# Rotating a sphere

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May 4, 2010, 09:22
#41
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Rick
Join Date: Mar 2010
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By that you mean drag and lift? I only have that in the monitors option, I don't have spin vector, drag is in x=1 and lift is y=1

Quote:
 Originally Posted by jack1980 Have you set the direction of the spin vector and lift vector perpendicular?

 May 4, 2010, 09:36 #42 Senior Member   Jouke de Baar Join Date: Oct 2009 Posts: 126 Rep Power: 9 In the boundary condition panel you can set something like spin vector or spin axis orientation? If for example cd is in x-direction and spin axis is in y-direction (which you should check) then cl should be in z-direction.

May 4, 2010, 11:07
#43
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Rick
Join Date: Mar 2010
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I put an image of the orientation of the mesh attached

In the boundary condition for the ball:
I have motion rotational and then a rotation-axis origin which I defined 0 for x,y,z
and I have rotation-axis direction in which I have 0 for x,y and 1 for z.

In the monitors I only have active the residuals, drag and lift. In the drag I have Force vector x=1 and in the lift I have force vector y=1,

I think it's ok...

Quote:
 Originally Posted by jack1980 In the boundary condition panel you can set something like spin vector or spin axis orientation? If for example cd is in x-direction and spin axis is in y-direction (which you should check) then cl should be in z-direction.
Attached Images
 Meshcoordinate.jpg (47.8 KB, 20 views)

 May 4, 2010, 11:15 #44 Senior Member   Jouke de Baar Join Date: Oct 2009 Posts: 126 Rep Power: 9 Yes that should be ok. Hmmm ... this is strange ... Could you perhaps upload your case somewhere, such that I can have a look at it?

 June 15, 2010, 06:51 #45 New Member   Rick Join Date: Mar 2010 Posts: 27 Rep Power: 9 I have a question regarding the Magnus (or lift force) it's about the expression that is used to calculate the Magnus force, I've found 2 of them and don't know which is the right one is it: Fl=1/2*cl**A*v^2 or Fl=1/2*cl**A*r**v I'd really appreciate the help

 June 15, 2010, 07:39 #46 Senior Member   Jouke de Baar Join Date: Oct 2009 Posts: 126 Rep Power: 9 They are both correct. However the upper definition is more conventional. This will give the correct force if you use the cl from FLUENT. Take care that A is the projected area of the sphere. ( \pi r^2 )

June 19, 2010, 18:37
#47
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Rick
Join Date: Mar 2010
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hello
I have another question, If you see the image I posted, it is a normal football where I did the analysis, I wanted to see more the edges and pattern, like this second image I found on the net
can anyone help?
best regards
Attached Images
 skinfriccoef15,3mssemrotrealiz.jpg (71.6 KB, 13 views) contour.jpg (25.1 KB, 12 views)

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