Mass flux update in simpleFoam and rhoSimpleFoam

trailer · June 14, 2021, 20:17

Hello to all,

I would like to know if anyone can clarify why the mass flux in simpleFoam is calculated as:

Code:

phi = phiHbyA - pEqn.flux();

And in rhoSimpleFoam:

Code:

phi = phiHbyA + pEqn.flux();

Why does the sign change?

trailer · June 14, 2021, 20:28

in simpleFoam it comes from the discretization of the continuity equation:

$\vec{v}_P = a_P^{-1} H(\vec{v}) - a_P^{-1}\nabla P$

$\nabla \cdot \vec{v} = 0$

$F = \vec{v}_f \cdot \vec{S_f} = \left (a_P^{-1} H(\vec{v}) \right )_f- \left (a_P^{-1}\nabla P \right )_f$

Where the .flux() function is used to rebuild the fluxes accounting for the implicit and explicit part resulting from the discretization of the laplacian operator (Description of flux() method)

For the rhoSimpleFoam part, I would appreciate the help!

June 14, 2021, 20:17	Mass flux update in simpleFoam and rhoSimpleFoam	#1
trailer Member Join Date: Mar 2021 Posts: 39 Rep Power: 5	Hello to all, I would like to know if anyone can clarify why the mass flux in simpleFoam is calculated as: Code: phi = phiHbyA - pEqn.flux(); And in rhoSimpleFoam: Code: phi = phiHbyA + pEqn.flux(); Why does the sign change?

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June 14, 2021, 20:28		#2
trailer Member Join Date: Mar 2021 Posts: 39 Rep Power: 5	in simpleFoam it comes from the discretization of the continuity equation: $\vec{v}_P = a_P^{-1} H(\vec{v}) - a_P^{-1}\nabla P$ $\nabla \cdot \vec{v} = 0$ $F = \vec{v}_f \cdot \vec{S_f} = \left (a_P^{-1} H(\vec{v}) \right )_f- \left (a_P^{-1}\nabla P \right )_f$ Where the .flux() function is used to rebuild the fluxes accounting for the implicit and explicit part resulting from the discretization of the laplacian operator (Description of flux() method) For the rhoSimpleFoam part, I would appreciate the help!