Multi Excitation Analysis And Dynamic Optimization Of High-Speed Herringbone Star Gearing System

In order to achieve a larger single-stage pressure ratio and improve combustion efficiency in turbofan engine,a herringbone star gear reducer is introduced between the low-pressure rotor and the fan,which increases the speed of the low-pressure compressor and the low-pressure turbine meanwhile reduces the speed of the fan,so that all parts can work at the optimal speed.Gearbox in GTF engine suffers from high input speed,high power density,and is affected by external non-inertial excitation generated by maneuvering flight and internal excitation caused by time-varying mesh stiffness,backlash and transmission error,thus the dynamic behavior of the gearbox is complex.Therefore,it is of great theoretical significance and engineering value to carry out the characterization of internal and external multi-source dynamic excitation of high-speed herringbone star gearing system and optimize its dynamic performance for realizing the lightweight and low vibration design and a smooth operation of gear system under multiple working conditions.Taking the high-speed herringbone star gearing system in GTF engine as the research object,this paper carries out the characterization of internal and external dynamic excitation,the dynamic modeling and analysis of gear system,the analysis of influences caused by multi working conditions and the optimization of system dynamic performance.The main research contents are as follows:(1)Simplify the components of gear system to mass points,the compound motion of the mass point in space is analyzed,and the expression of the absolute acceleration of the mass point in the local coordinate system is derived,which realizes the mathematical characterization of the external dynamic excitation;considering the factors of time-varying mesh stiffness,backlash and transmission error,the analytical expression of internal dynamic excitation is obtained.(2)Based on the lumped parameter method,considering the bending,torsional and axial movements of sun gear,planet,ring gear and carrier,the relative displacement in the direction of meshing line is analyzed,the dynamic model of gear system is built,and the dynamic differential equation of the system is established;then the dynamic equation is modified by introducing additional acceleration and gravity effect,and the dynamic behaviors of the system are solved when the foundation is in static state.(3)The key control parameters and the additional acceleration of the components under various maneuvering flight conditions are calculated,and the modified dynamic equations are constructed to solve the dynamic response of the system under multiple conditions.It is concluded that the components mainly deviate to the vertical axis of the aircraft when climbing and rolling,while the components mainly deviate to the horizontal axis of aircraft when yawing.Then two improvement measures are proposed and the improvement effect is evaluated.(4)Taking the mass and vibration acceleration of the system as the optimization objectives,the optimization mathematical model is established;the Latin hypercube sampling is used to establish a sample set,and the Kriging surrogate model is constructed to characterize the mapping relationship between the design variables and the objective function;the genetic algorithm is used to search the optimal parameters.The results after optimization have shown that the vibration acceleration of the system is reduced by 21.9%,and the overall mass is reduced by 18.4%,which means the optimization effect is satisfactory.