Boundary Conditions at a FluidSolid Interface

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Boundary Conditions at a Fluid-Solid Interface
by M Cieplak, J Koplik, and J Banavar
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Boundary Conditions

• Normal Component of Fluid Velocity must be zero.
• Tangential Component may only match the wall at
  some distance away.
• The distance is known as the Slip Length.

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Domain Setup

• Two walls parallel to the x-y plane.
• Periodic Boundary Conditions in the x y
  directions.
• N fluid atoms between the walls.

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Monatomic Fluid

• Two fluid atoms are separated by a distance r
  interact with the Lennard-Jones potential.

- size of the repulsive core Potential is
truncated and shifted at 2.2 .
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Polymeric Fluid

• Polymeric fluid composed of n 10 Lennard-Jones
  atoms tethered by a finitely extendible nonlinear
  elastic (FENE) potential.

• 30? and r0 1.5 , which keeps the atoms at
  r .

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Wall Organization

• Walls are constructed from two 001 planes of an
  fcc lattice. (96 atoms each with lattice constant
  0.85 .)
• Atoms tethered to fixed lattice site by a
  harmonic spring with a large spring constant.
• Wall-Atoms interactions are modeled by a distinct
  Lennard-Jones potential.

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Environment

• For monotonic fluid, temperature T fixed at

• For polymeric fluid,

• For thermal slip, T is assigned to one wall
  and for the other.

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Flow Structure Near Walls
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Resulting Flow Profile
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Slip Length Results
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References
M. Cieplak, J. Koplik, and J. R. Banavar, Phys.
Rev. Lett. 84, 803 (2001). P. A. Thompson and M.
O. Robbins, Phys. Rev. Lett. A 41, 6830 (1990).