CFD BASED PERFORMANCE ANALYSIS OF FRANCIS TURBINE DRAFT TUBE UNDER SEDIMENT EROSION

Abstract

The continuous growth of population, industrialization and technological advancements led to a substantial increase in energy demand. The energy generation from fossil fuels is being shifted to renewable energy sources due to their serious environmental problems. Among different renewable energy sources, hydropower is playing a major role in electricity generation because of economic and environmental friendly. However large hydro schemes are not encouraged to utilize due to environmental concerns. Hence, small, mini, and micro hydropower is being used for power generation and capacity of small hydro power in India up to 25 MW. This energy is clean to use and has much more potential in the northern side and north-east side of the India due to the presence of the high head. The hydro turbine is used to tap such potential energy and converts to mechanical energy and then further converted to electrical energy by coupling generator. In hydro power sector, the various components of hydraulic turbine come in contact with the water and hydro turbine faces various problems during its working period. The major problems associated with the hydro turbine is that of cavitation and silt erosion which erodes the turbine parts such as runner blade and draft tube etc. The silt erosion occurs due to the presence of the silt particles in the water which continuously strike the surface of the turbine parts, thereby, the material of the turbine gets eroded which makes decreasing in the efficiency of the power plant. Under the present work, an attempt has been made to investigate the effect of silt erosion on the performance of draft tube of Francis turbine by means of the commercial Computational Fluid Dynamic (CFD) software CFX under silt with water. The numerical simulations have been performed under different loading conditions i.e. 50%, 75% 100% and 125% and different silt concentrations i.e. 1000 PPM, 1500 PPM, and 2000 PPM using Tabakoff erosion model. The performance of draft tube has been analyzed by pressure and velocity contours. Based on the present numerical investigations, it has been found that efficiency decreases and erosion rate density increases with the increase of silt particle concentration. Based on the results the efficiency of draft tube has been found as 83.6% and 82.06% for silt free water and silt with water respectively. The outcome of the present study may be helpful to carryout further research on this aspect.