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

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COUPLING - Zone coupling mode specification

Structured Grids

COUPLING [MODE] {CHARACTERISTIC | ROE [HIGH | LOW]}

This keyword controls the zone coupling algorithm used for multi-zone solutions. The two possible options are defined below.

CHARACTERISTIC This is NASTD's original zone coupling algorithm that uses one-dimensional characteristic flow theory to set boundary flowfield variables based on local flow direction and strength. These boundary variables are then transferred between zones using interpolation factors stored in the grid file (the .cgd file).

ROE This newer zone coupling algorithm is more consistent with Roe's flux-difference splitting scheme, which is the default explicit operator. Instead of transferring flowfield variables between zones, this algorithm transfers flux cell "interface states," which are critical quantities in Roe's scheme. In this coupling mode, the zone boundary may be thought of as a "cell interface" in Roe's scheme.

The HIGH option, which is the default, turns on higher-order coupling at zone boundaries. With higher-order coupling the solution derivatives are also passed between coupled zones. This results in a slight increase in memory requirements. The derivative information is used to increase the accuracy of the coupling scheme and to improve robustness at coupled boundaries through the application of a TVD operator.

Roe coupling (HIGH or LOW) requires that the Roe, Van Leer, HLLE, HLLC, or Rusanov explicit operator be used. If RHS CENTRAL or RHS COAKLEY is specified, characteristic zone coupling will automatically be used.

In addition, since a TVD operator is used with higher-order Roe coupling, the default HIGH option cannot be used with a third-order fully upwind explicit operator, or with any of the fourth- or fifth-order explicit operators.

See Also: RHS, TVD

	`CHARACTERISTIC`		This is NASTD's original zone coupling algorithm that uses one-dimensional characteristic flow theory to set boundary flowfield variables based on local flow direction and strength. These boundary variables are then transferred between zones using interpolation factors stored in the grid file (the .cgd file).

	`ROE`		This newer zone coupling algorithm is more consistent with Roe's flux-difference splitting scheme, which is the default explicit operator. Instead of transferring flowfield variables between zones, this algorithm transfers flux cell "interface states," which are critical quantities in Roe's scheme. In this coupling mode, the zone boundary may be thought of as a "cell interface" in Roe's scheme. The `HIGH` option, which is the default, turns on higher-order coupling at zone boundaries. With higher-order coupling the solution derivatives are also passed between coupled zones. This results in a slight increase in memory requirements. The derivative information is used to increase the accuracy of the coupling scheme and to improve robustness at coupled boundaries through the application of a TVD operator. Roe coupling (`HIGH` or `LOW`) requires that the Roe, Van Leer, HLLE, HLLC, or Rusanov explicit operator be used. If `RHS CENTRAL` or `RHS COAKLEY` is specified, characteristic zone coupling will automatically be used. In addition, since a TVD operator is used with higher-order Roe coupling, the default `HIGH` option cannot be used with a third-order fully upwind explicit operator, or with any of the fourth- or fifth-order explicit operators.