Theory versus experiment of the rotordynamic and leakage characteristics of smooth annular bushing oil seals

摘要

This thesis provides a comparison of experimental rotordynamic coefficients forlaminar, smooth bushing oil seals to theoretical predictions from XLLubeGT andXLAnSeal. The experimental results come from a new test rig developed at theTurbomachinery Laboratory at Texas A&M University. The two software programswere developed to predict the static and dynamic characteristics of seals. XLLubeGT isa Reynolds equation based program while XLAnSeal is based on a bulk-flow Navier-Stokes model that includes temporal and convective acceleration terms. XLAnSeal wasused to predict the added-mass terms of the seals since XLLubeGT assumes those termsto be zero or negligible. The data used for input into the two seals code was the actualmeasured conditions from the test rig. As part of the input parameters, inlet inertiaeffects and thermal gradients along the seal were included. Both XLLubeGT andXLAnSeal have the capability to analyze straight bore seals with different inlet andoutlet clearances ? essentially a tapered seal ? but seal expansion caused by the radialdifferential pressure across the seal bushing was not included.Theoretical and experimentally determined dynamic characteristics includestiffness, damping, inertia terms and Whirl Frequency Ratio (WFR). Seal staticcharacteristics are also reported. They include: leakage, shaft center line loci andReynolds numbers. Test conditions include three shaft speeds: 4000, 7000 and 10,000rpm, three test pressures: 21, 45 and 69 bar [300, 650, and 1000 psi] and multipleeccentricities from 0.0 to 0.7. The results for the dynamic characteristics show goodcorrelation of the experimental data to the theoretical values up to an eccentricity ofabout 0.5. At higher eccentricities, the theory generally under-predicts the dynamiccharacteristics. Inertia terms are greatly under-predicted. The results for the staticcharacteristics also show good correlation to the experimental data, but they also have atendency to be under-predicted at higher eccentricities.