CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Pipe flow developing too quickly (http://www.cfd-online.com/Forums/main/111433-pipe-flow-developing-too-quickly.html)

qrie January 7, 2013 06:09

Pipe flow developing too quickly
 
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

FMDenaro January 7, 2013 06:36

Quote:

Originally Posted by qrie (Post 400450)
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?

qrie January 7, 2013 07:04

I have tried it for Re 10 and 100. Encountered the same problem in both cases.

FMDenaro January 7, 2013 07:43

Quote:

Originally Posted by qrie (Post 400461)
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?

qrie January 7, 2013 07:47

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 January 7, 2013 08:30

And I checked now, and turns out - yes for both I get it at the same x/D!

FMDenaro January 7, 2013 08:41

Quote:

Originally Posted by qrie (Post 400479)
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?

qrie January 7, 2013 08:43

Ok, will do that. I have given convective outflow bcs.

FMDenaro January 7, 2013 09:00

Quote:

Originally Posted by qrie (Post 400483)
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 ...

qrie January 7, 2013 09:06

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?

FMDenaro January 7, 2013 11:49

Quote:

Originally Posted by qrie (Post 400487)
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

qrie January 8, 2013 05:30

Yeah velocity is not diverging, however if I increase the pipe length too much it does.


All times are GMT -4. The time now is 23:28.