Settling velocity of sediments at high concentrations
Settling velocity of sediments at high concentrations
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DOI：
10.1016/j.coastaleng.2003.12.004
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发表时间：
2004-03
影响因子：
4.4
通讯作者：
T. Baldock;M. Tomkins;P. Nielsen;M. Hughes
中科院分区：
文献类型：
--
作者：
T. Baldock;M. Tomkins;P. Nielsen;M. Hughes
给出了人工泥沙和天然沙在高浓度下的沉降速度的新数据。这些数据与广泛使用的半经验Richardson和Zaki方程(Trans.安装化学。英语。32(1954)35)，给出了作为浓度函数的流速减小的精确量度和实验确定的经验幂n，这里提出了一种利用清水沉降速度和固定泥沙床内渗流的标准方程来确定n的简单方法。将得到的n值与海滩和滤砂的新的和现有的实验室数据进行比较。对于沙子，合适的n值与Richardson和Zaki对球体的建议有很大不同，并且通常更大，对应于高浓度下沉降速度的较大降低。对于浓度为0.4量级的细砂和中砂，利用球体的n值，受阻沉降速度降低到预期的70%左右。在浓度为0.15量级时，受阻沉降速度降至清水中沉降速度的一半以下。这些降低的沉降速度对于模拟靠近、位于片状水流层内和冲刷区的泥沙传输具有重要的意义。
New data on the settling velocity of artificial sediments and natural sands at high concentrations are presented. The data are compared with a widely used semiempirical Richardson and Zaki equation (Trans. Inst. Chem. Eng. 32 (1954) 35), which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n. Here, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds. The resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands. For sands, the appropriate values of n are found to differ significantly from those suggested by Richardson and Zaki for spheres, and are typically larger, corresponding to a greater reduction in settling velocity at high concentrations. For fine and medium sands at concentrations of order 0.4, the hindered settling velocity reduces to about 70% of that expected using values of n derived for spheres. At concentrations of order 0.15, the hindered settling velocity reduces to less than half of the settling velocity in clear water. These reduced settling velocities have important implications for sediment transport modelling close to, and within, sheet flow layers and in the swash zone.