Hello Everyone,
I am using chtMultiRegionSimpleFoam and my Openfoam version is 4.1.
I made my geometry in Salome and I am modelling a laminar fluid flow.
Now I want to change the flow to Turbulent, But I don't know what changes do I need to make in my case to model a Turbulent flow.
Can someone please guide me how to do this?
Thank you
Hi Raza,
As you are using chtMultiRegionSimpleFoam, I'm assuming you are simulating steady conjugate heat transfer between a fluid and a solid. As far as I'm aware, this solver does have the option to model turbulent flow, but I don't have any experience with this particular solver myself.
Probably you'll have a file called turbulenceProperties in your constant folder, and right now the keyword simulationType is set to laminar. To change to turbulent flow, set this keyword to RAS, and add a sub-dictionary RAS to the file, specifying which model to use etc. After that, you also need to add initial conditions files for k, epsilon/omega, etc. to your 0 folder. Generally OpenFOAM will not run when you forget to specify something, and from the error message it's usually fairly clear what you forgot
For examples and guidance you can take a look at the tutorials supplied with OpenFOAM, for example the lid driven cavity (OpenFOAM user guide, section 2.1.8 High Reynolds number flow). Also, a quick internet search on your particular solver results in quite a few seemingly useful hits:
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2012/MaaikeVanDerTempel/chtMultiRegionSimpleBoussinesqFoam7.pdf
https://openfoamwiki.net/index.php/Getting_started_with_chtMultiRegionSimpleFoam_-_planeWall2D
Hope this helps,
Sita
Hi Raza
i recommend you these two thesis based on open foam hope these might help.
you can download them as a .rar file.
also you can watch step by step tutorial from this link at youtube :
https://www.youtube.com/watch?v=0N6kZjNtcw8
Dear Dr. Javed,
I strongly recommend you to check also this high-quality master thesis done with both ANSYS-Fluent and OpenFOAM: "Numerical investigation of Active Flow Control applied to an airfoil leading edge", available in:
http://hdl.handle.net/2117/78769
I think it can be helpful to you!
Sincerely,
Jose
Basically you shuld activate the turb Model in the turbulencePropertyDict. Then in the 0 directory you need to define the proper BC for the new fields (for example k, eps, etc.).
hope can help
Franco
Hello Franco Concli ,
Thank you for your reply. Actually I started like this:
1. I changed the simulation type from laminar to RAS turbulence model and then put kEpsilon model in the turbulenceProperties file. This file is present in constant/fluid(region_name)/.
2. Then, I went to system/fluid/changeDictionaryDict. In this file, before there was only p,U and T. Then I added k and Epsilon.
3. After this, when I RUN the solver, it gives the following error:
--> FOAM FATAL IO ERROR: cannot find file file: /home/openfoam/run/final_geometry_turbulent/0/fluid/alphat at line 0. From function regIOobject::readStream() in file db/regIOobject/regIOobjectRead.C at line 72.
I don't know why what is the function of this file in turbulence modelling. because when I simulated turbulence model in simpleFoam solver, it didn't ask for it. But here in chtMultiRegionSimpleFoam it asks for it. I was thinking may be this solver needs alphat also to model turbulence flow, but I am not sure about it.
And the basic question I also want to ask that, Does this solver supports Turbulent flows OR not?
I shall be very thankful if you can help me out in this.
Thank you
Raza
Hi Sita Drost ,
Thank you so much for your reply.
I applied the changes you mentioned. But when I RUN the solver it gives the following error:
--> FOAM FATAL IO ERROR: cannot find file file: /home/openfoam/run/final_geometry_turbulent/0/fluid/alphat at line 0. From function regIOobject::readStream() in file db/regIOobject/regIOobjectRead.C at line 72.
Then What I did is that I copied that file from OpenFoam tutorials and put in the 0/fluid/ directory.
But it gave the same error. then I Opened the alphat file and copied its content and pasted in system/fluid/changeDictionaryDict, where I put the boundary conditions for p,U,T,k,Epilson etc.
Then, it gave me the same error, Then I also put the file in 0/ directory. where I have all other parameters also(p,U etc).
After this, the strange thing happens, when I RUN the solver, it says that
--> FOAM FATAL ERROR: cannot be called for a calculatedFvPatchField on patch inlet of field U in file "/home/openfoam/run/final_geometry_turbulent/0/fluid/U" You are probably trying to solve for a field with a default boundary condition. From function Foam::tmp Foam::calculatedFvPatchField::gradientInternalCoeffs() const [with Type = Foam::Vector] in file fields/fvPatchFields/basic/calculated/calculatedFvPatchField.C at line 187.
Now, if I simply remove the alphat entries from my system/fluid/changeDictionaryDict. it gives again the first error.
M not getting, what exactly is happening here.
I shall be very thankful if you can help me
Thank you
Raza
It should support turbulent flows. But onestly no idea about what alphat is. Units?
F
Hi Franco Concli ,
alphat is the Turbulent thermal diffusivity. I figured out the problem. Now, my solver is running but it stops right after 2 3 iterations saying
"Maximum number of iterations exceeded"
I have a question here, what is "time step continuity error"? because in my solver log file, its value is much higher.
Thank you
Time step continuity error Can appear if you have closed domains. It is not a problem of how your model is set up. But the sum of the fluxes across the boundaries is not zero due to numerical/mesh errors.
franco
Thank you for your reply.
Ok. so where could be the problem? because the solver is running without error with the laminar flow.
When I change the flow to turbulent by including k, Epsilon, alphat, and nut in my simulation. Then this error comes.
Is it due to the wrong boundary conditions for these parameters? I mean, what could be the reasons of non-zero fluxes across the boundaries.
Actually I am new to OpenFoam, so don't have idea of so much things.
Hopefully you can help.
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