Large Eddy Simulation of Wave-driven Hydrodynamics through Emergent Aquatic Vegetation

Vegetation in coastal wetlands provides natural protection against
storm surges and extreme waves. The capacity of this aquatic
vegetation to attenuate waves reaching a coastline depends on the
extent to which wave energy is dissipated by small-scale
hydrodynamic interactions within a canopy, which is often
parameterised using a drag coefficient ܥௗ. Existing models for
predicting ܥௗ are usually dependent solely on flow characteristics
and neglect the hydrodynamic impact of adjacent stems. In this
study, the flow structure inside a canopy under wave-driven
oscillatory flow conditions is examined numerically to
investigate the mechanisms that govern drag forces and wave
dissipation by emergent vegetation. Large Eddy Simulations of
oscillatory flow through an emergent canopy, modelled as an
array of rigid cylinders, show that the streamwise force exerted
on a cylinder inside an array is different to that of a single
cylinder, to an extent that depends on values of the KeuleganCarpenter
and Reynolds numbers. Moreover, vorticity and
velocity fields reveal that the structure of the flow around a single
cylinder is altered by the presence of neighbouring cylinders at
array densities typical of coastal vegetation stands. The results of
this study are beneficial for developing improved models for
vegetation-induced wave attenuation.