车用增压器涡轮内部脉动流场仿真研究

为了解车用增压器涡轮在脉冲进气条件下的性能,改善涡轮与发动机的匹配,采用数值模拟方法研究了径流有叶涡轮内部脉动流场。针对涡轮瞬时效率的计算,特别采用了相位平移方法。研究结果表明:由于涡轮级进口脉动气流的影响,涡轮流量和效率变化相对于压比均出现了滞后现象;脉动周期内转子进口攻角变化对叶轮内部速度场起主要影响作用;转子功率变化规律与涡轮级进口压力变化一致;适当提高涡轮设计流量能够增加涡轮有效利用发动机废气能量的能力。     

基于浸入实体法的矩形双螺杆泵流动特性数值模拟

为获得矩形双螺杆泵内部全流道的瞬态流动特性,基于浸入实体方法,采用CFD模拟平台,运用N-S方程和标准k-ε湍流模型对给定基本参数的螺杆泵典型设计工况进行瞬态数值模拟,得到了螺杆泵各过流部件在运转过程中的流动信息。计算表明:压力从进口到出口沿螺旋槽逐渐升高,增压效果明显,泵体各断面最大压差约280 k Pa;进口区域流场较为紊乱,互相啮合的转子螺旋槽内由于压差较大、速度较高,最大速度约11 m/s,在转子与泵壳壁面接触区域存在少量负轴向速度,为主要泄漏区域,泄露量较小,密封性能较好。     

1000MW级核主泵内部非定常流动特性

为了对1000 MW核主泵内部流场进行深入分析,应用商业计算软件CFD对核主泵进行了非定常数值模拟,得到主泵内部压力脉动特性。结果表明:核主泵内部压力脉动呈现周期性变化,叶轮叶片对流体的影响频率为转频f=24.2 Hz的整数倍及其谐波;在叶轮内脉动幅度从叶片前缘到后缘逐渐增加,而在导叶内从叶片前缘到后后缘逐渐减小,在泵壳内变化相对较小;不同工况下,脉动幅值在额定工况下最小,在小流量工况时最大,并且偏离额定流量越多,压力脉动越严重。     

混流式核主泵非定常流场的压力脉动特性分析

为研究核主泵内部流场压力脉动情况,采用大涡模拟方法对模型泵内部流场进行了三维非定常数值模拟,通过设置监测点,得到了不同位置处的压力脉动结果,并进行了频域分析.结果表明:核主泵模型泵内最大压力脉动发生在叶轮出口处,从叶轮进口到导叶出口,压力脉动先增大后减小,压力脉动频率主要受叶轮转频控制;在球壳内部压力脉动沿着球壳半径方向逐渐减小,且压力脉动频率与叶轮转频有关.     

轴流泵优化设计及压力脉动特性研究

为探究明渠流对轴流泵装置性能的影响及提升大型低扬程轴流泵装置的整体水力性能,基于泵装置悬空高度、明渠进水池宽度、明渠出水池宽度三个参数,对大型低扬程泵装置进行三维非定常数值模拟计算,通过优化分析选出最优轴流泵装置模型,优化后的模型水力效率由81.3%提升为84.5%,进一步分析了最优轴流泵装置模型在不同流量工况下的流场特性及压力脉动特性。结果表明,小流量工况下运行的泵装置压力脉动时域特性明显优于额定流量工况和大流量工况,转轮进口及导叶进出口处测点压力脉动系数值均不超过0.01;转轮进口处三种流量工况下最大脉动系数均低于0.015,小流量、大流量工况下导叶出口处的压力脉动系数接近0,额定流量工况下导叶出口处的压力脉动系数为0.122。     

混流泵作透平的数值计算与试验

为探究混流泵作透平内部的流动特性,选取1台比转速为220的混流泵进行外特性试验,采用全流场和结构化网格技术对透平内部流动状况进行数值模拟,得到不同流量工况下透平内部的流场分布和压力分布,并用速度三角形对透平内部流场变化进行分析。结果表明,透平进口到出口压力逐渐降低,随着流量增加,透平进出口压差逐渐增加,叶轮内部涡漩位置和大小发生变化,尾水管内液流圆周分速度方向发生变化;透平总水力损失随流量的增加而增加,其中叶轮水力损失占比最高,因此混流泵作透平的优化应集中在叶轮部分。     

分流叶片进口直径对离心泵空化特性影响

为探究分流叶片对离心泵空化性能的影响,以IS80-50-200模型泵为研究对象,在模型泵上设计添加了3种不同进口直径分流叶片,利用CFD软件对离心泵进行全流道三维定常湍流空化数值模拟,分析不同汽蚀余量对离心泵空化特性和叶轮内部流场的影响,探究叶轮空化初生和发展规律。结果表明:添加分流叶片后,泵的扬程、效率均有一定程度的提高,且分流叶片的进口直径对扬程和效率的影响不大;泵的H-Q曲线驼峰减弱;泵的抗空化性能均有提高。在研究的水力模型中,当离心泵短叶片进口直径为0.8D2时,泵的抗空化性能最好。添加分流叶片后,长叶片两侧压差减小,叶轮进口处的低压区范围变小,有利于提高泵的抗空化能力。     

CFD在涡轮排气管增压器流场分析中的应用

本文借助三维数值模拟软件Numeca,建立了涡轮排气管增压器涡轮机的网格模型,对涡轮排气管增压器(即增压器与排气管集成)的涡轮及排气歧管内部流场分布情况进行了稳态模拟.结果表明:涡轮排气管各进出口的总压差分布不均,以2#进口进气时总压损失最大,此外,对涡轮内部流场及温度场也进行了分析,流场及温度场整体分布比较均匀,流场局部还存在一定的改善空间.可见,CFD技术对于优化涡轮增压器涡轮及排气管的设计,改善增压器性能具有很好的指导意义.     

结构参数对混流式循环水泵性能影响的数值模拟

在混流泵的设计改造中,常用方法是改变叶片的进出口角、改变进口边以及叶轮外径的切削。这些结构参数的改变,也改变了泵的性能。保持泵蜗壳和叶轮外形尺寸不变,改变叶片进出口角的大小、调节进口边、适当切削叶轮外径,设计出一系列的泵,并借助于FLUENT软件模拟泵的内部流场,然后,改变工况求得对应流量的扬程,从而绘制出结构参数改变时对应的泵性能曲线,总结结构参数变化对性能曲线影响的规律。     

混流式水轮机导水机构三维定常CFD分析

基于三维N-S方程和标准k-ε紊流模型,采用CFD(计算流体力学)软件对HLA351-LJ-170混流式水轮机原型机的导水机构在小流量和大流量工况下分别进行了三维定常数值模拟,获得了流场的速度、压力分布变化规律。结果表明,CFD分析能较准确地预测导水机构内部流场的结构,数值模拟结果对水轮机选型和优化设计均具有重要的指导意义。     

熔盐泵空间导叶与叶轮的径向安装间隙对泵性能影响研究

为了探究空间导叶和叶轮之间的径向安装间隙对泵性能影响规律,选择某VS1型太阳能高温熔盐泵首级部分作为研究对象,在其他几何参数不变的前提下,以原导叶和叶轮径向间隙值为基础,通过沿径向逐次改变导叶进口和叶轮之间的相对位置,共设计了6组不同间隙下的导叶-叶轮组合方案,基于CFD方法对6种间隙方案(1.5～6.5 mm),进行了全流场数值模拟,并试验验证了数值算法的可靠性。研究表明：导叶与叶轮径向安装间隙对泵扬程和效率在不同工况下的影响具有显著差异性,存在较优间隙使泵性能整体最佳,间隙过大、过小时都会致使其性能劣化;与原间隙2.5 mm时相比,合适的间隙可使叶轮出口和腔体间隙处的主频压力脉动幅值分别降低20.6%和36.4%,泵内介质流动稳定性提升;导叶内流道压力梯度和腔体涡核心分布随间隙改变呈不同变化态势,间隙为4.5 mm时,导叶内流道压力梯度变化更为均匀有序,腔体内涡的范围和强度较其它方案削弱明显,泵内流态最优。     

挖掘机用复杂结构排气消声器的CFD仿真研究

建立了某挖掘机用复杂结构排气消声器的仿真模型,并利用CFD技术对消声器某入口流速下的流场进行了仿真,分析了该消声器内部气体的流动特性及压力分布特性,通过追踪消声器内部气体的踪迹发现内部的漩涡产生了较大噪声及压力损失,随着入口气体流速的增大,消声器出入口压力及总体压力损失都呈类 似于抛物线的规律变化.研究了试验和仿真环境中,不同工况下消声器的压力损失,各种工况中,误差率在最低速时仅为5.5%,最高速时达到了20.5%,说明入口流速对于仿真结果有很大的影响.研究表明CFD方法研究消声器压力损失的有效性.     

基于CFD的离心泵内部流场数值模拟

采用GAMBIT建模划分网格,基于CFD技术,采用雷诺时均N-S方程和RNG k-ε湍流模型对离心泵内部的二维湍流流动进行了数值模拟,得到了离心泵内部流场的压力分布、速度分布及气蚀特性规律。结果表明,叶轮内部流体从叶片入口到离心泵出口速度不断降低,压力不断升高。同时,得到了气蚀分布特性,在所研究工况条件下,气蚀首先在叶片两侧出现。模拟结果对工程实践和离心泵水力性能研究有一定的指导意义。     

Effect of rotational speed on unstable characteristics of lobe hydrogen circulating pump in fuel cell system

The hydrogen circulating pump is an essential component of hydrogen fuel cell systems. It plays a vital role in improving hydrogen utilization efficiency and optimizing hydrothermal control capabilities. Due to its compact design, high efficiency, and outstanding low-temperature adaption performance, the lobe hydrogen circulating pump has excellent potential for hydrogen recirculation in fuel cell vehicles (FCVs). This paper investigated the internal flow characteristics of a lobe hydrogen pump for FCV under different rotational speeds by experiments and computational fluid dynamics (CFD). Moreover, the lobe rotor domain was calculated using the dynamic mesh method. The effects of different rotating speeds on transient pressure pulsation, exhaust flow rate, external noise, and vibration were studied. The result reveals that the volumetric efficiency improves with the increased lobe rotor speed when the pressure ratio remains constant. The vibration acceleration level (VAL) and the external noise also increase. The vibration is most significant at the pump casing outlet and tends to decrease as the frequency increases. The sound pressure level spectrum has a discrete character in the low-frequency band, with peaks mainly concentrated at the rotating fundamental frequency and harmonics. The middle and high frequency bands have prominent broadband characteristics, and the energy is relatively concentrated.     

Systematic assessment of the anode flow field hydrodynamics in a new circular PEM water electrolyser

In this work, we investigated the key underlying flow characteristics of a circular unit cell proton exchange membrane (PEM) water electrolyser. In particular, we focused on investigating anode flow field design using computational fluid dynamics (CFD) tool. Transient, 3D single phase fluid flow simulation results were presented, and in-house experiments were conducted for validation against CFD simulation data identifying key performance parameters of the PEM water electrolyser: uniform water distribution, pressure drop and hydraulic retention time. The effects of the water flow rate, inlet and outlet sizing and different number of inlet and outlet configurations were considered. The main observation from the study was discussed to provide insight into the factors affecting the flow pattern. Among the studied flow field design cases, it was found that the average pressure drop decreased with increase in number of inlets, also flow profile can be grouped into different set, depending on number of inlets. The correlation between pressure drop and mean velocity profile for different inlet and outlet configurations provides a useful basis to properly design the high performance PEM water electrolyser.     

Optimal technical analysis of vacuum ejector for passive hydrogen recovery

In this study, the numerical analysis and experimental measurements are conducted on the internal flow field and temperature distribution of ejectors with different throat diameters. The computational fluid dynamics (CFD) is used to simulate different ejectors and investigate the effects of Mach number, pressure, and temperature distributions. The hydrogen Entrainment Ratio (ER) of ejectors is also measured for proton exchange membrane fuel cell applications. The experimental measurements and simulations of the hydrogen Entrainment Ratio of the ejectors showed that the recovery efficiencies are 59%, 53%, and 33% for the pipe diameters of 0.5, 0.7, and 1.0 mm at the inlet pressures of 340 kPa, respectively. In different area ratios, the larger area ratio of the nozzle leads to greater difference between the diameter of the throat and the diameter of the throat outlet. This causes a smaller recovery rate. In the internal flow field of the ejector, higher recovery rate can be achieved by using the closer location of the positive shock wave to the nozzle outlet.     

Pump-induced fluctuating pressure in a reactor coolant pipe

An analytical model is proposed to describe the propagation of pressure pulsations originated at the pump outlet through the inlet pipe of a pressurised water reactor (PWR). Pressure pulsations data from a pre-critical vibration monitoring programme (PVMP) for a C-E reactor are presented and compared with those calculated by the analytical model. The propagation of pump-induced pressure pulsation is important because of the potential for vibration and resultant damage of reactor internals.

The theory of pump-induced pressure pulsation distributions in the coolant annulus in a PWR has been developed by Penzes¹ and by Bowers and Horvoy² on the assumption that the pressure pulsations are due to excitations at the inlet nozzles. The pressures in the annulus are calculated based on prescribing the pressure at the inlet nozzles and on the concept of time dependent body force in the governing differential equations. The analytical model presented in the present paper and the theory given by Penzes¹ and Bowers and Horvoy² describe the propagation of pump-induced pressure pulsations in the critical regions (from the pump outlet through the inlet pipe and the coolant annulus in a PWR) for deterministic loads on PWR internals.

In the present analytical model the pressure pulsations are assumed to travel in plane waves so that the governing equation is one-dimensional in nature. The boundary condition at the pump outlet end of the inlet pipe is a time-dependent harmonic function; amplitudes for pump related frequencies are established based on an existing theory for hydraulic noise in centrifugal pumps.³ At the inlet nozzle end of the inlet pipe, due to the complexity of its acoustic characteristic, three types of boundary condition are considered—open, closed and piston-spring supported. Therefore, the analytical model essentially consists of a one-dimensional wave equation with time-dependent non-homogeneous boundary conditions. Closed-form solutions for the problem are derived using a linear transformation technique which reduces the problem to one involving a non-homogeneous differential equation with homogeneous boundary conditions.

Numerical examples are given for a typical reactor. Pressure power spectral density data are presented for data taken at inlet nozzles during a C-E PVMP. Distinct peaks at various pump related frequencies such as rotor speed, twice rotor speed, blade passing frequency and twice blade passing frequency, are observed. RMS pressures predicted by the analytical model at pump related frequencies are compared with those from PVMPs. The spatial distributions of the pressure field along the length of the inlet pipe for the three typical boundary conditions are given. Finally, the effect of the pipe geometry on the pressure field and the acoustic frequencies is analysed.     

基于正交试验的光伏水泵性能优化

以光伏水泵为研究对象,基于试验测试和理论分析建立光伏水泵出水量计算预测方法。采用正交试验设计优化方案,选取泵叶轮结构参数为优化变量,通过数值模拟和试验研究的方法,对该光伏水泵的性能进行优化和试验验证。结果表明：经优化后,光伏水泵系统的最低出水值下降至330 W/m²,水泵每日工作时长提升;光照辐射强度稳态时的泵出口压力脉动相较优化前有小幅提升,光照辐射强度瞬态变化时泵出口压力脉动波动幅度更平稳;优化后的模型泵叶轮进口低压区面积明显减小,叶轮出口压力显著增加,同时叶轮流道内速度分布更为均匀。     

基于流固耦合的斜流泵空间导叶多工况强度分析

空间导叶作为斜流泵的主要过流部件,对改善叶轮出口流场具有重要的意义,探究其内部流动以及与固体之间的相互作用尤为必要。通过对0.6Q_d、0.8Q_d、1.0Q_d、1.2Q_d和1.4Q_d5个不同流量工况点进行CFD仿真及流固耦合计算分析,结果显示空间导叶承受的总压随着流量的增加逐渐减小,空间导叶与上下盖板连接位置承受压力较大;随着流量的增加,空间导叶最大应力值和变形量均减小,其所承受应力主要集中于上盖板进口边以及导叶与上下盖板连接处,在上盖板两导叶叶片中间位置变形较为明显。研究结果可为斜流泵空间导叶结构设计和强度优化提供参考。     

杏林湾排涝泵站竖井贯流泵装置进出水流道流态的数值分析

运用三维湍流数值模拟方法对杏林湾排涝泵站竖井贯流泵装置进出水流道流态进行数值模拟,分析进水流道的流场均匀度和出水流道的扩散均匀性,提出优化方案。模拟结果表明,优化后的竖井贯流泵装置,在均匀进流的条件下,进水流道内的水流流态较好,竖井两侧流道内的水流流速分布较均匀,未出现明显的漩涡、回流等不良流态,水泵进流均匀、平顺;出水流道通过设置中隔墩的长度,不仅水流流态得到一定改善,而且中隔墩两侧水流流量分配基本均匀,有助于保证泵站良好的出水条件。