CFD based rotordynamic coefficients for labyrinth seals and impeller leakage paths

Abstract

The objective of this thesis is to explore the possibilities of Computational Fluid Dynamics to predict rotordynaniic coefficients for complicated geometries and high speed flows. Circulating flows, common in labyrinth seals, can not be predicted accurately using simple flow model like bulk flow. CFD approach is employed since it can accurately predict and capture recirculating zones using proper mesh distribution. The Impeller Leakage paths and Labyrinth Seals, typically, have a recirculation zone which affect the flow parameters like velocities and pressure. The forces exerted on the rotor and stator surfaces depend on the pressure drops across the seals as well as the RPM of the rotor. These forces are computed using the basic flow parameters like pressure and velocity distribution at the rotor and stator walls of the model. The rotordynamic coefficient prediction are done by inducing different whirl frequencies in the model. Instead of an infinitesimal eccentricity ratio used in Bulk Flow analysis, a finite eccentricity ratio (typically 101/c) is used. Perturbation methods and circular whirl orbit methods are used to predict the rotordynaniic coefficients for different cases. The circular whirl orbit method was used to predict the coefficients in complex geometries. Thermo-hydrodynamic analysis was (lone to examine the performance of the CFD analysis when subjected to heat transfer and fluid flows.