Numerical simulation of unsteady flow in multiphase rotodynamic pumps

To further investigate the mechanism of phase separation and gas accumulation in multiphase rotodynamic pumps, on the assumption of tiny bubbly flow, based on a two-fluid model, the gas-liquid two-phase unsteady flow in a multiphase rotodynamic pump, with an IGVF (inlet gas volume fraction) of 15%, was numerically simulated. In the simulation, the k-ε based SST (Shear Stress Transport) model was used for turbulence; the drag force and the added mass force were taken into consideration in the interfacial momentum transfer terms; the steady solution of single water phase flow was specified as the initial flow field. Under this IGVF, five flow rate conditions were simulated, and taking the most optimal working condition as an example, the two-phase flow field and its temporal evolution were analyzed; the evolution characteristic and the calculation method of pump head were explored. The results show that, due to different centrifugal forces on the two phases, the gas is distributed mainly around the hub; affected by the change of the flow passage and the rotation of the impeller, the air mass starts to form at the inlet of the impeller. In addition, the gas volume fraction field and pressure field fluctuate in transportation, which results in severe oscillation of the pump head and instability of the pump system. The comparison of the head characteristics between the simulation and the experiment validates the reliability of the numerical model and method.