Different turbulence models for stratified flow and salinity

Abstract

This paper documents a numerical modelling study to calculate the residual current and salinity distributions in a partially mixed estuary. A three-dimensional, time-dependent hydrodynamic model, ELCRIC, was performed and applied to the Danshuei River estuarine system and the adjacent coastal sea in Taiwan. The model experiments were conducted with different turbulence closure models and background diffusivities. Little difference was found in the results of the model with four turbulence closure schemes (k−kl, k−ε, k−ω, and UB (i.e. Umlauf and Burchard)). However, the predictive results reveal that the stratification and residual circulation are sensitive to changes in background diffusivity when the value of the background diffusivity is greater than 10−4 m2/s. The model was then verified using data for water surface elevation, tidal current and salinity measured in 2002 with different turbulence closure schemes and background diffusivities. Overall, the model simulation results were in reasonable agreement with time-series observations of water surface elevation and tidal currents. Among the schemes explored, the k−kl scheme with a background diffusivity of 10−5 m2/s provides the best simulations of the salinity time-series. Both the model experiments and the model/data comparisons highlight the importance of providing a more realistic parameterisation for turbulence mixing in the Danshuei River estuary. However, more detailed observations of the salinity time-series in different layers and locations are required to improve turbulence closures and for proper parameterisation.