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Old   April 23, 2007, 06:21
Default CFD Code Choice and General Advice
  #1
Alex Pope
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I am a self-taught CFD user with a limited amount of experience using Fluent (with Gambit) to analyse the aerodynamic performance of a Formula SAE car whilst completing my Masters degree.

Now working in industry, it was been decided that CFD will complement experimental work on an active cooling/thermal analysis project. I have been demonstrated CFX, Star-CCM+, CFDesign and FloWorks and need to choose one to use.

I feel that Star CCM+ offers the best compromise between ease of use and analysis power but I am put off by the price. Of the other packages, I would be most confident with the results from CFX but feel it would take a lot of learning, whereas I am concerned with the lack of mesh control and features in both Cfdesign and FlowWorks.

I intend to spend a lot of time becoming confident in the use of CFD, rather than just rushing into it, and already have several books on both CFD and thermal analysis.

I would appreciate any opinions on the above packages, particularly with regard to ease of use of CFX for a new user and the accuracy and any convergence problems with CFdesign and FloWorks.

Apologies for the long post but one final point is that I intend to 'borrow' the chosen software from the vendor for a week or so, after attending training, before committing.

Thanks.
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Old   April 23, 2007, 06:50
Default Re: CFD Code Choice and General Advice
  #2
Steve
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Can't help you with the code-choice aspect of your question, but the eval/training answer is that most (id not all) vendors will be keen to give you an evaluation period if they can smell your $$. Training is only normally provided if you have already taken the plunge and parted with money. Sometimes it'll be included in the price (in lieu of a discount perhaps). But don't expect to get training as part of an evaluation.
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Old   April 23, 2007, 06:58
Default Re: CFD Code Choice and General Advice
  #3
Alex Pope
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Thanks for the reply - I agree. It has been suggested by several of the vendors that if I attend (and pay for) the training then they will provide me with an evaluation period afterwards. I wouldn't expect to be given training for free as part of the evaluation period.
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Old   April 23, 2007, 07:38
Default Re: CFD Code Choice and General Advice
  #4
M
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for information, can you indicate what sort of yearly lease prices you have encountered?

thanks
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Old   April 23, 2007, 07:48
Default Re: CFD Code Choice and General Advice
  #5
Alex Pope
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I would not want to divulge actual prices as the discussions were assumed to be confidential. If you require further details then a quick phone call to any of the vendors would give you ball-park figures.
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Old   April 23, 2007, 07:56
Default Re: CFD Code Choice and General Advice
  #6
James
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One factor to remember in all this is the cost of your time. Typically in the US currently a man hour is costed at ~$100.

If you get a code that is more suitable, easier for you to use, gives better answers .. then you will easily save any difference in cost over the year.

This doesn't even take into account the value to your projects of having the right information at the right time .
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Old   April 23, 2007, 08:07
Default Re: CFD Code Choice and General Advice
  #7
Alex Pope
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That is a very good point.

There are a lot of factors. Whereas a code such as FloWorks or CFDesign will take a far shorter time to get used to there may be a point where a 'glass-ceiling' is hit and the software does not have the range of functions I need. At the opposite end of the scale (IMO), CFX would offer full functionality but at a cost of time to learn it in detail.

In my opinion CFdesign and FloWorks are very much aimed at the design engineer who has no interest in what is driving the code. CCM+ allows a design engineer to pick it up and put it down without having to understand it in much detail, but also allows more dedicated CFD-oriented users to access it's full functionality. CFX is in this league but would be harder to get used to and Fluent is aimed directly at the CFD guy. Does anybody agree with this?

I am aiming at the level of CCM+ - I do not intend to be able to write the code etc. but do intend to understand the terms of the NS equation, continuity equations (etc) to be able to use the CFD effectively.
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Old   April 23, 2007, 08:55
Default Re: CFD Code Choice and General Advice
  #8
myron
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There are other solvers out there, too. CFD++, AcuSolve to name a couple. Both very good codes.
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Old   April 23, 2007, 16:27
Default Re: CFD Code Choice and General Advice
  #9
Tim
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I'd agree with your summary of the codes. I've not used either Cfdesign or Floworks, but I've heard that they're very easy to use, but at the expense of accuracy and capability.

I've used Fluent, and Star-ccm+ (and star-cd and powerflow). Fluent and Star-cd are capable but suffer from being old technology that's not easy to use. ccm+ is much easier to use (the meshing in ccm+ makes gambit look like a joke) and it's getting much closer to fluent in terms of capability. I now use ccm+ for pretty much everything.

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Old   April 23, 2007, 18:17
Default Re: CFD Code Choice and General Advice
  #10
Ron Godwin
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Hi Alex,

What type of application are you trying to solve? I'm guessing that if you are leaning towards CFX and StarCCM+ that we are talking about something fairly demanding. Is it automotive?

I have used both CFX and CFdesign in the workplace and found them to be good tools. I found both tools fairly easy to use though CFX is a lot more expensive (watch out for the TECS fee) and Workbench didn't quite deliver all that ANSYS claimed - flashy front end.

I guess it's all a bit up in the air with the ANSYS/CFX - Fluent merger. I don't think anyone is really clear which technology will come out the other side. I bet the CFX sales guy will tell you anything though - those guys are usually pretty pushy

CFdesign has some pretty good motion capability and is more than capable of dealing with the problems that I have thrown at it. The technical support has also been really good.

I'm not sure what you mean by lack of mesh control though? I wish all CFD packages offered the same level of mesh intelligence and user interaction - I think the slider bars are cool. Is your geometry failing to mesh?

Hope this helps Ron
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Old   April 24, 2007, 03:38
Default Re: CFD Code Choice and General Advice
  #11
Alex Pope
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Thanks for the informative replies.

The application I will be using the software for is system level thermal analysis. It is not overly demanding, definitely not on the automotive scale.

I liked the CFdesign interface and felt there would be a very good level of technical support, but I have heard mixed things about the stability, especially problems with convergence and large tet meshes.

I also have heard that CFdesign is very good with movement but this would not be applicable for my use.

How would you rate Cfdesign for meshing small gaps, for instance looking at heat sink optimisation and thermal resistance (convection coefficient) analysis?

Have you had any convergence problems?

Have you performed any benchmarks, particularly with regard to thermal analysis?

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Old   April 24, 2007, 04:10
Default Re: CFD Code Choice and General Advice
  #12
Micaela
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Hi Alex, I used CFX (3years) in the past and I'm using CFdesign now. I can tell you that CFX is much more demanding in terms of mesh than CFdesign. It's not so easy to learn how to create a mesh and in particular a mesh that is "good" for CFX. In particular depending on the applications, the mesh quality needeed may be really different. CFX is also time and CPU demanding. If you have to run big models (like may be yours) you need a lot of time and a powerful CPU. If you have radiation problems you definetely need a lot of RAM to run your analysis. Cfdesign is really easy to learn and to use. It has an Intelligent Solution Control algorithm that works really fine. If you have convergence problem it's quite always a mesh issue (both in CFX and CFdesign!!!). With Cfdesign you don't need big machines to run your analysis and you have the response really faster! The reason for this is that CFX is based on Finite Volume methods, while CFdesign is based on finite elements method. The NS equations are always the same, the difference is in the methods that you use to solve them. CFdesign in this is much more faster. The accuracy always depends on how you use the code and implement the problem, it doesn't depend on the code itself. When I started with CFdesign I was also worried about the accuracy, but I tested myself that you can obtain the same accuracy that you have with CFX, in particular on thermal problems like yours! Finally you probably have less controls on the mesh in Cfdesign, than in CFX, but you don't need them! Hope this helps to make the best choice! Micaela
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Old   April 24, 2007, 04:16
Default Re: CFD Code Choice and General Advice
  #13
Alex Pope
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Thanks for the information.

Have you compared the CFdesign results to physical testing, especially thermal analysis?

If you have, how did it compare?

In what applications did you compare CFdesign to CFX and how did they perform?
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Old   April 24, 2007, 04:24
Default Re: CFD Code Choice and General Advice
  #14
Alex Pope
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Secondly, how does CFdesign perform for near wall analysis, i.e. calculation of convection coeficients in order to determine heatflux either through a sealed casing or to determine heat sink thermal resistance?
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Old   April 24, 2007, 05:18
Default Re: CFD Code Choice and General Advice
  #15
Trev
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Alex, I looked at several different CFD codes for electronics cooling (not sure if this is relevant thermal) back last year. I didn't really consider CFX or CCM+ as they seemed a bit too high end and not focused in this area. My shortlist was Icepak, Coolit, Floworks and cf design. I liked Floworks from a price point (don't ask your reseller for advanced support though) while Icepak and Coolit where way more expensive and a bit more clunky. In the end though we bought cf design for the following points: easy to understand, plugged into the CAD system, good accuracy, best trade off on functionality v price
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Old   April 24, 2007, 05:22
Default Re: CFD Code Choice and General Advice
  #16
Robin
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If it's near wall heat transfer in conjunction with heatsink interfacial resistance effects then it's sounding very like an electronics cooling type application. As such it falls well into the domain of Flomerics who acquired Nika who 'produce' FloWorks.
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Old   April 24, 2007, 05:34
Default Re: CFD Code Choice and General Advice
  #17
Alex Pope
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Thanks again.

My fears over the accuracy of CFdesign seem to be a bit unfounded. It is an electronics cooling application but at system level rather than board level.

Leaning towards CFdesign, I agree with the fact that it is a good compromise between cost and functionality, as I said before I was initially unsure of the accuracy.
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Old   April 24, 2007, 10:04
Default Re: CFD Code Choice and General Advice
  #18
Micaela
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Alex, I tested CFdesign in particular on valves problems and the accuracy against the experimental tests are about 1% 2%. Really not bad! I tested both CFdesign and CFX on lightning applications (natural convection+radiation)and the results were comparable, but with Cfdesign it took really less time to get the response. If your problem is the accuracy be sure that you have a valid support team from the provider: it's essential to let you understand how to manage the analysis!

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Old   April 25, 2007, 04:33
Default Re: CFD Code Choice and General Advice
  #19
Ben
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I have used CFDesign a bit and STAR-CCM+ a lot and would go for the later any day of the week. You mentioned support and CFDesign support can't hold a candle to CD support (although I am sure the same is true with any of the "big three"). From my experience CFDesign was a bit more "here's the software, see you next year at renewal" where as CD take a bit more interest in what you are doing and are far more helpful when it comes to more general CFD questions (which you will invariably will have if you are a CFD novice".

The glass ceiling you mentioned is also true, one thing that annoyed the hell out of me with CFDesign was the fact that you had no idea of what your mesh would be like until you built it and it was limited to purely tets, you also have a lot less control over the structure of the mesh. It was all very much one click CFD and I am not a fan of that. CCM+ gives you a lot more control over what you are doing and more options to control the simulation, CFDesign is "one click, here you go" type CFD, which I am sure is ok for some but limits your options fairly substantially, especially if you want to push your capabilities on further.

I guess you have to balance the financial with the capabilities and ease of use, but salesmen are always flexible and I am sure that if the guy from CD wants your business he will bend a bit! List prices tend not to mean anything other than a starting point for negotiation.

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Old   April 25, 2007, 08:29
Default Re: CFD Code Choice and General Advice
  #20
Ron Godwin
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Not sure which country you are in but I have found the support for cfdesign to be really good. Which version of cfdesign have you used? You can see the node points of the mesh and increase/decrease these points really easily in the latest version. It also gives you an element count early on......You can then adjust any of the solver settings by opening the intelligent solution control window, if you think you have to. Ron
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