
[Sponsors] 
June 21, 2010, 11:08 
second order schemes

#1 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
Hello everybody !
I'm running a simulation of flow around a ship with a komega SST turbulent model. I have an inlet, an outlet, four symmetry planes and a hull. I did the simulation with first order schemes for divergence, linear schemes for gradschemes and interpolation schemes, linearCorrected for laplacian and corrected for snGradSchemes. It worked and I obtained coherent results for the velocity, pressure, and forces on the hull. I'd like now to run it with second order schemes but I really don't know which one to choose because I tried some of them (linearUpwind, linearLimited, skewCorrected linear) on a previous simulation with an other hull and no one worked. Do you have some advice? is there a advisable second order scheme for this type of simulation? Is there an other scheme (grad, interpolation) I must change? thanks a lot for any advice ! Marine 

June 21, 2010, 21:31 

#2 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 34 
Why didn't they work? Could you post your fvScheme?
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

June 22, 2010, 01:15 
second order schemes

#3 
Senior Member
NAVEEN.K.M
Join Date: Mar 2009
Location: Bangalore, Karnataka, india
Posts: 114
Rep Power: 15 
hi marine,
Try leastsquares or liner which are second order schemes.If you use leastsquares you wil get da best results. Regards Naveen Bangalore 

July 6, 2010, 09:52 

#4 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
I tried linearUpwind then limitedLinear for the divergence terms, both time with limited 0.333 for laplacian and sngradschemes, and both worked. The problem was apparently the corrected shemes for laplacian and snGradschemes.
The linear scheme for divergence terms still doesn't work (pressure residuals decrease and continuity explode). My question now is do you know which one between linearUpwind and limitedLinear is the best for 2nd order accuracy? I attached the fvSchemes. thank you very much. Marine 

July 6, 2010, 09:54 

#5 
Member

Dear Marine,
Seems that Upwind implies 1st order. Default 2nd order scheme is Linear. 

July 6, 2010, 10:01 

#6 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
linearUpwind is a blend of first and second order, I would like to know if it can be more accuracy than limitedLinear because I don't find a lot of documentation about limitedLinear and I don't know how it works.
Linear schemes don't work with my simulation. Thanks ! Marine 

July 6, 2010, 10:04 

#7 
Member

Would you mind describing your case: Mach, boundary conditions.
Which solver do you use? 

July 6, 2010, 10:13 

#8 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
I'm running a simulation of incompressible flow around a ship with a komega SST turbulent model. The solver is simpleFoam.
I have an inlet, an outlet, four symmetry planes (it's a "double model" simulation, I don't know the english term) and a hull. The solver for pressure is GAMG, for U and turbulence PBICG. at the inlet : u,k,omega=fixedvalue p=zeroGradient at the outlet : u=zeroGradient p=fixedvalue k and omega=inletOutlet thank you Marine 

July 6, 2010, 10:17 
Try underrelaxation

#9 
Member

One possibility is to come back to "Gauss linear" for every div(x,y) scheme and try underrelaxing the solution for a few steps before increasing the U/R factors.


July 6, 2010, 11:14 

#10 
Member
Francois Gallard
Join Date: Mar 2010
Location: Edinburgh
Posts: 39
Rep Power: 14 
Hi,
And the problem can come from the mesh too, because higher order schemes are less dissipative and can require higher quality meshes. Can you post a screen shot of a cut of your mesh please ? Cheers, Francois. 

July 7, 2010, 03:50 

#11 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
I already tried to underrelax the solution, it just postponed the divergence of the solution.
I attached three pictures of my mesh (it's a mesh with polyhedrons so the cut with paraview isn't nice ). Regards, Marine Last edited by marine; July 7, 2010 at 04:30. 

July 7, 2010, 04:42 

#12 
Member

Hum... I think I misunderstood. Have you already succeed in having a converged solution? For me, you succeeded, with 1st order schemes. Am I right ?


July 7, 2010, 06:40 

#13 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
Yes it worked with first order schemes and with limitedLinear 1 schemes but when I switch to linear schemes it doesn't work anymore.


July 7, 2010, 07:03 

#14 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 34 
Check your local (cell) Peclet number. The linear scheme requires it to be less than 2 (see Ferziger and Peric for a reference).
In your application you might want to use limitedLinear or linearUpwind anyway, which ensure the boundness of the solution. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

July 8, 2010, 07:09 

#15 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
OK that explain why the linear scheme doesn't work, my Peclet number is too big.
I don't obtain the same results for the viscous forces on my hull with the linearUpwind scheme or the limitedLinear scheme (15% difference) . As they say in the book (Peric) that linearUpwind is unbounded I think is more accurate than limitedLinear ( I still don't know how this one works) and is comparable to the second order upwinded scheme we can find in Starccm+ or Fluent. Do you think I'm wrong? regards, Marine 

July 8, 2010, 08:07 

#16  
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 34 
Quote:
both limitedLinear and linearUpwind are bounded. What is different is how the boundness of the scheme is obtained (see table 4.10 of User's guide).
I believe the second order upwind scheme in commercial codes is close to linearUpwind than to limitedLinear, probably with limiters turned on. Something along the lines of div(phi, U) Gauss linearUpwindV cellMDLimited Gauss linear 1; (notice linearUpwindV becomes linearUpwind for scalars) which limits also the gradients. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

July 8, 2010, 09:30 

#17 
Member
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 14 
Thanks Alberto you helped me a lot !


October 19, 2010, 11:27 

#18  
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 368
Rep Power: 19 
Quote:
I really need some advices about the convection schemes choice for an external aerodynamics case (hybrid prismstetrahedrons unstructured mesh)... For all the details about the case and my previous numerical trials you can have a look at this post: http://www.cfdonline.com/Forums/ope...redgrids.html Apart from this, I would also like to know something more about the linearUpwind scheme: I've understood that this is a bounded "more than first order" upwinded scheme, but indeed in Ferziger and Peric's book it's mentioned like an unbounded scheme, so maybe you can adress me to some references about the limited implementation of such a scheme... Thank you in advance V. 

October 19, 2010, 12:08 

#19 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 34 
I have a few comments on what you posted.
 First your case barely converges also with upwind (residuals of the pressure are the highest (yellow line)). Reduce the tolerances on the linear solvers to something closer to your machine precision (10^12 for p, 10^10 for the rest: yes it will take more iterations, it does not matter).  Relax the turbulent quantities more than the velocity. Typically an URF = 0.4 works well.  As schemes, linearUpwindV for div(phi, U) and linearUpwind for the rest, with cellLimited modifier for gradients should work just fine.  Your mesh does not suffer of strong nonorthogonality, so I would not push the correctors too much (surely not to 8!).  Stay away from SFCD, QUICK, UMIST. They won't give you any significant advantage. All the love for QUICK comes from the fact that it is formally thirdorder accurate, but its dissipation error is still high, and its stability is not good. I hope this helps. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

October 19, 2010, 12:57 

#20  
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 368
Rep Power: 19 
Quote:
div(phi, U) Gauss linearUpwindV cellMDLimited Gauss linear 1; div(phi, k) Gauss linearUpwindV cellMDLimited Gauss linear 1; div(phi, epsilon) Gauss linearUpwindV cellMDLimited Gauss linear 1; am I right? Apart from this, I'll try to follow your advices and then I'll let you know what happens. Thank you once again Regards V. PSI'm sorry if I'm repetitive, but I'll be very glad if you can direct me to some more informations about the theoretical basis of the linearUpwind scheme in its bounded formulation 

Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
4th order schemes in channelOodles  maka  OpenFOAM Bugs  9  January 19, 2009 12:58 
Help for fourth order accurate convective schemes  Z.C.Wang  Main CFD Forum  0  January 15, 2009 07:53 
2nd order conservative schemes  taw  Main CFD Forum  1  September 16, 2008 08:05 
CFL condition for higher order schemes  Shyam  Main CFD Forum  2  February 14, 2008 15:24 
High order compact finite difference schemes  Mikhail  Main CFD Forum  6  August 5, 2003 11:36 