On the selection of turbulent model for the nearshore hydrodynamics modeling of coral reefs: Insight from an inter-comparison study

Natural coral reefs generally have rough and undulating topography. Due to the steep and variable topography from the deep to shallow water near the starting point of reef flats, the wave motion is quite complex and there are severe wave rolling and breaking on reef flats. To credibly simulate the wave evolution on reef flats, and the hydrodynamic performance of revetment breakwaters built on coral reefs, a suitable turbulence model is needed in the numerical simulation. In this study, a series of hydrodynamic numerical simulations with various RANS turbulence models are conducted adopting OlaFlow solver as the computational platform. The numerical results from three turbulence models, i.e. the standard k-ε, the buoyancy-modified k-ω SST, and the stabilized k-ω SST, are analyzed and evaluated utilizing different grid systems, where the grid number is 1.40, 2.37 and 3.52 million, respectively. By comparing the numerical results from the three different turbulence models, it is found that the stabilized k-ω SST turbulence model could give consistent and good results for the complex evolution process of waves on reef flats, and give acceptable results for the wave impact on structures. In contrast, the numerical results from the standard k-ε and the buoyancy-modified k-ω SST models present significant grid dependencies, indicating that the credibility of these results is doubtful. On the aspect of capturing the wave breaking and run-up, the results from the buoyancy-modified k-ω SST and the stabilized k-ω SST models are remarkably better than that from the standard k-ε model. As for the overtopping volume over breakwater, all three turbulence models present serious grid dependence and fail to obtain consistent numerical results. Finally, it is recognized that the stabilized k-ω SST model is a suitable turbulence model for the nearshore hydrodynamics modeling of coral reefs.