Performance Improvement of Cross-Flow Turbine With a Cylindrical Cavity and Guide Wall

The cross-flow turbine has been utilizing to develop small hydropower less than about 500 kW in the world. The turbine cost is lower than the other turbines because of its smaller number of assembled parts and more straightforward structures. However, the maximum efficiency of the cross-flow turbine is lower than that of traditional turbines. Improving the turbine efficiency without increasing manufacturing costs is the best way to develop small hydropower in the future. This study is aiming to improve the turbine efficiency at the design point and partial load. The runner's outflow angle varies with turbine speed and guide vane opening (GVO) in the typical cross-flow turbine. The tangential velocity component remains in the outflow in these conditions; thus, a change in the outflow direction along the runner's radial direction is helpful for performance improvement. The authors experimentally change the desirable outflow angle by attaching a cavity and a guide wall at the outside casing tip. The turbine performance test was conducted for various turbine speeds and GVOs. Next, flow visualization around the runner was performed. As a result, both of cavity and guide wall improve the turbine performance. The outlet flow patterns are different by attaching the cavity and the guide wall, especially between the partial and optimum load conditions.