Numerical investigation of the restored oyster reef flow field with the lattice Boltzmann method

Abstract

Oyster reefs play a dual role in the ecological and economic sustainability of global estuarine resources. Due to human activity and climate change, the prevalence of cosmopolitan oyster reefs has noticeably declined in recent decades, triggering a global restoration movement. However, the hydrodynamic functions of oyster reefs during and after restoration, particularly the impacts of growth and morphology on the flow field, remain poorly understood. This study employs the lattice Boltzmann method coupled with large-eddy simulation to simulate unidirectional flow around restored oyster reef models using the open-source Palabos library. It examines the effects of unidirectional flow velocity and reef morphology on hydrodynamic characteristics. The research analyzes spatial and temporal variations in velocity, vorticity, and turbulence structure around the reef. The findings indicated significant flow field differences between the initially restored reefs and those post-restoration. The dimensionless wake region scale parameters of the initially restored reefs exhibit hysteresis effects, generating larger turbulence during the post-recruitment stage than in the initial stage. Areas of high turbulence in the wake are associated with above-canopy flow, bypass flow, and within-canopy flow. The presence of gaps and branches in the reef leads to complex turbulence structures and irregular vortex shedding in the reef's wake at the post-recruitment stage. These results are valuable for assessing oyster reef resilience and planning effective restoration interventions.