Aerodynamics Post-Processing with SimScale and ParaView
Today we want to show you some aerodynamics post-processing operations with ParaView on your local computer that can help you to understand and analyze the results of an external aerodynamic simulation case.
For this you need the current version of ParaView which you can download directly from the ParaView website.
In the following we will use the simulation of the airflow around a futuristic car concept which you can find in the SimScale Project library. It demonstrates a CFD simulation in an early stage of a car body design using a quite coarse mesh to save computing time and to get qualitative insights into the aerodynamics of the design. Of course you can adapt everything this blog post is going to show you to other CFD simulations.
Some of the important performance indicators in external aerodynamics are drag and lift. ParaView allows to visualize these indicators with just a few mouse clicks. Drag and lift are basically the components in flow and opposed to the gravitation direction (X and Z direction in the example below) of the normal force on the surface caused by the pressure (which means that we will neglect the viscous contribution in this post).
By decomposing this normal force for every element of the surface mesh, it is possible to get a visualization of the drag and lift in just four steps:
1. Import the simulation results into ParaView and make sure you select all mesh regions of the result to be imported (also the surfaces!)
2. Extract the surface of the car from the case by applying the “Extract block” filter:
- “Filter” > “Alphabetical” > “Extract Block” and select the patches of the car’s surface
3. Compute the surface normals for every element of the surface mesh of the car:
- “Filter” > “Alphabetical” > “Generate Surface Normals”
4. Next we need to decompose the pressure distribution to drag and lift distribution: Calculate drag and lift distribution for the car
- “Filter” > “Alphabetical” > “Calculator”
- For Drag: Normals_X*p (Depending on the direction of the coordinate system, you might want to add a “-1*” to get the sign right; see image below)
- For Lift: Normal_Z*p (Again, depending on the direction of the coordinate system, you might want to add a “-1*” to get the sign right; see image below)
Please note: All coordinates and patch names in the images and text refer to the example simulation case that you can find in the project library. It may be necessary to adapt them if your case has another coordinate system. Now you can choose the new fields and visualize drag and lift.
The image below shows a color visualization of the drag on the surface of the car body. In this case, we are only interested in a qualitative assessment – if we would be interested in quantitative analysis, we could also compute the acting forces (taking the density value into account, since this was an incompressible simulation).
The next image shows a color visualization of the lift over the bottom of the car body shape.
This way, the aerodynamic performance of vehicle shapes can be analyzed fast and efficiently. ParaView is a great tool to get meaningful insights into simulation results computed with SimScale.
If you’re interested in aerodynamics simulations, you might also find this article interesting: Football Aerodynamics Simulation with SimScale.