# Extracting boundary conditions ?

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 September 3, 1999, 03:07 Extracting boundary conditions ? #1 Tim Franke Guest   Posts: n/a Could someone give me some hints for the following problem? To simulate the flow in a short tunnel caused by wind blowing directly on one entrance I found out that I have to place the inflow and outflow bc's far away from the tunnel (approx. 2km with 240m tunnel lenght) In order to get some detailed flow patterns in the tunnel caused by obstacles I have to refine the grid in the tunnel. Now I want to cut my former huge flow field remaining only a short volume (e.g. 20m) at the two entrances to save grid cells. What are possible bc's that I can extract from my first run to the decreased flow field ? Cheers, Tim

 September 3, 1999, 12:33 Re: Extracting boundary conditions ? #2 John C. Chien Guest   Posts: n/a (1). The information is not enough to know the geometry and the method used. (2). But, you can try to used the velocity and the pressure computed from the previous large domain problem and used it directly as the inlet conditions for the reduced size problem.

 September 3, 1999, 13:38 Re: Extracting boundary conditions ? #3 Janna J. Guest   Posts: n/a u can use different sizes of grids for different domains to save the overall size since the inlet/outlet extensions are necessary for the flow to develope.

 September 6, 1999, 03:09 Re: Extracting boundary conditions ? #4 Tim Franke Guest   Posts: n/a For an inlet condition I can either set the velocities or the pressure that I have got from the large domain calculation. What would you suggest ? Tim

 September 6, 1999, 14:28 Re: Extracting boundary conditions ? #5 John C. Chien Guest   Posts: n/a (1).The velocity.

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