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Research Papers: Gas Turbines: Structures and Dynamics

On the Predicted Effect of Angular Misalignment on the Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors

[+] Author and Article Information
Travis A. Cable

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: cable.travis@tamu.edu

Luis San Andrés

Mast-Childs Chair Professor
Fellow ASME
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: Lsanandres@tamu.edu

Karl Wygant

Director of Engineering,
Hanwha Techwin,
11757 Katy Fwy #1100,
Houston, TX 77079

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 5, 2016; final manuscript received September 5, 2016; published online November 2, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 042503 (Nov 02, 2016) (11 pages) Paper No: GTP-16-1306; doi: 10.1115/1.4034722 History: Received July 05, 2016; Revised September 05, 2016

Multiple-stage integrally geared compressors (IGCs) offer improved thermal efficiency and easier access for maintenance and overhaul than single-shaft centrifugal compressors. In an IGC, a main bull shaft drives pinion shafts, each having an impeller at its ends. The compression of process gas in the compressor stages induces axial loads along the pinion shafts that are transmitted via thrust collars (TCs) to the main bull gear (BG) shaft and balanced by a single thrust bearing. Manufacturing inaccuracies and a poor assembly process can lead to static angular misalignments of the TC and BG surfaces that affect the operating film thickness as well as the force and reaction moments of the lubricated mechanical element. In a follow-up to San Andrés et al. (2015, “On the Predicted Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors,” ASME J. Eng. Gas Turbines Power, 137(5), pp. 1–9), this paper presents an investigation of the performance of a single thrust collar configuration operating with increasing static angular misalignment of either the TC or BG. The flow model solves the Reynolds equation of hydrodynamic lubrication coupled to a thermal energy transport equation to determine the film pressure and bulk temperature fields, respectively. The model predicts performance parameters such as power loss and lubricant flow rate, and force and moment stiffness and damping coefficients. Predictions show that misaligning of either the thrust collar or bull gear alters the load-carrying area in the lubricated zone, shifts the pressure field with peak magnitudes doubling or more depending on the degree and direction of TC or BG misalignment. Static angular misalignment does not significantly affect the power loss, temperature rise, etc., but does have an effect on the dynamic coefficients (both axial and angular). Finally, a reduced complex dynamic stiffness matrix for the lubricated TC shows that some cross-coupled stiffness and moment coefficients are nonzero, indicating hydrodynamic coupling between axial and angular motions for the pinion and bull gear shafts. The coupling could affect the placement of the system natural frequencies and associated mode shapes as well as the system stability.

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References

Figures

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Fig. 1

(a) Cut view and (b) schematic view of a two-stage integrally geared compressor [1]

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Fig. 2

(a) Top and (b) side depictions of lubricated (noncontacting) zone between a thrust collar and bull gear [1]

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Fig. 3

Depiction of an aligned bull gear and a thrust collar with (a) no misalignment, (b) angular misalignment (αx) about the x-axis, and (c) angular misalignment (αy) about the y-axis

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Fig. 4

Depiction of an aligned thrust collar and a bull gear with (a) no misalignment, (b) angular misalignment (βx) about the x-axis, and (c) angular misalignment (βy) about the y-axis

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Fig. 5

Schematic representation of (a) imposed axial force on the thrust collar and (b) a hydrodynamic pressure field (p) acting on the thrust collar surface [2]

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Fig. 6

Typical finite-element mesh of the lubricated zone and a single control volume comprised of a row of finite elements

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Fig. 7

Contour plots of film thickness in a lubricated thrust collar. TC and BG with angular misalignment about the x and y axes (a) negative TC misalignment, (b) no misalignment, (c) positive TC misalignment, (d) negative TC misalignment, (e) no misalignment, and (f) positive TC misalignment.

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Fig. 8

Contour plots of hydrodynamic pressure in a lubricated thrust collar. TC and BG with angular misalignment about the x and y axes (a) negative TC misalignment, (b) no misalignment, (c) positive TC misalignment, (d) negative TC misalignment, (e) no misalignment, and (f) positive TC misalignment.

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Fig. 9

Normalized film thickness (h¯min) versus (a) TC misalignment angle α¯x and (b) TC misalignment angle α¯y. W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0 (a) −0.2 ≤  α¯x ≤ 0.2, α¯y = β¯x = β¯y = 0 and (b) −0.2 ≤  α¯y  ≤ 0.2, α¯x = β¯x = β¯y = 0.

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Fig. 10

Peak pressure (P¯max) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 11

Friction factor (f) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 12

Lubricant flow rate (Q¯) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 13

Lubricant temperature rise (ΔT¯) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 14

Axial stiffness (K¯zz) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 15

Moment-angle stiffness versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 16

Axial-force angle stiffness versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 17

Axial damping (C¯zz) versus thrust collar misalignment angle (α¯xorα¯y). W¯=1, ω¯=10, R2/R1=7.14, φ¯TC=φ¯B=1.0.

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Fig. 18

Depiction of the lubricated zone between a thrust collar and bull gear as a parallel channel

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Fig. 19

Minimum film thickness versus combined tip speed for a thrust load W = 5 kN. Comparison of results obtained with the current model and results in Ref. [5].

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