A tall cell-phone tower is 12 cm in diameter over much of the height. A wind blows at 25 m/s. The frequency of the vortices being shed from the tower is nearest:
A) 44 Hz
B) 33 Hz
C) 22 Hz
D) 0 Hz

Question

Quizplus · Accepted Answer

$0 \mathrm {~Hz}$
$\text {The temperature of the air is not given so assume standard conditions. The Reynolds}$$\text { number is}$
$$\operatorname { Re } = \frac { V D } { v } = \frac { 25 \times 0.12 } { 1.5 \times 10 ^ { - 5 } } = 2 \times 10 ^ { 5 }$$
$\text {Refer to Fig. $8.10$ and observe that this Reynolds number is too high for vortices to be}$ $\text {shed so $f = \underline { 0 \mathrm {~Hz} }$. There would be a large steady separated region behind the tower.}$ $\text {The temperature would be insignificant since the Reynolds number would be too}$$\text { large for any wind temperature. Vortices would be shed at a much lower velocity.}$

A Tall Cell-Phone Tower Is 12 Cm in Diameter Over