A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed ma...A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed material, and variations in the dimension of bed forms. The model predicts the changes in the grain size distribution with the time and space during degradation process. The numerical model proposes that the armoring process in degrading channels does not depend only on hydraulic characteristics of the flow but also on variation in the grain size distribution of sediments on the bed. The model was applied and compared with the results obtained from experiments conducted in 24 m recirculating flume for two sizes of sand; a good agreement was found between observed and calculated values.展开更多
The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important ...The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river dynamics.The transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent vortex in different flow conditions,the large-scale turbulent eddy structure adapted to a meander,etc.In this paper we study the laminar flow instability of the two-dimensional channel in a meander channel.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 above results could not be obtained in the traditional hydrodynamic stability theory so that our work in this paper would make up for the deficiency and blank in this aspect.展开更多
文摘A numerical model to simulate the bed degradation process in a straight alluvial channel with respect to time and distance is introduced. The simulation takes into account the effect of non uniformity of the bed material, and variations in the dimension of bed forms. The model predicts the changes in the grain size distribution with the time and space during degradation process. The numerical model proposes that the armoring process in degrading channels does not depend only on hydraulic characteristics of the flow but also on variation in the grain size distribution of sediments on the bed. The model was applied and compared with the results obtained from experiments conducted in 24 m recirculating flume for two sizes of sand; a good agreement was found between observed and calculated values.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2007CB714101)the National Natural Science Foundation of China (Grant Nos. 50979066, 50809045, 51021004)
文摘The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river dynamics.The transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent vortex in different flow conditions,the large-scale turbulent eddy structure adapted to a meander,etc.In this paper we study the laminar flow instability of the two-dimensional channel in a meander channel.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 above results could not be obtained in the traditional hydrodynamic stability theory so that our work in this paper would make up for the deficiency and blank in this aspect.
