Parametric Studies On Pump As Turbine Using CFD Analysis

Abstract

Small hydro is a valuable source of power generation in rural industries and remote village electrification. A low cost alternative to using traditional small hydro turbines is to use a pump as a hydro electricity generating turbine. One of the major limitations of pump running in turbine mode is poor part load efficiency. To improve the part load performance of PAT, flow regulating mechanism in the form of guide vanes can be provided. In the present study, CFD analysis of Centrifugal pump as turbine (PAT) is carried out with and without guide vanes using CFD package ANSYS CFX, in the wide range of discharge varying from 68 % to 145 %. Effects of casing eye enlargement were studied and Effects of suction eye removal were studied on PAT performance. For turbulence modelling, different turbulence modes were used viz. SSG, BSL, Standard k-epsilon and SST. Among various models, the results obtained with SST model are found to be in good convergence with experimental results. The maximum efficiency of PAT was found as 82.68% at rated discharge of 29 m3 /s. To improve the part load performance of PAT, two NACA profiles viz. 5520 and 6520 were selected. To optimize the profile and angle numerical simulations were carried out in the wide range of discharge. Among various options, NACA 6520 profile guide vanes (7 numbers) at an angle 23o with 225 mm diameter impeller was found to be most appropriate. By provision of guide vane the efficiency was improved in the range of 5-7% at different operating conditions. The casing eye enlargement led to 1.5 % to 3.5 % rise at different flow rates. Due to absence of casing eye rib, the PAT efficiency was increased by 12 % to 15 % at different flow rates.