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Research Papers: Hydrodynamic Lubrication

Investigation of Structural Conformity in a Three-Pad Adaptive Air Foil Bearing With Regard to Active Control of Radial Clearance

[+] Author and Article Information
Hossein Sadri

Institute of Adaptronics and Function Integration,
TU Braunschweig, Langer Kamp 6,
Braunschweig 38106, Germany
e-mail: h.sadri@tu-braunschweig.de

Henning Schlums

Institute of Adaptronics and Function Integration,
TU Braunschweig, Langer Kamp 6,
Braunschweig 38106, Germany
e-mail: h.schlums@tu-braunschweig.de

Michael Sinapius

Institute of Adaptronics and Function Integration,
TU Braunschweig, Langer Kamp 6,
Braunschweig 38106, Germany
e-mail: m.sinapius@tu-braunschweig.de

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received July 26, 2018; final manuscript received May 7, 2019; published online June 4, 2019. Assoc. Editor: Daejong Kim.

J. Tribol 141(8), 081701 (Jun 04, 2019) (12 pages) Paper No: TRIB-18-1296; doi: 10.1115/1.4043780 History: Received July 26, 2018; Accepted May 07, 2019

Various solutions for the design of oil-free bearings are discussed in the literature. Adding hydrodynamic preload to the foil bearings by profiling the inner bore of the bearing is one of the most frequently investigated methods for improving the bearing stability and damping character of the entire system. However, this approach leads to a reduced load capacity and thus to an increased lift-off speed of the foil bearings. Observations of this kind lead to the presentation of various solutions for active bearing contour adjustment, which benefits from different profiles of the lubricant film. Most of these concepts use piezoelectric stack actuators to generate the required alternating force, although the influence of the stiffness of adaptive elements on bearing performance is not fully discussed in the literature. The focus of this study is on the investigation of structural conformity, i.e., the harmonization of stiffness with respect to the requirements for shape control and load capacity of an adaptive air foil bearing (AAFB). The result may be a basis for the consideration of additional degrees of freedom in any concept with shape control as the main design framework in interaction between the lubricant and compliant structure in an air foil bearing from both static and dynamic points of view.

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References

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Figures

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Fig. 1

(a) Hardware prototype for active influence on bore clearance in an AAFB and (b) general configuration and coordinate system of an AAFB with three pads for circular and noncircular bore clearance

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Fig. 2

Definition of the clearance in an AAFB with noncircular bore and constant length of the support shell compared with the circular case

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Fig. 3

Test rig for investigating the shape morphing on a functional model for AAFB

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Fig. 4

Evaluated rp used in modeling the bore clearance (see Eq. (3) and Fig. 2) from scanning the investigated shell in the unloaded state just before and during the actuation

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Fig. 5

(a) Transfer function and (b) phase shift between excitation voltage and measured displacement signal from exciting and sampling the functional model for a frequency range of 0–100 Hz

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Fig. 6

Measured and fitted profiles of a single adaptive segment of AAFB under different static loading conditions, load angle = 0 deg

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Fig. 7

(a) Rigid-body model of the investigated adaptive segment and (b) local deformation, internal forces, and moments under 2.01 N static load, load angle = 0 deg

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Fig. 8

Measured changes of the lateral and rotational coordinates of the rigid-body model to describe the investigated shell under load

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Fig. 9

Evaluated values for extensional and torsional stiffnesses in the rigid-body model to describe the investigated shell under load

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Fig. 10

Reference coordinate system and general configuration of journal foil bearing with eccentric journal position

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Fig. 11

Iterative calculation of hydrodynamic pressure and film thickness considering reaction forces acting on an adaptive segment

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Fig. 12

Initial and deformed clearance of AAFB with preloaded configuration, ω = 20 krpm

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Fig. 13

Journal eccentricity, attitude angle of the AAFB, and minimum gas film thickness with two different configurations listed in Table 2

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Fig. 14

(a) Synchronous dynamic (stiffness and damping) coefficients and (b) modal impedance of the AAFB with two different configurations listed in Table 2, ω = 20 krpm

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Fig. 15

Journal orbits of the AAFB with two different configurations: (a) circular and (b) preloaded shape under 1 g mm imbalance excitation, ω = 20 krpm

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Fig. 16

FFT analysis of journal motions in (a) X-direction and (b) Y-direction under 1 g mm imbalance excitation, ω = 20 krpm

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Fig. 17

Bumps deflection of a single strip with ten bumps for a uniform load distribution (2 × 105 Pa) from Ref. [20] and the current study, foil thickness = 101.6 μm, bump pitch = 4.572 mm, bump half-length = 1.778 mm, bump height = 0.508 mm, and bump angle = 63.8 deg

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Fig. 18

Minimum gas film thickness of the single-strip bump-foil bearing investigated in Ref. [22] and the current study for different static loadings at 30,000 rpm, L = D = 38:1 mm; c = 31:8 μm; foil thickness = 101:6 μm; bump pitch = 4:572 mm; bump half-length = 1:778 mm; bump height = 0:508 mm; bump angle = 63:8 deg

Tables

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