Influence of impeller blade rounding and surface roughness on the internal hydraulics and performance of pump as turbine

Abstract

The Pump As Turbine (PAT) is an important technology for low-cost micro-hydropower and energy recovery, and hence the internal hydraulics of PAT needs to be clearly understood. Additionally, during its operation, the sediments in the water increase the roughness of the internal surfaces and may alter the internal hydraulics and PAT performance similar to a centrifugal pump or Francis turbine. The researchers tried hard to perform simple modifications such as impeller blade rounding to increase the efficiency of PAT. In this paper, the developed test rig is used to analyze the performance of the impeller blade rounding and is validated with a numerical model. This numerical model is further used to study the influence of impeller blade rounding and surface roughness on internal hydraulics and PAT performance. The impeller blade rounding at the most increased the PAT efficiency by 1-1.5 % at the Best efficiency point (Q=16.8 lps), mainly due to the wake reduction on the suction side and increased flow area. With increasing the surface roughness from 0-70 μm, the PAT efficiency is decreased maximum by 4 %. The efficiency was mainly reduced due to increased hydraulic losses at flow zone and disk friction losses at the non-flow zone.

Keywords

• pump as turbine
• impeller blade rounding
• cfd analysis of pat
• simple modifications in pat
• hydraulic analysis