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Turbulent viscosity in natural surf zones
Author(s) -
Grasso F.,
Ruessink B. G.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl054135
Subject(s) - turbulence , turbulence modeling , surf zone , turbulence kinetic energy , k epsilon turbulence model , reynolds stress , breaking wave , mechanics , reynolds stress equation model , dissipation , meteorology , geology , k omega turbulence model , viscosity , shore , turbulent diffusion , environmental science , physics , thermodynamics , oceanography , wave propagation , quantum mechanics
Waves breaking in the shallow surf zone near the shoreline inject turbulence into the water column that may reach the bed to suspend sediment. Breaking‐wave turbulence in the surf zone is, however, poorly understood, which is one of the reasons why many process‐based coastal‐evolution models predict coastal change during severe storms inadequately. Here, we use data collected in two natural surf zones to derive a new parameterization for the stability function C μ that determines the magnitude of the eddy viscosity ν t in two‐equation turbulent‐viscosity models, ν t = C μ k 2 / ε , where k is turbulent kinetic energy and ε is the turbulence dissipation rate. In both data sets, the ratio of turbulence production to dissipation is small (≈0.15), while vertical turbulence diffusion is significant. This differs from assumptions underlying existing C μ parameterizations, which we show to severely overpredict observed C μ for most conditions. Additionally, we rewrite our new C μ parameterization into a formulation that accurately reproduces our Reynolds‐stress based estimates of turbulence production. This formulation is linear with strain, consistent with earlier theoritical work for large strain rates. Also, it does not depend on ε and can, therefore, also be applied in one‐equation turbulent‐viscosity models. We anticipate our work to improve turbulence modeling in natural surf zones and to eventually lead to more reliable predictions of coastal evolution in response to severe storms.