Research On Motion Stability Of Rotor System With Faults Considering Oil Film And Seal Effects

Oil-film instability, one of the frequently confronted faults in rotor-bearing systems, has the characteristics of abruptness and destructiveness. The instability would contribute to excessive vibration at lower frequency on the basis of synchronous vibration. This would accelerate the nonsynchronous response of the system, and cause significant alternating stresses in the rotor. Due to the large vibration caused by the oil-film instability, many other faults such as the rub-impact of rotor-to-stator could appear, which would influence directly the catastrophes control and reliability of the system. For some rotating machines such as turbine machine, the seal force would significantly increase by the change of steam parameters and seal clearances, which would increase the probability of the rub-impact between the rotor and sealing device. So, the research on the dynamic characteristics of bearings and seals in the rotor-bearing-seal system is of great importance for the more stable and efficient rotating machines.This paper mainly studies motion stability of a rotor-bearing-seal considering the effect of oil-film, seal force, rub-impact between the rotor and the stator, and pedestal looseness. Firstly, a lumped mass model of a rotor-bearing system with two discs considering the gyroscopic effect is established. And the effect of two loading conditions determined by API Standard 617 (Axial and Centrifugal Compressors and Expander-compressors for Petroleum, Chemical and Gas Industry Services, Seventh Edition) on the onset of oil-film instability and nonlinear responses of the rotor-bearing system is studied. Moreover, the model validity is also examined by a finite element model and experiments. At the same time, the universality of the laws is verified by a rotor-bearing system with a stepped shaft and two different discs to some extent. Then, based on the lumped mass model established previously, the effects of the eccentric phase difference, eccentricity, bearing clearance, lubricant viscosity, and slenderness ratio of the right bearing(LID) on the first/second mode instability are further studied.Secondly, based on the two discs lumped mass model established previously, a new lumped mass model of a rotor-bearing-seal system is established, in which the seal is considered. Effects of the seal force on the first and second mode instabilities are investigated under two different eccentric phase differences of two discs, and several seal parameters (seal pressure, seal length and seal clearance), respectively.Then, in view of the rub-impact between the journal and bearing may be caused by the oil-film instability, based on the lumped mass model of rotor-bearing-seal system established previously, effects of the rub-impact on the first and second mode instabilities are investigated under two different eccentric phase differences of two discs, the stiffness of stator, and misalignment between the journal and bearing, respectively.Finally, in view of the pedestal looseness fault may be caused by the excessive vibration, the researches on vibration characteristics of the system is carried out based on the lumped mass model established previously under two different eccentric phase differences of two discs. Then, effects of eccentricities of two discs, loose clearance and pedestal mass on looseness are analysed under two loading conditions.