Characteristics and internal flow of a low specific speed pump used as a turbine

PAT (Pump as Turbine) has gradually been a popular solution for the small-scale hydropower generation. Because of the rich assortment and the low initial investment. However, PAT is designed as a pump but not a turbine. Therefore, a lot of research was conducted about the performance prediction and the loss distribution of pump and turbine mode. In this paper, we focused on the internal flow and loss mechanisms of the best efficient point of both modes. The characteristic and internal flow were investigated by experimental and computational approaches. The reasons of efficiency reduction in turbine mode and loss mechanisms were clarified by the computational results. The separation flow region occurs on the suction side or pressure side in non-BEP, and the swirling flow counter-rotates the PAT occurring at the outlet in BEP might be the reasons of the efficiency reduction. Moreover, because of the camber line shape of PAT, the separation flow occurs near the inlet could not reattach soon which induces the loss region. Furthermore, the secondary flow near the blade surface and the flow from the pressure side to suction side interfere with each other which induced the loss region.