## 1. Create Case

After opening SimFlow, we will create a new case named *car*

Go to

**New**panelProvide name

*car*Click

**Create Case**

## 2. Import Geometry

Firstly we need to Download GeometryCar_body

Click

**Import Geometry**Select geometry file

*car_body.stl*Click

**Open**

## 3. Imported Geometry Units

The STL geometry format does not store the unit in which the geometry was created. *Geometry size* shows the overall size of the model in each direction, what should help to choose the correct unit. In ours case, the default unit meter is correct.

To confirm default unit

*meter*, press**OK**

## 4. Geometry - Car Body

After importing geometry, it will appear in the 3D window

Click

**Fit View**to zoom in on the geometry

## 5. Meshing Properties - Car Body

After geometry is loaded, we can proceed to define meshing properties. To better resolve the flow around the car body, we want to refine mesh near the car geometry by specifying minimum and maximum refinement levels.

Go to

**Hex Meshing**panelSelect

**car_body**geometryEnable

*Meshing Geometry*Refine mesh near the surface of the car_body

*Refinement**Min 3**Max 5*

## 6. Base Mesh

Base Mesh is a domain mesh of our simulation from which the final mesh will be created by carving out the geometry of the car.

Go to

**Base**tabDefine base mesh parameters accordingly

*Min \({\sf [m]}\)**-6**0**0*

*Max \({\sf [m]}\)**14**6**8*Set the division of the base mesh

*Division**50**15**20*

## 7. Base Mesh Boundaries

We need to assign individual names to each side of the base mesh in order to be later able to define different conditions on each side.

Define boundary names accordingly

*X-**inlet*

*X+**outlet*

*Y-**bottom*

*Y+**top*

*Z-**symmetry*

*Z+**right*3 Define boundary types accordingly

*Y-**wall*

*Z-**symmetry*

## 8. Material Point

Material Point tells the meshing algorithm on which side of the geometry the mesh is to be retained. We are modeling car aerodynamics so our material point needs to be located inside the Base Mesh but outside the car body.

Go to

**Point**tabSpecify location inside base mesh but outside car geometry

*Material Point**0**3**2*

## 9. Start Meshing

Everything is now set up for meshing

Go to

**Mesh**tabPress

**Mesh**button to start meshing process

## 10. Mesh

After meshing is finished, the new mesh will be displayed in the graphics window. To show the mesh of the car body we can use the Graphics Object List.

Click

**Graphics Object List**iconSelect

**Mesh**to show meshes list

## 11. Mesh - Toggle Visibility

You can hide domain boundaries to inspect the mesh on the car body.

2 Hide the following objects

*bottom*

*inlet*

*outlet*

*right*

*symmetry*

*top*

## 12. Select Solver - SIMPLE

We want to analyze incompressible turbulent flow around the car body. For this purpose, we will use the SIMPLE (simpleFoam) solver.

Go to

**Setup**panelEnable

**Steady State**filterEnable

**Incompressible**filterSelect

*SIMPLE*(simpleFoam) solver**Select**solver

## 13. Turbulence

We are going to use the standard \(k{-}\omega \; SST\) model to handle turbulence. This model gives very good agreement with experimental data and is commonly used for aerodynamics applications.

Go to

**Turbulence**panelSelect turbulence model

*Turbulence Modelling**RANS*Change default turbulence model

*Model**\(k{-}\omega \; SST\)*

## 14. Boundary Conditions - Bottom (Flow)

We are simulating a car moving on a road. In this reference frame, the road has to move with respect to the car. We can achieve this by applying fixed velocity boundary condition on the bottom of the domain.

Go to

**Boundary Conditions**panelSelect

**bottom**boundary4 Set velocity

*U**Type**Fixed Value*

*U**Value \({\sf [m/s]}\)**20**0**0*

## 15. Boundary Conditions - Inlet (Flow)

On the inlet, we are going to apply constant velocity, similarly to the *bottom* .

Select

**inlet**boundaryChange boundary character

*inlet**Velocity Inlet*Define inlet velocity

*U**Reference Value \({\sf [m/s]}\)**20*

## 16. Boundary Conditions - Inlet (Turbulence)

We are simulating a car moving in otherwise stationary air. Therefore, we specify low turbulence intensity on the inlet.

Go to

**Turbulence**boundary conditions tab3 Set the following parameters accordingly

*k**Intensity \({\sf [-]}\)**5e-03*

*\(\omega\)**Mixing Length \({\sf [m]}\)**1e-03*

## 17. Boundary Conditions - Right (Flow)

On the right and top boundary, we are going to force velocity to be tangent to the boundary.

Select

**right**boundary conditionGo to

**Flow**tab4 Define slip wall condition

*Type**p**Zero Gradient*

*Type**U**Slip*

## 18. Boundary Conditions - Right (Turbulence)

Go to

**Turbulence**tab3 Change turbulent kinetic energy and frequency types to

*Type**k**Zero Gradient*

*Type**\(\omega\)**Zero Gradient*

## 19. Boundary Conditions - Top (Flow)

We need to repeat the same steps to the top boundary condition

Select

**top**boundary conditionGo to

**Flow**tab4 Define slip wall condition

*Type**p**Zero Gradient*

*Type**U**Slip*

## 20. Boundary Conditions - Top (Turbulence)

Go to

**Turbulence**tab3 Change turbulent kinetic energy and frequency types

*Type**k**Zero Gradient*

*Type**\(\omega\)**Zero Gradient*

## 21. Monitors - Forces

We want to monitor the simulation process by observing plots of the aerodynamic forces on the car

Go to

**Monitors**panelGo to

**Forces**tabEnable observing forces on the car_body boundary

*Monitored Boundaries**car_body*

## 22. Run Simulation

Go to

**Run**panelSet maximal number of iteration that solver can perform before stopping

*Number of Iterations**200*Click

**Run Simulation**button

Estimated computation time: 2 minutes

## 23. Monitor Forces

During the simulation, we can observe whether forces on the car body stabilize which will mean that our simulation converges

## 24. Postprocessing - ParaView

After the simulation is finished, we can proceed to post-processing

Go to

**Postprocessing**panelStart

**ParaView**

## 25. ParaView - Load Results

Make sure you have your case selected

*car.foam*Click

**Apply**to load results

## 26. ParaView - Set View Direction

After loading results, we have to rotate the domain or change view direction to see the car.

Click

**Set view direction to +Z**

## 27. ParaView - Display Velocity

We will now display velocity (U) contours.

Load latest results by clicking

**Last Frame**iconSelect

*U*(velocity) from the dropdown menuClick

**Rescale to data range**

## 28. ParaView - Coloring (I)

We can change the coloring scheme in ParaView to have nicer colors.

Click

**Edit Color Map**from the menu placed on the left side, if the panel is not already shown.Select

**Choose Preset**from the Color Map Editor placed by default on the right side of the ParaView

## 29. ParaView - Coloring (II)

We can now select a new Color Preset.

Select

**jet**preset**Apply**changes**Close**the window

## 30. ParaView - Coloring (III)

Now we can see the results with the new preset applied. We can also modify the number of displayed colors to see the results better.

Decrease color scale resolution to make velocity regions more distinguishable (non-smooth color transition)

*Number of Table Values**20*

## 31. ParaView - Import Geometry

To display results on the original geometry, we can import the geometry directly into ParaView.

Click

**Open**and select the original**car_body.stl**geometry to import it into ParaView.Click on the

**Visibility**icon to show the geometry.

## 32. ParaView - Final Results

Now we can see the final results with the original geometry.