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

Pipe flow developing too quickly

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 7, 2013, 06:09
Default Pipe flow developing too quickly
  #1
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
Hi,

I am simulating the development of a pipe flow. At the inlet, uniform velocity is imposed and it reaches a parabolic profile somewhere downstream and becomes fully developed. My problem, however, is that, the location at which it reaches the parabolic profile is too close to the inlet (on comparing with results from journal papers). Any suggestions on why this might be happening?

Thanks in advance,
Qrie
qrie is offline   Reply With Quote

Old   January 7, 2013, 06:36
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by qrie View Post
Hi,

I am simulating the development of a pipe flow. At the inlet, uniform velocity is imposed and it reaches a parabolic profile somewhere downstream and becomes fully developed. My problem, however, is that, the location at which it reaches the parabolic profile is too close to the inlet (on comparing with results from journal papers). Any suggestions on why this might be happening?

Thanks in advance,
Qrie

what about your Reynolds number?
FMDenaro is offline   Reply With Quote

Old   January 7, 2013, 07:04
Default
  #3
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
I have tried it for Re 10 and 100. Encountered the same problem in both cases.
qrie is offline   Reply With Quote

Old   January 7, 2013, 07:43
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by qrie View Post
I have tried it for Re 10 and 100. Encountered the same problem in both cases.

you get the same lenght x/D both at Re=10 and Re=100? Are you sure that the solution corresponds to the analytical parabolic velocity profile?
FMDenaro is offline   Reply With Quote

Old   January 7, 2013, 07:47
Default
  #5
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
I meant I get fully developed profiles much earlier in both cases compared to the respective values in the journal paper. Yes, the solution matches the Poiseuille parabolic profile.
qrie is offline   Reply With Quote

Old   January 7, 2013, 08:30
Default
  #6
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
And I checked now, and turns out - yes for both I get it at the same x/D!
qrie is offline   Reply With Quote

Old   January 7, 2013, 08:41
Default
  #7
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by qrie View Post
And I checked now, and turns out - yes for both I get it at the same x/D!
of course something wrong must be in the code... check in the code the actual value used for the Re number, try also if Re=500 gives you again the same x/D value ... what about the outflow BC?
FMDenaro is offline   Reply With Quote

Old   January 7, 2013, 08:43
Default
  #8
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
Ok, will do that. I have given convective outflow bcs.
qrie is offline   Reply With Quote

Old   January 7, 2013, 09:00
Default
  #9
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by qrie View Post
Ok, will do that. I have given convective outflow bcs.

Assuming that the code has no bug, what about the grid sizes and discretization of the convective terms? If your grid is too coarse and you are using first order upwind, maybe you have so much artificial viscosity that overcome the real one... but I am more for some bug ...
FMDenaro is offline   Reply With Quote

Old   January 7, 2013, 09:06
Default
  #10
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
The code uses second order central differences, and isn't coarse. I have refined it to the same size as in the paper. Its a direct solver, no artificial viscosity is used. Thanks, I will check for any bugs. Have already done that actually. Is there anything else that might be causing this?
qrie is offline   Reply With Quote

Old   January 7, 2013, 11:49
Default
  #11
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by qrie View Post
The code uses second order central differences, and isn't coarse. I have refined it to the same size as in the paper. Its a direct solver, no artificial viscosity is used. Thanks, I will check for any bugs. Have already done that actually. Is there anything else that might be causing this?
I have no other idea than checking for some bug in the input data... maybe somehow the value of the Re number is fixed to a small value...check also for the divergence of the velocity if is zero everywhere
FMDenaro is offline   Reply With Quote

Old   January 8, 2013, 05:30
Default
  #12
New Member
 
Join Date: Jun 2010
Posts: 20
Rep Power: 16
qrie is on a distinguished road
Yeah velocity is not diverging, however if I increase the pipe length too much it does.
qrie is offline   Reply With Quote

Reply

Tags
development length, pipe flow


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[ASK] Flow in Corrugated Pipe with FLUENT Primadhani FLUENT 1 May 11, 2011 21:41
Pipe Flow Saima CFX 1 January 10, 2011 17:41
flow in perforated pipe distributor pertupd ANSYS 0 August 12, 2009 09:36
outlet boudary condition for a flow in the pipe Atit CFX 2 November 9, 2004 18:43
stepped pipe flow Tom Cloutier Main CFD Forum 0 April 20, 2003 14:19


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