Dynamic analysis of arbitrary profile liquid annular seals and transient analysis with large eccentric motion

Abstract

One of the main objectives of this work is to develop a new dynamic analysis for liquid annular seals with arbitrary profile and analyze a general distorted interstage seal of the Space Shuttle Main Engine High Pressure Oxygen Turbopump (SSME-ATD-HPOTP). The dynamic analysis developed is based on a method originally proposed by Nelson and Nguyen (1988a, 1988b). The original method used an approximation scheme based on Fast Fourier Transforms (FFT) to compute the circumferential gradients of the zeroth order variables of the eccentric solution. A simpler scheme based on cubic splines is found to be computationally more efficient and has better convergence properties at higher eccentricities than the original method. The first order solution of the original analysis is modified by including a more exact solution that takes into account the variation of perturbed variables along the circumference and a new set of equations for dynamic analysis are derived. A unified solution procedure that is valid for both Moody's and Hirs' models is presented. Dynamic analysis based on the above improved method is developed for three different models; a) constant properties, b) variable properties, c) thermal effects (energy equation) with variable properties. Arbitrarily varying seal profiles in both axial and circumferential directions are considered. An example case of an elliptical seal with varying degrees of axial curvature is analyzed in detail. A case study based on predicted clearances (6 axial planes with 68 clearances/ plane) of an interstage seal of the SSME-ATD-HPOTP is presented. Dynamic coefficients based on external specified load are introduced for seals to analyze seals that support a pre-load. The other main objective of this work is to study the effect of large rotor displacements on the dynamics of an annular seal and the resulting transient motion. The linearized force-motion model typically used to estimate the seal forces during a transient motion is not accurate for large off-center operation of the seal. One of the objectives of this study is to identify the magnitude of these deviations and establish limits of effectiveness of using such a model...