FLEXIBILITY EFFECTS IN TILTING PAD JOURNAL BEARINGS WITH RADIAL OIL INJECTION

摘要

This paper gives a theoretical contribution to the combined fields of fluid-structure interaction and vibration control. The static and dynamic properties of tilting-pad journal bearings with controllable radial oil injection are investigated. The tilting-pads are modelled as flexible structures and their dynamics are described using a three dimensional finite element framework and linear elasticity. The oil film pressure and flow are considered to follow the modified Reynolds equation. The Reynolds equation is solved using a two dimensional finite element mesh. The rotor is considered to be rigid. In order to attain one common set of state variables, the Reynolds equation is linearised with respect to displacements and velocities of the nodal degrees of freedom. When all nodal points satisfy the static equilibrium condition, the system of equations is dynamically perturbed and subsequently condensed to a 2 by 2 system, keeping only the lateral motion of the rotor. The dependencies of the stiffness and damping (condensed) coefficients on the excitation frequency, pad flexibility and injection pressure are carefully investigated. Such coefficients are of fundamental importance when predicting fluid-structure interaction, i.e. rotor-bearing stability. The controllable radial oil injection and pad flexibility can strongly influence such stability properties as it is shown in the paper.