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 david89 May 17, 2013 06:27

problem of mass conservation with buoyantBoussinesqSimpleFoam

Hello Foamers,

I´m 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.
I´m using the buoyantBoussinesqSimpleFoam solver, and as a first step I simulated an isothermal flow, to make it easier because I´m 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
{
}

top
{
type fixedValue;
value uniform 302.15;
}

bottom
{
}

left
{
}

right
{
}
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 don´t understand why: with Boussinesq approximation density variation is neglected so the volumetric flow rate should be the same between inlet and outlet, isn´t 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, I´m 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. I´m using the buoyantBoussinesqSimpleFoam solver, and as a first step I simulated an isothermal flow, to make it easier because I´m 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 don´t understand why: with Boussinesq approximation density variation is neglected so the volumetric flow rate should be the same between inlet and outlet, isn´t 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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