光滑壁面明渠陡坡流速分布特性

在分析激光测速试验资料基础上,对比了光滑壁面明渠陡坡中均匀流和非均匀流垂向流速分布在不同水力条件下的规律。陡坡均匀流中κ值比非均匀流条件下为小,非均匀流中S2型非均匀流的黏性底层厚度和过渡层范围均小于S1型非均匀流,并且拟合出适合陡坡均匀流和非均匀流的统一流速分布公式。     

粗糙床面振荡紊流边界层运动的三维格子玻尔兹曼模拟

该文采用格子玻尔兹曼(LB)方法建立了紧密排列颗粒粗糙床面振荡紊流边界层模拟的三维数学模型。收集粗糙床面波浪水槽实验结果,对水槽实验条件下的振荡流边界层进行模拟,模拟得到的平均流速、紊动特性、等效粗糙高度、摩阻系数和边界层厚度等与实验结果进行了全面对比,并对三维涡旋结构进行了分析。结果表明,所建立的LB数学模型可以合理模拟粗糙床面振荡流边界层流动,能够反映三维涡旋特性,可进一步应用于粗糙床面振荡流紊动特性以及床面粗糙参数的研究。     

卵砾石河道摩阻流速计算方法探讨

通过水槽试验,采用6种方法:对数流速分布回归法、外延雷诺应力分布法、三维紊动能法、垂向紊动能法、韩其为经验公式法和拖曳力系数法,计算了卵砾石河床的摩阻流速。以韩其为计算摩阻流速的经验公式为标准,分析了各种方法中参数取值对计算结果的影响及其在不同水力和床面条件下各种方法的适用性。提出了2种可行的计算途径:光滑床面条件下各方法计算摩阻流速所得结果最大均方差为2.15,其中对数流速分布回归法较准确,三维紊动能法计算值普遍偏小;相对粗糙床面条件下各方法计算摩阻流速的结果均方差最大达到8.84,其中对数流速分布回归法和三维紊动能法较准确。     

壅水条件下水流阻力试验研究

壅水条件下的水流阻力及输沙特性,在水利工程的应用中占有十分重要的位置。对壅水条件下河道开展概化水槽试验,采用声学多普勒测速仪ADV对水流流速进行了测量,并对壅水条件下水流阻力和床面切应力等进行了分析。结果表明壅水条件下,水流流速沿垂线分布较均匀流条件下更加均匀,当壅水程度越大时,水流流速沿垂线分布越均匀,且流速分布大致上仍服从对数率分布;壅水条件下,随着水深的增大,摩阻流速不断减小;壅水条件下河道水流阻力系数随着非均匀系数及水力半径的增大而增大;引入壅水程度指标,并拟合得到了床面切应力随壅水程度指标的变化关系式。成果可为壅水条件下水流结构特征及输沙规律的研究提供参考。     

粗糙床面紊动产生机理初探

在分析已有近壁区光滑床面定性观察和定量测量结果的基础上，对完全粗糙床面明槽湍流偏斜系数Ｓ沿垂线的分布进行了讨论。结构表明：对于完全粗糙床面，当Ｈ／ｋｓ＞１．０，在ｙ／Ｈ＜０．２的范围内有Ｓ＞０，这意味着可能也存在低速条带，即流体紊动亦是由猝发所致；而对于Ｈ／ｋｓ＜１．０，即对于大尺度粗糙，紊动产生的途径有待进一步研究。     

波状床面消力池的流速分布和壁面阻力系数

根据S.A.Ead和N.Rajaratnam(2002)对波状床面消力池流速、边界层厚度和壁面阻力的试验成果,通过对试验资料的分析,研究波状床面消力池断面流速分布和最大流速沿程变化的规律;根据边界层理论,研究波状床面消力池边界层的发展和壁面阻力系数的变化规律。研究表明:波状床面消力池的断面流速分布具有相似性和分区性,断面流速具有同一分布规律,各断面以最大流速为界,将其分为边界层区域和混合区域,在边界层区,流速沿垂线不断增大,在混合区,垂线流速不断减小;消力池的最大流速沿程逐渐衰减;波状床面消力池的边界层厚度远大于光滑壁面的边界层厚度;壁面阻力系数大于光滑壁面的阻力系数。提出了断面流速和沿程最大流速的计算公式和波状床面消力池边界层厚度和壁面阻力系数的计算方法。对所提出的公式与S.A.Ead和N.Rajaratnam(2002)的试验成果进行了对比分析,验证了计算方法的正确性。     

清水冲刷不连续宽级配床面阻力特性及输沙规律试验研究(Ⅰ)——床面阻力特性

不连续宽级配床沙在天然河道中广泛存在,作为非均匀沙的特殊类型,其床面阻力与一般意义上的非均匀床面相比具有不同的特性。本文通过水槽试验对不连续宽级配床面阻力特性进行了探讨,引入峰度系数表征粗糙床面床沙粒径的非均匀性,将不连续宽级配床面与连续宽级配床面统一起来,根据试验数据拟合得到不连续宽级配床面阻力系数表达式,具有较好的精度。     

不连续宽级配河床垂线流速分布试验研究

不连续宽级配床沙在天然河道中广泛存在,作为非均匀沙的特殊类型,其床面水流特性与一般意义上的非均匀床面相比具有不同的特性.以不连续宽级配床沙为例对其床面垂线流速结构进行了试验研究,结果表明不连续宽级配近底床面垂线水流结构出现S型转折,S型位置与水流强度和床面形态有关.并提出了基于近底S型的水流垂线流速分段表示的流速公式及垂线流速S型平均转捩位置的计算公式.     

弯道床面剪切力的分布

本文根据弯道纵向垂线平均流速分布公式,建立了弯道床面剪切力沿程及沿河宽分布的计算公式。利用实测试验资料对公式的计算结果进行了比较,成果表明,计算值与实测值基本吻合。依据床面剪切力分布公式,结合前人的一些研究成果,较系统地分析了相对曲率半径r_0/B、来流条件τ_0、河床粗糙情况c、相对水深H/r_0、弯道中心角φ及河床断面形态h/H等因素对床面剪切力分布的影响,所得结论与试验成果是一致的。     

人工床面形态明槽水流的紊动性量测

使用两部件多普勒激光测速仪量测周期性一维人工定床上恒定平均水深的明槽均匀流的平均值和紊动特征值。研究了相同高度（水深的20％）和波长（高度的12．5倍）但三角形形状不同的两种床面形态：①由平坦区分隔开来的三角形隆起；②用缓坡上游面替代平坦区的近似沙垅的三角形隆起。研究了基于平均能坡和平均水深的总剪切流速作为可能的流速尺度的作用。对于远离床面的流区，流速差和雷诺剪应力分布通常极近似于平整床面的纵剖面。当使用总剪切流速作为尺度时，在充分远离回流和再附着区．大部分深度中的水流紊动特征值吻合得相当好，但是在水流较下区域，并不遵循平整床面的特性。揭示了对清水量测值和总悬移质榆沙率计算的可能关系。     

Numerical and experimental turbulence studies on shallow open channel flows

The standard shallow water equations (SWEs) model has been proven to be insufficient to consider the flow turbulence due to its simplified Reynolds-averaged form. In this study, the k-ε model was used to improve the ability of the SWEs model to capture the flow turbulence. In terms of the numerical source terms modelling, the combined SWEs k-ε model was improved by a recently proposed surface gradient upwind method (SGUM) to facilitate the extra turbulent kinetic energy (TKE) source terms in the simulation. The laboratory experiments on both the smooth and rough bed flows were also conducted under the uniform and non-uniform flow conditions for the validation of the proposed numerical model. The numerical simulations were compared with the measured data in the flow velocity, TKE and power spectrum. In the power spectrum comparisons, a well-studied Kolmogorov's rule was also employed to complement both the numerical and experimental results and to demonstrate that the energy cascade trend was well-held in the investigated flows.     

Longitudinal variations of hydraulic characteristics of overland flow with different roughness简

The evolution of the overland flow velocity along the distance downslope on smooth and granular beds in different cases is investigated by means of the electrolyte tracer via flume experiments.The results demonstrate that a non-uniform flow regime and a uniform flow regime exist in the development process of the overland flow.Owing to the different attributes of beds’roughness,the position of those zones with different flow regimes varies correspondingly:(1)the overland flow on granular beds enters into the uniform regime much sooner,additionally,the roll waves tend to appear because of the presence of the proper flow resistance imparted by the roughness(coarse sands),and large slopes(20o and 25o)which makes the flow velocities and depths to undulate spatially.Furthermore,the flow resistance of the overland flows with different roughness elements,that is the non-sands,the fine sands and the coarse sands,is calculated.A quadratic interpolation method of the third order accuracy is employed in the calculation of the longitudinal flow resistance.The results show that it is rational to use the bed slope to approximate the hydraulic energy slope over a relative small roughness(the present roughness),however on the other hand,if the mean flow velocities and depths rather than the local parameters are used to calculate the flow resistance,a considerable error will be induced within the non-uniform regime of the overland flows,including the acceleration zone and the roll-wave zone.     

壁面粗糙度突变对明渠流速分布的影响

应用激光测速仪在矩形水槽中实测了光滑和粗糙底板以及粗糙度突变情况下的时均流速分布，根据实测资料分析了粗糙度突变以后流速在内区和外区沿程变化情况，得到粗糙度改变后发展过程中的紊流，其流速在黏性底层区比粗糙度改变前和充分发展的紊流小，而在对数律区其流速增长最快。对y／H〉0．2的外区，发展中的紊流与充分发展的紊流在外区流速分布有明显的不同，其不同表现可从尾流强度系数П看出，П值变化从负值到正值，当形成新的均匀流后П值趋于常数。     

Experimental study of obstacle and bed roughness effects on behavior of turbidity current

Laboratory experiments were carried out to study the behavior of turbidity current under subcritical approach flow condition. In order to study the effects of solid obstacle and bed roughness on turbidity current, 24 experiments were conducted. Two trapezoidal macro-roughness elements with 0.01 m and 0.03 m height and three triangular obstacles with 0.1 m to 0.3 m height were used. The parameters such as front velocity, velocity profiles, body height, flow discharge, suspended load transport rate and efficiency of the obstacle were determined. It was found that under subcritical flow regime, the main portion of the turbidity current over the rough bed is controlled, if the obstacle height is 2–3 times of the body height. The growth of the front height depends on the inlet sediment concentration, the roughness elements and the obstacle height. The front velocity upstream of the obstacle over the smooth bed is independent of the obstacle height and significantly influenced by roughness elements. Simultaneous use of the bed roughness and obstacle significantly reduces the front velocity downstream of the obstacle. The flow discharge per unit width significantly decreases downstream of the obstacle. Simultaneous use of an obstacle and roughness elements decreases the flow discharge per unit width by about 90%. An obstacle with height equal to 0.75 of the initial height of the turbidity current with the smooth bed blocks about 65% of the suspended sediment. While, simultaneous use of the obstacle and the roughness elements blocks about 95% of the suspended sediment.     

Fully rough submerged plane wall-jets

This study presents the turbulent flow field in submerged plane wall-jets on horizontal fully rough walls detected by a Vectrino velocimeter. For the comparison between the fully rough and smooth submerged wall-jets, the smooth submerged wall-jet case was also revisited. The two-dimensional Reynolds averaged boundary layer equations of a steady turbulent flow are analyzed to determine the velocity and Reynolds shear stress profiles in the fully developed zone of smooth and fully rough submerged wall-jets. The response of the turbulent flow characteristics in submerged wall-jets to wall roughness is examined from the point of view of similarity characteristics, growth of the length scale, and decay of the velocity and turbulence characteristics scales; and compared with the response of those to smooth and transitionally rough walls. The significant observation is that with an appropriate scaling, the velocity, Reynolds shear stress and turbulence intensities in the fully developed zone of fully rough submerged wall-jets are reasonably similar. The rate of decay of jet-velocity on fully rough walls is greater than that on smooth wall, but it is less than that on transitionally rough walls due to the presence of roughness sub-layer on the fully rough walls. Analysis of the third-order moments of velocity fluctuations reveals that the jet-layer is associated with the arrival of low-speed fluid parcel causing an effect of retardation; while the inner-layer of circulatory flow is associated with the arrival of high-speed fluid parcel causing an effect of acceleration. Wall roughness influences the peak values (both positive and negative) of the third-order moments increasing them significantly. Thus, on fully rough walls, the arrival processes of low- and high-speed fluid parcels become stronger in the jet-layer and the inner-layer of circulatory flow, respectively. Also, the peak values of streamwise and vertical flux of turbulent kinetic energy increase significantly in the presence of fully rough walls.     

双峰型非均匀沙粗细颗粒相互作用对推移质输移的影响

为研究粗细颗粒间相互作用对非均匀沙输移的影响,采用推移质动态采集、图像识别和多普勒测速技术,实现了瞬时输沙量、颗粒组成与近壁脉动流速的实时同步监测。针对双峰型非均匀沙进行了211组推移质系列水槽试验,分析表明:推移质输移量与粗沙拣选度的随机波动与紊动猝发引起的流速脉动具有响应关系;推移质中细粒基本保持持续输移,而粗粒输移则具阵发性,并遵循促发、触发与失怙3种模式;颗粒组成结构对3种模式的实施过程有重要影响;它制约着泥沙中细粒对粗粒的激励、碰撞和解怙强度,使得推移质总沙、细沙和粗沙输移率随床沙组成的改变各自呈现出不同的变化规律;水流强度一定时,随床沙粗细比的减小,输沙率呈驼峰型曲线变化;只有适宜的粗细颗粒搭配(ηc)才能使非均匀推移质输沙率达到峰值,且大于该床沙组成中任一均匀沙的输沙率。     

人工加糙对明渠紊动特性影响的试验研究

利用激光测速仪，对光滑壁面及人工加糙的明渠紊流进行了试验，测量了光滑壁面、水力过渡面、水力粗糙面不同水深情况下明渠紊流的纵向时均流速及脉动流速。通过实测资料分析了人工加糙对明渠紊流紊动强度的影响，得到了光滑面、过渡面及粗糙面紊动强度的发展变化规律。