Tutorial: Thermomechanical Analysis of a Engine Piston

This article provides a step-by-step tutorial for a thermomechanical simulation of a engine piston. We take are analyzing the piston under a maximum pressure and temperatures.

We are following this workflow:

1. Prepare the CAD model and select the analysis type
2. Assign materials and boundary conditions
3. Create the mesh
4. Run the simulation and analyze the solutions

1) Prepare the CAD model and select the analysis type

Once you clicked the button above, you should see the following model of an engine piston.

1a) Create topological entities

Prior to start the simulation we recommend to create topological entities. You can also do that at any point of the simulation setup, but it makes sense to do it in the beginning.

We already created the entities covering the top, the rings and the ring grooves according to the following picture.

Now you only need to create the set for the interior and the skirt of the piston, which is basically everything other than what is already assigned to sets. The following picture shows what to do:

1. Hide all entities
2. Activate the box selection
3. Select all remaining parts
4. Hit the + next to Topological Entity Set and give it a name

1b) Create the simulation

Hitting the create simulation button leads to the following options:

Choose Thermomechanical as analysis type and create the simulation.

2) Assigning the material and boundary conditions

2a) Gravity

2b) Define a material

2c) Assign the boundary conditions

Now we need to assign both the thermal and mechanical boundary conditions. Let’s start with the thermal ones.

Therefore add a boundary condition and select convective heat transfer:

Define the convective heat flux boundary condition for all topological entities according to the following table:

geometric part	reference temperature [°C]	heat transfer coefficient [W/(K*m^2)]
top	1400	450
ring 1	450	150
ring 1 groove	450	1000
ring 2	450	150
ring 2 groove	380	400
ring 3	380	150
ring 3 groove	380	400
interior and skirt	380	650

Now we define the mechanical boundary conditions, which will be three pressure boundary conditions (top and the first two rings) and two remote displacements.

Once you created the three pressure boundary conditions assign them according to the following table:

Entity	Pressure [Pa]
Top	20e7
Ring 1	14e7
Ring 2	4e6

Now create the two remote displacements and give them the following properties:

Now all boundary conditions are assigned and we can proceed creating the mesh.

We don’t have to worry about the numerics and the simulation control settings, as their default values are optimized according to the chosen analysis type, hence valid for the majority of simulations. If you are a simulation expert however, you can have a look at them and change the settings as you like.

3) Mesh

To get the mesh we use the standard algorithm, which is a good choice in general as it is quite automated and delivers good results for the most geometries.

The only change we need to do here is changing the sizing to manual and define 1.8e-3 m as a cell size and enable 2nd order elements. Make sure your setting look like the picture below:

The resulting mesh will have about 235k nodes and look like this:

4) Start the simulation

Now we can start the simulation and after about 10 minutes we can have a look at the results.

5) Post-Processing

Analyze your results with the SimScale post processor. Have a look at our post-processing guide to learn how to use the post-processor.

Congratulations! You finished the tutorial!