Unstable head-flow characteristics of pump-turbine under different guide vane openings in pump mode

In order to obtain the unstable head-flow characteristics of pump-turbines under different guide vane openings, firstly, experiments are carried out on the pump-turbine model for a pump sto-rage power plant in pump mode. It is shown that the head gets higher value and its slope becomes stepper at a low flow rate; the unstable head-flow effect exhibits more obviously with decreasing guide vane ope-ning, but the flow rate range for the effect is shrunk. Further, a 3D geometrical model of the pump-turbine model is generated and a set of mesh for its fluid domain is created. The steady turbulent flows in the pump-turbine model are simulated by using the SST k-ω, standard k-ω, RNG k-ε and standard k-ε turbulence models at various flow rates under 19 mm guide vane opening, showing the SST k-ω turbulence model can result in more accurate performance curves than the others against the experimental measurements. Consequently, the flows in the pump-turbine model are simulated by means of that turbulence model at 13 mm, 19 mm and 25 mm guide vane openings and the head, torque and efficiency curves are obtained and compared with the experimental observations, and good agreement is demonstrated between them. Finally, the internal flow patterns in the unstable region, at part-load, best efficiency and over-load points are analysed at 19 mm guide vane opening. It is identified that the unstable head-flow effect is related to flow separation and vortex occurrence in the runner and a few stay vane passages.