Research On Multi-Field Coupling Vibration And Optimization Design Of Blade-Disk System In An Aircraft Engine

Blade-disk structure is the key component in an aircraft engine,working condition is very complex.It is under the comprehensive effects of centrifugal force,aerodynamic pressure,vibration and thermal stress.Blade-disk failure is one of the most common faults in an aircraft engine.It is crucial to guarantee blade-disk system to operate well.Because of the higher requirement of working load,efficiency and reliability in aircraft engine operation,blade structure is made much thinner and lighter.This makes the effects of aerodynamic pressure and temperature load more obvious,and causes blade vibration problem more serious.Once blade-disk system fails in an aircraft engine,the accident would be serious,and even be disastrous.For improving the aerodynamic stability and structural strength of compressor blade-disk system,it is very essential to make comprehensive consideration about the couple effects of aerodynamic pressure,temperature load and blade-disk structure.In current design and research of aircraft engine,blade-disk model is widely adopted with a single physical field.It is respectively to analyze the characteristics of aerodynamics,heat transfer,structural strength and vibration.That is to say,discrete analysis is developed in the single subject.Through uninterrupted update and repeated design optimization,it meets the performance requirements of aircraft engine.However,the actual operation condition can't be accurately simulated with this method.Meanwhile,the research cycle is too long,and the cost is too high.With the rapid progress of modern aviation industry,higher performance is required on the aircraft operation.Original technology of aerospace power can't meet the design of modern aircraft engine.So the new design and analysis methods are urgently developed to solve the shortage and problem in aircraft engine design,in which the coupling effects of aerodynamics,heat transfer and structural strength are fully considered.In this research,a new approach is put forward that multi-field coupling dynamic characteristics and optimization design are developed based on Kriging interpolation method.Taking an aircraft engine blade-disk system as the research object,related contents are studied including blade-disk vibration,3D flow field characteristics,load transfer on coupling interface,multi-field coupling dynamics and optimization design.Specific contents and research results are as follows:1.Based on cyclic symmetric technology and group-theoretic algorithm,blade-disk motion equation is established,and vibration modes are solved.Then physical simulation is developed to analyze the resonance vibration of blade-disk structure.The effects of blade aspect ratio are discussed on blade-disk vibration.The results show vibration modes coincide quite well between group-theoretic algorithm and FEA software.The low order natural frequencies are far away from the corresponding excitation frequencies,resonance vibration wouldn't be able to occur on the blade-disk structure.With the increase of blade aspect ratio ?,bending vibration frequencies decrease gradually.But the effects are complex on blade distorted frequencies.2.Considering the influence of stator-rotor interaction,compressor flow field is simulated,and the process of stator-rotor interaction is analyzed.Then the distribution law of unsteady aerodynamic load is researched,the effects of aerodynamic load are investigated at different pressure ratios,rotational speeds and ratios of stator-rotor blade number.The results exhibit that unsteady flow field area with lower speed is induced by stator-rotor interaction at rotor blade leading edge.Dominant fluctuation frequencies of aerodynamic pressure are manly at frequency doubling of stator-rotor interaction.In the interaction period T,variations of aerodynamic load take the contrary trend on pressure and suction surfaces.3.According to the problem of load transfer,Kriging interpolation model is introduced in multi-field coupling analysis.Compared with RSM method,Kriging model has a higher precision in load transfer.For further guaranteeing load transfer precision of multi-field coupling interface,errors of Kriging model are checked with different variation functions.Then the programs are compiled to achieve the transfer of aerodynamic pressure,temperature load and strutural deormation.The results show that Kriging interpolation based on Gaussian model is the most accurate in load transfer of multi-field coupling.Transfer precision on pressure surface is much higher than the precision on suction surface.Load distributions of structure filed and flow field coincide quite well before and after interpolation,it can meet the requirement of multi-field coupling dynamics calculation.4.With the load transfer method of Kriging model,multi-field coupling dynamics model is established on compressor blade-disk structure.Coupling iterations are achieved between multiple physical fields.Then analysis software is integrated on multi-field coupling dynamics.Blade-disk vibration characteristics are discussed at different types of loads.The results indicate that centrifugal force is the main source of deformation and stress in the compressor blade-disk system.Bending stress induced by aerodynamic pressure and temperature load can counteract part of that induced by centrifugal force.Temperature load causes the natural frequencies of blade-disk system to decrease,and makes blade-disk structure to vibrate more easily.5.Combining the methods of static frequency test,dichotomy and finite element analysis,blade mistuned parameters are identified successfully.Based on the analysis of multi-field coupling dynamics,vibration characteristics of tuned blade-disk and mistuned blade-disk are respectively researched under the effect of aerodynamic load.The results show stiffness mistuning causes the displacement and strain energy of blade-disk sectors different obviously.By the effect of aerodynamic load,it makes tuned blade-disk vibrate more heavily,and the vibration nonuniformity of mistuned blade-disk is enhanced.The maximal displacement and stress are mainly at the frequencies of blade natural vibration.6.Application of multi-field coupling dynamics and optimization design theory,multidisciplinary optimization design is developed on compressor blade-disk structure.Blade profile design parameters and multidisciplinary optimization objectives are selected successfully.With the Isight software,Kriging approximation models are constructed based on Latin hypercube design.Then multi-island genetic algorithm is adopted to carry out the optimization design of blade-disk system.The results exhibit that established Kriging approximation models are in the high precision,it can meet the requirement of multidisciplinary optimization design.Through the iterative optimization,compressor isentropic efficiency,the highest temperature and the maximum stress and deformation are taken a certain improvement.