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

The analysis of oil seals is of great concern for the proper design of high pressure centrifugal compressors, because they can have significant influence on the dynamic stability of the compressor rotor. The lack of adequate analytical tools highlight the need for this type of study. An analytical tool to evaluate the oil seal characteristics, perform linear stability analysis of the compressor rotor and nonlinear transient analysis of the compressor rotor and the seal ring has been developed. An iterative finite element method is used to solve the non-linear and coupled hydrodynamic and thermal equations for the pressure and temperature distributions in oil seals. The perturbation technique is employed to determine the static and dynamic characteristics of oil seals. The hydrodynamic forces are calculated by integrating the pressure distribution along and around the oil seal. Eigenvalue analysis is performed to do the linear stability analysis of the compressor rotor. A numerical integration technique is used to solve the non-linear equations of motion of the seal ring and compressor rotor. This analysis has the ability to handle tapered seals, circumferentially grooved seals and seals with shaft misalignment. Results obtained from linear stability analysis and non-linear transient analysis for different seal geometries, including shaft misalignment, are presented. For centered seals, results obtained are in good agreement with a previous finite difference analysis. At an operating eccentricity of 0.098, the maximum percentage differences in the cross-coupled stiffness and direct damping coefficients obtained from this analysis and the finite difference analysis are 5.1 % and 1.5 % respectively. For eccentric seals, use of the true temperature distribution gives significantly different results. At an operating eccentricity of 0.497, the maximum percentage differences in the cross-coupled stiffness and direct damping coefficients obtained from this analysis and the finite difference analysis are 17.7 % and 22.9 % respectively. This analysis shows that the sharp edge grooves decrease the axial flow rate. In addition, groove depth typically applied to industrial seals is shown to be effective in breaking up the hydrodynamic pressures. Tapered and circumstantially grooved seals are shown to enhance both the locking mechanism in the seal ring and the dynamic stability of the compressor rotor. The resulting computer program gives the designer of compressors with liquid seals a much needed capability that is not available from any other known source. / Ph. D.