Numerical study of turbulence and wave damping induced by vegetation canopies
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Vegetation canopies control mean and turbulent flow structure as well as surface wave processes in coastal regions. A non-hydrostatic RANS model based on NHWAVE (Ma et al., 2012) is developed to study turbulent mixing, surface wave attenuation and nearshore circulation induced by vegetation. A nonlinear k- model accounting for vegetation-induced turbulence production is implemented to study turbulent flow within the vegetation field. The model is calibrated and validated using experimental data from vegetated open channel flow, as well as nonbreaking and breaking random wave propagation in vegetation fields. It is found that the drag-related coefficients in the k- model Cfk and Cf can greatly affect turbulent flow structure, but seldom change the wave attenuation rate. The bulk drag coefficient CD is the major parameter controlling surface wave damping by vegetation canopies. Using the empirical formula of Mendez and Losada (2004), the present model provides accurate predictions of vegetation-induced wave energy dissipation. Wave propagation through a finite patch of vegetation in the surf zone is investigated as well. It is found that the presence of a finite patch of vegetation may generate strong pressure-driven nearshore currents, with an onshore mean flow in the unvegetated zone and an offshore return flow in the vegetated zone. A non-hydrostatic wave model is developed to study turbulent mixing and wave attenuation induced by vegetation. Drag-related coefficients in model greatly affect turbulent flow structure, but seldom change the wave attenuation rate. The bulk drag coefficient is the major parameter controlling surface wave damping by vegetation canopies. Induces strong nearshore circulation with onshore mean current in clear region and return flow in vegetated region. 2013.
