WIND User's Guide - Keyword Reference, RHS

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RHS - Explicit operator control

RHS scheme [order [modifier]] [zone_selector]

This keyword allows control of the explicit operator used within each zone. The parameter scheme specifies the type of differencing scheme, and must be one of the following:

   CENTRAL, COAKLEY, ROE, ROE_OVER, VANLEER, HLLE

The parameter order specifies the type of differencing order, and must be one of the following:

   FIRST, SECOND, THIRD, FOURTH, FIFTH

The modifier must be one of:

   CENTRAL, UPWIND, PHYSICAL, UPWINDBIASED

Not all combinations of options are valid.

If scheme is CENTRAL, second-order central differencing is used, and any values specified for order and modifier are ignored.

If scheme is COAKLEY, Coakley differencing is used and the following options are available for order. Any modifier that is specified is ignored. Following the usual conventions for displaying keyword syntax, optional keyword parameters are inside square brackets. Thus, RHS COAKLEY and RHS COAKLEY SECOND both give second-order Coakley differencing, fully upwind.

order Explicit Operator
FIRST First-order, upwind
[SECOND] Second-order, fully upwind
THIRD Third-order, upwind-biased

	order		Explicit Operator
	`FIRST`		First-order, upwind
	`[SECOND]`		Second-order, fully upwind
	`THIRD`		Third-order, upwind-biased

If scheme is ROE, VANLEER, or HLLE, Roe, Van Leer, or HLLE differencing is used, respectively.

If scheme is ROE_OVER, an alternative implementation of the Roe scheme from the OVERFLOW code is used. This implementation seems to be faster, and includes an entropy fix that prevents expansion shocks.

The HLLE scheme also includes a built-in entropy fix. Otherwise, the HLLE and Roe schemes give very similar results.

For all of the Roe, Van Leer, and HLLE schemes, the following options are available for order and modifier. Again, optional parameters are inside square brackets. Thus, RHS ROE, RHS ROE SECOND, and RHS ROE SECOND PHYSICAL all give second-order Roe upwind-biased differencing, modified for stretched grids.

order and modifier Explicit Operator
FIRST [UPWIND] First-order, upwind
FIRST PHYSICAL First-order, upwind, modified for stretched grids
[SECOND [PHYSICAL]] Second-order, upwind-biased, modified for stretched grids
SECOND CENTRAL Second-order, central
SECOND UPWINDBIASED Second-order, upwind-biased
SECOND UPWIND Second-order, fully upwind
THIRD [UPWINDBIASED] Third-order, upwind-biased
THIRD UPWIND Third-order, fully upwind
FOURTH [UPWINDBIASED] Fourth-order, upwind-biased
FOURTH CENTRAL Fourth-order, central
FIFTH [UPWINDBIASED] Fifth-order, upwind-biased

	order and modifier		Explicit Operator
	`FIRST [UPWIND]`		First-order, upwind
	`FIRST PHYSICAL`		First-order, upwind, modified for stretched grids
	`[SECOND [PHYSICAL]]`		Second-order, upwind-biased, modified for stretched grids
	`SECOND CENTRAL`		Second-order, central
	`SECOND UPWINDBIASED`		Second-order, upwind-biased
	`SECOND UPWIND`		Second-order, fully upwind
	`THIRD [UPWINDBIASED]`		Third-order, upwind-biased
	`THIRD UPWIND`		Third-order, fully upwind
	`FOURTH [UPWINDBIASED]`		Fourth-order, upwind-biased
	`FOURTH CENTRAL`		Fourth-order, central
	`FIFTH [UPWINDBIASED]`		Fifth-order, upwind-biased

If the RHS keyword is not used, the second-order upwind-biased Roe scheme with modifications for stretched grids (i.e., RHS ROE SECOND PHYSICAL) is used.

Notes

Roe zonal coupling requires that Roe, Van Leer, or HLLE differencing be used.
TVD flux limiting, and the default zonal coupling procedure (high-order Roe), can not be used with some of the higher-order explicit operators. See the TVD and COUPLING keywords for details.
Some of the explicit operators can not be used in a spatial marching calculation. See the MARCHING keyword for details.
If a first-order upwind explicit operator modified for stretched grids is used, test option 189 must be set.
A Roe, Van Leer, or HLLE explicit operator must be used in zones containing holes.
The ROE_OVER and VANLEER schemes cannot currently be used for multi-species flows.

See Also: COUPLING, MARCHING, TVD, HLLE, TEST 189