Numerical Investigations on Pump as Turbine

Abstract

Energy is a key input in the economic growth of the nation, in other words, there is close link between the availability of energy and future growth of a nation. Electricity demand in rural area is big problem today. Thermal power plant and big hydro power plant cannot be installed at such rural areas. The main limitation in installation of such plants is higher cost of turbine. In hydroplants, pumps can be used in turbine mode considering various advantages associated with pump e.g. ease of availability, proven technology, low initial and maintenance cost etc. The efficiency of Pump as Turbine (PAT) may be lower than the turbine but there is significant reduction in the capital cost of the plant. In the present study, literature review pertaining to pump running in pump and turbine modes is presented. CFD analysis of single stage end suction centrifugal pump (Head: 22 m, Discharge: 220 m3/hr) was done using commercial CFD package Fluent in pump and turbine modes. The 3-D computational model was discretized using unstructured tetrahedral grid and steady state simulations were carried out using Reynolds Averaged Navier Stokes equations along with standard k-ε turbulence model. To consider the rotational effects of impeller, moving reference frame model was used and SIMPLE algorithm was applied as pressure-velocity coupling. The performance was analysed at part load, rated and over rated conditions. The operating characteristics in both modes were predicted and validated with literature. The maximum efficiency in pump and turbine mode was found to be 87.54 % and 85.74 % respectively. The effects of guide vanes and different rotational speed are studied in the turbine mode.