Post-processing

Once the message Process '…', started on … has finished. is displayed, we can visualise the final results by pressing Postprocess (note that the problem must still be loaded; should this not be the case we first have to open the problem files again). Note that the intermediate results can be shown in any moment of the process even if the calculations are not finished.

On first entering the post-processing module, two windows - View Style and View Results - are accessible through the Windows menu (see Figure 26).

 

Figure 26 Accessing the View style and View results windows

The View Style or Select & Display Style window allows the user to select, which elements of the mesh to be post-processed, and how the results will be represented.

In the Select & Display Style window (see

Figure27) the label S Fluidmakes reference to the mesh of the Control Surface whereas S Fluid Bodyrefers to the body and S SurfaceSet 12 to the rest of lines.

The View Results window allows the user to choose the result to be represented and the way this result will be displayed (see

Figure27).

 

 

Figure 27 Select & Display Style and View Results window

Results Visualisation

First we will visualise the velocity distribution on the surface domain by plotting the iso-contours of the x- and y velocity components. This will be achieved by choosing the following options in the View Results window:

Steps:              (usually the last time step of the selection)

View:               Contour Lines

Results:            velocity

Component:    x-component    (Figure 28, left)

                        y-component    (Figure 28, right)

The postprocessing image can then be saved as a screenshot of the current window by using its Camera icon from the graphical menu. The Postprocessor module supports several image formats.

Figure 28 Contour lines of the x-component (left) and y-component (right) of the velocity vector

Note that the asymmetrical irregularities in the velocity distribution shown in Figure 28 are due to the coarse mesh chosen. By using finer mesh the contours would be smoother.

An overall impression of the flow pattern can be obtained by plotting the velocity vectors on the control surface (Figure 29). This plot is obtained by applying the following choices in the View results window:

View:               Display Vectors

Results:            Velocity

Component:     |Velocity|

Figure 29 Velocity Vectors distribution

Should the vectors appear drawn only over the control surface's boundaries, we have to make sure that the display style is set to Boundaries

If the vectors appear drawn in one colour only, we have to apply the following commands (Figure 30) and apply the Colour Mode option:

Figure 30 Vector Colour Menu

Finally, we can also plot the pressure distribution (Figure 31) over the cut plane, by applying the respective options in the View results window.

  

Figure 31 Pressure distribution (contour fill and contour lines)

Graphs

As the graphs will be visualised over a cross section only, we have to proceed by cutting the mesh at the desired position. To do the cut, follow the instructions of Figure 32.

Figure 32 The Do Cuts menu option

 

The cut plane will be perpendicular to the view drawn on the screen. By selecting the nodes of the mesh you can introduce points, either with the mouse or by introducing their co-ordinates manually in GiD's command line. In this example we will select a cut plane parallel to the original orientation of the control volume (XY-plane). In our case we used the points (0.0; 0.5) and (1.0; 0.5).

In the Select & Display Style window the cut planes will appear defined together with the previously explained entities (S Fluid, S SurfaceSet 12…) as Cut1, Cut2… All the entities can be turned on or off. By leaving only the cuts on we can plot and visualise the results over the cross section.

The graphs can be easily drawn using the View graphs window (Figure 33). Then select the variable to be drawn and select the border (Cut 1) as shown in Figure 33.

The resultant graph is shown in Figure 34.

     

Figure 33 Border graphs window

Figure 34 Y velocity component on medium section graph

For more details on the postprocessing steps, please refer to the Pre/Postprocessor user manual, or to the online help from the Help menu.