Stream Function

Stream Function = {yes | no}

Description / Usage

The stream function provides a visual representation of the flow field in incompressible fluids and is derived from the fluid velocity components identified in the Output Exodus II file card.

This auxiliary field triggered by “yes” on this card results in a nodal variable that is called STREAM in the output EXODUS II file.

The permissible values for this postprocessing option are:

yes	Calculate the stream function.
no	Do not calculate the stream function.

Examples

Following is a sample card:

Stream Function = no

Technical Discussion

This function is computed with an element-by-element volumetric flow calculation routine. Poor element quality can result in “kinks” in the stream function field when contoured.

It is important to construct a mesh whose elements are contiguously ordered in such a way that there are no isolated clusters as the elements are swept, i.e., element n+1 must be in contact with one of the previous n elements. NOTE: as of 4/2001 an automatic element reordering scheme based on Reverse Cuthill-McKee algorithm has been implemented in Goma. Automatic ordering can be assured by issuing the OPtimize command to the FASTQ meshing module (cf. Blacker 1988). Most other mesh generators do not provide this service, viz. they do not put out an element order-map field in the EXODUS II file.

NOTE: THIS FUNCTION IS NOT AVAILABLE IN THREE DIMENSIONS, but pathlines, which are equivalent to streamlines for steady flows can be computed in many graphics packages, like Mustafa (Glass, 1995).

References

SAND88-1326: FASTQ Users Manual: Version 1.2, Sandia Technical Report, Blacker, T. D. 1988.

Mustafa, Glass, M. W., Personal Communication, 1995