Research On The Dynamic Characteristics Of A Rotating Blade With Dovetail Joint Based On The Finite Element Theory

The blade is one of the main components of the aero-engine which is the power device in the aerospace field.The quality and structure design of the blade are directly related to the reliability and service life of the aero-engine because the working environment of the blade is extremely bad.In the working state,the blade not only bears its own centrifugal load,but also bears complex mechanical load.Under these complex external loads,the blade will produce severe vibration which will cause high cycle fatigue damage and fracture failure.This will bring incalculable economic losses,and even lead to major casualties.Therefore,it is necessary to study the vibration characteristics of the rotating blade with dovetail feature.Firstly,the detailed derivation of the element stiffness matrix and the mass matrix of the beam element considering shear deformation is introduced based on the elasticity and finite element method.Meanwhile,the elastic constraint model of the blade is established,and the modal analysis of the blade under the fixed constraint and free-state is carried out.The results are compared with that of the analytical method and the finite element software simulation respectively,which verifies the feasibility of the method adopted in this paper.On this basis,the influence of boundary support stiffness on the natural frequency and the mode shape is analyzed.Secondly,the dynamic model of the rotating blade was established based on the finite element plane beam element theory,and the dry friction model was established to simulate the constraint state of blade according to the contact characteristics of dovetail joint.The numerical integration method was used to calculate the dynamic response characteristics.The effects of the rotating speed,the friction coefficient and the excitation amplitude on the response characteristics of rotating blades were studied.Then,the mechanism of dry friction vibration reduction of the space rotating blade was studied.And the mechanism of vibration reduction was revealed from the angle of dry friction energy consumption ratio.Finally,on the basis of previous research,the contact structure between blades was improved.A contact platform was designed at the position where is close to the bladeroot.The inclined surface of the platform contacts with a rigid convex surface on the disk.Based on this new type of friction contact structure,a three-dimensional friction contact model was introduced into the contact surface,so that it can more accurately represent the contact state between the contact surfaces.The influence of the slope angle and initial preload on the vibration reduction effect of the blade was analyzed.