Tutorial: Thermal analysis of a differential casing
In this tutorial the thermal behavior of a front differential casing is simulated. The objective of this simulation is to analyze how hot the casing will get in operation mode as well as if there are any hot spots visible that could be avoided with a more suitable casing design.
To start this tutorial import the tutorial project into your ‘Dashboard’ via the link above. Once the ‘Workbench’ is open you will be in the ‘Geometries’ tab. The CAD model named “CAD-differential-casing_v1” would be displayed in the viewer, as shown below. You can interact with the CAD model as in any regular desktop application
Create a Heat Transfer simulation
To create a new simulation click on the ‘+’ option next to the ‘Simulations’ tab. Select the Heat Transfer analysis type and click ‘Ok’. After clicking ‘Ok’, a new tree will be automatically generated in the left panel with all the parameters and settings that are necessary to completely specify such an analysis.
All parts that are completed are highlighted with a green check. Parts that need to be specified have a red circle. While, the blue circle indicates an optional settings that does not need to be filled out
Since we are interested in a time invariant analysis, activate the steady-state option
Creating the mesh
Select the mesh option and set the parameters as shown in figure below. The default mesh parameters are used in this tutorial, with the use of first order elements.
Note that the results generated with First order elements might not be as accurate as with Second order elements. But choosing a Second order mesh will lead to longer computing times so it is avoided here.
As for the fineness of the mesh, Coarse is sufficient. As a rule of thumb, one should make sure, that the resulting mesh does have more than one volume layer across the cross section of the model. For actually starting the mesh operation hit the ‘Generate’ button, highlighted in the figure below
The Job Status box in the lower left will show the progress of the operation. Queued means that the SimScale platform is preparing a computer to carry out the operation, Computing means that the mesh operation is currently carried out. After the first seconds of computing, there will appear a Meshing Log tree item below our mesh operation in the tree: This is the direct command line output of the meshing framework, that in the beginning might be a bit cryptic but can be very useful if a meshing operation fails.
Once the mesh operation is finished, the Job status box will show the green Finished box, and The mesh immediately appears in the viewer. The advantage of running the mesh operation remotely is that you do not have to wait until the mesh is finished. You can simply move on and already work on the simulation setup since your local computer is not used at all for computing
You can also see the created elements of the mesh from inside at some cutout plane. To do so, apply a Mesh Clip filter by clicking on the Mesh Clip button (highlighted). Next you will see a cutting plane which you can adjust under Mesh Clip parameters. For example, in this case give Normal (y) a value of -1 in order to clip the mesh from the middle of the geometry. The black arrow shows the direction of clipping. Figure below elaborate the steps.
Creating Topological Entity Sets
Especially interesting for our simulation is the creation of Topological Entity Sets, which basically means that we can group faces together for later boundary condition assignment. To start, select the geometry element in the tree.
We create the first Topological Entity Set by selecting the first heated region at the inside of the casing (see image below). To create a topological entity set, click on the ‘+’ next to the Topological Entity Set.
Give an appropriate name for the Entity set, then click on Create new set.
After we confirmed the name of the topological entity set, the new set appears in the table. See below how the other face sets are defined. The idea is that internally, there are two different heat losses and externally we will assign natural convection as a cooling mechanism. We repeat this process until we have all of the topological entity sets defined:
Internal heat loss 1
Internal heat loss 2
Natural convection outside
Adding Material Model
Next, add the materials from the ‘Material Library’. First, we start with clicking on sub-tree “Materials”, click on ‘+’ from the options panel as shown. This pops-up a ‘Material Library’ from which we select “Aluminium” and click on ‘Ok’. This will then load the standard properties for Aluminium. Then, assign the material to the domain and save.
The next tree item Initial conditions allows to define the initial temperature within the casing. The green check indicates that default values have already been chosen for it, which we will leave unchanged and move on to Boundary conditions.
Now, we come to define the boundary conditions. To create a boundary condition, click on the ‘+’ option next to the Boundary conditions and select the required boundary condition from drop down menu, as shown in figure. We can see that we can define either temperature or heatflux boundary conditions. For our simulation, we’ll only need heatflux boundary conditions, since we will assign a specific heat loss inside the casing and a convection condition at the outside.
We will start with the first inner heat loss boundary condition for the face set heated-region-1. Select the Surface heat flux boundary condition from the boundary conditions drop down menu. Give a heat flux value of 2900 W/m^2, since this comes close to the thermal conditions we want to test in this simulation. Assign this to the heated region 1 entity set. Give an appropriate name to the boundary condition, such as ‘Heated region 1’.
The second boundary condition is also a heatflux boundary condition of type Surface heat flux with a value of 3600 W/m^2 assigned to face set heated-region-2.
The third boundary condition is a heatflux boundary condition of type Convective heat flux with a reference temperature of 293 K, an h value of 24 W/m^2 K assigned to the face set Outside. The value for the outside heat transfer coefficient for the convection boundary condition is taken from literature and is rather a rough assumption, since this coefficient won’t be constant over the whole surface in reality.
These three boundary conditions are sufficient to simulate the thermal scenario we are interested in: Heat loss from the inside and a natural convection at the outside faces of the casing.
The tree item Numerics allows us the control the solving mechanism in detail. In this tutorial, we use the default Numerics as shown in the figure below.
The next important tree item is Simulation Control which allows to steer the overall simulation settings. We choose a 8 core machine for the computation to have enough computing power for the considerably large mesh.
Start a simulation run
The last thing to do for running this simulation is to create a run. The new run is created by clicking on the ‘+’ symbol next to ‘Simulation Runs’. Give a name to the run and start the run.
The Job status box in the lower left again provides updates about the job status like we saw in the meshing operation. Also as we saw in the mesh operation setup, a Solver log is provided after a few seconds which shows the exact output of the actual solver run. The simulation run should take a few minutes to be carried out. Once the simulation run is Finished we can Post Process the results.
Once the simulation is finished, select the ‘Solution fields’ under the Run to post process the results on the platform. Or they can be downloaded and post-processed locally (e.g. with ParaView). Some post processing images from the SimScale platform post processor are shown below. Select the results and click “temperature” to visualize Temperature Profile.
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