Rotating a sphere

RiKR0K · May 4, 2010, 09:22

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?

jack1980 · May 4, 2010, 09:36

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.

RiKR0K · May 4, 2010, 11:07

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.

jack1980 · May 4, 2010, 11:15

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?

RiKR0K · June 15, 2010, 06:51

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* $\rho$ *A*v^2

or

Fl=1/2*cl* $\rho$ *A*r* $\omega$ *v

I'd really appreciate the help

jack1980 · June 15, 2010, 07:39

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 )

RiKR0K · June 19, 2010, 18:37

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

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May 4, 2010, 09:36		#42
jack1980 Senior Member Jouke de Baar Join Date: Oct 2009 Posts: 127 Rep Power: 16	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, 11:15		#44
jack1980 Senior Member Jouke de Baar Join Date: Oct 2009 Posts: 127 Rep Power: 16	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
RiKR0K New Member Rick Join Date: Mar 2010 Posts: 27 Rep Power: 16	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=1/2cl $\rho$ Av^2 or Fl=1/2cl $\rho$ Ar* $\omega$ *v I'd really appreciate the help

June 15, 2010, 07:39		#46
jack1980 Senior Member Jouke de Baar Join Date: Oct 2009 Posts: 127 Rep Power: 16	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 )