To realize a multienergy complementary system involving hydropower and other energy sources, hydraulic turbines frequently run under partial flow conditions in which a unique flow phenomenon, the channel vortex, occurs in the runner, causing fatigue failure and even cavitation to the turbine blade. Cavitation severely shortens the service life of the unit and terribly limits the output of the turbine under partial flow conditions. In this paper, a numerical model of a Francis turbine was created with tetrahedral grids; the large eddy simulation (LES) method based on the WALE subgrid scale model and the Schnerr–Sauer cavitation model was adopted to carry out numerical simulation of the Francis turbine; and a vortex identification method based on the Q criterion was used to capture and analyze the channel vortex. The calculation results showed that a negative impact angle at the inlet of the runner occurred when the turbine ran under partial flow conditions, leading to three different types of channel vortexes in the blade channel. Also, different channel vortexes caused cavitation on different positions on the runner, and the volume change of cavitation showed periodic properties.

The vortex rope in the draft tube is considered as the major contributor to pressure pulsation at partial load (PL) conditions, which causes the hydro unit to operate unstably. Based on the prototype Francis turbine HLA551-LJ-43 in the laboratory, J-grooves are designed on its conical section in this paper. We used numerical simulation to study the effect of the J-grooves on vortex suppression and energy dissipation in the draft tube. Four typical operating conditions were chosen to analyze the vortex suppression; the corresponding flow ratios Q* are 100%, 82%, 69%, and 53%, respectively. Entropy production theory is used to calculate the energy losses and assess the effect of the J-groove on energy dissipation under part-load conditions. By comparing entropy production, circumferential and axial velocity components, swirl intensity, pressure pulsation, and vortex distribution in a draft tube with and without J-grooves at different operating conditions, it can be concluded that the entropy production on the wall containing a conical section with J-grooves is obviously smaller than that without J-grooves, the effects of J-grooves on reducing circumferential velocity component V_u, pressure pulsation, and weakening vortex intensity and vortex rope in the conical section are obvious, especially at part load and deep part-load operating conditions. Using J-grooves shows better performance on vortex control and energy dissipation in the draft tube of a Francis turbine at partial load conditions.

This study focuses on the splitter blade pump–turbine as the research object to analyze the problems of hump characteristics and the hysteresis effect. We simulated the operation of the pump condition with small opening of the guide vane, analyzed the hydraulic loss by using the entropy production theory and entropy wall function, and investigated the study of internal flow transfer characteristics. In this paper, it was first verified that the maximum error of the energy loss calculated by the pressure method and the entropy production method was less than 6% for the working zone. From the quantified energy loss results, a significant instability feature was observed in the 0.65 Q_BEP–0.9 Q_BEP operating interval, accompanied by the phenomenon of the non-overlapping of the characteristic curves. The results show that the hump characteristic with hysteresis effect also exists in the splitter blade pump–turbine. The percentage of energy loss in the hump zone is in descending order of runner, guide vanes, spiral casing, and draft tube, but this changes again at low flow rates. By analyzing the high-entropy production region, it was found that the high-hydraulic-loss region is mainly distributed at the trailing edge of the long blade in the vane-less space, which is different from the traditional runner.