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28.1.2 Displaying Contours and Profiles

FLUENT allows you to plot contour lines or profiles superimposed on the physical domain. Contour lines are lines of constant magnitude for a selected variable (isotherms, isobars, etc.). A profile plot draws these contours projected off the surface along a reference vector by an amount proportional to the value of the plotted variable at each point on the surface. Sample plots are shown in Figures  28.1.11 and  28.1.12.

See also Section  28.1.5 for information about displaying contours or profiles on a surface that sweeps through the domain.

Figure 28.1.11: Contours of Static Pressure

Figure 28.1.12: Profile Plot of $y$ Velocity

Steps for Generating Contour and Profile Plots

You can plot contours or profiles using the Contours panel (Figure  28.1.13).

Display $\rightarrow$ Contours...

Figure 28.1.13: The Contours Panel

The basic steps for generating a contour or profile plot are as follows:

1.   Select the variable or function to be contoured or profiled in the Contours of drop-down list. First select the desired category in the upper list; you may then select a related quantity in the lower list. (See Chapter  30 for an explanation of the variables in the list.)

2.   Choose the surface or surfaces on which to draw the contours or profiles in the Surfaces list. For 2D cases, if no surface is selected, contouring or profiling is done on the entire domain. For 3D cases, you must always select at least one surface.

If you want to select several surfaces of the same type, you can select that type in the Surface Types list instead. All of the surfaces of that type will be selected automatically in the Surfaces list (or deselected, if they are all selected already).

Another shortcut is to specify a Surface Name Pattern and click Match to select surfaces with names that match the specified pattern. For example, if you specify wall*, all surfaces whose names begin with wall (e.g., wall-1, wall-top) will be selected automatically. If they are all selected already, they will be deselected. If you specify wall?, all surfaces whose names consist of wall followed by a single character will be selected (or deselected, if they are all selected already).

3.   Specify the number of contours or profiles in the Levels field. The maximum number of levels allowed is 100.

4.   If you are generating a profile plot, turn on the Draw Profiles option. In the resulting Profile Options panel (Figure  28.1.14) you will define the profiles as described below:

Figure 28.1.14: The Profile Options Panel

(a)   Set the "zero height'' reference value for the profile ( Reference Value) and the length scale factor for projection ( Scale Factor). Any point on the profile with a value equal to the Reference Value will be plotted exactly on the defining surface. Values greater than the Reference Value will be projected ahead of the surface (in the direction of Projection Dir.) and scaled by Scale Factor), and values less than the Reference Value will be projected behind the surface and scaled.

These parameters can be used to create fuller profiles when you need to display the variation in a variable which is small compared to the absolute value of the variable. Consider, for example, the display of temperature profiles when the temperature range in the domain is from 300 K to 310 K. The 10 K range in the temperature will be hard to detect when profiles are drawn using the default scaling (which will be based on the absolute magnitude of 310 K). To create a fuller profile, you can set the Reference Value to 300 and the profile Scaling Factor to 5 (for example) to magnify the display of the remaining 10 K range. In subsequent display of the profiles, the reference value of 300 will be effectively subtracted from the data before display so that the temperatures of 300 K will not be offset from the baselines. The profiles will then reflect only the variation of temperature from 300 K.

(b)   Set the direction in which profiles are projected ( Projection Dir.). In 2D, for example, a contour plot of pressure on the entire domain can be projected in the $z$ direction to form a carpet plot, or a contour plot of $y$ velocity on a sequence of $y$-coordinate slice lines can be projected in the $y$ direction to form a series of velocity profiles (as shown in Figure  28.1.12).

(c)   Click Apply and close the Profile Options panel.

5.   Set any of the options described below.

6.   Click the Display button to draw the specified contours or profiles in the active graphics window.

The resulting display will include the specified number of contours or profiles of the selected variable, with the magnitude on each one determined by equally incrementing between the values shown in the Min and Max fields.

Contour and Profile Plot Options

The options mentioned in the procedure above include drawing color-filled contours/profiles (instead of the default line contours/profiles), specifying a range of values to be contoured or profiled, including portions of the grid in the contour or profile display, choosing node or cell values for display, and storing the contour or profile plot settings.

Drawing Filled Contours or Profiles

Color-filled contour or profile plots show a contour or profile display containing a continuous color display (see Figure  28.1.15), instead of just drawing lines representing specific values. (Note that a color-filled profile display is often referred to as a "carpet plot''.) To generate a filled contour or profile plot, turn on the Filled option in the Contours panel during step 5 above.

Figure 28.1.15: Filled Contours of Static Pressure

To display smoothly shaded filled contours, you must turn on lighting and select a lighting interpolation method other than Flat in the Display Options panel or the Lights panel. Note that you will not get smooth shading of filled contours if the Clip to Range (see below) option is turned on. Smooth shading of filled profiles is not available.

Specifying the Range of Magnitudes Displayed

By default, the minimum and maximum values contoured or profiled are set based on the range of values in the entire domain. This means that the color scale will start at the smallest value in the domain (shown in the Min field) and end at the largest value (shown in the Max field). If you are plotting contours or profiles on a subset of the domain (i.e., on a surface), your plot may cover only the midrange of the color scale. For example, if blue corresponds to 0 and red corresponds to 10, and the values on your surface range only from 4 to 6, your plot will contain mostly green contours or profiles, since green is the color at the middle of the default color scale.

If you want to focus in on a smaller range of values, so that blue corresponds to 4 and red to 6, you can manually reset the range to be displayed. (You can also use the minimum and maximum values on the selected surfaces--rather than in the entire domain--to determine the range, as described below.) Another reason to manually set the range is if you are interested only in certain values. For example, if you want to determine the region where pressure exceeds a certain value, you can increase the minimum value for display so that the lower pressure values are not displayed.

To manually set the contour/profile range, turn off the Auto Range option in the Contours panel. The Min and Max fields will become editable, and you can enter the new range of values to be displayed. To show the default range at any time, click the Compute button and the Min and Max fields will be updated.

If you are drawing filled contours or profiles (as described above) you can control whether or not values outside the prescribed Min/ Max range are displayed. To leave areas in which the value is outside the specified range empty (i.e., draw no contours or profiles), turn on the Clip to Range option. This is the default setting. If you turn Clip to Range off, values below the Min value will be colored with the lowest color on the color scale, and values above the Max value will be colored with the highest color on the color scale. Figures  28.1.16 and 28.1.17 show the results of enabling/disabling the Clip to Range option.

You can also choose to base the minimum and maximum values on the range of values on the selected surfaces, rather than in the entire domain. To do this, turn off the Global Range option in the Contours panel. The Min and Max values will be updated when you next click Compute or Display.

Figure 28.1.16: Filled Contours with Clip to Range On

Figure 28.1.17: Filled Contours with Clip to Range Off

Including the Grid in the Contour Plot

For some problems, especially complex 3D geometries, you may want to include portions of the grid in your contour or profile plot as spatial reference points. For example, you may want to show the location of an inlet and an outlet along with the contours. This is accomplished by turning on the Draw Grid option in the Contours panel. The Grid Display panel will appear automatically when you turn on the Draw Grid option, and you can set the grid display parameters there. When you click Display in the Contours panel, the grid display, as defined in the Grid Display panel, will be included in the contour or profile plot.

Choosing Node or Cell Values

In FLUENT you can choose to display the computed cell-center values or values that have been interpolated to the nodes. By default, the Node Values option is turned on, and the interpolated values are displayed. For line contours or profiles, node values are always used. If you are displaying filled contours or profiles and you prefer to display the cell values, turn the Node Values option off. Filled contours/profiles of node values will show a smooth gradation of color, while filled contours/profiles of cell values may show sharp changes in color from one cell to the next.

If you are plotting contours to show the effect of a porous medium or fan, to depict a shock wave, or to show any other discontinuities or jumps in the plotted variable, you should use cell values; if you use node values in such cases, the discontinuity will be smeared by the node averaging for graphics and will not be shown clearly in the plot.

Storing Contour Plot Settings

For frequently used combinations of contour variables and options, you can store the information needed to generate the contour plot by specifying a Setup number and setting up the desired information in the Contours panel. When you click on the Display button, the settings for Options, Contours of, Min, Max, and Surfaces will be saved. You can then change the Setup number to an unused value (i.e., an ID for which no information has been saved) and generate a different contour plot. To generate a plot using the saved setup information, change the Setup number back to the value for which you saved contour information and click Display. You can save up to 10 different setups.


Note that the number of contour Levels, the surfaces selected for display in the Grid Display panel (when the Draw Grid option is activated), and the settings for profiles in the Profile Options panel (when the Draw Profiles option is activated) will not be saved in the Setup, nor will the Setups be saved in the case file.

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© Fluent Inc. 2006-09-20