CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Shall I use ideal gas model or other?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   January 19, 2006, 10:36
Default Shall I use ideal gas model or other?
  #1
summer
Guest
 
Posts: n/a
Hello, friends. Now I am trying to solve a 3d problem of a channel at steady state. My boundary condition is that the velocity inlet is 50m/s, and pressure outlet is 1atm. Others are solid wall. I would like to get the pressure drop from inlet to outlet. I try to use the ideal gas model in the materials and realized k-e model. How should I set the k and e at the inlet boundary condition? The default of both are 1. I used the default ones, but I can not get the convergent solution. Could you have any idea that how to solve it? Thanks!
  Reply With Quote

Old   January 19, 2006, 10:55
Default Re: Shall I use ideal gas model or other?
  #2
summer
Guest
 
Posts: n/a
By the way, I use the air as the flow and the channel is not staight. The cross section of the channel is semi-circular. Thanks!
  Reply With Quote

Old   January 20, 2006, 04:59
Default Re: Shall I use ideal gas model or other?
  #3
kharicha
Guest
 
Posts: n/a
Classical things to verify before changing the model:

1) Grid? y+ at the walls?

2) verify that your velocity profile at the inlet is not too simplistic, compare the velocity profile at some distance form the inlet, with the one at the inlet.

3) Do the same with k and epsilon, it should not be too different.

  Reply With Quote

Old   January 22, 2006, 16:01
Default Re: Shall I use ideal gas model or other?
  #4
summer
Guest
 
Posts: n/a
Hello, thanks ! What do you mean that the velocity profile at the inlet is not too simplistic. Does it mean the velocity profile at some distance from the inlet should be similar to that at the inlet?

Thanks!
  Reply With Quote

Old   January 23, 2006, 03:38
Default Re: Shall I use ideal gas model or other?
  #5
kharicha
Guest
 
Posts: n/a
It depends on the geometry of your duct, but usually it is not so different...

take a straight duct, assume you want to simulate the flow development along the duct...if you take a constant velocity at the inlet you will have some convergence problem. Because you have a reorganisation of the flow at the vicinity of your inlet. In addition to that a flat velocity profile never exists in reality, the velocity has to be equal to zero at the walls. I assume you model a laminar flow, if it is the case it is better to impose a parabolique profile. If the flow is turbulent, then take a constant velocity, but be carefull on the wall functions tat you will use (depends on y+).
  Reply With Quote

Old   January 23, 2006, 11:38
Default Re: Shall I use ideal gas model or other?
  #6
summer
Guest
 
Posts: n/a
O.K, thanks! I will try. Yesterday I changed the solver from seperated to coupled,and used the velocity of about 60m/s(it should be turbulent, I think). So I used k-e and ideal gas. It seemed to work, but when the residual went to 5*10-3, it oscillated. So do you know why? Thanks again. I would like to plot y+ and have a look at it. summer
  Reply With Quote

Old   January 24, 2006, 11:43
Default Re: Shall I use ideal gas model or other?
  #7
summer
Guest
 
Posts: n/a
By the way, the residual of continuty increases. I do not know why and how to make it smaller. Thanks!
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
User Defined Real Gas Model john FLUENT 1 October 25, 2012 14:05
Constant velocity of the material Sas CFX 15 July 13, 2010 08:56
Help!! calculate gas density by ideal gas law Mahe Phoenics 1 January 26, 2010 04:57
question about ideal gas thermal flow yong Main CFD Forum 0 January 7, 2006 00:58
Using ideal gas law to simulate pressure decline Björn Mattsson FLUENT 5 September 5, 2005 04:03


All times are GMT -4. The time now is 16:39.