Gas Film Pressure Research Articles

Lubrication Characteristics of Dry-Gas Seals with Spiral Grooves

To obtain an optimal range of structural parameters for dry-gas seals with good performance, this study employed advanced sensing technology to monitor and analyze the internal flow characteristics of dry-gas seals in real time. Additionally, the validity of the calculation program was verified through experimentation. Using steady-state performance parameters as evaluation indices, a calculation model with lubrication characteristics was developed. The results indicate that when there are 12 grooves, the gas film pressure distribution is uniform and has a high value. At pressures greater than 2 MPa, the opening force, leakage, and gas film stiffness change significantly due to enhanced dynamic pressure effects with high-pressure differences, which reduces the local contact forces and frictional forces. At a constant speed, decreasing the gas film thickness increases the pressure difference while increasing both the opening force and film stiffness; however, at higher rotational speeds where the gas flow becomes non-uniform, the stability of the gas film is affected, leading to increased frictional forces. When there are between 10 and 16 grooves with depths ranging from 5.0 to 6.0 μm, dynamic pressure effects caused by pressure gradients become apparent, resulting in good dry-gas sealing performance being achieved. This research provides a theoretical reference for optimizing the design of dry-gas seals, as well as their steady-state seal performance.

A Study on the Steady and Dynamic Performance of Dry Gas Seals with Combined Superelliptical Grooves and Holes on the End Face

Background:: Enhancing the stability and leakage control of Dry Gas Seals (DGS) under high parameters has been a crucial research focus. The design of end-face groove structures and surface texture shapes has been an essential aspect of DGS studies aimed at improving performance. Objective:: The proposed end-face gas seal utilizes superelliptical grooves and holes to improve its performance, aiming to obtain a patent. The use of superelliptical curves allows for a more precise and efficient geometric representation, resulting in a better sealing effect. Methods:: A theoretical analysis model for the steady and dynamic behavior of the seal is established using the lubrication theory and perturbation methods. The study investigates the distribution patterns of gas film pressure on the sealing end-face and gas flow characteristics within the film. This approach provides a new perspective for understanding seal performance and offers a theoretical basis for optimizing seal design. Results:: The results indicate that the combined end-face structure with grooves and holes ensures good sealing stability and effectively enhances leakage control performance. By optimizing the design of the superelliptical groove and holes on the end face, the performance of DGS can be significantly improved. Conclusion:: Within the parameter range studied, better steady-state performance is achieved for θ=40~80°, v=1.3~1.4, u=1~2, β=0.6~0.7, and λ=1.0~1.5. In addition, better dynamic performance is observed for θ=80~120°, v=1.1~1.2, u=2~3, β=0.9~1.0, and λ=2.0~2.5.

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.

Slip flow and thermal characteristics in gas thrust bearings with rough surfaces

PurposeThis study aims to investigate the rarefaction effects on flow and thermal performances of an equivalent sand-grain roughness model for aerodynamic thrust bearing.Design/methodology/approachIn this study, a model of gas lubrication thrust bearing was established by modifying the wall roughness and considering rarefaction effect. The flow and lubrication characteristics of gas film were discussed based on the equivalent sand roughness model and rarefaction effect.FindingsThe boundary slip and the surface roughness effect lead to a decrease in gas film pressure and temperature, with a maximum decrease of 39.2% and 8.4%, respectively. The vortex effect present in the gas film is closely linked to the gas film’s pressure. Slip flow decreases the vortex effect, and an increase in roughness results in the development of slip flow. The increase of roughness leads to a decrease for the static and thermal characteristics.Originality/valueThis work uses the rarefaction effect and the equivalent sand roughness model to investigate the lubrication characteristics of gas thrust bearing. The results help to guide the selection of the surface roughness of rotor and bearing, so as to fully control the rarefaction effect and make use of it.

Prediction of spiral groove dry gas seal performance and intelligent optimization of structural parameters

Using gas lubrication theory and finite difference methods, this study solve the gas film pressure equation in spiral groove dry gas seal and assesses key performance aspects like opening force, leakage rate, and gas film stiffness. It examines how structural parameters affect sealing performance and utilizes Latin hypercube sampling with a radial basis neural network, optimized by genetic algorithms, for predictive analysis. The effectiveness of control variable, orthogonal, and genetic algorithm methods in optimizing sealing performance is comparatively analyzed. Findings reveal a substantial impact of structural parameters on sealing performance with intricate interdependencies. The neural network, trained with 400 samples, achieves a prediction error below 3.6%. Genetic algorithm optimization of structural parameters notably enhances seal performance over other methods.

Elimination of gas entrapment in droplet-based 3D printing by induced electric-field

Gas entrapment during droplet deposition may induce pinhole defects in droplet-based 3D printing. However, achieving effective suppression of gas entrapment is challenging given that gas entrapment behavior is the physical essence of droplet impact. Inspired by that charged droplets will be deformed in the electric field, a method of suppressing gas entrapment by weakly charging the droplet was proposed. Here, a numerical model is developed to systematically investigate the gas entrapment behaviors during neutral droplet and charged droplet deposition. Results show that the electric field will be induced before the instant of droplet impact on the substrate, which fundamentally changes the gas entrapment behavior. Moreover, the competition mechanism between Maxwell stress and lubrication pressure during droplet deposition is revealed, and the pressure inside and outside the droplet bottom profile is quantified. Compared with the neutral droplet, the additional electric stresses act against the lubrication pressure, which increases sharply before the droplet touches the substrate. When the charge level reaches a critical value, the electric stresses are slightly stronger than the lubrication pressure at the bottom center, and the decrease rate of electric stresses along the horizontal distance r is higher than that of gas film pressure, leading to a central touchdown with residue concentric circle gas rings. Furthermore, the evolution of phase fraction, velocity field, and pressure field during droplet deposition with different charge level is investigated comprehensively. Based on this, the dimensionless scale of critical charge level to fundamentally eliminate gas entrapment is obtained. This work may provide new insights into various applications involving droplet deposition, such as eliminating pinhole defects in droplet-based additive manufacturing.

Research on Micro Gap Flow Field Characteristics of Cylindrical Gas Film Seals Based on Experimental and Numerical Simulation

Flexible support cylindrical gas film seals (CGFSs) adapt well to rotor whirling and have a good gas lubrication effect during thermal deformation. However, when a CGFS operates under the “three high” (high interface slip speed, high-pressure differential, and high ambient temperature) operating conditions, the complex deformation of the support structure is a crucial factor affecting the stability of the CGFS. A thorough and systematic analysis of the micro gap flow field characteristics of flexible support CGFSs is a fundamental problem when we study the deformation of the support structure under multiple physical field conditions. This study uses a cylindrical gas film high-speed rotor test rig to study and compare the sealing characteristics of experiments and numerical simulations and then optimizes and verifies the accuracy and effectiveness of the simulation model. A cross-scale gas film grid model is used to analyze the flow field characteristics and seal ability of different groove models and compare the mechanical characteristics and sealing performance. We also analyze the gas film pressure distribution in micro gaps and explore the impact of dynamic pressure groove microstructure on flow field characteristics. Results show that micro gaps are the primary conditions for generating hydrodynamic effects, and high rotational speed, high-pressure differential, and large eccentricity have a significant effect on improving hydrodynamic effects and enhancing gas film stability. However, an increase in these parameters can cause an increase in leakage rate. A single flow channel makes it easier to improve the hydrodynamic effect, gas film load-bearing ability, and gas film stability while reducing leakage rate. The analyses in this study supplement and improve the theory of the flow field characteristics of cylindrical annular micro gaps and provide a theoretical basis for exploring the relation between the support structural parameters of the CGFS and the mechanical characteristics of the micro gap flow field. This study provides important guidance to the establishment of a quantitative design theory of supporting structures.

The fluid-thermal-structural interaction analysis of a new multifoil aerodynamic thrust bearings

In the present study, a multiphysics simulation model was established to evaluate the effects of the fluid-thermal-structural interaction on the performance of multifoil gas lubrication thrust bearing. The thermal and elastic deformation mechanisms of multifoil bearings were studied in detail, and the effects of the preload ratio and foil structural parameters on the bearing performance were analyzed. The results show that the preload ratio determines the performance of the multifoil thrust bearing. A small preload helps the bearing maintain a low lift-off speed, whereas a large preload is helpful in improving the bearing load capacity. The thickness of the foil has a significant effect on the gas film pressure distribution and the down foil thickness plays a leading role in the load capacity.

Investigation on the effect of coating properties on transient mixed lubrication of gas foil bearing

To reveal the effect of coating properties on the mixed lubrication evolution during the start–stop process of gas foil bearing (GFB), a transient gas mixed lubrication-wear model for coating surface is established. In the developed model, a method of the extended equivalent modulus by the film thickness ratio is proposed, which can extend the classic Greenwood and Tripp contact model for homogeneous materials to the coating contact involving layered materials. Moreover, a gas foil bearing start–stop experiment is conducted to verify the predicted results of the developed model. The effects of coating materials and standard deviation of coating surface on the start–stop performance of GFB are investigated. Within the scope of this article, the results show that during start-up, the gas film pressure first increases and then decreases with the increase in time, the minimum film thickness increases, while the asperity contact decreases. The opposite evolution is observed during shut-down. Compared with uncoated GFB, the friction torque and lift-off speed of GFB with polyimide (PI) and polytetrafluoroethylene (PTFE) are reduced, with PI reducing friction torque by 24.27% and PTFE by 49.03%. The minimum lift-off speed with PTFE is the smallest. The lift-off speed, friction torque, and wear volume increase with the increase in the standard deviation of coating surface. The friction torque and lift-off speed decrease as the start–stop cycle increases until both reach stability. This paper can provide theoretical guidance for the design of the top foil coating surface of GFB.

Numerical Investigation of Unsteady Characteristics of Gas Foil Journal Bearings with Fluid–Structure Interaction

Gas foil journal bearings (GFJBs) have been widely employed in high-speed rotating machinery in the aviation industry. However, the role of fluid–structure interaction in the unsteady aerodynamic character of the gas film and the dynamic response of the elastic foils have not yet been clarified. In this study, an unsteady shearing flow interacting with an exciting deformation of the top or bump foils was investigated by means of a large eddy simulation with bidirectional fluid–structure interaction (BFSI). The result shows that the main frequencies and amplitudes of stable fluctuations of different flow field parameters at different positions are different. The oscillating duration in the solid domain is much less than that in the fluid domain. The main positions for the interaction between the gas film pressure and the elastic foil are on both sides of θ = π. Compared with the case without FSI, the presence of the elastic foil flattens the distribution of the pressure of the gas film. As the rotational speed increases, the main frequency and the amplitude of pressure in the fluid domain continuously increase. With FSI, there is no interference frequency near the main frequency, which improves the stability of the shearing flow. However, an interference frequency appears near the main frequency of total displacement in the solid domain. The analysis in this paper lays the foundation for unsteady fluid–structure interaction research.

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.

The Direct-Coupling Method for Analyzing the Performance of Aerostatic Bearings Considering the Fluid–Structure Interaction Effect

In the interest of analyzing the effect of the structural deformation root caused by gas pressure on the static features of aerostatic bearings, a fluid–structure interaction (FSI) model based on orifice-type aerostatic bearings is proposed that can predict the characteristics of aerostatic bearings more accurately by using the direct-coupling method (DCM). By using COMSOL Multiphysics, the governing equation matrix of the finite element model of structural deformation and gas film pressure was solved with the integral solution method, and the orifice boundary conditions were calculated with the root iteration method. At the same time, the static performance of I-shaped orifice-type aerostatic bearing with various supply pressures was analyzed theoretically and tested experimentally. The results show that in comparison with the calculation results without taking account of structural deformation, the theoretical values from the model derived in this paper considering the FSI effect are closer to the experimental values. Finally, by using the orthogonal design method, FSI simulation was carried out to analyze how the key dimension factors influence the structural stiffness of the spindle, and it is concluded that the thrust bearing’s stiffness is strongly influenced by the thickness of the thrust plate.

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.

Research on the influence of supersonic phenomena on the gas film flow field of micron-groove-orifice aerostatic journal bearings under high gas supply pressure

To solve the problem of performance degradation caused by supersonic phenomena under high gas supply pressures in orifice-compensated aerostatic journal bearings (OCAJBs), a double-row gas supply micron-groove-orifice aerostatic journal bearing (MGOAJB) is designed, and the SST k- ω turbulence model is used to analyze the influences of the supersonic phenomena on the gas film flow field under different gas supply pressures, gas film thicknesses and orifice diameters. Compared with traditional OCAJBs, under high gas supply pressure, supersonic phenomena occur near the gas film inlet in both the MGOAJB and the OCAJB. The Mach number, maximum pressure, temperature and Reynolds number of the OCAJB are higher than those of the MGOAJB, but the MGOAJB has a more stable gas film pressure due to pressure equalization. As the gas film thickness of the MGOAJB increases, the Mach number, Reynolds number and temperature near the gas film inlet increase, but the pressure decreases, the recovery of the pressure and temperature becomes more obvious when the gas velocity drops to a subsonic speed. With increases in the MGOAJB orifice diameter, the pressure, temperature and Reynolds number increase, the Mach number decreases, and the recovery of the pressure and gas temperature becomes more obvious.

Performance of the Compliant Foil Gas Seal with Surface Micro-Textured Top Foil

In various fields, micro-textures have been successfully applied to the surface of friction pairs to effectively improve flow field and friction performance. This paper aims to investigate how different textures affect the sealing performance of compliant foil gas film seals. In theoretical simulations, a facile method for characterizing the shape of micro-textures is proposed, and the equilibrium relationship between the gas film pressure, gas film thickness, and foil deformation is established. The transient Reynolds equation considering the eccentric convergence problem and abrupt Rayleigh step changes is solved to analyze the static and dynamic characteristics. The results show that (i) compared with the directionality of the texture, the gas volume accommodated by the texture has a greater impact on the sealing performance, and a convergent texture can effectively control the leakage rate; (ii) when the texture depth exceeds 9 μm, the sealing system may be unstable; (iii) the compliant foil seal is well suited to higher-speed service conditions, and the inverted triangular texture shows the best comprehensive sealing performance.

An analysis method of pressure characteristic for cylindrical intershaft gas film seal considering centrifugal expansion, rotor misalignment, and precession

To improve the weaknesses of large leakage and wear of dual-rotor intershaft labyrinth seal in aero-engines, the cylindrical gas film seal of metal rubber with a compliant feature is proposed to substitute this conventional seal. According to the dual-rotor operating condition, an analysis method of gas film pressure is presented considering the complex condition of rotor tilt, centrifugal expansion effect, and rotor circular precession. The characteristics of gas film pressure distribution are computed and comparisons are conducted in a complex operating state that the tilt rotor is in forward/backward circular precession under a homodromous/counter-rotating condition with/without the influence of centrifugal expansion. Besides, the formation mechanism of the gas film pressure caused by rotor rotational direction and circular precession direction is revealed. Also, the influence of rotor speed and seal ring speed on gas film pressure is analyzed when the rotor is tilted. The results indicate that for the dual-rotor cylindrical gas film seal with high rotating speed, the rotor tilt and centrifugal expansion effect have significant influence on the gas film pressure distribution, and the rotors’ rotational direction as well as rotor circular precession direction determines the maximum gas film pressure distribution area. The maximum pressure under a homodromous condition with backward precession is the highest; the maximum pressure under a homodromous condition with forward precession is the lowest. The former is 1.33% and 1.68% higher than the latter, respectively, with/without consideration of centrifugal expansion. The study method, which is generally suitable for the cylindrical gas film seal with single-rotor/dual-rotor, lays the foundation of performance analysis under complex operating conditions.

Rotordynamic Analysis of Piezoelectric Gas Foil Bearings with a Mechanical Preload Control Based on Structural Parameter Identifications

This paper presents a rotordynamic analysis and experimental characterization of a novel concept of a controllable gas foil bearing (C-GFB) with piezoelectric (PZT) actuators. The C-GFB consists of bump foil structures and three PZT actuators, and the PZT actuators push the bump foil structures in different displacements according to the driving voltage, enabling preload control. In order to predict the piezoelectric preload according to the driving voltage, an equivalent spring model for PZT actuators and foil structures is introduced. In addition, PZT parameters (a piezoelectric constant and stiffness) are measured through parameter identification tests using a latch. Next, static lubrication analysis for C-GFB reveals that the gas-film pressure reduces the effect of piezoelectric preload by up to a maximum of 11%, because the piezoelectric actuator has structural compliance so that it is structurally deformed by the pressure. Finally, nonlinear orbit simulation is performed, and the performance of real-time vibration control of C-GFB is evaluated. The real-time preload control is carried out at ~32.6 krpm, where the rotordynamic instability sufficiently occurs. As the driving voltage increases, the instability suppression and delay effect increase. In particular, when controlled at 150 V, the onset speed of the instability increases to 79.1 krpm. Consequently, this study demonstrates that the GFB with piezoelectric preloads is a simple, effective, and real-time method to improve the rotordynamic stability.

Rotordynamic Analysis of Gas Foil-Polymer Bearings Based on a Structural Elasticity Model of Polymer Layer along with Static-Load Deflection Tests

In this study, rotordynamic analysis is performed using a simple structural model for the polymer layer of gas foil-polymer bearing (GFPB) composed of an accumulated bump foil and a polymer layer with high structural damping. The simple model that considers the elastic behavior of a cylinder-shaped polymer layer is introduced, and the structural stiffness of the layer is estimated based on Hooke’s law for differential elements in the layer. In addition, the simple model is coupled with the structural stiffness of the bump foil in consideration with a series relationship, which represents the structural model of GFPBs. A GFPB with thickness of 2 mm is fabricated, and the structural model is validated via static-load deflection tests for the GFPB. As a result of model validation, the proposed model is found to be effective in predicting the elastic behavior under the lightly loaded condition of GFPB. Next, the static performances of GFPBs, namely, gas-film pressure, thickness, and journal positions with respect to different polymer layer thickness, are analyzed to evaluate rotordynamic stability of GFPBs. The results indicate that high thickness yields an increase in damping and a decrease in cross-coupled effects. Specifically, in this study, 3 mm-thick polymer gives the best stability performance given the predicted effective damping results. As a result, this work provides a reasonable model for structural elasticity of GFPBs and lays a foundation for the widespread use of GFPBs.

Numerical calculation and experimental study on friction and lubrication of Stirling engine piston ring

To solve the practical problem of Stirling engine piston ring, numerical model on friction and lubrication were established based on average Reynolds equation theory. Numerical calculation results show: piston rings are in the mixed lubrication state which gas lubrication film and micro-convex body contact existing simultaneously; contact pressure is 2 orders of magnitude less than gas film pressure; contact pressure is approximately linearly related to mean gas pressure. Simulated test rig was built and experimental results show: high-pressure working gas leak to intermediate chamber through piston rings, and the pressure of intermediate chamber drops sharply at lowest pressure of circulation; piston ring wear increases when rotational speed or working pressure increase. The accuracy of numerical model was proved by experimental phenomena and test data.

Investigations on start-up performances of novel hybrid metal rubber-bump foil bearings

In the frequent start-up process of aerodynamic bearings, contact easily occurs between journal and bearing bush. In this research, novel hybrid metal rubber-bump foil bearings (MR-BFBs) were proposed. Based on rough surface contact and ultra-thin film lubrication theory, we studied the start-up performances of MR-BFBs. The results showed that the changes in both RSm and Ra caused great changes in the parameters pmax and A0. The increased start-up times led to a decrease in the load ratio Wc/W0 and the total friction coefficient, and an increase in both the linear velocity, the gas film pressure and the minimum gas film thickness. With the increase in the composite roughness, both the critical rotation speed and start-up time exhibited an upward trend.