Rotordynamic coefficients for a load-between-pad, flexible-pivot tilting pad bearing at high loads

摘要

The dynamic and static performance of a flexure-pivot tilting pad bearing is presented ata load between pad configuration for various load and speed combinations. A similarwork performed on the same bearing at lower loads ranging from 0-1 MPa (0-150 psi) byAl-Ghasem was tested, whereas the current work investigates effects in the load rangebetween 1-2.2 MPa (150-320 psi). The bearing design parameters include: 4 pads withpad arc angle 72???? and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radialclearance 0.254 mm (0.010 in), bearing radial clearance 190.5 ????m (0.0075 in), preload0.25, and shaft nominal diameter of 0.11684 m (4.600 in). An important distinctionbetween the two sets of tests is the difference in experimental bearing radial clearance,which for this case measured 208 ????m (0.00082 in), and for Al-Ghasem??????s was 165.1 ????m(0.0065 in). The rotordynamic coefficients are determined experimentally using a test rigequipped with motion and load sensors. The rig is modeled using Newton??????s laws, whichis converted from the time to frequency domain using Fourier Transform to give complexdynamic stiffnesses. From the resulting complex dynamic stiffnesses the associated realand imaginary components are plotted as a function of excitation frequency and curvefitted via linear regression to give the rotordynamic coefficients. The primary objectiveswere to determine whether the real component of the complex dynamic stiffnesses couldbe better modeled with or without the mass coefficient and to contrast the rotordynamiccoefficients with an analytical model. Only in the load range of 1 to 2.2 MPa were theunloaded direct mass coefficients near or at 0, which would allow for a [K][C] model tobe used. The remaining real components are better represented with the mass term. Theanalytical model generally overpredicted the stiffness, damping and mass coefficients,especially for the direct components; the trends were generally consistent.