Measurement of the Dynamic Characteristics of a Large Sleeve Bearing

Abstract

The contribution of fluid lubricated bearings to the unstable whirl and “critical speeds” of any rotor system can be expressed in terms of certain linearized coefficients. The most important of these coefficients are those relating to vertical and horizontal translation of the journal relative to the bearing bush. Much work has been done on the theoretical derivation of these eight coefficients for hydrodynamically lubricated bearings, but there has been no published work on their direct experimental determination in the case of large turbo-type bearings. The paper describes the design and operation of a rig capable of measuring the dynamic oil film characteristics for bearings up to 28 in. dia running at speeds up to 4000 rpm. Coefficients measured on a 20-in.-dia bearing running in the laminar regime are compared with computed coefficients. Both theoretical and experimental coefficients are used to predict the dynamic characteristics of several large turbogenerator rotors running under test conditions on bearings of similar geometry. It is shown that predictions based on current theory considerably underestimate the stability and overestimate the stiffness of the test bearing.