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Old   December 4, 2002, 06:31
Default Former Fluent Users
  #1
Jan Rusås
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Dear CFX users,

I am considering changing to Fluent, but I really would like to get in contact with current CFX users that have used Fluent and discuss the differences or to get in contact with users of both programs. Please reply any comments by email. Thanks in advance Jan
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Old   December 4, 2002, 09:03
Default Re: Former Fluent Users
  #2
Bob
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Hi Jan, why are you considering the change ? if you dont mind me asking ? bob
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Old   December 4, 2002, 13:37
Default Re: Former Fluent Users
  #3
Holidays
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What are your applications? Dynamics, multiphase, combustion?

I believe the fully coupled solver to be quite competitive and the code openness to be an asset especially when dealing with complex physics and (stiff) chemistry as in multiphase and combustion or aqueous reactions for example.
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Old   December 5, 2002, 06:53
Default Re: Former Fluent Users
  #4
Sam Z
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Hi

Im a former Fluent user and about 6 months ago moved to CFX. I found it quite easy to move between the two, just some jargon that changes really.

The only thing I have to say is that in Fluent it is alot easier to make hybrid meshes, in CFX it is not intuitive at all, apparently that will change in CFX5.6

Also in Fluent there are only 2 modules, a pre processor and a combined solver and post processor. Not 3 (or 4 with the imminent Pre) like CFX. I think you will miss Post tho' thats an excellent visualisation tool. In Fluent for more complex visualisations the data has to be exported to Tecplot or the like.

Solver wise quite similar, more turbulence options in CFX with the k omega hybrid wall advantage not found in Fluent models. All the usual features are found. We recently compared the Eddy Dissipation Combustion model with CFX 5.5, CFX 4.4 and Fluent 5.4 on a simple coaxial burner configuration and got fairly comparable results.

Hope this helps
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Old   December 5, 2002, 07:59
Default Re: Former Fluent Users
  #5
Astrid
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Hi Jan,

Why do you want to switch? Do you still see no shedding......?

I have no experience with Fluent, but I suggest you to post a message in the Fluent forum too. Perhaps you will get more responses.

Astrid
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Old   December 6, 2002, 07:02
Default Re: Former Fluent Users
  #6
Jan Rusås
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Hi Bob, The answer could be; 1)Because I can 2)Why not

I am basically not unsatisfied with CFX, but it could also be interesting to see the capabilities of Fluent. It would be an ideal situation to be able to shift from year to year depending on which package that is must suited for your needs and at what cost. Regards Jan

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Old   December 6, 2002, 07:05
Default Re: Former Fluent Users
  #7
Jan Rusås
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Dear "Holidays" I know those phrases, and I do know my needs and the limitations in Fluent and CFX for solving my specific applications. Don't you think that CFX and Fluent are comparable as solvers? Jan
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Old   December 6, 2002, 07:09
Default Re: Former Fluent Users
  #8
Jan Rusås
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Hi Sam, Thanks for your input, I do think they was very valuable. Did you in anyway compare the speed for obtaining a solution for the different packages. Regards Jan p.s. hvad er .topse. ))
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Old   December 6, 2002, 08:33
Default Re: Former Fluent Users
  #9
Bob
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CFX has an implicit coupled solver, which makes it really efficient in say multiphase and chemistry problems where strong coupling is required for example; Fluent does not (it is explicit at the most?).

Can i ask again what didn't you managed to achieve with CFX more specifically (I guess I could search the site for your name maybe..

thanks, Bobby
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Old   December 6, 2002, 09:04
Default Re: Former Fluent Users
  #10
KG
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No Bob, Fluent has implicit and explicit coupled solvers.

Regards,
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Old   December 6, 2002, 09:07
Default Re: Former Fluent Users
  #11
Jan Rusås
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Hi Bob,

I am not unsatisfied with the performance and capabilities of CFX and I do not think that Fluent can solve all problems etc... I have now used CFX as an industrial user for 6 years and have most of the time been very satisfied, but it can be healthy to check what is on the other side some times. At least you also have a better position when discussing the price of renewal of license or purchasing additional capabilities, if you are in the position that you can shift software to another company. If microsoft was not so sure on there customers I believe the price would be much lower.

I did not want to start a large discussion in this forum about Fluent v.s. CFX, only to get in contact with people that have used both packages. ))

Regards Jan

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Old   December 8, 2002, 07:14
Default Re: Former Fluent Users
  #12
mystic_cfd
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hi jan

i'm a reverse case, so i'm being naughty... i used to work with cfx (mostly 4.2) before switching to fluent. in a commercial environment, i would be careful to include the cost of a code switch when investigating.

some comments on my experience:

- the tricks and shortcuts and frustrations you sorted out in the old code, will (for 70%) have to be solved again in the new code. it took me quite a while to learn how to get the solver to do what i want - also in terms of user coding and specialized post-processing.

- fluent and cfx have much the same capabilities, and the support staff can fill the gaps.

- meshing in cfx was frustrating, until you learned the ropes. in fluent (using gambit) i still cannot build a nice unstructured mesh. i get flat tets all over the place, which I missed at first because the mesher goes like a rocket and seldom complains with horrid geometries. now i am more careful and use a lot of substructures inside the flow domain to force the mesh to my liking.

- recently i solved a 2D case with a porous blockage and specified two velocity inlets (this was not the intention and perhaps give an indication of how serious you should take my rantings) - the surprise was that all the residuals converged beautifully. i later fixed the bc's, but somewhere in the wrong 2d, porous case, the conservation of mass got lost - the thing should at least have exploded my mass residual!

long story... the short version. in my opinion fluent does not offer much over cfx in terms of capabilities. your own skill with the code is more important. unless you have external motivation e.g. cost of licensing or business partners, switching is not a good option. rather spend the money on staff training.

enough blah, may the convergence be with you
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Old   December 9, 2002, 16:25
Default Re: Former Fluent Users
  #13
Neale
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Hello Jan,

I use both so I have compared Fluent 6 vs. CFX-5.5.1 on some industrial mixer cases. The executive summary on what I've found is that CFX-5's coupled solver behaves far smoother and is ~20-30 percent faster at getting a "converged" answer.

Since both codes use different definitions of convergence I used the %mass imbalance as a gauge. So, if you compare the CPU time it takes in both codes to reduce the global mass imbalance (m-dot-in - m-dot-out)/(max(m-dot-in,m-dot-out))*100, by 3 orders of magnitude, then CFX-5 is quite a bit faster.

The other thing that is noticable is when you compare the plots of imbalance on the way down. The plot in CFX-5 is very smooth compared to the same plot in Fluent. While this does not have much bearing on the particular case I was looking at it was quite nice to see how "stable" CFX-5 seems compared to Fluent 6. On problems with difficult physics I think this translates into less headaches using CFX-5.

In practice I never use the coupled solver in Fluent because it does not work. I've never been successful with it. The segregated solver is the real workhorse I'm not slagging the coupled solver either. I think the reason it doesn't work well POST http://www.cfd-online.com:80/Forum/cfx.cgi?post HTTP/1.1 Content-Length: 1958 Content-Type: application/x-www-form-urlencoded Cookie: CFD News and Announcements
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Old   December 9, 2002, 16:51
Default Re: Former Fluent Users
  #14
Neale
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Hello Jan,

I use both so I have compared Fluent 6 vs. CFX-5.5.1 on some industrial mixer cases. The executive summary on what I've found is that CFX-5's coupled solver behaves far smoother and is ~20-30 percent faster at getting a "converged" answer.

Since both codes use different definitions of convergence I used the %mass imbalance as a gauge. So, if you compare the CPU time it takes in both codes to reduce the global mass imbalance (m-dot-in - m-dot-out)/(max(m-dot-in,m-dot-out))*100, by 3 orders of magnitude, then CFX-5 is quite a bit faster.

The other thing that is noticable is when you compare the plots of imbalance on the way down. The plot in CFX-5 is very smooth compared to the same plot in Fluent. While this does not have much bearing on the particular case I was looking at it was quite nice to see how "stable" CFX-5 seems compared to Fluent 6. On problems with difficult physics I think this translates into less headaches using CFX-5.

In practice I never use the coupled solver in Fluent because it does not work. I've never been successful with it. The segregated solver is the real workhorse I'm not slagging the coupled solver either. I think the reason it doesn't work well POST http://www.cfd-online.com:80/Forum/cfx.cgi?post HTTP/1.1 Content-Length: 1892 Content-Type: application/x-www-form-urlencoded Cookie: CFD News and Announcements
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