Wind-US User's Guide - Keyword Reference, SMOOTHING

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SMOOTHING - Add dissipation to explicit operator

SMOOTHING [SECOND val1] [FOURTH val2] [SMLIMT val3] [zone_selector]

This keyword is used to apply dissipation to the explicit operator.

Structured Grids

For structured grids, the SMOOTHING keyword only applies when the ACCELERATE keyword is used for convergence acceleration. If the ACCELERATE keyword is not used, or if the iteration count is past the ending iteration specified with ACCELERATE, no smoothing is done.

The values val1, val2, and val3 are the second-order smoothing coefficient, the fourth-order smoothing coefficient, and the smoothing limiter, respectively. If the SMOOTHING keyword isn't used, no smoothing is applied. If the SMOOTHING keyword is used, but without specifying values, the default values listed below are used in the selected zones. No smoothing is done in non-selected zones. (The table also includes a "TVD-like" value for each smoothing parameter.)

Parameter Default "TVD-Like" Value
val1 1/4 < 1
val2 1/256 < 1/32
val3 0 1

Parameter	Default	"TVD-Like" Value
val1	1/4	< 1
val2	1/256	< 1/32
val3	0	1

The default values shown in the above table represent a Jameson-type smoothing, and are good for an Euler analysis. For viscous problems, it is recommended that val1, val2, and val3 be set equal to 1, 1/64, and 2, respectively.

See Also: BOUNDARY-DAMP, ACCELERATE, TEST 49

Unstructured Grids

Unlike structured grids, for unstructured grids smoothing is always applied, and is unrelated to the ACCELERATE keyword. The amount of smoothing is controlled by the LAX DAMPING and TVD keywords, not the SMOOTHING keyword. See the descriptions of those keywords for details.

However, even though smoothing in the unstructured solver is controlled differently, the values val1 and val3 specified with the SMOOTHING keyword are still used when CONVERGE LOAD is used to set the convergence criterion, and are driven to limiting values as the solution proceeds. This is a carry-over from the old unstructured solver, where the dissipation and slope limiting parameters were specified using the SMOOTHING keyword, and should be changed in the future.

The default values for val1 and val3, applied when the SMOOTHING keyword is not used, and when it is used but the corresponding parameter is not specified, are 0.25 and 1.0.

See Also: CONVERGE LOAD, LAX DAMPING, TVD