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Gas Turbines: Structures and Dynamics

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

[+] Author and Article Information
Christos I. Papadopoulos1

 School of Naval Architecture and Marine Engineering, National Technical University of Athens, 15710 Zografos, Greece e-mail: chpap@central.ntua.gr Machine Design Laboratory, Department of Mechanical Engineering and Aeronautics, University of Patras, 26504 Patras, Greece e-mail: pnikolak@mech.upatras.gr School of Naval Architecture and Marine Engineering, National Technical University of Athens, 15710 Zografos, Greece e-mail: kaiktsis@naval.ntua.gr

Pantelis G. Nikolakopoulos, Lambros Kaiktsis

 School of Naval Architecture and Marine Engineering, National Technical University of Athens, 15710 Zografos, Greece e-mail: chpap@central.ntua.gr Machine Design Laboratory, Department of Mechanical Engineering and Aeronautics, University of Patras, 26504 Patras, Greece e-mail: pnikolak@mech.upatras.gr School of Naval Architecture and Marine Engineering, National Technical University of Athens, 15710 Zografos, Greece e-mail: kaiktsis@naval.ntua.gr

1

Corresponding author.

J. Eng. Gas Turbines Power 134(11), 112502 (Sep 21, 2012) (9 pages) doi:10.1115/1.4007320 History: Received June 15, 2012; Revised July 18, 2012; Published September 20, 2012; Online September 21, 2012

In the present paper, a study of stiffness and damping in sector-pad micro thrust bearings with artificial surface texturing is presented, based on computational fluid dynamics (CFD) simulations. The bearing pads are modeled as consecutive three-dimensional independent microchannels, each consisting of a smooth rotating wall (rotor) and a partially textured stationary wall (stator). CFD simulations are performed, consisting in the numerical solution of the Navier–Stokes equations for incompressible isothermal flow. The goal of the present study is to characterize the dynamic behavior of favorable designs, identified in previous optimization studies, comprising parallel and convergent thrust bearings with rectangular texture patterns. To this end, a translational degree of freedom (DOF) along the thrust direction and a rotational (tilting) DOF of the rotor are considered. By implementing appropriate small perturbations around the equilibrium (steady-state) position and processing the simulation results, the stiffness and damping coefficients of the bearing are obtained for each DOF. The computed dynamic coefficients of textured thrust bearings are compared to those of conventional (smooth slider) designs. It is found that the dependence of bearing stiffness and damping on geometrical parameters exhibits the same trends for both DOFs. Both stiffness and damping are found to increase with bearing width. In general, increasing the bearing convergence ratio results in increased bearing stiffness and decreased damping. Finally, the present results demonstrate that properly textured parallel sliders are characterized by an overall dynamic performance that is superior to that of smooth converging sliders.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Top view of eight-pad thrust bearings for (a) B/L = 0.5, (b) B/L = 1.0, (c) B/L = 1.5

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Figure 5

Illustration of computation procedure of translational stiffness and average damping coefficient of thrust bearings: (a) imposed temporal variation of film thickness and corresponding rotor cross-flow (squeeze) velocity, and (b) resulting variation of load carrying capacity

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Figure 11

Nondimensional rotational stiffness and average damping coefficients kφ* and cφ* versus convergence ratio, k, for smooth and textured sector-pad sliders: (a,d) B/L = 0.5, (b,e) B/L = 1.0, (c,f) B/L = 1.5

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Figure 12

Parallel textured bearings with B/L = 0.5. Variation of normalized: (a,d) nondimensional load carrying capacity, (b,e) nondimensional translational stiffness coefficient, and (c,f) nondimensional average translational damping coefficient, versus relative groove depth, for parallel (a–c) and converging with k = kopt  = 1.3 (d–f) textured sliders. The values of untextured outlet lengths luo are kept constant at their optimal values.

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Figure 2

(a) Geometry of the fluid domain of a textured thrust bearing pad, (b) texture geometry parameters, defined at the pad midsector

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Figure 3

Sketch of translational motion of the rotor of a sector pad thrust bearing

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Figure 4

Sketch of tilting motion of the rotor of a sector pad thrust bearing

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Figure 6

Nondimensional average damping coefficient as a function of nondimensional mean translational (squeeze) velocity for optimal textured parallel thrust bearings with different values of B/L ratio. The geometry details are based on the optimization study of Ref. [17].

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Figure 7

Validation of present CFD results against literature data: (a) computed nondimensional pressure distribution versus nondimensional streamwise coordinate for a converging microbearing with texturing; (b) computed nondimensional average translational damping coefficient versus convergence ratio of rectangular tapered-land sliders with B/L = 0.5

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Figure 8

Color-coded contours of steady-state nondimensional pressure on the rotor surface of an optimal textured eight-pad parallel thrust bearing with B/L = 1.0 (luo  = 0.447, s = 0.412)

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Figure 9

Nondimensional load carrying capacity W* versus convergence ratio k for different B/L values, for sector-pad and rectangular sliders: (a) smooth sliders, (b) optimal textured sliders

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Figure 10

Nondimensional translational stiffness and average damping coefficients kz* and cz* versus convergence ratio, k, for smooth and textured sector-pad sliders: (a,d) B/L = 0.5, (b,e) B/L = 1.0, (c,f) B/L = 1.5

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Figure 13

Parallel textured bearings with B/L = 0.5. Variation of normalized: (a,d) nondimensional load carrying capacity, (b,e) nondimensional translational stiffness coefficient, and (c,f) nondimensional translational damping coefficient, versus untextured outlet length, for parallel (a–c) and converging with k = kopt  = 1.3 (d–f) textured sliders. The values of relative groove depths s are kept constant at their optimal values.

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