窄缝挑坎出流水舌出射角的计算

从窄缝挑坎收缩段水流的连续方程和能量方程入手,推导出了水流出射角的计算公式。分析了影响窄缝挑坎水流的出射角的各种因素,确定了水流出射角计算公式中参数的计算方法,从而能够计算直墙窄缝挑坎出流水舌的出射角。     

窄河谷大夹角挑流消能工体型优化研究

针对窄河谷大夹角条件下挑流消能易出现冲击两岸、冲坑过深的问题,采用水工整体模型试验方法对具有代表性的某水利枢纽深孔放水冲沙洞挑流鼻坎体型开展优化研究,并对比分析了水舌形态和下游河道冲刷特性。结果表明,不对称收缩的异型窄缝式消能工可使水流在狭窄河道归槽,水舌纵向拉伸效果较好,大幅减轻了河床冲刷;提出了收缩比、收缩角差、斜切面积比等特征参数适宜的挑流消能工体型,可供窄河谷大夹角条件下挑流消能设计参考。     

乌江东风水电站溢洪道水力设计的试验研究

本文通过半整体水工模型试验对其溢洪道水力设计中存在的问题进行了试验研究,采用了带急弯的曲面贴角窄缝挑流鼻坎并结合该工程的具体特点对其进行了局部修改后,较好地解决了该溢洪道水舌导向与消能防冲问题,并且大幅度的降低了出口边墙高度,方便了设计与施工,该成果已被设计单位采用.     

Y型窄缝挑坎水力特性试验研究

以斯木塔斯水电站为例,针对原矩形窄缝挑坎不能满足工程需求的问题,提出了一种Y型窄缝挑坎的体型设计方案,通过模型试验分析了不同工况下该体型流速、压强、水舌形态等各项水力特性.结果表明,Y型窄缝挑坎各项水力特性良好,消能效果显著.     

三角形鼻坎挑流水舌出射角的试验研究

挑流消能是水电工程建设中广泛采用的一种消能方式,挑流水舌上缘和下缘轨迹决定大坝下游的冲刷位置和范围,而上缘和下缘出射角决定水舌的轨迹,因此出射角的研究至关重要。基于三角形鼻坎挑流的物理模型试验结果,研究挑流水舌起挑断面横向脉动流速和平均水深对水舌出射角的影响。采用平均误差最小的分析方法,分别确定脉动流速和平均水深对出射角影响的权重系数,并提出水舌上缘和下缘出射角的计算方法。相比试验实测值,所提方法计算所得挑距的误差在5%以内,具有较高精度。     

关于直墙窄缝挑坎冲深估算方法的探讨

一、问题提要窄缝挑坎是近年来引入我国的一种新型批流鼻坎,许多研究和报导均表明,这种新型消能工对减轻下游局部冲深效果十分明显.但如何估算其下游局部冲深还是一个有待很好解决的问题.文献曾提出用水单位面积流量作为控制指标进行计算,但由于该量难以确定,限制了该法的实际应用.文献则提出以窄缝收缩段始端的单宽流量q作为计算的控制指标,得出如下计算公式:     

黄登水电站燕尾型挑坎挑流消能适用性试验研究

针对黄登水电站泄洪消能原方案存在的问题,通过1∶50整体水工模型试验,研究了传统挑坎（窄缝坎、扩散坎、斜切坎）与新型燕尾坎在黄登水电站表、底孔上的适用性问题,分析了燕尾坎对挑流消能的影响。结果表明,与传统窄缝坎相比,燕尾坎对上游来流的适应性更好,挑坎边墙的动水荷载小,在拉近最近挑距、避免对右岸边坡和下游围堰堰脚冲刷的同时,减小了电站尾水区附近水流的波动,水垫塘内底板基岩的冲淤结果满足“护坡不护底”的要求,可供类似工程参考。     

窄缝式消能工的冲刷特性

自从1954年葡萄牙的卡勃利尔(Cabril)坝泄洪洞首次采用窄缝式消能工以来,西班牙、伊朗、法国等也有工程采用了这种形式的消能工,但很少见到这方面的研究资料。1975年将窄缝挑坎引入我国。最近几年才引起了人们的重视,并取得了一些初步成果,龙羊峡、东江水电站的溢洪道上将准备采用窄缝挑坎。 本文仅就窄缝式消能工的流态特征及冲刷特性作一些初步的探讨。     

基于碰撞水舌入水分布形态的泄洪布置优化方法及应用

鉴于挑流水舌碰撞效果关系到水垫塘消能效率且其碰撞入水形态复杂难以测量的问题,根据挑流水舌的形态特点,提出应用二维高斯函数表示挑流水舌碰撞后入水流量分布形态规律。应用该方法计算了白鹤滩水电站泄洪水舌落水分布情况,并针对局部流量集中的现象优化了泄洪孔口布置,改善了泄洪流量空间分配。物理模型试验证明,水垫塘动水压力分布形式与所提算法计算结果较为吻合,且优化后的泄洪孔口布置方案有效降低了水垫塘动水冲击压力,可用于指导泄洪消能布置的设计。     

高坝泄洪诱发环境噪声试验研究

针对原型高坝大功率泄洪引起的噪声影响范围广、难以定量评估的问题,采用大尺度水工模型量测泄洪消能时的噪声场,根据噪声场的主要声源建立了噪声强度概化模型,对试验数据回归分析得出泄洪水舌入水时的辐射声功率。试验结果表明,水舌入水时辐射声功率与水舌入水角度有关,入水角度越小,辐射声功率越大;挑流水舌入水角度随着泄流量增大而逐渐减小,挑流水舌辐射声功率随着泄洪功率增大而呈抛物线增长。     

Falling jet flash evaporators for open cycle ocean thermal energy conversion

Evaporation from falling superheated water jets for application to open cycle ocean thermal energy conversion is considered. Analyses are performed to show that the interfacial resistance is of no importance to evaporator design and that evaporation is liquid side controlled. The heat exchanger performance is presented in terms of its effectiveness and change of bulk temperature. Unbroken planar and round jets and broken jets which are assumed to be composed of spherical droplets are considered. The analysis is shown to provide a rational basis for correlating experimental data for broken and unbroken jets. Corresponding desorption rates of dissolved noncondensable gas from water jets are then predicted.     

Statistical and spectral properties of tracer concentration in round buoyant jets

Spatial growth, temperature decay, and turbulence structure have been studied experimentally in axially-symmetric buoyant jets in transition to plumes and in fully developed plume flows. Temperature records obtained with fast response thermistors located in these flows form the basis for the study. The results obtained support previous asymptotic arguments pertaining to the rate of decay of mean temperature and r.m.s. temperature fluctuations. Spectral energy distributions in jets and plumes show that the evolution from buoyant jets to plumes is characterized by a significant shift in the wave number distribution of temperature variance density.     

中型拱坝表孔大单宽流量泄洪消能形式的研究

以龙潭嘴水电站工程整体水工模型试验资料为依据,采用表孔高低坎+二道坝研究了中型拱坝表孔大单宽流量泄洪消能形式。通过调整边、中表孔挑坎的位置高程及挑角来实现三孔水舌上下对撞和横向扩散碰撞消能。为达到水舌落点纵向拉开的目的,增大中表孔溢流曲线的长度,使中边表孔挑坎在纵向上形成差动。试验结果表明,在该消能形式布置下,水舌纵向拉开、横向扩散充分、对冲明显,同时在水垫塘内充分翻滚消能,对下游河道减轻了冲刷,消能效果较好。     

NUMERICAL SIMULATION OF THREE-DIMENSIONAL LAMINAR,SQUARE TWIN-JET IMPINGEMENT ON A FLAT PLATE,FLOW STRUCTURE,AND HEAT TRANSFER

The flow and heat transfer characteristics of impinging laminar square twin jets have been investigated numerically through the solution of three-dimensional Navier-Stokes and energy equations in a steady state. The simulations have been carried out for jet-to-jet spacings of 4, 6, and 8 and for nozzle-exit-to-plate distances between 0.25D and 5D. The calculated results show that the flow structure of square twin jets impinging on a heated plate is strongly affected by the jet-to-plate distance. In addition, for very small jet-to-plate distances (L z , 0.25D), no upwash fountain flow can form at the collision point where the jets are merely diverted in the transverse direction. For such nozzle-to-plate distances the wall jet fills the whole gap between the plates with no vortex motion around the twin jets.     

斜鼻坎挑流消能在黑石罗水库的应用

针对黑石罗水库现状连续式鼻坎消能效果较差,可能威胁河床及岸坡稳定的现状,通过水工模型试验,将挑流消能连续式鼻坎优化为斜鼻坎,即将鼻坎挑射角度由定值调整为渐次增大,同时偏转大角度挑射一侧反弧段边墙至泄槽轴线位置,去除小角度挑射一侧边墙及部分反弧段底板,迫使出坎水舌在平面上转向的同时沿竖向大幅拉开,在保证出射水流平顺归入河床的同时,增大挑射水流和空气的接触面积,最大限度消除水体能量,从而降低水股对落点的冲刷,达到保护河岸及相邻建筑物安全的目的。试验结果表明,斜鼻坎可以很好地适应狭窄地形条件,有效降低挑射水流对鼻坎下游的冲刷。研究成果为类似工程提供了参考。     

Heat transfer due to double laminar slot jets impingement onto an isothermal wall within one side closed long duct

In this study, heat transfer due to double impinging vertical slot jets onto an isothermal wall was investigated numerically for laminar flow regime. Navier–Stokes and energy equations were discretized with a finite volume procedure on a non-staggered grid arrangement using SIMPLEM (SIMPLE-Modified) algorithm. The effect of the jet Reynolds number, the jet-isothermal bottom wall spacing, and the distance between two jets on heat transfer and flow field was examined. Air was chosen as the working fluid (Pr = 0.71). It is found that multi-cellular flow is formed in the impingement region due to interaction between two jets and entrainment effects in the duct. The mean Nusselt number increases almost linearly with increasing of Reynolds number at isothermal surface. When Reynolds number of the first jet is higher than second one the heat transfer is enhanced significantly.     

双平行平面射流输运特性研究

平行射流输运特性研究具有较重要的理论意义和工程价值,对水平浓淡煤粉燃烧也有较重要的意义。本文实验研究了双平行平面射流动量、能量和质量输运,结果表明：速度分布表现为双射流相互吸引并最终汇合成单一射流;温度分布反映了冷射流为加热射流所卷吸;浓度分布反映了惯性力的占优作用。三种变量分布反映了动量、能量和质量输运性质的根本性区别。     

Measurements of concentration decays in underexpanded jets through rectangular slot nozzles

Previously studies of hydrogen releases have focused on hydrogen jets through round nozzles, but leaks are more likely to result in jets through slots. In this study, the concentration decays along the jet centerline were measured for underexpanded jets from rectangular slot nozzles with aspect ratios (AR) of 1–12.6 for storage pressures up to 3.7 MPa. The mass fractions along the jet centerlines decay inversely with distance from the nozzle as with axisymmetric jets but with a faster decay rate. All the data collapses onto a single curve when normalized by the proper factor of the downstream location, except for the jets from square nozzles (AR1). The decay rates for jets from rectangular nozzles with AR greater than unity are significantly larger than for the jets from square nozzles. The jets from square nozzles behave somewhat like the circular jets from circular nozzles due to the symmetric geometry, so the decay rate is closer to that of circular jets relative to the jets from the other rectangular nozzles. This database will be useful for model validations for the modeling of jets from rectangular nozzles.     

多股多层水平淹没射流新型消能工理论探析

针对高水头、大单宽流量水利水电工程泄洪消能问题,介绍了一种多股多层水平淹没射流新型的泄洪消能型式,基于国内外研究基础,探讨了基本理论并进行了对比分析,结果表明,该消能方式流态稳定性好、临底流速低、消能率高,值得推广应用.     

Numerical predictions of cryogenic hydrogen vertical jets

Comparison of Computational Fluid Dynamics (CFD) predictions with measurements is presented for cryo-compressed hydrogen vertical jets. The stagnation conditions of the experiments are characteristic of unintended leaks from pipe systems that connect cryogenic hydrogen storage tanks and could be encountered at a fuel cell refueling station. Jets with pressure up to 5 bar and temperatures just above the saturation liquid temperature were examined. Comparisons are made to the centerline mass fraction and temperature decay rates, the radial profiles of mass fraction and the contours of volume fraction. Two notional nozzle approaches are tested to model the under-expanded jet that was formed in the tests with pressures above 2 bar. In both approaches the mass and momentum balance from the throat to the notional nozzle are solved, while the temperature at the notional nozzle was assumed equal to the nozzle temperature in the first approach and was calculated by an energy balance in the second approach. The two approaches gave identical results. Satisfactory agreement with the measurements was found in terms of centerline mass fraction and temperature. However, for test with 3 and 4 bar release the concentration was overpredicted. Furthermore, a wider radial spread was observed in the predictions possibly revealing higher degree of diffusion using the k-ε turbulence model. An integral model for cryogenic jets was also developed and provided good results. Finally, a test simulation was performed with an ambient temperature jet and compared to the cold jet showing that warm jets decay faster than cold jets.