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DNS of duct flow

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Old   April 30, 2014, 06:33
Default DNS of duct flow
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Hello everyone
I have successfully make a DNS of channel flow with the solver given here:
http://www.cfd-online.com/Forums/ope...s-2-1-0-a.html
The result is good.
But when I use the solver(ico—DNS)to simulate a duct flow(all the boundarys I set as wall except the inlet and outlet which I set as periodic boundary).And the value of dp/dx is 2 times of the value of channel flow case.
I have changed the scheme of ddt to Euler/CN/backward.All the results are not good compared to results of Gavrilakis(1992,Direct numerical simulation of turbulent flow in a square duct).
I also have refined my mesh but still failed getting a good result.

Can you give me some advice?
Thank you very much!

I have attached my case here.

regards!

andersn
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File Type: zip Duct dns.zip (8.7 KB, 67 views)
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Old   May 3, 2014, 10:14
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Hi, andersn! I'm working in a duct of 1mm X 1mm, maybe there are some difference from yours . I found that the boundary condition of U in your dictionary of 0 is set as cyclic. should it be wall? i.e. fixedvalue? I have another question, How did you get the initial condition of p and U when your simulation parameters such as geometry size, and gradP changes?
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Old   May 3, 2014, 22:19
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hello Niu
To my case,the flow direction I set as periodic boundary condition.As for the initial condition of p and U,I set it according http://www.cfd-online.com/Forums/ope...s-2-1-0-a.html using the tool perturbU.what kind of your case?Are you working on duct DNS also?

I have update my meshes.
Code:
Domain size:6.4X1X1
grid:60*80*80
distance between first grid to wall:  0.002
the  stretching ratio:1.06
but the result seems worse.

Can anyone give me some suggestion?

regards!

andersn
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Old   May 6, 2014, 22:14
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Hello, anderson, in a duct flow , the boundary layer of wall of normal and that of wall of spanwise is superposed at the four corner, maybe the character of turbulence here don't agree the character of channel flow, not duct flow. How much is your duct flow and men velocity streamwise?
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Old   May 14, 2014, 21:53
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is the flow direction the only homogenous direction in the duct flow?As in channel flow, the homogenous directions are streamwise and spanwise
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Old   May 15, 2014, 21:57
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Thank you for your suggestion.what do you mean by that"only homogenous direction".In my case,the duct flow direction is along x-axis, while the other four boundaries are wall(no-slip).
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Old   May 15, 2014, 22:31
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Quote:
Originally Posted by andersn View Post
Thank you for your suggestion.what do you mean by that"only homogenous direction".In my case,the duct flow direction is along x-axis, while the other four boundaries are wall(no-slip).
That means the statistics in this direction won't vary.
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Old   May 15, 2014, 23:04
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yes,The flow direction is the only homogenous direction which I use periodic boundary condition.
I have try some numerical scheme,but the rms of velocity in the flow direction is not good either(the attached files).Is it the problem of fvScheme or PISO method?
why are DNS of channel flow and duct flow so different?
I have been confused by it for a few weeks.


regards!

andersn
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Old   May 15, 2014, 23:19
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Quote:
Originally Posted by andersn View Post
yes,The flow direction is the only homogenous direction which I use periodic boundary condition.
I have try some numerical scheme,but the rms of velocity in the flow direction is not good either(the attached files).Is it the problem of fvScheme or PISO method?
why are DNS of channel flow and duct flow so different?
I have been confused by it for a few weeks.


regards!

andersn
Perhaps, I see your scheme is quite different from the channel one. Have you tried the default schemes in channel flow as in tutorial?
Are you sure your simulation reached fully developed?
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Old   May 15, 2014, 23:35
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yes.this scheme is quite different from the channel one.
But at first I use the same scheme as the channel flow.I didn't change anything except the boundary condition of spanwise which I modified to wall.And I have refined my grid also.The flow time is so long and I am sure it has reached fully developed.

I have simulated the channel flow case also. And the result is good enough.
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Old   May 15, 2014, 23:49
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Quote:
Originally Posted by andersn View Post
yes.this scheme is quite different from the channel one.
But at first I use the same scheme as the channel flow.I didn't change anything except the boundary condition of spanwise which I modified to wall.And I have refined my grid also.The flow time is so long and I am sure it has reached fully developed.

I have simulated the channel flow case also. And the result is good enough.
ummm, I have no idea about this now
In my simulation, the steady state was reached after about 160000s while the deltaT=0.5s, so it's quite long
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Old   May 16, 2014, 00:04
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what kind of problem of yours? a duct flow or a channel flow?Can you share it with us.which solver did you use?Maybe the problem exist in fvSheme or polyMesh or something else.
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Old   May 16, 2014, 02:27
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Quote:
Originally Posted by andersn View Post
what kind of problem of yours? a duct flow or a channel flow?Can you share it with us.which solver did you use?Maybe the problem exist in fvSheme or polyMesh or something else.
Channel flow. I use the icoFoam changed as a DNS solver from the idea of Steven.
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Old   May 16, 2014, 05:43
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Hello Xianbei,
There are not homogenous in the two direction in duct flow(spanwise and normal wall).
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Old   May 16, 2014, 05:48
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Quote:
Originally Posted by andersn View Post
yes.this scheme is quite different from the channel one.
But at first I use the same scheme as the channel flow.I didn't change anything except the boundary condition of spanwise which I modified to wall.And I have refined my grid also.The flow time is so long and I am sure it has reached fully developed.

I have simulated the channel flow case also. And the result is good enough.
Dear andersn,
Did you initialize your U filed with perturbU or other ways when simulating channel flow?

Best Regards!
Z.Q. Niu
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Old   May 18, 2014, 22:05
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Quote:
Originally Posted by andersn View Post
what kind of problem of yours? a duct flow or a channel flow?Can you share it with us.which solver did you use?Maybe the problem exist in fvSheme or polyMesh or something else.
Code:
ddtSchemes
{
    default         backward;
}

gradSchemes
{
    default         Gauss linear;
    grad(p)         Gauss linear;
    grad(U)         Gauss linear;
    grad(UMean)     Gauss linear;//in order to calculate vt
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss linear;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div((nuEff*dev(T(grad(U))))) Gauss linear;

}

laplacianSchemes
{
    default         none;
    laplacian(nu,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DBEff,B) Gauss linear corrected;
    laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
    interpolate(U)  linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}
Code:
convertToMeters 1;

vertices
(
    (0 0 0)
    (12.56 0 0)
    (0 1 0)
    (12.56 1 0)
    (0 2 0)
    (12.56 2 0)
    (0 0 6.28)
    (12.56 0 6.28)
    (0 1 6.28)
    (12.56 1 6.28)
    (0 2 6.28)
    (12.56 2 6.28)
);

blocks
(
    hex (0 1 3 2 6 7 9 8)   (128 64 128) simpleGrading (1 10 1)
    hex (2 3 5 4 8 9 11 10) (128 64 128) simpleGrading (1 0.1 1)
);

edges
(
);

boundary
(
    bottomWall
    {
        type            wall;
        faces           ((0 1 7 6));
    }
    topWall
    {
        type            wall;
        faces           ((4 10 11 5));
    }

    sides1_half0
    {
        type            cyclic;
        neighbourPatch  sides1_half1;
        faces           ((0 2 3 1));
    }
    sides1_half1
    {
        type            cyclic;
        neighbourPatch  sides1_half0;
        faces           ((6 7 9 8));
    }

    sides2_half0
    {
        type            cyclic;
        neighbourPatch  sides2_half1;
        faces           ((2 4 5 3));
    }
    sides2_half1
    {
        type            cyclic;
        neighbourPatch  sides2_half0;
        faces           ((8 9 11 10));
    }

    inout1_half0
    {
        type            cyclic;
        neighbourPatch  inout1_half1;
        faces           ((1 3 9 7));
    }
    inout1_half1
    {
        type            cyclic;
        neighbourPatch  inout1_half0;
        faces           ((0 6 8 2));
    }

    inout2_half0
    {
        type            cyclic;
        neighbourPatch  inout2_half1;
        faces           ((3 5 11 9));
    }
    inout2_half1
    {
        type            cyclic;
        neighbourPatch  inout2_half0;
        faces           ((2 8 10 4));
    }
);

mergePatchPairs
(
);
Sorry for forgotting. here is the blockmesh and fvscheme
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Old   May 20, 2014, 22:01
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I have just got to know that the fvm used in DNS is not as accurate as spectral method. So if a fvm is used in DNS ,the mesh should be much finer. I got this from a doctor, and I want to confirm the message, if you know something about the accuracy of the two methods, please show to me
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Old   June 16, 2014, 11:09
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Quote:
Originally Posted by huangxianbei View Post
I have just got to know that the fvm used in DNS is not as accurate as spectral method. So if a fvm is used in DNS ,the mesh should be much finer. I got this from a doctor, and I want to confirm the message, if you know something about the accuracy of the two methods, please show to me
http://www.mcs.anl.gov/~fischer/nek5...00_dec2010.pdf

Is that helpful? I am using OpenFOAM for DNS pipe flow. I am also interested in this topic.
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Old   June 17, 2014, 04:23
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Hi,

why everybody use ico-DNS instead of pisoFoam, pimpleFoam or icoFoam for DNS in channel-flow??
These solvers should give the same results and their are still implemented in OF.

kind regards
Florian
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Old   June 17, 2014, 04:52
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Quote:
Originally Posted by itchy View Post
Hi,

why everybody use ico-DNS instead of pisoFoam, pimpleFoam or icoFoam for DNS in channel-flow??
These solvers should give the same results and their are still implemented in OF.

kind regards
Florian
I do pipe flow with pimplefoam, as it has fvOptions, which I can make pressure compensation for cyclic bc.
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