Characteristic time, length, and velocity scales of transverse flows in the surf zone
Characteristic time, length, and velocity scales of transverse flows in the surf zone
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冲浪区横流的特征时间、长度和速度尺度
DOI：
10.1142/s0578563415500060
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发表时间：
2015
影响因子：
2.4
通讯作者：
Yasunori Watanabe
中科院分区：
文献类型：
--
作者：
Junichi Otsuka;Yasunori Watanabe
超声波速度剖面仪（UVP）采集从换能器发射的超声波束沿着轴向速度的瞬时分布。本文在UVP测量的基础上，对一个实验室波浪水槽上的碎波带横流组织进行了实验研究。无论破碎机条件如何，在碎波区水槽的跨度上观察到了平均发散和收敛流。通过与Watanabe和Saeki [1999]先前计算中的流动演变进行类比，我们发现波浪破碎诱导的反向旋转涡的组织决定了破碎过程早期阶段横向流动的空间和时间变化，而与波浪水槽的宽度以及侧壁和底部的摩擦无关。所观察到的横向流动是由破碎波下产生的反向旋转的涡对和破碎波通过期间的方向变化驱动的。的基本特征的横向流演变在破碎过程中，根据破碎机的类型，统计讨论参数化速度，时间和长度尺度的横向速度的变化。无量纲长度和时间尺度与弗劳德数呈负线性相关（由相对于重力的相对横向对流定义）以及冲浪相似性参数，其指示与破碎波峰的投影相关联的重力效应定义了在倾翻位置处的主要滚子涡度和剪切强度，导致横向流动不稳定，形成有组织的横向流动结构。
An ultrasonic velocity profiler (UVP) acquires instantaneous distributions of axial velocity along the ultrasonic beam emitted from the transducer. In this paper, organizations of the transverse flows over a span of a laboratory wave flume in the surf zone were identified experimentally on the basis of UVP measurements. Ensemble mean divergent and convergent flows were observed over the span of the flume in the surf zone regardless of breaker conditions. By analogy with the flow evolution in a previous computation, by Watanabe and Saeki [1999], we identified that the organization of the wave-breaking-induced counter-rotating vortices determined the spatial and temporal variations in the transverse flows at the early stages of the breaking process regardless of the widths of wave flumes and friction on the sidewalls and bottom. The observed transverse flows were driven by pairs of counter-rotating vortices produced under the breaking waves and the change in the orientation during the passage of breaking waves. The fundamental features of the transverse flows evolving in the breaking process, depending on the breaker type, are discussed statistically to parameterize velocity, time, and length scales of the variations of the transverse velocity. The dimensionless length and time scales had negative linear correlations with the Froude number (defined by relative transverse convection with respect to gravity) as well as a surf similarity parameter, which indicates that the gravity effect associated with the projections of the breaking wave crests defines the primary roller vorticity and shear intensity at the plunging location, resulting in destabilization of the flows in the transverse direction to form organized transverse flow structures.