# LES

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 July 4, 2008, 09:08 y is initialized to GREAT as a #121 Senior Member   Maka Mohu Join Date: Mar 2009 Posts: 305 Rep Power: 11 y is initialized to GREAT as a result above the cutOff the expression reduces to: min(geometricDelta_(), GREAT) This is according to the following comment: Description Holds information (coordinate and yStar) regarding nearest wall point. Used in VanDriest wall damping where the interest is in y+ but only needs to be calculated upto e.g. y+ < 200. In all other cells/faces (since y gets initialized to GREAT and yStar to 1) the damping function becomes 1 Best regards, Maka.

 July 4, 2008, 09:13 Hi, I'm running LES with th #122 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Hi, I'm running LES with the oodles solver and the Spalart-Allmaras formulation for the LESmodel. I would like to know which LES delta to use in order to have delta=max(deltaX,deltaY,deltaZ). I think it is more appropriate for DES calculation but correct me if I'm wrong. Also, I'm using the backward scheme for time derivative and I went through some problems with convergence. The backward scheme is unconditionally stable but my calculation fails after a certain time. The cause is still unknown but I wonder if I could use a better scheme for the time derivative. Thanks for your help, Philippe

 July 7, 2008, 09:49 Good morning, I used a RANS s #123 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Good morning, I used a RANS solution to initialize my DES calculation and it solved the convergence problem. Still, I would like to know how to set delta=max(deltaX,deltaY,deltaZ) instead of using cubeRootVol. It would be much appreciated if anyone could give me this quick information. Regards, Philippe

 July 7, 2008, 09:57 There is no way, short of impl #124 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 14 There is no way, short of implementing it yourself. We never added this option for several reasons: 1. There is no unambiguous way to define deltaX,Y,Z on an unstructured mesh (or at least no easy way). 2. Tests on plane diffusers showed better behaviour using cuberoot of the volume. Admittedly these internal flow test cases were not ideal. 3. There is not that much difference in the value of delta except that the cuberoot method provides a smooth transition while the max method is discontinuous.

 July 7, 2008, 10:47 Hello, I hope this is an appr #125 Senior Member   Kārlis Repsons Join Date: Mar 2009 Location: Latvia Posts: 111 Rep Power: 10 Hello, I hope this is an appropriate place to ask about LES computational requirements - I know, that it can be very problem-specific, but what would be your estimation for learning purposes? I mean, to gain enough knowledge, to be ready for some serious solving!

 July 7, 2008, 11:38 Thank you Eugene, I referre #126 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Thank you Eugene, I referred to your thesis (4.5 Errors and Mesh Refinement) and the smoothed delta indeed makes more sense. I will investigate the smooth option for the LES delta. Best regards, Philippe

 July 13, 2008, 04:37 hello, I was trying a LES for #127 New Member   nikhil babu madduri Join Date: Mar 2009 Posts: 17 Rep Power: 10 hello, I was trying a LES for a turbulent flow over a circular cylinder. I have generated the mesh required but I am facing difficulty in running it for a particular set of parameters. Infact a simple cylinder case must be very easy but I dunno why I was ending up with all these following errors. I was implementing it for the case - rhoTurbFoam. Could anyone please help me out in running it successfully. And please also suggest what all parameters that I have to be ready with before running the simulation. #0 Foam::error::printStack(Foam:stream&) in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libOpenFOAM.so" #1 Foam::sigFpe::sigFpeHandler(int) in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libOpenFOAM.so" #2 Uninterpreted: [0xffffe420] #3 Foam::hThermo > > > >::calculate() in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libbasicThermophysical Models.so" #4 Foam::hThermo > > > >::hThermo(Foam::fvMesh const&) in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libbasicThermophysical Models.so" #5 Foam::basicThermo::addfvMeshConstructorToTable > > > > >::New(Foam::fvMesh const&) in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libbasicThermophysical Models.so" #6 Foam::basicThermo::New(Foam::fvMesh const&) in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/lib/linuxGccDPOpt/libbasicThermophysical Models.so" #7 main in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/applications/bin/linuxGccDPOpt/rhoTurbFo am" #8 __libc_start_main in "/lib/i686/libc.so.6" #9 Foam::regIOobject::readIfModified() in "/home/caelinux/OpenFOAM/OpenFOAM-1.4.1/applications/bin/linuxGccDPOpt/rhoTurbFo am" replies will be highly appreciated. thanq --Nikhil.

 July 28, 2008, 10:08 > Could anyone please help me #128 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 > Could anyone please help me out in running it successfully. And please also suggest what all parameters that I have to be ready with before running the simulation. rhoTurbFoam for LES? hi Nikhil, I think it would be a good habit for you to post questions in a more detailed way, such as you set-up, case discreption, etc. Regards, Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 3, 2008, 23:31 A nice day to you all! Could #129 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 A nice day to you all! Could someone write a manual of LES? I am having a hard time with LESProperties now. That would be very nice for the new Foamer. I have question concerning wall Function of LES in OpenFOAM. 1. Does LES in OpenFOAM use wall function? For I can't see any references of class nuSgswallFunctionFVpatchscalarField except in these two files, namely: nuSgswallFunctionFVpatchscalarField.H nuSgswallFunctionFVpatchscalarField.C Regards, Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 3, 2008, 23:38 Another question concerning ne #130 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Another question concerning new models of LES, The 1st one is You, D. and Moin, P. (2007), "A dynamic global-coefficient subgrid-scale eddy-viscosity model for large-eddy simulation in complex geometries", Physics of Fluids. The other is WALES. So, could any one shine some lights on how to implement them in OF. Is it possible? Is it easy? Thanks a lot! Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 3, 2008, 23:49 Dear developers: On the dev #131 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Dear developers: On the development of LES in OpenFOAM, what are your main concerns now? New LES models or wall treatment, or whatelse? What is the strength and weakness of LES in OF comparing with Fluent? Could you give me a little comments. Thank you. I am sorry for so many questions. Oh, this page is too long, why not divide it? Best Regards, Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 4, 2008, 02:04 Hi, Wei As far as I know, F #132 New Member   Guanghao Wu Join Date: Mar 2009 Location: Tokyo, Japan Posts: 15 Rep Power: 10 Hi, Wei As far as I know, Foam does not use wall functions in the LES models. You may use smaller mesh size near the boundary or use dynamic LES models. It is not so difficult to add a new LES model to OF. If you familiar with FOAM, you probably need 2-4 weeks(?) to do that. You may refer to other existing dynamic LES models like dynSmagorinsky. Anyway, reading LESModel, LESdelta and LESfilter in detail is necessary to implement a new dynamic LES model.

 September 4, 2008, 03:00 Hi Daniel and Guanghao, Abo #133 Senior Member   Cedric DUPRAT Join Date: Mar 2009 Location: Belgium Posts: 187 Rep Power: 10 Hi Daniel and Guanghao, About wall model, there are lots of way to check if there is or not wall model in OF for LES: 1- shearch for "wall model LES" and you will find in this thread discussion between Eugene de Villier and Rolando Maier about this question. 2- have a look on the only LES pH'D thesis on OpenFOAM (Eugene de Villier's one) and you will find all the details and more. "What is the strength and weakness of LES in OF comparing with Fluent?" Quite easy, if you whant to implement your own SGS model in LES or your own wall model, it's easier about LES SGS model, the main reference is Fureby C.et al. Phys. Fluids, Vol. 6, No. 11, 1997 "Differential subgrid stress models in LES" hope it helps, Cedric

 September 4, 2008, 03:30 Thank you, 吴老师, your inf #134 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Thank you, 吴老师, your information is very helpful! Regards, Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 4, 2008, 03:37 Hello Cedric, Thanks for shari #135 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Hello Cedric, Thanks for sharing and help! Much appreciated. Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 September 4, 2008, 08:52 Hi Daniel, I might add that #136 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Hi Daniel, I might add that a concern for LES is the calculation of delta. Indeed, nuSgs being related to the grid size, the method for the calculation of delta can have great influence. It becomes a big concern if you want to use a DES approach because delta triggers the transition between the RANS and the LES. In any way, you will also find information on this regard in Eugene de Villier's thesis. Best, Philippe

September 5, 2008, 22:36
Dear foamers, I have difficul
#137
Senior Member

Daniel WEI (老魏)
Join Date: Mar 2009
Location: Beijing, China
Posts: 689
Blog Entries: 9
Rep Power: 14
Dear foamers,
I have difficulties in initialize the field?
My ultimate question is how to set k and nuSgs field?
What principles shall I respect and observe?

For my test case is flow past a square cylinder, the b.c. are
1) Symmetry conditions at the lateral boundaries
2) Free slip boundary conditions were used on the top and bottom domain boundaries.
3) Convective boundary conditions at the downstream boundary. With the help of Takuya.*
4) No-slip boundary conditions at the cylinder surface.
5) Inflow velocity is set to uniform so that Re=22000;
6) Outlet p is set as fixedValue zero.

It seems no big trouble for me to set U & p field, but what about the k & nuSgs?
I have read the UG, and see how in turbFoam's cavity case to set k field, but I still have no good idea.

I remember Eugene said
Quote:
 p=0 and small k is fine. nuSgs doesn't matter because it is calculated from k and delta.
So, are the following setting okay?
<pre>*******************initial k*********************************start
internalField uniform 0;
boundaryField
{
cylinder
{
value uniform 0;
}
lateral1
{
type symmetryPlane;
}
lateral2
{
type symmetryPlane;
}
inlet
{
type fixedValue;
value uniform 2e-05; //zero or zeroGradient or a small value??
}
outlet
{
type inletOutlet; //zeroGradient or what..?? Why inletOutlet is preferred?
inletValue uniform 0; //If inletOutlet, then how to set these 2 value properly?
value uniform 0;
}
slip
{
type slip;
}
}

*******************initial k***********************************end

*******************initial nuSgs*****************************start
internalField uniform 0;
boundaryField
{
cylinder
{
}
lateral1
{
type symmetryPlane;
}
lateral2
{
type symmetryPlane;
}
inlet
{
}
outlet
{
}
slip
{
type slip;
}
}

*******************initial nuSgs*******************************end
</pre>

Daniel
__________________
~
Daniel WEI
-------------
Boeing Research & Technology - China
Beijing, China
Email

 September 8, 2008, 08:16 Its generally not a good idea #138 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 14 Its generally not a good idea to set k to zero. Rather use something like 1e-10. Unless your walls are well resolved, you should put nuSgsWallFunction on the nuSgs BCs for walls. InletOutlet, is a zeroGradient boundary when the flow is outward and a fixed value boundary when the flow is coming in. The inlet value is the level in case of inflow. solefire and songwukong like this.

 September 9, 2008, 13:45 Hi foamers, @ Eugene, what #139 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Hi foamers, @ Eugene, what would be the correct yPlus values at walls when using nuSgsWallFunction? Thanks, Philippe

 September 9, 2008, 16:23 Somewhere between 0 and 300. A #140 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 14 Somewhere between 0 and 300. Although if it is larger than about 10 you will be doing some kind of DES.

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