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中文核心期刊

粗糙床面物质交换特性及其主导机制实验研究

EXPERIMENTAL STUDY ON INTERFACIAL MASS EXCHANGE PROCESS AND ITS DOMINANT MECHANISM FOR ROUGH BED

  • 摘要: 粗糙底床泥-水界面区域的物质交换过程不仅与水动力作用有关,还涉及到底床物理特性和床面形态的影响. 为研究粗糙底床渗透率和床面微地形对泥-水界面物质交换过程的综合影响,通过实验室环形水槽实验,测量得到不同砂质平整底床和存在离散粗糙元床面条件下,泥-水界面物质交换通量和有效扩散系数的定量数据和变化特征,并采用参数化方法分析无量纲控制参数变化范围内界面物质交换特性的主导机制. 实验结果表明,粗糙底床渗透率和床面微地形共同对泥-水界面物质交换过程起重要作用. 与平整底床相比,离散粗糙元局部绕流结构驱动的附加泵吸交换不同程度增大了界面物质交换通量,其增强效应与底床渗透率和床面粗糙度的变化密切相关. 随底床渗透率和床面粗糙度的增大,有效扩散系数总体呈增大趋势,湍流渗透对界面物质交换的影响趋于增强,而泵吸交换的相对贡献趋于减弱. 因此,分析存在床面微地形粗糙底床的主导界面物质交换机制,需要考虑底床渗透率和床面粗糙度的综合影响.

     

    Abstract: The mass exchange across sediment-water interface for rough bed depends on not only the hydrodynamic condition, but also the physical feature of the sediment bed and the bedform configuration. To take the comprehensive impact of sediment permeability and microtopography for the rough bed on the mass exchange process across the sediment-water interface into account, quantitative data and variation characteristics of interfacial mass exchange flux and effective diffusion coefficient under different conditions of the sandy beds without and with discrete roughness elements have been measured and obtained by means of laboratory annular flume experiment. A parameterization method has been adopted to analyze the dominant mechanism of interfacial mass exchange within the variation range of non-dimensional controlling parameters. The experimental results indicate that the sediment permeability and microtopography of the rough bed play a key role in the interfacial mass exchange process. An additional bumping exchange driven by the local flow structure around each roughness element increases interfacial mass exchange flux to varying degrees as compared to that for the case of flat bed, and this enhancement effect is closely related to the variations of the sediment permeability and bed roughness. The effective diffusion coefficient tends to increase on the whole with the increasing sediment permeability and bed roughness. Turbulence penetration shows an enhanced effect on the interfacial mass exchange, and the relative importance of the bumping exchange shows an attenuated effect trend. Therefore, an analysis of the dominant interfacial mass exchange mechanism for the rough bed with microtopography should take the comprehensive impact of the sediment permeability and bed roughness into consideration.

     

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