Car - CFD Simulation SimFlow Tutorial

This tutorial presents a typical approach to external aerodynamic analysis. It considers a steady-state analysis for car body aerodynamic performance. The simulation includes symmetry conditions to reduce the size of the domain, modeling of turbulence, boundary conditions, and baseline postprocessing features.

SimFlow is a general purpose CFD Software

To follow this tutorial, you will need SimFlow free version, you may download it via the following link:
Download SimFlow

Open SimFlow and create a new case named car

Firstly we need to Download GeometryCar_body

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.

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

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.

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.

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.

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.

Everything is now set up for meshing

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.

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

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

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.

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.

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

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

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

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

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

Estimated computation time: 2 minutes

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

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

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

We will now display velocity (U) contours.

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

We can now select a new Color Preset.

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.

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

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