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RHS VISCOUS - Explicit viscous operator control

Structured Grids

RHS VISCOUS word1 word2 word3 [zone_selector]

Unstructured Grids

RHS VISCOUS {THIN-LAYER | TSL | FULL | FACETANGENT | MODE mode} [zone_selector]

This keyword allows control of the explicit viscous operator used within each zone.

Structured Grids

For structured grids, this keyword turns off the viscous terms in specified coordinate directions. The parameters word1, word2, and word3 are keywords controlling the viscous terms in the ξ-, η-, and ζ-directions, respectively. They may have the following values:

    Keyword   Meaning
VISCOUS Retain all viscous terms in this direction
INVISCIDNeglect all viscous terms in this direction

The default setting for structured grids is to use the full viscous terms in each direction, unless the RHS VISCOUS keyword is used to specify something different.

When INVISCID is set for a direction, the scalar implicit operator will be used in that direction (the full block implicit operator is used in viscous directions). This may be overridden using the IMPLICIT keyword.

Unstructured Grids

For unstructured grids, this keyword modifies how the viscous discretization is performed. The various options available are as follows:

    Keyword   Meaning
FULL Full viscous term discretization derived from the finite difference between cell centers and constructing other components from the average of cell gradients. Equivalent to MODE -5.

THIN-LAYER | TSL Pseudo thin-layer approximation for viscous terms obtained from the finite difference between cell centers. Equivalent to MODE 6.

FACETANGENT Full viscous term discretization derived from the finite difference between cell centers and preserving the component of gradient in the plane of the face from average of cell gradients. Appears to be more robust for skewed meshes in viscous dominated regions. Equivalent to MODE -9.
  • [Thomas, J. L., Diskin, B., and Nishikawa, H. (2011) "A Critical Study of Agglomerated Multigrid Methods for Diffusion on Highly-Stretched Grids," Computers & Fluids, Vol. 41, pp. 82-93]
MODE mode Testing option for alternate discretizations. Positive values of mode result in an additional correction associated with the jump in face-center reconstructed values. Other values correspond to different types of corrections to the computed face gradient. This option should be used carefully, as unexpected results can arise based on grid quality.

    |mode|   Meaning
1 Augment the average cell gradient with the finite difference between cell centers in face normal direction.
2 Only use the finite difference between cell centers in the face normal direction.
3 Only use the component of the average cell gradient in the face normal direction.
4 Not used.
5 Augment the average cell gradient with the finite difference between cell centers in the direction of the cell centers.
6 Use only the finite difference between cell centers in the direction of the cell centers.
7 Use only half of the augmentation applied in MODE 5.
8 Augment the average cell gradient with the finite difference between cell centers. The absolute value is taken of the denominator in the difference to guarantee to provide a dissipative viscous flux on skewed meshes.
9 Preserve the average cell gradient in the plane of the face and use finite difference between cell centers in the direction of cell centers.
10 Similar to MODE 9, but only uses the finite difference component.

The default setting for unstructured grids is to use the THIN-LAYER terms, unless the RHS VISCOUS keyword is used to specify something different.


Last updated 1 Apr 2016