Research On Method Of Turbine Tip Clearance Prediction Considering Engine Performance Degradation

The tip clearance of an aeroengine generally refers to the radial clearance between the rotor blade and the casing of an axial flow engine.If the clearance is too small,the friction between the blade and the casing will occur,and the excessive clearance will increase the fuel consumption rate of the engine.Meanwhile,after long-term use,the inevitably performance degradation of the engine will also make the change of tip clearance more complex.Therefore,it is urgent to carry out further research on the prediction method of turbine tip clearance.Firstly,this paper analyses the influencing factors and prediction methods of tip clearance in engine design state,focusing on the deterioration factors and their influencing mechanism which mainly affect the change of tip clearance in the process of engine performance degradation during long-term use,and establishes a prediction model of tip clearance in view of engine degradation factors.On this basis,four steady-state design points and one transient process of an aero-engine are simulated by self-compiled code,and the influence of different degradation factors on turbine tip clearance scale is obtained.The results show that the deformations of casing,blade and disc increase gradually with the degradation of gas temperature in front of turbine,which affects tip clearance.Temperature has the greatest influence on the deformation of the wheel disc.Under the steady-state condition of high-temperature takeoff,the clearance change value reaches 0.1560 mm after6×10~3 cycles.Moreover,with the long-term use of the engine,the creep deformation of the turbine blade will occur,which will gradually reduce the tip clearance.Then,aiming at a high-pressure turbine with active clearance control,the change rule of clearance control strategy after considering engine degradation is further studied.It is found that after adopting active clearance control scheme,the clearance values of design state are reduced by 1.26 mm,0.06 mm,1.23 mm and 1.27 mm respectively under the conditions of ground idle speed,high temperature take-off,maximum cruise and ground test.Under transient conditions,the active clearance control scheme can effectively prevent the clearance value from being too large or too small,and make the clearance change curve more smooth.Finally,the source code of tip clearance prediction developed in this paper is encapsulated and integrated,and a simulation software for tip clearance prediction is developed,which can realize the whole process of tip clearance prediction from geometric modeling,meshing,boundary setting to temperature field analysis,deformation prediction and clearance prediction through graphical interface operation.