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some problem about the library case

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Old   March 3, 2001, 12:14
Default some problem about the library case
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1 In the phoenics library case, the case v407 descrbed air flow around buildings. I have some question about the example. First, why it use laminar model? I think it should choose a turbulence model. Second, the building is so close with the boundary, I am afraid it can not express the flow correctly? 2 We know that wind velocity change with the height above the ground. But the inlet attribute define the velocity as a constant. How to express the velocity change in the inlet attribute? thank you for your help.
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Old   March 8, 2001, 10:42
Default Re: some problem about the library case
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Dear XVJ

In my oppinion the Phoenics library cases are only for illustrate some capabilities of the code, applied to quite simple configurations.

Don't worry about boundary conditions. Usually the tipical CO=1000*FIXP and VAL=0.0, allows the flow goes out or coming in through the boundary with good behaviour depending on the pressure calculation.

To implement the velocity changes over your "inlet" condition you should check for the Phoenics version you have. If it is re-compilable the you can go on, otherwise, as far as I know, you have no choise.

In case you have re-compilable version then you have to introduce some Fortran lines inside the GROUND.F (or GROUND.FOR) file, and to use the flag VAL=GRND in the INLET function (Q1 file).

Into GROUND file firstly you should reserve space for certain variables (use the funcion "make" in Group 1)and also the indexes: dxu2d, dyv2d or dzwnz for the distance between velocity cells, u1, v1 and w1 for velocities and p1 for pressure. You should having in mind that the pressure cells are displaced with respect to the velocity cells (if you are using staggered grid -default in Phoenics-) and you should take xg2d, yg2d and dz as the indexes for these cells in X, Y and Z direction respectively.

The inserted code should consider this GROUND indexes and the velocity distribution you want to introduce. Having inserted VAL=GRND you should move to the Section 12 inside the GROUP 13 into the GROUND file. Type there the cicles to assign the VALues to the variables the index for each is VAL, so you should separate the assigment for each var (use INDVAR).

Of course I have assumed you know how to manage the F array. If not, this will be a little more difficult but not imposible to explain. Let me know how far can you reach with this lines.

Best wishes

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