[alimea]

Hi all

I want to simulate the problem of sedimentation of a solid particle in a Newtonian and viscoelastic fluid.
At first in Newtonian fluid: as the solid particle moves with gravity in fluid, we need dynamic mess. Is there any other way to simulate this problem without dynamic mesh?

[piu58]

You may calculate the drag force for a particle in the free stream and modify the free stream velocity until the drag force equals the gravitation force. The free stream velocity equals the final falling velocity for this particle. This works for a single particle only.
If you want to investigate separation effect you may calculate the velocity for all the types of example particles which you want to have in your mixture. You may calculate the dropping time for every particle (out of the mixture) for every particle, which depends form it's form and it't starting height. Divide the total sedimentation time in time steps and calculate which particles will reach the floor in this time step. This will give you the composition of the sedimentation (size or form of the particles or both) layer for that step.

[alimea]

Originally Posted by piu58

You may calculate the drag force for a particle in the free stream and modify the free stream velocity until the drag force equals the gravitation force. The free stream velocity equals the final falling velocity for this particle. This works for a single particle only.
If you want to investigate separation effect you may calculate the velocity for all the types of example particles which you want to have in your mixture. You may calculate the dropping time for every particle (out of the mixture) for every particle, which depends form it's form and it't starting height. Divide the total sedimentation time in time steps and calculate which particles will reach the floor in this time step. This will give you the composition of the sedimentation (size or form of the particles or both) layer for that step.

Thanks for your answer.
I have just one particle and I have some purposes like calculating settling velocity, drag force, flow pattern ,etc . If I got true, you tell that I should suppose a value for a force stream over a stationary sphere and calculate the drag force. then investigate if the drag force equal to gravity force. if it is not, try it again with a new value for free stream velocity.

1- Did I get it correct?
2- Don't I need dynamic mesh?

[piu58]

> the drag force equal to gravity force

Yes. You don't need any real gravity in your simulation because the gravitational force may be calculated by the volume and the density difference.

If the forces are equal the free stream velocity has the same value like the sinking velocity in the gravitational field.

> stream over a stationary sphere

That doesn't need to be a sphere. It may be of interest how particles of different form come into the sediment.
For sphere you don't need any fluid simulation at all. The drag coefficient for spheres is well known. From it the total force can be calculated very easily.