Experimental Test And Numerical Simulation Of Interblade Vortices In A Low-Specific-Speed Francis Turbine Runner

When Francis turbines operate away from optimum conditions,the flow at the runner inlet will separate,which will develop into vortices in the blade passages.These visible vortices are called interblade vortices.The emergence of interblade vortices in the runner region may induce pressure fluctuation of the runner blades,even result in cracks on the blades.In addition,the interblade vortices may induce vortex cavitation,resulting in cavitation erosion,generating noise and causing damage to the blades,and affecting the unit’s safe and stable operation.To study the interblade vortices in the runner of Francis turbines,PIV was used to measure the flow field in the blade passages of a model Francis turbine.Combined with CFD numerical simulation technology,the complex flow patterns of the internal flow field were studied.The main works of this study are as follows:Firstly,the flow components of the model turbine were made partially transparent.And then,a PIV test stand was designed and constructed to test the flow field in the blade passages.Secondly,the software Visual C++ was used to write a program to process the images obtained from tests in batches.The flow lines and velocity vector diagrams in the runner were obtained to compare with the numerically simulated results of the interblade vortices.Thirdly,according to the design drawings of the turbine flow passage components,UG software was used to establish the water body model of the runner components,such as runner,volute,guide vane,and draft tube.With the use of IGG and Auto Grid5 modules in FINE/Turbo,the water model was structured and meshed separately.Fourthly,the Euranus module in FINE/Turb was used to perform a three-dimensional full-flow channel calculation of the model turbine.The pressure distribution diagram,velocity flow diagram,vorticity contour,etc.of the flow field in the turbine runner were obtained.Fifthly,by comparing the results of the numerical simulation with those from PIV test,the accuracy of the numerical calculation results was verified.The simulation can be used to predicate the distribution of interblade vortices that cannot be tested.