Problem 9.5

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Problem 9.5 [Difficulty: 2]
Given: Flow around American and British golf balls, and soccer ball
Find: Speed at which boundary layer becomes turbulent
Solution:
Basic equation ReD
ρ U D
μ

U D
ν
 and transition occurs at about ReD 2.5 10
5

For air ν 1.62 10
4

ft
2
s
 (Table A.9)
For the American golf ball D 1.68 in Hence U
ν ReD
D
 U 289
ft
s
 U 197 mph U 88.2
m
s

For the British golf ball D 41.1 mm Hence U
ν ReD
D
 U 300
ft
s
 U 205 mph U 91.5
m
s

For soccer ball D 8.75 in Hence U
ν ReD
D
 U 55.5
ft
s
 U 37.9 mph U 16.9
m
s
