涌潮潮头掺气的模型试验研究

Investigation of Aeration of Tidal Bore Front by Physical Experiments

强烈掺气的涌潮潮头在向河口上游推进的过程中对整个水域的环流结构、泥沙的输移、污染物的扩散乃至整个河口区域的生态平衡等都将产生巨大的影响,因此针对涌潮潮头掺气特征的研究就显得尤为重要。作者在玻璃水槽中模拟了涌潮潮头,运用高速摄像记录系统拍摄涌潮潮头掺气的状态,并对其破碎状态进行观测、统计和分析。通过试验中涌潮潮头形态与涌潮Froude数之间的响应关系与现实中二者之间的响应关系的一致性,检验了试验中所模拟的涌潮潮头形态的合理性。涌潮潮头破碎掺气要历经4个阶段且不断重复,最终在潮头形成一系列的气泡云;通过对比不同工况下涌潮潮头掺气的形态,提出潮头形态的变化主要与落潮流速和涌潮潮头高度相关。为深入定量地研究涌潮潮头的掺气特性,定义涌潮潮头的掺气长度,其与潮前水深及其流速、涌潮潮头的高度及其传播速度等因素密切相关;利用量纲分析确定涌潮潮头的相对掺气长度与涌潮强度和涌潮Froude数之间的函数关系后,运用非线性回归分析试验数据得到计算涌潮潮头掺气长度的经验公式;最后通过对钱塘江盐官段涌潮潮头掺气长度的几组观测值与经验公式计算值的对比与误差分析,验证了经验公式的实用性,为更好地预测涌潮潮头掺气的特征提供了量化的基础。

In the process of upstream propagation,the tidal bore with strong aeration has a great impact on water circulation,sediment transportation,pollutant diffusion,and ecological balance in the estuary.Hence,the aeration characteristics of a tidal bore is a particularly important research subject.The tide bore was generated in a rectangle glass flume,and the status of aeration was recorded and observed by high-speed camera.Through observation and statistical analysis of the crushing process of aeration of tidal bore in the flume,the response relationship between the status of aeration and the tidal bore Froude number was found to be consistent with that of the tidal bore happened in the estuary.The crushing process of tidal bore aeration experienced four stages repeatedly,then a series of bubble clouds was formed at the front of tidal bore.The aeration form had a close relationship with the velocity of ebb flow and the height of tidal bore.For the further study of aeration characteristics of tidal bore,the aeration length of tidal bore was defined,and it was related to the height and the propagation velocity of tidal bore and the depth and velocity of the ebb flow.Using the dimensional analysis to determine the function relationship between the relative aeration length of the tidal bore and the Froude number the intensity of tidal bore,an experimental formula was obtained to calculate the aeration length of tidal bore by nonlinear regression analysis.Eventually,the applicability of the empirical formula was verified by comparing several sets of observation values in Yanguan Station of the Qiantang River to the calculated values using the empirical formulas.