Gas Foil Thrust Bearings Research Articles

Preliminary Studies on Gas Foil Thrust Bearings with Stepped Foils

Preliminary Studies on Gas Foil Thrust Bearings with Stepped Foils

A comprehensive analysis of gas film pressure distribution in gas foil thrust bearings with PVDF sensor array

This research introduces an innovative approach for evaluating gas film pressure distribution in gas foil thrust bearings (GFTBs) utilizing polyvinylidene fluoride (PVDF) sensor arrays. Chosen for their exceptional sensitivity and rapid response, these sensors facilitate precise pressure analysis across various operational scenarios. The study investigates the pressure of integral and circumferentially separated GFTBs through experiments at 12 krpm to 16 krpm and loads of 60N to 120 N. The findings, derived from detailed PVDF sensor data and interpolation analysis, indicate that bearings with circumferential separation achieve more uniform pressure distributions. Experiments under extreme load conditions demonstrate that the separated type has a higher load-bearing capacity. This presents a novel PVDF-based measurement technique and advances the understanding of GFTB dynamics by correlating pressure distribution with operational parameters, thereby offering potential improvements in bearing design and performance.

Theoretical and experimental research on static stiffness, performance, and lift-off characteristics of multi-layer gas foil thrust bearings

In this study, a new comprehensive fully coupled elastic-hydrodynamic model is developed for a multi-layer gas foil thrust bearing (GFTB). The interaction effects among the top foil, back board, middle foil, and bottom foil, as well as the Coulomb friction effect, are considered. The stiffness and static characteristics obtained by the experimental and theoretical approaches are in good agreement, which verifies the accuracy of the model. The contribution of each foil layer to the overall stiffness and the load-carrying mechanism are analyzed. Interaction effects of the load, preload, and rotational speed on the static performance are investigated comprehensively. Furthermore, start-stop tests are performed to achieve the lift-off speed, start-up torque, and shut-down torque under various operating conditions.

Optimal Design of Boundary Angle for Gas Foil Thrust Bearing Thermal Performance

As the energy density and efficiency requirements of air compressors continue to increase, gas foil thrust bearings face a high risk of thermal failure due to their elevated speed and limited cooling space. This paper proposes a novel structure for gas foil thrust bearings with enhanced thermal characteristics. A thermo-elastic–hydrodynamic model is developed using a thermal-fluid–solid interaction approach to investigate aerodynamic and thermal performance. The load capacity and thermal characteristics of nine different boundary angles are analyzed. The model is validated, and the actual characteristics of gas foil bearings with various boundary angles are examined using a test rig. The results indicate that, compared to conventional gas foil thrust bearings with a boundary angle of 0°, the new structure with a boundary angle ranging from −10° to −5° not only maintains the load carrying capacity but also improves thermal characteristics. Furthermore, this improvement becomes more pronounced with higher rotational speeds. Therefore, the proposed optimization is advantageous in reducing the risk of thermal failure.

Optimizing Load Capacity Predictions in Gas Foil Thrust Bearings: A Novel Full-Ramp Model

Gas film thickness significantly influences the performance prediction of Gas Foil Thrust Bearings (GFTB). However, the Classical Model (CM) for GFTBs exhibits inaccuracies in describing gas film thickness. In this paper, we explore the differences in the details of gas film thickness modeling and propose a Parallel Segmentation Model (PSM), which fixes the errors of the CM in describing the gas film thickness in the ramp section, and a Full-Ramp Model (FRM), to which a more realistic description of the gas film in the flat section is also added. Comparative analysis, utilizing a publicly available test dataset based on the open-source GFTB structure, establishes that the FRM surpasses the CM and PSM in accurately predicting load capacity. In-depth analysis shows that the location of the minimum gas film thickness for determining the load capacity is located at the innermost circle of the free end of the top foil, whereas the FRM is subjected to the same load with a larger film thickness at this location, which may be due to the unique geometry of the top foil of the FRM. Subsequently, employing the FRM, a parametric study explores load capacity in GFTB, considering variables such as ramp height, top foil thickness, bump foil stiffness, ramp section extent, and top foil area. The results demonstrate that GFTB load capacity exhibits a linear increase with the expansion of the top foil area. Moreover, the load capacity increases with augmented top foil thickness and bump foil stiffness, albeit at a decreasing rate. Additionally, an increase in ramp section extent initially enhances load capacity, reaching a maximum value before declining. Similarly, an increase in ramp height initially augments load capacity, attaining a maximum before subsequent diminution.

Static performance analysis of gas foil thrust bearings under inclined thrust disc considering the slip flow effect

As one of the important components in air compressors for fuel cell vehicles, the static performance of the gas foil thrust bearings greatly affects the operating stability of the rotor system. In actual operation, thrust disc tilt and the slip flow effect often occur, which will change the characteristics of bearings. Therefore, this paper focuses on the static performance of gas foil thrust bearings under tilting conditions with account of the slip flow effect. Firstly, the gas film thickness equation is established when the thrust disc is inclined, and the Reynolds equation is modified by the boundary slip conditions. Secondly, the load capacity and friction torque of bearings are solved by the finite difference method and successive over-relaxation method. Finally, the sensitivity of rigid and elastic bearings to tilt angles is analyzed by comparing the static characteristics under tilting conditions. The results show that the load capacity will be overestimated without considering the slip flow effect, and the tilting of the thrust disc increases both the load capacity and friction torque. Furthermore, compared with rigid bearings, elastic foil bearings have better adaptability to tilting conditions, which is conducive to the stable operation of the rotor system.

Static Performance Measurements and Model Predictions of Gas Foil Thrust Bearing with Curved Incline Geometry

Gas foil thrust bearings (GFTBs) have been successfully used to support the axial load of oil-free microturbomachinery with low drag friction due to the low viscosity of gas or air used as a bearing lubricant. However, the widespread use of GFTBs in various high-power turbomachinery still needs reliable test data and an accurate predictive model. This research measures the height profile of a test GFTB to determine its actual incline geometry and estimate the drag torque of the GFTB. The measured GFTB height profile demonstrates that the incline geometry is closer to a quadratic curve than a line, which has been conventionally used to model GFTBs mathematically. The newly developed GFTB test rig is used to measure the lift-off speed, drag torque, and maximum load capacity of the test GFTB. A series of rotor speed-up tests estimate that the lift-off speeds of the GFTB increase with the increase in preloads. The maximum load capacity is determined by increasing the static load on the GFTB until a sudden sharp peak in the drag torque appears. The new GFTB model using quadratic incline geometry is in suitable agreement with the measured height profile of the GFTB incline and measured drag torque during the load capacity test. In addition, a comparison of the predicted GFTB performances reveals that the quadratic incline geometry model predicts a higher load capacity than the linear model.

Thermal analysis and optimization of bionic cooling channels of gas foil thrust bearings

Under high-temperature conditions, heat evacuation of foil bearing has a significant impact on bearing performance, including loading performance and reliability. During bearing operation, viscous dissipative heat in the lubricant gas film is the main source of heat generation. For foil bearings, enhancing the heat evacuation efficiency is essential to extend the bearing service life in high-temperature environments. For heat evacuation, foil-side cooling is a very effective method. For more in-depth analysis of thermal characteristics of the foil bearing, a three-dimensional (3D) thermal-elasto-hydrodynamic (TEHD) coupling model of multi-leaf thrust foil bearing (MLTFB) with cooling channel is established in this paper. In view of the good heat transfer performance and more uniform gas velocity distribution in bionic flow channels, various bionic cooling channels of foil bearings are proposed and the structural parameters are optimized. The effects of cooling channel type, cooling channel width, span ratio, cooling gas supply mode, and rotational speed on the thermal and loading performance of foil bearings are investigated. The studies demonstrate that the spider net round cooling channel exhibits higher heat transfer performance and improved uniformity of temperature. Compared to the cooling gas supply from inner edge, the cooling gas supply from the outer edge proves to be more effective. The maximum temperature of lubricant gas film can be greatly reduced with wider cooling channels and a smaller channel span at the outer edge. The maximum temperature of lubricant gas film and bearing load are reduced as the Reynolds number of cooling gas increases. There exists an optimal Reynolds number that can achieve the highest uniformity of temperature.

Numerical Investigation of Bump Foil Configurations Effect on Gas Foil Thrust Bearing Performance Based on a Thermos-Elastic-Hydrodynamic Model

The performance of gas foil thrust bearings is critical to the successful design and operation of the high axial load rotatory machines that employ gas foil bearings. However, our understanding of gas foil thrust bearings remains incomplete. To enhance our understanding and predict the performance of gas foil thrust bearings, we have established a detailed three-dimensional thermo-elastic-hydrodynamic model of a gas foil thrust bearing based on a fluid-thermal-structure interaction approach in this study. To validate the accuracy of our model, a gas foil thrust bearing test rig was developed. Moreover, we present a numerical investigation of the influence of bump foil configurations on gas foil thrust bearing performance. The results show that the gas foil thrust bearing that fixes the bump foil at the trailing edge and splits the bump foil into several strips exhibits a 36.4% increase in load capacity compared to the gas foil thrust bearing that fixes a whole piece of bump foil at the leading edge. Fixing the bump foil at the trailing edge and splitting it into several strips effectively decreases power loss and reduces the risk of bearing thermal failure.

Optimal design of top-foil wedge shape for a specific multi-layer gas foil thrust bearing by considering aerodynamic and thermal performances

Optimal design of top-foil wedge shape for a specific multi-layer gas foil thrust bearing by considering aerodynamic and thermal performances

A comparative study on inflow schemes of radial throughflow cooling for thermal management of a specific multi-layer gas foil thrust bearing

In order to illustrate the effects of radial cooling throughflow on the aerodynamic and thermal behaviors of gas foil thrust bearing, a three-dimensional fluid-solid coupled numerical investigation is conducted for a specific multi-layer gas foil thrust bearing under stable operating conditions in the present study, with two inflow schemes adopted, referred as radially-inward inflow scheme and radially-outward inflow scheme, respectively. The results show that the flow fields and the thermal behavior within the gas foil thrust bearings under the two inflow schemes are significantly different due to the difference in the inflow direction and the effect of centrifugal force caused by the high-speed rotation. The radial cooling throughflow can greatly alleviate the high temperatures in the film layer and improve the cooling capacity, but the increase of mass flow rate causes a non-monotonic change of static bearing load and an enhancement of viscous-shearing heat, as well as a significant rise of the air supply pressure. The radially-inward inflow scheme allows a lower peak temperature and a more uniform temperature distribution on the thrust plate and foil surfaces, while the radially-outward inflow scheme provides a lower area-averaged temperature and consumes less air supply pressure.

A Numerical Analysis of the Nonlinear Dynamics of Shimmed Conical Gas Foil Bearings

Conical gas foil bearings (CGFBs) have the potential to halve the number of necessary bearings in a conventional rotor system supported by gas foil bearings. Transient simulations of gas foil journal bearings and gas foil thrust bearings have proven their necessity to accurately predict the safe operating range of such bearings. This work presents the first transient model able to simulate the three-dimensional dynamics of CGFBs. The static behaviour of a single CGFB with a uniform bearing clearance is compared to a CGFB modified by thin metal shims and the resulting advantages of shimmed CGFBs are discussed. An investigation of the linear stability behaviour shows that the axial load of the bearing determines the stability of the equilibrium position. Furthermore, three transient simulations demonstrate the capability of the presented model to describe the nonlinear dynamics of a shimmed CGFB such as the occurrence of stable limit cycles and self-excited sub- and super-synchronous vibrations with and without a rotor unbalance. Additionally, waterfall diagrams are used to investigate the frequency response for different rotational speeds. The novel findings of this work are the importance of a non-uniform bearing clearance for the functionality of a CGFB and the identification of the axial force as a critical factor in maintaining bearing stability. These findings are specific to CGFBs and have not been discussed or mentioned in previous works.

Static and dynamic characteristics of aerodynamic thrust bearings based on fluid-thermal-structural interaction approach

The prominent thermal management problem makes it particularly important to predict the thermo-elastic behavior of hydrodynamic bearings. In this study, a coupling model of lubrication film hydrodynamics and rotor-bearing thermal elasticity mechanics was developed. The variation laws of thermal and static characteristics of gas foil thrust bearing were analyzed. The dynamic characteristics of the coupling model were determined using the perturbation method. The results show that ignoring the influence of foil and rotor thermal growth makes the predicted value of maximum gas film pressure low. When the friction coefficient is 0.6, the gas film pressure is underestimated by 29.8%. The temperature is overestimated when the film thickness is less than 8 μm, and the temperature is underestimated when the friction coefficient is greater than 0.3. The stiffness and damping coefficients are underestimated, up to 17.8% and 10.7% respectively.

Load-carrying characteristics of bump-type gas foil thrust bearings

The load capacity improvement of gas foil thrust bearings (GFTBs) is crucial in high-speed turbomachinery, which relies on the advanced design of foil structures and urgently requires a deep understanding based on comprehensive models. This paper presents an exhaustive model of GFTB combining isoparametric elements with contact mechanics, which enables the analysis of arbitrarily shaped foils. The proposed model considers bump interactions and frictional forces as well as the exact geometry of foils and bump height errors. Its accuracy is verified by comparison with commercial software simulations, experimental data and literature results. The impact of the bump foil arrangement along the radial and circumferential directions has been thoroughly analyzed based on the developed model. This work also fills a gap in the literature by obtaining the effects of bump height errors on bearing load-carrying performance. A drastic reduction of load capacity is observed when considering the bump height errors, and the reasons are explained in detail through analyzing the aero-elastic characteristics of fluid field. The results in this study can be instructive for bearing designers.

The Fluid-Structure-Thermal Performance Analysis of Gas Foil Thrust Bearing by Using Computational Fluid Dynamics

This paper presents a detailed three-dimensional (3D) thermo-elastic-hydrodynamic (TEHD) multi-physics model of the bump-type gas foil thrust bearing based on computational fluid dynamics (CFD). In this model, the moving mesh technology is applied in the fluid flow domain, and the new boundary condition of fully developed flow is applied at the inlet and outlet boundaries, which is consistent with the continuous property of fluid flow and has better convergence performance in CFD. The groove between pads is set as the symmetry boundary. The contact pairs with Coulomb friction and contact/separation behaviors are considered in the structure deformation and heat transfer. The simulation results indicated that the boundary pressure has a significant influence on the foil deformation. It also revealed the heat flux transfer path and temperature distribution in the gas foil thrust-bearing (GFTB) system.

Investigations on the Load Capacity of Multilayer Foil Thrust Bearing Based on an Updated Complete Model

Abstract The multilayer gas foil thrust bearing (MLFTB) has four layers of foil structures with each having unique configuration and function. In this article, an updated complete model of the overlapped foil layers of MLFTB is established to calculate more accurate foil deformations and bearing performance by considering sufficient possibilities of separations between adjacent foil layers. The accuracy of the model is validated through the load capacity tests of MLFTB, which is presented for the first time in open publications. Based on the complete model, influences of individual and combined key foil structural factors on bearing load-carrying performance and top foil deformations are studied, revealing the function mechanism of each foil layer and obtaining the method of adjusting two-dimensional stiffness distributions. Furthermore, parametric optimizations toward improving the load capacity of this type of foil thrust bearing are conducted based on a developed algorithm. This study provides sufficient theoretical knowledge and designing methods for further investigations of MLFTB.

Effect of herringbone groove structure parameters on the static performance of gas foil herringbone groove thrust bearings

The application of foil bearings technology into high speed and heavy load turbine machinery with high axial force is limited because of the insufficient load capacity of gas foil thrust bearings. This paper presents a new type gas foil thrust bearing, engraving the herringbone groove on the top foil surface of gas thrust foil bearing, relying on the pumping effect of herringbone grooves, so that the bearing load capacity of gas foil thrust bearings can be further improved by using the secondary pressure boosting effect of herringbone grooves on the basis of taper dynamic pressure effect. The physical models of non-groove gas foil thrust bearing and gas foil herringbone groove thrust bearings are established. The Reynolds equation, gas film thickness equation and foil deformation equation are coupling solved by finite difference method to obtain gas film thickness distribution and gas film pressure distribution for non-groove and herringbone grooves gas foil thrust bearing. The effects of the number of grooves, groove depth, groove width ratio, groove angle of the herringbone groove and the Taper inlet height on the friction torque, bearing load capacity and ultimate load capacity of the herringbone grooves gas foil thrust bearing are researched. Furthermore, when compared to the traditional non-groove gas foil thrust bearing, the optimal herringbone groove structure parameters are obtained, and a feasible method for optimizing the performance of gas foil thrust bearings is proposed.

Simulation and Experimental Verification of Dynamic Characteristics on Gas Foil Thrust Bearings Based on Multi-Physics Three-Dimensional Computer Aided Engineering Methods

This paper presents a method to simulate the dynamic operating characteristics of a gas foil thrust bearing based on linear elastic support and constant ambient temperature to mimic the transient structure–fluid interactions. In the physical model, the top and bump foils are simply represented by an infinite number of Hookean springs attached to a solid wall with a small amount of deformation, whereas the gas film in the bearing is under quasi-steady lubrication flow conditions with hydrodynamic pressure distributed on the little-deformed top foil. A three-dimensional multi-physics model in a cylindrical coordinate system is established via a commercial computer-aided engineering software package to predict the nominal dynamic characteristics of the gas foil thrust bearing. To verify the multi-physics model, an experimental bench was built in-house to measure the thrust force on the support of the bearing. With the pertinent bearing parameters being entered into the package, the simulations agree well with the experimental thrust forces. As a further step, a simulation model of a clamped-rotor gas foil thrust bearing design was thoroughly investigated under nominal operating conditions, resulting in predictions of underdamped oscillations in rotor motions. The phenomenon could be described using a linear mass–spring–damper model that is dependent on the gas film thickness. The stiffness and damping coefficients could serve as a base reference for rotor dynamics analysis. This concludes the potential development of a digital twin for gas foil thrust bearing systems.

Numerical investigation of Thermo-aerodynamic characteristics of gas foil thrust bearing

• Distribution of flow and temperature field in micro-clearance of GFTB are studied. • Temperature caused by viscosity dissipation accounts for more than 90% of aerodynamic heat. • The film temperature distribution is different when with or without viscous dissipation. • Temperature varies directly with rotate speed and inversely with film thickness. • Increase of wedge factor lowers the temperature and leads to reflux at the inlet. This study aims to reveal the thermo-aerodynamic characteristics of gas foil thrust bearings in the presence or absence of viscosity dissipation. The lubrication models in the cross-section of the gas film have been described, and the term of viscosity dissipation in energy equations is decoupled. The influence of different factors on gas film temperature distribution is discussed and compared. The results show when considering viscosity dissipation, the peak temperature is located near the circumferential outlet and the side of the outer diameter where has more shear stress. However, with the absence of viscosity dissipation, the peak value takes place near the end of the convergence channel where the gas compression is the most severe. Contrary to the case that without viscosity dissipation, gas film temperature decreases with the increase of wedge factor in the presence of viscosity dissipation. As wedge height increases, backflow will occur at the bearing entrance, reducing inlet temperature. When rotational speed increases, the gas film temperature caused by viscous dissipation increases much faster. The increase of film thickness reduces film temperature and bearing performance rapidly, but has no effect on the temperature distribution. This study confirmed that viscosity dissipation plays a significant role in the temperature rise and flow field of gas foil thrust bearings. More specially, temperature rise in the presence of viscosity dissipation accounts for more than 90% of the aerodynamic heat. The results obtained in this study are significant because they provide basic design guidelines for a temperature rise of the gas film.

Performance investigation and feasibility study of novel gas foil thrust bearing for hydrogen fuel cell vehicles

Centrifugal air compressors are promising due to their zero emissions, long driving range, and wide fuel sources. The gas foil thrust bearing (GFTB) is considered as one of the key components in the centrifugal air compressor to guarantee the system is oil-free and reliable due to there is self-acting and high speed. However, the gas foil thrust bearings were all of lower capacity in previous research. In this study, the effects of each foil and nominal clearance on the static performance are developed experimentally. The optimal GFTB with higher capacity is obtained. The feasibility study of the proposed GFTB is carried out, which is installed on the ultra-high-speed centrifugal air compressor. The result shows that the proposed GFTB can run stably and efficiently in the full speed ring, and the high-pressure ratio and large flow rate of the air compressor also can be ensured. The results play an important role in guiding the stable operation of centrifugal air compressors applied in hydrogen fuel cell vehicles (HFCVs).