Analysis of Transient Vaporous Cavitation in Pipes by a Distributed 2D Model

Abstract

The features of an axial-symmetric two-dimensional (2D) model in a transient cavitating pipe flow are investigated. A distributed vaporous cavitation model is proposed, based on the mass and momentum balance equations for a liquid-vapor mixture. A conservation form of the continuity equation allows a simple numerical solution. Both one-dimensional (1D) and 2D models are considered to quantify the effect of friction in the simulation of experimental data. The axial-symmetric 2D model allows the evaluation of the velocity profile and a more accurate estimate of the wall shear stress. The comparison between the results of numerical runs and experimental data of pressure head oscillations in transient cavitating pipe flows shows that the errors on maximum head oscillations of 2D model are generally greatly reduced with respect to those of the 1D model. As expected, the quasi-steady 1D model does not adequately represent the experimental data, with exception of the first maximum oscillations, whereas the 2D model allows for a better evaluation of the observed energy dissipation. In some cases, the 2D model does not estimate properly the experimental phase. This is probably due to the simplifying hypotheses, namely the neglecting of the convective terms, and it is influenced also by the release of dissolved gas, which can be important when the duration of presence of vapor increases. The 2D model also reproduces the observed experimental spikes better than the 1D model.