Study On The "S" Characteristics And Internal Flow Induction Mechanism Of Reversible Rump-turbine

In the energy interconnection,reversible pump-turbine is one of the core equipment which plays an important role in distributed energy storage and transition.With the increase of proportion and single capacity,the reliability of the reversible units is important to the safe operation of the system.The operational instability caused by “S” characteristic has become a critical point of design and operation of the reversible pump-turbine,which directly affects the stability of the units and causes the collapse of the electric power systems under the no-load start-up condition.In this study,flow induction mechanism and characteris tics on the “S” working condition of reversible pump-turbine in the pump storage units are investigated with the model test and three-dimensional unsteady numerical simulation.At the same time,the method on improvement of “S” characteristic by MGV(Misaligned Guide Vanes)devices based on internal flow induction mechanism are given.The main contents are described as follows.1.Model tests of reversible pump-turbine are carried out and basic system of the test platform is introduced.Based on the parameters of pumped-storage stations,the comprehensive error and relative calculation are discussed.The indexes of model test are consistent with the standard of IEC 60193-1999(“Hydraulic turbine,storage pump and pump turbine model acceptance test code”).The performance of the test is consistent with the design values.The results of model test provide the reliability verification and basic calculation parameters for the numerical simulation.2.The 3-dimensional physics model and grid are established based on the model.SST k-? turbulence model is used to simulate the three-dimensional total flow field,which can effectively capture the characteristics of the near wall area and the far-wall flow.The numerical simulation result s of the comprehensive characteristic are consistent well with experiment results,which indicate the reliability of the numerical calculation.Flow-induced mechanism of “S” working condition is revealed by the analysis of flow characteristics and evolution process of turbulence structure under the synchronous guide vane start-up process,based on which,the improvement methods of “S” characteristics are discussed.3.The curves of the four-quadrant full characteristic,“S” characteristic,full characteristic of model and “S” characteristic under MGV device with different opening are obtained by the model test s.Based on the analysis of the curves,the “S” characteristic can be improved by MGV device under different opening in reversible pump turbine under the low head no-load start-up working condition.The relationships between unit speed and unit discharge in the “S” characteristic region are given by the simulation under the MGV device.The effects of synchronous guide vane and MGV with the different arrangement mode on the “S” characteristic are discussed,based on which,the best mode of the MGV device with two pairs of uniformly dispersed symmetrical arrangement are obtained.The flow characteristics and improvement mechanism are given by the three-dimensional unsteady flow simulation under the best arrangement of MGV device,which can provide some references on the improvement of comprehensive hydraulic performance for the reversible pump-turbine.