Search

A swing-type guide vane is the most popular in a cross-flow turbine, which controls the water flow rate into the turbine. The flow under the guide vane may turn away from the optimum direction in partial load operation by the flow separation from the guide vane leading edge. Maintaining the ideal velocity triangle at the runner inlet is essential to improve the turbine efficiency and to avoid noise and vibration for partial load operation. It is essential to reveal how the angle and shape of those guide vanes affect the flow behavior at the runner inlet and turbine performance. Therefore, this study focuses on the flow characteristics around the guide vane and at the cross-flow runner inlet. The authors verify the evaluation by CFD simulation and compare turbine performance and internal flow between different operating conditions with two guide vanes, the swing-type, and circular segment type. As a result, it is revealed that the swing-type guide vane affects the flow direction, and especially the flow angle is far from the optimum at partial operation. The circular segment type shows superior performance at partial load than the swing-type guide vane.

The authors focus on a small propeller turbine utilizing the extremely low head and relatively much flow rate sites. The proposed propeller turbine by the authors previously had fixed pitch vanes, and the vane was made of a constant thickness metal plate to reduce manufacturing cost and required technology. The turbine was in a step in the casing and had an outer ring on the runner vane periphery. The structure effectively suppressed the tip leakage flow but had no significant effect on turbine efficiency improvement. This is the limit of the constant thickness blade rotor. So, this study focuses on making the runner by additive manufacturing by the 3D printer because it is faster and cheaper than conventional production methods and is expected to improve turbine efficiency and physical strength. This study aims to compare the performance of the new ring runner model designed to further improve the efficiency of the turbine by CFD analysis and experiment. As a result, the turbine efficiency improved, tip leakage flow was suppressed by attached to the outer ring compared with the previous model

Cross-flow turbine is widely used for small hydropower in run-of-river type stations because of its excellent partial load characteristics, easy manufacturing, and low cost. The Banki-Michell turbine is the origin, and various studies have focused on improving the turbine performance. The authors have developed a new cross-flow turbine with a cavity and a guide wall from the outer nozzle wall tip to suppress flow separation on the guide wall and make the casing smaller. However, little researches are focusing on vibration, and it is also essential to get knowledge for suppressing vibration and noise from the turbine aiming to install at higher head sites. Our previous studies showed that high-pressure fluctuation occurs near the outer nozzle tip, and the cavity suppresses the pressure fluctuations, but the suppression mechanism is not fully understood. Therefore, this study experimentally investigates the pressure fluctuation generation mechanism and the cavity’s effect on suppressing the vibration. Furthermore, it aims to suppress the vibration by modifying the nozzle tip shape. The vibration level was measured on a lab-scale turbine and CFD analysis to reveal the generation of pressure fluctuation. As a result, the predominant frequency of the vibration corresponds to the blade passing frequency and the pressure fluctuation at the nozzle tip. The cavity and nozzle tip shape show a significant influence on pressure and vibration characteristics and turbine performance.