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Research Papers: Gas Turbines: Structures and Dynamics

Squeeze Film Damper With a Mechanical End Seal: Experimental Force Coefficients Derived From Circular Centered Orbits

[+] Author and Article Information
Luis San Andrés, Adolfo Delgado

Mechanical Engineering Department, Texas A&M University, College Station, TX 77843

This condition requires sufficiently large loads to prevent stick-slip effects at the mechanical seal contact area.

Dynamic pressures in the discharge groove are not insignificant and contribute to the generation of an enhanced film inertia force coefficient. Figures  910 show measured pressures in the groove and film that evidence this effect.

The dynamic portions of the pressure signals are nearly identical, thus generating damping and inertia force coefficients of very similar magnitudes.

J. Eng. Gas Turbines Power 130(4), 042505 (Apr 29, 2008) (8 pages) doi:10.1115/1.2800345 History: Received May 10, 2007; Revised June 06, 2007; Published April 29, 2008

The paper presents parameter identification measurements conducted on a squeeze film damper (SFD) featuring a nonrotating mechanical seal that effectively eliminates lubricant side leakage. The SFD-seal arrangement generates dissipative forces due to viscous and dry-friction effects from the lubricant film and surfaces in contact, respectively. The test damper reproduces an aircraft application that must contain the lubricant for extended periods of time. The test damper journal is 2.54cm in length and 12.7cm in diameter, with a nominal clearance of 0.127mm. The damper feed end opens to a plenum filled with lubricant, and at its discharge grooved section, four orifice ports evacuate the lubricant. In earlier publications, single frequency force excitation tests were conducted, without and with lubricant in the squeeze film land, to determine the seal dry-friction force and viscous damping force coefficients. Presently, further measurements are conducted to identify the test system and SFD force coefficients using two sets of flow restrictor orifice sizes (2.8mm and 1.1mm in diameter). The flow restrictors regulate the discharge flow area and thus control the oil flow through the squeeze film. The experiments also include measurements of dynamic pressures at the squeeze film land and at the discharge groove. The magnitude of dynamic pressure in the squeeze film land is nearly identical for both sets of flow restrictors, and for small orbit radii, dynamic pressures in the discharge groove have peak values similar to those in the squeeze film land. The identified parameters include the test system damping and the individual contributions from the squeeze film, dry friction in the mechanical seal and structure remnant damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry-friction interaction at the mechanical seal interface. Squeeze film force coefficients, damping and added mass, are in agreement with simple predictive formulas for an uncavitated lubricant condition and are similar for both flow restrictor sizes. The SFD-mechanical seal arrangement effectively prevents air ingestion and entrapment and generates predicable force coefficients for the range of frequencies tested.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Test rig for dynamic force measurements and flow visualization in a sealed and SFD

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Figure 2

Cut view of SFD with mechanical seal and details of outlet flow restrictor and pressure sensor locations

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Figure 3

Schematic view of physical model representation for SFD and mechanical seal

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Figure 4

Equivalent viscous damping (dry friction+remnant) versus excitation frequency (dry SFD, end seal in place)

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Figure 5

Recorded load and ensuing displacement orbits for four amplitude load levels. Clearance circle noted (70Hz, lubricated SFD, CCO, 2.8mm diameter flow restrictor).

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Figure 6

Test system dynamic stiffness versus frequency. CCOs of amplitude D: 50μm (Ksx=853kN∕m, Ksy=885kN∕m; 2.8mm and 1.1mm flow restrictors). Solid lines represent analytical curve fits.

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Figure 7

Identified test system damping coefficients (Cs−yy) versus excitation frequency for increasing orbit amplitudes. (CCOs, lubricated SFD)

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Figure 8

Squeeze film damping coefficients (CSFDyy) versus excitation frequency for increasing orbit amplitudes (CCOs, lubricated SFD)

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Figure 9

Squeeze film damping coefficients (CSFDxx,CSFDyy) versus orbit amplitude (CCOs; flow restrictors: 1.1mm and 2.8mm in diameter)

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Figure 10

Dynamic pressure measurements at SFD land and discharge groove and film thickness. Frequency of 70Hz, 50μm orbit amplitude, supply pressure=0.31bar.

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Figure 11

Peak-peak dynamic pressures in SFD land and discharge groove. Tests at 0.31bar supply pressure and largest (50μm) orbit amplitude. 2.8mm and 1.1mm diameter flow restrictors.

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