A comparative numerical study of water circulation in the Persian gulf using different turbulence schemes

The complex process of turbulent mixing in the Persian Gulf which is a semi-closed sea makes it a good option for testing the performance of different turbulence schemes in the numerical simulation of water circulation in it.
    Calculating or predicting the flow and water circulation in such semi-enclosed sea, by taking the turbulence into account, is important in every respect, for example in terms of spread of contaminations, environmental, fisheries, shipping, and even the military. In this study, the 3D ocean model COHERENS (COupled Hydrodynamical Ecological model for REgioNal
Shelf seas) is used for water circulation simulation of the Persian Gulf. Cartesian coordinate system is used for horizontal direction and sigma coordinate with 10 layers is used for the vertical direction. Persian Gulf coastline and its bathymetry are based on ETOPO-2 data, which are obtained from the digital data of seabed and bulge of the earth with latitudinal and longitudinal geographical two-minute networks. The model is forced by climatologic monthly mean atmospheric forcing at 10-m reference height above ground derived from 54 years (1948–2002) of National Oceanic and Atmospheric Administration (NOAA) data. The advection scheme that is used for momentum and scalars is either total variation diminishing (TVD) scheme, which uses the super bee limiter. The uniform bottom friction coefficient was chosen at 0.005 (m/s) and uniform value for the bottom roughness length that was chosen as 0.015 (m), based on the bottom roughness of the basin. Four turbulence schemes are implemented in the model to test their performance. These include two turbulence closure schemes of k-ε, k-l (Mellor–Yamada), and two algebraic schemes of Pacanowski and Philander and flow-dependent scheme. For the k-ε and k-l models, we used one-equation model for transport equation, the “Blackadar” formulation for mixing length, and limiting conditions for turbulence variables are enabled. The stability functions are expressed in terms of the Richardson number. In the numerical simulation of water circulation in the Persian Gulf, the turbulence schemes are studied to investigate salinity and temperature parameters, flow patterns in the surface and bottom, meso-scale eddies and turbulence parameters including the turbulent kinetic energy and energy dissipation rate, the mixing length, eddy adhesion and eddy diffusivity. The model has been successful in simulating the intrusion of low salinity waters into the Persian Gulf and baroclinic instability and the formation of mesoscale eddies in the center of the basin. In comparison between the performance of schemas, the results show that the schemes are very sensitive in estimating the turbulence parameters and simulation of flow patterns, vorticity, salinity and temperature, show less sensitivity to the performance of various turbulence schemes.