CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Starcd vs openfoam

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   June 8, 2006, 10:46
Default hello, i have computed a si
  #1
New Member
 
Michael R.
Join Date: Mar 2009
Posts: 12
Rep Power: 8
michael is on a distinguished road
hello,

i have computed a simple model, which is called elbow in the star tutorial guide, with star-cd. Then i have converted the model to openfoam and tried to transfer the settings manually. I've normalized the results from foam with the pressure (multiplied with the pressure).

In the results there is a pressure difference between starcd and foam about 10 percent or more. The settings:

OpenFOAM:
Turbulenz model: Standard k - epsilon
Difference Scheme: upwind
Solver: simplefoam
pressureOutlet, 0 Pa

STAR:
air, density 1.205
Turbulenz model: k epsilon high reynolds number
Difference Scheme: UD
double precision
pressure outlet, 0 Pa

Then i've switched the solver to laminar, because of the influence of the turbulence model, but afterwards the difference is higher. Why is there such a big difference?
michael is offline   Reply With Quote

Old   June 8, 2006, 14:15
Default And you also normalized the vi
  #2
Assistant Moderator
 
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
Rep Power: 40
gschaider will become famous soon enoughgschaider will become famous soon enough
And you also normalized the viscosity? That's what I usually forget to do when I compare with the commercial solver we have here.
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request
gschaider is offline   Reply With Quote

Old   June 9, 2006, 03:05
Default yes, in star molecular viscosi
  #3
New Member
 
Michael R.
Join Date: Mar 2009
Posts: 12
Rep Power: 8
michael is on a distinguished road
yes, in star molecular viscosity and in foam the dynamic viscosity (mu/rho). what have been your results?
michael is offline   Reply With Quote

Old   June 9, 2006, 05:20
Default OK. Sorry for asking. My r
  #4
Assistant Moderator
 
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
Rep Power: 40
gschaider will become famous soon enoughgschaider will become famous soon enough
OK. Sorry for asking.

My results (for a more complicated "real life" geometry) with the commercial solver starting with an F using k-eps/inkompressible (==simpleFoam) showed 2.5% difference for the pressure drop (mass flows at selected control surfaces were in the order of 0% to 6%)
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request
gschaider is offline   Reply With Quote

Old   June 9, 2006, 06:41
Default thanks for your replies. my
  #5
New Member
 
Michael R.
Join Date: Mar 2009
Posts: 12
Rep Power: 8
michael is on a distinguished road
thanks for your replies.

my results are:

k - epsilon model:
1584 cells : 3.58 % difference
12672 cells: 1.89 % difference

1.89 % pressure loss is acceptable, but there is also a higher difference between inlet and outlet.

laminar:
1584 cells : 8.23 % difference
12672 cells: 6.68 % difference

8.23 % is very high

What commercial solver you've used? Are your results acceptable for a "real life" geometry? Perhaps there is some difference in the differencing schemes. What are your settings in both codes?

thanks!
michael is offline   Reply With Quote

Old   June 9, 2006, 10:02
Default "commercial solver starting wi
  #6
Assistant Moderator
 
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
Rep Power: 40
gschaider will become famous soon enoughgschaider will become famous soon enough
"commercial solver starting with an F": Fluent

TBH I don't know which discretization schemes. (It was a quick shot with the defaults of both solvers)

I was quite satisfied with the 2.5% (although it leaves room for improvement). It was in the range of what the partner could supply us data with. You can get bigger differences if you change the convergence criteria on the same solver.
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request
gschaider is offline   Reply With Quote

Old   June 30, 2006, 00:53
Default Hi to both, do you have so
  #7
Senior Member
 
Fabian Braennstroem
Join Date: Mar 2009
Posts: 407
Rep Power: 10
braennstroem is on a distinguished road
Hi to both,

do you have some more information about your 'benchmarks'. It would be
interesting to know the costs for each simulation using OpenFoam
compared to StarCD and Fluent!?
Are there any other comparisons between OpenFoam and other packages out
there?

Greetings!
Fabian
braennstroem is offline   Reply With Quote

Old   April 1, 2007, 21:57
Default Hello, I am very interested
  #8
New Member
 
Mark J.
Join Date: Mar 2009
Posts: 15
Rep Power: 8
vtk_fan is on a distinguished road
Hello,

I am very interested in this question as well. I am consulting for a major company here, and am wondering if the performance of OpenFOAM vs. Fluent would be comparable. For example, for an average external aerodynamic simulation, 3D, k-e, 1 million cells, hex-dominant grid, what would be the approximate time taken per iteration by OpenFOAM vs. Fluent? Also, would OpenFOAM take longer to converge, so that the total cost can be ascertained?

Even if OpenFOAM is free, the cost of a Fluent License (~20,000 US$) might be worth it if, let's say, it is 3-4 times faster than OpenFOAM at solving the above simulation. For time-bound projects, this is an important consideration. Any responses would be much appreciated.
vtk_fan is offline   Reply With Quote

Old   April 2, 2007, 04:42
Default From my experience, for an inc
  #9
Senior Member
 
Francesco Del Citto
Join Date: Mar 2009
Location: Zürich Area, Switzerland
Posts: 215
Rep Power: 9
fra76 is on a distinguished road
From my experience, for an incompressible, turbulent external flow simulation, each fluent iteration is faster than an OpenFOAM one, but OF requires less iteration to converge.
The overall time is shorter for OF. Please, notice that I run my test case in parallel on a case bigger than 1 million cells, and OF scales really very well, over a fast network.
However, setting up an OF case requires more experience for some numerical settings that can speed up or completly fail your simulation.
So, as always, it's not an easy decision!
fra76 is offline   Reply With Quote

Old   April 2, 2007, 21:11
Default Is there a place where I can g
  #10
New Member
 
Mark J.
Join Date: Mar 2009
Posts: 15
Rep Power: 8
vtk_fan is on a distinguished road
Is there a place where I can get a roadmap on OpenFOAM development plans? I am also interested in dynamic mesh motion (rigid body only) for aerospace applications. The range of motion can be quite large, a turn through 60 degrees for flap movement. Has anyone done any benchmark comparisons on this kind of problem anywhere with OpenFOAM and Fluent 6.3's dynamic mesh capability?

I had a huge bunch of trouble with Fluent 6.1's dynamic mesh capability because it was very buggy and limited to rectilinear motion of the moving boundary.
vtk_fan is offline   Reply With Quote

Old   April 2, 2007, 21:13
Default By the way, thanks Francesco f
  #11
New Member
 
Mark J.
Join Date: Mar 2009
Posts: 15
Rep Power: 8
vtk_fan is on a distinguished road
By the way, thanks Francesco for your information. Can you please provide some actual numbers and a more detailed description of your case? Many thanks.
vtk_fan is offline   Reply With Quote

Old   April 2, 2007, 23:15
Default You seem to be asking for very
  #12
Senior Member
 
Hrvoje Jasak
Join Date: Mar 2009
Location: London, England
Posts: 1,758
Rep Power: 21
hjasak will become famous soon enough
You seem to be asking for very specific performance numbers for cases of your interest - why don't you just run the test yourself and report the result?

Hrv
__________________
Hrvoje Jasak
Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk
hjasak is offline   Reply With Quote

Old   April 3, 2007, 06:53
Default I cannot add more details on m
  #13
Senior Member
 
Francesco Del Citto
Join Date: Mar 2009
Location: Zürich Area, Switzerland
Posts: 215
Rep Power: 9
fra76 is on a distinguished road
I cannot add more details on my tests, I'm sorry...
You can find some more hint here: http://www.cfd-online.com/OpenFOAM_D...es/1/3503.html
I've no experience with OF mesh movement, unfortunatly. However Fluent 6.3 should be much better of 6.1 on this side. Actually, it works quite well, but forget about hexcore meshing for that range of movement!
fra76 is offline   Reply With Quote

Old   April 3, 2007, 20:57
Default >By Hrvoje Jasak on Monday, Ap
  #14
New Member
 
Mark J.
Join Date: Mar 2009
Posts: 15
Rep Power: 8
vtk_fan is on a distinguished road
>By Hrvoje Jasak on Monday, April 02, 2007 - 09:15 >pm: Edit Post

>You seem to be asking for very specific performance >numbers for cases of your interest - why don't you >just run the test yourself and report the result?

>Hrv

I plan to run a reduced size test case (200,000 cells) this weekend, and will report the results. My Fluent license expired last year, and I will not be able to do a one-to-one comparison.

Please do not get me wrong. I think OpenFOAM is a great alternative, and since it is open-source, long term it has very bright prospects of being more widely used than Fluent after another few years. These questions are a reflection of the interest in the software.
vtk_fan is offline   Reply With Quote

Old   April 4, 2007, 01:24
Default Hi Mark, I can offer to run
  #15
Senior Member
 
Jens Klostermann
Join Date: Mar 2009
Posts: 117
Rep Power: 8
jens_klostermann is on a distinguished road
Hi Mark,

I can offer to run your testcase with Fluent, if you are willing to share the case (OpenFOAM case, incl. setup).

Jens
jens_klostermann is offline   Reply With Quote

Old   April 4, 2007, 21:49
Default Thanks Jens, I will definitely
  #16
New Member
 
Mark J.
Join Date: Mar 2009
Posts: 15
Rep Power: 8
vtk_fan is on a distinguished road
Thanks Jens, I will definitely take you up on your offer early next week.
vtk_fan is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
OpenFoam vs CFX5 mass balance in OpenFoam tangd OpenFOAM Running, Solving & CFD 33 May 23, 2010 16:36
CheckMesh error using a tutorial from OpenFOAM 114 with openFOAM 13 martapajon OpenFOAM Native Meshers: blockMesh 7 January 21, 2008 13:52
OpenFOAM users in Munich OpenFOAM benutzer in M%c3%bcnchen jaswi OpenFOAM 0 August 3, 2007 13:11
A new Howto on the OpenFOAM Wiki Compiling OpenFOAM under Unix mbeaudoin OpenFOAM Installation 2 April 28, 2006 08:54
Convert from StarCD 3.10 to StarCD 3.15 Jing CD-adapco 1 April 17, 2002 09:22


All times are GMT -4. The time now is 05:23.