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

NACA0012 with simpleFOAM

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 27, 2007, 09:19
Default I'm working on an airfoil prof
  #1
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 7
nuovodna is on a distinguished road
I'm working on an airfoil profile NACA0012. I wrote my mesh in Gambit and then i imported it in OpenFOAM. I'm going to solver it with simpleFOAM (incompressible and steady flow, using kepsilon model) but the solution isn't accurate i think. At the angle of attack = 15 not stall and the total force on the profile is very low (i've calculated them using ssimpleFoam found in the board). I'd like to know:

1) what are the correct boundary condition on k and epsilon (in what way i give the correct k and epsilon fixed values on inlet patch and in internal field?)

2) do i have to use another model of turbulence?

Thanks in advantage

Emanuele
nuovodna is offline   Reply With Quote

Old   November 27, 2007, 11:15
Default I think, you must use freestre
  #2
Senior Member
 
mkraposhin's Avatar
 
Matvej Kraposhin
Join Date: Mar 2009
Location: Moscow, Russian Federation
Posts: 172
Rep Power: 7
mkraposhin is on a distinguished road
I think, you must use freestream BC for infinity field, standard wall BC for walls on profile and inlet for inlet patch.

inlet: U - fixedValue, p - zeroGradient, k - fixedValue, epsilon - fixedValue
infinity field - U - freestream, p - freestreamPressure, k and epsilon - zeroGradient.
profile walls - U - fixedValue (0 0 0), p - zeroGradient, k and epsilon - zeroGradient
mkraposhin is offline   Reply With Quote

Old   November 27, 2007, 11:48
Default what are the fixed values of k
  #3
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 7
nuovodna is on a distinguished road
what are the fixed values of k and epsilon to setting? is there a mode to calculate them?
nuovodna is offline   Reply With Quote

Old   November 27, 2007, 21:44
Default what kind of model of turbulen
  #4
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 7
nuovodna is on a distinguished road
what kind of model of turbulence is better??

and for the better what are the boundary condition on the k epsilon or another variable?


what is the better schemes to use?
nuovodna is offline   Reply With Quote

Old   November 28, 2007, 03:44
Default For k/epsilon, I normally spec
  #5
Senior Member
 
Mark Olesen
Join Date: Mar 2009
Location: http://olesenm.github.io/
Posts: 776
Rep Power: 17
olesen will become famous soon enough
For k/epsilon, I normally specify turb. intensity and the mixing length. I don't say that you have good values for these, but I find them a bit easier to visualize than the raw tke and dissipation.

The boundary conditions for 10% turbulence and 5mm length scale would look something like this:

// k
dimensions [ 0 2 -2 0 0 0 0 ];
internalField uniform 1;
...
inlet
{
type turbulentIntensityKineticEnergyInlet;
intensity 0.1;
value 1;
}


// epsilon

dimensions [ 0 2 -3 0 0 0 0 ];
internalField uniform 200;
...
inlet
{
type turbulentMixingLengthDissipationRateInlet;
mixingLength 0.005;
value uniform 200;
}


NB: The stability of your calculation can be greatly affected by the initialization of epsilon.
olesen is offline   Reply With Quote

Old   December 2, 2007, 10:31
Default the value on inlet patch of k
  #6
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 7
nuovodna is on a distinguished road
the value on inlet patch of k and epsilon affect very greatly the solution...also using komega model you can choose the initial values very well....in what way can i fix this initial values (of k epsilon and omega) to obtain the correct solutions??
nuovodna is offline   Reply With Quote

Old   December 3, 2007, 05:52
Default Hello, what does "valu
  #7
Senior Member
 
Markus Rehm
Join Date: Mar 2009
Location: Erlangen (Germany)
Posts: 171
Rep Power: 7
markusrehm is on a distinguished road
Hello,

what does

"value 1;"

in k and

"internalField uniform 200;"

in epsilon stand for? It is the same as internalField, why do we need it in the BC-description?

Regards Markus
markusrehm is offline   Reply With Quote

Old   May 19, 2010, 05:58
Default
  #8
Member
 
Join Date: Apr 2010
Posts: 53
Rep Power: 6
bephi is on a distinguished road
Hi at all,
i'd like to continue this thread because I have a lot of trouble with bounding k/epsilon although there are so many threads concerning this topic.

so far I know that the initialization of k and epsilon is very important to achieve a stable calculation.

but actually I don't really know what went wrong. I would like to simulate a flow throw a piston valve using the simpleFoam solver with the RNG k_epsilon model.
Here are my settings. Maybe you can take a look what should be changed to get a stable calculation:
p
Code:
boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 476.2;
    }
U
Code:
boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform (0 0 -1);
    }
    outlet
    {
        type            zeroGradient;
    }
k
Code:
internalField   uniform 0.0003;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 0.0003;
    }
    outlet
    {
        type            zeroGradient;
    }
epsilon
Code:
internalField   uniform 1.35e-4;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 1.35e-4;
    }
    outlet
    {
        type            zeroGradient;
    }
nut
Code:
internalField   uniform 0.1;

boundaryField
{
    inlet
    {
        type            freestream;
        freestreamValue uniform 0.1;
        value           uniform 0.1;
    }
    outlet
    {
        type            freestream;
        freestreamValue uniform 0.1;
        value           uniform 0.1;
controlDict
Code:
application             simpleFoam;
startFrom             startTime;
startTime            0;
stopAt                 endTime;
endTime                7.2e-2;
deltaT                 3e-6;
writeControl             timeStep;
writeInterval            1000;
purgeWrite            0;
writeFormat            ascii;
writePrecision            6;
writeCompression        uncompressed;
timeFormat            general;
timePrecision            6;
graphFormat            raw;
runTimeModifiable        yes;
fvSchemes
Code:
ddtSchemes
{
    default steadyState;
}
gradSchemes
{
    default         Gauss linear;
    grad(p)         Gauss linear;
    grad(U)         Gauss linear;
}
divSchemes
{
    default         none;
    div(phi,U)      Gauss upwind;
    div(phi,k)      Gauss upwind;
    div(phi,epsilon) Gauss upwind;
    div(phi,R)      Gauss upwind;
    div(R)          Gauss linear;
    div((nuEff*dev(grad(U).T()))) Gauss linear;
}
laplacianSchemes
{
    default         none;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
    laplacian(DREff,R) Gauss linear corrected;
}
interpolationSchemes
{
    default         linear;
    interpolate(U)  linear;
}
snGradSchemes
{
    default         corrected;
}
fluxRequired
{
    default         no;
    p;
}
fvSolution
Code:
solvers
{
    p PCG
    {
        preconditioner   DIC;
        tolerance        1e-06;
        relTol           0.01;
    };
    U PBiCG
    {
        preconditioner   DILU;
        tolerance        1e-05;
        relTol           0.1;
    };
    k PBiCG
    {
        preconditioner   DILU;
        tolerance        1e-05;
        relTol           0.1;
    };
    epsilon PBiCG
    {
        preconditioner   DILU;
        tolerance        1e-05;
        relTol           0.1;
    };
    R PBiCG
    {
        preconditioner   DILU;
        tolerance        1e-05;
        relTol           0.1;
    };
    
}
SIMPLE
{
    nNonOrthogonalCorrectors 1;
}
relaxationFactors
{
    p               0.3;
    U               0.7;
    k               0.05;
    epsilon         0.05;
    R               0.7;
}
If there is something else to change or improve in my settings please let me know! I'll be very thankful!

Regards!
bephi 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
How to model VGs over a NACA0012 Franny Main CFD Forum 2 March 25, 2007 06:05
Simulation over a NACA0012 Jungleland6 CFX 4 October 30, 2006 04:48
HELP naca0012 maritozzo OpenFOAM Running, Solving & CFD 1 October 14, 2005 18:48
CD & CL on a NACA0012 wing Xwang FLUENT 7 March 26, 2004 15:42
NACA0012 exp.results muygun Main CFD Forum 7 November 11, 2002 18:41


All times are GMT -4. The time now is 02:05.