CFD BASED FLOW ANALYSIS OF. HILLY SMALL HYDROPOWER STATION

Abstract

Energy is the basic requirement for economic development. According to International Energy Agency (IEA), a threefold rise in India's electricity generation capacity is expected by 2020. As the non-renewable fossil energy sources continues to deplete, and realizing the summits held at Brazil and Kyoto to reduce the greenhouse gas emissions, hydropower has moved towards one of the top power development option to meet the fast growing energy demand. In hydropower sector, cost-effective design of different components is always a challenging task. For cost-effective design of hydraulic components highly complex flow, which is turbulent and three dimensional in nature, is to be analyzed critically. As such, there are various components which come in contact with the water, but turbine is the most critical component because it has a considerable influence on the cost of civil works, overall performance as well as life of any hydropower project. Turbines are usually designed according to the site conditions i.e. head and discharge. The economic viability of the Small Hydropower (SHP) schemes is oftenly difficult due to higher per kW cost compared to large units. Hence, it is very important that, the enough care should be taken at the inception stage itself to have optimum design of small turbines. The flow analysis inside the hydro turbine is very difficult and expensive -through experiments. Therefore, use of Computational Fluid Dynamics (CFD) as a tool for the analysis of flow in hydro turbines has increased in recent years. In the present study, flow analysis of Francis turbine is carried out using commercial CFD package `FLUENT'. The simulation is carried out at six different operating points with three different turbulence models. It is found that k-i SST model is more appropriate for the flow simulation in hydro turbines. The unequal flow distribution in stay vane passage has been found at lower than rated discharge. The regions of secondary flow, back flow, vortices and low pressure are observed in the draft tube at part load operating conditions. The operating characteristic curves predicted by the numerical simulation are presented. The CFD results are critically compared with model testing results and similar trend is observed. However, the deviation in results is more at part load conditions. Techniques to improve the part load performance are demonstrated.