Study On The Large Depth Open Channel Turbulence Characteristics

After the three gorges dam builded,reservoir sedimentation gradually forms the focus of attention.Perennial backwaters sedimentation shows a trend of increase,which seriously influence of the three gorges perennial backwaters' high-grade waterway construction.Turbulence characteristics of sediment-laden flow have a fundamental role in solving sediment transport and suspension.A comprehensive understanding of the turbulence characteristics of flow has important practical significance on solving the perennial backwaters sedimentation.This paper uses advanced ADCP and ADV to accomplish three dimensional flow velocity measurement in zhongxian reach and Zhuerqi reach.Through the measured data and theoretical analysis,the turbulence characteristics of flow in open channel water of large depth have been studied in detail,and following conclusions are got:?Reynolds stress's vertical distribution in natural backwater non-uniform flow of open channel and the lab gets the slope of-1 linear distribution,there is a certain deviation.But you can still use the Reynolds stress distribution to estimate the friction velocity of the flow conditions.The karmen constant of sediment-laden flow is no longer a constant value of 0.4,but the larger changes of the 0.3?0.8.?The velocity time sequence from 64 Hz sampling frequency ADV can see a complete cycle containing small cycles.Level 1 cycle is roughly in the 150s,the secondary period to its value in the 80s,about tertiary period almost at about 4s.Probability density analysis of each measuring point velocity near the bottom of the bed is skewed distribution more,in the middle area velocity distribution for normal distribution.?The vertical velocity distribution in natural open channel is more complex,which can be roughly divided into two forms of velocity distribution.One is a logarithmic velocity distribution.The second distribution curve is divided into two sections,one section is logarithmic distribution(bellow 0.2H),the other is a parabola distribution(above 0.2H).Distribution regularity of turbulence scale generally increases gradually from the surface of the water,encounter turning points at 0.2H?0.5H,gradually reduce until the bed,which illustrates the turbulent flow develops fully in 0.2H?0.6H and is limited by the bed and free surface.The 7#vertical mixing length distribution shows the mixing length equal one times the depth of the water in the range of 0.6H?0.8H.?The calculated maximum vortex scale is 2 times the depth of water,this is consistent with Kolmogorov's hypothesis that the maximum vortex scale has the same magnitude with water depth.Although the vertical vortex scale distribution is more dispersed,it can be seen that the maximum vortex scales appear in middle or bottom region.The energy spectrum of the low frequency(1Hz)slope consists with the Kolmogorov-5/3 law based on the energy spectrum analysis.