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-   -   Fluent 5.0 boundary condition issue with RSM (http://www.cfd-online.com/Forums/main/1412-fluent-5-0-boundary-condition-issue-rsm.html)

Flav October 18, 1999 17:37

Fluent 5.0 boundary condition issue with RSM
 
I'm in a french school of engineering, and I'm studying the 2D test case of a flate plate boundary layer with RSM model.

I have some experiment data from Smith and Smits experiment : the velocity inlet is defined by profiles for : u, v, uu, vv, ww, uv.

The purpose of my study is to modelise this particular boundary layer.

The issue that I can't manage to solve is the following : the profiles for uu, vv, and ww all should start at zero, from an experimental point of view.

Therefore, I put a point at the beginning of the all profiles, which coordinates are : x:0, y:0 uu:0 (the same for vv and ww). But when i plot uu=f(y), i can see that uu, vv and ww don't equal zero at the wall contact. Very strange, since the .prof files specifie that it should ! Why doesn't Fluent agree to set the wall values to zero ???

Thanks in advance if you can help. Flav

david October 19, 1999 23:40

Re: Fluent 5.0 boundary condition issue with RSM
 
Dear Flav,

Because of the control volume method Fluent takes, the data you see is the average value of the control volume near the boundary, not the boundary value you specified. I think the Fluent reference books do not explain this clearly.

You can plot the boundary value using Fluent's XY plot option. I believe you can see the correct results.

Regards, david


Flav October 20, 1999 04:57

Re: Fluent 5.0 boundary condition issue with RSM
 
Dear David,

First of all thanks a lot for answering my question. You're right when you say that what i see is the average value near the boundary layer. But in my case, the trouble is that it's not an average problem, since the value of uu set by Fluent at 0.0 is 6.0, whereas the whole profile should never exceed 4 according to my fluent .prof file !

In Fluent, i use the XYPLOT function, then i look at the Inlet profiles : 1) for velocity magnitude 2) for uu Reynolds stresses

Both of them where initialized at the inlet using .prof files. Both start by :

(x (0.0 .....)) (y (0.0 .....)) (u (0.0 .....)) or (uu (0.0 .....))

The fact is that it works fine for u, but not for uu. Has Fluent got a special treatment for the latter which could explain my problem ?

(Note that in XYPlot, turning On/Off the "Node value" option doesn't make a huge difference.

Cheers Flav



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