Comparative study on the flow characteristics of large-discharge and low-head hydraulic turbines with different discharge structures

Background Hydraulic turbines are widely employed to recover residual energy from liquid pressure in industries. A double-discharge turbine can achieve the desired effect in large-discharge and low-head operations than the single-discharge ones. Methods This paper numerically compares the working mechanisms of these two structures from three aspects: internal flow field, energy loss and load behaviors and experimentally verifies the hydraulic performance. Significant finding The results show that the maximum efficiency of a double-discharge turbine is 85.77 % and that of a single-discharge turbine is 82.6 % under large-discharge and low-head working conditions. The wall-entropy generation region of a double-discharge turbine is smaller than that of a single-discharge turbine. That is why the energy loss of a double-discharge turbine is small. Moreover, the blade load form of the double-discharge turbine is the front-load type, which can obtain more dynamic moments than the medium-load blade of the single-discharge turbine, increasing the blade work capacity. Simultaneously, the difference in load distribution affects the flow field, so that the volute of the double-discharge turbine significantly increases the flow velocity. And a large vortex at the outlet and the tongue results in a large energy loss.