This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time ...This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.展开更多
When a river channel is narrow,bifurcated,or intersected,or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel,local hydraulic jumps may develop in the channel.Natural ...When a river channel is narrow,bifurcated,or intersected,or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel,local hydraulic jumps may develop in the channel.Natural disasters such as landslides,floods,and debris flows occur upstream,will result in large transport rate of large-sized gravel particles.Those particles may be blocked in hydraulic jump areas,causing river channel water depth to rise.In this study,the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments.The ratio of upstream and downstream Froude numbers,particle size,Sediment supply intensity,and flow discharge all affected the sediment deposition rate.With increases in the ratio of upstream and downstream Froude numbers,particle size,and sediment supply intensity,the sediment deposition rate increased.The sediment deposition rate decreased with an increase in flow discharge.Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section,and an empirical formula was developed using those parameters to calculate the sediment deposition rate.Thus,to identify risks and prevent disasters in mountain rivers,local changes in hydraulic conditions and particle properties need to be jointly evaluated.展开更多
文摘This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51609162,51939007).
文摘When a river channel is narrow,bifurcated,or intersected,or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel,local hydraulic jumps may develop in the channel.Natural disasters such as landslides,floods,and debris flows occur upstream,will result in large transport rate of large-sized gravel particles.Those particles may be blocked in hydraulic jump areas,causing river channel water depth to rise.In this study,the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments.The ratio of upstream and downstream Froude numbers,particle size,Sediment supply intensity,and flow discharge all affected the sediment deposition rate.With increases in the ratio of upstream and downstream Froude numbers,particle size,and sediment supply intensity,the sediment deposition rate increased.The sediment deposition rate decreased with an increase in flow discharge.Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section,and an empirical formula was developed using those parameters to calculate the sediment deposition rate.Thus,to identify risks and prevent disasters in mountain rivers,local changes in hydraulic conditions and particle properties need to be jointly evaluated.
