CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

solidification viscosity governed through an additional variable

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 13, 2012, 05:02
Default solidification viscosity governed through an additional variable
  #1
New Member
 
Join Date: Sep 2012
Location: Europe
Posts: 25
Rep Power: 14
l.te is on a distinguished road
Hi dears,
I have a problem: I want simulate a resin material that enters in a cylindrical die, solidifies and exit from the other side of the die.
Solidification is governed by the resin viscosity, that increases with an additional variable, alfa, modeled as a volumetric transport equation (without diffusion) through the resin domain, with a additional variable source therm activated by the temperature of the die.
The problem is that the resin thermal equation and the transport equation related to the additional variable, don't meet the convergence: their residuals are stable about 10^-1 also for many and many iterations (4000). It seems that as the viscosity increases from the initial values (1.5 Pa*s), the system is less able to rase the residual as the resin viscosity grows.
If I set a costant viscosity of 1,5 Pa*s the simulation works and the residuals are raised below 10^-4.
If I set a costant high viscosity the simulation don'works because the residuals are stable about 10^0- 10^-1.
It is a problem that come when the viscosity becomes high.
How I can do to run the viscosity governed solidification process of this resin?
Can you help me?
l.te is offline   Reply With Quote

Old   September 13, 2012, 08:03
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
What Re number does this run at when the resin is at maximum viscosity?

CFX (and indeed all Navier-Stokes solvers I am aware of) do not run well at very low Re number (Re<0.01 or so) and will have troubles converging. This sort of simulation is best done on a stokes flow solver.
ghorrocks is offline   Reply With Quote

Old   September 13, 2012, 08:13
Default
  #3
New Member
 
Join Date: Sep 2012
Location: Europe
Posts: 25
Rep Power: 14
l.te is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
What Re number does this run at when the resin is at maximum viscosity?
CFX (and indeed all Navier-Stokes solvers I am aware of) do not run well at very low Re number (Re<0.01 or so) and will have troubles converging. This sort of simulation is best done on a stokes flow solver.
Hi, thanks for the reply!
Reynolds in this simulation is effectively very low: infact the velocity of the resin in the die is very low (0.002 m/s), the radius of the cylindircal part is 0.0025 m and the viscosity accordingly with the law of variation that I have, sould increase from 1.5 Pa*s to also 10^7 Pa*s (practically a solid). So Reynolds finally is about zero. What I can do in CFX, is there an option to switch to Stokes flow solver?
l.te is offline   Reply With Quote

Old   September 13, 2012, 08:23
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
So your Re=1e-9, I think that qualifies as low Re...

CFX cannot handle flows as slow as this. It does not have a stokes flow solver, you need to switch to one which does - or write your own, with no inertial terms Stokes flow solvers are a bit simpler than NS solvers.
ghorrocks is offline   Reply With Quote

Old   September 13, 2012, 09:19
Default
  #5
New Member
 
Talita Possamai
Join Date: Sep 2012
Posts: 23
Rep Power: 14
Possa is on a distinguished road
Hello l.te,

I agree with ghorrocks, you won't be able to solve that fluid flow with CFX as it is. CFX has it's limitations, and that's why people has to develop codes to solve some complex problems.

But, if I may, I have a suggestion for you:

Simplify your problem. Think on the aim of your work. Do you really need to have the fluid flow, or are you more interested in the solidification process as the resin pass through the die?

If so, then treat the resin as a solid. Adapt the solid material to behave like you need (play with material properties). If your die format is simple you can prescribe a estimated solid velocity profile.

Keep in mind that this is a suggestion to estimate your results with the CFX.

But if you really need to solve the fluid flow field, then you should follow ghorrocks suggestion.

Regards,
Possa.
Possa is offline   Reply With Quote

Old   September 13, 2012, 10:01
Default
  #6
New Member
 
Join Date: Sep 2012
Location: Europe
Posts: 25
Rep Power: 14
l.te is on a distinguished road
Hello dears, thanks for our suggestions!
In my work the resin (together with unidirectional glass fibers) is part of a cylindrical composite material that, passing with a continous low velocity through the heated die, solidifies and is pulled downstream from the die by means of a puller (this process is called pultrusion).

The aim of my work is exactly study the viscous forces between the die and the resin , (and them increase as the viscosity increase!), until a point (inside the die) at which the part detaches from the die. Pratically I want know what is the force to be provided at a puller to pull the composite out from the die, and to calculate it, I think that is fondamental to have a model with an initial resin defined as fluid, with its viscosity that grow with during the heating process in the die...
How I can do? I have learned CFX exactly to do this study..
l.te is offline   Reply With Quote

Old   September 13, 2012, 10:11
Default
  #7
New Member
 
Talita Possamai
Join Date: Sep 2012
Posts: 23
Rep Power: 14
Possa is on a distinguished road
Hello l.te,

Unfortunately, I believe you won't be able to solve it like you want in CFX. As I see it you have two options:

1 - learn another software, as suggested by ghorrocks, or develop a code of your own that is able to solve that;
2 - Think of a way to simplify your problem and model what you need in another way (remembering that the problem is the low Re number).

I suggest you talk with someone with experience in low Re number CFD. It also helps to do a bibliografic revision on articles and works in that area.

Regards,
Possa.
Possa is offline   Reply With Quote

Old   September 13, 2012, 10:29
Default
  #8
New Member
 
Join Date: Sep 2012
Location: Europe
Posts: 25
Rep Power: 14
l.te is on a distinguished road
Ok, many many thanks for the aid at all of you!
l.te is offline   Reply With Quote

Old   September 13, 2012, 20:19
Default
  #9
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
I am no expert in this area but I do not think that an increasing Newtonian viscosity is a good model for the polymerisation process going on in resin cure. Do you have any evidense to show it is a good model?

I would do a literature study, as recommended by Talita, and work out what is an appropriate model for this process. You may well be better off with an lagrangian FEA approach, such as ABAQUS, ANSYS Mechanical; with non-linear material properties.
ghorrocks is offline   Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem with divergence TDK FLUENT 13 December 14, 2018 07:00
Condensation as an additional variable Clark Griswold CFX 2 April 21, 2012 08:20
emag beta feature: charge density charlotte CFX 4 March 22, 2011 10:14
Replace periodic by inlet-outlet pair lego CFX 3 November 5, 2002 21:09
variable viscosity -NOT! George Bergantz Main CFD Forum 15 September 19, 2000 15:28


All times are GMT -4. The time now is 11:45.