# falling drop

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

 November 4, 2003, 12:35 falling drop #1 ozgur Guest   Posts: n/a hi, I need to find the external and internal velocity fields of a falling drop (let's say water droplet falling through air) under gravity (i.e. free fall). How should i define the liquid-gas interphase? which model i should use to solve this problem? (It seems that i should somehow define wall boundary condition at the interphase,since i couldn't get anything reasonable without that) I will appreciate any help even regarding constant- velocity falling drop (the otherway is quite complicated since the drag force is dependent on the velocity fields on the drop surface) Thanks in advance!

 November 5, 2003, 05:07 Re: falling drop #2 mateus Guest   Posts: n/a Hi! In your case you should use the VoF multyphase model. I have some expiriences with "water drop faling in water simulation" - it works quite well in Fluent. If you haven't done any work with VoF I guess you should first go trough tutorial case, and then work your way up. The thing is you are probabilly gonig to have to simulate this unsteady, so yu can increasse the inlet velocity the same way the doplet gains speed - it's not so complicated to calculate this even with drag. You can also let your droplet fall in your domain... I hope I helped MATEUS

 November 5, 2003, 09:11 !! FALLING DROP !! #3 ozgur Guest   Posts: n/a Hi MATEUS, First, thanks for your reply. I did not consider the multiphase model, since i have only one fluid particle at all. For the VoF model, it is said to be good for free surface flows ( I assume that i have a small enough drop so that it stays as spherical), stratified and slug flows, but i have something like droplet flow (as shown in 18.1 in Fluent manuel). Fluent recommends to use Discrete Phase Model for discrete phase vol.frac.<10, but i couldn't find a way out for my specific problem with that. So, in that sense, my problem seems a bit simpler, since i do not need to find out the trajectory of my drop, since i expect it to fall straight down. But i have to find out the terminal velocity (which depends on the fields on the liqid-gas interphase) of the drop and the velocity fields inside and outside the drops. If a manage that, then i will hopefully switch to the modelling mass transfer of a third component between the phases. Do you have perhaps more suggestions?

 November 6, 2003, 10:42 Re: !! FALLING DROP !! #5 ozgur Guest   Posts: n/a Thank you for your suggestions Thomas, Analytical drag equations for flow around fluid spheres are unfortunately limited to Re<1 (creeping flow) which is not my case.But, i can probably find an approximate value for that. (Actually, water-air system is just for a simple starting case. I have to apply my simulation to systems under high pressure like supercritical CO2 instead of air. Then i will have more coupling of the internal and external phases). I will look deeper to VoF model, and hope it will works for my single falling drop problem. But I have a feel that, somehow I will need to write a UDF to define the coupling of the internal and external flows at the interphase. Finally, I am from Turkey, but study M.Sc. Process Eng. in Hamburg/ Germany at the moment. You wonder because of my strange name? Where are u from by the way? özgür

 July 26, 2012, 05:15 #6 New Member   amit sarvaiye Join Date: Jul 2012 Posts: 4 Rep Power: 7 can you pleaase tell me how to create a droplet. i have worked with vof but only in the cases with volume fraction at inlet ranging fro 0 to 1. i dont know how to create a water droplet . please help

October 23, 2012, 03:56
#7
Member

Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 10
You need to create a circular/spherical register for 2d/3d case respectively. Assign liquid volume fraction of 1.0 in that register after initializing the case.

Quote:
 Originally Posted by amitsarvaiye can you pleaase tell me how to create a droplet. i have worked with vof but only in the cases with volume fraction at inlet ranging fro 0 to 1. i dont know how to create a water droplet . please help
__________________
SM

 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 bigfans FLUENT 7 November 8, 2016 12:28 Daniel L FLOW-3D 2 December 10, 2010 05:23 Resnick Main CFD Forum 0 November 20, 2007 15:50 Ron FLUENT 2 June 24, 2004 06:05 ozgur FLUENT 0 January 29, 2004 12:22

All times are GMT -4. The time now is 01:52.