hi.. this may appear naiev..but its worth thinking..i am modelling flow of water pearls on lotus leaf..as u all know that water doesnt stick to the leaf. how should i introduce this bc in the NS equations. i want to check out at which angle does the water pearls fall off the leaf if inclination of leaf is increased gradually w.r.t. the horizontal. and i want to check the frequency at which the large water pearl will break into small pearls if i vibrate it artificially. how do i introduce this frequency term in the NS equations? Should it go in the source term ?

Thank you

ram

Ram,

I'll try to outline one approach. It's based on a study of sloshing in a tank under earthquake accelerations!

This approach (there are surely other ways of approaching the problem) would use a VOF free surface treatment to represent your droplet at the leaf surface. To find some VOF (Volume Of Fluid) references, search earlier posts in this forum.

First you'll need to know the angle that the water forms with the leaf due to surface tension, and you'll need to know the surface tension between the water and the leaf.

Transform the NS equations into a reference frame attached to the leaf and (for example) use the leaf as the bottom surface of your mesh. In this formulation, the boundary conditions are pretty simple; the velocity at the leaf surface is zero in that frame.

In transforming the equations, the substantial derivitive (Du_i/Dt) transforms into an acceleration term for your mesh; use this to impose the vibration on the system. This can be treated as a source term or interpreted as a part of the body force (gravity).

This outline ignores any influence of air surrounding the droplet. Don't know if that's a good assumption or not.

I'm sure other posters will review, correct, and expand on this outline.

Good luck!

(1). I have taken pictures of lotus flowers and leaves for several years, several thousands of frames in early 90's. (2). I think, it is going to be very difficult to introduce the water droplet on the leaf in the first place. (3). So, you need to solve that problem first, because the water droplet does not just sit on the leaf waiting for you to run the test or simulation. (4).And the surface of the leaf is by no means flat at all. That's another problem, to simulate the real soft, curved leaf.

Thank you John and Jim for your kind suggestions. john what i am doing now is that nature is helping me have the droplet of water on the lotus leaf. i have a plantin a pond and in overnight the pearls of water form on it. i am taking the coordinate along the stem of the leaf as a major axis and i hold the leaf mechanically to tilt it with respect to a reference point so that the pearl of water slips out of the surface under gravity. And to the vibrational aspect, i use the dlicate mechanical apparatus to vibrate the leaf. Now that i have explained to you how i am doing, i am looking for data on lotus leaf anywhere on the web. can u help me locate it? i want to know the resonance and the natural frequency of the lotus leaf ..

regards

ram