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-   -   Lift and Drag (http://www.cfd-online.com/Forums/main/99550-lift-drag.html)

bagofmilk April 6, 2012 00:02

Lift and Drag
 
I'm new to CFD. I modeled a frisbee in SolidWorks and used Flow Simulation. I was wondering what your thoughts were on the better frisbee (see images attached). I know the ideal situation is to have a high ratio of Lift to Drag forces. It seems that FRISBEE B accomplishes that, but I'm wondering if it is likely to be more unstable during flight.

Any input is greatly appreciated.


FRISBEE - A
http://www.imageurlhost.com/images/t...01s73v_OEM.jpg

FRISBEE - B
http://www.imageurlhost.com/images/6...jdg3uf_New.jpg

truffaldino April 6, 2012 05:21

Check pitching moments relatively the center of gravity. The configuration with smaller pitching moment will be likely more stable.

bagofmilk April 6, 2012 09:05

So I've found that Pitching Moment is defined by a product of:

Cm [Coefficient of Pitch Moment] x 1/2 x (fluid density) x (velocity^2) x (cross-sectional area) x (disc diameter).

is Cm a function of the physical aspects of the frisbee? If not, can't I assume Cm to be equivalent between the two? (Obviously the two pics shown have identical initial conditions and boundary conditions.)

If it is a function of the physical aspects, what factors do I need to look into? Can I use SolidWorks or Flow Simulation to help me determine any of these coefficients?

Thanks!

-David

truffaldino April 6, 2012 11:20

Hello David,

Cm depends on the object shape, orientation (angle of attack) and reynolds number (speed). I have never worked with SolidWorks or Flow Simulation, but any serious CFD software should give force moments relatively a user defined axe as an output option.

Usually analysys of low-speed flows is a challenge due to considerable influence of the flow separation and turbulence modelling on the Drag and Lift. I do not know if SolidWorks is reliable enough for this kind of simulations: it seems that the turbulence modelling is a weak point of this software.

Truffaldino

P.S. you can take a look at this thesis:

http://biosport.ucdavis.edu/research...mmelThesis.pdf

bagofmilk April 6, 2012 17:41

Thanks! This is great info

bagofmilk April 6, 2012 17:46

I was able to find out that SolidWorks Flow Simulation can find the Center of Pressure and force moments by setting a torque "goal" equal to 0. But this thesis has some great background info.


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