# Wind Tunnel grid

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 June 20, 2001, 13:23 Re: Wind Tunnel grid #21 Garvin Forrester Guest   Posts: n/a That makes sense. You mentioned "all around the wall", you mean from the floor right. Are my B.C's O.K. Po,To at inlet: no-slip walls, slip floor: pressure ratio at exit.

 June 20, 2001, 13:45 Re: Wind Tunnel grid #22 John C. Chien Guest   Posts: n/a (1). If I were you, I would just use the simple non-slip boundary condition for all walls first. Just to see how it works. (2). If you have moving wall (floor) or something like that, you can always change it and check the effect. (3). I would also use the simple velocity inlet condition and downstream exit (parallel condition) condition first, and check the result. (4). Using inlet total pressure and exit static pressure conditions is also a standard approach. In your low speed flow, you can use either set of conditions.

 June 20, 2001, 18:42 Re: Wind Tunnel grid #23 Trac Guest   Posts: n/a So it's a ground effect problem - but you're modelling a slip wall in CFD when the wind tunnel wall won't be slip. Why not model exactly what's happening in the wind tunnel? If you want to get the same results from the wind tunnel as for the CFD you need to model the *exact* same thing. What is the ground doing in the wind tunnel?

 June 21, 2001, 08:47 Re: Wind Tunnel grid #24 Garvin Forrester Guest   Posts: n/a The grouind is stationery. Eventually I want to place a model in the tunnel. I have the Velocity and dynamic pressure in the section and boundary layer data. I agree with having no-slip on the walls. It must of been a typo. Any suggestions on time-step and CFL? I'm converging at over 3000 iterations(multi-grid). Does this sound right? This is my first time doing an internal flow problem.

 June 21, 2001, 13:34 Re: Wind Tunnel grid #25 John C. Chien Guest   Posts: n/a (1). The same story again. When you simulate a flow problem by CFD, remember to get the "mesh independent" solution. (2). Mesh refinement is required when dealing with viscous flows. (3). By the way, you could try to compute the flat plate flow ,say 200 FT long, and check your result against the test data or formula given in the Schlichting's book (boundary layer theory). (4). If you can't get the flat plate flow right, then don't expect to get good results for your wind tunnel.

 June 22, 2001, 07:11 Re: Wind Tunnel grid #26 Garvin Forrester Guest   Posts: n/a Thank you.

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