Effects of the Feedline and the Hydrostatic Pocket Depth on the Flow Pattern and Pressure Distribution

Abstract

The paper treats on a comparative basis the development of the flow and pressure maps in deep, and respectively, shallow hydrostatic bearing pockets. The numerical simulation uses a dimensionless formulation of the Navier-Stokes equations written for a body fitted coordinates system, and applied through a collocated grid. The present work is a continuation of the simulations performed by Braun et al. (1993, 1994a, 1994b) to cases where the length and diameter of the restrictor feedline is of consequence to the flow in both the shallow and the deep pocket. The model includes the coupling between the pocket flow and a finite length feedline flow, on one hand, and the pocket and the adjacent lands on the other hand. Geometrically, all pockets have the same projected footprint, lands length, and capillary feedline. This numerical study uses the Reynolds number Re based on the runner velocity (laminar range only), and the inlet jet strength F as the dynamic similarity parameters, while the dimensionless clearance C is used as a geometric parameter. The flow structures, and the physical reasons underlying the causes of the pressure variation inside the deep and shallow pockets [either longitudinally (radially) or transversally (circum-ferentially)], are discussed quantitatively and comparatively. It is further shown that the transversal pressure distributions under the runner are highly dependent on whether the flow is dominated by the rotation of the runner (hydrodynamic effects), or by the strength of the hydrostatic jet (F). Finally the longitudinal pressure curves in the depth of the pocket, and restrictor are presented and the nature of their variation discussed. The back step and Rayleigh step effects are also discussed on a comparative basis for the two types of pockets, and in conjunction with the Couette, and the jet dominated flow. The modification of the central vortical zones of the deep pockets into oblong vortical zones for the shallow pockets is presented, and its consequences are discussed.

Comparative Experimental and Numerical Analysis of Flow and Pressure Fields Inside Deep and Shallow Pockets for a Hydrostatic Bearing

“…Helene et al (21), in their two-dimensional studies of hydrodynamic journal bearing (HJB) pockets, reported similar results, but the open HJB literature does not contain much more information regarding these unusual profiles. Rather, one finds a very homogeneous set of reports whereby the pressure profile is either constant or ramped and contains a small peak at the point of jet impact on the shaft (Braun and Dzodzo (18), (24); San Andrés and Velthuis (26); Chaomleffel and Nicolas (27); Bou-Said and Chaomleffel (28) and others). To further verify and confirm the present results, a parametric numerical simulation using viscosity and clearance as the leading parameters has been performed.…”

Translating circular thrust bearings

“…The linear pressure variation in the recess is due to the translation or Couette flow effect and the contrast between Couette-dominated and injection-dominated flow has been discussed for the two-dimensional case on several occasions (e.g. Braun & Dzodzo, 1995). In practice, it is more common to prescribe the injection pressure and not the injection flow rate.…”

“…A good place to start is the Navier-Stokes simulation conducted by Braun & Dzodzo (1995) for a two-dimensional journal bearing. Their study presents detailed results for the pressure distribution and streamlines in the two basic flow regimes: a flow dominated by the Couette effects and a case dominated by the flow due to lubricant injection.…”

Validity of the modified Reynolds equation for incompressible active lubrication

“…Some good examples can be found in literature. [10][11][12][13][14] Normally, the injection (hydrostatic) pressure is treated by the cited authors as constant and the effect of deep and shallow pockets geometries on the pressure and flow profiles are investigated. In the present work, the injection pressure is treated as constant as well as time dependent, in order to simulate different schemes of application of the active lubrication concept.…”