# lu (lb unit) conversion, surface tension

So I’m using the shan-chen multiphase model to simulate coalescence of bubbles and now I want to estimate the surface tension.

First thing is the pressure doesn’t vary as expected, it does

http://i40.tinypic.com/t7bxg2.jpg
if the pressure is plotted against x through the center y coordinate

for a bubble like

http://i43.tinypic.com/2ywtnk8.jpg

I thought the maximum pressure would be in the center of the bubble as I’ve seen described in some pubs…
In any case if this is correct then that’s fine.

Using this I can plot the pressure against the inverse radius and I get a linear relationship as according to laplace’s law. Now my question is what are the units of this. I am using the introduction to geoscientists and engineers book but can’t figure out what ts^-2 and lu are and how I convert them to SI.

Any help would be appreciated!

Hi,

Two questions in order to better understand your problem:

1. Are you using the single-component or multi-component model (i.e. do you use 9 or 18 particle populations per cell on a D2Q9 lattice)?
2. What form of the interaction potential are you using?

i have the same question

D2Q9 single

lu is lattice units, so one lattice unit represents Dx metres. ts^-2 however i am not sure of. I am trying to do the same thing so I can attempt to model some real fluids, I just need a clear explanation on how to translate data from the simulation into pressure…

in Sukops book is ts means timeStep, so it is a “latttice” unit for time, so here Pressure is given in mu*ts^-2 which is a pressure in 2D (force per length)