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Research Papers: Other (Seals, Manufacturing)

A Model for Improved Prediction of Force Coefficients in Grooved Squeeze Film Dampers and Oil Seal Rings

[+] Author and Article Information
Adolfo Delgado1

Structural Mechanics and Dynamics Laboratory, GE Research Center, Niskayuna, NY 12309delgadoa@ge.com

Luis San Andrés

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843lsanandres@tamu.edu

In the following, the groove depth is noted with reference to the radial clearance c in the film land or smooth portion of a seal of SFD.

These equations do not include fluid convective terms since these are negligible for small amplitude centered motions. See Refs. 4,8 for a justification.

Equation 8 makes evident that fluid inertia effects are of importance for Reα>1.

At the edge of a groove-land region, no fluid inertia pressure drop or raise is accounted for. This oversimplification is reasonable for laminar flow conditions only.

The magnitude and phase of the dynamic pressure with respect to the film thickness provide the necessary information to define the inertial and viscous parts of the pressure field.

1

Work conducted as a Research Assistant while at Texas A&M University.

J. Tribol 132(3), 032202 (Jun 15, 2010) (12 pages) doi:10.1115/1.4001459 History: Received September 27, 2009; Revised March 14, 2010; Published June 15, 2010; Online June 15, 2010

Squeeze film damper (SFD) designs typically implement supply grooves to ensure adequate lubricant flow into the film lands. Oil seal rings, of land film clearance c, also incorporate short and shallow grooves (length30c,depth15c) to reduce cross-coupled stiffnesses, thus promoting dynamic stability without a penalty in increased leakage. However, extensive experimental results in the archival literature demonstrate that grooves do not reduce the force coefficients as much as theory predicts. A common assumption is that deep grooves do not influence a damper or oil seal ring forced response. However, unexpected large added mass coefficients, not adequately predicted, appear to be common in many tested SFD and oil seal configurations. In the case of oil seals, experiments demonstrate that circumferential grooves do reduce cross-coupled stiffnesses but to a lesser extent than predictions would otherwise indicate. A linear fluid inertia bulk-flow model for analysis of the forced response of SFDs and oil seal configurations with multiple grooves is advanced. A perturbation analysis for small amplitude journal motions about a centered position yields zeroth and first-order flow equations at each flow region (lands and grooves). At a groove region, a groove effective depth dη, differing from its actual physical value, is derived from qualitative observations of the laminar flow pattern through annular cavities. The boundary conditions at the inlet and exit planes depend on the actual seal or SFD configuration. Integration of the resulting first-order pressure fields on the journal surface yields the force coefficients (stiffness, damping, and inertia). Current model predictions are in excellent agreement with published test force coefficients for a grooved SFD and a grooved oil seal. The results confirm that large added mass coefficients arise from the flow interactions between the feed/discharge grooves and film lands in the test elements. Furthermore, the predictions, benchmarking experimental data, corroborate that short length inner-land grooves in an oil seal do not isolate the pressure fields of adjacent film lands and hence contribute greatly to the forced response of the mechanical element.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

SFD grooved configuration: (a) SFD with central feed groove and (b) SFD with end grooves and seals (1)

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Figure 2

Typical oil seal multiring assembly

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Figure 3

(a) Schematic view of streamlines in axially symmetric grooved annular cavity (ΔP=Ps−Pd). (b) CFD results of pressure driven streamlines across a 10c and 15c circumferential inner-land groove in a test oil seal in Ref. 37, (c=86 μm, ω=7000 RPM, D=117 mm).

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Figure 4

Schematic view of test SFD in Ref. 31. and close-up of CFD results of pressure driven streamlines in inlet groove (ΔP=Ps−Pd), (c=127 μm, D=127 mm).

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Figure 5

CFD results of pressure driven velocity vector field across 10c and 15c circumferential inner-land grooves in a test oil seal in Ref. 37, (c=86 μm, ω=7000 RPM, D=117 mm). The broken lines show null velocity.

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Figure 6

Schematic view of grooved annular cavity divided into flow regions

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Figure 7

View of rotating and whirling journal and coordinate system

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Figure 10

Direct damping (CXX) and added mass (MXX) coefficients versus inner-land groove depth to clearance ratio (dηIII/c). The solid lines represent predictions for two central inlet groove effective depths dηI=6c, 11c. The dotted lines enclose the range of experimental values from Ref. 37 for seals with inner-land groove depths dIII=0, 15c.

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Figure 11

Oil seal cross-coupled stiffness (KXY) coefficients versus journal speed. The solid lines represent predictions for smooth seal and an inner-land groove effective depth dηIII=0, 6c. The dotted lines represent test values from Ref. 37 for a smooth land seal and a inner-land grooved seal (dηIII=15c).

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Figure 12

Cut view of test squeeze film damper geometry and model squeeze film flow regions (not to scale) (31)

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Figure 13

Predicted SFD damping (CXX) and added mass (MXX) versus inlet groove depth to clearance ratio (dηI/c). The solid lines represent predictions for a discharge groove of depth dηIII=17c. The dotted lines represent range of experimental values in Ref. 31.

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Figure 14

Schematic view of a simple open ends SFD and boundary conditions

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Figure 15

Schematic view of two film lands separated by a central groove

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Figure 9

Predicted direct damping (CXX) and added mass (MXX) coefficients versus the central inlet groove depth to clearance ratio (dηI/c). The solid lines represent the predictions for three inner-land groove effective depths dηIII=0, 5c, 15c. The dotted lines enclose the range of experimental values from Ref. 37 for two seal clearances with inner-land groove depths dIII=0, 15c.

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Figure 8

Test grooved oil seal configuration (37) and flow regions for analysis

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