The Experimental Determination of Bearings Dynamic Coefficients in a Wide Range of Rotational Speeds, Taking into Account the Resonance and Hydrodynamic Instability

Abstract

Methods for the experimental determination of dynamic coefficients are commonly used for the analysis of various types of bearings, including hydrodynamic, aerodynamic and foil bearings. There are currently several algorithms that allow estimating bearing dynamic coefficients. Such algorithms usually use various excitation techniques applied to rotor–bearings systems. So far only a small number of scientific publications show how calculated dynamic coefficients of bearings change as speed rises. In the literature, there are no computation results that demonstrate changes in these coefficients either in a broad range of speeds (that would cover resonant speeds) or at speeds at which a phenomenon of hydrodynamic instability can be observed. This article fills the literature gap in question. For calculation purposes, the impulse response method based on an in-house algorithm (with a linear approximation using the least squares method) was applied. On its basis, the stiffness, damping and mass coefficients of a rotor–bearings system were calculated. It turns out that some of the obtained values of damping coefficients are negative at the resonant speed. Moreover, if the values are calculated at a speed at which the hydrodynamic instability phenomenon is present they are accompanied by considerably higher standard deviations. On the basis of our computation results and the literature review, capabilities and limitations of the method used for the experimental identification of dynamic coefficients of hydrodynamic bearings were discussed.