Numerical Simulation And Experiment Of Vortex Flow In Francis Turbine

The phenomenon of cavitation vortex and water hammer generated when the load changes in a high-speed,large-capacity Francis turbine is an important factor affecting the stability of the turbine.The exploration of energy characteristics,cavitation characteristics,pulsation characteristics,and flight characteristics of turbines will help us to better control the vibration of turbines,reduce cavitation,and improve overall operating efficiency and reliability.Therefore,a comprehensive analysis of the formation mechanism and influencing factors of the vortex belt is carried out through numerical analysis of two-phase flow based on the sliding grid,internal characteristic numerical method based on the static efficiency factor,and a real machine test of the model machine.The main research work of this paper is as follows:(1)Perform numerical simulation and real machine test respectively on the model machine,select different opening and rotation speeds to analyze and measure the operating efficiency of the turbine,collect 263 sample points each,and then draw the energy characteristic curve of the entire turbine.Sampling and comparing other points distributed on the two performance curves,and improving the finite element model and algorithm to reduce the error rate,in order to find a reliable numerical analysis method,so that the results of numerical calculation are more referential,and in part Alternative tests.The performance curve established by the finite element model has a mean square error range of 4.13%or less.(2)Using the two-phase flow simulation method and the Zwart-Gerber-Belamri cavitation model to analyze the turbulence of the turbine's full flow channel,and by setting up the pressure pulsation monitoring point,the vibration of the turbine's cavitation coefficient was analyzed and measured.Characteristics,vortex band shape,vibration amplitude,and frequency characteristics.Unsteady simulation was used to analyze the evolution of vortex belts.(3)By keeping the cavitation constant unchanged and changing one of the opening(flow rate)and rotational speed,the system oscillates the pulsation characteristics of the vortex belt under various working conditions,and tries to give the vortex zone of the draft tube and its cause.The mechanism and characteristics of the formation of pressure pulsations:the abrupt changes in the reflow state and the corresponding processes and results of energy and motion rebalance.(4)Using the singular value decomposition method to separate the prototype turbine vibration signal to ensure the accuracy of the pulsation characteristic test.At the same time,it is also used to measure the cavitation in the impeller area of the turbine,detect cavitation early,and improve the initial vacancy.The accuracy of the coefficient measurement.(5)The proposed turbine load rejection safety assessment method based on the joint solution of static efficiency factors is a numerical iterative calculation method that extracts the static efficiency alone.This method combines the static efficiency factor with the internal characteristics method and can significantly reduce Model capacity,reduce system internal consumption.The calculated speed increase value is compared with the value measured by the flyaway test to verify the accuracy of the calculation model.