Nonlinear Dynamic Behaviors Of Circumferential Rod-fastening Rotor Bearing System

Heavy-duty gas turbines are the most cost-effective power generation equipment and are extremely important for the development of modern industry.For the purpose of light weight,convenient manufacturing,optimized design,etc.,the heavy-duty gas turbines mostly adopt the roulette type rod rotor structure: the rod bolts(center or circumferential arrangement)are used to press the discs to form the rotor.Unlike integral rotors,the presence of rough contact(plane contact or end tooth contact)between the disks results in a non-linear change in stiffness as the shaft is deformed,and this change is more pronounced in heavy-duty rotors.In addition,the non-linear oil film forces in the heavyduty gas turbines can cause dangerous nonlinear dynamic behaviors such as oil film whirl and even oil film oscillation.Under the joint action of two nonlinearities,the roulette rod rotor bearing system has more complex nonlinear dynamic characteristics.For this reason,this paper studies the circumferential rod rotor bearing system with plane contact between the discs.Aiming at the special structure of the circumferential tie rod rotor and the nonlinear stiffness introduced by the contact between the discs,this paper establishes the mechanical model of the circumferential tie rod according to the coordinate transformation and energy principle.The model presents the tie rod as an additional moment(when the pretightening force is uneven)And the additional stiffness matrix;combined with the Hertz contact model,GW rough surface contact theory,the fitting function between the normal,tangential contact stiffness and normal contact pressure of the contact micro-element on the rough contact interface is calculated;The influence of the bending moment between the discs on the contact state between the discs,and the contact between the two contact discs and the two is defined as the contact beam unit,using the obtained contact stiffness fitting function and finite element simulation,The relationship between the relative rotation angles of the contact beam elements and their stiffness matrices is calculated,and the rate-of-change fitting function of the contact beam element stiffness matrix is constructed.Γ(?),where the function variable Υ It is the ratio between the relative rotation angle of the contact lens unit end faces and the critical relative rotation angle of the contact separation.Thereby,the nonlinear stiffness caused by the contact between the wheels in the circumferential tie rod rotor is constructed.According to the analysis of the nonlinear dynamic characteristics of the circumferential tie rod rotor bearing system,a reasonable simplified model of the circumferential tie rod rotor is constructed based on the existing experimental research.The nonlinear oil film force is introduced according to the Capone circular bearing model,and the obtained wheel disc is used.The nonlinear stiffness of the contact is established by the Timoshenko beam element to establish the dynamic differential equation of the circumferential tie rod rotor bearing system.Under the condition of rigid support,nonlinear bearing support,and considering or not considering nonlinear stiffness,the fourth-order Runge-Kutta method is used to solve the numerical results,and the calculation results are analyzed and discussed.Aiming at the dangerous instability phenomenon of oil film whirl,this paper uses the quantification method of the non-autonomous nonlinear system motion stability to analyze the stability margin of the rotor unbalanced mass eccentricity distance and bearing clearance two system parameters,and The impact disturbance margin of the rotor system was analyzed.