|
[Sponsors] |
Clarification needed for zero-flux boundary condition type |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
February 26, 2013, 20:07 |
Clarification needed for zero-flux boundary condition type
|
#1 |
Member
Join Date: Aug 2011
Posts: 33
Rep Power: 15 |
Hi folks!
I believe my question is generic to any of CFD software so I decided to put it in here. I have a really simple question that I cannot get it out of my head, regarding the zero flux boundary condition... For example, if I have a flow in a simple straight pipe. I would like to assign some BC's to my computational domain and I understand the velocity inlet BC, outlet BC, etc. I understand that the velocity, mass flux, temperature, pressure, etc. are specified with a constant value. (Dirichlet condition?) However, when it comes to the zero flux (Neumann condition?) for the remaining variables, referring to the textbooks and published paper, everyone seems to mention the word "zero flux" and give a mathematical expression of, like, dX/dn = 0 (where X is arbitrary variable and n is the normal vector to the surface) How does a gradient of an arbitrary variable (dX/dn) relate to a zero flux? I do not quite understand what is going on here. Zero flux means there is no flow of X across the face, doesn't it? But, a zero gradient of something, from my understanding, only means there is no change in the variable X in a particular direction which is normal to the surface in this case? Could you please clarify my question? Cheers, pchoopanya |
|
February 27, 2013, 05:38 |
|
#2 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,833
Rep Power: 73 |
Quote:
for example, see the Fourier flux q = - k Grad T at an adiabatic wall. Then q =0 implies dT/dn = 0. Hence, you have to discretize the zero normal derivative and computing your wall temperature that ensure the condition q=0 |
||
March 15, 2013, 16:48 |
|
#3 |
Member
Join Date: Aug 2011
Posts: 33
Rep Power: 15 |
thank you so much for your comment
|
|
March 16, 2013, 05:22 |
|
#4 | |
Senior Member
Join Date: May 2012
Posts: 551
Rep Power: 16 |
Quote:
I think the zero flux condition usually (always?) is followed by a zero normal velocity condition as well. So in this case we have zero diffusive flux across the boundary and the zero normal velocity condition should ensure zero convective flux across the boundary. |
||
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[Commercial meshers] Mesh conversion problem (fluent3DMeshToFoam) | Aadhavan | OpenFOAM Meshing & Mesh Conversion | 2 | March 8, 2018 01:47 |
Difficulty in calculating angular velocity of Savonius turbine simulation | alfaruk | CFX | 14 | March 17, 2017 06:08 |
Domain Imbalance | HMR | CFX | 5 | October 10, 2016 05:57 |
RPM in Wind Turbine | Pankaj | CFX | 9 | November 23, 2009 04:05 |
CFX doesn't continue calculation... | mactech001 | CFX | 6 | November 15, 2009 21:25 |