The Atwood number (A) is a
dimensionless number
Dimensionless quantities, or quantities of dimension one, are quantities implicitly defined in a manner that prevents their aggregation into unit of measurement, units of measurement. ISBN 978-92-822-2272-0. Typically expressed as ratios that a ...
in
fluid dynamics
In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...
used in the study of
hydrodynamic instabilities in density stratified flows.
It is a dimensionless density ratio defined as
:
where
is the density of the heavier fluid and
is the density of the lighter fluid.
Field of application
Atwood number is an important parameter in the study of
Rayleigh–Taylor instability and
Richtmyer–Meshkov instability. In Rayleigh–Taylor instability,
the penetration distance of heavy fluid bubbles into the light fluid is a function of acceleration time scale
where
is the gravitational acceleration and
is the time.
References
Dimensionless numbers of fluid mechanics
Fluid dynamics
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