INVESTIGATION OF CHARACTERISTICS AND DESIGNING PARAMETERS OF CROSS FLOW TURBINES

Abstract

In today’s world, renewable energy sector is growing rapidly to reach the power demand and micro hydro power is contributing a lot because of its low cost and easy installation. There are various types of turbines available to generate the electricity in micro hydro power but cross flow turbine also named as ‘Ossberger turbine’ is considered to be techno-economically viable option. Cross flow turbines basically are impulse type turbine which consist of nozzle, runner, casing and guide vane. The runner is of drum shape connecting two parallel discs by number of blades, mounted on shaft. The water from the nozzle strikes the blades for the first time converting the 2/3rd of potential energy into mechanical rotational output power. The water then crosses the shaft and again hit the runner blades on the opposite side and remaining 1/3rd energy gets converted into mechanical power. As water crosses the shaft of runner which is why it is named as cross flow turbine.The cross flow turbine has an advantage of high part load efficiency. These turbines can be manufactured locally as it has the advantage of easy fabrication. The blades can be manufactured by cutting the pipes along the length. They can also be used for low discharge and high head conditions, in case of hilly areas. The disadvantage of the cross flow turbine is that its efficiency is poor than the other conventional turbines. There is a large scope of efficiency improvement in cross flow turbine by properly designing the turbine parameters according to the site conditions. In this dissertation work, main focus is to improve the guiding mechanism for water flow inside turbine so that the losses can be reduced to positively affect the turbine output. For the same purpose, numerical approach is adopted and CFD analysis is carried out by using ANSYS CFX. The turbine is designed and modelled corresponding to a site conditions and analyzed to compute the output. The flow inside is guided throughout the turbine with the help of guide vane inside nozzle and also by introducing an interior guide vane inside runner between 1st stage and 2nd stage of power output. It is found that the efficiency of turbine get increased approximately 2.2% by using this interior guide vane inside runner. Work is also carried out to identify the optimum position of guide vane inside runner simultaneously with the opening of nozzle guide vane. For future studies, it is recommended to work out the effect of guide tube on the turbine performance at different site conditions. The profile and shape of guide tube also need to be worked out further in the future work