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-   -   URGENT HELP!!!!! (http://www.cfd-online.com/Forums/fluent/49946-urgent-help.html)

simone b. December 2, 2008 01:58

URGENT HELP!!!!!
 
Hi everyone,

I'm trying to simulate the flow around ship and I use multiphase flow VOF in FLUENT for analize this type of problem.

I have tryied the Wigley Hull test and i've got very good results but for a real hull the setting used for Wigley doesn't work very well

I have some problem about this simulation:

I don't have convergence with nothing of turbulence model used (RSM and k-w SST).

What can i do?? What type of setting is required??

If someone have any information or solution fot this type of problem please send me at my email : simone.bartesaghi@alice.it

Thank's for attention.

regards, simone

NAGA December 2, 2008 04:41

Re: URGENT HELP!!!!!
 
HI,

When u solve any Multiphsae problem pls do in the following way in which I used to do and had some success.

S1:Solve the problem with single phse for convergence for laminar flow.

S2:include multiphase and try to convege.

Even here if u go step by step like if ur Boundary condition say velocity x m/s, start with x/2 or x/4 and slowly march towards x if there is problem.

S3:Then include Turbulence model and solve it.

pls do note that Mass flow bc cannot be any of the MP models if all phases are incompressible.

pls try these and get back if needed.


simone b. December 2, 2008 05:20

Re: URGENT HELP!!!!!
 
Ok, I'll try this procedure. After that i post my result. if i have more problem i ask in the forum

Thank a lot

simone b. December 2, 2008 05:26

Re: URGENT HELP!!!!!
 
with single phase, the case run very well;

with coarse mesh with y+=600, the multiphase VOF in FLUENT run and give me a free-surface similar to that of the towing tank, but forces aren't correct!!!

With finer mesh (y+=50) the case diverge after 200 iteration...I don't have any idea for adjust this....

NAG December 2, 2008 06:17

Re: URGENT HELP!!!!!
 
hi, with y+ =600 i guess there wouldnt be no problem apart from forces..right.Now do change the Turbulence model one by one and check for that...possibly if your force is relying on pressure drag choose KE realizable with pressure gradient on...How much variation u get from real value?

simone b. December 2, 2008 06:52

Re: URGENT HELP!!!!!
 
Now i'm interested in only convergence of case, but my little experience with Wigley hull model tell me that with y+=300 the difference between force was about 40%, and with y+<50 with RSM is 0.5%


NAGA December 3, 2008 05:42

Re: URGENT HELP!!!!!
 
tell me, still findin problem



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