| In the power system,pumped storage power station undertakes many functions,such as peak load regulation,valley filling,emergency standby and directional service.With the optimization of energy structure and the development of smart grid,the large-scale development of pumped storage is urgent.At the same time,the social production requires more and more high performance of pumped storage power station,which requires continuous improvement of its core component,pump-turbine.In recent years,runner with splitter blades has been widely used,which plays an important role in improving performance curve,improving efficiency and stability of small flow and part load conditions,reducing pressure fluctuation,improving cavitation performance and reliability of runner.For the pump turbine which is a complex rotating machine,the unsteady pulsation caused by rotor-stator interaction is the key factor of the unit stability.Therefore,based on CFD(computational fluid dynamics)and FSI(fluid structure interaction)numerical calculation technology and relevant test data,this paper selected different flow and opening conditions of pump-turbine with splitter baldes for comparative analysis,and obtained the specific impact of flow and opening changes on rotor-stator interaction and vibration in pump mode,so as to provide effective reference for the stable operation of pump turbine unit.The main research contents are as follows:(1)External characteristics and internal flow analysis of the model:Based on the incompressibility of the fluid,the numerical calculation of the whole flow field was carried out for 9.8°,17.5°and 24.8°openings,and the external characteristic curve is obtained and compared with the test data.0.75Q_d,1.0Q_d and 1.25Q_d corresponding to each opening was choosed for internal flow analysis.The results show that the numerical simulation strategy adopted in this paper can predict the external characteristics and internal flow of the pump turbine with high accuracy.The flow stability is poor under the condition of small opening with high flow rate and large opening with low flow rate,especially for small opening with high flow rate,the obvious flow separation in stay-guide vanes results in serious energy loss.(2)Analysis of pressure pulsation under different flow conditions:Firstly,the frequency of pressure pulsation caused by rotor-stator interaction of pump mode was reasonably predicted according to the relevant theory.Then the unsteady monitoring was carried out under the condition of 0.75Q_d,1.0Q_d and 1.25Q_d with the optimal opening of 17.5°.The results show that the main frequencies of pressure pulsation in vaneless region are 5f_n,10f_n and 20f_n,the main frequency in runner area is 16f_n,and the main frequency near the outlet wall of draft tube is 5f_n.Compared with the pressure pulsation under different flow conditions,it is found that the flow instability under the condition of low flow rate of 0.75Q_d produces nonlinear frequency.There are significant differences in the pressure fluctuation in the vaneless region at different guide vane heights,and the amplitude of the main frequency10f_n near the bottom ring is larger than other heights,which indicates that the rotor-stator interaction near the bottom ring is relatively severe.From the vaneless region to the outlet of stay vane passage,the amplitude of rotor-stator interaction frequency decreases continuously,and the amplitude attenuation of each frequency is mainly concentrated in the guide vane passage.(3)Analysis of unsteady characteristics of pump mode under different opening:The rated operating conditions of 9.8°,17.5°and 24.8°were selected as the research object to and compare the influence of opening of the guide vane on the rotor-stator interaction.The results show that as the opening of the guide vane increases,the rotor-stator interaction intensifies,and the impact of the change in opening becomes more significant.The radial force of runner and the hydraulic torque of guide vane are larger and distributed regularly under 17.5°and 24.8°opening.The amplitude of 5fn is larger than the optimal opening at small and large opening,which indicates that deviation from the optimal opening will aggravate the difference of rotor-stator interaction between the long and short blade.Under the small opening of 9.8°,the outlet of the guide vane is full of low-speed vortex core,and the vorticity fluctuation is severe,resulting in a low-frequency 0.2fn,which propagates to the upstream vaneless region.(4)Analysis of the characteristics of vibration based on FSI:The flow field pressure of9.8°,17.5°and 24.8°opening rated conditions was selected as the prestress,and the dry and wet mode calculation was carried out for the structure of runner and guide vane.The results show that the deformation of runner structure mainly occurs at the low pressure side of crown and band,and the torsional deformation occurs in guide vane structure.In the modal mode,the relative vibration amplitude of the crown and band is larger,and the vibration at the crown is dominant.The additional mass of water in wet mode has little effect on the modal characteristics of runner structure,but it can significantly reduce the natural frequency and amplitude of structure.Comparing the natural frequency of each order in wet mode with the frequency of rotor-stator interaction,the combination of the number of long and short blades and guide vanes is reasonable,and there is almost no risk of resonance under rotor-stator interaction. |
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