River water flows around circular 20-cm-diameter pier at 0.01 m/s. the flow is:
A) Creeping flow
B) Flow with a wake
C) Stokes flow
D) Low-Reynolds-number flow

Question

Quizplus · Accepted Answer

$\text { Flow with a wake}$
$\text {Calculate the Reynolds number:}$
$$\operatorname { Re } = \frac { V D } { v } = \frac { 0.01 \times 0.2 } { 10 ^ { - 6 } } = 2000$$
$\text {Obviously this is not a creeping flow (a Stokes flow or a low-Reynolds-number flow).}$$\text { A cylinder or a sphere must be very small before a creeping flow is observed. Even}$ $\text {though the water temperature could be different from $20 ^ { \circ } \mathrm { C }$, the kinematic viscosity}$ $\text {could not be such that the $\operatorname { Re } < 5$.}$

River Water Flows Around Circular 20-Cm-Diameter Pier at 0