool, validated for complex cavitating flows configurations, in order to improve the understanding of the physical mechanisms that control the three-dimensional unsteady effects involved in the mechanisms of instability.