The Impact of Pad Elasticity on Frequency-Dependent Linear Dynamic Coefficients of Tilting-Pad Journal Bearings

Abstract

The frequency-dependent dynamic coefficients of tilting-pad bearings are significantly influenced by the pad pivot elasticity. In addition to the elasticity of the pivot, there is also the flexibility of the structure that predominantly leads to a bending of the pad. For the calculation of the dynamic coefficients, it is common to describe the structural stiffness by a support stiffness in series with the lubricant film. For this purpose, the stiffness according to Hertz's theory is widely used. This approach only allows the rigid body motion of the pad in the theoretical model. However, the elasticity of the pad leads to a film thickness characteristic, which cannot be represented with a pure rigid-body motion. Additionally, the structural elasticity already includes the stiffness of the contact between the pad and the support and, therefore, the elasticity according to Hertz cannot simply be added. This paper investigates the influence of dynamic pad deformation on dynamic bearing coefficients considering the contact boundary conditions, and examines whether it can be replaced by a suitable support stiffness. A 3D finite element model provides the eigenmodes for calculating the dynamic coefficients by perturbed Reynolds equations within a thermo-elasto-hydrodynamic (TEHD) bearing analysis. The model is validated with measurement data.