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Governing Body: China Association for Science

Organizer: Chinese Mechanical Engineering Society Guangzhou Mechanical Engineering Research Institute Co.,Ltd

Chief Editor: HE Shizhong

Address: No2,Xinrui Road,Huangpu,Guangzhou

Postcode: 510700

Telephone: 02032385313

Email: rhymf@gmeri.com

CN:CN44-1260/TH

ISSN:ISSN0254-0150

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    Volume 49,2024 Issue 6
    • Performance Analysis and Influence of Elevation Error on High Speed Circular Pad Thrust Bearing Supported by Disc Springs
      ZHANG Fan; HU Zhijian; LI Zhenhua; WANG Jianmei; YUAN Xiaoyang

      Abstract:Regarding the load-bearing performance of high-speed circular pad thrust bearings used in the shaft system of vertical dry gas sealed helium compressors,a lubrication performance calculation model and a stirring power consumption calculation formula for disc spring supported thrust bearings were established.Based on the model,the performance variation of circular pad thrust bearings with rotational speed and load were analyzed,and the influence of elevation error on bearing lubrication performance and support disc spring performance were also analyzed.The results show that the ratio of stirring power consumption to friction power consumption in bearings increases and decreases with the increase of speed and load,respectively.At the highest speed,stirring power consumption is more than twice that of friction power consumption.The elastic adaptive adjustment technology can effectively improve the impact of elevation error on the flatness of bearing pads.However,the larger the elevation error,the greater the difference in lubrication performance of each pad and the accumulated deformation energy of the disc springs.Therefore,for high-speed vertical rotor systems,the design of thrust bearings must consider the impact of stirring power consumption on bearing temperature rise,and further research is needed on the impact of elevation error on the stability of high-speed rotor systems.

    • Static Characteristic Analysis of Misaligned Gas Foil Texture Thrust Bearings
      HE Zhenpeng; WANG Zhi; YAN Guohua; LIU Yong; LUO Wendong; GUO Yuhang; ZOU Yuchen

      Abstract:In order to study the effects of the distribution,number,density,placement angle and depth of different shapes of texture on the bearing performance of the misaligned gas foil thrust bearing,the Reynolds equation for the gas foil thrust bearing was solved by combining Successive Over Relaxation (SOR) and the finite difference method (FDM),and the load carrying capacity and frictional moment of the bearing were obtained by MatLab simulation under different texture parameters.The results show that the bearing load carrying capacity is significantly increased when the texture is distributed at the junction of the base area and the wedge area of the thrust bearing compared to other distribution methods.The load carrying capacity and frictional moment of the bearing increase first and then decrease with the increase of the proportion of micro-texture.The bearing performance is best improved when the maximum cross section of different shaped texture is placed along the radial direction of the thrust bearing.The micro-texture can improve the bearing performance only when its depth reaches a certain range.It is found that there exists optimal number,density,and depth of micro-textures that can make the thrust bearing have a higher bearing load capacity at a smaller friction torque.Compared to the bearings without texture,the elliptical micro texture with optimal micro-texture parameters can increase the load carrying capacity by 41.22% and reduce the friction torque by 0.81%.

    • Research on Error Averaging Ability of Air Pad
      ZHANG Penghai

      Abstract:In order to investigated the main influencing factors of the error averaging ability of the orifice-compensated air bearing,an error motion prediction model of a single air pad was established,and the defined averaging coefficient was used to discuss the quantitative relationship among the error motion of the air pad,the form error of the rail and the structural parameters of the air pad.The results show that,for the long waves of the rail form error (with wave number from 0 to 1),when the wave number gradually increases,the averaging coefficient gradually decreases from 1 to close to 0.For the short waves of the rail form error (with wave number from 1 to 10),when the wave number is close to or equal to a positive integer,the average coefficient takes the minimum value close to 0.And when the wave number is close to or equal to a positive integer plus 0.5,the average coefficient takes the local maximum value less than 0.25.Among the structural parameters,the width of the air land has a great influence on the error averaging ability,while the air pad gap and the diameter of the orifice restrictor basically have no influence on the error averaging ability.When the moving speed is less than 10 000 mm/s,the moving speed has a very weak influence on the error averaging ability.

    • Numerical Analysis on Pressure Drop and Wind Resistance Temperature Rise of Stepped Inclined Grate Teeth Sealing
      LI Chi; ZHANG Bo; MA Zhuang; ZHANG Jingzhou; WANG Jiayou

      Abstract:To study the effects of rotational speed, inlet pressure, and the ratio of backlash to tooth width on the pressure drop and wind resistance temperature rise characteristics of inclined grate teeth seals, a two-dimensional stepped inclined grate seal model was established.Numerical simulation calculations were performed on the stepped inclined grate teeth seals to obtain the inlet and outlet pressure differences and wind resistance temperature rise under different speed, inlet pressure, and the ratio of backlash to tooth width, as well as the temperature and pressure of the jet at the last stage tooth gap.It is found that there is a high-temperature zone on the leeward side of the oblique grate tooth, which is caused by three factors,the friction effect of rotation,the step geometry and the mixing effect at the meeting point of two large-size vortices.The momentum exchange between the wall-attached large-size vortex and the main flow increases with the increase of rotational speed,while the momentum exchange between the main flow and the large-size vortex in the cavity weakens with the increase of rotational speed.The wind resistance temperature rise decreases with the increase of the ratio of backlash to tooth width, and increases with the increase of rotational speed, but the relationship with the inlet pressure is not obvious. The pressure difference between the inlet and outlet increases with the increase of rotational speed, and decreases with the increase of the ratio of backlash to tooth width. The pressure of the exit jet increases with the increase of the inlet pressure. The fitting formulas of pressure difference and wind resistance temperature rise coefficient were obtained respectively, and the fitting result was in line with expectations.

    • Effect of Cavitation on Sealing Performance of Inclined Groove Mechanical Seal
      LIAO Wenbo; ZHOU Jianfeng

      Abstract:The cavitation effect of lubricating film has a significant impact on the seal performance of hydrodynamic pressure mechanical seals.Kerosene-based magnetic fluid lubrication upstream pumping mechanical seal with inclined groove was taken as the research object.By considering the cavitation heat effect as well as the viscous temperature effect,the calculation model of lubricating fluid film was established to study the influences of working conditions and structural parameters on the seal performances using the volume fraction of gas phase in the liquid film as an indicator,and the results were compared with those based on the model only considering the viscous temperature effect.It is found that,due to the cavitation heat model considering the variation of saturated vapor pressure of liquid film medium with temperature,the opening force,leakage rate and volume fraction of vapor phase when considering the thermal effect of cavitation are smaller than the corresponding results when considering the viscosity-temperature effect only,but the variation regularity of each parameter is basically the same under the two conditions.The cavitation effect is enhanced by increasing the rotational speed and the groove diameter ratio,while the cavitation effect is weakened by increasing the inlet pressure,film thickness,radial angle and number of grooves.An increase in rotational speed,groove depth,radial angle,and groove diameter ratio will lead to an increase in leakage rate,while an increase in inlet pressure and groove number can improve sealing performance.

    • Research on Sealing Axial Aerodynamics of Air Flotation Air Circulation Machine
      XIAO Yunfeng; DENG Ruiyang; KONG Xiangyu; ZHANG Yinghan; SUN Xinyue

      Abstract:In view of the low accuracy of the theoretical empirical formula of axial force at the double-sided high-speed rotor end of the traditional air circulation machine,the numerical calculation takes a long time,this paper establishes a narrow gap calculation domain geometric model including double-sided high-speed rotor,and checks the accuracy of the model through experiments.On the basis of axial aerodynamic generation,the axial force is compared and calculated by theoretical formula method and CFD numerical calculation method.Based on the numerical simulation results of axial force,the calculation formula of axial force on the back side of the existing wheel is partially corrected,and a new set of axial aerodynamic calculation formula suitable for air flotation ACM is proposed,and the results show that the minimum error at the compressor end is reduced from 59% to 13% of the original formula,the maximum error is reduced from 261% to 75% of the original formula,the minimum error at the turbine end is reduced from 63% to 2% of the original formula,and the maximum error is reduced from 98% to 8% of the original formula.The new calculation method greatly reduces the error value of the axial force and aims to solve the problem that plagues the engineering side of how to accurately calculate the pneumatic axial force.

    • Static Performance Analysis of Integral Top Foil Gas Dynamic Thrust Bearings
      LIU Yuming; MA Xizhi; ZHENG Wenjie; CHENG Junkang; ZHAO Kai

      Abstract:The integral top foil gas dynamic pressure thrust bearing has the advantages of simple manufacturing process and high load capacity,which consists of several bearing sectors with independent bump foil,but has a complete annular top foil sheet.In order to investigate the working mechanism and static performance of this new bearing,the corresponding static performance analysis model was proposed and the cyclic boundary coupling condition was used to set the pressure at the inlet and outlet of the gas stream to be equal.The effects of the speed,minimum film thickness and wedge height on the static performance of the integral top foil thrust bearing were analyzed through numerical simulations,and the analysis results were compared with those of the separated top foil bearing under the same operating conditions.The results show that the top foil sheet of the integral top foil bearing will change from wedge-step to wedge-land geometry under load,and the trailing edge of the single tile sector will be bent upward due to deformation to produce a secondary wedging effect,thus forming two air film pressure peaks.And the integral top foil bearing also has a larger bearing area than the separated type bearing,so its load capacity will be higher.Due to the negative pressure zone at the top foil step,the optimal wedge height interval of the inegral top foil is delayed compared with the separated top foil,and a higher load capacity and a smaller friction torque can be achieved when the wedge height is around 50 μm.When the minimum film thickness is increased,both the load capacity and the frictional torque are reduced.

    • Research on Deformation of Split Type Carbon Ring Seal Structure under Force Load
      LI Lu; DING Xuexing; WANG Ruixia; XU Jie; HONG Xianzhi; BAO Xin

      Abstract:In order to explore the influence of the structural parameters of the split type carbon ring seal on the radial deformation of the sealing surface,the numerical calculation was used to solve the pressure control Reynolds equation to obtain the gas film pressure.The fluid-solid thermal coupling simulation was conducted in combination with the finite element analysis software to explore the influence of different structural parameters on the radial deformation of the carbon ring under specific working conditions,and the radial deformation characteristics of the main sealing surface was analyzed.The results show that the installation position of the anti-rotation pin has the greatest influence on the radial deformation of the carbon ring,and the radial deformation can be reduced by selecting the appropriate installation position.When the external convex structure is uneven and the ratio of the center angle is large,the radial deformation is small.The larger the ratio of the lap joints on both sides,the smaller the radial deformation.The selection of tension spring and compression spring has little influence on the radial deformation of carbon ring.The larger the spring pressure,the smaller the radial deformation.However,when the spring pressure is too high,it can easily lead to increased wear,fracture of the carbon ring,and even the failure of seal.The refore,appropriate spring pressure should be selected based on actual working conditions.The research results provide a reference for the structural optimization design of split carbon ring seals.

    • Dynamic Characteristics Analysis of Gas-Bearing Rotor System Based on Fluid-Structure Coupling
      MA Hailong; MA Wenqi; ZHENG Shaolin; QIN Yubin

      Abstract:The cutting force suffered by the machine tool in the cutting process can be assumed to be the combined force of the steady state force and the dynamic disturbing force.In order to investigate the dynamic characteristics of electric spindle system supported by gas bearings,sine wave was used as dynamic disturbance loading form,and the dynamic characteristics of a simplified model of a gas bearing rotor system were studied by combining the harmonic excitation method with the bidirectional fluid-structure coupling numerical simulation.The dynamic stiffness and damping coefficients were identified.Through modal analysis,the system vibration modes and natural frequencies of the rotor under different steady-state forces were obtained.The results show that with the increase of steady-state force,the growth rate of Kyy of the lower radial bearing is greater than that of Kxx,while the cross stiffness and cross damping are almost unchanged.The main stiffness of the lower radial bearing is greater than the cross stiffness,and the main damping is greater than the cross damping.When the steady-state force ranges from 50 N to 200 N,the y-shift at the lower end of the rotor first increases and then decreases with the increase of dynamic disturbance frequency.The resonance frequency of the system increases with the increase of the steady-state force.

    • Experimental Study on Dynamic Characteristics of Foil Dynamic Pressure Gas Bearing-Rotor System
      ZHANG Fei; JIA Chenhui; LI Dongdong; LU Yanhui; YANG Luqiang

      Abstract:Based on the lubrication analysis model and dynamic characteristics mathematical model of foil dynamic pressure gas bearing,the dynamic equation of foil dynamic pressure gas bearing-rotor system was established combining Newton’s mechanical equation,and the calculation method of the stiffness and damping coefficient was studied.The vibration and speed of the foil dynamic pressure gas bearing-rotor system was tested,and the stiffness and damping coefficient was calculated.The linear and nonlinear instability phenomena of the foil dynamic pressure gas bearing-rotor system during the acceleration process was analyzed combining the mapping method,and the influence of speed on the stiffness and damping coefficient was studied.The results show that the main stiffness coefficient of the foil dynamic pressure gas bearing rotor-system increases with the increase of speed,while the cross stiffness decreases with the increase of speed and the trend of change is relatively gentle.The damping coefficient decreases with the increase of speed.The damping of the system suppresses disturbances and the accumulation of low-frequency energy,avoiding foil vibration and effectively improving the stability of the system operation.The proposed dynamic characteristic coefficient calculation method,combined with gas lubrication theory and dynamic model,and combined with experimental testing,can effectively obtain the dynamic characteristics of the bearing-rotor system.

    • Research on Heat and Mass Transfer Law of High Speed Foil Face Gas Film Seal
      ZOU Yinrong; CHEN Yuan; LI Yuntang; LI Xiaolu; WANG Bingqing; JIN Jie; ZHANG Cong

      Abstract:To explore the thermal performance of high parameter compliant foil face gas film sealing and carry out structural optimization design.Based on fluid simulation analysis software,a thermal performance analysis model for foil face gas film seal was established.Considering the real gas effect of air medium,the gas flow and heat transfer characteristics of the sealing face were studied,and the influence of different working conditions and structural parameters on the highest and average temperatures of various fluids and solid domains on the sealing face was analyzed.The results show that the heat of the foil face gas film seal is mainly concentrated on the flat foil and the sealing dam.As the rotational speed increases or the inlet pressure and minimum gas film thickness decrease,the average and maximum temperatures of each fluid and solid domain of the sealing ring component increase.The average and maximum temperatures of each fluid and solid domain decrease with the increase of wedge height and pitch ratio.

    • The Load Capacity Properties of Spiral Groove Journal Gas Bearings under Various Reynolds Values
      ZHANG Xin; YIN Yufeng; TANG Jie

      Abstract:To investigate the variation of carrying capacity of a spiral-groove gas radial bearing under different Reynolds numbers,a gas bearing lubrication model modified by Ng-Pan theory was established.The model was solved using the finite difference method to obtain the bearing characteristics under different Reynolds numbers.The effects of geometric parameters and groove parameters on carrying capacity were analyzed.The results show that the carrying capacity of the spiral-groove gas radial bearing in non-laminar lubrication state is greater than that in the laminar lubrication state.The geometric parameters of the bearing have a significant influence on the bearing characteristics.As the eccentricity increases,the bearing capacity increases divergently,and the difference between the bearing capacity in the non-laminar lubrication state and the laminar lubrication state increases.As the aspect ratio increases,the bearing capacity increases convergently.Among the groove parameters,groove width ratio and groove depth ratio have a significant impact on the bearing characteristics,and the bearing bearing capacity increases with the increase of groove width ratio and groove depth ratio.While the influence of the number of grooves on bearing bearing capacity is not significant,and the helix angle only has a significant impact on bearing capacity in non-laminar lubrication state.The inlet pressure of bearing has obvious influence on carrying capacity.As the inlet pressure increases,the bearing capacity increases in laminar lubrication state and fluctuates greatly in non-laminar lubrication state.

    • Analysis of Static Characteristics of Bidirectional Pressure Equalizing Groove Throttling Static Pressure Gas Bearings
      LU Ran; QI Xiangyang; FU Shuangsong; MA Wenzhu; LI Zeyan; WU Chengliang

      Abstract:To further optimize the static performance of static pressure gas radial bearings,a composite throttling type static pressure gas radial bearing with axial and circumferential pressure equalizing grooves was proposed based on the traditional small hole throttling.Fluent was used to compare and analyze the static characteristics of the bearings with traditional orifice throttling and different forms of composite throttling,and the influence of the cross-sectional shape of the equalizing groove and the gas supply pressure on the static characteristics of bearings was explored.The orthogonal experiments were used to explore the influence of the structural parameters of the restrictor on the bearing characteristics.The results show that the composite throttling static pressure gas bearing improves the static characteristics of the bearing to a certain extent,and the best effect is achieved when the pressure equalizing groove is arranged in a “mouth” shape and the cross-sectional shape is rectangular.An increase in gas supply pressure can also improve the static characteristics of bearings.The influence of the diameter of the orifice and the depth of the equalizing groove on the static characteristics of bearings is larger than that of the depth of the orifice and width of the equalizing groove.The increase in the diameter of the orifice and the depth of the equalizing groove results in a trend of first increasing and then decreasing in the bearing capacity and stiffness of bearings.

    • Texture Design of Inner Race and Its Effect on Two-Phase Flow in Angular Contact Ball Bearing with Oil-Air Lubrication
      WANG Baomin; YAN Ruixiang; FANG Wenbo; ZHU Shengqiao; LIU Hongqin

      Abstract:Aimed at the problem of low lubricant oil and poor retention on the inner ring of angular contact ball bearings with oil-air lubrication,a lubrication efficiency enhancement method was proposed by designing circular dimple-shaped surface texture on bearing inner ring raceway.Based on the air-liquid two-phase flow model and the multiple reference frame method,the numerical model of oil-air two-phase flow inside textured angular contact ball bearing cavity was established,and the effect of inner ring texture on bearing oil-air two-phase flow was analyzed.The results show that the surface texture can significantly improve lubricant oil retention on the inner ring,while improving the distribution of lubricant oil inside bearing cavity.The oil-air two-phase flow is more irregular in the vicinity of the micro texture,and the resulting pressure and velocity gradients are conducive to improving the bearing capacity of oil film.With the increase of rotational speed,the lubrication efficiency enhancement of inner ring texture is relatively weakened,while with the increase of oil supply,the lubrication efficiency enhancement of inner ring texture is more significant.

    • Embedded Improvement of Ventilation Structure in Aircraft Engine Bearing Cavity and Study on Oil Gas Two Phase Flow Characteristics
      YAN Yang; REN Guozhe; XU Wenfeng; ZHAO Huan; SUN Dan; ZHANG Chengfeng

      Abstract:In order to study the oil-gas two-phase flow characteristics in the bearing chamber of an aeroengine and improve the oil return effect of lubricating oil,an embedded improvement scheme was proposed for the ventilation structure of the bearing chamber.A two-phase flow solution model for the bearing chamber based on the Euler-Euler method was established,and the flow characteristics and oil return characteristics of conventional bearing chamber and embedded improvement bearing chamber under different operating conditions were analyzed.The results show that after the embedded improvement of the ventilation structure of the conventional bearing chamber,the lubricating oil is blocked by the embedded ventilation wall.Under the action of air shear force and gravity,the lubricating oil on the right side of the ventilation port moves downstream through the ventilation port,reducing the amount of lubricating oil flowing out of the ventilation port and increasing the amount of lubricating oil flowing out of the return port,thus significantly improving the return oil efficiency.As the embedding depth increases,the lubricating oil flowing out of the vent is further suppressed,the volume fraction of the lubricating oil in the chamber further increases,and the return oil efficiency is further improved.Compared with conventional bearing cavities,when the oil flow rate is 200 L/h and the rotation speed is 15 000 r/min,the embedded improvement scheme has the most significant improvement in oil return efficiency,and the oil return efficiency is increased by 16.72%,18.80%,and 20.19% respectively for the improved schemes with embedded depths of 8 mm,10 mm,and 12 mm.

    • Optimization of Load-Carrying Capacity Performance of Bump Foil Dynamic Pressure Gas Bearing Based on Fluid-Structure Interaction
      LI Dongdong; JIA Chenhui; ZHANG Fei; LU Yanhui; YANG Luqiang

      Abstract:Based on the finite element software Ansys Workbench,the finite element model of the motion of the bump foil dynamic pressure gas bearing in the compressible fluid medium was established,and the fluid-structure coupling numerical simulation of the motion state of the bearing was carried out by using the 6DOF dynamic grid calculation method.The influence of different speed and bump foil structure parameters (length ratio,height and thickness of bump foil) on bearing performance was discussed.The simulation results show that the distribution of the bearing gas film pressure corresponds to the deformation of the flat foil,indicating that the proposed fluid-structure coupling method can effectively reflect the lubrication state of the bump foil dynamic pressure gas bearing.With the increase of rotational speed,the dynamic pressure effect of the bearing is enhanced continuously,the load-carrying capacity increases,and the structural deformation of flat foil is increased,resulting in fluctuations in the convergence zone of gas film pressure.With the increase of the length ratio of the bump foil and the thickness of the bump foil,the load-carrying capacity increases rapidly at first and then becomes stable,while the height of the bump foil has little effect on the load-carrying capacity,indicating that the load-carrying capacity can be improved by increasing the length ratio of the bump foil and the thickness of the bump foil appropriately.

    • Heat Transfer Characteristics of Double Air-cooled External Rotor Permanent Magnet Synchronous Motor with Different Dynamic Seal Structures
      GAO Congcong; NING Jianrong; ZHANG Jianyi

      Abstract:In order to strengthen the sealing at the small clearance of the stator-based dual air-cooled external rotor permanent magnet synchronous motor and ensuring the heat dissipation of the clearance,the numerical simulations of the flow field and heat transfer characteristics of the small clearance of the motor with different labyrinth sealing structures under different working conditions were carried out by using computational fluid dynamics,taking into account the rotational factor.The influences of different labyrinth sealing structures at the upper and lower clearance on the overall sealing performance of the motor and the heat dissipation of the stator sidewalls were explored by analyzing the pressure and velocity at the clearance.The sealing performance and heat dissipation were evaluated using leakage and Nusselt number as evaluation factors.The results show that when the axial fan operates with suction,it is more conducive to improving the sealing performance of the motor and ensuring the heat dissipation at the clearance.Adding labyrinth seals at the upper and lower stator clearances can effectively improve the sealing performance of the motor in the dual air-cooled system,and the greater the total pressure drop of the sealing structure at the upper and lower clearances,the smaller the leakage.The average Nussell number of the stator sidewall at the clearance will decrease due to the addition of the labyrinth seal.When the incoming temperature is lower than the wall temperature,the extent of decrease of average Nussell number will increase with the increase of the flow-blocking effect of the sealing structure,and when the incoming temperature is higher than the wall temperature,the extent of decrease of average Nussell number will increase with the decrease of the flow-blocking effect and the notch vortex strength.Compared to the unsealed structure,the stator side double groove structure effectively ensures the heat dissipation of the clearances while improving the overall sealing performance of the motor.The research results provide a reference for the design of the sealing and heat dissipation structure at the internal clearances of the external rotor permanent magnet synchronous motor.

    • Design and Loading Characteristics Analysis of Aerostatic Bearings for Radial Inflow Turbogenerator
      WU Tan; CAI Shuting; GAO Xiaolei; GUO Baoguo; ZHANG Lijun

      Abstract:In order to improve the load carrying capacity and stiffness of the aerostatic bearings of the radial inflow turbogenerator for the organic Rankine cycle (ORC) system,the aerostatic bearings with R245fa as the lubricating medium was designed by gauge pressure ratio method,and the effects of rotor eccentricity,orifice size and inlet pressure on the load carrying capacity and stiffness of the aerostatic bearings were analyzed.The results show that the bearing load capacity and stiffness increase with the increase of speeds under the same air supply pressures.At the same speed,the load capacity and stiffness of the bearing at the air supply pressure of 0.7 MPa is slightly higher than those at other air supply pressures.The greater the eccentricity of the aerostatic bearings,the greater the load carrying capacity.The load carrying capacity and stiffness of the aerostatic bearings increases with the increase of rotational speeds under the same air supply hole diameter.The larger the air supply hole diameters,the greater the bearing capacity and stiffness of the aerostatic bearings.

    • Optimization of Cylinder Side Sealing Teeth for Double Side Labyrinth Sealing Structure Based on CFD
      LI Zhenghui; ZHANG Xiuheng; LI Ying; WANG Yunshuai

      Abstract:Aimed at the problem of internal flow field and leakage of compressor labyrinth seal,optimization research was carried out on the cylinder side sealing teeth in the double-sided labyrinth seal structure.Three types of cylinder side sealing tooth structures,such as triangular,rectangular,and cycloidal were designed,different geometric ratios of tooth height,tooth width,and sealing tooth clearance between the cylinder side and piston side sealing teeth were selected from 1∶2 to 1∶6,and the double-sided sealing models with different sealing tooth structures were established.The sealing performance of the double-sided sealing models was analyzed by CFD dynamic mesh transient simulation,and was compared with that of the single-sided sealing tooth structure model.The results show that the leakage of the double-sided sealing tooth structures reduced by 25.8% to 56.0% compared with the single-sided sealing tooth structure.The sealing performance of cylinder side sealing teeth with three different shapes is in descending order:triangular,rectangular,and cycloidal.Among the five different geometric ratios of cylinder side sealing tooth models,the sealing performance is arranged from strong to weak as 1∶4,1∶5,1∶2,1∶6,and 1∶3.The sealing performance of the triangular cylinder side sealing tooth structure that the geometric ratio of the sealing teeth between cylinder side and piston side is 1∶4 is the best,and the leakage rate is reduced by 56% compared to the single-sided sealing tooth structure.

    • Esign and Experimental Study on Bump-Foil Gas Bearing Used in Centrifugal Air Compressor
      HUA Wencan; YANG Shanju; WANG Qi; ZHANG Lijun; ZENG Yiming

      Abstract:The bump foil dynamic gas bearing was developed for the hydrogen fuel cell centrifugal air compressor with a rated power of 26 kW and a spindle diameter of 22 mm.The static and dynamic characteristics experiments and durability experiments of the bearings were carried out on the built experimental bench,and the bearing hysteresis curves and static stiffness curves were obtained,as well as the three-dimensional spectrum diagram of the air compressor rotor system’s acceleration and deceleration vibration,and the time domain diagram from 30 000 r/min to 95 000 r/min.The experimental results show that there exits a nonlinear characteristics between the static stiffness and the displacement of the bearing.After more than 100 000 times of starts and stops of the air compressor,there is only slight wear on the surface of the flat foil,and there is almost no change in the height of the bump foil,indicating that the bearing has good durability.The rotor vibration is mainly on the fundamental frequency,the main amplitude is about 1 μm in the full speed range,and there was no obvious low-frequency and high-frequency vibration.The maximum stable speed of the two-stage air bearing centrifugal air compressor can reach 95 000 r/min,and it exhibits good thermal performance.

    • Numerical Analysis of Working Characteristics of Aerostatic Spherical Gas Bearings
      ZHANG Ke; LIU Dapeng

      Abstract:The Reynolds equation was modified in response the problem that the continuity equation used in the derivation of the conventional master Reynolds equation was not applicable at the throttle bore of a hydrostatic gas bearing.Based on the angle-preserving transformation method,Newton’s iteration method,finite difference method and relaxation iteration method,the modified Reynolds equation was calculated for the region of the bearing gas film flow field,and the distribution of gas film pressure along the circumferential direction at the apex angle of the orifice distribution cone was obtained under different air supply pressures.The influence of air supply pressure and radial eccentricity on the radial load capacity and axial load capacity of aerostatic air spherical bearings was analyzed.The results show that the radial bearing capacity and axial bearing capacity of aerostatic spherical air bearings are affected by the coupling of static pressure effect and dynamic pressure effect.The greater the air supply pressure,the greater the radial bearing capacity and axial bearing capacity,and the greater the air consumption.The greater the radial eccentricity,the greater the radial bearing capacity and axial bearing capacity,and the radial eccentricity has little effect on the gas consumption.The larger the diameter of the orifice,the greater the radial bearing capacity,axial bearing capacity and air consumption.

    • Static Characterization of Porous Tilting Pad Bearing Considering Pivot Offset
      XU Shicheng; LIU Jiabao; XIE Shaozhang; GUO Xueyan; XIA Peng

      Abstract:In order to investigate the effect of pad pivot offset on the static performance of porous tilting pad bearings,a thermal hybrid lubrication model of porous tilting pad bearings was proposed,and Fluent software was used to analyze the static characteristics of the bearings.The grid iteration algorithm and the pad motion UDF were used to simulate the motion and swing of each pad of the bearing along the pivot,and the effects of eccentricity,rotor speed,gas supply pressure and pivot offset on bearing load capacity,mass leakage,friction torque and temperature rise were studied.The results show that increasing the bearing pivot offset can improve the bearing load capacity,especially under conditions of high eccentricity,high speed,and low gas supply pressure,the increase in bearing load is more significant.When the eccentricity and speed are the same,appropriate pivot offset can significantly reduce the gas consumption of the bearing.However,pivot offset increases the frictional torque,causing the rotor temperature to rise.Therefore,a reasonable pivot offset should be selected to avoid the adverse effects of temperature rise on the bearings.This study provide a reference for the optimization design of porous tilting pad bearings.

    • Study on Rotordynamic Characteristics for Three Labyrinth Seals with Inlet Preswirl
      XIANG Songying; LIU Lijun; WANG Sichen

      Abstract:To explore the dynamic characteristics of the rotors of labyrinth seal considering inlet preswirl,based on Murphy’s small displacement principle,the governing equations of steam flow excitation force and rotor vortex displacement were established,and a multi-frequency elliptical vortex model was built by user-defined functions.The exciting forces of three labyrinth seals,straight tooth labyrinth seal(SLS),inclined tooth labyrinth seal(ILS),stepped tooth labyrinth seal(STLS) were numerically solved under different inlet preswirl ratio,the seal dynamic characteristic coefficient was obtained by fast Fourier transform,and the stability of the rotor and the leakage of the seals were analyzed.The results show that the direct stiffness coefficients of the three labyrinth seals decrease first and then increase in the range of eddy frequency from 40 Hz to 180 Hz,showing a strong frequency correlation.While the influence of sealing structure and inlet preswirl on damping coefficient can be ignored.The damping coefficient slowly decreases to a negative value and then becomes stable with the increase of vortex frequency.STLS has the smallest damping coefficient and the worst stability,while ILS has the best stability.Increasing the inlet preswirl ratio will reduce the effective damping coefficient and lead to a decrease in leakage rate.STLS exhibits the best sealing performance under different preswirl conditions,with a 15% and 7% reduction in leakage compared to SLS and ILS,respectively.The cross stiffness of the three labyrinth seals increases from negative to positive in the studied vortex frequency range of 20 Hz to 200 Hz,while the effective damping decreases to negative.Therefore,the stability of the rotor system of the labyrinth seals is poor,which may induce rotor instability.

    • Study on Discharge Coefficient of Aerostatic Bearings Based on FLUENT
      DENG Zhifang; ZHANG Jianbo; CHEN Ce; ZHANG Kun; DING Boyao

      Abstract:When studying the characteristics of aerostatic bearings with orifices by solving the Reynolds equation,it is usually assumed that the discharge coefficient is a constant of 0.8,which may affect the accuracy of solving the Reynolds equation.A method which combined Fluent and Reynolds equation was proposed to obtain the discharge coefficient in the aerostatic thrust bearings with inherent orifices.The discharge coefficients were calculated by comparing the mass flow rate obtained by FLUENT and Reynolds equation simulations.The influence of parameters such as gas film thickness,gas supply pressure,and orifice diameter on the orifice coefficient was analyzed.The results indicate that the discharge coefficient increases first and then decreases with the increase of film thickness,decreases with the increase of gas supply pressure,and increases with the increase of orifice diameter.However,the discharge coefficient is not sensitive to changes in bearing radius and orifice length.The bearing capacity from solution of Reynolds equation with the discharge coefficient obtained by this solution method is agreement with that from FLUENT,verifying the correctness and feasibility of this solution method.

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