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Heat Transfer and Thermal Elastic Deformation Analysis on the Piston/Cylinder Interface of Axial Piston Machines

[+] Author and Article Information
Matteo Pelosi

Maha Fluid Power Research Center, Department of Agricultural and Biological Engineering and School of Mechanical Engineering,  Purdue University, 1500 Kepner Drive, Lafayette, IN 47905mpelosi@purdue.edu

Monika Ivantysynova

Maha Fluid Power Research Center, Department of Agricultural and Biological Engineering and School of Mechanical Engineering,  Purdue University, 1500 Kepner Drive, Lafayette, IN 47905mivantys@purdue.edu

J. Tribol 134(4), 041101 (Aug 21, 2012) (15 pages) doi:10.1115/1.4006980 History: Received December 16, 2011; Accepted May 20, 2012; Published August 21, 2012; Online August 21, 2012

The piston/cylinder interface of swash plate–type axial piston machines represents one of the most critical design elements for this type of pump and motor. Oscillating pressures and inertia forces acting on the piston lead to its micro-motion, which generates an oscillating fluid film with a dynamically changing pressure distribution. Operating under oscillating high load conditions, the fluid film between the piston and cylinder has simultaneously to bear the external load and to seal the high pressure regions of the machine. The fluid film interface physical behavior is characterized by an elasto-hydrodynamic lubrication regime. Additionally, the piston reciprocating motion causes fluid film viscous shear, which contributes to a significant heat generation. Therefore, to fully comprehend the piston/cylinder interface fluid film behavior, the influences of heat transfer to the solid boundaries and the consequent solid boundaries’ thermal elastic deformation cannot be neglected. In fact, the mechanical bodies’ complex temperature distribution represents the boundary for nonisothermal fluid film flow calculations. Furthermore, the solids-induced thermal elastic deformation directly affects the fluid film thickness. To analyze the piston/cylinder interface behavior, considering the fluid-structure interaction and thermal problems, the authors developed a fully coupled simulation model. The algorithm couples different numerical domains and techniques to consider all the described physical phenomena. In this paper, the authors present in detail the computational approach implemented to study the heat transfer and thermal elastic deformation phenomena. Simulation results for the piston/cylinder interface of an existing hydrostatic unit are discussed, considering different operating conditions and focusing on the influence of the thermal aspect. Model validation is provided, comparing fluid film boundary temperature distribution predictions with measurements taken on a special test bench.

Copyright © 2012 by by ASME
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References

Figures

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Figure 1

Axial piston machine rotating kit and main components

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Figure 2

Piston-oscillating forces and piston/cylinder coordinate systems

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Figure 3

Piston/cylinder inclined position and film thickness definition

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Figure 4

Piston-oscillating eccentricities micro-motion (left) and piston macro-motion (right) over one shaft revolution

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Figure 5

Piston/cylinder fluid film finite volume discretization scheme

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Figure 6

Piston/cylinder Reynolds equation reference system

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Figure 7

Cylinder block, piston guide, and piston meshes

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Figure 8

Unstructured mesh configuration for tetrahedron elements (left) and base cell C0 typical three neighbors layout (right)

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Figure 9

Cylinder block and piston typical boundary conditions

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Figure 10

Instantaneous thermal fluxes to piston and cylinder surfaces with exaggerated fluid film thickness

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Figure 11

Piston/cylinder model coupled numerical domains

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Figure 12

The complete numerical algorithm scheme

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Figure 13

Piston and cylinder block solid domain and displacement chamber pressure boundary condition

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Figure 14

Piston/cylinder interface unwrapped thermo-elastohydrodynamic pressure field and fluid film thickness over one shaft revolution

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Figure 15

Piston/cylinder interface unwrapped pressure ΔhP and thermal ΔhT elastic deformations over one shaft revolution

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Figure 16

Piston (left) and cylinder block (right) temperature distributions

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Figure 17

Piston (left) and cylinder (right) fluid film boundary surfaces temperature distribution at ϕ = 0 deg

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Figure 18

Piston/cylinder fluid film mechanical viscous dissipation over one shaft revolution

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Figure 19

Piston (left) and cylinder block (right) radial (x-y) thermal elastic deformations

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Figure 20

Piston (left) and cylinder (right) fluid film boundary surfaces’ thermal elastic deformations at ϕ = 0 deg

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Figure 21

Special piston/cylinder test rig allows fluid film dynamic pressure and temperature field measurements

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Figure 22

Special piston/cylinder test rig numerical discretization with thermal boundary conditions

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Figure 23

Cylinder temperature distribution with measured (left) and simulated (right) cylinder surface boundary temperatures

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Figure 24

Piston/cylinder interface measured and simulated unwrapped dynamic pressure field over one shaft revolution

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