Urea-SCR喷雾模拟计算中CFD的模型选择

数值模拟计算的模型选择对计算结果的准确性十分重要,不同的模型产生的不同结果差异很大,该文论述了采用计算流体力学技术模拟urea-SCR喷雾过程的优越性,利用spalart-allmaras模型、标准k-ε模型和标准k-ω模型对喷嘴雾化进行了数值模拟,分析了各模型的收敛性,速度矢量,动压力分布等物理量。结果表明:spalart-allmaras模型存在失真的情况,标准k-ε模型和标准k-ω模型在尿素SCR喷嘴模拟方面的应用是可行的。     

Urea-SCR喷雾模拟计算中CFD的模型选择

数值模拟计算的模型选择对计算结果的准确性十分重要,不同的模型产生的不同结果差异很大,该文论述了采用计算流体力学技术模拟urea-SCR喷雾过程的优越性,利用spalart-allmaras模型、标准k-ε模型和标准k-ω模型对喷嘴雾化进行了数值模拟,分析了各模型的收敛性,速度矢量,动压力分布等物理量。结果表明：spalart-allmaras模型存在失真的情况,标准k-ε模型和标准k-ω模型在尿素SCR喷嘴模拟方面的应用是可行的。     

圆柱绕流的二维数值模拟和尾迹分析

为指导机械设计中参数和布局的选择,研究固定在水流中的圆柱结构件的受力情况和流场分布．利用FLUENT中的三种湍流模型对雷诺数为3900的圆柱绕流进行二维数值模拟并进行对比,得到升力因数、阻力因数、分离角、斯特劳哈尔数和涡街尺寸等参数的模拟结果,与参考文献中的实验结果对比验证二维模拟的预测精度．RKE（Realizable k-ε）和雷诺应力模型（Reynolds Stress Model,RSM）均能在此雷诺数下得出接近实验结果的流场,RSM模型使用POWER LAW离散格式的结果优于QUICK格式．与三维模拟的对比表明二维模拟适合在设计初期的快速估算,能够快速得到合适精度的模拟结果．     

神光Ⅲ靶场室内空气流动三维数值仿真

在靶场室内环境优化预测问题的研究中,由于神光Ⅲ装置靶场中间层室内空气流动存在绕流回流,对系统稳定性造成影响.为此利用标准k-ε模型、RNG k-ε模型和SST k-ω模型各自特点,分别利用三种模型对流场进行了数值仿真.结果表明三种模型预测的气流组织主体上基本相似,都预测了回流漩涡和绕流的产生,均能满足工程计算精度需求,与在房间外延空气回流区域,采用RNG k-ε模型和SST k-ω模型的分析结果基本一致,在靶球附近绕流区域,二者所得的速度与标准k-ε模型偏差接近10％,说明改进方法更有优势.     

履带式两栖运输设备多湍流模型的研究

关于履带式两栖运输设备精确建模问题,针对履带式两栖运输设备水上受湍流影响大,但湍流模型难于选择的问题,为达到使用恰当湍流模型提高仿真精度的目的,采用对比阻力系数和绕流场云图的方法进行湍流模型适用性的研究,明确各种湍流模型的特性。以某型履带式两栖运输设备水下绕流场为计算对象,基于RANS方程的求解,分别采用Spalart-All-maras、标准k-ε、RNG k-ε、Realizable k-ε、标准k-ω、SST k-ω湍流模型。对比多组仿真结果,表明Realizable k-ε、SSTk-ω模型计算得到的总阻力相对误差最小,RNG k-ε模型对复杂形体周围流场描绘最详细,Spalart-Allmaras模型也有较好的计算精度。     

两种湍流模型在风洞拐角流场计算中的应用及比较

为降低风洞拐角压力损失,提高其气动性能,使用雷诺应力模型(Reynolds Stress Model,RSM)和k-ε湍流模型对其流场进行数值模拟,分析和比较两种模型在压力损失因数、壁面摩擦损失和二次流损失上的异同,得出:使用两种模型均能发现拐角压力损失因数并不随雷诺数变化而变化;使用RSM得到的压力损失因数与实验值更为接近;相同雷诺数下,使用RSM计算得到的壁面摩擦损失因数比k-ε湍流模型的大,但两种模型得到的壁面摩擦损失因数变化趋势一致;两种模型计算得到的二次流损失随雷诺数变化规律一致,但是在相同雷诺数下,使用k-ε湍流模型计算得到的二次流损失比RSM大.     

碳纤维出丝槽流系统结构尺寸优化

为减小碳纤维原丝生产工艺中双扩散过程对原液细流进入浴槽凝固成初生纤维的影响,必须保证出丝槽流系统中流场的稳定性.采用时变雷诺方程和标准k-ε湍流模型,模拟计算不同形状和结构尺寸的喷丝孔外罩对碳纤维出丝槽流系统流域中湍流的影响.利用不同长高比二维矩形钝体模型计算高雷诺数下绕流的情形,对比不同尺寸下尾流内湍流的大小,分析得到较优的结构参数.结果表明,外罩长高比是影响湍流大小的主要因素;长高比增大有利于减弱尾流内的湍流;当长高比接近4时,喷丝口处湍流较小,但长高比再增大,湍流减小程度不明显.     

SHG-Ⅱ-Z型除尘脱硫装置三维三相流场的数值模拟

利用FLUENT软件对SHG-Ⅱ-Z型除尘脱硫装置内的三维三相流场进行数值模拟,采用RNG k-ε湍流模型及混合模型作为计算模型,选择SIMPLE算法进行计算。根据计算结果分析了设备内气、液、固三相的体积分数和速度矢量等参数的分布,并对不同横截面的湍动耗散率和湍流动能进行了分析,分析结果表明该设备具有较好的除尘脱硫效果。模拟计算结果对设备的优化设计和实际运转有一定的指导作用。     

原位脱碳流化床煤气化反应器的数值模拟

为了减少温室效应,对于煤气化过程中CO_2的减排与零排放技术的研究成为必要。本文建立了全面的煤气化反应器的数值模型,对以CaO作为吸收剂的原位脱碳的流化床煤气化反应器进行了数值模拟。模拟以简化结构的二维反应器为求解域,应用标准k-ε模型描述气相湍动,EDC模型描述反应器中湍流与反应的偶合,EDC模型将详细的化学动力学融入到湍流混合中。讨论了反应器中温度、气速、压力及气体产物的分布。     

发动机舱对流换热CFD模拟的基础问题

为合理选择进出口尺寸及布置发动机舱各部件,进一步降低舱内最高温度,对比标准k-ε模型、RNG k-ε模型和可实现的k-ε模型等3种湍流模型及2种壁面函数对温度场模拟的精度.由模拟与实验对比可知：可实现的k-ε湍流模型、增强型壁面函数更适合模拟热流场.利用CFD计算不同进出口尺寸及换热器与发动机间距对舱内温度场的影响,结果表明进出口尺寸对舱内最高温度影响较大.     

涡扇发动机特性仿真中的Zooming技术研究

为解决某型涡扇发动机尾喷管改型中的流量匹配问题,利用iSIGHT软件平台集成零维发动机性能仿真程序和三维混合室和尾喷管的流场计算程序,运用零维和三维相结合的数值缩放(Zooming)技术,实现了混合室和尾喷管型面以及进出口面积的自动修正,解决了尾喷管和发动机在设计点与非设计点流量匹配的问题.准确的反映了混合室和尾喷管三维流动效应对流量系数、推力系数以及发动机工作点的影响.该方法可为实现涡扇发动机其它部件的Zooming技术提供有意义的参考.     

CFD simulation and optimization of ICEs exhaust heat recovery using different coolants and fin dimensions in heat exchanger

In this paper, finned type heat exchangers with different fin dimensions in the exhaust of a gasoline engine are modeled numerically for improving the exhaust energy recovery. RNG k-ε viscous model is used and the results are compared with available experimental data presented by Lee and Bae (Int J Therm Sci 47:468–478, 2008) where a good agreement is observed. Also, the effect of fin numbers, fin length and three water-based nanofluid coolants (TiO₂, Fe₂O₃ and CuO) on the heat recovery efficiency are investigated in different engine loads. As a main outcome, results show that increasing the fin numbers and using TiO₂-water as cold fluid are the most effective methods for heat recover. Furthermore, an optimization analysis is performed to find the best fins dimensions using response surface methodology.     

Identifying Noncooperative Subjects at a Distance Using Face Images and Inferred Three-Dimensional Face Models

We present an approach to identify noncooperative individuals at a distance from a sequence of images, using 3-D face models. Most biometric features (such as fingerprints, hand shape, iris, or retinal scans) require cooperative subjects in close proximity to the biometric system. We process images acquired with an ultrahigh-resolution video camera, infer the location of the subjects' head, use this information to crop the region of interest, build a 3-D face model, and use this 3-D model to perform biometric identification. To build the 3-D model, we use an image sequence, as natural head and body motion provides enough viewpoint variation to perform stereomotion for 3-D face reconstruction. We have conducted experiments on a 2-D and 3-D databases collected in our laboratory. First, we found that metric 3-D face models can be used for recognition by using simple scaling method even though there is no exact scale in the 3-D reconstruction. Second, experiments using a commercial 3-D matching engine suggest the feasibility of the proposed approach for recognition against 3-D galleries at a distance (3, 6, and 9 m). Moreover, we show initial 3-D face modeling results on various factors including head motion, outdoor lighting conditions, and glasses. The evaluation results suggest that video data alone, at a distance of 3 to 9 meters, can provide a 3-D face shape that supports successful face recognition. The performance of 3-D–3-D recognition with the currently generated models does not quite match that of 2-D–2-D. We attribute this to the quality of the inferred models, and this suggests a clear path for future research.      

Three-dimensional effects in multi-element high lift computations

In an effort to discover the causes for disagreement between previous two-dimensional (2-D) computations and nominally 2-D experiment for flow over the three-element McDonnell Douglas 30P-30N airfoil configuration at high lift, a combined experimental/CFD investigation is described. The experiment explores several different side-wall boundary layer control venting patterns, documents venting mass flow rates, and looks at corner surface flow patterns. The experimental angle of attack at maximum lift is found to be sensitive to the side-wall venting pattern: a particular pattern increases the angle of attack at maximum lift by at least 2°. A significant amount of spanwise pressure variation is present at angles of attack near maximum lift. A CFD study using three-dimensional (3-D) structured-grid computations, which includes the modeling of side-wall venting, is employed to investigate 3-D effects on the flow. Side-wall suction strength is found to affect the angle at which maximum lift is predicted. Maximum lift in the CFD is shown to be limited by the growth of an off-body corner flow vortex and consequent increase in spanwise pressure variation and decrease in circulation. The 3-D computations with and without wall venting predict similar trends to experiment at low angles of attack, but either stall too early or else overpredict lift levels near maximum lift by as much as 5%. Unstructured-grid computations demonstrate that mounting brackets lower the lift levels near maximum lift conditions.     

Numerical investigation of cyclic variations in gasoline engines using a hybrid URANS/LES modeling approach

Cycle to cycle variations are an important aspect in the development and optimization process of internal combustion engines. In this study the feasibility of using a detached eddy simulation (DES) SST model, which is a hybrid URANS/LES model, to predict cycle to cycle variations is investigated. In the near wall region or in regions where the grid resolution is not sufficiently fine to resolve smaller structures, the two-equation RANS shear-stress transport (SST) model is used. In the other regions with higher grid resolution an LES model is applied. First, the numerical requirements associated with the hybrid URANS/LES and the employed solver are studied in detail. The numerical dissipation of the spatial scheme and the choice of the temporal scheme including the step size are evaluated. In addition, the accuracy of the solver for moving meshes, which are required for engine calculations, is assessed. The modeling constant linking the grid size to the DES filter length scale is determined by calculating a decaying homogeneous isotropic turbulence test case for different grid resolutions. The final applications of the model are two different engine cases with increasing complexity. The first case is the statistically stationary flow through an engine intake port. The time resolved flow structure predicted by the DES SST model is analyzed and the resulting time-averaged velocity fields are compared to experimental data at different locations. The second application is a motored multi-cycle simulation of a series production engine. The instantaneous flow development during the intake and compression stroke of one single cycle is studied and the ensemble-averaged and the instantaneous velocity fields as well as the resolved velocity fluctuations are compared to optical measurements. Special emphasis is placed on the cyclic differences of the velocity fluctuations at the time of ignition in the vicinity of the spark plug and the expected influence on the combustion process.     

Transient heat transfer and gas flow in a MEMS-based thruster

Time-dependent performance of a high-temperature MEMS-based thruster is studied in detail by a coupled thermal-fluid analysis. The material thermal response governed by the transient heat conduction equation is obtained using the finite element method. The low-Reynolds number gas flow in the microthruster is modeled by the direct simulation Monte Carlo (DSMC) approach. The temporal variation of the thruster material temperature and gas flowfields are obtained as well as the thruster operational time limits for thermally insulated and convectively cooled thrusters. The predicted thrust and mass discharge coefficient of both two-dimensional (2-D) and three-dimensional (3-D) micronozzles decreases in time as the viscous losses increase for higher wall temperatures.     

An Efficient Multibody Dynamics Model for Internal Combustion Engine Systems

The equations of motion for the major components in an internalcombustion engine are developed herein using a recursive formulation.These components include the (rigid) engine block, pistons, connectingrods, (flexible) crankshaft, balance shafts, main bearings, and enginemounts. Relative coordinates are employed that automatically satisfy allconstraints and therefore lead to the minimum set of ordinarydifferential equations of motion. The derivation of the equations ofmotion is automated through the use of computer algebra as the precursorto automatically generating the computational (C or Fortran) subroutinesfor numerical integration. The entire automated procedure forms thebasis for an engine modeling template that may be used to supportthe up-front design of engines for noise and vibration targets.This procedure is demonstrated on an example engine under free(idealized) and firing conditions and the predicted engine responses arecompared with results from an ADAMS model. Results obtained by usingdifferent bearing models, including linear, nonlinear, and hydrodynamicbearing models, are discussed in detail.     

Robustness assessment and adaptive FDI for car engine

A new on-line fault detection and isolation （FDI） scheme proposed for engines using an adaptive neural network classifier is evaluated for a wide range of operational modes to check the robustness of the scheme in this paper. The neural classifier is adaptive to cope with the significant parameter uncertainty, disturbances, and environment changes. The developed scheme is capable of diagnosing faults in on-line mode and the FDI for the closed-loop system with can be directly implemented in an on-board crankshaft speed feedback is investigated by diagnosis system （hardware）. The robustness of testing it for a wide range of operational modes including robustness against fixed and sinusoidal throttle angle inputs, change in load, change in an engine parameter, and all these changes occurring at the same time. The evaluations are performed using a mean value engine model （MVEM）, which is a widely used benchmark model for engine control system and FDI system design. The simulation results confirm the robustness of the proposed method for various uncertainties and disturbances.