加速度不对称波浪作用下的底部边界层动力特性

Hydrodynamic characteristics of bottom boundary layer under acceleration-skewed waves

为了研究加速度不对称波浪对底部边界层的影响,建立加速度不对称波浪作用下的底部边界层数学模型,复演物理模型试验中的流速剖面、紊动强度和床面剪切应力,在此基础上探讨加速度不对称波浪边界层的动力特性。结果表明,波峰半周期内正向加速阶段的加速度比较大,引起较快的边界层发育、较大的流速梯度和较大的紊动能量,产生了正向的周期平均床面剪切应力;这些现象随加速度不对称系数的增大而更加明显;在振荡水槽中,加速度不对称波浪边界层内存在底部反向和顶部正向的时均流动,加速度不对称系数的增大会增强底部反向流速;在开敞水域中,时均流速在整个边界层内都是正向的,底部出现"流速外突"的现象,顶部流速趋于均匀分布,加速度不对称系数的增大会减弱底部正向流速。

In order to study the effect of acceleration-skewed waves on the bottom boundary layer,a numerical model was developed to reproduce the velocity profiles,turbulent intensity,and bottom shear stress as measured in a physical model experiment. Based on this,the hydrodynamic characteristics of the boundary layer under the acceleration-skewed waves were examined. Numerical results show that greater flow acceleration in the positive accelerating stage within a wave crest half-cycle leads to quicker development of the boundary layer,a larger velocity gradient,and greater turbulent intensity,resulting in positive period-averaged bottom shear stress. These features become more pronounced when the degree of acceleration skewness increases. In the oscillating water tunnel,the time-averaged current velocities are positive and negative in the upper and lower regions of the boundary layer,respectively,and the negative near-bed current velocity increases with the degree of acceleration skewness.In the open sea,the time-averaged current velocity is positive over the whole boundary layer,velocity over-shooting is found in the lower region,the velocity is uniform in the upper region,and the positive near-bed current velocity decreases with the increase of the degree of acceleration skewness.