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Many simulation programs, including SimScale, provide tools for processing the simulation data. However, there are also dedicated post-processing programs such as ParaView. SimScale’s post-processing environment is fairly intuitive and I use it for quick visualizations. ParaView has more options, and has generally proven itself to be more reliable in my opinion. I’ll talk about both programs here, so you can choose which post-processor you like using. Furthermore, SimScale is introducing a new post-processor as of the time of writing so I’ll talk about that as well.
SimScale
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Forces
Force data is accessed separately from SimScale’s main post-processing environment. During and after a simulation run, you can check the simulation forces by going to the left navigation panel and selecting the Force plot under the run you want to analyze. This should bring up a plot of all forces at each simulation iteration. To find drag, add the forces acting in the z direction at the most recent iteration. The only significant contributions should be from pressure and viscous forces. And remember to double the result because only half of the car was simulated. To find lift or down force, repeat in the y direction.
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 Figure 4.1: SimScale’s force plot. |
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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. Add a visualization by filter by finding the desired filter in the list and clicking the plus symbol to on the right side of the label. This will bring up a panel, with settings specific to that toolfilter. The 3 that I use most often are cross-sections, isovolumes, and streamlinesCutting 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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 Figure 4.2: SimScale’s legacy interface. Tools can be found in the upper left panel, settings show up in the bottom left, and there are some other settings at the top, 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. |
If you add a visualization filter for a certain parameter, say pressure, you will notice that a scale bar is automatically generated. The scale bar is automatically scaled relative to the maximum and minimum values in the domain. I always preferred to change this the range to round numbers and kept the range consistent between simulations to make comparisons easier. This is done by going to the panel with the post-processing tools and clicking the drop-down arrow to the left of Results. Then select the parameter you’re using, which for this example is SCL: Pressure. In the panel that opens, you can change the colour scheme, the number of divisions in the scale, the range of the scale, toggle logarithmic mapping, and toggle node averaging.
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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. |
SimScale Beta Interface
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Beta Interface
Selecting New Beta Interface will bring you to a similar but slightly different interface. 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 can 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/
To use a program other than SimScale, the results need to be downloaded. In the left navigation panel, click on the run you want to analyze. In the panel that opens find the download button and click that. (Insert picture) The result files can get quite large, especially if you’ve saved the results at more than one time point.
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 Figure 4.10: After adding all filters added 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 columns between Result and wallShearStress 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 accurate. |
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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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One type of analysis that SimScale has not implemented yet is graphing. ParaView has several graphing filters, and can also export data to .csv files if another graphing program is preferred. |
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If you’ve been following along, you’ve now completed a CFD simulation in SimScale. I tried to make this guide brief, if you’d like to learn more about fluids, aerodynamics, or CFD simulations I’ll add some more resources below.
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Midnight Sun PDF Library: Always a useful place to go. There’s 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 useful for understanding solar car aerodynamics, although it is focused on challenger class vehicles.
Fluid Mechanics 101: A YouTube channel with very detailed videos on specific topics in computational fluid dynamics. Great resource if you want to learn more about a specific topic, like a certain algorithm or turbulence model or algorithm.
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 turbulence and estimating initial conditions.
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