[chandra shekhar pant]

Dear Foamers,
I am trying to see the effect of time varying effect of pressure gradient on the periodic channel in OpenFOAM v1906, thus wondering if, it is correct to use the

vectorCodedSource

at the inlet volume by creating a cellzone using inlet area \times deltax (streamwise direction resolution) in topoSetDict. If that is somehow mimicking the actual pressure gradient then I have following questions:
1. What should be the value of deltax for defining the cellzone in topoSetDict
2. What should be the magnitude of this source term in the

USource[celli] += vector(?, 0,0 )

should it be the exact value of dp/dx or something different.
Any comment/suggestion would be very much appreciated, many thanks in advance.

[chandra shekhar pant]

Hello All,
I guess I figured this out, so the basic principle is that the fully developed channel means that it's kind of steady state and the pressure gradient force is exactly balanced by the wall shear stress. So the body force to be applied inside the fvOptions is the magnitude of dpdx, now there are 2 questions:
1. Where should this force be applied and how?
2. What is the magnitude of this force and how it should be incorporated in the fvoptions?
Answers to the questions
1. Using topoSetDict create cellzone as:

/*--------------------------------*- C++ -*--------------------------------
actions
(

/// for creating volumetric force

{
        name 	source1;
        type	cellSet;
        action	new;
        source	boxToCell;
        box     (0 0 0) (Lx Ly Lz);
        
    }

    {
        name    source1;
        type    cellZoneSet;
        action  new;
        source  setToCellZone;
        sourceInfo
        {
            set source1;
        }
    }
 );

After creating this zone, check if this is what is been expected using paraview:

1.

foamToVTK -cellSet source1

2. ParaFoam should be opened in the main case file
3. Through the existing opened paraFoam file, open the VTK and open the source1.vtk file on the top of the previous opened file so that we can see both the whole domain and the zone where we intend to apply the force.

2. For applying the body force using:

codedSource
{
    type            vectorCodedSource;
    selectionMode   cellZone;
    cellZone        source1;

    fields          (U);
    name            codedSource;
	// modified to include the pressure wave

	codeAddSup
    #{  
 forAll(cellsZone,i)
			{
        		const label celli = cellsZone[i];
        		
        		
        		USource[celli] -= vector(dpdx*V[celli], 0, 0 ); 
}
    #};

	
	
    
    codeCorrect
    #{
   
    #};
    codeConstrain
    #{
    #};  
    code
    #{
            $codeInclude
            $codeCorrect
            $codeAddSup
            $codeConstrain
    #};
    }

Then I checked the results from this procedure against the utility vectorSemiImplicitSource in fvoptions using:

pressureGradient
{
    type 		vectorSemiImplicitSource;
    selectionMode   all;
   volumeMode specific;    
    injectionRateSuSp
     { 
   U ((dpdx 0 0) 0);
    }

and got the exact answers.