Seal inlet disturbance boundary conditions for rotordynamic models and influence of some off-design conditions on labyrinth rotordynamic instability

摘要

Systematic parametric studies were performed to better understand seal-inlet rotordynamics.A CFD-perturbation model was employed to compute the seal-inlet flowdisturbance quantities. Seal inlet disturbance boundary condition correlations wereproposed from the computed seal-inlet quantities using the important parameters. Itwas found that the cosine component of the seal-inlet swirl velocity disturbance W1Chas a substantial impact on the cross-coupled stiffness, and that the correlations forW1C and W1S should be used to replace the historical guess that seal inlet W1C = 0and W1S = 0. Also, an extremely precise relationship was found between the swirldisturbance W1C and the seal-inlet swirl velocity (????Rsh ?????? ????W0). Thus, the numberof experiments or computer runs needed to determine the effect of spin speed, shaftradius and/or inlet swirl velocity on the cross-coupled stiffness is greatly reduced byplotting the simplified relationship of the cross-coupled stiffness against the swirl slipvelocity. The benefits of using the new seal-inlet boundary condition correlationswere assessed by implementing them into a CFD-perturbation model. Consistentlyimproved agreement with measurements was obtained for both liquid annular sealsand gas labyrinth seals.Further, the well-established CFD-perturbation model with new boundary conditioncorrelations was employed to investigate the rotordynamics of two off-design situations. The first case considered the influence of labyrinth seal teeth damage onthe performance and the rotordynamic characteristics of impeller eye seals in centrifugalcompressors. The second case considered the influence of rotor-axial-shifting onrotordynamic forces for high-low labyrinth seals in steam turbines during the start-upand shut-down process. The results should provide useful information for labyrinthseal design and fault diagnosis of stability problems in turbines and compressors.