8.8.3. Export Mechanical Load File

The selected CFX data that is exported by CFD-Post is interpolated onto the Ansys surface from the associated CFX boundary. The interpolated data is then exported to an Ansys load file. For details on how to associate a boundary with an Ansys surface, see Specify Associated Boundary Check Box.

When verifying the load applied to the surface in Mechanical, note that the Pressure variable available in CFD-Post is not the same as the element stress representing the static structural load. The element stress variables, Normal Stress, Shear Stress, and Stress (the latter being the combination of Normal Stress and Shear Stress) are vector quantities, whereas the Pressure variable is a scalar quantity.

To compare actual boundary data in CFD-Post with the data that is exported:

Load the fluid results file into CFD-Post.
Create a new vector variable named Surface Force Density.
Specify the components as follows: X => Force X / Area, Y => Force Y / Area, and Z => Force Z / Area.
Color the FSI boundary by Surface Force Density.

The plot of Surface Force Density on the FSI boundary should look similar to the plot of Imported Pressure in Mechanical. There will be some minor differences due to interpolation and differences in mesh density.

For an example of using this option, see Mechanical Import/Export Commands.

Note: One-way FSI cases with porosity transfer only the fluid quantities for 2D Temperature, 3D Temperature, Heat Transfer Coefficient, and Heat Flux.

Note: Transfer of data between Fluent and Mechanical through CFD-Post is based on nodal data. Values that are visualized in CFD-Post may differ from values that are exported. For example in cases where Wall Heat Flux values are zero on the mapped surface, you would see zero total flux on the surface, as this calculation is based on face data. However, nodal data may have nonzero values on surface edge nodes, as it is interpolated from all faces that touch those nodes, including the ones from the neighboring surface (which may have nonzero flux). This is the data that will be mapped to Mechanical.

8.8.3.1. Options Tab

8.8.3.1.1. File

The File setting specifies the filepath and filename of the file to be exported. You may click the Browse icon to select the name and location of the file to be exported. The default name is export.sfe or export.xml (depending on which File Format is chosen) and the default filepath is your current working directory.

8.8.3.1.2. Location

The Location setting selects the Mechanical surface object to export, which is generated by importing a .cdb file. For details, see Import Mechanical CDB Surface.

Note: The Mechanical load file does not contain mesh coordinate data, and must be interpreted along with the .cdb file originally imported into CFD-Post.

8.8.3.1.3. Unit System

The Unit System setting specifies the units for the exported data. By default, this uses the global units system selected in Edit > Options. For details, see Setting the Display Units.

8.8.3.1.4. Boundary Data

The Boundary Data setting specifies Hybrid or Conservative boundary values. If Boundary Data is set to Current, this setting is picked up from each variable. For details, see Variables Details View.

8.8.3.1.5. Export Data

The Export Data setting has the following options:

Option	Description
`Normal Stress Vector`	Exports `Normal Stress` variable data onto imported `surf154` surfaces. `Normal Stress` is a vector variable calculated from the normal component of `Force`.
`Tangential Stress Vector`	Exports `Shear Stress` variable data onto imported `surf154` surfaces. Shear stress data is calculated from the tangential component of `Force`.
`Stress Vector`	Exports `Stress` variable data onto imported `surf154` surfaces. Stress data is calculated by vector summing the normal stress and shear data.
`Heat Transfer Coefficient`	Exports convection variable data onto imported `surf152` surfaces. When selected, the Specify Reference Temperature check box will appear. See Specify Reference Temperature, below.
`Heat Flux`	Exports the `Heat Flux` variable data onto the `surf152` surfaces.
`Temperature`	Exports the `Temperature` variable data on the nodes of the imported surface.

8.8.3.1.6. Fluids

Fluids is available only if either the Tangential Stress Vector or Stress Vector options are selected. The Fluids setting specifies which fluids, or All Fluids, that will affect the elements shear or stress values.

8.8.3.1.7. Specify Reference Temperature

Specify Reference Temperature is available only if the Heat Transfer Coefficient option is selected. Select this check box to enable you to specify a fixed reference temperature value or expression.

If you specify a reference temperature, then the exported heat transfer coefficient is calculated based on Heat Flux and Temperature data. If the case models radiation, then the heat transfer coefficient also includes the contribution to the heat flux from radiation.
Note that the variable Surface Heat Transfer Coef is not recognized by CFD-Post for one-way FSI.
If you do not specify a reference temperature, the exported data is based on the Wall Heat Transfer Coefficient and Wall Adjacent Temperature. This includes only the convective contribution to the heat flux, and does not include any radiative contribution.

For Fluent Cases: To transfer HTC from Fluent cases without specifying a reference temperature (method 2 above), the following variables have to be exported to the DAT/CDAT file:

Wall Func. Heat Tran. Coef (which will be converted to the CFX variable Wall Heat Transfer Coefficient)
Temperature. In Fluent, the wall adjacent temperature is calculated by averaging the adjacent cell temperatures to the wall nodes.

Note: Enabling (or disabling) Specify reference (bulk) temperature affects all further calculations of the associated Ansys variables on the relevant locator (for example, Wall Adjacent Temperature on <surface name>), and so potentially changes any plots of these associated Ansys variables.

8.8.3.2. Formatting Tab

The Formatting tab enables you to specify only a precision value. This setting is the same for the Export command. For details, see Export.