# Lift and Drag

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 April 6, 2012, 00:02 Lift and Drag #1 New Member   David Join Date: Apr 2012 Posts: 4 Rep Power: 7 Sponsored Links 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

 April 6, 2012, 05:21 #2 Senior Member     Join Date: Jan 2011 Posts: 248 Blog Entries: 5 Rep Power: 10 Check pitching moments relatively the center of gravity. The configuration with smaller pitching moment will be likely more stable.

 April 6, 2012, 09:05 #3 New Member   David Join Date: Apr 2012 Posts: 4 Rep Power: 7 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

 April 6, 2012, 11:20 #4 Senior Member     Join Date: Jan 2011 Posts: 248 Blog Entries: 5 Rep Power: 10 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

 April 6, 2012, 17:41 #5 New Member   David Join Date: Apr 2012 Posts: 4 Rep Power: 7 Thanks! This is great info

 April 6, 2012, 17:46 #6 New Member   David Join Date: Apr 2012 Posts: 4 Rep Power: 7 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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