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-   -   problem of mass conservation with buoyantBoussinesqSimpleFoam (http://www.cfd-online.com/Forums/openfoam-solving/117919-problem-mass-conservation-buoyantboussinesqsimplefoam.html)

david89 May 17, 2013 06:27

problem of mass conservation with buoyantBoussinesqSimpleFoam
 
Hello Foamers,

Im trying to simulate an air flow within a channel of a rectangular section, in which air is heated by the top surface of the channel.
Im using the buoyantBoussinesqSimpleFoam solver, and as a first step I simulated an isothermal flow, to make it easier because Im totally new with CFD and OF.
I put no slip-condition for velocity and pressure BC.
Then I tried to introduce the following BC for temperature:
internalField uniform 290.15;

boundaryField
{
in
{
type fixedValue;
value uniform 290.15;
}

out
{
type zeroGradient;
}

top
{
type fixedValue;
value uniform 302.15;
}

bottom
{
type zeroGradient;
}

left
{
type zeroGradient;
}

right
{
type zeroGradient;
}
With the isothermal simulation I get the same volumetric flow rate at inlet and outlet (I used patchIntegrate utility). With the non-isothermal one I get different values for the flow rate and I dont understand why: with Boussinesq approximation density variation is neglected so the volumetric flow rate should be the same between inlet and outlet, isnt it?
Does anybody know the answer to this problem?

Regards
Davide.

Tushar@cfd May 27, 2013 07:20

Quote:

Originally Posted by david89 (Post 428212)
Hello Foamers,

Im trying to simulate an air flow within a channel of a rectangular section, in which air is heated by the top surface of the channel.
Im using the buoyantBoussinesqSimpleFoam solver, and as a first step I simulated an isothermal flow, to make it easier because Im totally new with CFD and OF.
I put no slip-condition for velocity and pressure BC.
Then I tried to introduce the following BC for temperature:
internalField uniform 290.15;

boundaryField
{
in
{
type fixedValue;
value uniform 290.15;
}

out
{
type zeroGradient;
}

top
{
type fixedValue;
value uniform 302.15;
}

bottom
{
type zeroGradient;
}

left
{
type zeroGradient;
}

right
{
type zeroGradient;
}
With the isothermal simulation I get the same volumetric flow rate at inlet and outlet (I used patchIntegrate utility). With the non-isothermal one I get different values for the flow rate and I dont understand why: with Boussinesq approximation density variation is neglected so the volumetric flow rate should be the same between inlet and outlet, isnt it?
Does anybody know the answer to this problem?

Regards
Davide.

Hello,

Are you running two cases:

(1) Isothermal case: What are the boundary conditions which you have applied for this case?

(2) Non-Isothermal case: I think Top surface heated is the BC for this.

Am I right?

Can you please upload the contour & streamline plots for the same?


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