Modelling coupled turbulence - Dissolved oxygen dynamics near the sediment-water interface under wind waves and sea swell

WATER RESEARCH

卷:44

Article

Chatelain, Mathieu^1,2  Guizien, Katell^1,2 

[1] CNRS, LOBB, UMR 7621, Observ Oceanolog, F-66651 Banyuls Sur Mer, France

[2] Univ Paris 06, LOBB, UMR 7621, UPMC,Observ Oceanolog, F-66651 Banyuls Sur Mer, France

关键词: Wave boundary layer;    Mass transfer;    Turbulent diffusion;    Unsteady flow;    Sediment diagenesis;   

DOI  :  10.1016/j.watres.2009.11.010

来源: Elsevier

【 摘 要 】

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 30 s). 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) over bar < 0.05. VAR(Sh) < 0.1%). In the turbulent regime, the cycle-averaged Sherwood number is larger ((Sh) over bar approximate to 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. Ass result of these two processes, when the wave period decreases, the Sh minimum increases and the (Sh) over bar maximum decreases. Sh values vary little, ranging from 0.17 to 0.23. For periods up to 30 s, oxygen penetration depth into the sediment did not show any intra-wave fluctuations. Values for the laminar regime are small (<= 1 mm for mu = 2000 g m(-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. (C) 2009 Elsevier Ltd. All rights reserved.

【 授权许可】

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