6 CFD Post-Processing Tips You Must Know: How to Improve Visualization Productivity and Quality 10X
Post-processing CFD data is the most vital step in deriving right conclusions from modeling, presenting the results to decision-makers and ensuring best product designs. Output files generated by CFD are often huge, making it a daunting task to efficiently create effective visualizations. Product decisions require optimization studies which, in turn, means a large number of individual CFD simulations. In addition, generating images, animations, and playing with colors have never been the forte of CFD folks.
Years of experience using many popular CFD visualization tools, for a wide range of industries, made me realize that certain ‘best practices’ should always be applied.
In this article, I discuss six tips that will make post-processing more productive, and produce impressive presentations for your meetings. The illustrations and examples are based on ParaView, a powerful visualization tool, but the tips can be applied to most other tools as well.
1. Use ‘state’ files to automatically generate pipeline
Absolutely must-know. You should never re-generate all the post-processing steps (contours, streamlines, vectors, slices, filters etc.) again and again for cases with identical/similar geometry. Save and reuse the ‘state’ file and load it anytime you want to perform post-processing pipeline on a similar CFD model. This is also extremely powerful for design explorations where differences in modeling scenarios are small or none.
‘State’ files are light-weight in size and therefore you can save them at regular intervals, without worrying about storage capacity. Such a feature is available in most of the stand-alone post-processing tools.
2. Group surfaces, extract zones
This is a big time-saver when your model has a large number of surfaces/zones. Grouping similar geometric entities will allow you to efficiently change colors, transparency, display/hide scenarios, light effects, and visuals. To illustrate it further, look at the post-processing model below where the similar parts have been extracted and grouped together.
Moreover, you should also extract zones that your analysis is most focused on, making your file easier to handle.
Example of ParaView ‘pipeline’ with surface groupings and block extracts
3. Don’t misuse streamlines
Flow streamlines (pathlines, stream tracers are some other names) are a great way to visualize and understand the flow patterns. They are also, probably, the most misused visualization method. Too many streamlines, seed points not appropriately chosen, colored by random scalars are some of the problems.
How not to misuse streamlines
4. Save what you NEED
This tip is very important when your CFD simulations are generating huge amounts of data. In most situation, we know the quantities that are needed for the analysis. By default, CFD solvers save many primary and derived scalars/vectors in output files. This implies that your CFD simulations are saving data, for each point of your computational mesh, for a large number of quantities. Think about it, how many times have you used flow variables other than temperature, velocity, and pressure in your reports?
5. Camera, views, lights
Believe it or not, I have seen people trying to manually adjust the 3D camera view to get images with the exact same view for different CFD cases. The resulting comparison images from such effort look ugly, to say the least. In ParaView, you can save/load views, undo them and even sync camera for multiple cases. Also, use lights in a way that enhances your CFD and makes life easy for people looking at your reports.
Two different cases with fixed camera view
6. Start with gray scale, and transparency
So many times, CFD engineers create images with a myriad of colors. Having access to the whole color spectrum does not mean we should use all of them. Using too many colors does not add any value and instead distracts the viewer from focusing on the message. This is not only true for CFD visualizations but any other visuals and even UI design.
Let’s use all the colors we have got!
Do you have a tip that post-processing engineers must know?
There are many other features/tips for better CFD post-processing and visualizations and one post cannot do justice to them all. And that’s why I am working on articles/tutorials that will focus on major methods of CFD post-processing, one at a time.
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