Vortex Pump as Turbine—A Type Turbine for Energy Generation or Recovery Based on Computational Fluid Dynamics Prediction

An experimental vortex pump with a specific speed of 76 is investigated to get its performance and flow structure under noncavitation and cavitation conditions when the pump operates as turbine in the reverse direction by using computational fluid dynamics (CFD) method. A method is proposed to extract hydraulic, volumetric, and mechanical efficiencies for the first time. It is shown that a vortex pump can operate as turbine but it is subject to poor cavitation performance. The performance conversion factors of flow rate and head are 2.33 and 2.74 which are much larger than existing centrifugal pumps as turbine with the same specific speed. The conversion factor of efficiency is 0.98, which agrees with the conversion factor of efficiency for a centrifugal pump as turbine. There are a rope cavity and a vortex flow in the same rotational direction of the impeller. It is shown that flow structure is complex in the impeller in pump and turbine modes, particularly on the blade-to-blade surface, while static pressure profile in the volute and impeller as well as the space between the casing and the impeller is simple. The flow in the space between the impeller and the casing cannot be regarded as a forced vortex in both modes. The cavitation performance improvement and rope cavity control may be key issues in the future.