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Research Papers: Gas Turbines: Structures and Dynamics

Effect of Operating Conditions on the Elastohydrodynamic Performance of Foil Thrust Bearings for Supercritical CO2 Cycles

[+] Author and Article Information
Kan Qin

Queensland Geothermal Energy
Centre of Excellence,
School of Mechanical and Mining Engineering,
The University of Queensland,
Brisbane 4072, Queensland, Australia
e-mail: k.qin1@uq.edu.au

Ingo H. Jahn

Centre for Hypersonics,
School of Mechanical and Mining Engineering,
The University of Queensland,
Brisbane 4072, Queensland, Australia
e-mail: i.jahn@uq.edu.au

Peter A. Jacobs

Queensland Geothermal Energy
Centre of Excellence,
School of Mechanical and Mining Engineering,
The University of Queensland,
Brisbane 4072, Queensland, Australia
e-mail: p.jacobs@uq.edu.au

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 18, 2016; final manuscript received September 9, 2016; published online November 8, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 042505 (Nov 08, 2016) (10 pages) Paper No: GTP-16-1349; doi: 10.1115/1.4034723 History: Received July 18, 2016; Revised September 09, 2016

In this paper, a quasi-three-dimensional fluid–structure model using computational fluid dynamics for the fluid phase is presented to study the elastohydrodynamic performance of foil thrust bearings for supercritical CO2 cycles. For the simulation of the gas flows within the thin gap, the computational fluid dynamics solver Eilmer is extended, and a new solver is developed to simulate the bump and top foil within foil thrust bearings. These two solvers are linked using a coupling algorithm that maps pressure and deflection at the fluid structure interface. Results are presented for ambient CO2 conditions varying between 0.1 and 4.0 MPa and 300 and 400 K. It is found that the centrifugal inertia force can play a significant impact on the performance of foil thrust bearings with the highly dense CO2 and that the centrifugal inertia forces create unusual radial velocity profiles. In the ramp region of the foil thrust bearings, they generate an additional inflow close to the rotor inner edge, resulting in a higher peak pressure. Contrary to the flat region, the inertia force creates a rapid mass loss through the bearing outer edge, which reduces pressure in this region. This different flow fields alter bearing performance compared to conventional air foil bearings. In addition, the effect of turbulence in load capacity and torque is investigated. This study provides new insight into the flow physics within foil bearings operating with dense gases and for the selection of optimal operating condition to suit CO2 foil bearings.

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References

Figures

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Fig. 1

The architecture of supercritical CO2 turbomachinery system

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Fig. 2

Comparison between Eilmer-laminar and Reynolds equation: (a) pressure (in Pa) contour for low-density condition—Eilmer-laminar, (b) pressure (in Pa) contour for high-density condition—Eilmer-laminar, (c) pressure (in Pa) contour for low-density condition—Reynolds equation, (d) pressure (in Pa) contour for high-density condition—Reynolds equation, (e) comparison of pressure at the medium radius for low-density condition, and (f) comparison of pressure at the medium radius for high-density condition

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Fig. 3

Computational domain of the foil thrust bearing, not to scale [35]

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Fig. 4

Comparison of measurements and numerical simulation (Eilmer-laminar) at fixed rotational speed of 21,000 rpm

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Fig. 5

Comparison of maximum deformation between Eilmer-laminar and numerical results from Ref. [34]

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Fig. 6

Density (solid line, in kg/m3) and dynamic viscosity (dashed line, in ×106kg/(m s)) at different operating conditions

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Fig. 7

Rotational Reynolds number at different operating conditions (based on 5 μm gap and 50,000 rpm)

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Fig. 8

Pressure and deflection at the medium radius from different computational meshes, operating condition: 1.4 MPa and 300 K, rotational speed: 50,000 rpm, and initial stator–rotor separation: 5 μm

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Fig. 9

Performance comparison at the different operating conditions from laminar fluid solver—solid line: load capacity in N and dashed line: torque in N mm, Eilmer-laminar

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Fig. 10

Pressure increase at the different operating pressures, operating temperature fixed at 400 K, Eilmer-laminar

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Fig. 11

Radial velocity profile at the ramp region (circumferential angle: 5 deg) for the different operating conditions, bold line: Vr = 0, Eilmer-laminar. (a) 0.1 MPa and 400 K, ρ = 1.33 kg m−3; (b) 0.7 MPa and 400 K, ρ = 9.38 kg m−3, and (c) 1.4 MPa and 400 K, ρ = 19.01 kg m−3.

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Fig. 12

Radial velocity profile at the ramp region (circumferential angle: 25 deg) for the different operating conditions, bold line: Vr = 0, note that the inner radius velocity profile is so small that they are difficult to see, Eilmer-laminar. (a) 0.1 MPa and 400 K, ρ = 1.33 kg m−3; (b) 0.7 MPa and 400 K, ρ = 9.38 kg m−3, and (c) 1.4 MPa and 400 K, ρ = 19.01 kg m−3.

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Fig. 13

Streamlines close to stator and rotor, operating condition: 0.1 MPa and 400 K, ρ=1.33 kg m−3. The rotational direction is anticlockwise, Eilmer-laminar. (a) Stator—pressure (in Pa) contour and streamline, (b) rotor—pressure (in Pa) contour and streamline, (c) stator—radial velocity (in m/s), and (d) rotor—radial velocity (in m/s).

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Fig. 14

Streamlines close to stator and rotor, operating condition: 1.4 MPa and 400 K, ρ=19.01 kg m−3. The rotational direction is anticlockwise, Eilmer-laminar. (a) Stator—pressure (in Pa) contour and streamline, (b) rotor—pressure (in Pa) contour and streamline, (c) stator—radial velocity (in m/s), and (d) rotor—radial velocity (in m/s).

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Fig. 15

Local deflection (in μm) for two identical operating conditions, rotational direction: anticlockwise, Eilmer-laminar. (a) 0.1 MPa and 400 K and (b) 1.4 MPa and 400 K.

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Fig. 17

Performance at stator and rotor, operating condition: 4.0 MPa and 400 K, the rotational direction in anticlockwise, Eilmer-turbulent. (a) Stator—pressure contour and streamline and (b) rotor—pressure contour and streamline.

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Fig. 16

Performance comparison at the different flow regimes, the operating temperature is fixed as 400 K

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