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-   -   congence??? (https://www.cfd-online.com/Forums/cfx/22702-congence.html)

 prayskyer June 13, 2006 01:58

congence???

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!!!

 Fred June 13, 2006 02:53

Re: congence???

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.

 prayskyer June 13, 2006 03:28

Re: congence???

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)

 Fred June 13, 2006 15:15

Re: congence???

Then set the outlet to 8 atm. Where is the problem?

 prayskyer June 13, 2006 20:50

Re: congence???

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:)

 prayskyer June 13, 2006 21:55

Re: congence???

i am wrong again!it's still subsonic!

the problem still on!!!

 Fred June 14, 2006 06:45

Re: congence???

YOu can try to change the outlet to an opening. This is more stable then a subsonic outlet.

 prayskyer June 14, 2006 07:28

Re: congence???

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?

 Fred June 14, 2006 10:48

Re: congence???

i dont see the benefit in doing this. why do you do this? why not 0atm and 8 atm?

 prayskyer June 14, 2006 20:08

Re: congence???

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:)

 prayskyer June 14, 2006 20:12

Re: congence???

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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