Research

17 pages, 4866 KiB

Open AccessArticle

Numerical Analysis via Mixed Inverse Hydrodynamic Lubrication Theory of Reciprocating Rubber Seal Considering the Friction Thermal Effect

by Bongjun Kim, Junho Suh, Bora Lee, Yondo Chun, Geuntae Hong, Jungjoon Park and Yonghun Yu

Appl. Sci. 2023, 13(1), 153; https://doi.org/10.3390/app13010153 - 22 Dec 2022

Cited by 2 | Viewed by 1478

Abstract

This study investigates how operating conditions such as ambient temperature and sealing pressure affect sealing performance for a typical U-cup seal. The developed analysis method combines inverse fluid lubrication (IHL) theory and the Greenwood–Williamson contact model (G–W model), and the effect of increasing [...] Read more.

This study investigates how operating conditions such as ambient temperature and sealing pressure affect sealing performance for a typical U-cup seal. The developed analysis method combines inverse fluid lubrication (IHL) theory and the Greenwood–Williamson contact model (G–W model), and the effect of increasing surface temperature due to frictional heat generated between two surfaces is considered. Commercial FE software (ABAQUS) was used to simulate the interference fit analysis of rubber seals and the pressurized process. Through this model, the film distribution, working fluid leakage, and friction force in the sealing area were discussed according to the operating parameters, such as sealed pressure, rod velocity, and ambient temperature. The simulation results demonstrate the effect of fluid viscosity on oil film formation (which varies with ambient temperature), the effect of increasing the surface temperature, and the effect of surface roughness at a very small film thickness. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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18 pages, 4758 KiB

Open AccessArticle

Quasi-Static Sliding Wear Analysis of 3D Rough Surface Considering Changes in the Point of Contact

by Yunji Kim, Junho Suh, Bora Lee, Yondo Chun, Keejun Park and Yonghun Yu

Appl. Sci. 2022, 12(23), 12465; https://doi.org/10.3390/app122312465 - 06 Dec 2022

Viewed by 1338

Abstract

This study analyzed adhesive wear in periodic sliding motion using a quasi-static deterministic wear model that considered changes in the point of contact of asperities as well as changes in the surface and statistical parameters. The contact pressure was calculated using the semi-analytical [...] Read more.

This study analyzed adhesive wear in periodic sliding motion using a quasi-static deterministic wear model that considered changes in the point of contact of asperities as well as changes in the surface and statistical parameters. The contact pressure was calculated using the semi-analytical method (SAM) based on the periodic properties of the rough surface, and the wear was analyzed by obtaining the wear depth for each node using the Archard wear model. We took into account that the sliding distances of the upper moving surface and the lower stationary surface are different according to the actual size of the two objects. We compared the results of the quasi-static wear analysis with the truncation model and the deterministic fixed model, which did not consider the change in the asperity contact point. In the truncation model, an error in the estimation of the radius occurred in the process of fitting the tip of asperities with a sphere. As the asperities became flatter by wear, this error accumulated, which revealed a difference in the deterministic wear analysis results. As a result of the wear analysis on the periodic surface, the RMS roughness of the positively skewed surface decreased the fastest, the skewness increased in the negative direction, and the kurtosis initially decreased and then increased. In addition, wear scars occurred due to the difference in wear depth between the lower stationary surface and the upper moving surface. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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18 pages, 9885 KiB

Open AccessArticle

Thermo-Hydrodynamic Analysis of Low-Temperature Supercritical Helium Spiral-Grooved Face Seals: Large Ambient Temperature Gradient

by Rong Wang and Shaoxian Bai

Appl. Sci. 2022, 12(21), 11074; https://doi.org/10.3390/app122111074 - 01 Nov 2022

Viewed by 1133

Abstract

Hhighly efficient and reliable sealing technology is essential to improve the efficiency of precooled aeroengines. To explore the effects of large ambient temperature gradients on the sealing performance, the thermo-hydrodynamic characteristics of a supercritical helium spiral-grooved face seal were studied numerically, under low-temperature [...] Read more.

Hhighly efficient and reliable sealing technology is essential to improve the efficiency of precooled aeroengines. To explore the effects of large ambient temperature gradients on the sealing performance, the thermo-hydrodynamic characteristics of a supercritical helium spiral-grooved face seal were studied numerically, under low-temperature conditions. Considering the real gas effect of helium, the thermal deformations of the seal were analyzed numerically, under different temperature gradients. Additionally, the distributions of the pressure, temperature, and film thickness of the gas film were calculated, and the sealing performances of the seal under a wide range of working conditions were evaluated simultaneously. Results showed that a turning point occurred at the sealing pressure of 1.6 MPa in both the dynamic pressure effect and temperature rise of the gas film under the ambient-temperature gradient, leading to the transformation of the sealing gap, from convergent to divergent. The temperature gradient contributed to decreasing the thermal deformation and improving the sealing performance of the face seal. As the temperature gradient increased, although a mutational phenomenon existed near the sealing temperature of 250 K with both the dynamic pressure effect and the temperature rise, the variation of the opening force was within 120 N and the leakage was more than halved, indicating the broad application prospects of gas face seals in precooled aeroengine systems. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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17 pages, 7833 KiB

Open AccessArticle

CFD Analysis on the Heat Dissipation of a Dry-Lubricated Gear Stage

by Lucas Hildebrand, Florian Dangl, Constantin Paschold, Thomas Lohner and Karsten Stahl

Appl. Sci. 2022, 12(20), 10386; https://doi.org/10.3390/app122010386 - 15 Oct 2022

Cited by 4 | Viewed by 2005

Abstract

Power losses in gearboxes result in frictional heating. Sufficient heat transfer from the gearbox to the environment is required for reliable operation. The heat dissipation from gears is linked to their interaction with fluids in the gearbox. Recent research has demonstrated the use [...] Read more.

Power losses in gearboxes result in frictional heating. Sufficient heat transfer from the gearbox to the environment is required for reliable operation. The heat dissipation from gears is linked to their interaction with fluids in the gearbox. Recent research has demonstrated the use of Computational Fluid Dynamics (CFD) to predict the gearbox fluid flow and no-load losses in an isothermal manner. This study focuses on a numerical analysis of the heat dissipation within a dry-lubricated gearbox under atmospheric conditions. Spur gears and helical gears are investigated. The air flow in the gearbox as well as the heat dissipation over the gear surfaces are evaluated in detail. The results show that the gear geometry and the circumferential speed have a strong impact on the air flow. Especially, the axial inflow of air to the gears has a great influence on the heat dissipation. Conveying effects of helical gears lead to a multidirectional airflow, resulting in higher values of the heat transfer coefficient on the gear surface compared to spur gears. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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17 pages, 5603 KiB

Open AccessArticle

Structural Design and Lubrication Properties under Different Eccentricity of Magnetic Fluid Bearings

by Ao Wang, Jiabao Pan, Huaibiao Wu and Jin Ye

Appl. Sci. 2022, 12(14), 7051; https://doi.org/10.3390/app12147051 - 13 Jul 2022

Cited by 2 | Viewed by 1352

Abstract

As a lubricant, the viscosity of the magnetic fluid changes with the external magnetic field, which improves the bearing capacity of the oil film and hence the lubrication effect, and has a promising application in bearings. Based on the Roelands viscosity theory, the [...] Read more.

As a lubricant, the viscosity of the magnetic fluid changes with the external magnetic field, which improves the bearing capacity of the oil film and hence the lubrication effect, and has a promising application in bearings. Based on the Roelands viscosity theory, the Shliomis model is used to derive the viscous temperature, viscous pressure, and magnetic viscosity characteristics of magnetic fluids under the influence of an applied magnetic field, and further proposes a structural model of magnetic fluid lubricated bearings to investigate the pressure, temperature and magnetic intensity distribution of magnetic fluids under different eccentricity conditions. The results show that the viscosity of the magnetic fluid decreases exponentially with increasing temperature, rises linearly with increasing pressure, and increases and stabilizes with increasing magnetic induction strength. Because the minimum film thickness point is the dividing point between the convergent wedge and the dispersed wedge, the pressure distribution of the lubricant film separates high pressure from low pressure at the minimum film thickness, and the differential pressure increases with the increase in eccentricity. The temperature distribution of the high-temperature zone is mainly distributed in the middle of the film, and the minimum film thickness zone and the maximum temperature increases with the increase in eccentricity. The magnetic intensity distribution of the strong magnetic field is mainly concentrated in the minimum film thickness zone, and the magnetic induction intensity increases with the increase in eccentricity. The results of this study have certain research significance for solving the problem of the poor lubrication effect of bearing lubricant due to high temperature. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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12 pages, 3736 KiB

Open AccessArticle

Experimental Characterization of Chemical Properties of Engine Oil Using Localized Surface Plasmon Resonance Sensing

by José Antonio Heredia-Cancino, Roberto Carlos Carrillo-Torres, Francisco Félix-Domínguez and Mario Enrique Álvarez-Ramos

Appl. Sci. 2021, 11(18), 8518; https://doi.org/10.3390/app11188518 - 14 Sep 2021

Cited by 5 | Viewed by 1730

Abstract

The chemical properties of engine oil are part of the main parameters to evaluate its condition since oxidation starts chemical reactions that alter its operating conditions. In this work, the chemical properties of engine oil were analyzed based on the standard ASTM E2412 [...] Read more.

The chemical properties of engine oil are part of the main parameters to evaluate its condition since oxidation starts chemical reactions that alter its operating conditions. In this work, the chemical properties of engine oil were analyzed based on the standard ASTM E2412 by FT-IR spectroscopy to evaluate the lubricating oil condition. Furthermore, a sensor based on the position of the localized surface plasmon resonance (LSPR) band of silver nanoparticles (AgNP), synthesized by the laser-assisted photoreduction method, was developed. This plasmonic sensor can detect changes in the permittivity of the oil, caused by the modification of the chemical properties of the lubricant. The response of the sensor during the study of degraded oil resulted in a notorious displacement to higher wavelengths of the LSPR band as mileage increases. The results of FT-IR analysis were correlated with the measurements of the proposed sensor presenting linear trends with good correlation (R² > 0.9491). Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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26 pages, 17832 KiB

Open AccessArticle

Statistical Analysis for Transmission Error of Gear System with Mechanical and Thermal Deformation Uncertainties

by Joon-Ho Lee, Hee-Sun Choi, Jong-Hyeon Sohn, Geun-Ho Lee, Dong-Il Park and Jin-Gyun Kim

Appl. Sci. 2021, 11(14), 6582; https://doi.org/10.3390/app11146582 - 17 Jul 2021

Cited by 6 | Viewed by 2610

Abstract

We establish a robust algorithm to analyze the influence of system uncertainties on the transmission error of a spur gear pair under 2D simplification. The algorithm provides a way of generating smooth cutter profiles with machining uncertainties and measuring the thermal deformation through [...] Read more.

We establish a robust algorithm to analyze the influence of system uncertainties on the transmission error of a spur gear pair under 2D simplification. The algorithm provides a way of generating smooth cutter profiles with machining uncertainties and measuring the thermal deformation through the uncertainties in material properties. Then, it produces realizations of gear tooth profiles based on the analytical method for accuracy and computational efficiency. Numerical investigations show the statistical analysis on the tooth contact analysis by comparing steel and plastic gears. It is worthwhile remarking that the plastic gear is susceptible to the geometric error caused by thermal deformation. Moreover, although the impact of thermal deformation on steel gear may seem slim, it can have a noticeable influence when it exists with mechanical uncertainties together. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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15 pages, 5639 KiB

Open AccessArticle

Journal Bearing: An Integrated CFD-Analytical Approach for the Estimation of the Trajectory and Equilibrium Position

by Franco Concli

Appl. Sci. 2020, 10(23), 8573; https://doi.org/10.3390/app10238573 - 30 Nov 2020

Cited by 3 | Viewed by 2130

Abstract

For decades, journal bearings have been designed based on the half-Sommerfeld equations. The semi-analytical solution of the conservation equations for mass and momentum leads to the pressure distribution along the journal. However, this approach admits negative values for the pressure, phenomenon without experimental [...] Read more.

For decades, journal bearings have been designed based on the half-Sommerfeld equations. The semi-analytical solution of the conservation equations for mass and momentum leads to the pressure distribution along the journal. However, this approach admits negative values for the pressure, phenomenon without experimental evidence. To overcome this, negative values of the pressure are artificially substituted with the vaporization pressure. This hypothesis leads to reasonable results, even if for a deeper understanding of the physics behind the lubrication and the supporting effects, cavitation should be considered and included in the mathematical model. In a previous paper, the author has already shown the capability of computational fluid dynamics to accurately reproduce the experimental evidences including the Kunz cavitation model in the calculations. The computational fluid dynamics (CFD) results were compared in terms of pressure distribution with experimental data coming from different configurations. The CFD model was coupled with an analytical approach in order to calculate the equilibrium position and the trajectory of the journal. Specifically, the approach was used to study a bearing that was designed to operate within tight tolerances and speeds up to almost 30,000 rpm for operation in a gearbox. Full article

(This article belongs to the Special Issue Tribology and Mechanical Transmissions)

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