|RHS scheme [order [modifier]] [ZONE range1[,range2[, ... rangen]]]|
|RHS scheme [order] [ZONE range1[,range2[, ... rangen]]]|
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 format is essentially the same as for a zone_selector, except that the word ZONE is required if a range is being input.
For structured grids, the following choices are available for scheme:
CENTRAL, COAKLEY, HLLC, HLLE, ROE, ROE_OVER, RUSANOV, VANLEERThe parameter order specifies the differencing order, and must be one of the following:
FIRST, SECOND, TWOTHREE, THIRD, FOURTH, FOURFIVE, FIFTHThe modifier must be one of:
CENTRAL, UPWIND, PHYSICAL, UPWINDBIASED, BLENDEDNot 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.
|[SECOND]||Second-order, fully upwind|
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.
See Also: COUPLING, MARCHING, TVD, HLLE, ENTROPY FIX, TEST 189
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, SECONDThe default for order is SECOND.
If the RHS keyword is not used, the second-order HLLE scheme (i.e., HLLE SECOND) is used.
See Also: ENTROPY FIX