Cavitating Flows

There are very few differences between the fluid dynamics of liquids and gases. The viscosity of water, for example, is 10^-2 poise at 20° C while the viscosity of air at this temperature is about 2 X 10^-4 poise. The kinematic viscosity of water is 10^-2 cm^2/sec compared with 0.15 cm^2/sec for air. As one would expect from simple kinetic theory, the viscosity of gases increases with increasing temperature; the viscosity of liquids on the other hand decreases rather rapidly as the temperature rises. While the speed of sound in water is about four times that in air, there is a more interesting consequence of the equation of state. A pressure pulse with an intensity of several hundred psi, which propagates as a strong shock in air, will propagate acoustically in water with a negligible production of entropy.