Turbulence Driven Hyporheic Exchange Processes with Highly Permeable Channel Beds

具有高渗透性通道床的湍流驱动的潜流交换过程

• 批准号: 0738690
• 负责人: Thorsten Stoesser
• 金额: $ 24.98万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-02-01 至 2012-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738690&HistoricalAwards=false
• 关键词: Turbulence; Driven; Hyporheic; Exchange; Processes

TURBULENCE DRIVEN HYPORHEIC EXCHANGE PROCESSES WITH HIGHLY PERMEABLE CHANNEL BEDSThe main objective of this project is to investigate the effect of spatial and temporal heterogeneity created by episodic turbulent events and coherent flows on hyporheic exchange with permeable channel beds. The fundamental challenge is the evaluation of the effect of coherent flow structures on hyporheic exchange processes and the ability to provide accurate predictions of fluid and solute influxes into and outfluxes from the hyporheic zone. This will be the first study that investigates the instantaneous flow field and will advance knowledge of the hydrodynamics as well as transport processes of hyporheic zones, which are critical to quantitatively analyze stream eco-systems. The numerical method proposed, i.e. Large-Eddy Simulation, provides impressive predictive accuracy in flows which feature pronounced periodic components and/or in which turbulence transport is dictated by the dynamics of large scale eddies as present in flows over permeable beds or around flow obstacles. This study will be the first to model explicitly the individual particles that constitute the hyporheic zone. Consequently, governing flow and transport processes are represented explicitly and can be studied in microscopic detail.Two distinct scenarios will be investigated, (a) flow over a flat gravel-type bed where hyporheic exchange is solely induced by large-scale turbulence created and induced by the texture of the bed and (b) flow over submerged and emergent boulder-type obstruction buried in a gravel-type bed, where hyporheic exchange is driven by both quasi-steady pressure gradients and large-scale coherent flow structures as a consequence of vortex shedding from the flow obstruction. Quantification of the exchange will be accomplished by adding a tracer study to the hydrodynamic investigations, with which mass and momentum exchange can be calculated directly. Further evidence of the effect of coherent structures on hyporheic exchange will be provided by a detailed statistical analysis of the mean and instantaneous flow field especially at the interface for instance with quadrant analysis, probability density functions, etc. The outcome of the proposed research is a comprehensive understanding of the physical mechanisms of turbulence driven hyporheic exchange and will provide very accurate quantification of exchange rates for different conditions.

本项目的主要目的是研究由间歇性湍流事件和相干流引起的时空非均匀性对具有渗透性河床的潜流交换的影响。最根本的挑战是评估相干流结构对潜流交换过程的影响，以及提供准确预测流体和溶质流入和流出潜流区的能力。这将是第一项研究，调查瞬时流场，并将推进知识的流体动力学以及运输过程的潜流区，这是至关重要的定量分析流生态系统。所提出的数值方法，即大涡模拟，提供了令人印象深刻的预测准确性，在流动的特点明显的周期性成分和/或湍流运输是由大规模的涡流的动力学表现在可渗透的床或周围的流动障碍。这项研究将是第一个明确建模的个别粒子，构成的潜流区。因此，控制流和运输过程的代表明确，可以在微观细节研究。两个不同的情况下，将进行研究，（a）流过一个平坦的砾石型床，其中潜流交换是完全诱导的大规模湍流产生和诱导的纹理床和（B）流过淹没和涌现的巨石型障碍物埋在砾石型床，其中，准稳态压力梯度和大尺度相干流结构都驱动了潜流交换，而大尺度相干流结构是由流动障碍物的旋涡脱落引起的。 将通过在流体动力学调查中增加示踪剂研究来实现交换的量化，从而可以直接计算质量和动量交换。通过对平均流场和瞬时流场的详细统计分析，特别是在界面处，例如象限分析、概率密度函数等，将提供相干结构对潜流交换影响的进一步证据。 拟议的研究结果是一个全面的了解湍流驱动的hyporheic交换的物理机制，并将提供非常准确的量化不同条件下的汇率。