Research Papers: Elastohydrodynamic Lubrication

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

[+] Author and Article Information
Haiping Gao, Baoren Li, Xiaoyun Fu

School of Mechanical Science and Engineering,
Huazhong University of Science and Technology,
Wuhan 430074, China

Gang Yang

School of Mechanical Science and Engineering,
Huazhong University of Science and Technology,
Wuhan 430074, China
e-mail: ygxing_73@hust.edu.cn

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received September 20, 2014; final manuscript received March 2, 2015; published online April 29, 2015. Assoc. Editor: Min Zou.

J. Tribol 137(4), 041501 (Oct 01, 2015) (13 pages) Paper No: TRIB-14-1231; doi: 10.1115/1.4030022 History: Received September 20, 2014; Revised March 02, 2015; Online April 29, 2015

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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Fig. 1

A typical rod seal system and its deformed shape: (a) initial state before installed and (b) pressured state

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Fig. 2

Interpolation method of the fluid node displacement by using the solid node displacements

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Fig. 3

Displacement relation between the leader point (L) and the follower point (F), (λf = 1)

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Fig. 4

Mesh shape comparison between the conventional moving mesh strategy (mesh 1) and the proposed strategy (mesh 2) after the solid part (seal) is large deformed

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Fig. 5

Meshes distribution, deformation, and movement of the U-cup rod seal system

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Fig. 6

The pressure distribution under the fluid pressure of 7 MPa when the rod is static: (a) pressure distribution contour and (b) pressure distribution of the solid along the seal zone

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Fig. 7

Rod speeds change with time at different target rod speeds

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Fig. 8

The pressure distributions (a)–(c) and mesh shape (d) at the rod speed of 400 mm/s, instroke

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Fig. 9

The pressure distributions (a)–(c) and mesh shape (d) at the rod speed of 400 mm/s, outstroke

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Fig. 10

Development processes of the fluid pressure and film thickness in the seal zone at the rod speed of 200 mm/s, instroke

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Fig. 11

Development processes of the fluid pressure and film thickness in the seal zone at the rod speed of 400 mm/s, instroke

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Fig. 12

Pressure and film thickness development processes of the seal zone at the rod speed of 200 mm/s, outstroke

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Fig. 13

Pressure and film thickness development processes of the seal zone at the rod speed of 400 mm/s, outstroke

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Fig. 14

Pressure and film thickness distributions along the seal zone, steady-states, and instroke

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Fig. 15

Pressure and film thickness distributions, steady-states, and outstroke

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Fig. 16

Y-axis fluid velocity composite distributions along: (a) the minimum film thickness lines and (b) the maximum pressure lines in the lubricating zone, during instroke (rod speeds > 0) and outstroke (rod speeds < 0)




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