A Study On The Hydrodynamic Instability And Meandering Processes Of Bend River

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.