Experimental Study of Two-Phase Suspended Sediment Transport in Breaking Waves

这个项目是为了研究破碎波中的大尺度湍流结构以及这些大涡流与可蚀层的相互作用。实验室实验将在一个25米长、0.9米宽、0.75米深的倾斜水槽中进行，该水槽配备了可编程波浪发生器。泥沙颗粒的平坦床将被放置在水槽底部的凹槽中。体积三分量测速（V3V）系统将用于在溢出波和俯冲波条件下，在可蚀层上方的三维流动体积中同时测量沉积物颗粒速度、沉积物颗粒位置和流体速度。两相流测量将用于了解大涡流的拓扑结构，以及大涡流在河床泥沙吸收过程中的作用和水柱上悬浮泥沙的分布。智力优势：该项目将建立在首席研究员（PI）之前的工作基础上。它将解决破碎波的几个方面，这些方面仍然知之甚少，对于成功地预测冲浪区和海滩转变中的沉积物运输的数值方案的发展至关重要。在三维流动体积中测量三分量流体速度将使研究大涡流的演变以及它们如何从上层向底部对流。结合使用高速数字电影摄像机的流动可视化，测量结果将揭示大涡流的产生机制以及沿波峰的非均匀波浪破裂对其结构的影响。体积流体速度测量也将使研究人员能够检查底部大涡流的冲击。这一过程是瞬态的、三维的，其特点是撞击区瞬时湍流动能大，剪应力大。使用V3V系统同时测量可蚀地层上的颗粒位置、颗粒速度和流体速度是一项创新，将使项目研究人员能够解决破碎波中沉积物运输的三个基本问题。第一个问题涉及悬沙输运的适当底边界条件；具体而言，如何参数化破碎波湍流对泥沙吸收速率的影响。第二个问题涉及大涡流和悬浮粒子之间的相互作用。拟议的研究将回答以下问题：沉积物颗粒的瞬时速度与流体颗粒的瞬时速度有多接近？悬浮泥沙输运与湍流输运之间是否存在直接联系？泥沙分布过程可以模拟为扩散过程吗？第三个问题是破碎机类型对输沙的影响。研究者将解决以下问题：外冲浪区悬浮载荷运输的数量和方向如何与初破时的波浪特性相关？与其他机制（如板流输运）相比，这种输运方式有多重要？更广泛的影响：该项目将提供高质量的数据集，以测试和改进冲浪区破碎海浪和沉积物运输的详细模型。这样的模型将促进对破碎波如何侵蚀或沉积沉积物和影响滨水特性的理解。V3V在两相流测量方面的进展也将促进其在其他研究领域的发展和应用。研究人员将能够从PI的研究网站上下载测量数据。该项目将通过让本科生和研究生参与实验研究来培养下一代研究人员。获得拟议的V3V系统将为学生提供最先进的测量仪器，以进行流体力学的实验研究。将为本科生和研究生班开发两个使用V3V的新实验，以加强学生对流体力学原理的学习。PI还将使用该设备在涉及K-12学生的研讨会上进行流体流动现象的现场演示。这些活动的结果将是吸引更多的高中生（包括美国原住民学生）攻读科学和工程专业的大学学位，为本科生提供研究经验，通过支持有能力的学生进行基础研究，建立一个具有全国竞争力的研究生项目，并维持一个现代化的流体力学实验室，以供继续研究和教育。

This project is to investigate the structure of large-scale turbulence in breaking waves and the interaction of these large eddies with an erodible bed. Laboratory experiments will be carried out in a 25 m-long, 0.9 m-wide and 0.75 m-deep tilting flume equipped with a programmable wave generator. A flat bed of sediment particles will be placed in a recess in the flume floor. A volumetric three-component velocimetry (V3V) system will be used to measure sediment particle velocities, sediment particle locations, and fluid velocities simultaneously in a three-dimensional (3-D) flow volume above the erodible bed under spilling and plunging wave conditions. The two-phase flow measurements will be used to understand the topology of large eddies, and the role of large eddies in the sediment pickup process at the bed and the distribution of suspended sediment over the water column.Intellectual Merit: This project will build on prior work of the principal investigator (PI). It will address several aspects of breaking waves that are still poorly understood and are critical to the development of successful numerical schemes for predicting sediment transport in the surf zone and beach transformation. Measurement of three-component fluid velocities in a 3-D flow volume will enable thestudy the evolution of large eddies and how they are convected from the upper layer to the bottom. In conjunction with flow visualization using a high-speed digital movie camera, the measurements will shed light on the generation mechanisms of large eddies and the effect on their structure of non-uniform wave breaking along the wave crest. The volumetric fluid velocity measurements will also allow the investigator to examine the impingement of large eddies on the bottom. This process is transient and three-dimensional, characterized by large instantaneous turbulent kinetic energy and shear stresses in the impingement area.The simultaneous measurement of particle location, particle velocity, and fluid velocity over an erodible bed using a V3V system is innovative and will allow the project's investigator to address three fundamental problems in sediment transport in breaking waves. The first problem relates to the appropriate bottom boundary conditions for suspended sediment transport; specifically, how to parameterize the effect of breaking wave turbulence on the sediment pick-up rate. The second problem concerns the interaction between large eddies and suspended particles. The proposed research will answer questions such as: How closely do the instantaneous velocities of sediment particles follow those of fluid particles? Is there a direct link between suspended sediment transport and turbulence transport? Can the sediment distribution process be modeled as a diffusion process? The third problem concerns the effect of breaker types on sediment transport. The investigator will address the following questions: How do the quantities and direction of suspended load transport in the outer surf zone relate to the wave characteristics at incipient breaking? How important is this mode of transport compared to other mechanisms such as sheet-flow transport?Broader Impacts: This project will provide a high quality data set to test and improve detailed models of breaking waves and sediment transport in the surf zone. Such models will advance understanding of how breaking waves erode or deposit sediments and impact water-front property. Advances in two-phase flow measurements using V3V will also stimulate their development and application in other research fields. Researchers will be able to download the measured data from PI's research website.The project will train the next generation of researchers by engaging both undergraduate and graduate students in experimental investigation. Acquisition of the proposed V3V system will provide students with a state-of-the-art measurement apparatus to conduct experimental investigation in fluid mechanics. Two new experiments using V3V will be developed for both an undergraduate and a graduate class to enhance student learning of fluid mechanics principles. The PI will also use the equipment to conduct live demonstrations of fluid flow phenomena in workshops involving K-12 students. The outcomes of these activities will be to attract more high school students (including Native American students) to pursue a college degree in science and engineering, to provide research experiences to undergraduate students, to build a nationally competitive graduate program by supporting capable students to conduct basic research, and to maintain a modern fluid mechanics laboratory for continued research and education.