Laboratory and numerical investigations on characteristics of air bubbles in plunging breakers on beach

Abstract

We present an experimental-numerical study on air entrainment and the statistics of air bubbles in plunging breaking waves in surf zones on a beach. In the experimental investigation, the evolution, numbers, and sizes of air bubbles in breaking waves are recorded. The relations are discussed between microscopic behaviors of these air bubbles and influential macrocopic factors including distance to the wave-breaking point, wave height, water depth, and depth of measurement. Empirical expressions for bubble sizes are formulated as functions of these factors. Base on three-dimensional, high-resolution, air-bubble-resolving numerical modeling, a further study is conducted on details of the fields of velocity, vorticity, and turbulence kinetic energy. It is conjectured with evidence that the number of bubbles is linearly correlated to turbulence kinetic energy within breaking waves. The multiscale physical phenomena and correlations between air bubbles behaviors and their influential factors revealed in this study shed light on understanding and quantifying air bubbles characteristics in breaking waves within surf zones.