[gentodin]

Hi I was comparing ANSYS fluent and OPEN FOAM as a solver recently and was wondering what are the hardcoded difference between them that cannot be changed.

I am running a simple case from CFDNINJA with the same settings in Openfoam.

I notice both use a different linear solver where Ansys is using AMG(algebraic Multigrid) while Openfoam is using Conjugate gradient solver. (I can change it to GAMG but I have yet to understand fully how AMG's algorithm work.)

I was also wondering why the following occurs where the console ouput for ANSYS fluent is different from Openfoam where the fluent iterates all equation at the same time until all equation satisfy the residual but openfoam iterates one equations by one equations (I.e. Velocity equation then temperature equation).

Console output of ANSYS fluent: Ansys fluent console output.png
Console output of Openfoam: Openfoam console output.png

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Do linear solvers affect the output of a cfd simulation? i.e. oscillation occurs for OF but not ANSYS in my simulation when I use a turbulence model with exactly the same input.

Setup for ANSYS fluent:
Realizable K-e
Standard wall function
Transient, PISO algorithm
Energy equation: on
No gravity
Fluid Material: Ansys database, Water(h20) liquid
Linear Solver: AMG
(Other settings were left at default)

Setup for Openfoam:
Solver used: BuoyantBoussinesqPimpleFOAM
Realizable K-e
Standard Wall function
Pimple converted to PISO algorithm.
Temperature equation on.
No gravity
Fluid material same as ANSYS.
Linear solver: Conjugate gradient based.
(Othersettings were set to be the same as ANsys fluent as shown in the attachmend below)

Geometry 2D mixing elbow case from CFD NINJA : https://www.youtube.com/watch?v=Pjee...NJA%2FANSYSCFD

My input files for OpenFOAM are attached here:
https://entuedu-my.sharepoint.com/:f...Xvv7Q?e=S2U6vD

Ansys fluent settings:
https://entuedu-my.sharepoint.com/:f...mkTgw?e=dQWWPg

I am at lost as I have been working on getting similar results but my Openfoam simulation kept oscilliating.