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

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RHS - Explicit operator control

Structured Grids

RHS scheme [order [modifier]] [ZONE zone_selector]

Unstructured Grids

RHS scheme [order] [ZONE zone_selector]

This keyword allows control of the explicit operator used within each zone. The parameter scheme specifies the general type of differencing scheme, order specifies the differencing order, and (for structured grids) modifier specifies the type of spatial differencing.

The zone specification is optional. If used, it must be preceded by the ZONE keyword.

Structured Grids

For structured grids, the following choices are available for scheme:

   CENTRAL, COAKLEY, HLLC, HLLE, ROE, ROE_OVER, RUSANOV, VANLEER

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

   FIRST, SECOND, TWOTHREE, THIRD, FOURTH, FOURFIVE, FIFTH

The modifier must be one of:

   CENTRAL, UPWIND, PHYSICAL, UPWINDBIASED, BLENDED

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

If scheme is ROE, VANLEER, HLLE, HLLC, or RUSANOV, then Roe, Van Leer, HLLE, HLLC, or Rusanov 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 to prevent expansion shocks. Otherwise, the HLLE and Roe schemes give very similar results.

The following options are available for order and modifier with all of the Roe, Van Leer, HLLE, HLLC, and Rusanov schemes. 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
	`TWOTHREE BLENDED`		Blended second-order central, third-order upwind-biased
	`THIRD [UPWINDBIASED]`		Third-order, upwind-biased
	`THIRD UPWIND`		Third-order, fully upwind
	`FOURTH [UPWINDBIASED]`		Fourth-order, upwind-biased
	`FOURTH CENTRAL`		Fourth-order, central
	`FOURFIVE BLENDED`		Blended fourth-order central, fifth-order upwind-biased
	`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 as the default.

Notes

Roe zonal coupling requires that Roe, Van Leer, HLLE, HLLC, or Rusanov differencing be used.
TVD flux limiting, and the default zonal coupling procedure (high-order Roe), cannot be used with some of the higher-order explicit operators. See the TVD and COUPLING keywords for details.
Some of the explicit operators cannot 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, HLLE, HLLC, or Rusanov explicit operator must be used in zones containing holes.
The ROE_OVER scheme cannot currently be used for multi-species flows.
The Van Leer scheme cannot be used with ROTATE or GRAVITY.

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

Unstructured Grids

For unstructured grids, the following choices are available for scheme:

   HLLC, HLLE, ROE, RUSANOV

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

   FIRST, SECOND

The default for order is SECOND. If the RHS keyword is not used, the second-order HLLE scheme (i.e., HLLE SECOND) is used as the default.

See Also: ENTROPY FIX

Last updated 1 Apr 2016