大尺度散粒体周围水流的紊动特性
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摘要
为探讨大尺度散粒体周围水流的紊动特性,采用高度Δ=5 cm的正方体、球体和四面体概化河床孤礁形态,基于声学多普勒测速仪测量明渠紊流的6组数据,研究脉动流速的统计特性以及紊动强度、雷诺应力和紊动能的分布特征。结果表明:大尺度散粒体周围水流脉动流速的统计参数与散粒体形态密切相关;标准差σ_u~+、峰度K_u的垂线分布较为均匀,σ_u~+沿程分布呈先增大后减小的变化趋势,散粒体上、下游各断面中垂线上的K_u总体大于3,多呈高狭峰,散粒体上游偏度S_k基本为负,下游S_k随水深的增大由正逐渐变为负; 3种散粒体周围水流的纵向紊动强度T_u~+的垂线分布较为均匀,沿程各断面的T_u~+随弗劳德数F_r的增大而增大;正方体的T_u~+总体最大,球体T_u~+次之,四面体T_u~+最小; 3种散粒体周围水流的雷诺应力R~+的垂线分布从近水面到槽底呈逐渐增大的趋势,紊动能E~+的垂线分布呈两端小、中间大的趋势; R~+、E~+在散粒体下游2Δ附近有最大值;大尺度散粒体的阻水面积与其对下游水流的影响强度及范围呈正相关。
In order to investigate the turbulence characteristics of the flow around large scale granular mixtures,we apply a cube,a sphere and a tetrahedron with the same height of Δ = 5 cm to generalize the reef shape in gravel-bed rivers respectively,and study the statistical characteristics of fluctuating velocity,and the turbulence parameters such as turbulence intensity, Reynolds stress and turbulent kinetic energy based on 6 sets of data measured by acoustic doppler velocimeters in an uniform turbulent open-channel flow. The results show that the statistical parameters of fluctuating velocity are closely related to the shape of large scale granular mixtures, the vertical distributions of standard deviation σ_u~+ and kurtosis K_u are more uniform,the longitudinal distribution of σ_u~+ increases first and then decreases,and kurtosises on the vertical line at upstream and downstream sections are larger than 3,most of which present a high narrow peak.The skewness S_k at upstream section is basically negative,while S_k at downstream sections gradually becomes negative with the increase of water depth. The vertical distributions of longitudinal turbulence intensity T_u~+ around the 3 kinds of large scale granular mixtures are more uniform and T_u~+ along the longitudinal sections increases with the increase of Froude number F_r.T_u~+ of the cube is the largest,T_u~+ of the sphere is the second,and T_u~+of the tetrahedron is the smallest.The vertical distributions of Reynolds stress R~+ around the 3 kinds of large scale granular mixtures increase gradually from the free surface to the bed.The vertical distributions of turbulent kinetic energy E~+ around the 3 kinds of large scale granular mixtures are small at both ends and large in the middle.R~+ and E~+ have the maximum value near the 2Δ section of the downstream.The hindrance area of large scale granular mixtures is positively correlated with the intensity and extent of its influence on the downstream flow.
In order to investigate the turbulence characteristics of the flow around large scale granular mixtures,we apply a cube,a sphere and a tetrahedron with the same height of Δ = 5 cm to generalize the reef shape in gravel-bed rivers respectively,and study the statistical characteristics of fluctuating velocity,and the turbulence parameters such as turbulence intensity, Reynolds stress and turbulent kinetic energy based on 6 sets of data measured by acoustic doppler velocimeters in an uniform turbulent open-channel flow. The results show that the statistical parameters of fluctuating velocity are closely related to the shape of large scale granular mixtures, the vertical distributions of standard deviation σ_u~+ and kurtosis K_u are more uniform,the longitudinal distribution of σ_u~+ increases first and then decreases,and kurtosises on the vertical line at upstream and downstream sections are larger than 3,most of which present a high narrow peak.The skewness S_k at upstream section is basically negative,while S_k at downstream sections gradually becomes negative with the increase of water depth. The vertical distributions of longitudinal turbulence intensity T_u~+ around the 3 kinds of large scale granular mixtures are more uniform and T_u~+ along the longitudinal sections increases with the increase of Froude number F_r.T_u~+ of the cube is the largest,T_u~+ of the sphere is the second,and T_u~+of the tetrahedron is the smallest.The vertical distributions of Reynolds stress R~+ around the 3 kinds of large scale granular mixtures increase gradually from the free surface to the bed.The vertical distributions of turbulent kinetic energy E~+ around the 3 kinds of large scale granular mixtures are small at both ends and large in the middle.R~+ and E~+ have the maximum value near the 2Δ section of the downstream.The hindrance area of large scale granular mixtures is positively correlated with the intensity and extent of its influence on the downstream flow.
引文
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[2] BAKI A B M, ZHU D Z, RAJARATNAM N. Mean flow characteristics in a rock-ramp-type fish pass[J].Journal of hydraulic engineering,2014,140(2):156-168.
[3] BAKI A B M, ZHU D Z, RAJARATNAM N. Turbulence characteristics in a rock-ramp-type fish pass[J].Journal of hydraulic engineering,2015,141(2):1-12.
[4] THOMAS B B, ROY A G. Effects of a pebble cluster on the turbulent structure of a depth-limited flow in a gravelbed river[J].Geomorphology,1998,25:249-267.
[5] LAMARRE H, ROY A G. Reach scale variability of turbulent flow characteristics in a gravel-bed river[J].Geomorphology,2005,68(1):95-113.
[6] LACEY R W J,ROY A G. The spatial characterization of turbulence around large roughness elements in a gravelbed river[J].Geomorphology,2008,102:542-553.
[7] LACEY R W J, RENNIE C D. Laboratory investigation of turbulent flow structure around a bed-mounted cube at multiple flow stages[J]. Journal of hydraulic engineering,2012,138(1):71-84.
[8]曹永港.考虑尺度效应的泥沙颗粒周围水动力特性研究[D].天津:天津大学,2012.
[9] TRITICO H M, HOTCHKISS R H. Unobstructed and obstructed turbulent flow in gravel bed rivers[J].Journal of hydraulic engineering,2005,131(8):635-645.
[10]周林勇,付旭辉,王磊,等.基于三维数模礁石航道水流结构分析[J].水运工程,2017(6):132-138.
[11]王晋军.粗糙床面的阻力特性[J].水动力学研究与进展(A辑),1992,7(2):132-137.
[12]王晋军.大尺度粗糙水流特性初探[J].水利学报,1993(1):68-71+79.
[13] GORING D G,NIKORA V I. Despiking acoustic doppler velocimeter data[J]. Journal of hydraulic engineering,2002,128(1):117-126.
[14] MARTIN V,FISHER T S R,MILLAR R G,et al.ADV data analysis for turbulent flows:low correlation problem[C]//American Society of Civil Engineers. Hydraulic Measurements and Experimental Methods Specialty Conference.Colorado:ASCE,2002:1-10.