In fluid mechanics, the Roshko number (Ro) is a dimensionless number describing oscillating flow mechanisms. It is named after the American Professor of Aeronautics Anatol Roshko. It is defined as
R
o
=
f
L
2
ν
=
S
t
R
e
R
o
=
0.212
R
e
−
4.5
valid over [ 50 <= Re < 200]
R
o
=
0.212
R
e
−
2.7
valid over [200 <= Re < 2000]
S
t
=
f
L
U
,
R
e
=
U
L
ν
where
St is the dimensionless Strouhal number;
Re is the Reynolds number;
U is mean stream velocity;
f is the frequency of vortex shedding;
L is the characteristic length (for example hydraulic diameter);
ν is the kinematic viscosity of the fluid.
Note: Linear relation between Ro# and Re# from Roshko's Caltech Thesis (figures 9-10); tested in air [over range Re=50 to Re=2000]
The kinematic viscosity of air at 15 °C is 1.48
×10
−5 m
2/s.
at 20 °C, the kinematic viscosity is 1.525
×10
−5 m
2/s.
at 25 °C, the kinematic viscosity is 1.57
×10
−5 m
2/s.
