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.     

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。     

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。     

圆管壁粗糙度对圆管内流态影响研究

基于尼古拉兹圆管实验思想,利用颗粒流程序中的流体计算模块,实现了对圆管壁粗糙度的模拟,进而分析了不同粗糙度对圆管断面流态分布的影响以及在不同压力差作用下平均流速与圆管壁粗糙度之间的关系。研究结果表明:圆管内流体流速受管壁的扰动影响,在横截面上呈U型分布,而非抛物线型分布;圆管壁对管内流体流态的影响范围随管壁粗糙度变化而变化,圆管管壁相对粗糙度越大,管内受扰动流体范围越大,即管内层流范围越小;在管壁粗糙度一定的情况下,圆管断面流量随上下端面压力差的增大而增大;在相同压力差作用下,圆管断面流量随管壁相对粗糙度增大而逐渐减小,颗粒的阻流作用明显;随着管壁粗糙度的增大,圆管上下端面受压力差作用的影响范围也随之增大,使管内流体流态变得更加复杂。     

壁面粗糙度突变对湍流边界层的影响

本文探讨了湍流在流动不同粗糙度的壁面时粗糙度突变对为点下游流动的影响，假定粗糙度突为引起的扰动小扰动，流动物理量的扰动值满足自似分布，本文分析了得到了描述突点下游流动特性的长度尺度，速度剖面，时均流速及摩阻流速的表达式，并通过实验对理论分析的理论进行了验证。     

用分形几何理论研究圆管糙率及其实用意义

在已有紊流阻力定律与试验研究基础上,分析了当量糙率KS在计算紊流沿程阻力损失中的重要作用,以及我国水利工程沿程阻力损失计算和工程应用现状。以圆管内壁糙率为例,用分形几何理论研究了圆管糙率的分形特征,给出了圆管糙率分数维的数学模型和算例。论证了圆管糙率分数维和当量糙率KS的关系,分别讨论了管道纵、横向糙率分数维的计算方法,提供了将前人所建立的紊流阻力定律与试验结果直接用于工程实际的途径。     

DIRECT NUMERICAL SIMULATION OF TURBULENT FLOW IN A STRAIGHT SQUARE DUCT AT REYNOLDS NUMBER 600

This article presents the direct numerical simulation results of the turbulent flow in a straight square duct at a Reynolds number of 600, based on the duct width and the mean wall-shear velocity. The turbulence statistics along the wall bisector is examined with the turbulent flow field properties given by streamwise velocity and vorticity fields in the duct cross section. It was found that the solutions of the turbulent duct flow obtained in a spatial resolution with 1.2×10⁶ grid points are satisfactory as compared to the existing numerical and experimental results. The results indicate that it is reasonable to neglect the sub-grid scale models in this spatial resolution level for the duct flow at the particular friction Reynolds number.     

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。     

MODIFIED LOG-WAKE LAWS FOR TURBULENT FLOW OF THE OUTER AND INNER REGIONS IN SMOOTH PIPES

Based on theoretical analysis two modified log-wake laws for turbulent flow in smooth pipes are obtained,one is applicable to the outer region and other one to inner region,the new law for the outer region fits the velocity profile measured in smooth pipes by Zagarola very well and the effect of Reynolds number can be taken into consideration,the velocity profile for inner region satisfies the wall boundary conditions ,equals zero at the pipe wall and smoothly joins up with the velocity profile in outer region,the adopted eddy viscosity model is consistent with Laufer’s,Nunner’s and Reichardt’s experimental data.     

Bottom shear stress in unsteady sewer flow.

The properties of unsteady open-channel turbulent flow were theoretically and experimentally investigated in a circular cross section channel with fixed sediment deposits. Velocity and turbulence distribution data were obtained using an ultrasonic velocity profiler (UVP). Different uniform flow conditions and triangular-shaped hydrographs were analysed. The hydrograph analysis revealed a dynamic wave behaviour, where the time lags of mean cross section velocity, friction velocity, discharge and flow depth were all evident. The bottom shear stress dynamic behaviour was estimated using four different approaches. Measurements of the velocity distribution in the inner region of the turbulent layer and of the Reynolds stress distribution in the turbulent flow provided the analysed data sets of the bottom shear stress. Furthermore, based on the Saint Venant equation, the bottom shear stress time behaviour was studied using both the kinematic and the dynamic flow principles. The dynamic values of the bottom shear stress were compared with those for the steady flow conditions. It is evident that bottom shear stress varies along the generated flood hydrograph and its variation is the function of the flow unsteadiness. Moreover, the kinematic flow principle is not an adequate type of approximation for presented flow conditions.     

Effects of Bed Load Movement on Mean Flow Characteristics in Mobile Gravel Beds

The effects of bed-load movement on mean flow characteristics were experimentally investigated using particle image velocimetry (PIV). The gravel beds associated with open-channel flow are hydraulically rough, and two types of grain with different median diameters were used. The flow field and bed load motion images were simultaneously obtained via the particular experimental setup. The mass of sediment particles instantaneously moving on the bed, i.e., the sand-wave, was observed in the experiment. It was found that the sand-waves have an average friction angle of 11.2° and heights ranging from 2.2 d ₅₀ to 3.8 d ₅₀. The mean velocity profiles on the mobile bed can also be represented with logarithmic distribution with deviations occurred in the near wall region. Based on the Schultz–Grunow formula, a modified equation is developed in this study to better express the flow resistance factor in terms of the Reynolds number and the ratio of flow depth to roughness height.     

EXPERIMENTAL STUDY OF FRICTION FACTOR FOR GROUNDWATER FLOW IN A SINGLE ROUGH FRACTURE

To study the relationships between the friction factor f and the flow type in a single rough fracture, the formulae of f for both unconfined and confined flows are deduced based on previous studies. The relationships between f and the Reynolds number (Re) for different relative roughnesses are investigated experimentally. The Moody-type diagram, based on the deduced formula of f, is also plotted and the hydraulic characteristics of the flow in a rough fracture are analyzed. Results show that the Moody-type diagram of the experiment has a similar distribution to that of the conventional Moody diagram. It is found that the value of f in the experiment is much smaller than that of the conventional Moody diagram and turbulent flow appears easier for rough fractures, which can be explained by the separation phenomenon in boundary layers. The critical Re ranging from 650 to 700 in rough fractures is concluded based on the experimental results. It also can be concluded that the friction factor f is related not only with the Re and the relative roughness but also with the absolute roughness.     

粗糙壁面溢流反弧水力特性及紊流边界层的研究

本文对溢流反弧（Ｒ＝１００ｃｍ）不同粗糙度模型水力特性进行了系统试验，探讨了壁面粗糙度对反弧水流流速、压强分布及边界层发展的影响。综分析了流速分布的影响因素，得出反弧水流边界层外部势流流速不受粗糙度影响的结论，给出了边界层内流速指数随粗糙度变化的关系式。试验表明粗糙度对离心力压强影响甚微。给出了反映壁面粗糙度影响的边界层厚度计算式。     

Velocity and concentration measurements in initial region of submerged round jets in stagnant environment and in coflow

Velocity and concentration fields are measured in submerged round jets in a stagnant environment and in coflow using laser Doppler anemometry and laser-induced fluorescence. Measurements are made in the initial region within distances of 40 jet exit diameter at jet Reynolds number between 1000 and 5000 and coflow-to-jet velocity ratio from 0 to 0.43. Different behaviors of jet spreading and dilution are found in jets at three different ranges of Reynolds number in which the jets are classified as initially laminar, transitional or turbulent. In the zone of established flow, the jet centerline velocity and concentration decay with downstream distance at different rates in the three groups of jets. For jets in coflow, axial development of normalized forms of centerline mean excess velocity and mean concentration at different velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale. Turbulence properties inside a jet are increased by the presence of a strong coflow. Inside the zone of flow establishment, some strange features are observed on jet turbulence properties. The length of zone of flow establishment increases from the turbulent jets, to the transition jets and to the laminar jets. The zone lengths for concentration are shorter than those for velocity by one to two jet exit diameters. Both lengths are shortened further in the presence of a coflow. For jets a stagnant environment and in the strong jet flow region of jets in coflow, jet widths increase linearly with downstream distance in transitional and turbulent jets. Self-similarity of radial profiles of mean velocity or excess velocity, mean concentration, turbulence intensities and concentration fluctuation level is explored in the zone of established flow.     

NUMERICAL SIMULATION OF TURBULENT FLOW CHARACTERISTICS IN A CURVED PIPE WITH A BAFFLE

A numerical study on the characteristics of developing turbulent flow in a curved pipe with a baffle was carried out in body-fitted coordinates with the k-ε model turbulence. A curved duct of square cross-section was examined first, and the results agree very well with the experimental data. Then two kinds of pipes, a normal curved pipe and that with a baffle were studied. The computational results are presented and compared with each other to illustrate the changes of the flow after adding the baffle. The longitudinal velocity in the pipe with a baffle was characterized by outer velocity bigger than the inner one. The secondary flow was characterized by four-vortex structure with the intensity reduced, which results in the equability of the flow field of the cross-section compared with that without a baffle, and has much more significant meaning in engineering.     

明渠渠底糙率突变对紊流摩阻流速及壁面切应力影响的试验分析

通过激光测速仪,对壁面糙率突变时的明渠紊流进行试验,测量了糙率突变不同水深情况下明渠紊流的纵向时均流速和脉动流速。通过实测资料分析不同糙率突变和不同水深的紊流摩阻流速变化情况和水流的壁面切应力的特点。     

柔性管紊流区域减阻效果机理实验研究

为探讨柔性管的紊流区域减阻效果的产生机理,采用高精度高频率响应特性的应变仪对柔性管外径随雷诺数的频率变化特性进行了研究.研究结果表明:随着雷诺数的增加,全频带的外径脉动的均方根值加大,但高频带外径脉动的均方根值减小,说明柔性管管壁脉动确实改变了原刚性管的脉动流场,大尺度涡的运动加剧,低尺度涡运动减弱,从而使得能量损失减少,减阻效果增大.     

梅花形十字板加糙的原理及实践

：梅花形十字板加糙具有形体小、阻力大、进入阻力平方区雷诺数小、适应水流方向变化等优点，完美地解决了大变态非恒定流河工模型的加糙问题，其在淮河防洪模型中的应用取得了满意的成果。     

INFLUENCE OF YOUNG'S MODULUS ON DRAG-REDUCTION IN TURBULENT FLOW USING FLEXIBLE TUBES

In order to develop technologies of friction drag reduction with a flexible tube to be used for water transport, experimental studies were carried out on the influence of Young's modulus on the turbulent drag reduction. The friction coefficients of flexible tubes with different Young's modulus were examined by using a sleeve-tube structure. The fluctuating vibration of the outer wall and the fluctuating pressure on the inner wall of the tubes were measured with a laser displacement sensor and a pressure sensor. The results are as follows. The smaller the Young's modulus of a flexible tube and the larger the Reynolds number, the larger the turbulent drag reduction rates become. The transition from laminar flow to turbulent flow can be delayed with an appropriate Young's modulus. Non-dimensional amplitude of fluctuating vibration on the outer wall is smaller than that of a viscous sub-layer thickness, and is positively correlated with the friction drag reduction.     

STUDY ON TURBULENCE FEATURES NEAR AN OSCILLATING CURVED WALL

In pursuit of possibly true turbulent characters and for exploring a change in turbulence structures near an oscillating flexible wall-curved surface, a sinusoidal oscillation mode was forced to a curved wall, whose vibrations disturbed the flow with an interacting effort between the fluid and the structure. The methodology used was the Large Eddy Simulation (LES) with fluid-structure interaction. The oscillating configuration was on a Fourier sinusoidal mode from the measurements of a Francis hydro turbine blade vibration. The effects of the vibration on the skin friction coefficient, vortices, turbulent coherent structures, and other statistical quantities were studied. The results showed that the streamwise velocity gradient along the normal direction and the normal velocity gradient along the spanwise direction were considerably increased within the viscous sublayer because of the oscillating wall, which additionally caused the low speed streaks to stay away from the wall and the high-momentum flows to be toward the wall. As a result, the streamwise vortices were much more elongated along the downstream to get an energy balance, and the wall skin friction coefficient or the wall friction velocity rose up.