Hydrodynamics of Mangrove Roots and its Applications in Coastal Protection

Mangroves are tropical and sub-tropical coastal trees able to resist severe conditions including hurricanes and tropical storms. A potential characteristic of their resilience property is their complex root systems, which can be highly efficient to dissipate tidal energy. To further understand the key hydrodynamic parameters of mangrove trees, we modeled the rigid mangrove root system with a simplified array of circular cylinders (patch) and presented the simulation of the patch wake structure. Five patch porosities ranging from $\varphi =86$%to 96% $\left({\displaystyle \varphi =1-N\left({\frac {d}{D}}\right)^{2}}\right)$ were considered in numerical simulations with ANSYS Fluent. The complex two-dimensional flow structure of the cylinder wake was captured for various streamwise location including far wake region. In addition, the vorticity, and turbulence intensity contours were computed and analyzed. We compared the wake signature of the patch with a single cylinder of the same diameter. We found that, unlike the canonical cylinder, the vorticity field for the porous patch delays the formation of von Kármán vortex street due to the small vortices in the near wake. An increase in patch porosity gives rise to the delay of vortex street formation and decays the wake vorticity and turbulent kinetic energy. The characteristic of the wake structure behind the patch could be used as guiding reference for coastal protection structures inspired by mangrove roots. Additionally, we present mangrove application in coastal protection.