Gas Foil Bearing Technology Advancements for Closed Brayton Cycle Turbines

Howard, Samuel A.; Bruckner, Robert J.; DellaCorte, Christopher; Radil, Kevin C.

doi:10.1063/1.2437506

Cited by 12 publications

(6 citation statements)

References 11 publications

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“…Reynolds Equation Prediction of Apparent Friction Coefficient versus Pressure Reynolds Equation Prediction of Apparent Friction Coefficient versus Modified Reynolds NumberThis result contradicts the previously published experimental results of Dobler & Miller[11] and Howard et al[3] (Fig. 3 & 4), as well as the results of the current work, which all suggest that friction coefficient increases with pressure.…”

contrasting

confidence: 99%

“…Elimination of the oil system reduces weight, maintenance costs, and risks associated with oil leakage and degradation. In closed-loop, unmaintainable systems, such as the closed Brayton cycle (CBC) power generation system proposed for human and robotic space exploration, eliminating the oil system provides the necessary benefit of maintaining a contaminatefree working fluid [2] [3].…”

Section: Figure 1 -Rigid Hydrodynamic Bearingmentioning

confidence: 99%

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High Pressure Performance of Foil Journal Bearings in Various Gases

Briggs

Prahl

Bruckner

et al. 2008

STLE/ASME 2008 International Joint Tribology Conference

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Foil bearings offer several advantages over traditional oil-lubricated bearings in closed Brayton Cycle (CBC) systems, such as those proposed for long-term space power generation. Proposed CBCs require foil bearings to use an inert gas lubricant at pressures as high as 3.0 MPa as the bearing lubricant. The High Pressure Rig (HPR) at the NASA Glenn Research Center is used to measure foil bearing power loss using potential CBC working fluids at and beyond proposed CBC peak pressures. In the current study foil journal bearing power loss is measured in helium, nitrogen, and carbon dioxide from atmospheric pressure to 4.83 MPa and at shaft speeds from 10 krpm to 42 krpm. Bearings operating in helium show no increase in power loss with increasing pressure for the conditions tested. Bearings operating in nitrogen show increases in power loss with increasing pressure at speeds above 19 krpm, while increases in bearing power loss during carbon dioxide testing were seen at 15 krpm. At speeds above these thresholds, power loss is shown to increase more rapidly in carbon dioxide than in nitrogen. Results suggest that bearing power loss performance is dependent on both gas density and shaft speed.

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contrasting

confidence: 99%

Section: Figure 1 -Rigid Hydrodynamic Bearingmentioning

confidence: 99%

High Pressure Performance of Foil Journal Bearings in Various Gases

Briggs

Prahl

Bruckner

et al. 2008

STLE/ASME 2008 International Joint Tribology Conference

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“…ACM design is similar to that of a turbocharger, i.e., the rotor is driven by a turbine and pressurized air is provided by a blower impeller. The majority of contemporary high-speed rotating machines use aerodynamic foil bearings, which have very good operational properties [1][2][3][4][5][6]. However, even better functional properties can be achieved with tilting pad journal bearings (TPJBs), which have excellent dynamic characteristics.…”

Section: Introductionmentioning

confidence: 99%

Specific Features of Aerodynamic Journal Bearings with Elastically Supported Pads

Šimek

2017

Lubricants

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Aerodynamic bearings with elastically supported tilting pads have operational properties comparable with widely-used foil journal bearings. They combine the excellent stability of tilting pad bearings, as a result of very small cross-coupling stiffness terms, with the positive properties of foil bearings, namely their ability to adapt to changing operating conditions and presence of additional damping due to friction between elastic members and bearing casings. Air cycle machines (ACMs) are used in the environmental control systems of aircrafts to manage the pressurization of the cabin. An ACM with the abovementioned type of bearings and an operational speed of 60,000 rpm was designed and successfully tested, even under conditions of strong external excitation. Some problems with rotor stability in certain operation regimes were encountered. Rotor relative vibrations measured at both bearing locations increased substantially when excitation frequency was close to the lowest rotor eigenvalues. In spite of that and the 1000 start/stop cycles passed by the end of the test, any traces of wear on the bearing sliding surfaces were negligible. When the bearing distance had to be shortened in order to insert the machine into the defined space, the rotor quickly became unstable at relatively low speeds. Although rotor stability reserve was reduced only slightly, the rotor had to be redesigned in order to achieve stability. Operation characteristics of aerodynamic bearings with elastically supported tilting pads are presented together with rotor dynamic analysis and validated with measured results.

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“…GFBs, as a type of compliant, self-acting hydrodynamic fluid film bearings using ambient gas as lubricant, have shown many advantages including inherent simple structure, no complex oil lubrication and sealing system, excellent high-speed operation characteristics and tolerance for high temperatures [2]. To date, GFBs have been successfully used in many oil-free machinery applications, such as air cycle machine in aircrafts [3], turbochargers [4,5], turbojet engine [6,7], and micro gas turbine engine [8][9][10]. However, there are still some issues that hinder the development of GFBs.…”

Section: Introductionmentioning

confidence: 99%

“…2 To date, GFBs have been successfully used in many oil-free machinery applications, such as air cycle machine in aircrafts, 3 turbochargers, 4,5 turbojet engine, 6,7 micro gas turbine engine. [8][9][10] However, there are still some issues that hinder the development of GFBs. A special frictionresistant coating is needed on the surface of top foil to extend the applicable bearing life.…”

Section: Introductionmentioning

confidence: 99%

Theoretical investigation of hybrid foil-magnetic bearings on operation mode and load sharing strategy

Zhang

Yin

Guan

et al. 2022

Proceedings of the Institution of Mechanical Engineers, Part J:

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This paper presents a theoretical investigation on operation mode and load sharing strategy of hybrid foil-magnetic bearings (HFMBs). According to the inherent characteristics of gas foil bearings (GFBs) and active magnetic bearings (AMBs), six possible work scopes are discussed to understand the operation mode of HFMBs. A numerical model coupling the calculations of the film pressure in GFBs and the magnetic forces in AMBs is conducted to predict the operation performance of HFMBs. The accuracy of the model is proved by comparing the predicted and tested friction torques. Analysis on the static and dynamic performance of HFMBs within three representative cases is conducted by varying the load sharing ratio. The dynamic supporting stiffness and operation position of HFMBs can be obviously enhanced by adjusting the operating mode and load sharing strategy. Results show that the direct stiffness and dynamic damping of HFMBs adopting hybrid mode are significantly higher than those adopting AMB or GFB independent mode.

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Gas Foil Bearing Technology Advancements for Closed Brayton Cycle Turbines

Cited by 12 publications

References 11 publications

High Pressure Performance of Foil Journal Bearings in Various Gases

High Pressure Performance of Foil Journal Bearings in Various Gases

Specific Features of Aerodynamic Journal Bearings with Elastically Supported Pads

Theoretical investigation of hybrid foil-magnetic bearings on operation mode and load sharing strategy

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