鸭嘴河烟岗水电站泥沙模型试验研究

通过泥沙模型试验研究,分析不同入库水沙条件下进入取水口内水流的含沙量和颗粒级配,通过合理控制水库泥沙淤积和水库泄空冲沙,可保证设计所需长期有效的日调节库容。设计中取消了地下沉沙池,以水库代替沉沙池进行沉沙和冲沙是可行的方案。     

沉沙池S型集沙涵结构优化研究

沉沙池是农业灌溉工程中的重要水利设施之一，对降低水流含沙量、提高水流利用率有着重要作用。为提高沉沙池排沙效率，在渭干河干渠S型沉沙池结构基础上设计了直线型集沙涵结构，通过原型观测试验结果，与物理模型试验和数值模拟相结合，明确了S型和直线型集沙涵水流水力特性。试验结果表明，Fluent软件可有效模拟局部沉沙池运行过程，由于S型集沙涵末端水流流速较小，导致集沙涵内泥沙出现淤积，直线型结构则能有效提高集沙涵内整体水流流速，集沙涵末端廊道内水流流速从0 m/s提升至0.4～0.7 m/s,从而提高沉沙池排沙效率。该研究可为优化沉沙池结构、提高沉沙池排沙效率提供科学依据和技术支撑。     

某水库泄洪排沙洞水力特性及排沙效果研究

针对某水库引水发电洞前泥沙淤积的问题,在某引水发电洞附近新增泄洪排沙长隧洞,通过水工模型试验研究了不同工况下排沙洞的水力特性(沿程压力、流速、流量、流量系数、空穴数等),并对比试验值与设计值,验证了排沙隧洞设计的合理性。以塑料沙为模型沙,通过河工模型试验,确定了冲沙漏斗的大小,比选了排沙方案,给出了排沙洞洞口布置的合理位置,使发电洞达到"门前清"的效果。研究成果为类似工程提供参考。     

西河出居沟水电站泥沙模型试验研究

通过泥沙模型试验研究,分析不同入库水沙条件下进入水电站取水口内水流的含沙量和颗粒级配,通过合理控制水库泥沙淤积和水库泄空冲沙,可保证设计所需长期有效的日调节库容。通过试验表明以水库代替沉沙池是可行的。     

青松水电站首部枢纽水工泥沙模型试验

通过泥沙模型试验,研究了不同入库水沙条件下进入取水口内水流的含沙量和颗粒级配．通过合理控制水库泥沙淤积和水库泄空冲沙。可保证设计所需长期有效的日调节库容。通过试验表明以水库代替沉沙池是可行的。     

西河出居沟水电站泥沙模型试验研究

通过泥沙模型试验研究．分析不同入库水沙条件下进入水电站取水口内水流的含沙量和颗粒级配．通过合理控制水库泥沙淤积和水库泄空冲沙．可保证设计所需长期有效的日调节库容。通过试验表明以水库代替沉沙池是可行的。     

双弧形导沙坎相对高度对取水口冲沙效果的影响

取水口前易发生泥沙淤积,泥沙进入输供水系统后可能会造成机组及管路损坏,常需设置拦排沙措施以避免泥沙进入.针对取水口的拦排沙问题,进行了新型双弧形导沙坎在较低水位运行条件下导沙坎体型参数、水动力条件对取水口前淤积泥沙冲刷效果的影响试验.结果 表明,高度适宜的双弧形导沙坎有利于冲沙廊道内螺旋流的形成与发展,能有效减少泥沙淤...     

小浪底水库库区支流东洋河及西阳河泥沙淤积规律分析

针对小浪底水库蓄水后泥沙淤积影响支流淤积的问题,以小浪底水库库区支流东洋河、西阳河为例,介绍了干流及支流泥沙观测断面的布置及测验方法,并分析了东洋河、西阳河泥沙淤积观测结果.结果表明,干流三角洲淤积体已在支流河口形成了拦门沙坎,致使支流河底纵向坡度变小甚至变为倒坡,这对小浪底水库运行及黄河干流及其支流排沙将产生不利影响...     

“库中库”模式在湖泊型多沙水库中的应用

为解决多沙河流上的湖泊型水库的泥沙淤积问题,提出利用水库地形条件,通过在库区设置拦沙墙形成"库中库"的排沙蓄水模式,并以德日苏宝冷水库为例,对设置拦沙墙的防沙及冲沙效果进行了物理模型试验和水流泥沙数值模拟研究。结果表明,在多沙水库中采用"库中库"模式既可防止副库区淤积,又能增强主库区的拉沙效果,是一种解决湖泊型水库库区泥沙淤积的有效工程措施。     

水电站近坝区水沙输移二维数值模拟

以萨拉康水利工程为例,采用平面二维水沙模型对近坝区域的水沙运动进行计算研究,分析了敞泄排沙条件下上引航道、泄洪闸、厂房等区域的泥沙淤积分布。结果表明,萨拉康水利枢纽工程运行30年后,泄洪闸前的泥沙淤积不会影响闸门安全运行;上引航道口门区主要受主流回流的影响,产生回流淤积;厂房段的拦沙坎与冲沙底孔可有效保护厂房进水口。     

船用柴油机多缸流动不均匀性的数值模拟与优化

采用数值模拟方法建立整机冷却水腔三维模型,研究大型船用柴油机的多缸流动不均匀性问题。分析了进出口位置和不同进口流量对流量不均匀度的影响。结果显示:冷却水腔进出口位置对各缸不均匀性有较大影响;进口位置布置于V型机端面中部,且出口位置靠近机体轴向中部,均有利于使各缸压力损失均匀并提高进水均匀性。对原冷却水腔结构优化后,流量不均匀度从7.10%下降至3.91%;各缸流量不均匀度基本不随进口流量的增加而变化;且A、B两列气缸流量基本一致。     

某船用汽轮机短座阀流量与提升力特性数值模拟计算

由于汽轮机内部空间的限制及船用汽轮机多工况的要求,部分船用汽轮机采用了短座阀。因扩压段长度的大幅减小．阀门的气动性能及强度振动特性产生较大变化,对汽轮机总体性能有较大的影响。本文对某短座阀在试验研究的基础上进行了数值计算分析：通过气动试验,得到某船用汽轮机短座阀的流量系数与提升力系数曲线簇;基于可压缩,N-S方程,利用S-A湍流模型及有限积分法,采用四面体非结构性网格．对此阀门进行了数值模拟计算。通过对该阀门的数值计算得到在不同相对开度及不同压比下的计算结果与试验结果吻合良好;得到对各种短座阀广泛适用的计算方法．为船用调节阀、旁通阀的设计和性能分析提供了重要依据。     

Numerical evaluation of a PEM fuel cell with conventional flow fields adapted to tubular plates

In this research a 3D numerical study on a PEM fuel cell model with tubular plates is presented. The study is focused on the performance evaluation of three flow fields with cylindrical geometry (serpentine, interdigitated and straight channels) in a fuel cell. These designs are proposed not only with the aim to reduce the pressure losses that conventional designs exhibit with rectangular flow fields but also to improve the mass transport processes that take place in the fuel cell cathode. A commercial computational fluid dynamics (CFD) code was used to solve the numerical model. From the numerical solution of the fluid mechanics equations and the electrochemical model of Butler-Volmer different analysis of pressure losses, species concentration, current density, temperature and ionic conductivity were carried out. The results were obtained at the flow channels and the catalyst layers as well as in the gas diffusion layers and the membrane interfaces. Numerical results showed that cylindrical channel configurations reduced the pressure losses in the cell due to the gradual reduction of the angle at the flow path and the twist of the channel, thus facilitating the expulsion of liquid water from the gas diffusion layers and in turn promoting a high oxygen concentration at the triple phase boundary of the catalyst layers. Moreover, numerical results were compared to polarization curves and the literature data reported for similar designs. These results demonstrated that conventional flow field designs applied to conventional tubular plates have some advantages over the rectangular designs, such as uniform pressure and current density distributions among others, therefore they could be considered for fuel cell designs in portable applications.     

Investigation of liquid water heterogeneities in large area proton exchange membrane fuel cells using a Darcy two-phase flow model in a multiphysics code

Proper management of the liquid water and heat produced in proton exchange membrane (PEM) fuel cells remains crucial to increase both its performance and durability. In this study, a two-phase flow and multicomponent model, called two-fluid model, is developed in the commercial COMSOL Multiphysics® software to investigate the liquid water heterogeneities in large area PEM fuel cells, considering the real flow fields in the bipolar plate. A macroscopic pseudo-3D multi-layers approach has been chosen and generalized Darcy's relation is used both in the membrane-electrode assembly (MEA) and in the channel. The model considers two-phase flow and gas convection and diffusion coupled with electrochemistry and water transport through the membrane. The numerical results are compared to one-fluid model results and liquid water measurements obtained by neutron imaging for several operating conditions. Finally, according to the good agreement between the two-fluid and experimentation results, the numerical water distribution is examined in each component of the cell, exhibiting very heterogeneous water thickness over the cell surface.     

A numerical study of unsteady natural convection induced by iso-flux surface cooling in a reservoir model

Unsteady natural convection in a reservoir model subject to constant cooling at the water surface is considered in this paper. In such a case, the unequal heat loss resulting from a varying water depth creates a horizontal temperature gradient which in turn drives a horizontal exchange flow between the coastal region and the main water body of the reservoir. Understanding of the flow mechanisms pertinent to this flow is important for predicting the transport of nutrients and pollutants across the reservoir.The present numerical simulations impose random perturbations at the water surface in order to trigger flow instabilities. First, numerical tests are carried out to investigate the flow response to different perturbation amplitudes. These tests reveal a linear range of the flow response to the perturbations. Subsequently, the transient flow development at different stages is described in details based on numerical data, and the effects of the Grashof number on the unsteady flow are examined.     

潘口水电站泄洪洞三维数值模拟

为研究采用数值模拟方法分析岸边泄洪洞水力特性的可行性,采用Fluent商业应用软件对潘口水电站岸边泄洪洞进行了三维数值模拟,得到了泄流能力、典型断面流速、沿程底板压力、水面线及洞顶富余等水力要素的分布特点。数值计算结果与模型试验结果比较表明,两者吻合较好,可见采用数值模拟方法研究潘口水电站泄洪洞的水流特性具有可行性,各种边界条件的设定较为合理,能够模拟出真实情况下的各项水力指标,研究结果对体型优化有一定指导作用。     

新江海河河网地区水量水质联合调度模拟及引水方案

为分析南通市通州区新江海河地区不同引水方案下的水质改善效果,采用一维圣维南方程组和对流扩散方程,以水量模型和水质模型间流量、水位资料的信息传输廊道为媒介,构建水量水质耦合模型,通过控制南通闸引水量,模拟分析了不同引水方案对新江海河各断面CODcr和氨氮浓度变化的影响。结果表明,由于新江海河水动力条件不足,污染物本底浓度较高,导致工程引水对其水质改善效果有限,针对其水质污染特点,提出了加强控制污染物入河量的建议,为当地水利工程调度工作和改善新江海河水体水质提供了依据。     

An implicit numerical scheme for the simulation of three-dimensional two-phase flows in light water nuclear reactors

ABSTRACT

An implicit numerical scheme is presented for solving the two-fluid model widely used in the analysis of a gas–liquid two-phase flow in light water nuclear reactors (LWRs). The pressure equation is established by combining the momentum and mass conservation equations. The implicit calculation of each governing equation is separated into phase- and space-link steps. In the phase-link step, the interfacial momentum and heat transfers are implicitly calculated. Then the solution accounting for the convection and diffusion terms is calculated simultaneously in space. The phase- and space-link steps are repeated for convergence. The numerical scheme is implemented in CUPID, which is a multidimensional two-phase flow analysis code for LWRs, and verified against a set of conceptual two-phase flow problems which include typical thermal hydraulic phenomena in LWRs. Calculations are performed using four numerical schemes, semi-implicit ICE and SMAC schemes, an implicit scheme, and an implicit scheme with increased time step size, and the results are discussed.     

An experimental and numerical investigation on the cross flow through gas diffusion layer in a PEM fuel cell with a serpentine flow channel

A serpentine flow channel is one of the most common and practical channel layouts for a polymer electrolyte membrane (PEM) fuel cell since it ensures the removal of water produced in a cell with acceptable parasitic load. During the reactant flows along the flow channel, it can also leak or cross to neighboring channel via the porous gas diffusion layer due to the high pressure gradient caused by the short distance. Such a cross flow leads to a larger effective flow area altering reactant flow in the flow channel so that the resultant pressure and flow distributions are substantially different from that without considering cross flow, even though this cross flow has largely been ignored in previous studies. In this work, a numerical and experimental study has been carried out to investigate the cross flow in a PEM fuel cell. Experimental measurements revealed that the pressure drop in a PEM fuel cell is significantly lower than that without cross flow. Three-dimensional numerical simulation has been performed for wide ranges of flow rate, permeability and thickness of gas diffusion layer to analyze the effects of those parameters on the resultant cross flow and the pressure drop of the reactant streams. Considerable amount of cross flow through gas diffusion layer has been found in flow simulation and its effect on pressure drop becomes more significant as the permeability and the thickness of gas diffusion layer are increased. The effects of this phenomenon are also crucial for effective water removal from the porous electrode structure and for estimating pumping energy requirement in a PEM fuel cell, it cannot be neglected for the analysis, simulation, design, operation and performance optimization of practical PEM fuel cells.     

The behaviour of adsorbent energy storage beds

A numerical study is made of the behaviour of packed beds containing adsorbent material used for energy storage.The basic model assumes that air at a given absolute humidity and at either a high or low temperature is available to charge or discharge the store, the air flow direction for the charging case being opposed to that for the discharging case. When air flows through the bed, transfer of heat and water vapour to the air stream is assumed to teh governed by surface transfer coefficients, while difusion of heat and water vapour in the fluid flow direction is neglected. For periods of no air flow, diffusion in the direction of the bed axis occurs; and for both the air flow and no air flow cases, heat transfer through the container walls is included.From the foregoing, three operating modes are possible—charging, discharging and no flow—and when charging or discharging there may be variations in the air flow rate. A repeatable random number sequence is used to determine the mode of operation at each time step during the numerical integration, and the magnitude of the random number determines the air flow rate.For this random number sequence the effects of wall losses and adsorption capacity of the adsorbent (on store performance) are studied.