# extrapolating interface curvature onto the wall

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

July 29, 2016, 09:56
extrapolating interface curvature onto the wall
#1
Senior Member

Saideep
Join Date: Apr 2015
Location: INDIA
Posts: 172
Rep Power: 4
Dear FOAMers,

I am trying to extrapolate an internal field variable (interFOAM's - interface curvature variable, k) onto the wall boundary as shown in the picture.

I would like to solve for the following equation:
cos (\theta) = 2ra/(r2+a2).

I know the value of 'r' based on dimensions of my model and based on extrapolation I would like to know the value of 'a' run time and then determine theta.

Can anyone direct me on how to extrapolate the interface curvature onto the wall please.

Thanks,
Saideep
Attached Images
 extrapolate.png (5.3 KB, 11 views)

 July 29, 2016, 11:02 #2 Member   Vignesh Join Date: Oct 2012 Location: Darmstadt, Germany Posts: 63 Rep Power: 6 Hi Saideep, What afkhami did was fit a circle to the part of interface close to wall and thats how he gets the extrapolated contact line. From which you can get the r, a. Why do you need interface curvature ? __________________ Thanks and Regards Vignesh

 July 29, 2016, 11:35 #3 Senior Member   Saideep Join Date: Apr 2015 Location: INDIA Posts: 172 Rep Power: 4 Hi Vignesh; Thanks for that. I had a different picture. If I understand you correctly, values are obtained after reaching a steady state..? I was thinking it is a parameter to be updated from curvature every time step. -- I am trying to include dynamic c.a. model based on empirical relations. (Cox, Bracke etc) because I never reach a mesh independent solution for my case of capillary rise when gravity is turned off and flow is only due to surface tension force. So, I was thinking Afkhami's procedure does the trick. Saideep

July 29, 2016, 11:45
#4
Member

Vignesh
Join Date: Oct 2012
Posts: 63
Rep Power: 6
Quote:
 Originally Posted by Saideep Hi Vignesh; Thanks for that. I had a different picture. If I understand you correctly, values are obtained after reaching a steady state..? I was thinking it is a parameter to be updated from curvature every time step. -- I am trying to include dynamic c.a. model based on empirical relations. (Cox, Bracke etc) because I never reach a mesh independent solution for my case of capillary rise when gravity is turned off and flow is only due to surface tension force. So, I was thinking Afkhami's procedure does the trick. Saideep
Steady state ... yes more or less. Have you tried introducing slip ? (Navier BC) It also results in mesh independent solution. By the way do you get the results matching the theory ?
__________________
Thanks and Regards

Vignesh

 July 29, 2016, 12:09 #5 Senior Member   Saideep Join Date: Apr 2015 Location: INDIA Posts: 172 Rep Power: 4 Hi, I tried to introduce partial slip b.c(slip length = delta/2) as he mentions in his paper but still far from convergence. Improves slightly over no-slip b.c but still not satisfactory. I have a question regarding the dynamic c.a.: hope you can help me out here, any dynamic c.a. relation is seen to increase the c.a. at wall surface over the static c.a. In my case I have flow caused due to force "\sigma*cos(\theta)". Upon increase in c.a., the force causing flow is reducing and the results are quite far from analytic predictions. My case in figures. pic1.jpg pic2.jpg Comparing to analytic solution the static c.a seems to be better except that I dont get to a mesh independent solution. Any idea over that?? Saideep

 July 29, 2016, 12:44 #6 Member   Vignesh Join Date: Oct 2012 Location: Darmstadt, Germany Posts: 63 Rep Power: 6 Code: I tried to introduce partial slip b.c(slip length = delta/2) as he mentions in his paper but still far from convergence. Improves slightly over no-slip b.c but still not satisfactory. Did you try Afkhami's Dynamic Contact Angle model ? Also have a look at this paper Comparison between numerical models for the simulation of moving contact lines Code: any dynamic c.a. relation is seen to increase the c.a. at wall surface over the static c.a Not necessarily ... For receding case or when ca < 0 it might be less than the static value. Code: Comparing to analytic solution the static c.a seems to be better. Any idea over that?? For capillary flow in a tube problem (or any spontaneous capillary flow), inertial forces dominate only at the very early stages during which the rise is rapid, after that the rise slows down. So its safe to use static ca. Dynamic ca if used must be switched off after this rapid rise because after this velocity drops down hence the capillary number. So it does not make sense to use DC model. Have a look at this paper The transition from inertial to viscous flow in capillary rise by N. Fries, M. Dreyer My understanding of contact angle and capillary flows is very less. If you find anything wrong please correct me. Hope this helps !! __________________ Thanks and Regards Vignesh

 August 1, 2016, 07:09 #7 Senior Member   Saideep Join Date: Apr 2015 Location: INDIA Posts: 172 Rep Power: 4 Hi, Thanks for the paper seems to be quite interesting. I have a quick question. I am using the partial Slip b.c on wall for velocity. But I am dealing with dimensions in scale of e-5m. Partial slip requires me to specify "valueFraction" calculated as 1/(slip length + 1). If I consider my slip length as "delta/2" as mentioned in papers, I always end up with values close to 0.999999---. So, ultimately I am close to a no-slip b.c and see not much of difference. Any idea how can I better this factor? Thanks; Saideep

 August 1, 2016, 07:20 #8 Member   Vignesh Join Date: Oct 2012 Location: Darmstadt, Germany Posts: 63 Rep Power: 6 Hi Saideep, I have no idea !! But do you see mesh convergence ? __________________ Thanks and Regards Vignesh

 August 1, 2016, 07:27 #9 Senior Member   Saideep Join Date: Apr 2015 Location: INDIA Posts: 172 Rep Power: 4 No. Using partial slip also does not solve the problem.

 Tags extrapolation

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post ngoc_tran_bao CFX 24 May 3, 2016 21:16 CFD XUE FLUENT 0 July 8, 2010 06:49 hills1 CFX 2 October 12, 2009 05:36 mumdad FLUENT 1 June 6, 2008 05:50 Andrea CFX 2 October 11, 2004 05:12

All times are GMT -4. The time now is 03:27.