[paullees]

I am very new to openFoam (just installed it) but before I dive into it I would like to know if it can do what I would like to do. Can you simulate a fan via the use of rotating reference where all non moving parts are bodies of revolution about the fan?
Is it also possible to use multiple stationary and rotating reference frames?

Thanks in Advance.

[mattijs]

No, there is no pre-supplied solver that can do what you want.

(however OpenFOAM was created to implement these kinds of problems easily and efficiently so you might want to try implementing it yourself)

[henry]

Any code can easily be changed to operate in a rotating reference frame, e.g. for simpleFoam the momentum equation would be:

UEqn
(
fvm::div(phi, U)
- fvm::Sp(fvc::div(phi), U)
+ turbulence->divR(U)
+ (2*Omega ^ U) // Coriolis force
+ Fcent
);

where e.g.

dimensionedVector Omega
(
"Omega",
dimensionSet(0, 0, -1, 0, 0),
vector(0, 0, 2*M_PI*1200/60)
);

// Calculate the centrifugal force
volVectorField Fcent = (Omega ^ (Omega ^ mesh.C()));


MRF is a lot more tricky and I will implement it as soon as it is important enough for someone to be prepared to sponsor the work.

[paullees]

Thanks for the info, I am not really at the level to start writing any code but I will be sure to watch and see what becomes avaiable. This type of method is vital for the design of many fluid handling devices so I hope it gets implemented soon.

[henry]

That all depends on someone paying for the work. I have been approached several times to implement MRF but so far no one has been willing to pay for my time to do it.

[paullees]

Even the SRF is very widely used though and would be an nice addition. Lets hope you can find someone in a position to put up the money.

[henry]

SRF is trivial and can be implemented in any solver by anyone using OpenFoam simply by including the source terms I posted above into the momentum equation. I don't think there is any need to us to include this as a standard feature in all solvers as the number of users needing it is not large enough to warrant the overhead and it can be added by them so easily.

[paullees]

Well maybe when I am feeling adventerous I will give it a go.

[olivier]

HI Henry,
I am implementing MRF method.
the velocity at cell P (in absolute frame) is related to the velocities at its neighboring cells.
So In order to convert the velocity in cell N ( which is the neighbor of P, P is adjacent to the interface and N is in the
rotating frame). I use a volVectorField F=Diag()*omega ^ mesh.C(), after that if cellI is not in the interface F[cellI]=0.

my questions is:

1-what you think about this Idea?
2-when I add this term in the momentum equation as:
U = rUA*(UEqn.H()-F) or by add it like source term.
I had the non realistic physical results.
what you think about that ?

If you have some suggestions, I'm very interested to know them.
thank you

[gameoverli]

Hi, Henry and foamers:

I am trying to use openfoam to simulate wind field in hurricane. one question would be how the coriolis force of earth is added in openfoam. by looking your message in this thread, it seems what I need to do is only finding out the omega vector of earth's rotation. however, I am trying to understand why you add a term fvm::Sp(fvc::div(phi), U) in U equation. does this have something to do with the coriolis force and Fcent you added in U equation?

thanks

[bfiedler]

This is new, and may have the information that you need:

http://openfoamwiki.net/index.php/Ho...Make_a_Tornado

[Whyman]

Hi guys!

I have only one question about what is written below.
How would you calculate the tangential force if the rotation "Omega" is not constant?

Thank you

Originally Posted by henry

Any code can easily be changed to operate in a rotating reference frame, e.g. for simpleFoam the momentum equation would be:

UEqn
(
fvm::div(phi, U)
- fvm::Sp(fvc::div(phi), U)
+ turbulence->divR(U)
+ (2*Omega ^ U) // Coriolis force
+ Fcent
);

where e.g.

dimensionedVector Omega
(
"Omega",
dimensionSet(0, 0, -1, 0, 0),
vector(0, 0, 2*M_PI*1200/60)
);

// Calculate the centrifugal force
volVectorField Fcent = (Omega ^ (Omega ^ mesh.C()));


MRF is a lot more tricky and I will implement it as soon as it is important enough for someone to be prepared to sponsor the work.

[impecca]

Does anyone can tell me why either multile or single reference frame (MRF, SRF) are not implemented in the transient solver? such as pisoFoam or pimlpeFoam?. is there any practical or physical reason? Please do shed some lights on my ignorance.

Yusik

[a_fluent]

Hello
i want to simulate a T channel in single rotating reference frame. i studied user guide and tutorial . according to them i should choose 2D option in solver ( Define-Solver-2D) not axisymmetric or axisymmetric swirl . but when i just choose 2D after that in defining boundary condition for fluid when i choose moving reference frame, it doesn't ask for rotational speed?
i would be grateful if anyone could help me.

[Big Kahuna]

Originally Posted by henry

That all depends on someone paying for the work. I have been approached several times to implement MRF but so far no one has been willing to pay for my time to do it.

Hello Henry,

I read your post from many, many years ago, in which you say you are willing to do coding for others if they pay you for your time. Are you still willing to offer your services for payment? I have a problem with OpenFOAM and I know I cannot solve it by myself. I need an expert to help me solve it.

Jack