2D NUMERICAL MODEL FOR TRANSIENT VAPOROUS CAVITATION

摘要

The features of distributed vaporous cavitation models in transient cavitating flow are investigated. The proposed mathematical models are defined by the mass balance and momentum equations for liquid-vapour mixture. A new conservation form of the continuity equation allows a simple numerical solution without the need of shock equations for condensation. Both 1D and 2D models are considered to quantify the effect of friction in the simulation of experimental data. An axial-symmetric 2D flow is assumed, thus allowing the evaluation of the velocity profile and of the wall shear stress. The equations are solved by using the MacCormack scheme. The comparison between the results of the numerical runs and the experimental data of pressure head oscillations in transient cavitating flows shows that the models allow a good simulation of measured maximum heads, useful for engineering purpose. As expected, the 1D model does not represent adequately the experimental data, except the first maximum oscillations, whereas the 2D model allows for a better evaluation of observed energy dissipation. In some cases, the 2D model does-not estimate properly the experimental phase and dissipations. This is probably due to the process of dissolved gas release and solution that can explain the reduction of the wave speed, and the energy dissipation not due to friction if a relaxation process is assumed.