A numerical study of flow and mass transport processes around active filtering, partially burrowed freshwater mussels
Creators: name: Wu, Hao
Publisher: name: University of Iowa
Year: 2026
Subjects: subject: Drag forces
subject: Freshwater mussels
subject: Mass transport processes
subject: Numerical simulations
subject: Sediment entrainment
subject: public abstract
subject: Ecology
subject: FOS: Biological sciences
subject: Turbulence

description: Freshwater mussels play several important roles for stream ecology. They actively filter organic matter from the water column to obtain food and burrow part of their shell into the substrate to prevent being dislocated by the flows. However, the interactions between mussels and the hydrodynamic conditions inside their habitat were poorly understood. The primary goal of this study is to understand flow, turbulence and mass transport processes around mussels, to describe the main mechanisms that are responsible for the dislocation of mussels from the substrate and the entrainment of particles from the bed, and how these mechanisms are affected by the main physical parameters associated with isolated mussels and mussel bed. Obtaining such knowledge is necessary to improve mussel habitat conditions. A fully 3-D eddy-resolving numerical model based on the Detached Eddy Simulation approach is developed to investigate flow in a flat-bed channel containing active filtering, partially burrowed freshwater mussels. Simulations conducted for isolated mussels show that the interactions between the incoming flow and the exposed part of the mussel generate large-scale coherent structures. These large-scale coherent structures play a very significant role in controlling the near-bed flow. They affect the drag force acting on the mussels, the capacity of the flow to induce sediment entrainment from the bed and the transport processes around mussels.
description: To investigate the effect of mussel-to-mussel interactions on flow hydrodynamics, mussel bed stability and the scalar concentration field characterizing mixing between the filtered water originating in the excurrent siphons and the water in the incoming flow, several series of simulations were performed in open channels containing large arrays of mussels. Even for cases with relatively high mussel bed density, the flow structure around the mussels in the array bears many similarities with that observed around an isolated mussel. Mussel clustering increases the capacity of the mussels to resist dislodgement by the overflow and lowers the bed erosion potential.
description: The present study provides detailed information on the structure and the spatial development of the (width-averaged) turbulent boundary layer induced by the interaction of the incoming flow with the emerged parts of the mussels. The vertical profiles of width-averaged streamwise velocity, scalar concentration and turbulent kinetic energy (TKE) inside the boundary layer are analyzed. With proper nondimensionalization, the streamwise velocity, scalar concentration and TKE profiles are found to be self-similar inside the outer region extending from the top of the mussels to the top edge of the boundary layer. Analytical models are proposed to describe the self-similar profiles of these variables. In addition, an analytical model containing three subzones is proposed to characterize the velocity profile from the channel bed to the top of the boundary layer.