11.1 Vortex shedding from the alternate downstream
sides of a bluff body in a fluid flow may excite structural resonances,
for example, in boiler economiser tubes, chimneys, fins, or propeller
blades. The frequency of shedding is given in terms of the Strouhal
number, Sn
, and this in turn is a function
of the Reynolds number, Re
. The Strouhal number
is defined as:
where:
|
f
|
= |
frequency
of shedding of vortices, Hz. |
|
Sn
|
= |
Strouhal number = 0.2 very approximately for rough surfaces
and Re
in the range 3 x 102 to
3 x 105.
|
|
V0
|
= |
free-stream velocity, m/s. |
|
d
|
= |
effective
diameter of trailing edge or characteristic width, m. |
|
Re
|
= |
|
|
υ
|
= |
kinematic
viscosity of fluid (dynamic viscosity/density), m2/s.
|