Coordinate System

Coordinate System = {char_string}

Description / Usage

This card is required for each material section in the Problem Description File. It is used to specify formulation of the equations to be solved. Valid options for {char_string} are as follows:

CARTESIAN	For a two (x-y) or three (x-y-z) dimensional Cartesian formulation.
CYLINDRICAL	For an axisymmetric (z-r) or three-dimensional cylindrical (z-r-\(\theta\)) formulation; the three-dimensional option has not been tested.
SPHERICAL	For a spherical (r-\(\theta\)-\(\phi\)) formulation.
SWIRLING	For a two-dimensional formulation (z-r-\(\theta\)) with a swirling velocity component that is independent of azimuthal coordinate.
PROJECTED_CARTESIAN	For use in the analysis of the three-dimensional stability of a two-dimensional flow field. The formulation (x-yz) has a z-velocity component that is independent of the z-direction.

Examples

The following is a sample card that sets the coordinate system to Cartesian:

Coordinate System = CARTESIAN

Technical Discussion

Note the coordinate ordering for the CYLINDRICAL and SWIRLING options where the z-direction is first followed by the r-component (which in lay terms means the modeled region/part will appear to be ”lying down.”) If the SWIRLING option is activated, Goma expects a third momentum equation for the \(\theta\)-direction, i.e. EQ = momentum3, as explained in the equation section. The third component is basically the azimuthal \(\theta\)-velocity component, and the appropriate boundary conditions must be applied, e.g., on the w-component as described in the Category 4 boundary conditions for Fluid Momentum Equations.

References

No References.