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[OpenFOAM-2.1.0] kklOmega RAS Turbulence Model (low Re)

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Old   January 24, 2012, 10:13
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Actually, I tried yesterday night for a few times, but got a worse curve.
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Old   January 24, 2012, 20:15
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Quote:
Originally Posted by egp View Post
Why would you guess this? The Schubauer and Klebanoff (S&K) case is a well-known experiment with very low free-stream turbulence, i.e.,

U=50.1 m/s
Tu = 0.3%
nut/nu = 1

Given these parameters, I compute kt and omega to be:

kt = 1.5*(0.003*50.1)^2 = 0.0339
omega = k/nut = 0.0339/1.5e-5 = 2259

It's interesting to note that the paper by Walters and Cokljat (2008) did not use the S&K dataset for validation and only used the ERCOFTAC T3A-, T3A, T3B benchmarks. These latter cases have a varying degree of free-stream turbulence and are typically used to demonstrate bypass transition. In contrast, the S&K with low FST is more a test of natural transition.
Hi egp, what are the differences between natural transition with bypass transition? To natural transition, the flow features are just in laminar flow but not from laminar to turbulent, right?

In addition, do you have literatures about the ERCOFTAC T3A-, T3A, T3B benchmarks and the S&K' s ? Could you sent a copy to me? I have the paper by Walters and Cokljat, however, I could not find the literature of their test cases. Thanks.

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Old   April 11, 2012, 17:24
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Hi, I'm trying to use the kklOmega turbolence model to simulate the flow around a 2d naca 0012; here my initial/boundary conditions:

domain:

k
inletOutlet (5.4e-3)
kt
inletOutlet (5.4e-3)
kl
inletOutlet (0)
nut
inletOutlet (1e-5)
nuTilda
inletOutlet (1e-5)
omega
inletOutlet (5.4e5)
p
outletInlet (0)
U
inletOutlet (0 2.9886 0.2615)

wall:
k
kqRWallFunction (0)
kt
inletOutlet (5.4e-3)
kl
fixedValue (0)
nut
nutkWallFunction (1e-5)
nuTilda
zeroGradient
omega
zeroGradient
p
zeroGradient
U
fixedValue (0 0 0)

Omega becomes negative after some iterations and the solutions doesn't seem to converge to a reasonable value.
I have also problems with the evaluation of the wallShearStress that becomes very high aft of the predicted transitional region.

I can't see where I fail.

Any suggestion is appreciated.

Thank you!!
Attached Images
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File Type: png cf.png (6.9 KB, 145 views)
File Type: jpg mesh2.jpg (96.8 KB, 169 views)
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File Type: txt fvSchemes.txt (2.2 KB, 49 views)
File Type: txt fvSolution.txt (2.8 KB, 35 views)
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Old   April 11, 2012, 17:39
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Quote:
Originally Posted by lucaBonfiglio View Post
I can't see where I fail.

Any suggestion is appreciated.

Thank you!!
The last time I used it, I used it with a VERY VERY small time step on the LRN
mesh and then everything works fine.

It seems all LRN models have convergence problem.
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Old   April 11, 2012, 18:07
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Hi Daniel,

Do you mean that I've to deal with a finer mesh?
I'm using simpleFoam so there shouldn't be time step problem, Am I wrong?

Thank you for the reply!
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Old   April 13, 2012, 21:48
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Hiya EGP, I have run a kkl-omega case and I am trying to post process the data, however I am having trouble in plotting the Cf versus (Re)x graph to find transition. I have sampled the wall shear stress to find the skin friction coefficient, but I am unsure of getting the (Re)x data from my simulation. Your help would be much appreciated!
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Old   April 23, 2012, 21:53
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Hi everyone

Sorry if this question sounds stupid, but has anyone tried or does anyone know if this model works well with wall functions? (y+ ~ 50)

also when I was trying to set up a case, I got this error when trying to run

Code:
Starting time loop

Time = 4e-06

Courant Number mean: 0.0052655 max: 0.613429
DILUPBiCG:  Solving for Ux, Initial residual = 0.999999, Final residual = 2.16698e-08, No Iterations 2
DILUPBiCG:  Solving for Uy, Initial residual = 1, Final residual = 1.38978e-08, No Iterations 2
DILUPBiCG:  Solving for Uz, Initial residual = 1, Final residual = 3.06486e-08, No Iterations 2
DICPCG:  Solving for p, Initial residual = 1, Final residual = 0.0996709, No Iterations 238
time step continuity errors : sum local = 2.92672e-07, global = -2.47733e-08, cumulative = -2.47733e-08
DICPCG:  Solving for p, Initial residual = 0.853218, Final residual = 9.43328e-07, No Iterations 496
time step continuity errors : sum local = 6.22475e-11, global = -1.59298e-13, cumulative = -2.47734e-08
DILUPBiCG:  Solving for kt, Initial residual = 1, Final residual = 6.62784e-06, No Iterations 1
DILUPBiCG:  Solving for kl, Initial residual = 1, Final residual = 1.11568e-07, No Iterations 2
bounding kl, min: 0 max: 0.029737 average: 0.0050596


--> FOAM FATAL ERROR: 

    request for volScalarField k from objectRegistry region0 failed
    available objects of type volScalarField are

30
(
((((1-exp((-sqrt((((sqr((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)|nu)|(omega+omegaMin)))|Av)))*CmuStd)*sqrt(((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)))*min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin))))
(kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt))
kt_0
nut
(((CR*(1-exp((-max((((kt|nu)|((1.41421*mag(skew(grad(U))))+ROTVSMALL))-CbpCrit),0)|Abp))))*omega)|((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL))+SMALL))
kt
kt_0_0
((CrNat*(1-exp((-max((((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu)-(CnatCrit|((1-exp((((-Cnc*sqrt(kl))*y)|nu)))+ROTVSMALL))),0)|Anat))))*(1.41421*mag(skew(grad(U)))))
(min((((((((C11*(1-exp(((-CtauL*(kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)))|sqr(((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))*omega)+ROOTVSMALL))))))*(1.41421*mag(skew(grad(U)))))*sqr(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))))*sqrt((kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt))))*min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin))))|nu)+((((C12*(1-exp((-sqr(max((((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu)-CtsCrit),0))|Ats))))*((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu))*sqr(y))*(1.41421*mag(skew(grad(U)))))),((0.5*(kl+(kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt))))|sqrt((2*magSqr(symm(grad(U)))))))*(2*magSqr(symm(grad(U)))))
(kt+kl)
kl_0_0
kl_0
(sqrt((kt+kl))|(omega+omegaMin))
(nu*magSqr(grad(sqrt(kt))))
(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL))
(1-exp((((-Cnc*sqrt(kl))*y)|nu)))
(nu*magSqr(grad(sqrt(kl))))
nu
((((((1-exp((-sqrt((((sqr((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)|nu)|(omega+omegaMin)))|Av)))*min((kl|(Cint*((kl+kt)+kMin))),1.0))*(1|(A0+(As*(sqrt((2*magSqr(symm(grad(U)))))|(omega+omegaMin))))))*sqrt(((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)))*min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin))))*(2*magSqr(symm(grad(U)))))
(2*magSqr(symm(grad(U))))
min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))
kl
(((((1-exp((-sqrt((((sqr((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)|nu)|(omega+omegaMin)))|Av)))*min((kl|(Cint*((kl+kt)+kMin))),1.0))*(1|(A0+(As*(sqrt((2*magSqr(symm(grad(U)))))|(omega+omegaMin))))))*sqrt(((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)))*min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin))))
p
min((((((((C11*(1-exp(((-CtauL*(kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)))|sqr(((min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))*omega)+ROOTVSMALL))))))*(1.41421*mag(skew(grad(U)))))*sqr(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))))*sqrt((kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt))))*min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin))))|nu)+((((C12*(1-exp((-sqr(max((((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu)-CtsCrit),0))|Ats))))*((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu))*sqr(y))*(1.41421*mag(skew(grad(U)))))),((0.5*(kl+(kt-((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt))))|sqrt((2*magSqr(symm(grad(U)))))))
((exp(-sqr((((Css*nu)*(1.41421*mag(skew(grad(U)))))|(kt+kMin))))*(min((Clambda*y),(sqrt((kt+kl))|(omega+omegaMin)))|((sqrt((kt+kl))|(omega+omegaMin))+SMALL)))*kt)
(1.41421*mag(skew(grad(U))))
omega
((sqr(y)*(1.41421*mag(skew(grad(U)))))|nu)
y
)


    From function objectRegistry::lookupObject<Type>(const word&) const
    in file /opt/OpenFOAM/OpenFOAM-2.1.x/src/OpenFOAM/lnInclude/objectRegistryTemplates.C at line 131.

FOAM aborting

#0  Foam::error::printStack(Foam::Ostream&) in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#1  Foam::error::abort() in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#2  Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const& Foam::objectRegistry::lookupObject<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> >(Foam::word const&) const in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/lib/libincompressibleRASModels.so"
#3  Foam::incompressible::turbulentMixingLengthDissipationRateInletFvPatchScalarField::updateCoeffs() in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/lib/libincompressibleRASModels.so"
#4  Foam::incompressible::RASModels::kkLOmega::correct() in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/lib/libincompressibleRASModels.so"
#5  
 in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/bin/pisoFoam"
#6  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#7  
 in "/opt/OpenFOAM/OpenFOAM-2.1.x/platforms/linux64GccDPOpt/bin/pisoFoam"
Aborted
can anyone shed me some light on what I have done wrong?

Thanks

Last edited by strikeraj; April 23, 2012 at 22:53.
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Old   April 25, 2012, 09:49
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strikeraj,

You need to have a y+ of less then one cuz this model uses near wall approach and you can't use a wall function, it simply does not give you transition.
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Old   April 25, 2012, 21:20
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Quote:
Originally Posted by Vahini View Post
strikeraj,

You need to have a y+ of less then one cuz this model uses near wall approach and you can't use a wall function, it simply does not give you transition.

Yes Strikeraj, I agree to Vahini. I guess, this method should be given the same fine grids as like as LES if you solve a three-dimension problem ...
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Old   April 25, 2012, 21:21
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Thanks Sandy and Vahini
I guess I missed the obvious part in the model lol
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Old   April 27, 2012, 08:52
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Hey!

How does one know, that the kinamatic turbulent viscosity nut and nuTilda have to be set to the viscosity of the fluid (1.5e-5)?
And why did you calculate omega with the formula:
nut = kt/omega

In the official paper from D. Keith Walters it says that:
mut = rho * Cmu,std * kt/omega
with Cmu,std = 0.09

so in your formula Cmu,std is missing.

greetings
Christian
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Old   May 6, 2012, 16:01
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I would like to use the new kklomega model for a Velomobile study (A typical low Reynolds case). Would anyone of you be willing to give me some advice? See http://openfoamforvelomobiling.blogspot.com/. The Velox team (http://www.hptdelft.nl/en/) have done windtunnel tests on their body. It would be very interesting to compare their results with those of the kklomega model...
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Old   May 6, 2012, 20:29
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what is the "new kklomega model " ?
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Old   May 7, 2012, 03:19
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Dear Sandy

I mean this:

Version 2.1.0 includes the k-kl-omega (low-Re) model for Reynolds-average simulation of incompressible flows with a boundary layer that undergoes a transition from laminar to turbulent flow. The model is described in D. K. Walters and D. Cokljat, J. Fluids Eng. 130:121401 (2008) and is based on the model k-w with an additional transport equation included to predict low-frequency velocity fluctuations that trigger transition in the boundary layer.
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Old   June 21, 2012, 10:05
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Hey,

I have a 2D airfoil simulation with settings like the above. Mesh is from blockMesh, checkMesh is fine, standard kOmegaSST converges but applying kkLOmega crashes. omega explodes, I tried all kinds of limiters but they have no effect. Any idea?

Help would be greatly appreciated

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Old   June 21, 2012, 10:21
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Quote:
Originally Posted by MadsR View Post
Hey,

I have a 2D airfoil simulation with settings like the above. Mesh is from blockMesh, checkMesh is fine, standard kOmegaSST converges but applying kkLOmega crashes. omega explodes, I tried all kinds of limiters but they have no effect. Any idea?

Help would be greatly appreciated

Mads
Last time, I used a very very small time step to keep it stable.
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Old   June 21, 2012, 10:29
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Hmm, I am running it in steady mode for a steady problem.
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Old   June 21, 2012, 22:32
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I have tried running this without wall functions, but openfoam will replace the files in the 0 folder with files that have wall functions and back up the old ones having a .old extension. How can I run a turbulence model (kklomega inthis case) without wall functions?
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Old   June 22, 2012, 02:01
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I think you need to edit the 0/nut file that openfoam creates and remove the wall function for nut.
Then you can move back your .old files to the original.
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Old   June 22, 2012, 12:20
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Quote:
Originally Posted by onyir View Post
I think you need to edit the 0/nut file that openfoam creates and remove the wall function for nut.
Then you can move back your .old files to the original.

Thank you so much - this worked - it's running now without replacing the initial condition files.
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