Calculation of Saffman Lift Force

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 August 4, 2010, 09:37 Calculation of Saffman Lift Force #1 New Member   Jeff Join Date: Aug 2010 Posts: 11 Rep Power: 6 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?

 August 4, 2010, 10:07 #2 Senior Member   Join Date: Jul 2009 Posts: 191 Rep Power: 8 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?

August 4, 2010, 10:27
Saffman lift
#3
New Member

Jeff
Join Date: Aug 2010
Posts: 11
Rep Power: 6
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.

Your ideas are much appreciated
Attached Images
 geometry.jpg (33.7 KB, 23 views) mesh.jpg (97.5 KB, 21 views) velocity.jpg (66.1 KB, 28 views)

 August 4, 2010, 11:11 #4 Senior Member   Join Date: Jul 2009 Posts: 191 Rep Power: 8 At first galnce, I would also expect the particle lift to want to move it toward the opposite wall, due to the flow acceleration and lower pressure on top. But have you plotted the pressure distribution on the particle? I would be curious as to what the pressure looks like on the particle surface. And of course there is always the obligatory question of are you sure you don't have a sign error somewhere - only asked because I have made that mistake many times in the past. Edit - I posted the above without fully understanding what you are interested in. Sorry about that. When I saw the term Saffman, I mistakenly thought back to work I had done years ago on Saffman vortices. I think you are probably referring to the lift due to shear. I don't know if you have seen this article, but if not it may be of some help to you - web2.clarkson.edu/projects/crcd/me437/downloads/1_4Lift.pdf Hope that link works Last edited by agd; August 4, 2010 at 13:31.

 Tags lift, particle, saffman

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post CFD_MAN FLUENT 5 September 9, 2010 04:51 Kai Yan Main CFD Forum 0 July 16, 2008 07:07 Rola FLUENT 1 November 12, 2006 14:29 AB CD-adapco 6 November 15, 2004 05:41 CFD MAN Main CFD Forum 0 November 26, 2002 19:26

All times are GMT -4. The time now is 08:01.

 Contact Us - CFD Online - Top