[AndreaCFD]

Dear members,

I am trying to implement a Linearized Navier-Stokes solver for incompressible fluids inside OpenFoam. I read some articles and discussions in the forum but I some concepts which are not clear to me.

Knowing that the LNSE are:



where is the equilibrium solution and U and p are the small perturbations from it.

I wanted to modify the icoFoam.C solver in the following way:

	        fvVectorMatrix UEqn
        (	
			fvm::ddt(U)-
			fvm::laplacian(nu, U)+
			fvm::div(phi_zero, U)+
			fvc::div(phi,U_zero)
        );

and defining in the createFields.H the new quantities:

Info<< "Reading field U_zero\n" << endl;
volVectorField U_zero
(
	IOobject
		(
		"U_zero",
		runTime.constant(),
		mesh,
		IOobject::MUST_READ,
		IOobject::NO_WRITE
		),
	mesh
);

surfaceScalarField phi_zero
(
	IOobject
		(
		"phi_zero",
		runTime.constant(),
		mesh,
		IOobject::READ_IF_PRESENT,
		IOobject::NO_WRITE
		),
		//fvc::flux(U_zero)
	linearInterpolate(U_zero) & mesh.Sf()
);

I already calculated the U_zero velocity field in a previous simulation and I want the solver to read it from the constant folder. The file is like :

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U_zero;
}
dimensions      [0 1 -1 0 0 0 0];


internalField   nonuniform List<vector> 
30000
(
.
.
.
)
;
boundaryField
{
.
.
.
}

------------------------------------------------------------------------------
The solver compiles good and the simulation runs but the results I get are not the ones I expected.
I do not understand whether there is something wrong in the code or there is a mistake in the initial and boundary conditions I set.

Can somebody help me please?

Thanks in advance,

Andrea

[stanweer]

Your code seems to be right.

What boundary conditions did you use?

[dlahaye]

Does pEqn.H require corresponding modification? The current implementation seems to solve for a non-physical pressure. The pressure-velocity coupling makes the model non-linear as is likely to affect the computed velocity field.

Does it make sense to modify scalarTransportFoam from a scalar field being convected (as currently the case) to a velocity field being convected. In this way the pressure field is no longer in your way.