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

Simulation of varying contact angles for a large droplet of water on a surface

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 24, 2012, 16:06
Default Simulation of varying contact angles for a large droplet of water on a surface
  #1
New Member
 
Christina P.
Join Date: Oct 2012
Posts: 22
Rep Power: 14
cp703 is on a distinguished road
Hi. In an attempt to determine how well ANSYS/CFX deals with scenarios were surface tension effects play a significant role in fluid flow, my adviser has suggested that I first try to model a large droplet of water on a surface and vary the contact angle. To do this, I have scoured the ANSYS tutorials and the internet (to be honest, most of the useful information has come from the cfd-online.com forums...). I created an air/water fluid domain (in the shape of a rectangular prism) with the walls all having a no slip wall boundary condition. I defined an initialized water volume fraction in the shape of a sphere near the "bottom" (in terms of the direction of gravity g in the -y direction) of the domain. After including all the surface tension effects (including specifying the wall contact angle in the wall BC), there doesn't seem to be any difference in the shape of the droplet when I change the wall contact angle.

After investigating problems that people have had with free surface models and taking into account surface tension, etc. I feel like I've covered my bases: I have the multiphase free surface model turned on and the free surface model turned "on", the surface tension coefficient specified for water in air, the surface tension model set to "continuum surface force", turned on and then off the volume fraction smoothing, changed the curvature under relaxation factor, etc.

I really feel like I am missing something. Is this a silly thing to try in CFX? Am I going about it totally wrong?
cp703 is offline   Reply With Quote

Old   October 25, 2012, 07:03
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
I have done this exact same benchmark study with CFX years ago. The wall contact angle will work when the solver is setup properly. I cannot recall the exact settings I used, but I do remember that I systematically tried EVERY multiphase option available to find out what everything did. There was a few non-default options which helped.

One thing I can remember is that steady state simulations didi not work. It really needed to be transient.

But the main thing I remember is that this exact simulation runs faster and more accurately under Fluent, so I moved to fluent. How much faster? About 20 times faster. For this type of simulation CFX really is miles behind.
ghorrocks is offline   Reply With Quote

Old   October 25, 2012, 14:53
Default
  #3
New Member
 
Christina P.
Join Date: Oct 2012
Posts: 22
Rep Power: 14
cp703 is on a distinguished road
Wow...I'm not sure if I'm relieved that it's not just me who has struggled with this or embarrassed that it took me so long to just post my problem. If you don't mind, I have a follow-up question for you, ghorrocks. Would you say that the inability of CFX to handle this sort of thing would extend to flow in very small, open channels? That's ultimately what I'm working toward, but if a switch to Fluent would be advantageous I'd rather do it now than later (though I've never used it at all).

Thanks for your insight!
cp703 is offline   Reply With Quote

Old   October 25, 2012, 18:32
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
My work in this area was for MEMS (inkjet printers to be precise). But the general principle is applicable to all free surface flows with low Re number. So I suspect your small open channel will qualify for that.

Make sure you use the correct words. CFX can handle this type of simulation. It is just much slower than other simulation codes for equivalent accuracy.

And yes, even though I am a CFX disciple I will recommend you move to Fluent. Also Flow3D has some interesting abilities in this area, that is worth a look too.

Are you looking for high accuracy? Or do you just want a general idea of what the flow does? How complex is the flow you want to model?
ghorrocks is offline   Reply With Quote

Old   July 20, 2013, 04:40
Default
  #5
New Member
 
kartik patel
Join Date: Jul 2013
Posts: 1
Rep Power: 0
Kartikpatel is on a distinguished road
How to do the simulation of this kind of condition? If you have any relevant material then please give me.
Kartikpatel is offline   Reply With Quote

Old   July 20, 2013, 07:08
Default
  #6
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
Here's a good FAQ to start you off: http://www.cfd-online.com/Wiki/Ansys...ible_answer.3F
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
droplet impact on a dry surface.... VOF again rogerspass FLUENT 1 June 27, 2016 03:12
Linear analytical solution oto the 2D free sloshing water surface elevation bearcat Main CFD Forum 7 August 5, 2011 21:13
Dynamic mesh in Fluent to study tire in contact with road surface lihuang FLUENT 10 March 8, 2011 11:21
Use smoke density to simulate water Wei-zhi Liao Main CFD Forum 0 February 13, 2006 04:06
CFX bubble simulation with free surface model adma CFX 6 February 3, 2006 12:17


All times are GMT -4. The time now is 13:15.