Cavitation number

Physical key figure
Surname	Cavitation number
Formula symbol	${\displaystyle \sigma }$
dimension	dimensionless
definition	${\displaystyle \sigma ={\frac {p-p_{\text{v}}}{{\frac {1}{2}}\rho U^{2}}}}$
${\displaystyle \rho }$ Density of the fluid ${\displaystyle p}$ static pressure ${\displaystyle p_{\text{v}}}$ Vapor pressure ${\displaystyle U}$ Flow velocity

The cavitation number is a dimensionless number from the similarity theory and is used to describe fluids in fluid mechanics . It has a similar structure to the Euler number . The cavitation number is a measure of when the fluid cavitates . Its definition is: ${\displaystyle \sigma }$

${\displaystyle \sigma ={\frac {p-p_{\text{v}}}{{\frac {1}{2}}\rho U^{2}}}}$

With

• the pressure in the undisturbed flow ${\displaystyle p}$
• the vapor pressure of the fluid ${\displaystyle p_{\text{v}}}$
• the density of the undisturbed fluid ${\displaystyle \rho }$
• the flow velocity . ${\displaystyle U}$

In the counter is the pressure difference that will be zero when the onset of cavitation is theoretically expected. The denominator represents the dynamic pressure of the flow.

When the pressure of the fluid drops so far that it is less than or equal to the vapor pressure of the fluid, the fluid goes into the gas phase - it cavitates; in so occurs theoretically on cavitation. In real fluids, foreign particles and other properties not taken into account in the idealization can lead to the cavitation being shifted to a pressure other than . ${\displaystyle p}$ ${\displaystyle p_{\text{v}}}$ ${\displaystyle \sigma \leq 0}$ ${\displaystyle p_{\text{v}}}$

swell

• A. Keller, R. Huber, Laws of scale for cavitation, Technical University of Munich ( Memento from November 20, 2004 in the Internet Archive )

Individual evidence

1. ↑ Heinz M. Hiersig (Ed.): Lexicon of engineering knowledge basics . Springer Verlag, 2013, ISBN 978-3-642-95765-9 , pp. 371 ( limited preview in Google Book search).