Thermo-elastohydrodynamic lubrication simulation of reciprocating rod seals under transient condition

A numerical soft elastohydrodynamic lubrication model of a reciprocating hydraulic seal has been used to simulate the performance of a U-cup seal and a step seal in a conventional actuator. The model consists of coupled steady state fluid mechanics, deformation mechanics, contact mechanics, and thermal analyses, with an iterative computational procedure. The results indicate that for a given seal roughness and stroke length there is a critical rod speed above which the seal will not leak. The critical speed is dependent on both seal roughness and sealed pressure.

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On Transient EHL of a Skew Roller Subjected to a Load Impact in Rolling Bearings

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.739.108 ◽

2017 ◽

Vol 739 ◽

pp. 108-119

Author(s):

Xiao Ling Liu ◽

Da Tong Song ◽

Pei Ran Yang

Keyword(s):

Steady State ◽

Film Thickness ◽

Elastohydrodynamic Lubrication ◽

Transient Condition ◽

Skew Angle ◽

Transient Effect ◽

Outer Race ◽

Minimum Film Thickness ◽

Finite Line ◽

Load Impact

Based on the non-steady state operating condition in machine elements, numerical analysis of a transient elastohydrodynamic lubrication (EHL) finite line contact between a skewed roller and an outer race in cylindrical roller bearings was carried out, and a complete numerical solution of skewed roller pairs EHL under the transient condition was obtained. The effects of the load impact, together with the skewing angle impulses on the lubricating performance of skew roller pairs were discussed. Results show that, different from the steady state, the transient effect of the skew roller lubrication is mainly governed by the skew angle impulse, and the load impact. The film dimple is generated during the load impact, or the skewing angle impulse due to the normal approach velocity of the film. Compared to that of the ideal roller, the minimum film thickness decreases due to the roller skew when the transient load happens. Variation in the skewing angle leads to contrary distribution of the film thickness at the two half parts of the roller. Meanwhile, it can decrease the minimum film thickness and be harmful to the lubrication compared to the steady state. Consequently, the transient effect in the process of lubrication of skew roller pairs should not be neglected.

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A Strongly Coupled Fluid Structure Interaction Solution for Transient Soft Elastohydrodynamic Lubrication Problems in Reciprocating Rod Seals Based on a Combined Moving Mesh Method

Journal of Tribology ◽

10.1115/1.4030022 ◽

2015 ◽

Vol 137 (4) ◽

Cited By ~ 8

Author(s):

Haiping Gao ◽

Baoren Li ◽

Xiaoyun Fu ◽

Gang Yang

Keyword(s):

Fluid Structure Interaction ◽

Elastohydrodynamic Lubrication ◽

Moving Mesh ◽

Moving Mesh Method ◽

Fluid Structure ◽

Strongly Coupled ◽

Structure Interaction ◽

Fluid Field ◽

Mesh Method ◽

Rod Seals

Soft elastohydrodynamic lubrication (EHL) problems widely exist in hydraulic reciprocating rod seals and pose great challenges because of high nonlinearity and strong coupling effects, especially when the EHL problems are of high dimensions. In this paper, a strongly coupled fluid structure interaction (FSI) model is proposed to solve the transient soft EHL problems in U-cup hydraulic reciprocating rod seals. The Navier–Stokes equations, rather than the Reynolds equation, are employed to govern the whole fluid field in the soft EHL problems, with the nonlinearity of the solid taken into consideration. The governing equations of the fluid and solid fields are combined into one equation system and solved monolithically. To determine the displacements of nodes of the fluid field, a new moving mesh method based on the combination of the Laplace equation and the leader–follower methods is put forward. At last, the proposed FSI model runs successfully with the moving mesh method, and the boundaries of the hydrodynamic lubrication zones and the hydrostatic zones are formed automatically and change dynamically during the coupling process. The results are as follows: The soft EHL problems show typical characteristics, like the constriction effects of the lubricating films, and the law of dynamic development of the lubricating films and the fluid pressures is revealed. The minimum stroke lengths needed to generate complete lubricating films vary with the rod speeds and movement directions, so the design of the rod seals should be paid close attention to, in particular the rod seals of short stroke lengths. Furthermore, along with the dynamic development processes of the fluid pressures during the instroke of U-cup seals, the lubricating film humps expand and locate between the fluid pressure abrupt points and the outlet zones. After the U-cup seals reach the steady-states, the fluid abrupt points disappear and no changes of the film humps are observed. Theoretically, the proposed method can be popularized to solve similar soft EHL problems.

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Remarks on Modeling the Oil Film Generation of Rod Seals

Lubricants ◽

10.3390/lubricants9090095 ◽

2021 ◽

Vol 9 (9) ◽

pp. 95

Author(s):

Oliver Feuchtmüller ◽

Nino Dakov ◽

Lothar Hörl ◽

Frank Bauer

Keyword(s):

Film Thickness ◽

Hydrodynamic Lubrication ◽

Elastohydrodynamic Lubrication ◽

Numerical Results ◽

Physical Parameters ◽

Oil Film ◽

Polished Rod ◽

Rod Seals ◽

Potential Remedy ◽

Theory And Experiments

The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model—both based on the Reynolds equation for thin lubricating films—were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.

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The Grooved Lip Effect on Reciprocating Hydraulic Rod Seal Performances in Transient Condition: Elastohydrodynamic Lubrication

International Journal of Applied Mechanics and Engineering ◽

10.2478/ijame-2020-0017 ◽

2020 ◽

Vol 25 (2) ◽

pp. 11-21

Author(s):

Y. Bahi ◽

M. El Gadari ◽

M. Rahmoune

Keyword(s):

Computational Models ◽

Current Model ◽

Elastohydrodynamic Lubrication ◽

Axial Direction ◽

Transient Condition ◽

Slight Effect ◽

Lip Seal ◽

Sealing Performance ◽

Pattern Shape ◽

Average Film Thickness

AbstractIt is commonly known that the sealing performance of dynamic seals is significantly influenced by the surface finish. To reduce friction effect and leakage ratio, new generations of grooved lip or shaft have emerged, but only two computational models were performed up to now with a textured elastomeric lip: spiral groove in the axial direction or micro-cavities according to the circumferential direction. However, if the numerical results have confirmed the slight effect of the grooved lip on the rotary lip seal performances, it seems relevant to investigate the influence of such grooves on the reciprocating hydraulic rod seal behavior.Thus, the scope of this work is to perform a parametric study of the grooved lip throughout a one-dimensional elastohydrodynamic model by taking into account the elasticity of the lip and the shaft roughness.After confirming the validity of the current model, numerical simulations have been performed and compared with experiments. The effect of lip grooves on the hydraulic rod seal behavior in outstroke and instroke shaft motion has been underlined. Thereby, it is shown that the leakage and the average film thickness are sensible to both the depth and the density of the lip groove. Additionally, a slight effect of the pattern shape is observed on the friction force.

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