Aerodynamics of Sports Balls - Penn Engineering（空气动力学运动球-佩恩工程）.pdf

Aerodynamics of Sports Balls Bruce D. Kothmann January 2007 Unless Otherwise Specified, All Data From Mehta, R.D., “Aerodynamics of Sports Balls” Annual Review of Fluid Mechanics, 1985.17:15 Spherical Sports Balls • Complex Aerodynamics : Rotation Non-Uniform Surface • Begin with Non-Rotating Uniform SphereSpherical Symmetry Implies Aerodynamic Force Must be Opposite to Direction of Flight (Drag) • Then Consider Seams SpinAsymmetryLift 2 Drag on Non-Rotating Uniform Sphere Dimensional Analysis • Drag (F ) Depends on: D – Speed, V F f V ,D ,ρ ,μ ,k – Diameter, D D ( ) – Density, ρ – Viscosity, μ F D – Roughness Length, k C D 2 • 6 Parameters Minus 3 0.5ρ V A Dimensions (Mass, Length, Time) = 3 Dimensionless k Parameters Re ρ VD ε – Significantly Reduce Experimental D Testing Required μ – Match Re and ε to Find CD and Then Compute Drag ˆ CD f (Re, ε ) 3 Experimental Data for Drag on Non-Rotat