Unsteady Flow Analysis of an Axial Flow Hydraulic Turbine with Collection Devices Comprising a Different Number of Blades

We previously devised a new type of portable hydraulic turbine that uses the kinetic energy of an open-channel flow to improve output power by catching and accelerating the flow. The turbine contains an axial flow runner with an appended collection device and a diffuser section that is not axisymmetric. The objective of this study is to determine how interference between the collection device and the runner influences performance characteristics of the turbine. We investigated the performance characteristics of the turbine and flow field for different numbers of blades during both unsteady and steady flow. During an unsteady flow, the maximum values of power coefficients for three and two blades increased by approximately 8.8% and 21.4%, respectively, compared to those during a steady flow. For the three-blade runner, the power coefficient showed small fluctuations, but for the two-blade runner, the power coefficient showed large fluctuations. These fluctuations in the power coefficient are attributed to fluctuations in the loading coefficient, which were generated by interference between the runner and the diffuser section of the collection device.