MEASUREMENTS VERSUS PREDICTIONS FOR ROTORDYNAMIC CHARACTERISTICS OF A FLEXURE PIVOT-PAD TILTING PAD BEARING IN AN LBP CONDITION AT HIGHER UNIT LOADS

Dynamic and static performance data are presented for a 117 mm diameter flexure-pivot tilting pad bearing in a load-between-pad configuration for speeds between 6000 and 12000 rpm and unit loads between 1-2.2 MPa. The present work is a continuation of 2005 tests on the same bearing by Al-Ghasem and Childs with unit loads at 0-1 Mpa. The rotordynamic coefficients are measured via a test rig that uses hydraulic shakers to excite the bearing stator. A psuedo-random excitation method is used to measure the complex direct and cross-coupled dynamic stiffness coefficients over a broad frequency range. The real and imaginary parts of these coefficients are curve fitted to produce a constant-coefficient [K][C][M] bearing model. For the static load direction y, the direct added-mass coefficient M(yy) was needed to model the bearing' "frequency dependence". The direct unloaded mass coefficients M(xx) was generally near zero. The analytical model generally predicted the correct trends for the change in rotordynamic coefficients with increasing loads but did not predict the measured orthotropy between results in the loaded and unloaded directions.