Research On The Flow Field Structure And Manning Coefficient Of Complicated Mountain Channel

The shape and distribution of large roughness elements in mountainous channel determine the resistance of water flow,and thus control the distribution of water depth and velocity along the way,as well as the longitudinal cutting and lateral expansion of erosion.However,the local destruction of water flow uniformity makes it difficult to describe the distribution of velocity profiles,and it is difficult to quantify the flow resistance of complex river channels in mountainous areas.Based on the field investigation in the core area of the Winter Olympics in Zhangjiakou City,this paper derives the relationship between the Manning coefficient sub-items of hydraulic elements such as gravel and vegetation and the total Manning coefficient of the river channel,and uses simulated gravel to carry out physical model experiments and studies.The influences of gravel size and density on the flow field structure,turbulence intensity and Manning coefficient are discussed.The main conclusions are as follows:(1)The laying of stones changes the water flow structure.The water level changes are divided into rising section(6-9m),slow fluctuation section(9-13.5m),sharp fluctuation section(13.5-14.5m)and wake rising section(14.5-16m)).Under different conditions,the water level changes in the rising section are basically the same,but when approaching the tail(14m)of the fluctuating section,the water depth reaches the lowest value,and is close to the critical water depth h_c=6.4cm,where the flow pattern changes from gradual flow to rapid flow.(2)The loss of water flow machinery along the way is mainly concentrated in the fluctuation section(9-15m),accounting for more than 90%.The dissipation ratio increases with the decrease of rock density in the weak dissipation section(9-13.5m),and decreases in the strong dissipation section(13.5-1 5m).The dissipation ratio of the two sections is as high as the water flow.40%of initial energy.(3)Under different experimental conditions,the relationship between the relative turbulence intensity in each direction is:longitudinal>transverse>vertical.The relative turbulence intensity of the water body before the stone paving section remains stable,with the longitudinal and lateral directions at about 0.1,and the lateral direction below 0.05;in the stone paving section,the relative turbulence intensity appears twice as a whole,showing an M-shaped change trend,and the average is paved.2-4 times before the paragraph.At the back of the wave section(14m),the relative turbulence intensity is reduced to be similar to that before the paving section;the horizontal and longitudinal relative turbulence intensity after the paving section remains basically stable,but the vertical direction still continues to increase,which is the turbulence of the hydraulic jump.majority direction.(4)The theory deduces the relationship between the total Manning coefficient of the river with hydraulic elements such as rocks and vegetation and its sub-items,namely n2=?nb2+?nv2+?ns2,Among them,? and ? are determined by river bed hydraulic parameters,vegetation and rock characteristic parameters.(5)The Manning coefficient of the side wall of the glass water tank n_b=0;under different experimental conditions,the Manning coefficient before the paving section has a high value area(between 7-8m),and the Manning coefficient in the paving section increases with the stone The increase in density showed a trend of first increasing and then decreasing.Based on theoretical analysis and flume experiments,this paper studies the flow structure and resistance mechanism of complex rock-shaped rivers in mountainous areas,as well as their potential effects on erosion and sediment transport.The research results have theoretical significance for hydraulic calculations of complex rivers,and are useful for mountain rivers.Comprehensive management design has practical significance.