SENSITIVITY STUDY OF A 2nd ORDER TURBULENCE MODEL IN A STRATIFIED TIDAL RIVER

Abstract eng:
Eddy viscosity calculated from the turbulent model has significant effects on vertical stratification. In this study, a three dimensional hydrodynamic model was applied to a strongly stratified tidal river. The model employed a 2nd order turbulent model (Mellor and Yamada, 1982) that has been widely used in the applications to large-scale geophysical flows. Field observations salinity and velocity at surface and bottom stations in Apalachicola River show strong stratification dependent to the river flow and tidal conditions. Using the default turbulent model parameters model predictions overestimate current and salinity stratification. In order to improve the performance of the turbulent model, a correction factor of eddy viscosity was proposed to allow the slight adjustment of the turbulent eddy viscosity that is very sensitive to the calculation of the vertical stratification. Sensitivity study was conducted determine the optimal correction factor within the range between 1.0 to 1.2. For the case study in Apalachicola River, results show that the increase of the turbulent eddy viscosity to a 1.12 factor results in the best agreement between model predictions and observations. The result from this study also shows that the default parameters in some second order turbulent model may not be universal to all situations. Using the proposed correction factor of the eddy viscosity will provide a useful approach for modelers to turbulent model performance in predicting turbulent mixing in the stratified flow.

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