Numerical research on unsteady flow rate characteristics of pump as turbine

Pump as turbine (PAT), an effective and simple way to recover energy from high pressure fluid, has been one of hot issues in scientific research and engineering applications. Unlike previous computational fluid dynamics (CFD) work on PAT's velocity and pressure fields, this paper first focused on the internal flow rate characteristics, attempted to reveal the periodic rules of flow rate distribution. The transient CFD calculation was performed on a conventional centrifugal pump as turbine, time dependent flow rate was captured and analyzed in computational fluid domains by Lagrangian and Eulerian viewpoints. The results show that time-averaged velocity varies in an overall decline trend from cross section 1-8 of the volute. Net fluid passing into in certain some sections and out in other sections in the gap region between the rotor and volute. The frequent bi-directional flow in the regions of the gap and the lateral chambers is found. The flow rate is significant out of the rotor at section 8 on prediction of turbine performance when ignoring the bilateral chambers in CFD. Experiments were carried out to verify the accuracy of numerical results for three specific speeds of PAT.