31.1.2 Node Values

Node values are explicitly defined or obtained by weighted averaging of the cell data. Various boundary conditions impose values of field variables at the domain boundaries, so mesh node values on these boundary zones are obtained by simple averaging of the adjacent boundary face data. In addition, for several variables (e.g., node coordinates) explicit node values are available at all nodes.

Computation of node values is performed in two steps:

1.   Values at all nodes are initialized to the weighted average of the surrounding cell values. The weights are the inverses of the distances between the nodes and the cell centroid.

2.   At boundaries, these node values are overwritten with the simple average of the boundary face values. Variables for which explicit node values are available at boundaries are indicated by bnv in Tables  31.3.1- 31.3.14.

For example, in Figure  31.1.1, the value at node $n1$ will be computed from the weighted average of the values in the surrounding cells ( $c1$- $c6$). The value at node $n2$ will be computed from the simple average of the boundary faces ( $bf1$ and $bf2$) if there are explicit boundary values available for the variable in question.

Figure 31.1.1: Computing Node Values

Note that explicit boundary node values are not available for custom field functions.

Vertex Values for Points That are Not Mesh Nodes

The values of the nodes on surfaces are linearly interpolated from the mesh node data. For zone surfaces, the nodes on the surface and the zone correspond; thus, the values are identical. For surfaces that are not zone surfaces (e.g., isosurfaces, plane surfaces, etc.), the node values are interpolated from mesh nodes on the cell faces intersected by the postprocessing surface. For point surfaces the value is interpolated from all the mesh nodes of the cell containing the point.