加速度不对称波浪作用下的底部边界层动力特性

摘要

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.