Author(s)

Falilou Coundoul^1*#, Evrad M. D. Ngom^1*, Frédéric Y. Moulin^2*

¹Institut Polytechnique de Saint-Louis, Université Gaston Berger, Saint-Louis, Senegal.
²Institut de Mécanique des Fluides de Toulouse, UMR 5502-Université de Toulouse, Occitanie, France.

In this article dedicated to the modeling of vertical mass transfers between the biofilm and the bulk flow, we have, in the first instance, presented the methodology used, followed by the presentation of various results obtained through analyses conducted on velocity fields, different fluxes, and overall transfer coefficients. Due to numerical constraints (resolution of relevant spatial scales), we have restricted the analysis to low Schmidt numbers (S_c=0.1, S_c=1, and S_c=10) and a single roughness Reynolds number (Re_*=150). The analysis of instantaneous concentration fields from various simulations revealed logarithmic concentration profiles above the canopy. In this zone, the concentration is relatively homogeneous for longer times. The analysis of results also showed that the contribution of molecular diffusion to the total flux depends on the Schmidt number. This contribution is negligible for Schmidt numbers S_c≥0.1, but nearly balances the turbulent flux for S_c=0.1. In the canopy, the local Sherwood number, given by the ratio of the total flux (within or above the canopy) to the molecular diffusion flux at the wall, also depends on the Schmidt number and varies significantly between the canopy and the region above. The exchange velocity, a purely hydrodynamic parameter, is independent of the Schmidt number and is on the order of 10% of in the present case. This study also reveals that nutrient absorption by organisms near the wall depends on the Schmidt number. Such absorption is facilitated by lower Schmidt numbers.

Epilithic Biofilm, Passive Scalar Transport, Direct Numerical Simulation, Navier-Stokes

Coundoul, F. , Ngom, E. and Moulin, F. (2024) Numerical Modeling of Mass Transfer in the Interaction between River Biofilm and a Turbulent Boundary Layer. Open Journal of Fluid Dynamics, 14, 1-23. doi: 10.4236/ojfd.2024.141001.