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Old   June 13, 2006, 01:58
Default congence???
  #1
prayskyer
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i did some a computation! i chose air(idea gas) as fluid, and reference pressure=14atm;energy model----total energy;k-e model;intial condition=automatic

BC:inlet---mass rate;total tempreture=1200K; outlet----reletive pressure=-600000Pa;

it never congence,but when i turn outlet's reletive pressure to 0Pa,it congence,it that 14atm have some problem?if not,where can i modify them?

how this could happen,and what can i do? thanks in advance!!!

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Old   June 13, 2006, 02:53
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Fred
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Do you mean convergence?

A negative pressure is not very well chosen because there is no negative pressure in the universe. Under domain you can set the reference pressure to 0 atm and then calculate or set every pressure as it is in real.
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Old   June 13, 2006, 03:28
Default Re: congence???
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prayskyer
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but 14atm-600000Pa=800000Pa,it's a positive value!

if i set 0 for reference pressure,then the outlet's pressure will really become negative value (0--600000Pa=-600000Pa)
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Old   June 13, 2006, 15:15
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Fred
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Then set the outlet to 8 atm. Where is the problem?
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Old   June 13, 2006, 20:50
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prayskyer
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haha,i found it!the inlet is subsonic,but outlet is supersonic,i set them wrong!

so this flow from subsonic area into supersonic area,is some suggestions i can concern?

thanks all of u
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Old   June 13, 2006, 21:55
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prayskyer
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i am wrong again!it's still subsonic!

the problem still on!!!
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Old   June 14, 2006, 06:45
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Fred
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YOu can try to change the outlet to an opening. This is more stable then a subsonic outlet.
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Old   June 14, 2006, 07:28
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prayskyer
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i try!but it seems not that problem there!

seems that outlet's relative pressure -600000,

IN CFX,can i put negative value like -600000 there?
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Old   June 14, 2006, 10:48
Default Re: congence???
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Fred
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i dont see the benefit in doing this. why do you do this? why not 0atm and 8 atm?
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Old   June 14, 2006, 20:08
Default Re: congence???
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prayskyer
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0atm and 8atm can't congence either!

i try once! i don't know why?

how long can i solve this problem,help me!

thanks
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Old   June 14, 2006, 20:12
Default Re: congence???
  #11
prayskyer
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could anyone help me!

prayskyer@yahoo.com.cn

this is my e-mail!i can send this to u!

thanks a lot!

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