Transient Thermal Analysis In ANSYS®

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Unlike steady-state thermal analysis in ANSYS®, the boundary conditions that are applied as heat input and others are affecting the system with changing with the changing time in transient thermal analysis. For problems that there are abrupt changes in thermal situations such as heat exchanger analysis, rocket nozzle analysis, or engine analysis.

In these engineering systems, heat or other thermal inputs are changing with changing times.

Thermal stress is another situation that occurs because of the contraction or expansion of material with the changing temperature. To assess the thermal stresses and see failures because of them, transient thermal analyses can be linked to structural analyses in ANSYS Workbench.

In most engineering thermal analyses in ANSYS®, nonlinearities are very important. Material properties change with the changing temperature and this leads to nonlinearities in FEA problems. Nonlinearities are solved with special iterations that require more computational sources.

Steps To Make Transient Thermal Analyses In ANSYS®

Like the other analysis types in ANSYS®, you need to follow a bunch of steps to make transient thermal analyses in ANSYS®. Each step requires special professions. To obtain correct and reliable results from our transient thermal simulations, we need to take special care of each step.

Drag And Drop Transient Thermal Analysis In ANSYS® Workbench

When you open the ANSYS® WB on your computer, there will be a list that shows all the analysis systems on the left side of your screen. From this list, drag the ‘Transient Thermal’ into the project schematic with your mouse.

Definition Of Materials In ANSYS® Engineering Data

Specification or definition of materials in ANSYS® which will be used in transient thermal analyses is very important. There are a bunch of features that ANSYS® provides to users about monitoring materials;

You can select a material from ANSYS® material library if they are proper for your model.
You can change the material properties of existing materials in ANSYS® Engineering Data.
You can add your material into ANSYS® Engineering Data by specifying your material properties.

You can moderate the materials that you will use in ANSYS® transient thermal analyses.

Import Your Geometry Inside ANSYS® Environment

Import or create your geometry in ANSYS® Workbench.

At the geometry tab that you dragged inside the ANSYS® project schematic, you can create new geometry by using the options of; ‘New SpaceClaim Geometry…’ or ‘New DesignModeler Geometry..’.

Or you can ‘Browse’ a created geometry from another CAD environment. We recommend you that browse your geometry in .stp or .iges extensions.

Open The Mechanical Interface Then Adjust The Geometries

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Double click on the ‘Model’ tab to open Mechanical Interface. And make basic adjustments to each geometry inside the model.

Adjust the required geometric options in Mechanical.

After entering into the ANSYS® you can make the basic adjustments below;

Select materials in the Mechanical interface for each geometric feature.
Adjust nonlinearities and stiffness behaviors for each geometric body.
You can specify reference temperature also.
If you are expecting thermal strain from your body, you can adjust the thermal strain effects for each body individually.

Nonlinearities and thermal strain effects require much more computational sources. So, you need to consider the elongation of analysis solving time when you are adjusting these options in ANSYS® Mechanical.

If you have the assembly, you need to check the contacts between the geometric bodies to obtain assemblies.

Create Required Mesh Structure For Transient-Thermal Analysis

Mesh structure example in ANSYS® Mechanical.

Creating a well and optimized mesh structure requires and another kind of profession. When you are creating the mesh structure, you need to consider a bunch of things;

Mesh must be finer at the regions where nonlinearities are expected.
Mesh structure must be finer at where the regions physically affected most.
Transferring regions such as contacts must have finer mesh structures.
Bulk bodies, regions where nonlinearities are not expected, and regions that are not physically affected could have a coarser mesh structure.

From this article, you can find out important mesh options that are required in ANSYS® transient thermal analyses.

Specify The Required Boundry Conditions For Your System

Right-click on ‘Transient Thermal’ in ANSYS® Mechanical and see all boundary conditions available. Here you can find out thermal boundary conditions and their properties.

Temperature: You can define temperature to each body and each geometric feature in ANSYS® Mechanical. Click on the link and see how to define temperature in ANSYS® Mechanical for transient thermal analyses.
Convection: Convection is a very important thermal phenomenon that you will probably use in your transient thermal analyses. You can find the theoretical and application information about convection boundary conditions for your transient thermal analyses if you click on the link.
Radiation: You can assign radiation from faces or bodies to faces or bodies to see the effects of radiative actions in your transient thermal analyses in ANSYS®. Click to see the theory and application of radiation in ANSYS® Mechanical.
Heat Flow: If you need to define a specific rate of heat flow through bodies or faces in your transient thermal analyses in ANSYS®, click to see how to do it.
Perfectly Insulated: If you are dealing with the theoretical works with ANSYS® transient thermal analyses, this property can be required. You can thermally isolate the sides or sections of geometries in ANSYS® transient thermal analyses.
Heat Flux: Heat flux is also defined as a boundary condition in ANSYS Mechanical transient thermal analyses.
Internal Heat Generation: You can define internal heat generation to a body or geometry in ANSYS® transient thermal analyses.

Define Initial Temperature For Your Bodies

Definition of initial temperature in ANSYS® Mechanical transient thermal analysis.

You can define the initial temperature for your analysis in ANSYS® transient thermal as above. Click on the ‘Initial Temperature’ section then define your initial temperature as shown above.

Adjust Step Controls For Boundry Conditions Of Transient Thermal Analysis

This is also a very important step to obtain successful transient thermal analyses in ANSYS®. Step and time controls of each boundary condition provide the simulation of the real problem inside the ANSYS® simulation environment.

You can adjust the timing of each defines boundary condition in ANSYS® precisely with step controls.

Insert Required Solution Selections

Select the required ANSYS® transient thermal solutions.

From the ‘Solution’ section, you can insert required solutions to see after solving transient thermal analysis in ANSYS®. There are a bunch of solutions available such as ‘Temperature, ‘Total Heat Flux’ etc. as you see above.

Then click on the ‘Solve’ button to solve built transient thermal analysis in ANSYS®.

Conclusion

You can obtain ANSYS® analysis reports that are automatically created in ANSYS® if you wish. It includes very detailed information about the transient thermal analysis that you made in ANSYS®.

This article is created for educational and information sharing purposes with ANSYS® Academic license. Images used courtesy of ANSYS, Inc.

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