潮流作用下环礁断面的流动特征研究

A study of the flow characteristics across an atoll reef transect under the effects of tidal currents

本文首先通过循环水槽试验测量分析了正向和反向潮流影响下概化环礁断面的流动特性,试验结果表明:在正向流和反向流作用时,礁坪上仅存在亚临界流,并可观察到经典的壁面有界流动流速剖面特征;沿礁的平均水位与各个测线上的流速随潮流幅值的增大而增大。本文随后采用雷诺平均的Navier-Stokes方程并结合标准的k-ωSST湍流模型建立数值水槽,进一步研究了多种水动力与礁型因素影响下前后礁外礁缘处的流速变化规律。数值模拟结果表明:后礁外礁缘处的平均流速均大于前礁外礁缘处;平均流速随潮流幅值的增大而增大,随礁坪水深、礁坪宽度、潟湖宽度和礁前斜坡坡度的增大而减小;最后基于数值模拟结果提出了预测各种因素影响下前后礁外礁缘处流速的幂函数型经验公式。

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-ωSST 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.