Numerical Study of the Hydrodynamics of Mangrove-Inspired Structures for Coastal Protection

Mangrove forests are present on most of the shorelines in tropical regions. The submerged roots of mangroves have a vital role in multiple phenomena that happens along with the hydrodynamic interaction with incoming water flow, including sediment transport, shoreline erosion, CO2 capture, and wave mitigation, among others. The complicated hydrodynamic behavior of the mangrove roots with the incoming water flow can be related to the free stream velocity, the diameter of the roots, and the space between them. This study uses two-dimensional numerical simulations to estimate the flow characteristics through and around mangrove trees at a reasonable computational cost for practical applications. We modeled the mangrove trees as a constant circular array of diameter (D) containing small circular cylinders of diameter (d), which vary their size to represent different porosities. The numerical simulation uses Unsteady Reynolds Average Navier-Stokes simulations (URANS) with the k-omega shear-stress transport (SST) turbulence model at five Reynolds numbers based on the diameter of the porous cylinder within the subcritical regime (Re-D = 600, 1200, 1900, 2500, 3000), and at four different porosities of the array (phi = 0%, 47%, 70%, and 86%). The results of this simplified model show that the developed 2-D models capture the main characteristics of the flow behavior in the near and far wake of a porous cylinder, which agrees with previous experimental and more advanced numerical works. The porous bodies (phi = 0%, 47%, 70%) exhibit more elongated vortices than a solid cylinder (phi=0%) and a vortex street with delayed vortex roll-up in the near wake. Arrays with medium (phi=70%) and high (phi=86%) porosities reach smaller values of maximum velocity deficit in the wake compared with low porosity (phi=46%) and a solid cylinder (phi=0%). However, as the porosity increases, the velocity recovery in the far-wake occurs at a lower rate. The simulations developed in this study illustrate the main features of the flow and the forces of simplified mangrove models providing valuable insights to practitioners and engineers in the early design of engineered mangroves for coastal and marine life protection.