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 JPBodner August 4, 2010 09:37

Calculation of Saffman Lift Force

Hi all

I've got a model of a sphere (representing a small particle) attached to a wall. There is another wall a few diameters away, creating channel flow around the particle. In essence, I'm trying to numerically calculate the lift/drag on a particle to compare against the theoretical results from the literature. Re is low (<<1).

My drag force appears to be resonable, but my lift force is negative, meaning that the particle is forced towards the wall instead of away, as expected.

Has anyone played with this scenario? Any ideas on why the lift force is in the wrong direction?

 agd August 4, 2010 10:07

Your post is not entirely clear on the problem geometry. I gather you have a spherical particle attached to wall 1, with wall 2 in close proximity. There is flow over the sphere and between the 2 walls, and the particle lift moves the particle towards wall 1(?) 2(?). Can you clarify the problem setup?

 JPBodner August 4, 2010 10:27

Saffman lift

3 Attachment(s)
Yes, you are correct. The particle is on wall 1, with wall 2 in proximity. (the effect of the wall-wall distance is the primary variable I am interested in) The flow is between the two walls, flowing over the particle as well. Theoretically, a lift force should exist that acts to remove the particle from the surface and entrain it into the free-stream. This is the so-called Saffman lift. (I am not trying to model the actual particle motion, just the steady-state flow field).

Pictures are attached for the case of a very close wall-wall distance. The model uses one plane of symmetry through the sphere center. Flow is from left to right in these pics.