Study On The Influence Of Runner Cone Perforation On The Draft Tube Vortex In Hydro-turbine

The demand of electricity continuously grows.It pushes the hydro-turbine to a high-efficiency,high-power,large-scale and high-speed level,meantime,it calls for the further improvement of operation stability.Hereby,the stability of power plant and working safety attract more and more attention.This thesis focuses on the generation and evolution of vortex ropes in the draft tube of a full-passage flow,carrying out the experimental and numerical investigation on the inner flow of model turbine with different shape of runner cone.The flow features and vortex rope charatersitics of inner flow are studied,and the components and magnitude of pressure fluctuations are analyzed.To do this,firstly the experimental systems are established and the three-dimensional simulations are performed.With the numerical results,the new different shape with perforation of cone are designed,and further simulations and experiments are subsequently carried out.The experiments mainly use the high-speed imaging system for the flow visualization,and the pressure fluctuations are measured.Secondly,the unsteady simulations for the full-passage flow under large and small opening partial conditions are performed,the interblade vortex,vortex rope and flow separation are captured.The vortex rope evolution and pressure fluctuation features are analyzed.Then,the influence of perforated cone on the vortex rope and pressure fluctuations are analyzed.Using FFT(fast Fourier transform),the preesure fluctuations are post-processed.The results show that the pressure fluctuation energy of the monitoring points decreases with the decrease of the volume of cavitation vortices in the draft tube.Finally,with numerical simulation and experimental results,the pressure fluctuation features under different cone shape are discussed.It is found that the outside of the elbow has the maximum pressure fluctuation energy,and after the perforated method,the main frequency frequency of the pressure fluctuation decreases,and the energy peak-to-peak value becomes smaller and the high-frequency component increases.In thesis through unsteady three-dimensional simulation of a model a Francis hydro-turbine mode,the experimental results are verified under two partial flow conditions.Also,the magnitude and components of pressure fluctuations before and after perforation are analyzed.The effects of cone shape on the flow instabilities and corresponding pressure fluctuations is clarified.The result present that the perforated method has a positive effect on reducing the pressure pulsation level of the draft tube,which could serve a important guide for the engineering design of hydro-turbine.