26.13.5 Monitoring Volume Integrals

At the end of each solver iteration or time step, the volume or the sum, volume integral, volume average, mass integral, or mass average of a field variable or function can be monitored in one or more cell zones. You can print and plot these convergence data, and also save them in an external file. The external file is written in the ANSYS FLUENT XY plot file format described in Section  29.9.6. The report types available are the same as those in the Volume Integrals dialog box, as described in Section  30.7.

Monitoring volume integrals can be used to check for both iteration convergence and mesh independence. For example, you can monitor the average value of a certain variable in a particular cell zone. When this value stops changing, you can stop iterating. You can then adapt the mesh and reconverge the solution. The solution can be considered mesh-independent when the average value in the cell zone stops changing between adaptions.

Overview of Defining Volume Monitors

You can use the Volume Monitor dialog box (Figure  26.13.8) to create volume monitors and indicate whether and when each one's history is to be printed, plotted, or saved. You can also define what each monitor tracks (i.e., the volume or the sum, integral, or average of a field variable or function in one or more cell zones).

Monitors (Volume Monitors) Create...

Figure 26.13.8: The Volume Monitor Dialog Box

The procedure for defining volume monitors is as follows:

1.   Enter a name for the monitor under the Name heading, and use the Plot, Print to Console, and Write check buttons to indicate the report(s) you want (plot, print out, or file), as described below.

2.   If you are plotting the data or writing them to a file, specify the parameter to be used as the $x$-axis value (the $y$-axis value corresponds to the monitored data). In the X Axis drop-down list, select Iteration, Time Step, or Flow Time as the $x$-axis function against which monitored data will be plotted or written. Time Step and Flow Time are valid choices only if you are calculating unsteady flow. If you choose Time Step, the $x$ axis of the plot will indicate the time step, and if you choose Flow Time, it will indicate the elapsed time.

3.   If you are plotting the monitored data, specify the ID of the graphics window in which the plot will be drawn in the Window field. When ANSYS FLUENT is iterating, the active graphics window is temporarily set to this window to update the plot, and then returned to its previous value. Thus, each volume-monitor plot can be maintained in a separate window that does not interfere with other graphical postprocessing.

4.   If you are writing the monitored data to a file, specify the File Name.

5.   Indicate the frequency at which you want to plot, print, or write the volume monitor by entering a number under Get Data Every. A default value of 1 will allow you to monitor at every Iteration or Time Step.

6.   Indicate whether you want to update the monitor every Iteration or every Time Step by selecting the appropriate item in the drop-down list. Time Step is a valid choice only if you are calculating unsteady flow. If you specify every Iteration, and the Reporting Interval in the Run Calculation task page is greater than 1, the monitor will be updated at every reporting interval instead of at each iteration (e.g., for a reporting interval of 2, the monitor will be updated after every other iteration. If the reporting interval is 2 and monitor frequency is at Get Data Every 3 Iterations, then the monitoring will be done at multiples of six, which is the least common multiple of the two numbers). If you specify every Time Step, the reporting interval will have no effect; the monitor will always be updated after the specified number of time steps.

7.   Choose the integration method for the volume monitor by selecting Volume, Sum, Max, Min, Volume Integral, Volume-Average, Mass Integral, or Mass-Average in the Report Type drop-down list. These methods are described in Section  30.7.

8.   Specify the variable or function to be integrated in the Field Variable drop-down list. First select the desired category in the upper drop-down list. You can then select one of the related quantities in the lower list. (See Chapter  31 for an explanation of the variables in the list.)

9.   In the Cell Zones list, choose the cell zone(s) on which you wish to integrate.

10.   Remember to click OK in the Volume Monitors dialog box after you finish defining all volume monitors.

Printing, Plotting, and Saving Volume Integration Histories

There are three methods available for reporting the selected volume integration. To print the volume integration in the console window after each iteration, Enable the Print to Console option in the Volume Monitor dialog box. To plot the integrated values in the graphics window indicated in Window, enable the Plot option. If you want to save the values to a file, enable the Write option and specify the File Name. You can enable any combination of these options simultaneously.

If you choose not to save the volume integration data to a file, this information will be lost when you exit the current ANSYS FLUENT session.

Plot Parameters

You can modify the attributes of the plot axes and curves used for each volume-monitor plot. Click the Axes... or Curves... button in the Volume Monitor dialog box for the appropriate monitor to open the Axes dialog box or Curves dialog box for that volume-monitor plot. See Sections  29.9.9 and 29.9.10 for details.