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Détail de l'auteur
Auteur Daejong Kim
Documents disponibles écrits par cet auteur
Affiner la rechercheDesign and performance prediction of hybrid air foil thrust bearings / Donghyun Lee in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 4 (Avril 2011)
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 4 (Avril 2011) . - 13 p.
Titre : Design and performance prediction of hybrid air foil thrust bearings Type de document : texte imprimé Auteurs : Donghyun Lee, Auteur ; Daejong Kim, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aerospace components Aerospace engines Damping Design engineering Elasticity Finite difference methods Friction Hydrostatics Machine bearings Orifices (mechanical) Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been recognized as the most promising for oil-free turbomachinery. However, the applications of AFBs to the relatively large turbomachinery have many technical challenges due to limited load capacity and wear during start/stops. A hybrid air foil bearing (HAFB), which combines the benefits of AFB and hydrostatic air bearing, was introduced earlier by the authors, and the experimental studies showed much larger load capacity at low speeds and much lesser friction torque during start/stop than hydrodynamic counterpart. The benefit of HAFB was recognized through the experimental studies, and the concept of hybrid operation was further developed to thrust air foil bearings. This paper presents novel design features of the hybrid air foil thrust bearing (HAFTB) with radially arranged bump foils and preformed Rayleigh step contour, and presents simulated static and dynamic characteristics of the HAFTB. A 2D thin plate equation in cylindrical coordinate was solved with the finite difference method for the prediction of the top foil deflection. Parametric studies were performed to evaluate the effect of various design parameters on the static and dynamic performances of HAFTB. At low speeds, a design with orifice located at the center of land region showed the highest load capacity, while a design with orifice located near the leading edge of land region showed the highest load capacity at high speeds. Direct and coupled bearing coefficients were also calculated for various operating conditions. The direct stiffness increases with supply pressure but the direct damping decreases with supply pressure. In addition, typical hardening effect of gas film accompanying increase of stiffness and decrease of damping was predicted in high frequency excitations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Design and performance prediction of hybrid air foil thrust bearings [texte imprimé] / Donghyun Lee, Auteur ; Daejong Kim, Auteur . - 2012 . - 13 p.
Génie Mécanique
Langues : Anglais (eng)
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 4 (Avril 2011) . - 13 p.
Mots-clés : Aerospace components Aerospace engines Damping Design engineering Elasticity Finite difference methods Friction Hydrostatics Machine bearings Orifices (mechanical) Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been recognized as the most promising for oil-free turbomachinery. However, the applications of AFBs to the relatively large turbomachinery have many technical challenges due to limited load capacity and wear during start/stops. A hybrid air foil bearing (HAFB), which combines the benefits of AFB and hydrostatic air bearing, was introduced earlier by the authors, and the experimental studies showed much larger load capacity at low speeds and much lesser friction torque during start/stop than hydrodynamic counterpart. The benefit of HAFB was recognized through the experimental studies, and the concept of hybrid operation was further developed to thrust air foil bearings. This paper presents novel design features of the hybrid air foil thrust bearing (HAFTB) with radially arranged bump foils and preformed Rayleigh step contour, and presents simulated static and dynamic characteristics of the HAFTB. A 2D thin plate equation in cylindrical coordinate was solved with the finite difference method for the prediction of the top foil deflection. Parametric studies were performed to evaluate the effect of various design parameters on the static and dynamic performances of HAFTB. At low speeds, a design with orifice located at the center of land region showed the highest load capacity, while a design with orifice located near the leading edge of land region showed the highest load capacity at high speeds. Direct and coupled bearing coefficients were also calculated for various operating conditions. The direct stiffness increases with supply pressure but the direct damping decreases with supply pressure. In addition, typical hardening effect of gas film accompanying increase of stiffness and decrease of damping was predicted in high frequency excitations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p.
Titre : Design of three-pad hybrid air foil bearing and experimental investigation on static performance at zero running speed Type de document : texte imprimé Auteurs : Daejong Kim, Auteur ; Donghyun Lee, Auteur Année de publication : 2011 Article en page(s) : 10 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aerospace components Hydrostatics Machine bearings Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Design of three-pad hybrid air foil bearing and experimental investigation on static performance at zero running speed [texte imprimé] / Daejong Kim, Auteur ; Donghyun Lee, Auteur . - 2011 . - 10 p.
Génie Mécanique
Langues : Anglais (eng)
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p.
Mots-clés : Aerospace components Hydrostatics Machine bearings Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 5 (Mai 2012) . - 13 p.
Titre : Extended three-dimensional thermo-hydrodynamic model of radial foil bearing : case studies on thermal behaviors and dynamic characteristics in gas turbine simulator Type de document : texte imprimé Auteurs : Daejong Kim, Auteur ; Jeongpill Ki, Auteur ; Youngcheol Kim, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Computational fluid dynamics Cooling Damping Elasticity Gas turbine power stations Gas turbines Hydrodynamics Impellers Machine bearings Perturbation techniques Rotors Shafts Small electric machines Softening Thermal resistance Viscosity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Environment-friendly microturbomachinery has its broad current and future applications in fuel cells, power generation, oil-free industrial blowers and compressors, small aero propulsions engines for missiles and small aircrafts, automotive turbo chargers, etc. Air foil bearings (AFBs) have been one of the popular subjects in recent years due to ever-growing interests in the environment-friendly oil-free turbomachinery. AFBs have many noticeable attractive features compared to conventional rigid-walled air/gas bearings such as improved damping and tolerance to minor shaft misalignment and external shocks. In addition, the low viscosity of air or gas allows very low power consumption even at high speeds. A turbine simulator mimicking 50 kW power generation gas turbine was designed. The turbine simulator can generate the same thermodynamic conditions and axial thrust load as the actual gas turbine. In this paper, the 3-D thermo-hydrodynamic (THD) model developed for single radial AFB was further extended to the turbine simulator configuration by extending the solution domain to the surrounding structures including two plenums, bearing sleeve, housing, and rotor exposed to the plenums. In addition, a computational fluid dynamic (CFD) model on the leading edge groove region was developed for better prediction of inlet thermal boundary conditions for the bearing. Several case studies are presented through computer simulations for hydrodynamically preloaded three-pad radial AFB in the hot section. It is found that both bearing and rotor should be provided with cooling air to maintain the temperature of both the rotor and top foil below 300 °C. It is also found that the higher thermal contact resistance between the rotor and hot impellers reduces the axial temperature gradient of the rotor. Dynamic performance of the bearing was evaluated using the linear perturbation method for operation at elevated temperature. The softening effect of the bump foil at elevated temperature results in a decrease of both stiffness and damping coefficients compared to the values at room temperature. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000005 [...] [article] Extended three-dimensional thermo-hydrodynamic model of radial foil bearing : case studies on thermal behaviors and dynamic characteristics in gas turbine simulator [texte imprimé] / Daejong Kim, Auteur ; Jeongpill Ki, Auteur ; Youngcheol Kim, Auteur . - 2012 . - 13 p.
Génie mécanique
Langues : Anglais (eng)
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 5 (Mai 2012) . - 13 p.
Mots-clés : Computational fluid dynamics Cooling Damping Elasticity Gas turbine power stations Gas turbines Hydrodynamics Impellers Machine bearings Perturbation techniques Rotors Shafts Small electric machines Softening Thermal resistance Viscosity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Environment-friendly microturbomachinery has its broad current and future applications in fuel cells, power generation, oil-free industrial blowers and compressors, small aero propulsions engines for missiles and small aircrafts, automotive turbo chargers, etc. Air foil bearings (AFBs) have been one of the popular subjects in recent years due to ever-growing interests in the environment-friendly oil-free turbomachinery. AFBs have many noticeable attractive features compared to conventional rigid-walled air/gas bearings such as improved damping and tolerance to minor shaft misalignment and external shocks. In addition, the low viscosity of air or gas allows very low power consumption even at high speeds. A turbine simulator mimicking 50 kW power generation gas turbine was designed. The turbine simulator can generate the same thermodynamic conditions and axial thrust load as the actual gas turbine. In this paper, the 3-D thermo-hydrodynamic (THD) model developed for single radial AFB was further extended to the turbine simulator configuration by extending the solution domain to the surrounding structures including two plenums, bearing sleeve, housing, and rotor exposed to the plenums. In addition, a computational fluid dynamic (CFD) model on the leading edge groove region was developed for better prediction of inlet thermal boundary conditions for the bearing. Several case studies are presented through computer simulations for hydrodynamically preloaded three-pad radial AFB in the hot section. It is found that both bearing and rotor should be provided with cooling air to maintain the temperature of both the rotor and top foil below 300 °C. It is also found that the higher thermal contact resistance between the rotor and hot impellers reduces the axial temperature gradient of the rotor. Dynamic performance of the bearing was evaluated using the linear perturbation method for operation at elevated temperature. The softening effect of the bump foil at elevated temperature results in a decrease of both stiffness and damping coefficients compared to the values at room temperature. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000005 [...]
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 3 (Mars 2012) . - 09 p.
Titre : Start-stop characteristics and thermal behavior of a large hybrid airfoil bearing for aero-propulsion applications Type de document : texte imprimé Auteurs : Daejong Kim, Auteur ; George Zimbru, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Abrasion Aerodynamics Aerospace components Aerospace propulsion Friction Machine bearings Rotors Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air/gas foil bearings (AFB) have shown a promise in high-speed micro to mid-sized turbomachinery. Compared to rolling element bearings, AFBs do not require oil lubrication circuits and seals, allowing the system to be less complicated and more environment-friendly. Due to the smaller number of parts required to support the rotor and no lubrication/seal system, AFBs provide compact solution to oil-free turbomachinery development.While foil bearing technology is mature in small industrial machines and power generation turbines, its application to aero-propulsion systems has been prohibited due to the reliability issues relevant to unique aero-propulsion environments such as severe rubbing due to the very slow acceleration of typically heavy rotors. This paper presents a hybrid air foil bearing (a combination of hydrostatic and hydrodynamic) with 102 mm in diameter designed for aero-propulsion applications, and preliminary test results on start-stop friction characteristics and thermal behavior at low speeds below 10,000 rpm are presented. The bearing could withstand 1000 start/stop cycles with 6 rev/s2 acceleration under a static load of 356 N (43.4 kPa). DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000003 [...] [article] Start-stop characteristics and thermal behavior of a large hybrid airfoil bearing for aero-propulsion applications [texte imprimé] / Daejong Kim, Auteur ; George Zimbru, Auteur . - 2012 . - 09 p.
Génie mécanique
Langues : Anglais (eng)
in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 3 (Mars 2012) . - 09 p.
Mots-clés : Abrasion Aerodynamics Aerospace components Aerospace propulsion Friction Machine bearings Rotors Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air/gas foil bearings (AFB) have shown a promise in high-speed micro to mid-sized turbomachinery. Compared to rolling element bearings, AFBs do not require oil lubrication circuits and seals, allowing the system to be less complicated and more environment-friendly. Due to the smaller number of parts required to support the rotor and no lubrication/seal system, AFBs provide compact solution to oil-free turbomachinery development.While foil bearing technology is mature in small industrial machines and power generation turbines, its application to aero-propulsion systems has been prohibited due to the reliability issues relevant to unique aero-propulsion environments such as severe rubbing due to the very slow acceleration of typically heavy rotors. This paper presents a hybrid air foil bearing (a combination of hydrostatic and hydrodynamic) with 102 mm in diameter designed for aero-propulsion applications, and preliminary test results on start-stop friction characteristics and thermal behavior at low speeds below 10,000 rpm are presented. The bearing could withstand 1000 start/stop cycles with 6 rev/s2 acceleration under a static load of 356 N (43.4 kPa). DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000003 [...]
in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 12 p.
Titre : Thermohydrodynamic analyses of bump air foil bearings with detailed thermal model of foil structures and rotor Type de document : texte imprimé Auteurs : Donghyun Lee, Auteur ; Daejong Kim, Auteur Année de publication : 2011 Article en page(s) : 12 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Convection Foils Machine bearings Rotors Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A new thermohydrodynamic analysis model for bump air foil bearings with a detailed thermal model of bump foil structures and rotor is presented. In the developed model, temperatures of lubricating air film, top foil, bump foils, bearing sleeve, and rotor are calculated simultaneously through an iterative process. Reynolds equation and 3D energy equation were applied to the air film, and energy equations were applied to all the other structures around the bearing. Energy and momentum equations were applied to cooling channels to predict spatial temperature distribution along the cooling channels. The thermal growth of the rotor, foil structure, bearing sleeve, and centrifugal growth of the rotor are also considered. For the accuracy of the model, effective heat transfer resistance between the top foil and bearing sleeve was measured for various conditions and implemented into the thermal analysis around the cooling channels. The model was also bench marked with published experimental results for verifications. Using a developed model, parametric studies were performed with different bearing nominal clearances, applied loads, rotating speeds, and cooling conditions through channels. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Thermohydrodynamic analyses of bump air foil bearings with detailed thermal model of foil structures and rotor [texte imprimé] / Donghyun Lee, Auteur ; Daejong Kim, Auteur . - 2011 . - 12 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 12 p.
Mots-clés : Convection Foils Machine bearings Rotors Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A new thermohydrodynamic analysis model for bump air foil bearings with a detailed thermal model of bump foil structures and rotor is presented. In the developed model, temperatures of lubricating air film, top foil, bump foils, bearing sleeve, and rotor are calculated simultaneously through an iterative process. Reynolds equation and 3D energy equation were applied to the air film, and energy equations were applied to all the other structures around the bearing. Energy and momentum equations were applied to cooling channels to predict spatial temperature distribution along the cooling channels. The thermal growth of the rotor, foil structure, bearing sleeve, and centrifugal growth of the rotor are also considered. For the accuracy of the model, effective heat transfer resistance between the top foil and bearing sleeve was measured for various conditions and implemented into the thermal analysis around the cooling channels. The model was also bench marked with published experimental results for verifications. Using a developed model, parametric studies were performed with different bearing nominal clearances, applied loads, rotating speeds, and cooling conditions through channels. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]
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