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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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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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