Atwood number
The Atwood number is a dimensionless number in fluid dynamics used in the study of hydrodynamic instabilities in density stratified flows. It is a dimensionless density ratio defined as
where
= density of heavier fluid
= density of 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, 
[1] where g is the gravitational acceleration and t is the time.
References
- ^ Glimm, J.; Grove, J. W.; Li, X.-L.; Oh, W.; Sharp, D. H. (2001). "A critical analysis of Rayleigh–Taylor growth rates". J. Comput. Phys. 169 (2): 652–677. Bibcode 2001JCoPh.169..652G. doi:10.1006/jcph.2000.6590.
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