# Pipe flow developing too quickly

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

 January 7, 2013, 06:09 Pipe flow developing too quickly #1 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 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

January 7, 2013, 06:36
#2
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,752
Rep Power: 41
Quote:
 Originally Posted by qrie 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

 January 7, 2013, 07:04 #3 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 I have tried it for Re 10 and 100. Encountered the same problem in both cases.

January 7, 2013, 07:43
#4
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,752
Rep Power: 41
Quote:
 Originally Posted by qrie 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?

 January 7, 2013, 07:47 #5 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 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.

 January 7, 2013, 08:30 #6 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 And I checked now, and turns out - yes for both I get it at the same x/D!

January 7, 2013, 08:41
#7
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,752
Rep Power: 41
Quote:
 Originally Posted by qrie 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?

 January 7, 2013, 08:43 #8 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 Ok, will do that. I have given convective outflow bcs.

January 7, 2013, 09:00
#9
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,752
Rep Power: 41
Quote:
 Originally Posted by qrie 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 ...

 January 7, 2013, 09:06 #10 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 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?

January 7, 2013, 11:49
#11
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,752
Rep Power: 41
Quote:
 Originally Posted by qrie 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

 January 8, 2013, 05:30 #12 New Member   Join Date: Jun 2010 Posts: 20 Rep Power: 9 Yeah velocity is not diverging, however if I increase the pipe length too much it does.

 Tags development length, pipe flow

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Primadhani FLUENT 1 May 11, 2011 20:41 Saima CFX 1 January 10, 2011 17:41 pertupd ANSYS 0 August 12, 2009 08:36 Atit CFX 2 November 9, 2004 18:43 Tom Cloutier Main CFD Forum 0 April 20, 2003 13:19

All times are GMT -4. The time now is 08:50.