Study On The Stream Of The River Hydraulic Characteristics Of Pebble Bed

In this paper,the flow velocity distribution law of the pebble River in the mountain stream and the starting of the sediment particles and the variation of the roughness coefficient were studied respectively through the experiment of the interior sloping glass tank.Some analysis and discussion are also made on the river resistance.The main achievements of the study have certain guiding significance for the hydraulic calculation of mountain river in practical engineering.The study shows that:(1)When the slope is in a certain range and the water depth is shallow,the vertical flow velocity of the water flow in the pebble bed is in logarithmic distribution,and the maximum velocity point should be in the free surface position on the vertical line.But with the increase of the water depth,the width to depth ratio of the flow becomes smaller,and the vertical velocity distribution law will change,which is biased towards the two function distribution.The transverse distribution of tank line average velocity distribution function with form of power.Based on the measured data,the authors have fitted the vertical velocity distribution and transverse velocity distribution of the flow under different conditions,and obtained the relation.(2)Based on the concept of two-way exposure proposed by Bai Tamagawa,based on the relationship between the drag force coefficient,the lift force coefficient and the longitudinal relative exposure,the frequency of the drag force coefficient is analyzed to obtain the drag force.The probability that the coefficient value is within the range of 0.8 to 1.22 is greater than 96%.For the convenience of calculation,the mean value of this interval is taken as 1.01;the change of Reynolds number will affect the average ratio of the drag coefficient to the lift coefficient,when Renault When the number is greater than 25000,the C_D/C_L average tends to a constant of 1.29.(3)On the basis of relative exposures between sediment particles,through theoretical analysis and formula derivation,the mathematical expectation of the relative exposure??at the start of sediment particles with different particle sizes on the slope is obtained.Taking the general state as the starting standard,considering the relative exposure and the composition of sediment particles on the bed during the derivation of the formula,and using the relevant knowledge of statistics and mechanics,the non-uniform start drag of non-uniform sand under general motion is obtained.Force formula.According to the starting drag force and the average velocity of the vertical line,the starting velocity formula was deduced.(4)The influence of the sediment particles,flow rate,width to depth ratio,Froude number,Reynolds number and other factors on the roughness coefficient under different conditions is analyzed,and the relationship between the factors and the roughness coefficient is fitted through the measured data,and a series of fitting formulas with good correlation are solved.