Wind tunnels are usually built in a way o produce uniform flow before reaching the object. Therefore, you could use velocity inlet as BC for inlet and pressure outlet as the B.C for outlet. This is a normal B.C for Fluent if your are using it. Otherwise you should find equivalent.

you must be given the same conditions in the experimental test.

velocity inlet and the other sides pressure outlet

Dear Aamir,

my modest recommendations are:

1. http://www.diva-portal.org/smash/get/diva2:1016255/FULLTEXT02.pdf

2.http://cdn.intechopen.com/pdfs/43193/InTechDesign_features_of_a_low_turbulence_return_circuit_subsonic_wind_tunnel_having_interchangeable_test_sections.pdf

3. Stark, Will (2010): Building and Testing a Wind Tunnel. Applied Science Research Paper. URL: http://roundtable.menloschool.org/issue8/6_Stark_MS_

Roundtable8_Winter2011.pdf

4.] Mehta,R.D.; Bradshaw,P. (1979): Design Rules for Small Low-Speed Wind Tunnels. The Aeronautical Journal of the Royal Aeronautical Society, Vol. 83, pp. 443-449.

5.Chen, Kai; Jin, Xin-Yang ; Zhao, Ji-Da (2009): Design and Characteristics of a Large Boundary - Layer Wind Tunnel with Two Test Sections. The Seventh AsiaPacific Conference on Wind Engineering,Taipei / Taiwan.

With great respect

Dušan Regodić Thank you so much .

Best type of BC'S are conditions where you specifiy everything. However, the pressure inlet and outlet BC's are the most physically accurate cond. for such problems.

You should embed the free stream turbulence information also. Otherwise, what is the difference between closed and open test section? Forget about Fluent! Such software should not dictate what one should do. It should be other way round. The software should be able to simulate physical conditions.

Adding to the previous answers, I would also like to point out the importance of the domain extents for simulation. If you consider a truncated domain for the test section, then chances are that the a uniform velocity BC at inlet would not depict the correct developed boundary layer; hence best to start from an extended upstream location. As for the exit, again, the best recourse would be to take an extended domain and apply Riemann BCs. I suppose Fluent has it listed as pressure far-field BC.

One thing I would like to add concerns the outlet BCs. You may want to invest in non-reflecting boundary conditions as opposed to a Dirichlet pressure condition. Some solvers have an in-built characteristic-based BC for such situations.

If you want to venture for more sophisticated (less numerically dispersive) conditions, maybe you can take a look at the perfectly matched layer (PML) approach. Note though, the latter uses a fictitious zone and modifies the governing equations in them; albeit, these BCs usually need to be added manually to most codes (if open-source, at least). Then again, it all boils down to how accurate a solution you intend to get in a realistic timeframe. Good luck!

Not sure what kind of results/research you are trying to validate because that might influence how to answer the question. Is it surface pressures or integrated forces? What's the target Re range to know the susceptibility to flow separation across the range of angle of attack? Or is it a bluff body? Or is it simply flowfield data acquired through diagnostics (PIV, Hot-Wire, etc)?

All of these questions point towards the relative importance of reproducing the inlet geometry. Most tunnel inlets maintain some level of flow angularity in the entry to the test section. This is a good reason (along with boundary layer growth mentioned by above) to include the inlet geometry. Since it's a low turbulence tunnel, presumably tunnel turbulence intensity is relevant and should thus be correctly modeled.

Freestream component turbulence intensity reduction as a function of inlet to test section area ratio is given by 1/C^2 where C is the contraction ratio. So if you know the test section turbulence intensity you could back out what it would be post-screen and post-honeycomb or the equivalent of your inflow boundary.

Good luck indeed!