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    Effects of Bearing Stiffness Anisotropy on Hydrostatic Micro Gas Journal Bearing Dynamic Behavior

    Source: Journal of Engineering for Gas Turbines and Power:;2007:;volume( 129 ):;issue: 001::page 177
    Author:
    L. X. Liu
    ,
    Z. S. Spakovszky
    DOI: 10.1115/1.2180813
    Publisher: The American Society of Mechanical Engineers (ASME)
    Abstract: The high-speed microhydrostatic gas journal bearings used in the high-power density MIT microengines are of very low aspect ratio with an L∕D of less than 0.1 and are running at surface speeds of order 500m∕s. These ultra-short high-speed bearings exhibit whirl instability limits and a dynamic behavior much different from conventional hydrostatic gas bearings. The design space for stable high-speed operation is confined to a narrow region and involves singular behavior ( and , 2005, “ Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vibr. Acoust., 127(3), pp. 254–261). This together with the limits on achievable fabrication tolerance, which can be achieved in the silicon chip manufacturing technology, severely affects bearing operability and limits the maximum achievable speeds of the microturbomachinery. This paper introduces a novel variation of the axial-flow hydrostatic micro gas journal bearing concept, which yields anisotropy in bearing stiffness. By departing from axial symmetry and introducing biaxial symmetry in hydrostatic stiffness, the bearing's top speed is increased and fabrication tolerance requirements are substantially relieved making more feasible extended stable high-speed bearing operation. The objectives of this work are: (i) to characterize the underlying physical mechanisms and the dynamic behavior of this novel bearing concept and (ii) to report on the design, implementation, and test of this new microbearing technology. The technical approach involves the combination of numerical simulations, experiment, and simple, first-principles-based modeling of the gas bearing flow field and the rotordynamics. A simple description of the whirl instability threshold with stiffness anisotropy is derived explaining the instability mechanisms and linking the governing parameters to the whirl ratio and stability limit. An existing analytical hydrostatic gas bearing model is extended and modified to guide the bearing design with stiffness anisotropy. Numerical simulations of the full nonlinear governing equations are conducted to validate the theory and the novel bearing concept. Experimental results obtained from a microbearing test device are presented and show good agreement between the theory and the measurements. The theoretical increase in achievable bearing top speed and the relief in fabrication tolerance requirements due to stiffness anisotropy are quantified and important design implications and guidelines for micro gas journal bearings are discussed.
    keyword(s): Hydrostatics , Anisotropy , Bearings , Rotors , Gas bearings , Stiffness , Whirls , Journal bearings , Stress , Stability AND Design ,
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      Effects of Bearing Stiffness Anisotropy on Hydrostatic Micro Gas Journal Bearing Dynamic Behavior

    URI
    http://yetl.yabesh.ir/yetl1/handle/yetl/135785
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    • Journal of Engineering for Gas Turbines and Power

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    contributor authorL. X. Liu
    contributor authorZ. S. Spakovszky
    date accessioned2017-05-09T00:23:49Z
    date available2017-05-09T00:23:49Z
    date copyrightJanuary, 2007
    date issued2007
    identifier issn1528-8919
    identifier otherJETPEZ-26935#177_1.pdf
    identifier urihttp://yetl.yabesh.ir/yetl/handle/yetl/135785
    description abstractThe high-speed microhydrostatic gas journal bearings used in the high-power density MIT microengines are of very low aspect ratio with an L∕D of less than 0.1 and are running at surface speeds of order 500m∕s. These ultra-short high-speed bearings exhibit whirl instability limits and a dynamic behavior much different from conventional hydrostatic gas bearings. The design space for stable high-speed operation is confined to a narrow region and involves singular behavior ( and , 2005, “ Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vibr. Acoust., 127(3), pp. 254–261). This together with the limits on achievable fabrication tolerance, which can be achieved in the silicon chip manufacturing technology, severely affects bearing operability and limits the maximum achievable speeds of the microturbomachinery. This paper introduces a novel variation of the axial-flow hydrostatic micro gas journal bearing concept, which yields anisotropy in bearing stiffness. By departing from axial symmetry and introducing biaxial symmetry in hydrostatic stiffness, the bearing's top speed is increased and fabrication tolerance requirements are substantially relieved making more feasible extended stable high-speed bearing operation. The objectives of this work are: (i) to characterize the underlying physical mechanisms and the dynamic behavior of this novel bearing concept and (ii) to report on the design, implementation, and test of this new microbearing technology. The technical approach involves the combination of numerical simulations, experiment, and simple, first-principles-based modeling of the gas bearing flow field and the rotordynamics. A simple description of the whirl instability threshold with stiffness anisotropy is derived explaining the instability mechanisms and linking the governing parameters to the whirl ratio and stability limit. An existing analytical hydrostatic gas bearing model is extended and modified to guide the bearing design with stiffness anisotropy. Numerical simulations of the full nonlinear governing equations are conducted to validate the theory and the novel bearing concept. Experimental results obtained from a microbearing test device are presented and show good agreement between the theory and the measurements. The theoretical increase in achievable bearing top speed and the relief in fabrication tolerance requirements due to stiffness anisotropy are quantified and important design implications and guidelines for micro gas journal bearings are discussed.
    publisherThe American Society of Mechanical Engineers (ASME)
    titleEffects of Bearing Stiffness Anisotropy on Hydrostatic Micro Gas Journal Bearing Dynamic Behavior
    typeJournal Paper
    journal volume129
    journal issue1
    journal titleJournal of Engineering for Gas Turbines and Power
    identifier doi10.1115/1.2180813
    journal fristpage177
    journal lastpage184
    identifier eissn0742-4795
    keywordsHydrostatics
    keywordsAnisotropy
    keywordsBearings
    keywordsRotors
    keywordsGas bearings
    keywordsStiffness
    keywordsWhirls
    keywordsJournal bearings
    keywordsStress
    keywordsStability AND Design
    treeJournal of Engineering for Gas Turbines and Power:;2007:;volume( 129 ):;issue: 001
    contenttypeFulltext
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