The following picture demonstrates what should be visible after importing the tutorial project.
Figure 2: Imported CAD model of the golf ball in the SimScale workbench.
1.2. Use Geometry Operations on the CAD
The first step for this simulation is the creation of an enclosure. This will be the domain that will be used for the external CFD analysis. Select a new ‘Geometry Operation‘, then pick the ‘Enclosure‘ option.
Figure 3: Adding a new geometry operation for an enclosure creation.
Then fill in the dimensions of the domain, like bellow, where L is the diameter of the golf ball:
Figure 4: The size of the domain according to the reference length of the model.
In more details, the size of the domain is as following. Click on ‘Start‘.
Figure 5: The dimensions of the domain.
After a few seconds, the enclosure will be created.
1.3. Create Topological Entities
Create a topological entity set for the golf ball:
Hide the walls of the Enclosure by selecting each one of them on the workbench, then right-click and choose the ‘Hide selection’ option.
Figure 6: Hiding the walls of the domain.
Activate the box selection at the top of the page.
Drag it across the model until all the faces are selected.
Click on the ‘+’ next to the Topological Entity Sets.
Name your new set and click on the checkmark.
Figure 7: Adding a topological entity set containing all the faces of the golf ball.
1.4. Create the Simulation
After you finish with the topological entity set, proceed to click the ‘Create simulation‘ option to get started.
Figure 8: Creating a new simulation.
Select the ‘Compressible‘ analysis, which is used for cases where the Mach number in any point of the domain reaches a value bigger than 0.3. This golf ball simulation will be using a high velocity, so the compressible analysis is the best fitting.
Figure 9: The compressible fluid flow analysis type.
Switch the Turbulence model to ‘k-omega SST‘ in the panel that appears:
Figure 10: Choosing the k-omega SST turbulence model for the compressible CFD analysis.
2. Assigning the Material and Boundary Conditions
Now we will set up the physics for the simulation.
2.1. Define a Material
In this simulation, we want to analyze the airflow around a solid body. Therefore we need to assign properties to the fluid region. Click on the ‘+’ icon next to the Materials option of the simulation tree on the left of the page, and then choose ‘Air‘ in the panel that pops up, and apply:
Figure 11: Material list for a compressible fluid flow analysis.
The flow region that was created due to the Geometry operation at the beginning of the simulation is automatically selected for the material.
Figure 12: Properties of air for the flow region material assignment.
Just confirm the selection by hitting the check button next to the material’s name. You can also create a custom fluid by changing the properties and the materials name.
2.2. Assign the Boundary Conditions
In order to assign Boundary Conditions on the golf ball, click on the ‘+’ icon next to the BoundaryConditions, and click on the types described in this section.
Figure 13: Adding a boundary condition.
In order to have an overview, the following picture shows the boundary conditions applied for this simulation:
Figure 14: Overview of the boundary conditions for the golf ball.
a. Velocity Inlet
Assign a ‘Velocity Inlet‘ of 59 \(m/s\). This is close to the average Ball Speed an average male golf player achieves[1].
Figure 15: Velocity inlet for the airflow around the golf ball.
b. Pressure Outlet
Assign a ‘Pressure Outlet‘ condition of 101325 (Pa) at the highlighted face below:
Figure 16: Pressure outlet boundary condition.
c. Slip Walls
Add a Slip Wall boundary condition on the top, bottom, and right face of the domain. Leave only the symmetry plane unassigned.
Figure 17: Slip walls boundary condition.
d. Symmetry
Assign a Symmetry condition on the symmetry plane. If you want to learn more about this boundary condition, click here.
Figure 18: Applying a symmetry boundary condition.
e. Rotating Walls
Did you know?
The golf ball rotates like the following photo, so the negative z direction is chosen for the rotation axis, in regards to the coordinate system of the CAD model.
Figure 19 : Rotation of a golf ball. Source: (http://en.wikipedia.org/wiki/Magnus_effect [2])
We will define the condition according to the spin rate of an average male golf player. Create a new ‘wall’ boundary condition:
Figure 20: Applying a rotating walls boundary condition to the ball.
Select ‘Rotating wall’ for (U) velocity.
Set the Turbulence wall to ‘full resolution’.
The spin rate of an average male golf player (rotational velocity) is 343 \(rad \over \ s \) [1].
According to the coordinate system, we need to orientate it on the negative z-direction.
Assign it to the topological entity set of the golf ball by clicking on it as you can see below:
Figure 21: Assigning the boundary condition to the topological entity of the golf ball.
2.3. Simulation Control & Numerics
Fill the simulation control panel in like below:
Figure 22: Simulation control panel.
Leave the Numerics panel at its’ default state.
3. Mesh
Access the global mesh settings by clicking on ‘mesh’ in the simulation tree:
Figure 23: Mesh properties panel.
Choose the ‘Standard‘ algorithm, and keep the default settings.
3.1. Meshing Refinements
This project needs some refinements. If you want to learn more about using the Standard meshing tool, and using refinements, click on this.
a. Create Geometry Primitives
Prior to adding refinements, you must create some Geometry Primitives sets.
Figure 24: Creation of a new geometry primitive.
Click on the ‘+’icon under the Geometry Primitives at the right of the screen.
Choose the ‘Sphere‘ option.
Figure 25: Dimensions of the first spherical geometry primitive.
Name your entities, and define its’ center and 0.1 (m) radius.
Create a second Sphere with a smaller radius (0.05 (m)):
Figure 26: Dimensions of the second spherical geometry primitive.
b. Assign Region Refinements to the Spheres
In order to add refinement regions, click on the under theMesh:
Figure 27 : Adding region refinements.
Add a region refinement to the first sphere:
Figure 28: Region refinement for the big spherical region.
And one more fine region refinement to the smaller sphere, to create a more dense mesh there:
Figure 29: Region refinement for the small spherical region.
Watch out!
Do not click on the ‘Generate’ button after you are done with the mesh settings, otherwise the physics of the simulation will not be taken into consideration during the meshing procedure. Instead of generating it at this point, your mesh will be automatically created after you start a new run later on.
4. Start the Simulation
After all the settings are completed, proceed to clicking the ‘+’ icon next to the Simulation Runs, in order to get started with the analysis. Initially, your mesh will be generated, and then the program will go on with the run.
Figure 30: Create a new simulation run
While the results are being calculated you can already have a look at the intermediate results in the post-processor.
Did you know?
Your results are being updated in real time! That means that you can already look into the intermediate results during the solver calculates the simulation.
5. Post-Processing
When the simulation is completed, you can check the convergence and the results of the simulation. You can access them under the completed run:
Figure 31: The results of the simulation.
The convergence plot indicates whether the solution is reliable, or whether some changes should be made in the settings, like making the mesh finer, or increasing the simulation time. In the following picture you can see how the residuals of your simulations will appear in the plot if you set the end time at 2000s and let it fully converge:
Figure 32: Convergence plot of the simulation.
In order to view the results of your golf ball simulation, click on the ‘Solution Fields’ tab under your finished run. This will redirect you to the post-processor.
If you wish to see the pressure distribution on the symmetry plane and your golf ball, follow these steps:
Make sure the post processor shows the results for the final timestep -2000 \(sec\)-.
Go to the Parts Color and choose the ‘Pressure‘ from the Coloring drop down menu.
Figure 33: Visualization of the pressure distribution across the Symmetry plane and the ball.
Applying for the continuous legend will add smoothing to the results:
Right-click on the color mapping legend at the bottom of the page.
Select the ‘Use continuous scale’ feature from the menu that appears.
Figure 34: Applying the continuous legend feature on the pressure results.
This is how the symmetry plane will appear afterwards:
Figure 35: The pressure distribution with the use of the continuous scale
Finally, for streamline visualization:
Click on the ‘Add Filter’ option.
Select the ‘Particle Trace‘.
Figure 36: Adding a particle trace filter
Click on the circle icon next to the Pick Position.
Apply the seed point on the Inlet face, as close to the Symmetry face and the center of the y-axis as possible.
The Num v represents the number of streamline rows along the z-axis. Set it to ‘2’. The Num u represents the number of rows along the y-axis. Make sure it is big enough that it covers the whole y dimension of the domain.
Select ‘Pressure’ as Coloring.
For this case you can have the Trace both directions option disabled, as the flow here travels from the inlet only towards the positive x direction.
Figure 37: Setting the particle trace seeds.
With these settings, this is how the streamlines will finally appear:
Figure 38: The resulting streamlines
For more information, have a look at our post-processing guide to learn how to use the post-processor. Congratulations! You finished the tutorial!
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