植被群落作用下河道水流紊动能分布

植被广泛存在于自然河道中,对河流水流特性产生一定影响。利用交错排列的竹签模拟非淹没的刚性植被群落,通过水槽试验,探讨了单个植被群落对水流紊动能分布的影响。结果表明：纵向、横向和垂向三个方向的紊动能分布受到植被群落不同程度的影响,尤其是纵向上紊动能分布在植被群落下游变化较大,呈现两个峰值;植被群落下游靠近植被群落处,横向上紊动能分布为水槽中心附近最大,向两侧逐渐减小,在水槽中心紊动能沿垂向均显著增加。     

丹尼尔式鱼道内水流紊动特性试验研究

鉴于鱼道内紊流状况是影响鱼类能否顺利通过的重要因素,为提高丹尼尔式鱼道内过鱼效果,通过物理模型试验,分析了鱼道在不同工况下的水力特性,并重点研究了水流的紊动特性。结果表明,池室中的流场具有明显的主流区和回流区;横向u、纵向v、垂向w紊动强度分布形式大致相同,由紊动强度较大的主流区向回流区扩散（由主流区向回流区逐渐减小）;在xy平面上,雷诺应力随离边墙的距离增大而减小;水流通过隔板跌落处紊动能达到最大值,并沿程减小。     

低佛氏数水跃下游水流紊动特性的试验研究

本文应用CDL-86型超声多普勒流速仪,对佛氏数Fr=2.16～4.34的水跃跃前断面和跃后水流的紊动特性进行了试验研究;分析了跃后水流的紊动能量、紊动强度衰减率和水跃消能率等;Fr=2.99可能是这些量变化的突变点或转折点;并通过对试验资料的回归计算得出了跃后水流的紊动能和紊动强度及其衰减率随佛氏数变化的计算式,给出了计入多种影响因素的水跃消能率计算式.认为低佛氏数水跃跃前断面流速分布不均匀以及紊动值的大小对跃后水流有较大影响,近低区较大流速梯度和较大的水流紊动作用是造成水跃下游河床冲刷破坏的主要原因之一.     

含植物河道的水流垂向流速分布试验研究

河道植物可保持水土并净化水质,对生态系统有很好的修复作用,但河道植物会降低河道的输水和泄洪能力,因此研究植物对水流特性的影响非常重要。为此使用PVC圆柱棒模拟刚性植物,在矩形平底水槽中,采用三维多普勒超声测速仪(ADV)对含刚性植物河道的水流流速垂向分布规律进行了试验研究,分析了含刚性植物明渠水流的流速变化规律。结果表明,无植物区域水流流速垂向分布呈"J"型,符合半对数分布关系;有植物区域,无论是否淹没,水流流速垂向分布呈"S"型,淹没条件下流速垂向分布大体分为植物区域和植物区域以上部分两个区域;植物区域流速垂向分布曲线在局部区域内有一个极小值,取得极小值的拐点在相对淹没度为0.5附近;植物区域以上部分流速垂向分布呈"J"型。     

基于数值模拟的风生流场的量化特性及参数优化分析

为研究风生流场的量化特性,数值模拟了矩形水槽风生流场,分析了风生流数值模拟中风应力拖曳系数和垂向紊动粘性系数两个主要参数的误差。结果表明,风生流场垂向流速分布呈抛物线形,断面平均流速为零,流速回旋中心位于水深1/3处,存在最大正向流速和最小反向流速且流速比为2.41。通过分析风应力拖曳系数和垂向紊动粘性系数误差对数值模拟结果的影响,研究了快速实现风生流数值模拟参数优化的方法。对香溪河流速分布的模拟分析,验证了该流速中存在风生流场,且通过参数优化方法快速实现了风生流参数的优化,与实测值对比表明该方法的精度较高。     

洞庭湖流速垂向分布特性

根据洞庭湖不同测点的野外实测数据,结合测点的环境状况(有无水生植被),分析洞庭湖不同位置的流速垂向分布规律,发现底部无水生植物影响的主湖区与航道中心时均流速分布呈"J"形,采用对数律对流速剖面进行拟合,相关系数在0.95以上;在有水生植物分布的洲滩,时均流速的垂向分布偏离"J"形,具有明显的3层结构,且冠顶以上水流时均流速垂向分布满足对数律;受淹没水生植物影响,冠层内部的时均流速及切应力减小,有利于泥沙的沉积。     

海流能水平轴水轮机尾流场流速研究

运用简化风车理论,对海流能水平轴水轮机叶片进行设计,在浪流水槽中进行水轮机模型试验,应用计算流体力学软件Fluent对水轮机进行数值模拟,研究水流流速、尖速比、桨距角和叶片尺寸对尾流场流速的影响。研究结果表明,尾流截面轴心处流速比边缘流速小,横向机组间最佳轴间距为2D。水轮机下游8D范围内为急速增大区,纵向机组间最佳纵间距为8D。水流流速越大、尖速比越小、叶片尺寸越小对下游机组布置越有利,桨距角对尾流场流速恢复影响不明显。     

三维数值波浪水槽内孤立波特性分析

内孤立波对密度层化水体的水动力及分层特性具有显著影响。为揭示内孤立波特性,建立了规则地形下可有效模拟弱非线性内孤立波的分层流三维数值波浪水槽,研究了内孤立波在规则地形条件下的传播,成功捕捉到了水体表面存在的辐聚流和辐散流,探讨了内孤立波传播过程中流速、紊动能和紊动能耗散率的分布与演化特性,为进一步利用数值波浪水槽研究内孤立波能量特性分布、改善层化水体的水生态环境提供了可靠的方法与手段。     

串联环翼式桥墩间冲刷防护影响研究

环翼式桥墩纵向串联布置时,为深入研究桥墩局部冲刷防护问题,从减小冲坑大小和近底垂向流速的方向出发,通过制作桥墩模型,设计正交试验,研究单向水流条件下桥墩间距、下游侧桥墩防冲板的安装高程及数量对两个纵向串联桥墩中下游侧桥墩的冲刷深度的影响,并对所测结果进行极差分析和SPSS方差分析。结果表明,下游侧桥墩防冲板安装高程的显著性比两桥墩间中心间距大小和下游侧桥墩防冲板安装数量的显著性要高,且下游侧桥墩防冲板的安装数量对桥墩冲刷的影响最小,影响效果从大到小依次为下游侧桥墩防冲板的安装高程、桥墩间距、下游侧桥墩防冲板的安装数量。     

低佛氏数水跃消能问题的近代研究评述

在很多水电站中,不论河床式水电站的溢流坝、泄水闸或者是引水道,底流水跃常被用来作为下游消能的一种有效措施.而这种水跃往往是低佛氏数的,例如引水闸或泄水闸的低堰上,或者大单宽中等高度的溢流坝下游的水跃均是跃前佛氏数小于4.5的低佛氏数水跃.对水跃的研究已有一个多世纪的历史,尤其是对于平底矩形水槽内的二元自由水跃,已取得了大量的试验资料和比较完整的可靠的水力设计方法.但对于低佛氏数水跃的消能机理研究还是从本世纪50年代开始的.低佛氏数水跃消能的显著特点是来流的泄水功率高而水跃消能率低,例如当Fr=2～5时,其时均消能率只有20～45%,这说明在水跃下游的水流中,还有大量地未被消散掉的余能(即紊动能和波动能)将造成跃后水流强烈的紊动和波动,需要流经一段距离后才能消失,给下游消能防冲带来较大的困难.因此,近年来国内外     

横隔板式鱼道水力特性数值模拟研究

为改善堤、坝等阻碍鱼类洄游的现状应用了鱼道、鱼闸等过鱼设施,采用RNG κ-ε湍流模型和有限差分法对兴隆水利枢纽工程鱼道进行了数值模拟,分析了淹没孔口式横隔板鱼道的流态和紊动能,研究了过鱼池和休息池的水力特性。结果表明,淹没孔口式横隔板鱼道的孔口水流具有固定特性,紊动能的分布空间较广,消能效果较好。过鱼池和休息池内水流的流态较稳定,能满足过鱼对象的需求。     

Flow structure and heat transfer induced by embedded vorticity

Several vortex generator shapes are used to increase heat and mass transfer in open and internal flows. Here we report a three-dimensional numerical study investigating the effects of longitudinal and transverse vortices on the heat and mass transfer mechanisms generated by rows of trapezoidal vortex generators. The turbulent macrostructures of these streamwise vortices appear greatly to enhance radial convective transfer. Due to Kelvin–Helmholtz instability, the shear layer shed from the tab’s edge becomes unstable and generates periodic transverse vortices that enhance fluid mixing and heat transfer. A global performance analysis of the high-efficiency vortex (HEV) heat exchanger designed to exploit these embedded vortices, shows that the HEV is very competitive with other multifunctional heat exchangers/reactors, especially due to its very low energy consumption.     

Energy distribution on the focal plane of a parabolic cylindrical concentrator with angular defocusings

The concentrating capability of an ideal parabolic cylindrical reflector that is exposed to collimated radiation flux with longitudinal and transverse angular defocusings is examined. The energy distribution on the focal plane of the concentrator is studied.     

Buckling of functionally graded plates under thermal,axial, and shear in-plane loading using complex finite strip formulation

A complex finite strip method was used to study the buckling of functionally graded plates (FGPs) under thermal and mechanical (longitudinal, transverse, and shear in-plane) loading. The mechanical characteristics of FGPs were assumed to vary through the thickness, according to power law distribution. The nonlinear temperature distribution in the direction of the plate thickness was assumed according to thermal conduction steady state conditions. In complex finite strip method, the polynomial Hermitian functions were assumed in the transverse direction and the complex exponential functions were used in the longitudinal direction to evaluate the standard and geometric stiffness matrices that have the ability of calculating the critical shear stress in contrast to trigonometric shape functions. The solution was obtained by the minimization of the total potential energy and solving the corresponding eigenvalue problem. In addition, numerical results for FGPs with different boundary conditions were presented and compared with those available in the literature and the interaction curves of mechanical and thermal buckling capacity of FGPs were obtained.     

部分灌浆失效(有缝)拱坝及重力墩的承载力研究

本文通过物理模型试验,分析研究了拱坝在部分灌浆失效(存在纵横缝)情况下的应力分布及位移.分析了纵横缝及地震荷载对坝体工作状态的影响.通过超载试验研究了有缝拱坝及重力墩的破坏形态与最大承载力,指出了做好纵横缝灌浆的重要性.     

Two-dimensional Temperature Distribution of Strip in Preheating Furnace of Continuous Annealing Line

Two-dimensional temperature distributions of the steel strip are studied by the energy balance method with the aid of finite-element analysis. The space of the preheating furnace is divided into several enclosures in which the mechanisms of heat convection, heat radiation, and contact heat transfer are taken into account. The longitudinal and transverse temperature distributions of the strip are finally iteratively calculated by using the method of energy balance. The strip exhibits a significant temperature rise after contact with the rolls and shows a nonuniform temperature distribution along the width direction with smaller magnitude at two sides.     

Zone conditional assessment of flame-generated turbulence with DNS database of a turbulent premixed flame

Zone conditional two-fluid equations are derived and validated against a DNS database for a turbulent premixed flame. The conditional statistics of major flow variables are investigated to understand the mechanism of flame-generated turbulence. The flow field in the burned region shows substantially increased, highly anisotropic turbulence to conserve mass through a flamelet surface. The transverse component may be larger than the axial component for a distributed pdf of the flamelet orientation angle in the middle of the flame brush. The opposite occurs due to redistribution of turbulent kinetic energy and flamelet orientation mostly normal with respect to the mean flow at the end of the flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms induced by fluctuating pressure and velocity on the flame surface. Ad hoc modeling of some interfacial terms may be required for further application of the two-fluid model for modeling turbulence in turbulent premixed combustion simulations.     

基于小波分析的湍流参数提取方法

在定容燃烧弹内，利用孔板平动法生成湍流，用热线风速仪测量容弹内的速度，用小波分析技术将湍流分解为具有不同频带的组分，方便地获得了湍流强度、湍流尺度、湍流能谱等湍流特征参数。对具有不同频带的湍流积分时间尺度进行详细研究，结果表明，整个湍流的积分时间尺度代表所有湍流涡的平均寿命，与湍流频率和湍流能量分布有关。     

Reflection and refraction of plane wave at the interface between elastic and thermoelastic media with three-phase-lag model

The problem of reflection and refraction phenomenon due to longitudinal and transverse waves incident obliquely at a plane interface between uniform elastic solid half-space and thermoelastic solid with three-phase-lag model half-space has been studied. In thermoelastic solid medium, potential functions are introduced to represent two longitudinal waves and one transverse wave. The amplitude ratios of various reflected and refracted waves to that of incident wave are derived. These amplitude ratios are further used to find the expressions of energy ratios of various reflected and refracted waves to that of incident wave. The graphical representation is given for these energy ratios for different directions of propagation. The law of conservation of energy at the interface is verified.