GENERALIZED ANALYSIS OF HYDRODYNAMIC GROOVED BEARING AND SEAL CONFIGURATIONS

Abstract

The grooved surfaces, which are now-a-days finding increasing application in hydrodynamic bearings and seals in high speed rotating machines, offer considerable flexibility in controlling their performance character-istics. Suitably designed grooves and wedges on the surface of a plain hydrodynamic sleeve can be used to modify its performance characteristics depending on its use either as bearings or as seals. The finite element method has been considered as a very suitable technique for solving the equations governing the flow-field in the clearance space of the bearings and seals having complex geometries in the form of steps, wedges, grooves etc. The studies on the performance characteristics of the grooved configurations in bearings and seals have been presented in three different sections - one for the grooved bearings and the other two for the seals. The study is oriented twoards the evaluations and critical interpretations of the static and dynamic perfor-mance characteristics of the grooved bearings and seals. In general, the journal-bearing or shaft-seal axes are skewed. Hence, in the analysis, the degrees of freedom associated with skew displacements have also been consi-dered. The static performance characteristics have been investigated in terms of fluid film load capacity and moment, attitude angle, and leakage, friction coefficient parameter and temperature rise parameter. For the studies on the dynathic characteristics, the fluid film stiffness and the damping coefficients have been evaluated for diff-erent grooved configurations. The linearized and the nonlinear equations of disturbed motion of the journal or of the seal have been derived for the general case which includes four degrees of freedom. The stability margins for the linearized systems, in terms of critical nondimensianal mass and critical nondimensional mass moment of inertia of the journal or the seal have been obtained using Routh criteria. The stability studies have. also been made in terms of motion trajectories, obtained by numerically integrating the linearized and nonlinear equations of motion, by the Runge Kutta method•