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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

THE DISTRIBUTION AND MOTION OF AIR BUBBLES IN THE WAKES OF STEADY BREAKING WAVES

J. H. Duncan
Department of Mechanical Engineering University of Maryland College Park, MD 20742

C. Y. Li
Department of Mechanical Engineering University of Maryland College Park, MD 20742

M. P. Miller
Department of Mechanical Engineering University of Maryland College Park, MD 20742

X. Liu
Department of Mechanical Engineering University of Maryland College Park, MD 20742

Abstract

Experimental measurements of the two-phase flow in two steady breaking waves with the same phase speed but different breaking intensities are presented. The measurements include the mean and root-mean-square surface height profiles of the breakers; the vertical distributions of mean horizontal velocity in the wakes; and the radii, spatial distributions, and velocities of the bubbles in the wakes. At positions ranging from 0.6 to 1.0 gravity wavelengths behind the breaker, the vertical distributions of void fraction are near zero at the free surface, reach peaks at depths between 10 and 20 mm below the free surface and tend to zero at larger depths. The bubbles move downstream in the reference frame of the wave and rise vertically at speeds that are less than that of a bubble of the same size rising in a quiescent fluid. Near the surface, the mean horizontal water and bubble velocities are equal, but in the wake shear layer the bubbles move more slowly than the water. The void fractions for the stronger breaker are larger than those for the weaker breaker.