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What Are the Scalar Names in the Post-Processor?

What does “All velocity”, “All velocity [node]”, “Pressure_e”, and “Pressure_n” stand for? In this article, we will answer the potential questions regarding the format and meanings of scalar names in the SimScale post-processor.

The model in this picture is a pipe junction and the picture shows the most common scalar names
Figure 1: Scalars in the post-processor.

Solution: Scalar Names

The following table shows some scalar names you will see in the post-processor. This is a brief list only. In addition, you will see the combination of ‘scalar_name’ + ‘[node]’ and ‘axis_name’ + ‘velocity’ + ‘[node]’.

Scalar NamingExplanation
T1Passive scalar value
X Velocity (m/s)Velocity component of x-axis
All Velocity (m/s)Magnitude of the velocity vectors of x, y, and z (Cell value)
All Velocity [node] (m/s)Magnitude of the velocity vectors of x, y, and z (Node value)
Table 1: Scalar naming in the standard post-processor.

In Incompressible (LBM) and Pedestrian Wind Comfort (PWC) analysis types, a similar naming convention is used.

Scalar NamingExplanation
Pressure_e (Pa)Pressure (Cell value)
Pressure_n (Pa)Pressure (Node value)
Table 2: Scalar naming in the LBM and PWC post-processor.

Cell and Node Values

What do cell value and node value stand for? Let’s check the following examples:

post-processing image of the pressure values on the cells
Figure 2: Pressure contour on mid-section of the pipe on cells.
post-processing image of the pressure values on the nodes
Figure 3: Pressure contour on mid-section of the pipe on nodes.

Both images show the pressure distribution on the mid-cross section of a pipe model. The first image looks as if pixelated. Because Pressure (Pa) scalar shows cell values. This is a coarse mesh, therefore we see sudden pressure transition. In a fine mesh, the transition would be smoother.

If you zoom-in to the pipe junction, you will see that the pressure contour is smoother on node values. This is because the gradient is interpolated between the nodes (node is simply a corner of a cell). In cell values representation, contours are generated with respect to the individual value of the cell.

cell values displayed within simscale
Figure 4: Representation of cell values.
node values being demonstrated within simscale
Figure 5: Representation node values.

In order to capture the flow effects more accurately, it is advised to reduce the element size until the cell size has no more influence on the results. The following articles can help to teach meshing and mesh visualization:

Compare Node and Cell Values to Judge the Mesh Quality

Fine mesh for improved mesh quality
Figure 6: Refined mesh to compare cell and node values for improved mesh quality

Ideally, reduce the element size until the results from cell values are equal to node values.

comparison between node and cell values
Figure 7: Pressure contour and Comparison of cell and node values

Note

If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.

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