8 - Cavitation

Summary

Here, following a brief account of early observations of the effects of cavitation on ship propellers, we present methods of estimation of conditions at inception of cavitation followed by an outline of the development of linearized theory of cavitating sections. Application of this theory is made to partially cavitating sections, employing the rarely used method of coupled integral equations. The chapter concludes with important corrections to linear theory and a brief consideration of unsteady cavitation.

HISTORICAL OVERVIEW

Cavitation or vaporization of a fluid is a phase change observed in high speed flows wherein the local absolute pressure in the liquid reaches the vicinity of the vapor pressure at the ambient temperature. This phenomenon is of vital importance because of the damage (pitting and erosion) of metal surfaces produced by vapor bubble collapse and degradation of performance of lifting surfaces with extensive cavitation. It is also a source of high-frequency noise and hence of paramount interest in connection with acoustic detection of ships and submarines. Both “sheet” and “bubble” forms of cavitation are shown in Figure 8.1.

One of the earliest observations of the effects of extensive cavitation on marine propellers was made by Osborne Reynolds (1873) when investigating the causes of the “racing” or overapeeding of propellers. The first fully recorded account of cavitation effects on a ship was given by Barnaby (1897) in connection with the operation of the British destroyer Daring in 1894.