Geometric Effects in Tilting-Pad Dynamic Coefficients and Critical Speeds of a Rotor

Due to unavoidable manufacturing tolerances in production lines, the dynamic behavior of systems namely their natural frequencies may changes from one sample to another. In rotating machinery the vibration amplitudes and their associated critical speeds are seriously affected by these manufacturing uncertainties. In rotating structures tilting pad bearings have important role in vibration characteristics and stability of system. Manufacturing tolerances and clearances of tilting pad bearings play an important role in determining their stiffness and damping. In this paper an industrial case study is presented that considers the effects of bearing clearances in dynamic behavior of an industrial centrifugal compressor. The study first calculates the effect of the 5 pad tilting pad bearing clearance tolerances on its stiffness and damping coefficients and then investigates the changes in the bearing dynamic coefficients on a centrifugal compressor critical speeds and responses. The results show that with the change of bearing clearances within the tolerances bound, considerable change in compressor first critical speed is observed.