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-   -   Keeping freestream conditions... (http://www.cfd-online.com/Forums/cfx/18985-keeping-freestream-conditions.html)

 Arman A. May 15, 2002 19:07

Keeping freestream conditions...

I am working on a free flight analysis for a model airplane. I have a domain(rectangular box)that is 10 times larger than the model. I am trying to figure out its stall angle by giving velocity components. I have the left vertical face and bottom face as a velocity inlet, to force freestream conditions, and pressure outlet at the right vertical face. What I have observed is that the flow loses its angle of attack as it approaches the model. I have not used the pressure far-field option because it is incompressible flow(40mph). Please let me know if there are any other options to keep the flow at the same angle of attack as it approaches the model.

 Robin May 16, 2002 08:25

Re: Keeping freestream conditions...

Hi Arman,

What boundary condition do you have a the top face?

As an alternative, you could specify the angle at the inlet on the front face, define a periodic between the top and bottom, and an outlet at the back. Your domain is large enough that there should be no interaction between the aircraft and the periodic.

Which code are you using?

Robin

 Arman A. May 17, 2002 06:48

Re: Keeping freestream conditions...

Hi Robin, thanks for replying. I have the top face as a wall which I'm sure is not the best approach for this problem. By code do you mean the program or the solvers? I am using Fluent 3d, segregated with standard k&e viscous model. Also I did not understand your definition of periodic. Is it a boundary condition type? I tried looking for it under the boundary conditions list and haven't been able to find it. I would appreciate it if you could clarify that for me. Thanks again.

Arman

 Robin May 17, 2002 21:36

Re: Keeping freestream conditions...

Hi Arman,

Well, to begin with this is the CFX users forum, so you may be better off posting this to the Fluent forum (or perhaps just switching to CFX :)

That said, you will have a lot of problems if your top boundary is a wall, since the boundary condition requires that the flow be parallel to it. As a start, you could switch it to an outlet.

Fluent does have a periodic boundary condition, although in Fluent 4 it is referred to a cyclic. Periodic boundaries are defined as pairs. The conditions at each boundary are identical, thus periodic (as though the domain were repeating infinately in this direction). Flow which exits one boundary will enter the other with the exact same characteristics.

Although your problem is not actually periodic, the large spacing between your aircraft and the boundary will be sufficient to eliminate most periodic effects.

Regards, Robin

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