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

Boundary condition for non newtonian flow (need to solve a differential equation)

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 14, 2011, 00:17
Smile Boundary condition for non newtonian flow (need to solve a differential equation)
  #1
Member
 
Guifan Li
Join Date: Apr 2011
Location: New York City, U.S.
Posts: 96
Rep Power: 6
liguifan is on a distinguished road
Hi,

I am now to use non-newtonian boundary inlet condition for my pipe. But as I notice that:

As the velocity profile is not pure parabolic shape. I need to solve the following equation

p+(1/r)*(d/dr)*[r(A+(A-B)/(1+K*(dV/dr))*dV/dr]=0

Can anyone tell me how to put this equation as boundary condition. Really stuck with it.

Please give me some hind on details.
liguifan is offline   Reply With Quote

Old   September 14, 2011, 01:46
Default
  #2
New Member
 
Claudio Wolfer
Join Date: Aug 2011
Posts: 9
Rep Power: 5
wWieWalter is on a distinguished road
Hi,

I never used such a BC, but I would solve your equation externaly (with Matlab) on a face equally like your's and the try to map these solution witch mapFields. I guess that it also should be possible to map the solution directly by a list of points.

Good luck.
wWW
wWieWalter is offline   Reply With Quote

Old   September 14, 2011, 02:51
Default
  #3
Member
 
Guifan Li
Join Date: Apr 2011
Location: New York City, U.S.
Posts: 96
Rep Power: 6
liguifan is on a distinguished road
Quote:
Originally Posted by wWieWalter View Post
Hi,

I never used such a BC, but I would solve your equation externaly (with Matlab) on a face equally like your's and the try to map these solution witch mapFields. I guess that it also should be possible to map the solution directly by a list of points.

Good luck.
wWW
Thanks for replying my post.

It worth a try by using directMapped. For this static case, if I can successfully export data in same format directMapped accept, that will do.

But what I actually want to do it to implement more complex function that velocity change will time and location. I am not sure directMapped can not manipulate that kind of thing. So I still need to solve an equation that U is a variable inside.

Do you have any idea to build a new boundary condition that can solve equations?

Cheers!
liguifan is offline   Reply With Quote

Old   September 14, 2011, 07:24
Default
  #4
Member
 
Eysteinn Helgason
Join Date: Sep 2009
Location: Gothenburg, Sweden
Posts: 52
Rep Power: 7
eysteinn is on a distinguished road
For a boundary condition changing with time and space you should be able to use groovyBC
See:
http://openfoamwiki.net/index.php/Contrib_groovyBC

/Eysteinn
eysteinn is offline   Reply With Quote

Old   September 14, 2011, 10:37
Default
  #5
Member
 
Guifan Li
Join Date: Apr 2011
Location: New York City, U.S.
Posts: 96
Rep Power: 6
liguifan is on a distinguished road
Quote:
Originally Posted by eysteinn View Post
For a boundary condition changing with time and space you should be able to use groovyBC
See:
http://openfoamwiki.net/index.php/Contrib_groovyBC

/Eysteinn
Hi Eysteinn,

Thank for replying.

groovyBC is a very powerful tool. But it lack a function I need to implement my velocity.

My velocity is dependent on time and locatation.

It is like something u(r,t)= real(i*exp(i*w)* Bessel(i*t))

where i is complex number and w is constant. Bessel is the Bessel function that can resolve complex number( This is not conclude in the OpenFOAM). I think the only way to do is to import a math libarary that can resolve Bessel(i*t).

That why I want to implement a new boundary in fvPatchfield.

Cheers!
liguifan is offline   Reply With Quote

Old   September 15, 2011, 07:48
Default
  #6
Assistant Moderator
 
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,912
Rep Power: 40
gschaider will become famous soon enoughgschaider will become famous soon enough
Quote:
Originally Posted by liguifan View Post
Hi Eysteinn,

Thank for replying.

groovyBC is a very powerful tool. But it lack a function I need to implement my velocity.

My velocity is dependent on time and locatation.

It is like something u(r,t)= real(i*exp(i*w)* Bessel(i*t))

where i is complex number and w is constant. Bessel is the Bessel function that can resolve complex number( This is not conclude in the OpenFOAM). I think the only way to do is to import a math libarary that can resolve Bessel(i*t).

That why I want to implement a new boundary in fvPatchfield.

Cheers!
WolframAlpha informs me that your expression is

Imag(e^(i w) (i t)^n t^-n I_n(t))

with I_n being the modified Bessel function. That shouldn't be to hard to get to a pure "real" form (especially if n=0)
gschaider is offline   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
Domain Imbalance HMR CFX 3 March 6, 2011 21:10
External Radiation Boundary Condition (Two sided wall), Grid Interface CFD XUE FLUENT 0 July 8, 2010 06:49
How can apply mass flow rate boundary condition? Sima Phoenics 1 December 1, 2007 19:55
Slip boundary condition what is inside normunds OpenFOAM Running, Solving & CFD 2 June 4, 2007 06:45
New topic on same subject - Flow around race car Tudor Miron CFX 15 April 2, 2004 06:18


All times are GMT -4. The time now is 10:14.