CFD-based Francis Turbine Spindle Seal Research On Improvement Of Pump Plate Device Structure

In order to avoid the significant impact on the stability of the unit due to water leakage during the operation of the turbine,a pump plate structure can be installed in the gap of the runner crown of the francis turbine.However,as the leakage water flows into the pump plate structure,the sediment will wear the structure in the process of operation.Therefore,it is of great significance to explore the internal pressure changes and sediment distribution of the pump plate structure under different water flow conditions for the design and transformation of hydraulic turbines.In this paper,the hydraulic turbine with a pump plate device added to the Hongshanzui First Stage Power Station was taken as the research object,and the two-phase flow of water and sand in the gap of the runner's crown was studied numerically.Firstly,a three-dimensional model was established based on the design drawings.Secondly,the ICEM software was used to divide the fluid domain into the hybrid grids,and the Ansys CFX software was used to numerically simulate the different water flow conditions.Finally,the simulation data was processed and analyzed.The research results of this paper can provide guidance for similar designs and modifications of hydraulic turbines.The main work and conclusions can be draw as follows:(1)According to the data of the power station,the two-phase flow of water and sand in the gap between the upper crown of the runner was numerically simulated based on the RNG k-? turbulence model and the solid-liquid two-phase flow model,and the simulation results of the distribution of sediment and the actual internal wear of the pump plate structure were compared to verify the rationality and necessity of the solid-liquid two-phase flow numerical simulation inside the pump plate structure.(2)Based on the actual river sediment situation,the solid-liquid two-phase flow of pump plate structure with different sediment particle sizes and different sediment volume fractions was set and calculated respectively.The results show that when the sediment diameter d is between 0.01 and 0.1mm,the larger the sediment diameter is,the easier it is to produce a difference in solid-liquid velocity and cause water and sand separation,resulting in sedimentation in the gap between the inlet and the comb ring.When the sediment volume fraction is 1% to 15%,only changing the sediment concentration gradient does not change the sediment distribution law,and the larger the sediment volume fraction is,the easier it is to produce siltation.It is recommended that the hydropower station adopt measures such as sand blocking nets and grit chambers at the water intake to intercept the sediment.(3)By comparing with or without pump blades and adjusting the comb ring gap,the effect of the pump blades and comb ring gap on the internal flow characteristics of the pump plate structure was explored.The results show that the pump blades can increase the fluidity of the pump plate structure by more than 30%,which significantly improves the sedimentation phenomenon.As the comb ring is an important structural component of the pump plate,the change of the comb ring gap also has a great impact on the internal flow of the pump plate structure.Analysis shows that when the comb ring gap is reduced to2 mm,the water pressure inside the pump plate structure drops by 50% as a whole,making it more difficult for sediment to enter.It is recommended to install a pump plate device with pump blades during the transformation of the power station,and minimize the width of the comb ring gap within the allowable range of the process.