Abstract:

A hydraulic model of pump-turbine unit which has “S” characteristic curves, was developed to study the effect of MGV on the “S” characteristics and determine the openings of pre-opened guide vanes in the “S” operation region. The external characteristics and internal flow were simulated by using a three-dimensional incompressible flow model, with a model for turbulence calculation and the SIMPLEC algorithm coupled with a second-order upwind scheme for discretization and solution of flow field. The simulations were verified with experimental data. Analysis on the calculated internal flow and external characteristics reveals that the MGV method can effectively prevent the unit from entering turbine braking mode. As the pre-opening increases, the flow non-uniformity becomes more significant and the water ring between runner and guide vanes tends to disappears gradually. The vortex rope in draft tube can be weakened by increasing the pre-openings. These results would provide a basis for stability of pump-turbine at start-up stage.