Investigation of the wedge-shaped propelled surface for laser propulsion in water environment

Abstract

Dynamics of laser-induced cavitation bubbles on different wedge-shaped propelled surfaces, including 30°-surfaces, 90°-surfaces and 180°-surfaces, were investigated for laser propulsion in water environment by means of an optical beam deflection method. The expansion of the bubble on the three kinds of surfaces was simulated numerically. The pressure fields on the inner side of the surfaces and the energy that the propelled surfaces received from the expanding bubble were investigated numerically. For the three kinds of surfaces, the collapse times of the nonspherical bubbles were all less than the Rayleigh collapse time of the spherical bubble. The bubble on a narrow-shaped surface grew faster in a certain direction, which indicates that the propelling force was concentrated spatially and temporally. However, the most narrow-shaped surface did not get the most propelling energy. The repetition rate and spatial array density of the laser pulse cannot be too high, because of the scattering effect of the bubble. As a result of the laser plasma shielding and bubble scattering, high pulse energy does not necessarily result in a high propelling force. The narrow-shaped surfaces experienced higher shock damage, and emitted stronger noise.