Use of the Cathare 1D pump model to predict the two-phase characteristic of a pump for petroleum fluids

A simulation of two-phase flow in a multi-stage helicoidal production booster-pump performed at CEA Grenoble is presented. A 1D model used in the CATHARE code for nuclear safety has been adapted. Modifications were necessary to allow computations of petroleum fluids and to calculate multi-stage pumps. A two-fluid, two-component, 7-equation model is used. Mass, momentum and energy balance equations are written for each phase, gas and liquid. In our application, the gas phase is a mixture of a non condensable gas and of the vapour of the same component as the liquid phase. Then two mass balance equations are written for the gas phase. All these equations are written in the rotating frame in the impellers, considering centrifugal and Coriolis forces and curvature effects. A specific set of constitutive relations is adopted in order to account for three-dimensional effects in the impeller such as head losses at the impeller inlet or outlet, pre and post rotation. Calculations results at nominal capacity and in part-load conditions, for a single-stage and a 3-stage geometries are presented. They are compared with the corresponding full scale experimental results from the IFP (Institut Francais du Petrole) two-phase pumps data-bank. Some tendencies can be observed, like the flow stratification and the interfacial friction effects or the influence of the flow angles at impeller's outlet on the two phase pressure gain. The effects of the void fraction, pressure, and homologous flowrate on the degradation are rather well predicted by the model. A correct prediction of the two-phase pressure gain can be obtained when the single-phase losses distribution is entered carefully. The multi-stage calculations are also satisfactory in this case. (authors)