Numerical and Experimental Study on Vortex Rope with MGV in the Micro-Class Hydro Francis Turbine

Abstract

Energy consumption is a huge part of our daily life. Today we gather most of our energy from coal, oil and natural gas also known fossil fuels. Generating electricity on our planet, requires plenty of massive power plants and transmission grid system delivery to the power. Renewable energy comes from a source that is not depleted when using such as wind, solar and hydropower. Hydropower is the largest source of renewable energy which is capture the energy of falling water to generate electricity as well can be efforts produce number of benefits such as a water supply, flood control and irrigation system. Micro-hydropower installation can provide power to the out-settlement or small community. These usually range between 5kW-100kW of electricity output.

In this study, numerical and experimental analysis of 3kW micro-class Francis turbine carried out to predict performance of the turbine. A Draft tube is one of the most important part of Francis turbine which connects the runner exit to the tailrace where the water is being finally discharged at atmospheric pressure from the reaction turbine. There are several issues in the draft tube like pressure pulsation, effect of cavitation on draft tube performance, vortex rope study etc. At part-load condition vortex form it hits structure constantly which is affect the performance of the turbine. This study focused on prediction of vortex behavior at the draft tube and numerical results obtained the hydraulic performance of 3kW micro-class Francis turbine with the inlet pipe, a spiral casing with 12 guide vanes, 6 stay vanes and the runner having 13 blades and a draft tube. Ansys CFX software used to simulate for the numerical analysis of micro-class Francis turbine. Three misaligned guide vane (MGV) openings with 5 different MGV openings were chosen to analyze the influence of the pressure pulse in the turbine. Additionally, PIV technique was used to investigate flow velocity in the draft tube.

In the numerical simulation, different sets of operating points were selected to get performance characteristics of the turbine and best efficiency point indicated 91.67% efficiency at 0.02m3/s, power output 3.32kW. For misaligned guide vanes, more options can be tried out by misaligning more guide vanes, at higher angles. Additionally, based on the numerical analysis of a Francis turbine, the results for efficiency obtained from simulation are found to good agreement with the model results obtained from the manufacturer.

From the performed experiment on performance test of Francis turbine using the Francis turbine experimental set-up in the Flow Informatics Laboratory at Korean Maritime and Ocean University. The experimental analysis of the turbine showed a significant result. The turbine operated at different vane angle setting were obtained and tested by varying the parameters as a guide vane angle in the 6 different range of between 2-12 degrees, speed, and 500-1700 rpm respectively. The lowest difference between the experimental and numerical results was 2.03% and the maximum difference between the experimental and numerical results was 6.12 %. Numerical efficiency higher than experimental efficiency.