PERFORMANCE ANALYSIS OF CROSS FLOW TURBINE USING A GUIDE TUBE AND A DRAFT TUBE

Abstract

A promising comer of the future hydropower market remains the economical and ecologically acceptable exploitation with micro hydro range sites, where conventional turbines are neither economical nor ecologically undisputed. In hilly region micro hydro up to 100 kW have momentous role in utilization of mechanical power and electricity generation. The capacity of micro hydro power plant up to 5.0 kW is considered under development of water mill program by Ministry of New and Renewable Energy (MNRE), Govt. of India. The popularity of the turbines under micro hydro lies in the fact that they should be less costly and can be fabricated locally. There are various types of turbines that can be used in micro hydro. Cross-Flow turbine has been considered techno-economically viable for such sites. Cross flow type runner can be fabricated locally, which results in the poor efficiency. The vanes can be made even from the pipes cut along the length. Also this kind of runner is suitable for low discharge and high head conditions, which is a common case in the hills. A cross flow turbine has a drum shape runner consisting of two parallel discs connected together by a series of curved vanes or blades. The problem with the fabrication of cross flow turbine runner at the local level is that its efficiency decreases due to lack of proper design and fabrication. The low efficiency is the basic inspiration to improve the existing design of cross flow runner. Number of attempts has been made to improve the efficiency of cross flow turbine by adapting certain fluid machines related concepts. It is observed from literature review that the efficiency of cross flow turbine can be increased by introducing guide tube to guide the crossing flow towards the second stage of the runner. Further a draft tube can be introduced to extract kinetic energy available at outlet of cross flow runner. In order to analyze the combined effect of a guide tube and a draft tube on fluid flow analysis is not available. Under the present study a CFD analysis on flow pattern inside the runner obtained for different type of guide tubes and a draft tube has been attempted. The results of this analysis are used to study the performance of a cross flow runner in order to suggest improvements in cross flow turbine.