Performance Analysis and Design Optimization of Micro- hydro Cross- flow Turbine

Abstract

Micro-hydropower plants (MHP) give the best solution to the power needs of rural and small communities which serve as decentralized power source to meet the local population requirement. Energy requirements for lighting, cooking, heating, drying, agro-processing and other small scale industrial activities can be met through these MHPs in the most reliable way in the rural areas of the country like Nepal. Cross- flow turbines are used widely in such MHPs due to their simple design, easier maintenance, low initial investment and modest efficiency. Also, because of their suitability under low heads, their efficient operation under a wide range of flow variations and ease of fabrication, cross- flow turbines have been extensively employed.

The research work comprises of both experimental studies and numerical investigation of the cross- flow turbine. Experiments are conducted in dedicated test rig available in Fluid Engineering Laboratory of Korea Maritime and Ocean University (KMOU). With robust computer technologies and design developments, a CFD based study on the design, performance characteristics, flow analyses and design optimization are carried out in this study work. A previously made test rig (Hyosung Ebara Engineering Company, South Korea, 2009) was reviewed and maintained to conduct the experiments.

During the experiment, pump provides the required head and the flow through the turbine. Electro-magnetic flow meter and pressure transducer at the upstream side are used for the flow rate and pressure measurement respectively. The turbine was coupled to powder brake through torque meter and the required parameters were recorded in the data logger. Experiments were conducted at various rpm and flow rates. For numerical simulation, two phase (air & water at 25°C) steady state with SST turbulence model was selected in the commercial CFD code ANSYS CFX 13.0. The design parameters include 10 m head, 0.1 m3/s flow rate and 642 rotational speed. Numerical results obtained from the simulation were compared with the experimental results. Several major parameters that affect the cross-flow turbine efficiency were studied and design modifications were done to enhance the turbine performance.

In order to enhance the efficiency of the turbine, various design modifications have been proposed and evaluated numerically. Nozzle shape modification, guide vane angle variation, blade numbers variation, air layer insertion, casing length and diffuse angle variation were done simultaneously during the process and finally the optimized design was proposed. Velocity distribution, pressure contours, output torque etc. in the flow domain and the several stages of flow inside the runner were also characterized.