실험실에서 생성된 풍파 쇄파 아래에서의 응집구조 특성

Abstract

The results of an experimental investigation of coherent structures generated beneath breaking wind waves are presented in this study. In a wind-wave flume, the velocity fields in the streamwise vertical plane beneath wind-generated waves were obtained by using a digital particle image velocimetry (DPIV). Three different winds were tested so that the wind-generated waves break either microscale or large-scale pattern near the end of the flume unless their amplitude is too small to break. The subsurface coherent structures in the velocity fields were visualized by the vorticity-based conditional sampling. Then, the characteristics of coherent structures generated by the two different breaking phenomena, or microscale and large-scale wave breaking, were experimentally investigated. It was found that the direction of rotation of coherent structures was alternating either counter-clockwise or clockwise depending on each microscale breakers. In contrast, a single strong clockwise rotating coherent structure was mostly produced underneath the crest of large-scale breaking waves.