# Jumping droplets velocity - interFoam

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

October 6, 2015, 08:25
Jumping droplets velocity - interFoam
#1
New Member

Zinedine
Join Date: Sep 2010
Posts: 12
Rep Power: 7
Dear foamers,

I am undertaking some OF simulations of droplets coalescence uponm hydrophobic surfaces.

Initially 2 water droplets with the same radius R and contact angle of 160o are set onto the surface. They then coalesce to form a droplet. Owing to energey forces this formed droplet then jumps from the surface.

I attach a snaphot of a simulation of 2 droplets with initial radius R=100micro and contatcd angle = 160o.

This is this jumping velocity I wish to compute.

To do so I compute the is veloocity using 2 methods:

1. I firstly compute the velocity by evaluating the Centre of Gracity (COG) of the droplets. I use the following code baryCenter221.zip (i.e. Rise of a spherical bubble terminal velocity)
to evaluate the position of the COG.
I made the following changes as indicated in red:

forAll(alpha1, cellI){

// Integration of {mass}
//////sumM += (1-alpha1[cellI])*mesh.V()[cellI]*rho2.value();
sumM += (alpha1[cellI])*mesh.V()[cellI]*rho1.value();

// Integration of (mass*height)
////sumMY += (1-alpha1[cellI])*mesh.V()[cellI]*rho2.value()
///// *mesh.C()[cellI][1];

sumMY += (alpha1[cellI])*mesh.V()[cellI]*rho1.value()
*mesh.C()[cellI][1];

} (Eq . 1)

Upon evaluating thre COG at each time step, I plot the COG location vs time.

My velocity is then obtained by taking the slope of the linear part of the plot.

2. I also compute the velocity of the jumping droplet by using Paraview.
I use the following equation to evaluate the velocity:

Udrop = integral_Omega (alpha1*U) dOmega / integral_Omega (alpha1) dOmega (Eq. 2)

I found the same velocity using both methods, however the obtained jumping velocity is TWICE bigger as published experimental and numerical for similar work.

I have been going round and round to find where the error is .... I believe I am missing something silly and very simple while post processing and evaluating this jumping velocity.

Are the equations (Eq . 1) & (Eq . 2) used to compute the velocity correct ?
Am I avaluating the COG correctly ?

I hope you will be able to help me out I am getting mad .....

Kindest regards

Z.
Attached Images
 snapShotsR100.png (37.5 KB, 12 views)

 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 muyuntao Fluent UDF and Scheme Programming 1 November 10, 2015 14:42 DanM OpenFOAM Running, Solving & CFD 11 January 5, 2013 07:21 rassilon OpenFOAM 2 September 22, 2010 21:55 spk Main CFD Forum 3 July 9, 2010 08:42 chong chee nan FLUENT 0 December 29, 2001 06:13

All times are GMT -4. The time now is 21:57.

 Contact Us - CFD Online - Top