分层水体通过复杂地形河道时的特性和机理：一种实验室模拟与实地水道观测有机结合的研究方法探索

分层水通过复杂地形时流场和密度场的动力机制重要而复杂，其理论围绕着随地形影响而变化的组合弗劳德常数，当其处于临界状态下时常常伴随着剪切不稳定或内波等现象。目前国内外的研究主要侧重于峡湾、大陆架等渐浅地形条件，而对于渐窄渐深水道的研究还不够完善。本项目拟应用实验室理想状态下的水槽模拟实验，利用PIV-PLIF（粒子成像技术-平面激光诱导荧光技术）得到同一时刻分层水的速度和密度场，模拟分层水体通过渐窄渐深水道，研究地形和初始弗劳德常数对分层水混合速率和动力机制的影响，并建立相应的理论模型。在此基础上，本项目拟运用杭州湾南部螺头水道现场锚系和剖面观测的数据，分析其在具体条件下的动力机制和湍流特性，并进一步验证实验室模拟的理论模型。该项目的研究成果将完善地形条件对分层水动力机制的理论，同时丰富对螺头水道附近海域的动力环境的研究，对进一步了解近海海洋动力机制具有重要的意义。

The gravitational exchange of two layer fluids with different densities is an important dynamics in the coastal ocean. The hydraulics of the two-layer flow highly depend on the composite Froude number along the channel. It has been reported that several physical phenomena (such as Kelvin-Helmhotz or Holmboe shear instabilities and internal waves) are associated when the two-layer flow in the critical condition (G=1). Although the mechanics on the maximal of two-layer hydraulic exchange have been developed over the past decades, most of previous researches focused on the situation with shoaling depth, such as fjord and continental shelf. The proposed project will investigate the hydraulics of the two-layer exchange flow through a channel with the combination of a deepening and contraction. The laboratory simulations obtain velocity and density field simultaneously by using the combined PIV-PLIF (particle image velocimetry – planer laser induced fluorescence) technology. By varying the inflow Froude number and channel width and depth, the dynamics of the two-layer flow is characterized by entrainment rate and buoyancy flux. The mechanism is then validated using in-situ observations including moored ADCP data and ship-based velocity and density measurements in Luotou channel in the Hangzhou Bay. The result of this project will explore the theory on the two-layer exchange flow hydraulics; in the addition, it also helps understand the dynamics near Luotou Channel. This study will improve our understanding of coastal dynamics and benefit in protecting our environment.