
[Sponsors] 
April 28, 2013, 02:42 
arterial wall

#1 
Member
bitak
Join Date: Jul 2009
Posts: 56
Rep Power: 9 
Hello all.
I want to simulate arterial wall (free wall model) and so I should to define mass transfer condition in wall .( I need to have suction velocity=4e8 m/s and diffusion coefficient= 5e8 m^2/s) my geometry is a cylinder. my boundary condition: At inlet I have specific concentration. at outlet I have no change in concentration. at wall my concentration comes from mass transfer equation. How I can simulate this problem in CFX ????????????? Pleas answer to me. I really need to know 

April 28, 2013, 06:06 

#2 
Member
bitak
Join Date: Jul 2009
Posts: 56
Rep Power: 9 
I can not read your reply!!!!!!!!!!!!!!!!!!!!!!!!11


April 28, 2013, 06:41 

#3 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
Don't worry about the spam which was posted here before  I have removed the post and banned the user. What an idiot.
Now to answer your question.... First of all, you will need to define the X and Y directions and what the symbols in the equation mean. Without some definitions it is useless. But I can see two general approaches for modelling this mass transfer: 1) You can define a boundary condition and/or a source term at the arterial wall to model the mass flux through the artety wall. 2) You can put a solid domain around the blood domain to model the artery itself. You can then model diffusion in this as well, so the effect of the aretery wall is more directly modelled. Note that you will still need to specify a boundary condition on the outside face of the artery wall, it will just be a boundary condition more suited to the artery outside wall, which persumably means the interface to the intercellular region. 

April 28, 2013, 07:43 

#4 
Member
bitak
Join Date: Jul 2009
Posts: 56
Rep Power: 9 
Vw: suction velocity at wall
D: diffusion coefficient C: concentration Co: inlet concentration Cw: wall concentration 

April 28, 2013, 07:50 

#5 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
In that case the equation appears to be defining the concentration along the artery as a whole. That is the whole cross section is lumped together and a 1D approach used to model the concentration.
CFX is a 3D solver so cannot really model 1D effects. It models the 3D effects. So if you want to match the equation model in CFX I would set the inlet concentration to C0, the concentration at the walls at Cw and let CFX handle the rest. 

April 28, 2013, 08:08 

#6 
Senior Member
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 196
Rep Power: 6 
I don't know if it will be helpful but there is this paper:
Coupled Fluid–Structure Interaction Hemodynamics in a ZeroPressure State Corrected Arterial Geometry  Vavourakis, Papaharilaou, Ekaterinaris  Journal of Biomechanics, Volume 44, Issue 13, 2011
__________________
Lefteris 

July 1, 2013, 01:29 

#7 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 
hi，
have you solve your problem? do you konew how apply the @ outlet flux = 0? 

July 2, 2013, 09:01 

#8 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 

July 2, 2013, 18:50 

#9 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
The documentation describes source terms pretty well, have a read. I do not think the tutorials cover source terms so you might need to ask CFX support for an example.
But this application looks straight forward. In fact you might not need a source term at all. Define your C as an additional variable, put a flux defined as your final equation at the wall and an outlet condition on the end. This will do it  but it will be modelling the concentration in 3D, not 2D as you equation suggests. 

July 3, 2013, 02:18 

#10 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 
Thanks for your reply, I will read the source terms in the documentation carefully. Beginning of the simulation, I have the same idea as you. I defined volumetric additional variable. Although I could find the answer in "http://www.cfdonline.com/Forums/cfx/103928outletboundaryconditionadditionalvariable.html" for the outlet, I was puzzled by the boundary condition of unit concentration on the wall. In the mass transfer equation for the wall, cw is the concentration on the wall, note vw is the water infiltration velocity but the solute, D the kinematic diffusivity, ∂C/∂n the concentration gradient normal to the wall. cw is relationship with the∂C/∂n. And I am no idea about how to set the ∂C/∂n, maybe the source terms will work.
To be honest, I can finish the simulation in the fluent. In fluent, the diffusive flux is approximated in two parts: primary gradient and secondary gradient (this equal contains cw and∂C/∂n ). Then I get a new equal without ∂C/∂n. And the two macros in fluent are available to enable me to the necessary geometrical variables of the cell and calculates the secondary gradient term in equation respectively. The problem is that I failure to find the similar macros as the fluent. Any suggestion? Thanks! 

July 3, 2013, 07:22 

#11 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
In your equation I presume Cw is the concentration of the wall. What is Vw?


July 3, 2013, 09:16 

#12 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 

July 3, 2013, 19:10 

#13 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
Does that means the walls are porous and liquid is flowing through them?


July 3, 2013, 21:29 

#14 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 

July 4, 2013, 07:17 

#15 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
So how are you modelling the infiltration velocity if you do not have a porous domain?


July 4, 2013, 09:13 

#16 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 
well, in our simulation the vw is too small to induce the change of the velocity. So, it is logical to take this way. The problem is how to express ∂C/∂n in the cfx.


July 4, 2013, 16:28 

#17 
Member
bitak
Join Date: Jul 2009
Posts: 56
Rep Power: 9 
I think we should define additional variabel and the Vw is velocity for transport of paticles in the wall
in the wall BC for additional variable the transfer coefficient is true and (density*Vw) is mass flux in this option and value is zero. what is your oponion????? 

July 4, 2013, 20:06 

#18 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
So what defines Vw, if you are not modelling it directly?


July 4, 2013, 22:20 

#19 
New Member
zhouqishan
Join Date: Jun 2013
Posts: 8
Rep Power: 5 
Hi, bitak. In my opinion you make some mistake. The completely equation is in the attached thumbnail.
Note vw is the water infiltration velocity, Kw a permeability coefficient of the solute; The paper ' Stagnant Film Model for Concentration Polarization in Membrane Systems' will help you. The kw is too small for the vw, so the kw can be assumed to be 0, and then we obtain the simpler equation as your attached thumbnails. (cw is the concentration on the wall, D the kinematic diffusivity, ∂C/∂n the concentration gradient normal to the wall. ) Thanks for your reply, Glenn. I have no idea in the cfx. But in the fluent, I can solve the simple equation for the wall with Taylor series (showed in the attached). In the two equation, there are two parts is uncertain: cw and ∂C/∂. So I can get the cw without a porous domain. 

July 5, 2013, 07:34 

#20 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,412
Rep Power: 97 
CFX has a variable for the wall normal vector. This should help you get the normal gradient.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Error finding variable "THERMX"  sunilpatil  CFX  8  April 26, 2013 07:00 
tmerge utility creates unwanted interface/walls comes in the final mesh  dinesh2n@gmail.com  OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ...  11  January 20, 2012 07:23 
Patches for OpenFOAM 1.7 on MacOS X  gschaider  OpenFOAM Installation on Windows, Mac and other Unsupported Platforms  101  September 21, 2011 05:37 
UDF for wall slipping  HFLUENT  Fluent UDF and Scheme Programming  0  April 27, 2011 12:03 
Quick Question  Wall Function  D.Tandra  Main CFD Forum  2  March 16, 2004 05:29 