After performing a conjugate heat transfer (CHT) simulation in ANSYS Fluent or ANSYS CFX software, you may be interested in the thermal stresses generated in your model. ANSYS Workbench 13.0 makes it easy to perform this type of analysis by transferring the volumetric temperature field from your CFD solution and applying it as a body temperature load in a static structural system.
The geometry cells are typically shared between the two systems but there’s no requirement to do so. The CHT bodies in your CFD analysis do need to overlap with the solid bodies in your structural system to enable accurate load mapping.
In the structural setup you’ll now see an imported load object. A right-click on this object allows you to import a pressure or body temperature load from the CFD solution. For a thermal stress analysis import a body temperature load.
In the details view for the imported body temperature you’ll be prompted for the structural body to which to map the temperature load and the CFD domain to use as the source. You can then update the imported load object to view the mapped temperature load and some diagnostics about the mapping process.
Make sure you check those diagnostics. So what do you do if some nodes were not mapped correctly? Well the mapping is actually performed in the background using ANSYS CFD-Post and there’s an interpolation tolerance setting in CFD-Post that’s used by the mapping process. To adjust this setting launch CFD-Post and go to “Edit > Options > CFD-Post”. You’ll see the interpolation tolerance which defaults to 0.5, which means 0.5 percent of the CFD domain extent. If you change this and close CFD-Post, it gets saved in your preferences and will be used when mapping data to your structural simulation. Increasing this value should help map structural nodes that lay outside of the CFD mesh (due to a course mesh on a curved surface for example). Decreasing this value may help the mapping around sharp corners.
Lastly, since the mapping is performed in CFD-Post, MAPDL users can perform the mapping manually too. I won’t provide all the details here, but the main steps are:
- Write out a CDB file containing the solid mesh.
- Load the CFD results in CFD-Post and import the CDB file.
- Export a load file containing BF commands with the mapped temperature from CFD-Post.
- Read the load file into MAPDL.
Feel free to follow up to this blog post if you want more details on this approach.
If you’re looking for more information on fluid structure interaction then consider the ANSYS CFX Fluid Structure Interaction (FSI) 2-day training course. Further information can be found in the Training Center at ansys.com. Classes are typically scheduled on request. Also watch for the upcoming Fluent FSI training course in the New Year. This will include 1-way and 2-way FSI between Fluent and ANSYS Mechanical using version 14.0. I’ll have more to say on Fluent–Mechanical FSI in future blog posts.