# problem of mass conservation with buoyantBoussinesqSimpleFoam

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 May 17, 2013, 06:27 problem of mass conservation with buoyantBoussinesqSimpleFoam #1 New Member   Join Date: May 2013 Posts: 3 Rep Power: 6 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.

May 27, 2013, 07:20
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Quote:
 Originally Posted by david89 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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