Analysis Of Bistable Characteristics Of A Biased Disk Rotor With Squeeze Film Damper

Squeeze Film Damper(SFD)is a damping mechanism which commonly used in the rotor system of aero-engine,however,rotor system will has a sudden change in amplitude due to the failure of damper.In this paper,the principle of bistable response,sealing structure medium parameters and structural parameters of Squeeze Film Damper on bistable response were analyzed,in order to provide reference for the application of Squeeze Film Damper,and improve the engine's reliability and safety.The characteristics of structure,motion and force of single-disc symmetrical rotor and offset rotor were analyzed.The nonlinear characteristic mechanism of the oil film force of the squeeze film damper was analyzed from the angle of the journal's motion.Under the condition of semi-oil and short bearing,based on Reynolds equation,squeeze film damper-single disc spanning rotor system's disk and journal's dynamic equation of motion were derived and established;under the condition of steady-state circular motion,the dynamic equations were numerically solved,combined with the damper motional feature,the principle of bistable for rotor system was explained:Nonlinear oil damping and nonlinear oil stiffness make the damper failure and exhibit hard spring characteristics,this feature will make the critical speed of the rotor system to increase slowly with the increase of vibration;and the vibration level rises slowly,so the non-concentric motion of the oil film journal will become more and more intense;the intense non-concentric motion makes the oil film generate a negative pressure environment to separate out air,besides,the damper will inhale external air due to the pressure difference.It will create cavitation in the oil film and finally cause a decrease in the circumferential distribution of the damper's oil film.When the circumferential distribution of the damper's oil film reaches to a minimized situation,the oil film stiffness and oil film damper are greatly reduced from the initial state.These features will reduce the critical speed of the rotor to current operating speed.At this time,rotor system passes critical speed,the vibration's level drops instantaneously and a sudden change in amplitude occurs.Optimizing the squeezing oil film damper-single-span mid-bias rotor system,taking into account the damper seal structure,based on the Muszynska seal model,under the condition of semi-oil film and short bearing,the dynamic equation of motion of the squeezed oil film damper-single-span mid-bias rotor system with the action of sealing fluid excitation force was deduced and established,the numerical solution of the dynamic equation of motion was calculated.The influence of the structural media parameters of the Muszynska seal model on the bistable response of the rotor system was analyzed.The analysis results showed that when the sealing radius gap?_s changes within a large range,the bistable response range of the rotor system changes by no more than 0.5%;when the sealing length l,the sealing radius R_f and the sealing pressure drop?P vary within a large range,The variation of the bistable response range of the rotor system exceeds 5%.Taking the concentric squeeze film damper as the researching object,based on the typical 0-2-1 low pressure rotor test bench of engine,the finite rotor system's element model with squeeze film damper was established,and the finite element model was calculated.The effects of oil film length L,oil film radius R,oil film radius gap C,oil film viscosity?,oil supply pressure p,rotor system acceleration rate?(5)and unbalance amount U on the bistable response of the rotor system were analyzed.The simulation results show that the bistable response of the rotor system increases with the increase of the unbalance U.The oil supply pressure p is a non-sensitive parameter to the bistable response of the rotor system;Lubricating oil viscosity?,oil film length L,oil film radius R and acceleration rate?(5)are sensitive parameters to the bistable response of the rotor system.The bistable response interval of the rotor system decreases with the increase of the above parameters until it completely disappears;However,when the oil film viscosity?,the oil film length L and the oil film radius R are excessively large,the rotor system is more and more disordered.The bistable response interval of the rotor system increases with the increase of the oil film radius gap C,and the rotor system will be oscillated.