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ANSYS CFX – Flow around a cylinder / Parameters

Source: sharcnet

During a parametric study, the original set of files used to set a problem up is copied for each Design Point, using file space. To minimize the use of file space, minimize the number of unnecessary Design Points.

When working with exported Design Points, you should limit the project schematic only to systems that are involved in the Design Point changes. Having other systems (for example, a CFX system) in the project that are not involved in the Design Point update will mean duplication of these systems’ database/results files for every exported Design Point, and this can use a significant amount of disk space.

If you generate a large number of Design Points in a Design of Experiments (DOE), it is possible that a small proportion of them will fail to update, preventing the DOE cell from becoming up-to-date. In such a case, you cannot continue with the rest of this design exploration analysis. The DOE can be modified to remove these failing Design Points by selecting Design of Experiments > Type > Custom and then manually deleting the Design Points that failed to update successfully. Provided that sufficient Design Points remain for adequate analysis, then the DOE can be updated and you can continue with the analysis

Limitations When Using Parameters and Design Points with ANSYS CFX

  • Although the names of design parameters can be modified using the Parameter Manager within ANSYS Workbench, this is not recommended, because the new names will not be reflected within the CFX application user interfaces.
  • In a design points study, when you have some up-to-date design points, it is recommended that you avoid editing the Results cell and running CFD-Post interactively. Most editing and viewing actions result in an underlying state change and therefore make the design points appear out-of-date, requiring another update.
  • If an input parameter is defined in CFX-Pre directly in the physics setup (that is, not using an expression) then it should be removed by clearing the parameterization check box next to the parameter setting before any physics changes are made that would make the parameter not applicable. If it is not removed, then any attempt to change the value of this parameter through Workbench, or run multiple design points, will result in a physics error of the form: “The parameter <parameter name> is present in the object <path> but it is not physically valid.“, referring to the parameter that was set as a Workbench input parameter. If this occurs, then one way to remove the input parameter is to enter the following into the Command Editor:  delete /PARAMETERIZATION/INPUT FIELD: <parameter name> where <parameter name> is the input parameter name. Once the parameterization has been removed, the new physics settings can be re-applied in CFX-Pre to remove the physics error and allow the design point update to complete successfully.

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