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-   -   why did the message always come out? (http://www.cfd-online.com/Forums/cd-adapco/53366-why-did-message-always-come-out.html)

Lee June 25, 2003 18:49

why did the message always come out?
 
When I run a roundpipe model(which is a semi-circe,at one end of the pipe the bounday type is inlet,the other end is outlet,and there is a symmetry boundary),I set the outlet boundary as the prescribed flow split(fs=1),but the information file always shows one warning message:

*** WARNING #001 *** FLUID INFLOW DETECTED AT SOME OUTFLOW BOUNDARIES WHERE MASS FLUXES ARE FORCED TO ZERO.

IF THIS CONDITION PERSISTS, YOUR RESULTS MIGHT BE WRONG

THE OUTFLOW BOUNDARY MIGHT NOT BE WELL SPECIFIED OR THE GRID MIGHT BE TOO COARSE NEAR THE OUTFLOW BOUNDARY

but I think I the meshs created are enough fine,so what is the reason to cause this warning message?

Thank you very much for your help!

Best Regards, Lee


4xF June 26, 2003 07:37

Re: why did the message always come out?
 
You get back flow at the outlet boundary. Solution: Use a pressure boundary instead.

Lee June 26, 2003 08:24

Re: why did the message always come out?
 
First,thank you very much! Second,I just want to know why the warning message always comes out and what is the proble reason to cause the problem.

I think if the model simply like this one can't be modeled by the inlet and outlet boundary type(note,the inlet flow velocity is 50+20*sin(time),and diameter is 38 milimeters),how can the star-cd model the other complex models?

So I really want to know where the problem is.

Thanks a lot for who can help me out this problem!

lee


marco June 27, 2003 04:48

Re: why did the message always come out?
 
Hallo!

If you are doing a subsonic transient calculation you shouldn't use 'OUTLET' but 'PRESSURE'. Look at the methodology manual, page 5-5.

Marco

4xF June 28, 2003 09:58

Re: why did the message always come out?
 
Small hint: Flow is unsteady with an unsteady boundary layer. So, it is most likely that you get back flow at the outlet and therefore a pressure boundary condition has to be applied instead of an outlet BC.


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