The best 3 answers to “Why is visulization important for CFD?”

cfd-guerrilla Last year, FieldView jumped into Altair’s bed, and now got a baby named AcuFieldView in the latest AcuSolve package. Recently, FLOW 3D was married happily with EnSight (CEI), and will get EnSight 10 integrated into FLOW 3D in a few months (this fall).

It seems most CFD software vendors now are aware of the importance of  post-processing capabilities. Competition for buyers will be extended from brains to eyeballs. If your CFD software can only draw black and white lines, or can only generate mediocre animations, it seems it will prepare to die, soon.

The trend of getting better visualization and post-processing tools is surely driven by the demands from the customer, although “A lot of times, people don’t know what they want until you show it to them.”

So, if you ask so many called CFDers (CFD engineers, CFD specialist, CFD analysts,  CAE engineers…) why they think visualization is so important. You probably will get all sorts of answers. But probably, the top 3 answers would be:

#1. “My boss can only read colourful things.”

The sad truth is that most of the times the supervisors of the CFDers don’t know CFD (why should they know?). Images and videos are the only format they are expecting. Yes (or No) is another term they can understand. Unless you can convert the unit of Pascal to Dollar, they will have no interest in numbers or plots.

Unfortunately, current CFD software does not have the built-in capability to convert Pascal to Dollar. This job need real CFD analysts (not CFD guerrillas mentioned below) to read through the numbers, and draw some black-and-white lines to transform boring numbers to physics (performance) then possibly  to costs.

When the colorful things are the only things you can produce from CFD software, what else can your boss expect?

#2. “What? You don’t know the purpose of CFD simulation is just to create colorful pictures and dazzling videos? even my boss knows it.”

CFD or CAE simulation is not new for managers. Almost all engineering managers in almost all sectors now can talk about simulation, can talk about CAE, can talk about PLM. As a result, more and more designers join the CAE Jihad  (as mentioned in a previous post).

So, most of CFDers are actually CFD guerrillas. Today, they are working on a oil/water/air separation project; next day they will work on car aerodynamics projects. Maybe one week later, they will work on thermal management projects.  For them, CFD is just a vending machine: need coke? insert coins;  need sandwich? insert coins again.

When you have no time to check the contents in the can, or contents in the sandwich box, you have to assume anything in the can (spit from the vending machine) should be coke; anything in the sandwich box should be delicious sandwich. You just need polish the packaging (your images, videos) and then pass them to your boss (who only read colorful things). Mission completed and you are ready for next CFD target.

#3. “My supervisor told me I need lubricate my dry research with colorful CFD.”

Even in the ivory tower, CFD can still be a fashion, sometimes, even in Mechanical Engineering department.

After spending days and nights in the boring lab (usually with special odors depending on the departments you are in), you probably are lucky enough to get some correlations (often expected; occasionally, unexpected) among some parameters.  Instead of going ahead to write your thesis, or a paper, your supervisor may ask you to try some simulations to “support” your findings.

Now you become a CFD guerrilla.  You target is clear: to support or match your experiment. Your mission is clear: elegant plot and colorful images for your thesis or paper, and possibly fancy videos for conference presentations. Surely, you will find ways to match your simulation with any data you get in the given timeframe.

Your paper, your thesis, and your presentation now get an excellent facelift. And in your CV, now you can honestly claim yourself as an experienced CFDer.

Nothing wrong, possibly except your CFD simulation. Your system has fluid does not necessarily mean you need CFD.

Not uncommon, a calculator can be more accurate than your CFD software if you know how to calculate. If you don’t know how to calculate, your CFD software cannot help much, and eventually you are only using the visualization capabilities of your CFD software. So, you fully understand why visualization is important for CFD, and you will teach your students using your CFD experience when you become a professor.

I know there are probably some other good answers. If you get one, please post it in the comments box below.

Of course, no one can deny the importance of post-processing and visualization. These tools and capabilities are there to help you dig more information efficiently, e.g., calculating the standard deviation of temperature in a region, extracting vortex core region, locating flow separation. Visualization is serving you as a road map when you exploring your results.

It is equally undeniable that these images or video will be able to help you explain the results to other people. But the main purpose of these tools is for you to explore your results, not just to present your results.

 

Comments

  1. Great article. A couple thoughts. If you want your boss to understand your CFD, show them results that look like what they’re used to – true engineering plots of integrated quantities. Also, visualization is perhaps not the best name. Postprocessing, while bland, conveys more of what you need – processing of CFD results into engineering data, not just visualizing something. (Don’t get me wrong – viz is important.)

    • Thanks John for your thoughtful input. As you rightly pointed out visualization is just a component (sometimes important; sometimes not) of post-processing, which is always important.

      The reality is the increase of CFD licenses sold generally outpaces the increase of full time CFD analyst (which in most company is relatively not changed). So, more and more designer or mechanical engineers are doing a lot of CFD simulations.

      They usually expect some sort of turn-key solutions (because CFD simulation is their part time job). This is nothing wrong. The problem is, unfortunately, current CFD software still has very limited intelligence in checking problems in the simulation setups, e.g., are the wall functions valid for the mesh and boundary conditions? Or is the drag law valid for the phases defined and in the multiphase flow regime?

      This is the reason why a lot of such new CFD users get frustrated with detailed CFD simulation setup (remember they have other roles). For them, CFD simulation likes a black box.

      It is an exciting development that we can see more and more CFD users. The problem is not on these part time CFD users; it is on 1). Slow development in CFD solver intelligence (most of the time, you need a full time analyst to confirm the settings). Most CFD solver vendors like to talk how fast, how accurate, how many models, or now how easy to use for non-CFDers (usually limited to pre- and post-processing tools); and 2). The management often has the misconception that CFD software is so matured (also, not cheap) that it should like a turn-key solution. Engineer just imports CAD model then presses a button. So the management may use these part time CFDers as guerrillas for specific CFD projects.

      Shengwei

    • Hi John, I very much agree with your second point. Data visualization packages are really tools for analyzing results. Without one, you just end up with a bunch of numbers. Of course, you could perhaps integrate the results to get some collective value, but this will not let you see any interesting behavior (flow patters, etc…) that may be occurring in the problem.

      Also, the Visualization Toolkit (VTK) is a great tool for performing data analysis. It’s basically a library for processing and visualizing data and it contains all the math and rendering capabilities built in. All you need to do develop your own visualization solution is to couple it with a GUI package such as QT in C or the native Java Swing (and write the code to set up the visualization pipelines). I wrote an article about this if anyone is interested: http://www.particleincell.com/2011/vtk-java-visualization/

  2. I agree with John, in my experience the engineering plotting is where decisions get made. CFDers today demand both stunning graphics and high quality engineering plots.

    A second trend we are seeing in the market is the push towards parametric CFD for optimization and performance prediction. This new way of working turns traditional post processing on its head in that engineers need to Plow through 100s of simulations and in the end they model performance using integrated quantities.

    • Hi Durrell, thank you very much for your contribution on this topic.

      I totally agree with your comment on the second trend. More and more simulations, and larger and larger models. Managing and fully utilizing tera or even peta scale simulation data desperately needs a higher-level post-processing tool (a tool that can explore through numerous simulation results to get systematic insights) and simulation data management system.

      It is nice to see Tecplot Chorus is tackling this challenge.

      Shengwei

  3. I think Larry Flynt got it right when he said, “It’s all about the graphics.” Several of my regular clients like to use the material from my reports for their sales and marketing. Consequently, I wind up devoting a lot of my time to producing “snappy” graphics when post processing. Advances in this realm are always welcome.

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