旋流器中较强旋液体流动的数值计算

本文针对水力旋流器中存在着较强旋流，从而引起各向异性湍流流动的特点，以强旋流场的代数应力模型为基础，得出可模拟水力旋流器中液相湍流流动的各向异性的ｋ－ε模型，成功地计算出其流场中的速度分布，计算结果同用ＬＤＡ所测得的结果比较一致。     

空腔回流区水沙特性的计算分析

建立了回流区水深平均平面二维水流泥沙数学模型，提出了平衡输水模式下回流区泥沙淤积计算方法；工江科学院空腔回尼沙淤积水槽试验数据，验证了回流区泥沙淤各计算方法的可行性和精度；通过数模计算分析，一方面加深了空腔回流区环流结构及含沙量分布的机理认识，另一方面研究了模型主炫对回流区水沙特性的影响。     

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.     

掺气坎射流出射角的修正方法

掺气坎后射流出射角受到来流水深和射流紊动扩散的影响,不等于挑坎的挑角,计算掺气空腔长度时,应该对出射角进行修正。而目前采用的考虑紊动扩散对出射角影响的修正方法存在不合理的假设。考虑到坎末水流流态为充分发展的紊流,射流边缘处于紊动能耗散区,提出了一种紊动扩散对出射角影响的修正方法。采用该方法计算的射流紊动扩散角与试验结果更吻合。对出射角修正后,结合简单的抛射体公式,就能较精确地估算掺气空腔长度。     

亚临界雷诺数下波浪型圆柱绕流的数值模拟及减阻研究

采用大涡模拟数值方法对亚临界雷诺数Re=3000下波浪型圆柱的绕流现象进行研究分析。研究结果表明,波浪型圆柱的三维尾迹涡结构能得到很好的控制,它在轴向方向呈现周期性正负涡的交替分布特性。随着幅值的增大,波浪型圆柱表面的自由剪切层得以延展,使得旋涡的脱落发生在波浪型圆柱下游较远处,从而达到减阻的目的。波浪型圆柱与普通直圆柱相比,其幅值对平均阻力系数及脉动升力系数的减少及尾迹控制有着更重要的影响,最大减阻可达16%。     

基于CCHE模型的乌斯满引水枢纽水流数值模拟

通过CCHE2D平面二维水沙数学模型,采用非线性k-ε紊流闭合模型,有限元法离散控制方程和时间行进格式求解方程对塔里木河乌斯满枢纽模型进行二维水流特性数值模拟。分析了枢纽上下游水流水面形态变化、断面流速变化以及水位高程变化。探讨了引水闸及泄洪闸对计算河段水流流态的影响。将各典型断面水面高程变化与物理模型试验实测值进行对比,得到二者水面变化趋势基本一致。结果表明:CCHE软件能较好地运用于引水枢纽工程水流运动的数值模拟。     

环境水对混凝土静力强度影响的研究进展

对环境水对混凝土静力强度影响的一系列试验研究成果进行了综述,分析了湿态混凝土静力强度降低的物理机理;指出现有的研究大多为定性的解释,定量的研究较少;提出应研究多因素相互作用对混凝土静力强度产生的影响,并采用有限元法来模拟湿态混凝土各个界面的连接耦合。     

Role of Local Flow Conditions in River Biofilm Colonization and Early Growth

Direct numerical simulations of a turbulent boundary layer flow over a bed of hemispheres of height h are performed using an immersed boundary method for comparison with river biofilm growth experiments performed in a hydraulic flume. Flow statistics above the substrates are shown to be in agreement with measurements performed by laser Doppler velocimetry and particle image velocimetry in the experiments. Numerical simulations give access to flow components inside the roughness sublayer, and biofilm colonization patterns found in the experiments are shown to be associated with low shear stress regions on the hemisphere surface. Two bed configurations, namely staggered and aligned configurations, lead to different colonization patterns because of differences in the local flow topology. Dependence with the Reynolds number of the biofilm distribution and accrual 7 days after inoculum is shown to be associated to local flow topology change and shear stress intensity. In particular, the shear stress τ on the surface of the hemispheres is found to scale as , where Re_t = u^*h/ν, with u^* as the log law friction velocity and ν as the fluid kinematic viscosity. This scaling is due to the development of boundary layers along the hemisphere surface. Associated with a critical shear stress for colonization and early growth, it explains the increasing delay in biomass accrual for increasing flow velocities in the experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of Rigid Unsubmerged Vegetation on Flow Field Structure and Turbulent Kinetic Energy of Gradually Varied Flow

The influence of rigid unsubmerged vegetation on flow structure and turbulent kinetic energy of gradually varied flow are experimentally investigated in this research. Natural reed stems of different densities are employed to examine the effects of the rigid unsubmerged vegetation on the flow in rivers. The results reveal that the vegetation existence significantly changes the gradually varied flow state from type M1 to type M2 in the vegetation section. The traditional power law describing the vertical flow velocity profile is evidently invalid when the vegetation density becomes high. With the irregularity index proposed in the research, the irregularity of vertical flow velocity profile in vegetated reach can be exponentially described in relation to the vegetation density. Furthermore, the turbulent kinetic energy is found to increase and reach a maximum value near the end of the vegetation section that is a potential localized erosion area. The results of the research have significances in river ecological restoration applications utilizing aquatic vegetation. Copyright © 2014 John Wiley & Sons, Ltd.     

长江流域水体硅含量分布特征及影响因素研究综述

随着“长江大保护”的推进,长江流域水体中浮游生物的生长状态成为日益热门的话题。硅作为六大生源要素之一,是影响浮游生物生长繁殖的要素之一,对流域生态系统的结构和稳定起到至关重要的作用。首先介绍了河流中硅的形态分类,讨论了对不同形态硅的研究意义。随后综述了国内外研究成果,对长江流域硅含量的时空分布特征进行整理分析,探讨可能影响河流、水库及河口硅含量分布的因素,对比分析了长江与国内外其他河流硅含量差异的原因,展望了长江流域硅含量当前研究的不足及未来研究方向。研究成果可为硅元素对长江流域浮游生物生长的影响等相应研究提供思路与建议。