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July 30, 2010, 10:39 
4th order central scheme

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Hi,
I was wondering if there are any fourth order centeral differencng schemes in OpenFOAM. Sincerely, Maani 

July 31, 2010, 07:24 
4th order central scheme

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ata kamyabi
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Hi Mani
How are you? I think there is not. Good luck Best regards Ata 

July 31, 2010, 07:41 

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Hi dear Ata,
Thanks for the reply. I appreciate your time. If there are not, then what about the "Cubic" Scheme? In page U112 it says "Fourth order, unbounded". Also I wanted to know if linear is second order or 1st order. Again at U112. I am running LES simulations and I need higher order centraldifferencing schemes (upwind/TVD/NVD are too dissipative) for div, grad and laplacian terms. Bests Maani 

August 1, 2010, 01:41 

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I have a serious problem!
Does anybody know what are the best highorder discretization schemes for LES? I know that QUICK is too dissipative! Sincerely, Mani Mahdinia 

August 1, 2010, 02:37 
4th order central scheme

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ata kamyabi
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Hi Mani
Are you sure in U112? There is fourth order scheme for surface normal gradient, are you mean it? Best regards Ata 

August 1, 2010, 03:27 
Upages

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Hi,
Yes. But I meant: OF 1.5 User guide p 112 which is equal to: OF 1.6 User guide p 116 which is equal to: OF 1.7 User guide p 116. Here it says: linear = second order, unbounded cubicCorrected=fourth order unbounded Sincerely, Maani 

August 1, 2010, 08:11 
I have 1.6

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ata kamyabi
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Hi
Excuse me I have 1.6 Best regards Ata 

August 1, 2010, 08:53 
My mistake

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Hi ata,
I know it was my mistake. Sorry. Do you think they are 2nd and 4th order for all the terms like grad/div/lap? Sincerely, Maani 

August 1, 2010, 09:10 
4th order central scheme

#9 
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ata kamyabi
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Hi Mani
Your welcome, no problem. It seems replying via forum is not fast and very easy for me. Are you at Sharif University of Technology in Department of Mechanical Engineering? If it is true or you are at Tehran we can have easier conversation. You can send an Email to me and I'll send you my phone number. However I think that it is fourth order only for normal gradient at faces. Best regards Good luck Ata 

August 1, 2010, 13:50 

#10 
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Alberto Passalacqua
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Hello,
cubic and cubicCorrected are fourth order central schemes. For gradients, there is the "fourth" scheme. Best,
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August 1, 2010, 14:12 

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Thanks alberto,
I have a question. Is it odd that I get better results with the QUICK scheme (which as you know, is too dissipative) than the cubic Scheme in LES? I have to mention that my grid is relatively, coarse. Sincerely, Maani 

August 1, 2010, 14:43 

#12  
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Alberto Passalacqua
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Quote:
 What do you mean with "better results"? Your results compare better with experiments, or there are unphysical results with cubic?  Is your grid satisfying the stability criterion for central schemes? A suggestion: A finite volume scheme is second order whatever you do, so I would suggest you to use "linear" for convection, and leastSquares for gradients. They usually work fine. Best,
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Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

August 1, 2010, 15:02 
The problem

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Dear Alberto,
Regarding your first inquiry: I am simulating a release of a higher density fluid (saltwater mixture) underneath a lower density ambient fluid (water). I am also solving the concentration equation along with NS. I use the dynamic Smagorinsky method is used for the simulation. The runs are in 3D. Here are two animations: http://mech.sharif.edu/~mahdinia/A1.htm http://mech.sharif.edu/~mahdinia/A2.htm I tried these: 1) Linear schemes for div/grad/lap/interpolation: The 3D instabilities at the interface of the two fluids are not created as they are supposed to. 2) Cubic schemes for div/grad/lap/interpolation: The 3D instabilities at the interface of the two fluids are created along with unphysical waves. 3) QUICK schemes for div/lap and Cubic for grad/interpolation: The 3D instabilities are created as they should be created physically, in the horizontal and spanwise directions. I can put some 3D pictures if required. I am not sure why the QUICK scheme gives the best results. Regarding your second inquiry: I don't know about the stability criterion for central schemes. But the the location of interest is in the middle of the domain and the grid there is nearly fine enough. Is the QUICK scheme always not appropriate for LES or it may be used for some of the flows in nature? Sincerely, Maani 

August 1, 2010, 15:53 

#14  
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Alberto Passalacqua
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Quote:
I would suggest an experiment to understand what is going on there, since you tried different combination of schemes.
About QUICK, it has been quite widely used in the literature for LES (they essentially use a bounded version called BQUICK). I would try to avoid upwinded schemes in LES, especially if you are interested in capturing details. Best,
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Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

August 1, 2010, 16:38 
Thanks

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Thanks,
I'll do the above and see if the things get right. Sincerely, Maani 

August 1, 2010, 22:48 

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Daniel WEI (老魏)
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@Maani: I am afraid that in many occasions, the comparison conclusion based on coarse grid simulations would be quite misleading.
I find a hard time to see how higher order (I mean higher than second) works for finite volume method. Since FV need estimation of a variety of items, so I think it would be pretty hard to get a order higher than 2nd. I am thinking is it possible to build finite difference scheme in openfoam framework, any ideas?
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August 1, 2010, 22:56 

#17  
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Alberto Passalacqua
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Quote:
Quote:
Best,
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Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

August 1, 2010, 23:07 

#18 
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Daniel WEI (老魏)
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Hey, what! I feel I left behind in life. Any Good papers on that? Could you share some links? And why you think it's not easy to implement them?
You know it would be great that openfoam could continue serving as not just for FV but for a many CFD C++ class Basis. For example: For finite volume, we build dir ./src/finiteVolume For finite area, we build dir ./src/finiteArea (as in extend fork) For discontinuous Galerkin methods, we build dir ./src/discontinuousGalerin ....
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August 1, 2010, 23:11 

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*****************
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~ Daniel WEI  Boeing Research & Technology  China Beijing, China Last edited by lakeat; August 2, 2010 at 14:04. 

August 1, 2010, 23:23 

#20  
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Daniel WEI (老魏)
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Quote:
Concerning the Schemes, I am also very interested. I guess the openfoam team must have done a lot of works on testing the different schemes. So, 1. You mean Code:
gradSchemes { default leastSquares; grad(p) leastSquares; grad(U) leastSquares; } 2. Will "boundedBackward" be better than backward ddt? I know there is not formal documentation on these schemes items for openfoam, but do you any information on where we can find papers showing the foamtechniques progress in detail other than (http://powerlab.fsb.hr/ped/kturbo/OpenFOAM/)? Thanks and good night!
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