波流边界层内湍流拟序结构特征及其对底摩擦力的影响机理研究

Studies of wave-current interaction (WCI) play significant roles in sediment transport and marine energy exploitation. Existing studies have identified the non-linear characteristics of WCI by experimental approaches, and quantified the non-linearity using analytical and numerical models. However, there still lacks fundamental investigations of the non-linear interaction mechanism. The main objective of this project is to provide a comprehensive understanding of coherent structures in the bottom boundary layers of a combined wave-current flow. Based on physical experiments and numerical approaches, this project aims to investigate the changes of coherent structures induced by wave motions and reveal the physical mechanism of bed shear stress enhancement caused by WCI. Experiments will be conducted in a wave-current flume to measure velocity vectors using PIV techniques. This will be used to analyze temporal and spatial distributions of coherent structures under the effects of different wave conditions. In particular, time-averaged and phase-averaged spacing between low-speed streaks and quadrant contributions to Reynolds shear stress will be clarified. The experimental data will be used to establish the probability density function of streak spacing distributions, temporal and spatial distributions of turbulent vortex scales. Numerical simulations will be conducted using LES model to provide detailed information of variations of bed shear stress within one wave cycle. This will be used to clarify the correlation between streak spacing and bed shear stress values. Based on the experimental investigations, theoretical analysis and numerical simulations, the whole project aims to reveal the changes of velocity profiles and bed shear stress induced by wave-current interaction. The study can also provide theoretical basis for the development of sediment transport models.

波流相互作用研究对泥沙运移和近海新能源利用均有着极其重要的作用。已有研究主要通过实验发现了波流相互作用的非线性特征，并通过解析方法和数值模拟方法加以量化，但对其作用机理仍不明确。本项目着眼于波流边界层内湍流拟序结构，应用物模试验和数值分析方法，探究波浪作用下湍流拟序结构变化特征，揭示波流相互作用底摩擦力增加的物理机制。进行波流水槽试验，使用PIV技术获得速度矢量，分析不同波浪条件下湍流拟序结构时间、空间分布特征，获得低速条带间距时间平均和相位平均值、不同象限事件对雷诺应力的贡献，构建条带间距的概率密度分布函数，探讨湍流旋涡尺度的时间、空间分布规律。利用大涡模拟方法开展数值模拟研究，获得底摩擦力时间分布特征，构建低速条带间距与底摩擦力之间相关关系。基于物模试验所得规律，综合理论分析和数值模拟研究，揭示波浪对湍流边界层内流速和底摩阻力的影响机制。本课题的研究将为泥沙运移模型的发展奠定理论基础。

波流相互作用研究对泥沙运移和近海新能源利用均有着极其重要的作用。已有研究主要通过实验发现了波流相互作用的非线性特征，并通过解析方法和数值模拟方法加以量化，但对其作用机理仍不明确。本项目着眼于波流边界层内湍流拟序结构，系统研究了波浪作用下湍流拟序结构变化特征，揭示了波流相互作用底摩擦力增加的物理机制。通过实验和数值方面，全面回顾了波流相互作用这一科学问题的进展；概要介绍了已有研究的优点和局限性，并对今后该领域的研究、发展提出了建议。通过物模实验探究了湍流拟序结构特征，基于PIV、氢气泡实验技术，针对低速条带间距首次提出了积分空间尺度新方法，克服了海量样本数据处理的障碍，实现了波流条件下低速条带间距的实时测量。通过两个不同尺度水槽中的物模实验，首次提出了在强波弱流条件下涡粘系数的三层分布模型，并通过与大型振荡水洞实验数据对比，发现该数学模型可广泛适用于不同波流条件、壁面条件，弥补了传统理论在强波弱流条件下不再适用的不足，对于波流相互作用数值模拟以及泥沙运动模型均具有重要意义。通过物模实验和数值模拟实验，系统性地探究了波流共同作用下边界层内底摩擦力及湍流特征历时变化过程。通过物模实验，研究了湍流影响下Stokes漂流的物理过程及数学表达式。本研究可为海洋资源开发、泥沙运移预测提供科学依据，具有重要的学术价值和工程应用价值。