Abstract
An undershot-type cross-flow water turbine does not require a casing for open channels and hence considerable simplification is attained. However, because this water turbine does not have a casing and has a free surface, it is believed that the internal flow considerably changes with the flow rate. We investigated the effect of flow rate on the performance of this water turbine with straight blades by an experiment and numerical analysis. As a result, the following facts became clear. When a flow rate is small, the power becomes small, but turbine efficiency becomes large. This is because the first-stage shock loss becomes small in a low rotational speed region and the second-stage shock loss becomes small in a high rotational speed region.
