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Research Papers: Gas Turbines: Structures and Dynamics

Nonlinear Identification of Mechanical Parameters in a Squeeze Film Damper With Integral Mechanical Seal

[+] Author and Article Information
Adolfo Delgado

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

Luis San Andrés

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

The equivalent viscous damping coefficient representative of “dry friction” is inversely proportional to the amplitude of motion and excitation frequency; hence then the nonlinear character of the test SFD-mechanical seal system.

As demonstrated in a prior paper (6), cross-coupled force coefficients are negligible since the damper operates without oil cavitation.

J. Eng. Gas Turbines Power 131(4), 042504 (Apr 13, 2009) (7 pages) doi:10.1115/1.2967498 History: Received April 02, 2008; Revised April 04, 2008; Published April 13, 2009

End seals in squeeze film dampers (SFDs) aid to increase their damping capability while maintaining low lubricant flow rates and reducing the severity of air ingestion. This paper presents measurements of the forced response in a SFD integrating a contacting end seal and with closed flow ports, i.e., no lubricant through flow. The system motion is nonlinear due to the dry-friction interaction at the mechanical seal mating surfaces. Single parameter characterization of the test system would yield an equivalent viscous damping coefficient that is both frequency and motion amplitude dependent. Presently, an identification method suited for nonlinear systems allows determining simultaneously the squeeze film damping and inertia force coefficients and the seal dry-friction force. The identification procedure shows similar (within 10%) force coefficients than those obtained with a more involved two-step procedure that first requires measurements without any lubricant in the test system. The identified SFD damping and inertia force coefficients agree well with model predictions that account for end flow effects at recirculation grooves. The overall test results demonstrate that the nonrotating end seal effectively eliminates side leakage and avoids air ingestion, thus maintaining a consistent damping performance throughout the test frequency range. The nonlinear identification procedure saves time and resources while producing reliable physical parameter estimations.

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Copyright © 2009 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 (Ref. 7)

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Figure 3

Dimensions of squeeze film land (no oil throughflow condition). Film radial clearance c=0.127 mm.

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Figure 4

Schematic of the equivalent representation of the SFD with mechanical seal

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Figure 5

Elements of a four-input/two-output representation of the nonlinear mechanical seal-SFD system (15)

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Figure 6

Recorded load (top) and ensuing displacement orbits (bottom) for four load magnitudes. Clearance circle noted. (60 Hz, lubricated SFD, CCO).

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Figure 7

Dry friction force identified from circular centered orbits. The dotted line represents dry friction estimated from energy method and tests under dry conditions.

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Figure 8

Real part of dynamic stiffnesses versus frequency. Circular centered orbits of amplitude x,y: 50 μm(Ksx=853 kN∕m,Ksy=885 kN∕m).

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Figure 9

Imaginary part of linear impedance function versus excitation frequency. (CSFDxx) Circular centered orbits of amplitude x,y: 50 μm (no throughflow).

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Figure 10

Squeeze film damping coefficient (CSFDyy) versus orbit amplitude (circular centered orbits, no throughflow, flow restrictor: 2.8 mm (3))

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Figure 11

Squeeze film damping coefficients (CSFDxx,CSFDyy) and system damping coefficients (Cs−xx,Cs−yy) versus excitation frequency for increasing orbit amplitudes (circular centered orbits, no throughflow)

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