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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal—Part I: Unidirectional Load Tests

[+] Author and Article Information
Luis San Andrés

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

Adolfo Delgado

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

This deficiency does not just occur in SGDs but also in liquid annular seals and hydrostatic bearings as the extensive literature attests.

Loads of lower magnitude could not induce motion in the test system. Sometimes for the lowest load, stick-slip occurred over certain frequency ranges, see Ref. 13 for details.

J. Eng. Gas Turbines Power 129(3), 858-864 (Jul 25, 2006) (7 pages) doi:10.1115/1.2436571 History: Received July 18, 2006; Revised July 25, 2006

Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus not generating enough damping capability. Single frequency, unidirectional load tests were conducted on a SFD test rig replicating a commercial jet-engine configuration. The damper journal is 2.54cm in length and 12.7cm in diameter, with nominal clearance of 0.127mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports, and a mechanical seal ring in contact with the damper journal. A wave spring pushes the ring ensuring tight sealing to prevent gas ingestion. The mechanical seal also serves to contain the lubricant within the squeeze film land for extended periods of time and; while in operation, to prevent contamination of the ball bearing cartridge. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and motion amplitude dependent, albeit decreasing rapidly as the motion parameters increase. Identified squeeze film force coefficients, damping and added mass, agree well with predictions based on the full film, short length damper model.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Assembly cut view of SFD with mechanical seal

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Figure 2

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

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Figure 9

Squeeze film damping coefficients (CSFDxx,CSFDyy) versus displacement amplitude. Unidirectional load tests (excitation frequency: 20Hz and 60Hz, lubricated SFD).

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Figure 8

Identified system damping coefficients (Ctxx,Ctyy) versus displacement amplitude. Unidirectional load tests (excitation frequency: 20Hz and 60Hz, lubricated SFD).

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Figure 7

Derived squeeze film damping coefficients (CSFDxx,CSFDyy) versus excitation frequency. Unidirectional load tests (lubricated SFD).

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Figure 6

Identified system damping coefficients (Ctxx,Ctyy) versus excitation frequency. Unidirectional load tests (lubricated SFD).

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Figure 5

Dynamic stiffnesses from unidirectional load (single frequency) excitation tests and analytical model (amplitude of motion 39μm, Ksx=788kN∕m, Ksy=823kN∕m, Mtxx=19.7, Mtyy=18.4, lubricated SFD)

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Figure 4

Equivalent viscous damping (dry friction+residual) versus excitation frequency (test-Dry SFD, end seal in place)

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Figure 3

Work exerted by input force (=dissipated energy) estimated from combined damping model (dry SFD, end seal in place)

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