[gomz]

Hello,

I am Tom, new to CFD/OpenFOAM and very happy about this Forum, which already helped me. Thank you all!

I have a question which will be pretty simple, but I can't find a solution here or in the documentation. It is about codeStream.
I use the rhoSimpleFoam/squareBend tutorial with rhoSimpleFoam. I set the longer path as heatWalls and I want to try some alphatWall calculations.


So what I want to do is using a different calculation for alpha on a specific patchType. For this, I have a formula and I want to implement this via codeStream. This works with a set constant (e.g. alpha = 0.05).

The next step is to use the cell pressure. For this I found out, that I can access these values with

U.boundaryField()[patchi].patchInternalField()
whereas patchi is found by
const label patchi = mesh.boundaryMesh().findPatchID("bottom")

or

const scalarField& UCells = U.internalField();

forAll(UCells,CellI)
{
UCells[CellI];
}

My problem is, that I don't know how the cells, vectors etc. in OpenFOAM are handled. I want to use the cell average pressure to calculate the alphatWall. But since this is just at the wall, I don't know how to express that - or if using codeStream in 0/alphat is even the right thing to do. I can express my Solution in comments, maybe someone can help me translate this to code.

// some constants & pre-calculations needed for formula
f_d = 0.5;  // just example 
f_w = 0.73*f_d;

// the example formula is: alphat = (p^f_w)*(f_d^0.1) 
//
//

// from here on, I am not sure. Therefore I write in comments.


// There should be a loop over all boundary (wall) cells, but I don't know 
// how to achieve this (wallCells/cellID etc.)

forAll(wallCells, cellID) 
{
   // I have to read the value of p out of the iterated cell
    p_t = p.boundaryField()[patchi].patchInternalField() ?
   // Thats the whole patch, doesnt make sense to me. 

   // Then I can calculate alpha
   alphat = pow(p_t,f_w)*pow(f_d,0.1)
}

I hope my problem is understandable and somebody can help me. If there is additional information material I am also interested. Thank you in advance!

Best regards
Tom

Source from access velocity code:
Access to the velocity at boundary cells

[SHUBHAM9595]

Hey Tom,

You are almost there. You just have to initialize the field (in your case Pressure) specifically for your patch.

const fvMesh& mesh = refCast<const fvMesh>(d.db());
const label id = mesh.boundary().findPatchID("your_patch"); 
const fvPatch& patch = mesh.boundary()[id];

f_d = 0.5;  
f_w = 0.73*f_d;

scalarField ptemp(patch.size(), scalar(0));
scalarField alphat(patch.size(), scalar(0));

forAll(alpha[i], i)
{
 ptemp[i] = p[i];
 alphat[i] = scalar(pow(ptemp[i],f_w)*pow(f_d,0.1));
}

For additional info, you can refer the link below.
http://wiki.openfoam.com/Programming1

[EricS]

Hi!


I'm facing a similar problem: I'm trying to get the average pressure value on a patch. So far I wrote the following:

   

    throat
    {
    type            flowRateOutletVelocity;
    volumetricFlowRate     #codeStream
        {
            codeInclude
            #{
                #include "fvCFD.H"
            #};

            codeOptions
            #{
                -I$(LIB_SRC)/finiteVolume/lnInclude \
                -I$(LIB_SRC)/meshTools/lnInclude
            #};

            //libs needed to visualize BC in paraview
            codeLibs
            #{
            -lmeshTools \
            -lfiniteVolume
            #};

            code
            #{    
        /* CYCLE EXPLAINED
        input = CPI = massFlowRate * deltaP
        1. massFlowRate = CPI / deltaP;
        2. compute first timestep with the massFlowRate just calculated;
        3. compute deltaP (which is deltaP = p_amb - p_throat = 0 - p_throat = -p_throat);
        4. correct massFlowRate with the new value of p_throat;
        5. keep iterating...
            massFlowRate^(i+1) = - CPI / p_throat^(i)
        */
                const IOdictionary& d = static_cast<const IOdictionary&>
        (
                    dict.parent().parent()
                );
                const fvMesh& mesh = refCast<const fvMesh>(d.db());
                const label id = mesh.boundary().findPatchID("throat");
                const fvPatch& patch = mesh.boundary()[id];
                vectorField U(patch.size(), vector(0, 0, 0));            // initialization of the vector field
        const CPI = xxx;                        // Power Input in Watt        
                const surfaceVectorField& p = patch().lookupObject("p");    // get throat's pressure
        const massFlowRate = -CPI/average(p);                // compute corresponding massFlowRate
                writeEntry(os,"", massFlowRate);
            #};
        };
    value            uniform (0 0 0);        
    }

The idea is to get the average pressure of the "throat" patch then use that value to compute a massFlowRate to correct the value step by step.
The problem is that I keep facing errors that are surely caused by errors in my code but I'm not able to fix it properly, do you have any guess on how to repair it?
Thank you!