Research On Multi-Point Vibration Characteristics And Fatigue Of Civil Aviation Engine High-Pressure Compressor Blade

High-pressure compressor is a typical system of multi-force field coupling,where the high-speed rotating blades suffer a complex load of centrifugal force,aerodynamic force,etc.The complex and alternating loads could lead the blades to abnormal vibrations,and the blades exceedingly tend to fatigue failure when working in such situation for a long term.Hence,the fatigue life prediction and damage assessment of the blades with unrestricted life should be run through the whole life cycle of blade design,manufacture and maintenance.In addition,in view of the maintenance and repair of blades in service,the accurate research findings of blade vibration analysis,life prediction and damage assessment can provide theoretical support for the blades replacement and maintenance,and then avoid the potential flight accidents.A reasonable and effective calculation model of the compressor blade is the basis of the numerical simulation,and is the premise of obtaining reliable results.Therefore,in this paper,digital modeling,multi-point vibration characteristics and fatigue damage of the blade under complex load are carried out based on experimental investigations and numerical simulation.Data denoising,smoothing and deblocking,as well as characteristic boundary extraction and fitting,were performed based on actual point cloud data of blade.A blade airfoil section line composed of multiple arcs was constructed by fitting based on the 3D point cloud data partitioning and constraint fitting algorithm presented for blade airfoil,realizing more accurate feature extraction of blade aerodynamic airfoil.A converse blade modeling method was proposed for joint fitting of multi-section line and segmented surface according to the features of blade aerodynamic airfoil,a digital model was built for compressor blades,and a 3D physical blade model was put forward in accordance with the requirements of research.Secondly,a numerical method and model was selected for simulation calculation.The blade structure and flow field model were discretized in the computational domain,and a finite-element discrete model was built for the blade structure,as well as a simulation model for the blade flow field.The actual working conditions and mechanics characteristic of blades were analyzed,and the conditions of simulation calculation were laid out for blade simulation model calculation and boundary parameter setting.A vibration modal test was conducted on the blade structure,and modeling was validated in accordance with the result of blade structure and flow field simulation calculation.Thirdly,based on the digital reverse modeling method,the blade calculation models with different precision were established.Moreover,considering the influence of complex load in multiple loading conditions,the effect of modeling precision on the simulation results of blade flow field and vibration characteristics was analyzed.A fluid-structure interaction dynamic model of compressor blade,which considers the complex coupling effect of the gas and blade was established to carry out response analysis.The Campbell diagram was then introduced to determine the critical conditions of the blade,and the blade dynamic stress distribution of these working speeds was calculated.Combined with the study on the stress distribution of the blade,further study on actual blade vibration response test was carried out to determine the cause of blade failure and the blade failure risk point,and to obtain the change rule of blade strain response at the failure risk point under different amplitude excitation.Finally,based on the fatigue test for titanium alloy specimen of the compressor blade,the application characteristics and scope of the S-N curve and the Chaboche model was firstly discussed,and then the calculation accuracy of the fatigue damage calculation for the compressor blade with these two models was analyzed.Comprehensive considering the structural characteristics,material properties and actual operating conditions of the compressor blades,a fatigue damage model was then established.According to the aero-engine typical operating speed,the complete working cycle was simplified to five typical cycle conditions.Furthermore,the process of programming load spectrum for fatigue analysis of the blade dangerous point was finished based on the calculation results of the stress distribution for the compressor blade.After analyzing the loading parameters of different cycle conditions in the load spectrum,the effects of different load factors(including below fatigue limit loading,load order,etc.)on the development of blade fatigue damage were studied.Eventually,the multistage loading fatigue life and damage behavior of the compressor blade were predicted considering the actual operating conditions.