9.3. Interpolate Results Command

Ansys CFX enables the values from one results file to be interpolated onto a CFX-Solver input file containing another mesh.

The major benefit of interpolation is the ability to use the solution from a simple model to provide initial conditions for another, perhaps more complex, model (thereby increasing the likelihood of converging the complex model simulation) or to continue a run with a different mesh or other settings.

Interpolation can be used with modified geometry or boundary conditions. Interpolation can also be used to interpolate the solutions from a model with different mesh topology. For example, the initial guess for a problem having one domain can be interpolated from one or more results files having a solution that spans multiple domains. When the shape of the model has changed and the initial values files do not fully overlap with the new mesh, the CFX-Interpolator extrapolates values for the points in the new mesh that lie outside the Initial Values File(s), based on the interpolated values on the mapped nodes. See Using the CFX-Interpolator in the CFX-Solver Modeling Guide for more details on how the CFX-Interpolator works.

The CFX-Interpolator is most commonly invoked through settings on the Run Definition tab on the Configuration or Execution Control details view in CFX-Pre, or, the Define Run dialog box of the CFX-Solver Manager. For details, see Run Definition Tab in the CFX-Pre User's Guide, Run Definition Tab in the CFX-Pre User's Guide and Run Definition Tab, respectively.

However, if you want to manually use the interpolator to write variables into a specific Solver Input File (not invoked from the Run Definition tab) then you can choose Tools > Interpolate Results from the CFX-Solver Manager. In this case the specified Mesh File is used as the target file, and will be modified by the interpolation process. The text output is written into the CFX-Solver Manager's Interpolation dialog box. You can then run the resulting target file in the CFX-Solver, using the variables written into the target file by the CFX-Interpolator as the initial conditions for the run.

To manually interpolate the results from a source file to a target file, you can use the Interpolate Results command as follows:

Select Tools > Interpolate Results.
The Interpolation dialog box is displayed.
Select the Interpolate method.
Set Results File to the name of the source file. You can click Browse to select the file using a browser.
Set Mesh File to the name of the target file. You can click Browse to select the target file using a browser.
You can interpolate onto a CFX-Solver Input file.
Optionally set double precision by selecting Executable Settings > Double Precision. For details on the precision of the executables, see Double-Precision Executables.
Optionally set the capability for solving a problem of large size by selecting Executable Settings > Large Problem. For details on the problem size capability of the executables, see Large Problem Executables.
If required, under Interpolator Memory, adjust the memory configuration. For details, see Configuring Memory for the CFX-Solver.
Optionally select Threading Control, then choose an Option:
- None
  Use only one thread.
- Number of Threads
  Set Number of Threads to the maximum number of threads that may be used by the interpolator.
- Hardware Capacity Fraction
  Set Value to the number of threads used by the interpolator as a fraction of those available on the current hardware.
Click Interpolate.
The output window on the right displays details of the interpolation process.
Once completed, a message is displayed. Click OK to close it.

You can also run the interpolator from the command line. For details see Using the Command Line to Interpolate Results.

Note:

To save the results to a text file, right-click in the text output window and select Save As.
Interpolating results from a source file to a target file that already contains solution data is not recommended. See Interpolating Onto a Solver Input File with Results Fields in the CFX-Solver Modeling Guide for details.
Following the steps above, the interpolation is performed in Initial Guess mode. See Using the CFX-Interpolator in the CFX-Solver Modeling Guide for details.

To generate a comparison of two files, you can use the Interpolate Results command. The comparison is stored as new variables with the prefix Difference. These variables can be used in CFD-Post to determine regions where the solution has changed significantly. A comparison of two files can be generated as follows:

Select Tools > Interpolate Results.
The Interpolation dialog box is displayed.
Select the Calculate Differences method.
Set Original Results to the name of the original results file. You can click Browse to select the file using a browser.
Set Modified Results to the name of the modified results file. You can click Browse to select the file using a browser.
Optionally, set the precision: under Executable Settings, select Override Default Precision and choose either Single or Double.
For details, see Double-Precision Executables.
If required, under Interpolator Memory, adjust the memory configuration. For details, see Configuring Memory for the CFX-Solver.
Click Calculate Differences.
The output window on the right displays details of the differencing process.
Once completed, a message is displayed. Click OK to close it.

Note: CFD-Post now also supports comparison of two results files without the use of the CFX-Interpolator. For details, see Case Comparison in the CFD-Post User's Guide.