A study of the flow characteristics across an atoll reef transect under the effects of tidal currents
In this paper,the flow characteristics across an idealized atoll transect under the influence of forward and backward tidal currents are measured via the circulating flume experiments.Experimental results show that the subcritical flows as well as the classical wall bounded flow profiles on the reef flat can be observed under the action of both forward and backward currents.Both the mean water level along the reef and the velocity along each sampling line increase with the increase of the magnitude of tidal flowrate.Subsequently,the Reynolds-Averaged Navier-Stokes equations with the standard k-ω SST turbulence model are adopted to establish a numerical flume,and the flow variations at the outer edges of both front and back reefs with various hydrodynamic and morphological factors are further studied.Numerical results show that the mean flow at the outer edge of the back reef is consistently greater than that at the outer edge of the front reef.It also increases with the increase of the magnitude of tidal flowrate,but decreases with the increase of reef-flat water level,reef flat width,lagoon width and fore-reef slope.Finally,via numerical simulation,empirical formulas based on the power law are proposed to predict the velocities at the outer reef edges for the front and the back reefs,respectively,by taking all the factors above into consideration.
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