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Local Nusselt Number Calculation

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Old   August 12, 2019, 11:25
Default Local Nusselt Number Calculation
  #1
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Hello Everyone,

I am trying to calculate the local nusselt number along the bottom of a cavity heated from below. Based on inputs from several posts, I have tried to modify buoyantBoussinessqPimpleFoam to calculate temperature gradient.

But, I am not sure if my procedure is right. Also I do not how to calculate the local Nusselt number. The values of grad T are unphysical.

Kindly please help me solve this problem. I have attached the modified solver and a testCase. I am using OpenFOAM v6.

The method of calculation of temperature gradient is as given below, which is added in the main file heatFoam.C
Code:
//wallGrad
         
        const fvPatchList& patches = mesh.boundary();

            forAll(wallGradT.boundaryField(), patchi)
            {
                const fvPatch& currPatch = patches[patchi];

                if (isA<wallFvPatch>(currPatch))
                {
                    wallGradT.boundaryFieldRef()[patchi] =
                        -T.boundaryFieldRef()[patchi].snGrad();
                }
            }
I add the following to the createFields.H
Code:
volScalarField wallGradT
            (
                IOobject
                (
                    "wallGradT",
                    runTime.timeName(),
                    mesh,
                    IOobject::NO_READ,
                    IOobject::AUTO_WRITE
                ),
                mesh,
                dimensionedScalar
                (
                    "wallGradT",
                    T.dimensions()/dimLength,
                    0
                )
            );
Thank You.

With Thanks & Regards,
Pavithra.
Attached Files
File Type: gz heatFoam.tar.gz (3.4 KB, 2 views)
File Type: gz hotRoom.tar.gz (2.4 KB, 1 views)
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Old   September 4, 2019, 11:28
Default
  #2
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Hojatollah Gholami
Join Date: Jan 2019
Posts: 93
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Quote:
Originally Posted by Pavithra View Post
Hello Everyone,

I am trying to calculate the local nusselt number along the bottom of a cavity heated from below. Based on inputs from several posts, I have tried to modify buoyantBoussinessqPimpleFoam to calculate temperature gradient.

But, I am not sure if my procedure is right. Also I do not how to calculate the local Nusselt number. The values of grad T are unphysical.

Kindly please help me solve this problem. I have attached the modified solver and a testCase. I am using OpenFOAM v6.

The method of calculation of temperature gradient is as given below, which is added in the main file heatFoam.C
Code:
//wallGrad
         
        const fvPatchList& patches = mesh.boundary();

            forAll(wallGradT.boundaryField(), patchi)
            {
                const fvPatch& currPatch = patches[patchi];

                if (isA<wallFvPatch>(currPatch))
                {
                    wallGradT.boundaryFieldRef()[patchi] =
                        -T.boundaryFieldRef()[patchi].snGrad();
                }
            }
I add the following to the createFields.H
Code:
volScalarField wallGradT
            (
                IOobject
                (
                    "wallGradT",
                    runTime.timeName(),
                    mesh,
                    IOobject::NO_READ,
                    IOobject::AUTO_WRITE
                ),
                mesh,
                dimensionedScalar
                (
                    "wallGradT",
                    T.dimensions()/dimLength,
                    0
                )
            );
Thank You.

With Thanks & Regards,
Pavithra.
Dear Pavithra
Nu=hL/K Nusselt number calculated based on the definition. In some article uses Nu=-wallGradT/(T-T_init)*L (L or D_h) and for that, you can use paraview and calculator for definition. Or uses swak4Foam in controlDic
Quote:
NusseltNumber
{
functionObjectLibs
("libsimpleSwakFunctionObjects.so");
type patchExpression;
outputControlMode timeStep;
outputInterval 1;
patches(wall);
verbose true;
variables
(
"T_inf=300;"
"D=0.00762;"
);
expression "D*snGrad(T)/(T-T_inf)";
accumulations (average);
log true;
}
or
code base on this topic
Quote:
volScalarField wall_localNusselt
(
IOobject
(
"wall_localNusselt",
runTime.timeName(),
mesh,
IOobject::NO_READ,
IOobject::AUTO_WRITE
),
mesh,
dimensionedScalar("wall_localNusselt ",dimless,0.0)
);

forAll(wall_localNusselt.boundaryFieldRef(),patchi )
{
wall_localNusselt.boundaryFieldRef()[patchi] = wallGradT[patchi]/((T_hot-T_ini)*length);
}

wall_localNusselt.write();
}
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Old   September 23, 2019, 02:16
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  #3
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Join Date: Apr 2019
Location: India
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Quote:
Originally Posted by Hgholami View Post
Dear Pavithra
Nu=hL/K Nusselt number calculated based on the definition. In some article uses Nu=-wallGradT/(T-T_init)*L (L or D_h) and for that, you can use paraview and calculator for definition. Or uses swak4Foam in controlDic

or
code base on this topic

Dear Sir,



Thank You somuch for your help and sorry for the late reply. I have used a similar method to calculate the Nusselt number.



Thank You once again.



- Pavithra
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