26.13.4 Monitoring Surface Integrals

At the end of each solver iteration or time step, the average, mass average, integral, flow rate, or other integral report of a field variable or function can be monitored on a surface. 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 Surface Integrals dialog box, as described in Section  30.6.

Monitoring surface 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 on a surface. 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 on the surface stops changing between adaptions.

Overview of Defining Surface Monitors

You can use the Surface Monitors dialog box (Figure  26.13.7) to create surface monitors and indicate whether and when each one's history is to be printed, plotted, or saved. It also allows you to define what each monitor tracks (i.e., the average, integral, flow rate, mass average, or other integral report of a field variable or function on one or more surfaces).

Monitors (Surface Monitors) Create...

Figure 26.13.7: The Surface Monitors Dialog Box

The procedure for defining surface monitors is as follows:

1.   Enter a name for the monitor under the Name heading, and use the Plot to Console, Print, and Write check buttons to indicate the report(s) you want (plot, printout, or save to a 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 surface-monitor plot can be maintained in a separate window that does not interfere with other graphical postprocessing.

In order to have multiple monitors display in a single graphics window, you can set the Window ID to correspond to the same ID for different monitors. This is useful when you have multiple monitor displays on the screen, you can set all monitors to the same display. For example, for three different monitors, you can set the Window ID to 1 for each of the different monitors in order to display all three monitors in a single window. The name of the monitors ( surf-mon-1.out, etc.) will be different, but only the Window ID will remain the same. So that each monitor has data that is stored in a different file, but the data is displayed in the same window.

Note that surface and volume monitors cannot be displayed in the same window.

If multiple monitors are plotted in the same window, make sure you set an axes range that can be applied to all the monitors. This axes range will be the same for all the monitors in the shared plot window. Otherwise, the most recently defined monitor, sharing the same window as the other monitors, will determine the axes range. If the default option of Auto Range (in the Axes dialog box) is enabled for all the monitors sharing the same plot window, then the default value for Minimum will be the minimum value of all the monitors, and the default Maximum will be the maximum value of all the monitors. Modifying plot attributes can be achieved by clicking the Curves and the Axes button. See Sections  29.9.9 and 29.9.10 for details about plot options.

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 surface 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. 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.

6.   Choose the integration method for the surface monitor by selecting Integral, Standard Deviation, Flow Rate, Mass Flow Rate, Volume Flow Rate, Area-Weighted Average, Mass-Weighted Average, Sum, Facet Average, Facet Minimum, Facet Maximum, Vertex Average, Vertex Minimum, or Vertex Maximum from the Report Type drop-down list. These methods are described in Section  30.6.

7.   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.)

8.   In the Surfaces list, choose the surface or surfaces on which you wish to integrate.

9.   Click OK in the Surface Monitors dialog box after you finish defining all surface monitors.

Printing, Plotting, and Saving Surface Integration Histories

There are three methods available for reporting the selected surface integration. To print the surface integration in the console window after each iteration, enable the Print to Console option in the Surface Monitor dialog box. To plot the integrated values in the graphics 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 surface 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 surface-monitor plot. Click the Axes... or Curves... button in the Surface Monitor dialog box to open the Axes dialog box or Curves dialog box for that surface-monitor plot. See Sections  29.9.9 and 29.9.10 for details.