CNRS, UMR 7621, LOBB, Observatoire Océanologique, F-66651 Banyuls/mer, France.
Water Res. 2010 Mar;44(5):1361-72. doi: 10.1016/j.watres.2009.11.010. Epub 2009 Nov 14.
A one-dimensional vertical unsteady numerical model for diffusion-consumption of dissolved oxygen (DO) above and below the sediment-water interface was developed to investigate DO profile dynamics under wind waves and sea swell (high-frequency oscillatory flows with periods ranging from 2 to 30s). We tested a new approach to modelling DO profiles that coupled an oscillatory turbulent bottom boundary layer model with a Michaelis-Menten based consumption model. The flow regime controls both the mean value and the fluctuations of the oxygen mass transfer efficiency during a wave cycle, as expressed by the non-dimensional Sherwood number defined with the maximum shear velocity (Sh). The Sherwood number was found to be non-dependent on the sediment biogeochemical activity (mu). In the laminar regime, both cycle-averaged and variance of the Sherwood number are very low (Sh <0.05, VAR(Sh)<0.1%). In the turbulent regime, the cycle-averaged Sherwood number is larger (Sh approximately 0.2). The Sherwood number also has intra-wave cycle fluctuations that increase with the wave Reynolds number (VAR(Sh) up to 30%). Our computations show that DO mass transfer efficiency under high-frequency oscillatory flows in the turbulent regime are water-side controlled by: (a) the diffusion time across the diffusive boundary layer and (b) diffusive boundary layer dynamics during a wave cycle. As a result of these two processes, when the wave period decreases, the Sh minimum increases and the Sh maximum decreases. Sh values vary little, ranging from 0.17 to 0.23. For periods up to 30s, oxygen penetration depth into the sediment did not show any intra-wave fluctuations. Values for the laminar regime are small (<or=1mm for mu=2000gm(-3)d(-1)) and decrease when the flow period increases. In the turbulent regime, the oxygen penetration depth reaches values up to five times larger than those in the laminar regime, becoming asymptotic as the maximum shear velocity increases.
开发了一种一维垂直非稳态数值模型，用于研究风浪和涌浪（周期为 2 至 30 秒的高频振荡流）下的溶解氧（DO）在水-底界面上下的扩散-消耗情况。我们测试了一种新的 DO 剖面建模方法，该方法将振荡紊流底层模型与基于米氏方程的消耗模型相结合。流态控制着波浪周期内氧气传质效率的平均值和波动，这由用最大剪切速度（Sh）定义的无量纲舍伍德数（Sherwood number）表示。研究发现，舍伍德数与沉积物生物地球化学活性（mu）无关。在层流区，平均循环和 Sherwood 数的方差都非常低（Sh<0.05，VAR（Sh）<0.1%）。在紊流区，平均循环的 Sherwood 数较大（Sh 约为 0.2）。Sherwood 数也存在波浪内周期波动，随着波浪雷诺数的增加而增加（VAR（Sh）高达 30%）。我们的计算表明，在紊流区高频振荡流作用下，DO 传质效率由：（a）扩散边界层的扩散时间和（b）波浪周期内扩散边界层的动力学控制。由于这两个过程，当波浪周期减小时，Sh 的最小值增加，最大值减小。Sh 值变化不大，范围在 0.17 到 0.23 之间。对于周期不超过 30 秒的情况，氧气在波浪内的穿透深度没有任何波动。层流区的值较小（对于 mu=2000gm(-3)d(-1)，值小于等于 1mm），随着流周期的增加而减小。在紊流区，氧气的穿透深度达到了层流区的五倍以上，随着最大剪切速度的增加而趋于稳定。
