Structural Safety Analysis And Assessment Method Of High Bypass Ratio Turbo-fan Engine Due To Bird Ingestion

When high bypass ratio turbofan engine is operating,flying birds will be easily ingested,which will influence the structural safety of the engine.In this context,foreign countries paid much attention to the structural safety of aircraft engine due to bird ingestion and therefore formulated airworthiness regulations to standardize the requirements of minimum structural safety for engines due to bird ingestion and guidelines on the analyses,simulations,experiments and other research measures to achieve those structural safety requirements.However,domestic researches in this field are still at the initial stage,and lack effective analysis means and assessment methods.In this paper,the structural safety of high bypass ratio turbofan engine due to bird ingestion was taken as the research object.By researching engine bird ingestion airworthiness compliance system and process,load transmitting and distribution laws of engine’s typical bearing structure when the engine was ingesting a bird,dynamic response numerical analysis,safety analysis of key bearing parts in the whole engine,etc.,major findings were shown as below:(1)Based on the research background and significance of structural safety analysis and assessment of high bypass ratio turbofan engine’s bird ingestion,the development history of researches on the origin,formulation and modification of domestic and abroad bird ingestion airworthiness clauses and researches and application prospects of airworthiness compliance verification methods were deeply introduced.Then a detailed introduction of theoretical development and engineering technology of structural safety analysis of aircraft engines was carried out,which pointed out that domestic researches should pay more attention to the analysis,verification,design and related flow norms of airworthiness compliance and the technical development tendencies of organic combination of analysis,modeling,simulation,testing and other engineering technologies to support the verification of airworthiness compliance.(2)In accordance with the requirements,evidence collecting process and verification methods of aircraft engine bird ingestion airworthiness regulation,researching that existing valid aeronautical engine ingesting bird airworthiness regulation requires were dissected,and equipment,supporting conditions and related experiments to support the verification were introduced.Then the technical requirements and key technologies of the verification of engine bird ingestion airworthiness conformance were interpreted and abroad technical routes were concluded.Besides,internal logic relations among technical routes were systematically collated,and then a design process based on analyzing and verifying the conformance of high bypass ratio turbofan engine’s bird ingestion was put forward.It was indicated that a conformity analysis on the requirements of bird ingestion airworthiness regulation can be conducted by integrating inductive analysis,modeling and simulation and experimental verification.In addition,the design process should at least include four levels,which were respectively basic analysis verification,component level analysis and verification,module level analysis and verification and complete engine level analysis and verification.Moreover,related research work should form a closed-loop.Currently,the research focus should be module level analysis and verification,so that domestic research vacancy can be made up.(3)Taking the dynamic response of load-carrying structure of the engine when ingesting birds as the research object,simplification method of typical bearing structure of the engine was studied.On this basis,the experimental method of load transmitting of typical structure of an engine during bird ingestion was carried out under laboratory conditions.Bird ingestion simulation experiments were also conducted by simulating the fan under different ingestion speeds and rotating speeds.Furthermore,influencing laws of load transmitting and distribution of typical load-carrying structure of an engine during bird ingestion were explored.Research results showed that the built simulated fan rotor with simplified design existed two obvious load transmitting paths,in which,one transferred along the axis and support;the other transferred along the support plate and casing.The load transmitting sequence of the vibration in each characteristic position was the front drum bucket-front support plate/front casingback casing.The vibration intensity of each characteristic position had rather big relationship with the change of the initial impact energy,small relationship with the rotating speed change in being impacted.(4)Aiming at the dynamic response analysis of the bearing structure of the engine during bird ingestion,finite element modeling and numerical analysis of the dynamic response and load transmitting of the typical load-bearing structure of the engine during bird ingestion were carried out.The effects of equivalent stiffness changed of the front fulcrum of a fan on the dynamic response of bird ingestion structure were discussed.The results of the bird-suction experiment with a simulated fan rotor validate the effectiveness of the FEM modeling and analysis method.Research findings indicated that the experimental value well verified the validity of the finite element model and the accuracy of the analysis method;the influences of equivalent stiffness changed of the front fulcrum of the fan was quite obvious;The acceleration response amplitude of dynamic response had negative relationship with the equivalent stiffness.The vibration intensity and transmitting speed of each characteristic position had close relationship with the impact energy change,structural stiffness and non-linear factor change brought by the rotating speed and bird digestion speed change.A Synthetical Critical Response Parameters analysis method was developed to analyze and assess 12 groups of bird ingestion into test rig simulation cases,the most serious test status was estimated and the dynamic response of key components’ exchanging rules with rotating and ingestion speed were obtained.(5)By combining above experimental results,aiming at problems related to structural safety verification of high bypass ratio turbofan engine’s bird ingestion compliance,critical parameter analysis method of engine’s ingesting birds and damage characterization of fan blades were respectively analyzed.Models about dynamic response of critical components’ ingesting birds were built,verified,simulated and compared,thus creating a structural safety analysis process and systematically evaluate the structural safety of critical components’ ingesting birds.Research results showed that the maximum damage of fan blades which ingested birds was located near 70% of the blade height.When the whole engine ingested a big bird by 70% of the blade height,following unsafe consequents would be caused: The ingestion of a big bird leaded to deflection of blade tip and to mutual effects between blades and between blades and casing;impulse load resulted in sharp increase of stress level of three fulcrum bearing groups;at the same time,the stress levels of the casing,support plate,connecting rod,base and other components would also rise due to the transit of impulse load;although the bird was cut by the blades,the pieces still had great kinetic energy which would have a great impact energy damage on downstream runner pieces of the fan.