CFD analysis of pump as turbine to study the influence of blade and shroud rounding on the internal flow physics for performance enhancement.

Pump as turbine (PAT) is effectively used in the micro-hydro power plants as stand-alone or grid-connected and energy recovery applications. Generally, the efficiency of the PAT is lower than the conventional turbines as it is not explicitly designed to generate power. Therefore, in literature, various techniques are proposed for performance improvement of the PAT, such as rounding of blades and shroud, back cavity filling, etc., as minor modifications. In the same line, it is critical to understand the internal flow physics to reduce the losses and understand the potential improvement. In the present paper, Computational Fluid Dynamics is proposed to understand the effect of blade and shroud rounding on the performance of PAT with internal flow physics. The change in the flow physics after modifications by impeller rounding is presented essentially at Best Efficiency Point (BEP). It is noticed that the efficiency of PAT is increased from 68.5 % to 70. 2 %, mainly due to the reduction of flow separation at the impeller flow zone, validating the experimental results from the literature. However, as the pump is not designed for turbine applications and there are no guide blades, the hydraulic losses due to flow separations are significant even after blade and shroud rounding. There is further scope for performance improvement by redesigning the impeller. [ABSTRACT FROM AUTHOR]