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Old   April 6, 2012, 00:02
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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


FRISBEE - B
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Old   April 6, 2012, 05:21
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Check pitching moments relatively the center of gravity. The configuration with smaller pitching moment will be likely more stable.
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Old   April 6, 2012, 09:05
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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
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Old   April 6, 2012, 11:20
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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
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Old   April 6, 2012, 17:41
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Thanks! This is great info
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Old   April 6, 2012, 17:46
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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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