Improvement of Performance of Undershot Cross-Flow Water Turbines Based on Shock Loss Reduction

Abstract

Undershot cross-flow turbines are applicable to shallow open channel flows and are characterized by a simple structure free of guide vanes or a casing. Since these water turbines operate in a free surface flow field, the optimum inlet blade angle and outlet blade angle are considered to vary with the flow rate in the open channel; however, guidelines for setting these angles are yet to be established. In this study, a method to improve the performance of an undershot cross-flow water turbine based on shock loss reduction was proposed. First, by varying the blade angle of the straight blades of the turbine, the inlet blade angle and outlet blade angle which reduced shock loss in the first-stage inlet region and second-stage inlet region were investigated through free surface flow analysis. From the results, it was shown that by taking the inlet and outlet blade angles which minimize the first-stage and second-stage shock losses for straight blades and applying them to curved blades, shock loss is reduced, thereby improving turbine efficiency and turbine output.