In
fluid mechanics
Fluid mechanics is the branch of physics concerned with the mechanics of fluids ( liquids, gases, and plasmas) and the forces on them.
It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and ...
, the Roshko number (Ro) is a
dimensionless number
A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1) ...
describing oscillating flow mechanisms. It is named after the American Professor of Aeronautics
Anatol Roshko
__NOTOC__
Anatol Roshko (15 July 1923 – 23 January 2017) was a Canadian-born physicist and engineer. He was the Theodore von Kármán Professor of Aeronautics, Emeritus, at the California Institute of Technology, Pasadena, CA.
Roshko is know ...
. It is defined as
:
:
:
where
* St is the dimensionless
Strouhal number;
* Re is the
Reynolds number;
* U is mean stream velocity;
* ''f'' is the frequency of
vortex
In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in ...
shedding;
* ''L'' is the characteristic length (for example
hydraulic diameter The hydraulic diameter, , is a commonly used term when handling flow in non-circular tubes and channels. Using this term, one can calculate many things in the same way as for a round tube. When the cross-section is uniform along the tube or channel ...
);
* ''ν'' is the
kinematic viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
of the fluid.
Correlations
Roshko determined the correlation below from experiments on the flow of air around circular cylinders over range Re=50 to Re=2000:
:
valid over
50 <= Re < 200:
valid over
00 <= Re < 2000
Ormières and Provansal
[Ormières and Provansal (1999), Figure 5] investigated vortex shedding in the wake of a sphere and found a relationship between Re and Ro in the range 280 < Re < 360.
Notes
References
*
*
*
{{NonDimFluMech
Dimensionless numbers of fluid mechanics
Fluid dynamics