A novel test rig for the dynamic characterization of large size tilting pad journal bearings

P Forte,D Saba,E Ciulli

doi:10.1088/1742-6596/744/1/012159

Abstract

The present work concerns the realization of a test bench for the dynamic characterization of high performance tilting pad journal bearings, within a collaboration between the Department of Civil and Industrial Engineering of Pisa, GE Oil&Gas and AM Testing. The objective is to cover journal diameters of interest of GE, from 150 to 300 mm, with peripheral speeds up to 150 m/s, static load up to 270 kN, dynamic loads up to 30 kN and frequencies up to 350 Hz, performances that make the apparatus very competitive worldwide. The adopted configuration has the test article (TA) floating at the mid-span of a rotor supported by two rolling bearings. The TA is statically loaded by a hydraulic actuator and excited dynamically by two orthogonal hydraulic actuators. Construction was recently concluded and preliminary tests are under way. In order to assess in advance the possible accuracy of the tests, a dynamic lumped parameter model of the test bench was developed to perform virtual experiments, including several possible sources of experimental errors and uncertainties. The model was implemented using reduced stiffness and mass matrices obtained from Finite Element Analysis by Component Modal Synthesis.

Highlights

Tilting pad journal bearings (TPJB) are commonly used in turbomachinery for their characteristics of stability at high rotational speeds
According to the classical analytical approach [1] the dynamic behavior of a journal tilting pad bearing is determined by n+2 degrees of freedom, namely the two degrees of freedom that describe the motion of the journal center in the transverse plane and the rotations of the n pads
The assumption of synchronous pad rotation brings to a formulation of the dynamic equilibrium dependent only on the rotor degrees of freedom and to reduced matrices of the dynamic coefficients, 2x2, with the main diagonal composed of direct coefficients and the secondary diagonal of cross-coupled coefficients

Summary

Introduction

Tilting pad journal bearings (TPJB) are commonly used in turbomachinery for their characteristics of stability at high rotational speeds. The bearing is loaded statically and it is dynamically excited by two independent actuators in two orthogonal directions. Even in this case hydraulic actuators were selected because, while presenting significant limitations in performance as frequency increases, they allow to reach high values of load with acceptable size and mass.

Results

Conclusion