The Hydrodynamic Forces and the High Frequency Noise Resulting from Cavitation on Underwater Bodies

Citation

Daily, James Wallace (1945) The Hydrodynamic Forces and the High Frequency Noise Resulting from Cavitation on Underwater Bodies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5S51-F383. https://resolver.caltech.edu/CaltechETD:etd-03262007-103144

Abstract

Water Tunnel measurements were made of the hydrodynamic forces and moments, and of the high frequency noise resulting from cavitation on underwater bodies. All stages of cavitation from incipient to the full cavity were covered by the investigations. The main findings of the force measurements are: 1. There is no sudden increase in drag with inception of cavitation. The sharp rise occurs only after the normal flow pattern is completely altered by an appreciable amount of visible cavitation. 2. A qualitative comparison of cavitation and separation indicates that they have the same basic effect on the flow in the boundary layer, and hence on the skin friction drag. For blunt bodies with severe separation for noncavitating conditions, the first appearance of cavitation does not immediately alter the flow pattern nor the drag. 3. Cavity drag measurements agree closely with values calculated from measured pressure distributions and for a given value of the cavitation parameter, K, are proportional to the bubble size relative to the diameter of the body. 4. Cavity cross force and moment depend on the cavity shape, and hence on the shape of the body at the point where cavity separation occurs. With spherical tipped noses so proportioned that the cavity separates on the spherical segment, not only at zero but at the maximum yaw, the cross force is zero independent of yaw, and the moment is caused by the drag only. Other shapes produce asymmetrical cavities and definite cross forces and moments. 5. With complete projectiles the conditions for cavity flow with tail sticking through the side of the cavity are reproduced. A low cross force with a zero or stabilizing moment is obtained. Measurements of the sound emitted in the 20 to 100 KC frequency range with the beginning and growth of cavitation show: 1. With appearance of the slightest trace of cavitation, the acoustic pressure increases to several times the value of the background noise. 2. The maximum noise is measured when the zone of cavitation is limited to a very narrow band of small bubbles. With further growth the measured sound drops off. 3. The main source of sound is in the region of the trailing edge of the cavitation zone where the vapor bubbles are collapsing. If, as at advanced stages, the vapor bubbles are entrained and swept down stream before collapsing, the noise level drops

Thesis Files