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 Figure 4.1: SimScale’s force plot. In this simulation, the Pressure force z was -6.7637 N and the Viscous force z was -11.0686 N. This means the full car would have a pressure drag of 13.5274 N and a viscous drag of 22.1372 N, for a total drag of 35.6646 N. |
Legacy Interface
To visualize the results, go to the navigation panel, go to the simulation run, and select Solution field. You might be asked if you would like to use the Legacy Interface or the new Beta Interface. In the Legacy interface, there will be a list of tools in the upper left and a geometry viewer on the right. These tools are called filters in ParaView and SimScale’s beta version is switching to that terminology so I’ll call them filters. There are also some other settings at the top of the geometry viewer, most notably the time frame settings (Black rewind, play, and fast-forward symbols). Most of the time, make sure you are analyzing the most recent time point in the simulation as this is likely the most accurate data available. Add a filter by finding the desired filter in the list and clicking the plus symbol on the right side of the label. This will bring up a panel, with settings specific to that filter. The 3 that I use most often are Cutting Planes, Isovolumes, and Particle Traces. After adding a filter, it can be found as a sub-item under the label. A filter’s visibility can be toggled by clicking the eye symbol to the left of it and can be removed by clicking the minus symbol to the right of it.
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SimScale can also display the mesh over a cross-section when post-processing simulation data. I’ve never run into mesh size limitations with this method so even if the Mesh Clip tool wasn’t working on a mesh, this method might. Obviously this method requires the simulation to be solved first and so it shouldn’t be used to develop the mesh initially, but could be useful later on. This is particularly useful for checking if any unexpected results are actually artifacts from mesh defects. |
Beta Interface
Selecting New Beta Interface will bring you to the new interface. Maybe by the time you’re reading this, SimScale will have made this
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the default interface. Either way, it’s pretty similar to the old one. The geometry viewer is mostly the same, but the panel in the upper left is different. There’s a section called Parts Color, which allows the colour and opacity of the geometry to be controlled or allows the geometry to be coloured according to a simulation variable. There’s also a button that says Add Filter. This is where you can add all the visualizations that were available in the legacy interface. After adding the filter, many of the same options from the legacy interface now will show up in a new section of the left panel. You can toggle the visibility of the filter by clicking the slider to the right of its name and you can delete a filter by clicking the garbage
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icon to the right of that slider. One other big difference is that the range of a scale bar is changed by directly interacting with it. Simply click the minimum or maximum value and type in the desired value.
ParaView
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ParaView can be downloaded here: https://www.paraview.org/download/
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After it loads, I would change the time point to be the most recent time point that was simulated as this should be the most accurate point of the simulation. Now, we can start processing the data. ParaView works by adding filters to the data file. Every filter you add will show up in the Pipeline Browser, below the .foam file. To see a list of all the filters ParaView has, go to the top menu bar, hover over Filters, and then hover over Alphabetical.
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Learning all of these filters is beyond the scope of this guide and unnecessary for our team, so I will explain how to find the drag value and leave you to research or experiment with whatever else interests you. Since we only simulated half of the car, let’s add a Reflect filter. In the Properties panel, select X Min as the plane and click Apply. In the geometry viewer, you should see the full car now, not just half.
Next, add an Extract Surface filter, click Apply.
Add a Generate Surface Normals Filter, click Apply.
Now add a Calculator filter. In the Properties panel, you should see Result Array Name, a text bar with “Result” written by default, another text bar below that, and then a bunch of buttons with mathematical operations. You can change the Result Array Name to whatever you want to call your calculated quantity, I usually leave it as the default unless I’m using multiple calculations. In the empty text bar, this is where you enter the formula that you want calculated. Type “-p * Normals_Z” and click Apply. This multiplies the pressure value at each point on the car’s surface with the z component the normal vector at each point along the surface.
Now add an Integrate Variables filter and click Apply. This should bring up a panel with a table in it. Scroll until you find Result (or whatever you called the calculated value), record the value beneath it, keep scrolling until you find wallShearStress, and record the third value beneath that (the z component). The values in this table are values that have been integrated across the surface we that was extracted earlier. Integrating our the calculated result gives the pressure drag of the car, while integrating the wall shear stress gives the viscous drag. Add the magnitude of each together drag component to get the total drag.
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  Figure 4.10: After The results after adding all of the filters for the drag calculation, as can be seen in the Pipeline Browser. It should be noted that in the table on the right, I hid the The columns between Result and wallShearStress were hidden so that they were both visible in the image. By default they are separated by several other columns. Also don’t pay too much attention to these drag numbers, this simulation is likely not that accurateParaView is reporting a pressure drag of 14.1503 N and a viscous drag of 22.1323 N, for a total drag of 36.2826 N. This is about 1.73% higher than the drag calculated by SimScale. |
Once again, the same process could be used in the y direction to calculate the lift or downforce. I’ll end here and let you experiment with other visualizations, ParaView has filters for everything that SimScale has and more. Some of them require the internalMesh mesh region though.
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Midnight Sun PDF Library: Always a useful place to go. There’s There are resources for many different aspects of vehicle engineering, with some that are specific to solar cars.
The Leading Edge: There’s a paper copy in the bay. Very helpful for understanding solar car aerodynamics, although it is focused on challenger class vehicles.
The Efficient Engineer: A YouTube channel focusing on explaining general engineering concepts with excellent animations. This is a good place to learn some fundamental fluid concepts.
braintruffle: An odd name but this is a newer YouTube channel that is creating a series of videos on the continuum approximation for fluids. They conceptually explain the assumptions and statistics used to simplify fluids from quantum mechanical entities to a continuum of field values. Future videos will look at discretizing the continuum for simulations.
Fluid Mechanics 101: A YouTube channel with highly detailed videos on specific topics in computational fluid dynamics. Great This is a great resource if you want to learn more about a specific topic, like a certain algorithm or turbulence model.
SimScale: There’s also several resources provided by SimScale. They have a wiki section and webinars for simulation theory, forums where people discuss issues they encountered during simulations, pretty good documentation to explain how to use their product, and you can also look at example projects to learn how other people handled certain simulation problems directly in SimScale.
LEAP Australia: A blog that has some useful articles. I mostly looked at their boundary layer articles.
CFD-Online: I haven’t looked through this site very thoroughly, but I did use it to learn about estimating initial conditions.