DPM-accurracy?

David Segersson

Hi! I'm having trouble with the particle tracking in FLUENT 6.1 giving inaccurate results:

I'm trying to model raindrops falling through the air and hitting a surface (the ground or a building).

I drop a large number of particles in a steady-state flow field, using no turbulent dispersion and inert particles. I drop the particles approximately 70m, through a uniform flow field and then examine where they hit the ground.

Since the flow field I use is totally uniform, 3m/s everywhere, even by the ground, one would expect all the particles to fall the same way, and thus ending up in a pattern similar to how they were injected. This shows out to be almost the case, most of the particles falls as expected, but a few percent end up a few decimeters from their expected location on the ground.

I have tried decreasing the integration length scale down to 0.001m, but it doesn't help. And I guess that since the windfield is homogenous it shouldn't matter so much what length scale I use. I'm beginning to think that the mesh is affecting the particle tracking, even if it shouldn't considering the uniform flow field. I have also tried refining the mesh and using tetraedral as well as hexaedral cells, but without finding any clear cause to the inaccuaracy.

I would appreciate any help on how to get better accurracy when tracking particles. // David