【作者】 杨燕华；

【导师】 白玉川；

【作者基本信息】 天津大学 ， 港口、海岸及近海工程， 2012， 博士

【摘要】 本文以明渠河流,特别是弯曲型河流为研究对象,采用稳定性理论、三维水流数值模拟和室内自然模型试验三种方法,研究了河流的水动力不稳定性及河流蜿蜒过程。根据弯道水流的运动特征,建立了正交曲线坐标系下弯道水流稳定性模型,着重讨论了弯曲河道明渠层流稳定性特征问题,与顺直河道进行了对比。并做了详尽的分析,主要包括不同河岸弯曲程度下的中性曲线、临界雷诺数、扰动增长率等值线的变化情况及雷诺数变化对扰动特征值的影响等。分析表明:与顺直河道相比,弯曲河道稳定中性曲线前移,失稳临界雷诺数降低,对扰动波数的响应范围加大,流动更容易失稳。建立了正交曲线坐标系下弯曲河道中多尺度紊流结构动力演化模型,将大尺度拟序涡体结构看作是一种扰动,来研究弯曲河道中多尺度紊流结构的动力演化特征,从理论上分析了弯曲河道二维紊流涡体结构的演化特征,计算了不同弯曲度和雷诺数条件下河道中涡体的扰动增长率变化。结果表明:弯道中小尺度涡的扰动增长率变化较大尺度涡更剧烈,且小尺度涡对河道弯曲度和雷诺数的改变更敏感。建立了描述弯道水流的三维模型,进行了一系列的数学模型计算,分析了弯曲度、河宽、水深、流速对连续弯道水流运动特性的影响。运用自然模型法模拟天然河流演变过程,以顺直河道作为初始河道,通过控制比降和初始河槽宽深比来观察顺直河道的演变过程,阐述了河道形态在上述因素变化时的演变趋势,初步探讨了试验中出现的不同河型的成因及发展过程。更多还原

【Abstract】 The stability theory, a three-dimensional flow mathematical model and experimental study were adopted to study the Instability dynamic process of open channel, especially of a meander channel.The model of the stability characteristic theory of the open channel flow in a curved channel in orthogonal curvilinear coordinate system was established. The characteristics of instability of laminar flow in the meander channel have been examined in this paper and the results have been compared with those in a straight channel. And something is discussed in detail, for instance: the neutral curve, the critical Reynolds number, contour of growth rate, and characteristic spectrum. The results show that it is essentially different from that in a straight channel: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily.The model of the large structure of the open channel turbulence in a curved channel in orthogonal curvilinear coordinate system was established. The coherent vortex structure was considered as a kind of disturbance to study the evolution characteristics of multi-scale turbulent structures in a meander channel. We adopt theoretical method to study the evolution characteristic of the two dimensional turbulent vortex structures in a meander channel. The disturbance growth rates under different bank curvatures and Reynolds numbers are simulated. The result showed that the change of growth rate of smaller vortices is more intensive than bigger vortices; moreover, smaller vortices are more sensitive to Reynolds numbers than bigger ones.A three-dimensional mathematical model was established to simulate the flow in open channel. Numerical experiments were carried out with this model to study the influence of curvature, water depth, channel width and bed topography on flow in channel bends.The evolution process of river channel was studied and the change and tendency of channel patterns by controlling the gradient and the breadth depth ratio was observed, while the regular river was set as the initial channel. The course and evolution process of the different river patterns were studied.更多还原