On the Mechanism of Cavitation Damage by Non-Hemispherical Cavities Collapsing in Contact with a Solid Boundary

Author: Naudé, Charl François

Year: 1960

Degree: Dissertation (Ph.D.)

Advisor: Ellis, Albert T.

Committee Member: Unknown, Unknown

Option: Mechanical Engineering

DOI: 10.7907/QACP-9A29

Abstract

A perfect fluid perturbation theory, which neglects the effect of gravity, and which assumes that the pressure inside a cavitation bubble remains constant during the collapse process, is given for the case of a non-hemispherical, but axially symmetric cavity which collapses in contact with a solid boundary. The theory suggests the possibility that such cavities may deform to the extent that the cavity wall strikes the solid surface before minimum cavity volume is reached.

High speed motion pictures of cavities generated by spark methods are used to test the theory experimentally. It is found that the theory describes the change of shape of such cavities fairly well, and that the phenomenon of the cavity wall striking the solid boundary does indeed occur.

By studying the damaging effects of various cavities of this type on aluminum samples, it is shown that pressures resulting from the cavity wall striking the surface are much higher than pressures caused by compression of gases inside the cavity. It is furthermore found that the estimated impact velocities of the cavity walls on the solid boundary can account for water hammer pressures sufficiently large to have caused the observed damage.

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