Optimum Design In Spiral Case Rebuild Of Francis Turbine And Numerical Simulation

In the study of hyraulic machine characteristics computer-aided design tools become increasingly important to support the machine design and performance prediction.In particular,Computational Fluid Dynamics(CFD)are more and more used by hydraulic machine manufacturers.On one hand it is applied in order to save experimental resourses and shorten the period of exploitation for new productions,on the other hand it is able to show detailed flow features,which are not assessable by experimental tools,so the research is very significant in theory and economy.In the paper,the method is put forward to decrease the slit erosion in tail part of the spiral case by change the shap of the tail to improve it's life based on spiral case rebuild insread of replace it.In engineering ,cut the tail part which has eroded seriously,design a new tail part which has enlarged section,then the flow velocity is decreased.At first,three-dimentional modeling and meshing of the new designed spiral case and former one has been performed in the same way.Use CFD tools to compare the differance of the two spiral case in the same working condition.The new spiral case has more perfect characteristics than the old model,It decrease the velocity of the flow and the slit erosion.The orientation of optimum design for spiral case of francis turbine was shown. The main research work of this paper is as follows:(1) The flow characteristics in spiral case is complicated,the new spiral case and the old one do not conform to the formula V_u· r - K strictly, V_u·r of new spiral case is larger than the old one in the part Φ < 145°;(2) average V_u of the new designed spiral case is less than the old onesignificantly in tail part,the life of new spiral case is 120% longer than the old one ,the conclusion drawed from numerical simulation;(3) the floe angle of the new spiral case increase greatly than the old one in the part(p < 85° ,it should chang the shap of the stay vane of the new designed spiral case or the clash will be too strong to loss more energe than normal.