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-   -   about 3ddp &3d (http://www.cfd-online.com/Forums/fluent/33513-about-3ddp-3d.html)

zwdi April 18, 2004 13:15

about 3ddp &3d
 
Hi everyone,

I met reverse flow in my 3DDP calculation when I used velocity and turbulent parameter(k,epsilon)UDF as inlet boundary conditions. I want to initializ calculation from velocity inlet. When I choose calculate from velocity inlet,even though my velocity inlet has value larger than 0, Fluent only use 0 as initial velocity value. But when I change calculation from 3ddp to 3d, Fluent can use my current velocity profile value as the initial value. Also reverse flow disappeared in my calculation. For my case, I think results got from 3ddp is much better than those got from 3d. So could somebody know why I could not initialize calculation from my current velocity value(not 0) when I use 3ddp? Add one point, for constant velocity inlet value and constant turbulent parameters, there is no this problem. Only by using UDF turbulent parameter and velocity inlet and 3ddp, this problem happened.

Thanks a lot.

Best regards, Zwdi

co2 April 18, 2004 14:19

Re: about 3ddp &3d
 
what do you mean by UDF turbulent parameter ?

zwdi April 18, 2004 14:36

Re: about 3ddp &3d
 
Thanks for your response.

I have the experimental data of turbulent intensity and turbulent length sacle for inlet boundary conditions. Then I can calculate turbulent kinetic energy and turbulent dissipation rate for inlet boundary conditions. By using UDF I can input these data into Fluent boundary conditions panel. Same situation is for velocity inlet boundary conditions. The problem is that Fluent could not set the initial velocity value as my current velocity value even though I initialized from velocity inlet. Fluent always set initial velocity value as 0m/s. In this case, reverse flow appeared in my calculation, which affects my results convergence. This problem disappeared when i use constant turbulent parameter(such as intensity 10%, length scale 1m). And if I changed from 3ddp to 3d, this problem also disappeared. I don't know what causes this problem. Thanks again for your time.

Best regards, Zwdi


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