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

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GRADIENTS - Gradient computation

Unstructured Grids

GRADIENTS {CELL_AVERAGE | LINEAR_PRESERVING} [zone_selector]

The default gradient computation procedure in Wind-US for unstructured grids (CELL_AVERAGE) is a carry-over from the initial unstructured solver in Wind-US 1.0. In the reformulated unstructured solver introduced in Wind-US 2.0, this has been shown to be stable, but unable to preserve an initially-linear arbitrary function in the computational mesh.

Specifying LINEAR_PRESERVING causes gradients to be computed more accurately, and will preserve linearity. This will result in lower numerical dissipation, and should be specified whenever second-order accuracy is important. For example, for computing accurate drag values on a body at cruise conditions, using LINEAR_PRESERVING is essential.

The default procedure will eventually be changed to LINEAR_PRESERVING, but there are currently some stability issues for some cases that have yet to be completely resolved.

See Also: DEBUG 18, DEBUG 19