基于计算流体动力学的迷宫型灌水器流量预测

通过反求迷宫型灌水器注塑产品的实物结构,建立其流量数值预测的物理模型,分别采用层、紊流模型对40～150 kPa压力下的灌水器流量进行数值计算,并相应开展该灌水器流量与压力关系的试验测试.试验结果验证了计算流体动力学(CFD)方法预测灌水器流量的可行性,同时对比发现紊流模型的计算值更接近于试验值.通过对迷宫流道内流场分布的研究表明,由于流道曲折度较大,其内流体流动状态的转折点大幅度提前,在雷诺数Re=250～300之间时,流动就开始过渡到紊流状态,从而导致灌水器内的流动在40～150 kPa压力测试范围内均处于一种紊流状态.     

灌水器内圆弧形流道的液固两相流场分析

针对迷宫流道灌水器结构细微复杂等特点，利用计算流体动力学方法对其流道内流场进行液固两相数值模拟。采用雷诺应力模型和壁面函数法模拟流体流动，采用离散相模型跟踪颗粒运动轨迹。研究表明，每个单元流道不同部位的流体流速相差较大，在圆弧顶部和右下侧均出现不同大小的漩涡，沿流动方向漩涡呈扩大趋势；小颗粒的跟随性比大颗粒的跟随性好，但更易受湍流脉动的影响，部分颗粒会在涡团中心处沉淀下来，导致流道堵塞，灌水器的堵塞实验结果验证了数值分析的正确性；相对颗粒直径而言，颗粒密度对其运动轨迹的影响要小得多。     

一体式压力补偿灌水器快速设计新方法

为降低压力补偿灌水器制造和装配的复杂性,设计了新型的一体式压力补偿灌水器,并基于快速成形技术,提出了一体式压力补偿灌水器的快速实验和定型方法。采用正交实验设计方法,取压力补偿区结构参数为因素,设计并制作一体化滴管进行其水力性能实验分析,结果表明,补偿区流道单元个数和剪切深度对灌水器补偿性能影响显著,而且滴头体上迷宫流道尺寸对灌水器流量影响最大。建立了关键结构参数相对于流量和流态指数的关系式,通过实验验证了其正确性。最后进行了压力补偿区液固两相流抗堵塞机理计算流体动力学分析,为新型压力补偿灌水器的结构设计提供了理论依据。     

惯性粒子分离器流场特性的PIV试验研究

惯性粒子分离器因具有流动损失小、砂尘分离效果明显的特点而成为直升机发动机进气道的标准配置。论文采用PIV测速技术对惯性粒子分离器矩形截面模型进口、中心体驼峰区域、清除流(包括分叉区域)、主气流流场在高速进气状态下,进行分段测量,研究了该模型流道在设计型线下的流动特性;对比数值计算,显示出该流场的局部流动细节结构。进一步地验证了湍流模型数值计算方法可应用于惯性粒子分离器流道流场特性的研究。     

绕后台阶与准方腔耦合流道流场的数值计算与试验研究

用Galerkin有限元法对绕后台阶与准方腔耦合流道流场进行数值模拟。数学模型采用的是流函数—涡量形式的N-S方程,分别计算了雷诺数214.2、428.4和642.6三种情况下流场的结构,计算所得瞬态流场和稳态流场以直观速度矢量图和等值线图的形式给出,并绘出了部分纵截面上速度分布剖面图,分析了雷诺数对流场结构的影响。同时应用近年来发展起来的且获得广泛应用的全场瞬时速度测量技术,即粒子图像测速技术PIV)对流场进行了试验研究,所得速度矢量图与数值计算结果吻合较好。计算和试验结果表明:绕后台阶与准方腔流道流场比较复杂,同时具有后台阶流动和方腔流动的结构特征。研究结果对工程实际具有重要意义。     

双流道泵内非定常流动数值模拟及粒子图像测速测量

为探讨双流道泵内部的非定常流动机理,采用Fluent软件,基于滑移网格技术、 湍流模型计算了一双流道泵在不同工况下的内部流动,并将计算结果与粒子图像测速仪(Particle image velocimeter, PIV)实测结果进行比较。结果表明：计算所得双流道泵内部流场符合叶轮机械内部流动的一般规律,且与PIV实测结果总体变化趋势一致;由于双流道泵结构特殊,其进口处的流动状态与普通叶轮相差较大,出口处的流动状态与普通叶轮类似;叶轮进口处,流体基本沿流道吸力面流动,流道工作面上的相对速度很小,存在严重的脱流和旋涡;叶轮出口处,压力面和吸力面的速度趋于相等,射流—尾迹现象并不明显;由于叶轮—蜗壳动静干涉,两个叶轮流道内的静压分布有所不同;同一流道内,静压随着半径的增加而逐步增大,压力面侧静压大于吸力面侧;蜗壳流道内静压随半径增大,最大静压值在隔舌处。此项研究不仅加深了人们对双流道泵内非定常流动图画的理解,从而进一步完善双流道泵设计方法,同时也可为其他类型泵的内流研究提供借鉴。     

进口节流式滑阀内流场的有限元计算与PIV研究

用有限元法(FEM)和粒子图像测速技术(PIV)对三种不同开口度下进口节流滑阀沿进口流道、节流口、阀腔以及出口流道的流场进行了数值计算和试验可视化研究。数值模拟的数学模型采用的是连续性方程和Navier-Stokes方程的流函数—涡量式,有限元法用于方程的离散。自行编制的有限元计算程序用来计算求解区域离散点上的流函数及涡量值,再根据流函数及涡量与速度分量之间的关系求出各结点上的速度矢量。对于粒子图像测速试验,光源采用双脉冲Nd:YAG激光器,再用柱透镜和球面镜调制得到1.0mm片光照射流场。30～50μm的聚苯乙烯小球用做示踪粒子,Kodak ES1.0 CCD照相机拍摄流场图像,所得图像用FFT相关算法进行处理,结果用Tecplot输出,数值计算和PIV试验表明,滑阀内部有三个部位产生涡旋。数值计算又表明滑阀开度对阀内部流场结构有影响。研究对于定性分析阀内能量损失、噪声以及对阀的结构和流道的设计有重要实际意义。     

板式空气预热器数值模拟研究

建立了板式结构的空气预热器换热板片及其流道模型,利用计算流体力学软件对流道内流体的流动和传热进行了数值模拟,对比不同定距柱尺寸对设备性能的影响,分析了流道内的速度场、温度场和压力场,并与试验结果进行了比较,得到模拟分析结果与试验偏差在15%以内,说明该数值模拟研究方法可以作为设计优化的可靠手段。     

示踪粒子在离心泵内流场跟随性的影响因素分析

以修正后适用于低雷诺数下粒子在离心泵叶轮内运动方程为基础,给出离心泵内流场粒子成像测速(Particle imagevelocimetry,PIV)测试中示踪粒子跟随性的数学表述。据此对离心泵内流场中示踪粒子的运动进行数值计算,讨论粒子跟随性对粒子物理特性和离心泵内流场性质的依赖关系。并在现有几种模型基础上对比讨论各项力对粒子跟随性的贡献,指出各模型的优缺点。计算结果表明,密度接近流体的密度的中性悬浮粒子跟随性较好;对于密度较大的粒子只有粒子直径足够小才能跟随到一定范围内湍流角频率的流动;粒子径向跟随性比周向复杂得多;在离心泵叶轮内低速漩涡区粒子跟随性较差,尤其是在径向方向上;离心泵叶轮旋转引起的离心力和科氏力以及流道弯曲产生的离心力对粒子跟随性影响很大。通过了解和掌握这些因素的影响,对于离心泵内流场PIV测试中采用合适的示踪粒子和控制粒子跟随性误差具有重要的理论指导意义。     

微注塑成形中熔体充模流动分析及其数值模拟

借鉴宏观熔体的流变学理论和建模技术,针对微尺度流道中的聚合物熔体流动特性,采用模型修正方法,建立反映微小通道中熔体流动特性的理论模型.同时,应用数值模拟方法,研究微尺度粘度、壁面滑移和熔体与模具间的表面传热系数对微小熔体流动的影响关系,并与相关试验数据进行比较.结果表明,微流道中的熔体粘度明显小于传统理论下的粘度值,且与微流道的特征尺寸成正比.随微流道特征尺寸减小,滑移系数也明显减小,壁面滑移速度则增大.考虑局部表面传热系数时微流道中的熔体温度分布具有尺寸效应.微尺度流道中的熔体流动行为与宏观熔体有许多不同.     

Flow behaviour analysis and experimental investigation for emitter micro-channels

The existing research of the flow behavior in emitter micro-channels mainly focuses on the single-phase flow behavior.And the recent micro-particle image velocimetry(PIV) experimental research on the flow characteristics in various micro-channels mainly focuses on the single-phase fluid flow.However,using an original-size emitter prototype to perform the experiments on the two-phase flow characteristics of the labyrinth channels is seldom reported.In this paper,the practical flow of water,mixed with sand escaped from filtering,in the labyrinth channel,is investigated.And some research work on the clogging mechanism of the labyrinth channel’s structure is conducted.Computational fluid dynamics(CFD) analysis has been performed on liquid-solid two-phase flow in labyrinth-channel emitters.Based on flow visualization technology-micro-PIV,the flow in labyrinth channel has been photographed and recorded.The path line graph and velocity vector graph are obtained through the post-treatment of experimental results.The graphs agree well with CFD analysis results,so CFD analysis can be used in optimal design of labyrinth-channel emitters.And the optimized anti-clogging structures of the rectangular channel and zigzag channel have been designed here.The CFD numerical simulation and the micro-PIV experiments analysis on labyrinth-channel emitter,make the "black box" of the flow behavior in the emitter channel broken.Furthermore,the proposed research promotes an advanced method to evaluate the emitter’s performance and can be used to conducting the optimal design of the labyrinth-channel emitters.     

涡轴发动机无叶片粒子分离器流道设计

流道设计是粒子分离器设计的核心内容。本文介绍无叶片粒子分离器流道的设计原理、设计流程和设计方法,重点讨论了各结构元素的不同设计给粒子分离器的性能带来的影响,以及如何采用CFD数值模拟的手段对粒子分离器的两相流场进行计算分析,初步建立了基于两相流CFD分析的流道设计方法。最后,给出了按本文方法对某粒子分离器进行设计和结果分析,并对其粘性流场分析结果进行了说明。     

Investigation of oxygen and water distributions in the modified parallel-serpentine cathode channels of a unit polymer electrolyte membrane fuel cell

In this paper, the measurement of water and oxygen distributions along the modified parallel serpentine cathode flow channels has been performed using a gas chromatograph (GC). Generally, it is difficult to directly profile oxygen and water distributions where water concentration nearly reaches saturation levels. Here, the measurement of high levels of water saturation in cathode channels was carefully performed according to operating conditions such as cell voltage and air stoichiometry. GC measurement was also carried out to understand the oxygen and water distributions under channel flooding conditions. In addition, the oxygen and water vapor distributions by GC measurements for the base-line case were compared with computational fluid dynamics (CFD) simulation results. For the entrance of the flow channel, the simulated results show a good agreement with the measured results. However, some discrepancy between calculated and experimental results is found for the flow channels near the cathode outlet.

     

基于细胞沉积的人工骨微管设计及三维流场分析

针对人工骨微管中细胞均匀粘附和营养成分顺利运输所需流速条件,研究支管与主管道之间的夹角对支管中流速的影响以及沿主管道不同位置的支管中液体速度分布,并结合自然骨微观结构以及流体力学中的能量守恒和流量守恒原理,提出一种强化微循环结构并进行三维粘性流场数值分析,将分析结果与单纯仿形结构的流场分析结果比较,结果表明,该结构流速分布更均匀,支管内流速得到很大程度的提高,有利于细胞均匀粘附和进一步提高人工骨设计孔隙率。     

Three-dimensional computational fluid dynamic analysis of the conventional PEM fuel cell and investigation of prominent gas diffusion layers effect

A full three-dimensional, single phase computational fluid dynamics model of a proton exchange membrane fuel cell (PEMFC) with both the gas distribution flow channels and the membrane electrode assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region are developed and numerically solved using a finite volume based computational fluid dynamics technique. In this research some parameters such as oxygen consumption, water production, velocity distribution, ohmic losses, liquid water activity and fuel cell performance for straight (base case) and prominent gas diffusion layers were investigated in more detail. The numerical simulations reveal that prominent gas diffusion layer improves the transport of the reactant gases through the porous layers; it is due to increase of the mentioned fuel cell efficiency, and prominent gas diffusion layers yield appreciably higher current density. Finally the numerical results of proposed CFD model (base case) are compared with the available experimental data that represent good agreement.     

ECT measurement and CFD–DEM simulation of particle distribution in a down-flow fluidized bed

In the present study, a combined model of computational fluid dynamics and the discrete element method (CFD–DEM) was used to simulate the particle distributions in a down-flow fluidized bed (DFB) with a newly designed particle–air distributor. In the simulation model, particle motion is calculated by solving Newton’s equations and the flow field of air is predicted by the Navier–Stokes equations. The calculation was made for the same geometric and operating conditions as the experiment which was carried out for comparison with the simulation using electrical capacitance tomography (ECT). The numerical predictions for the axial and radial profiles of the particle distribution agreed well with the experimental results.     

同向出流倒锥式旋流器的结构模拟分析

基于现有油水分离的研究成果,提出了一种新型旋流器——同向出流倒锥式旋流器,介绍了其结构及工作原理。基于计算流体力学(CFD)方法,运用Fluent软件对其内部流场进行了数值模拟分析,通过观察流场特性,分析了新型旋流器的典型结构参数(溢流管直径、溢流管伸入长度、锥角和出水口尺寸)对其分离性能的影响。     

钛合金曲面磨粒流加工扰流流道仿真与试验研究

针对具有复杂曲面的钛合金工件磨粒流抛光后表面粗糙度Ra不均匀问题,提出一种具有扰流结构的仿型约束加工流道。借助计算流体动力学（CFD）分析软件,结合SST k-ω湍流模型、离散相模型（DPM）和Oka冲蚀模型,仿真分析原始流道和5种不同扰流角度的扰流流道内磨粒流动力学特性。数值模拟结果表明：扰流流场中的磨粒流相较于原始流场在工件表面具有更大的湍流动能、动压力和冲蚀速率,其中扰流角度为30°时冲蚀均匀性较好。基于仿真条件搭建了磨粒流加工试验平台,使用原始流道和30°扰流流道分别进行了加工试验。试验结果表明：使用原始流道加工5 h后,工件表面曲率不同区域的表面粗糙度Ra值分散,加工效果均匀性较差;使用扰流流道加工5 h后,工件表面各区域表面粗糙度Ra的均匀性明显优于无扰流流场的加工均匀性。     

PIV measurements over a double bladed Darrieus-type vertical axis wind turbine: A validation benchmark

Vertical axis wind turbines (VAWTs) are very attractive for in-home power generation since they can be adopted even at low wind speeds and highly variable wind direction. Even if significant experimental research activity has been carried out to improve VAWTs performance, the ability to accurately reproduce flow field characteristics around turbine blades by CFD (computational fluid dynamics) techniques represents a powerful approach to further enhance wind turbines performance. Thanks to CFD, in fact, it is possible to reproduce flow characteristics with a detail level impossible to achieve by experiments. Nevertheless, in order to appropriately analyze the flow structure by CFD application, an accurate validation is essential, and high-quality measurements of some main flow characteristics are required. In recent publications the authors investigated, both experimentally and numerically, the performance of an innovative double bladed Darrieus-type VAWT, with the aim to define an optimal configuration also focusing on self-starting ability of the prototype by employing CFD technique. Nevertheless, comparison between experiments and numerical results was made only in terms of power and torque coefficients. To overcome such limitation, in this paper the authors propose an experimental benchmark case for CFD results validation, describing detailed flow field in correspondence of one pair of blades of the innovative Darrieus-type VAWT in static conditions. Measurements were performed employing Particle Image Velocimetry (PIV) technique on a scaled model of the turbine blades realized by 3D printing. An uncertainty analysis was also performed which showed a high accuracy of the obtained experimental results. The measurements of the main flow characteristics (bi-dimensional velocity components) were then used for a test case CFD validation of two different turbulence models.