A bubbly oil-lubricated squeeze film damper. Part 1: A finite-element model

Abstract

The non-linear vibration of a squeeze film damper (SFD) supported rotor assembly is closely linked to the presence of air bubbles in the lubricant, due to cavitation, where the discrete gas phase influences the squeeze film pressure profile and gives rise to a non-linear stiffness force. The aim of this paper is to assess the ability of a computational model for homogeneous bubbly oil to predict the influence of air bubbles on the film reaction forces under various operating parameters. The numerical model which considers the solubility of gas and the growth of gas bubbles was developed using the finite-element software, FEMLAB™. Parametric studies of eccentricity ratio, whirling frequency, and supply pressure were conducted to evaluate the influences of air bubbles on the pressure field and hence the squeeze film forces. Results show that an increase in eccentricity ratio and whirling frequency enhances the growth of air content in lubricant and hence increases the radial (stiffness) to tangential (damping) force ratio in an SFD, whereas an opposite effect is gained by applying higher supply pressure. Compared with the classical theoretical half-film model predictions, the bubbly oil model provides a more realistic estimation with respect to different damper operating conditions. From the simulation findings, it can be concluded that the homogeneous two-phase flow model reasonably describes the bubbly oil behaviour in SFDs and effectively shows the rise in stiffness force due to the growth of air bubbles. The homogeneous model can be easily applied to the well-established lubrication equation and solved with efficiency. However, any possible interfacial effects between the liquid and gas phases are inevitably concealed. The success of the current model allows its subsequent coupling with a structural rotor to form a multi-disciplinary model for unbalance analysis.