弱剪切平面湍流射流的直接数值模拟

采用直接数值模拟方法研究了弱剪切平面湍流射流的涡量场。其中“弱剪切”是指射流出口速度与伴随流速度的大小在同一数量级(文中为2：1)。计算结果精确捕捉到了大涡卷起、两涡配对及特殊的三涡合并现象。纵向速度U的平均分布与实验值符合得很好。由于涡量场关于射流轴线的完全对称性，雷诺应力的分布较为特殊。图6参8     

矩形管湍流冲击射流流动与传热的数值研究

采用SIMPLE算法和RNG k-ε湍流模型,通过求解三维N-S方程和能量方程,对雷诺数为10000和冲击高度为4倍喷管水力直径的矩形管湍流冲击射流进行了数值模拟。结果发现在冲击面附近的射流横截面上,伴随着两个反向旋转涡对的出现,形成了主流速度的两个偏心峰值。分析认为双偏心速度峰值的形成是由冲击面产生的涡量向上游截面扩散而引起的。温度场和冲击面局部№数分布的研究结果表明：射流的传热特性受流动结构的控制,采用矩形管湍流射流可以获得较大的冲击区和较均匀的冷却效果。     

转炉氧枪超音速射流特性的数值模拟研究

运用Fluent模拟计算软件,并与工业实验相结合,对150 t提钒转炉用氧枪所产生的超音速氧气射流特性进行综合研究.通过对数值模拟与实验数据的分析,研究了马赫数、设计流量对氧枪射流长度、径向速度、动压分布及湍动能分布的影响,以此优选氧枪的设计参数,并将该优选氧枪应用于实际提钒转炉的冶炼过程中.工业实验结果表明:马赫数2...     

湍流非预混射流火焰倾斜冲击壁面的直接数值模拟研究

采用直接数值模拟方法,选取17组分、73步简化的甲烷化学反应机理,对三维湍流平面甲烷射流火焰倾斜冲击壁面进行了研究.分析了相同湍流强度、不同Damk?hler数的两个算例.两个算例出现了不同程度的熄火,算例B的熄火现象比算例A更明显.同时,观察到当量混合分数等值面的凸起结构与火焰熄火现象存在一定关联.定量分析了火焰面平均曲率与熄火的相关性,发现在剪切流动中熄火区域的平均曲率大于燃烧区域的平均曲率;在壁面附近的熄火区域曲率的大小与壁面熄火模式相关．     

湍流分层射流火焰的直接数值模拟

使用直接数值模拟和详细化学反应机理研究了三维甲烷/空气湍流分层射流火焰．火焰呈V形,由稳燃棒进行稳燃．分析了不同流向位置处的火焰分层现象,在上游出现了前支撑火焰,下游出现了后支撑火焰．下游火焰的燃烧强度大于上游火焰的．通过对火焰结构的进一步分析,发现前支撑燃烧向后支撑燃烧的转变与H2基团在产物侧的积累有关．同时,后支撑火焰中出现了H2基团的优先输运现象,这增强了预热区的化学反应强度,从而增强了燃烧强度．对火焰位移速度与切向应变率的联合分布的分析表明,较小的切向应变率对应较大的位移速度．与下游相比,上游负火焰位移速度的概率较大,这是由较大的正切向应变率造成的．     

扇形喷嘴射流行为的数值模拟研究

以高压扇形喷嘴射流行为为研究对象,建立了描述扇形喷嘴射流行为的三维数学模型,采用数值模拟方法对不同入口压力、收缩角和V型切槽半角条件下扇形喷嘴射流特性进行研究.研究结果表明:当扇形喷嘴几何参数不变时,随着入口压力增加,射流冲击核心区域内水的流速显著增加,射流冲击宽度变化不显著;随着V型切槽半角的增加,射流冲击核心区域内...     

带有射流控制的新型扑翼获能特性数值模拟研究

为了研究扑翼的获能机理,以NACA0012为基准翼型提出了一种添加射流控制的扑翼获能装置,并基于动网格技术进行了数值计算,研究了当雷诺数Re=13 800时射流位置、射流方式等关键参数对扑翼获能效率的影响规律。结果表明,与原型扑翼相比,添加射流控制能够有效提升扑翼的获能效率。另外,采用射流速度遵循正弦规律的新型射流控制方式不仅能增强扑翼运行结构的稳定性,而且能在一定程度上提升扑翼的获能效率。     

入流滑移条件对两相射流特性影响的大涡模拟研究

研究了入流滑移条件对空间发展的气粒两相平面湍射流的非定常流动特性的影响。以Re数13000的平面不可压缩湍射流流动为例,气相场用Euler方法求解,通过大涡模拟(large-eddy　simulation,LES),直接求解大尺度涡运动的Navier-Stokes方程,小尺度涡用标准Smagorinsky亚格子模式模拟。颗粒相的运动用Lagrangian方法直接求解。在不同入流滑移条件下(U     

入流条件对同轴射流旋流燃烧室内湍流流动模拟的影响

应用一种新的代数Reynolds应力模型对同轴射流旋流燃烧室内两股射流为同向旋转和反向旋转条件下的湍流旋流流动进行了数值模拟。为得到合理的流场分布结果，研究了入流条件对同轴射流旋流燃烧室内湍流流动模拟结果的影响。计算中对旋流燃烧室进口处两股旋转射流的轴向与切向速度采用了均匀分布和实验测量分布两种方式来给定。将两种进口速度分布条件下得到的燃烧室内气体轴向与切向速度分布计算结果与实验数据进行了比较。     

燃气多射流切圆预混流动特性的数值模拟

利用FLUENT软件对所设计的多射流切圆预混多孔介质燃烧器进行流场模拟,主要研究流道结构、预混室的几何结构、空气和燃气速度及压力等因素对空气系数的影响,并重点分析速度、压力流场与湍流动能及湍流动能耗散率的变化分布,确定合理的预混室参数。     

Turbulent flow in the near field of a round impinging jet

This paper reports on detailed measurements of the turbulent flow in the stagnation region of a single impinging jet issuing from a round pipe with diameter D and a length of 76D. The distance between the pipe exit and the flat impingement plate is 2D, and the Reynolds number (based on the bulk velocity and pipe diameter) is 2.3 × 10⁴. Mean velocity components and Reynolds stresses were determined by using a two-component LDA. A modified one-component LDA was used to perform near-wall measurements with minimum wall distances of approximately 40 μm. PIV measurements were taken in a small field of view (approximately 4 × 5 mm²) to study instantaneous reversals in the near wall region.     

两相圆孔射流颗粒喷入方法关键问题的直接数字模拟研究

对两相圆孔射流颗粒喷入方法的关键问题进行了直接数值模拟研究.气相采用可压缩的N-S方程直接求解,颗粒相采用拉格朗日方法( Lagrangian)跟踪实际颗粒的运动.主要探讨了空间发展的两相圆孔射流在采用直接数值模拟算法的前提下,颗粒喷入的方法以及喷入方法对两相圆孔射流中不同直径颗粒的扩散特点.在拉格朗日坐标系下实际跟踪了每一个颗粒运动的轨迹,通过反复的数值试验研究发现,颗粒喷入方法是可信的,得到数值模拟结果成功地再现了不同直径颗粒扩散特性.     

Coherent structures in a fully developed stage of a non‐isothermal round jet

Direct numerical simulation (DNS) was performed for a non‐isothermal air jet with a Reynolds number of 1200 in order to reveal coherent structures of the developed jet. A fourth‐order central finite difference was applied to the simulation. An effort was also made to enable experimental visualization (dye mixing and PTV) to support the validity of the instantaneous structures by DNS. Computational results for two types of inlet profiles suggested that nozzle conditions scarcely affect the turbulence statistics and the coherent structures in a jet‐established stage. Two‐point correlations of velocity and temperature show that similar distributions denoting the temperature can be used as an indicator of a vortex. A conceptual model of a hairpin‐shaped vortex was proposed and validated by two‐point correlations and PDF analysis for vortex alignment. The hairpin‐shaped vortex stands with legs inclined downstream. The inclination angle and the tilting angle between the two legs are ?45° and 40°, respectively. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 342–356, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20014     

Large eddy simulation of flow and scalar transport in a round jet

Large eddy simulation (LES) was performed for a spatially developing round jet and its scalar transport at four steps of Reynolds number set between 1200 and 1,000,000. A simulated domain, which extends 30 times the nozzle diameter, includes initial, transitional, and established stage of jet. A modified version of convection outflow condition was proposed in order to diminish the effect of a downstream boundary. Tested were two kinds of subgrid scale (SOS) models: a Smagorinsky model (SM) and a dynamic Smagorinsky model (DSM). In the former model, parameters are kept at empirically deduced constants, while in the latter, they are calculated using different levels of space filtering. Data analysis based on the decay law of jet clearly presented the performance of SGS models. Simulated results by SM and DSM compared favorably with existing measurements of jet and its scalar transport. However, the quantitative accuracy of DSM was better than that of SM at a transitional stage of flow field. Computed parameters by DSM, coefficient for SGS stresses, C_R and SGS eddy diffusivity ratio, Γ_SGS, were not far from empirical constants of SM. Optimization of the model coefficient was suggested in DSM so that coefficient C_R was nearly equal in the established stage of jet but it was reduced in low turbulence close to the jet nozzle. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 175–188, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20001     

DNS investigation on flame structure and scalar dissipation of a supersonic lifted hydrogen jet flame in heated coflow

Direct numerical simulation (DNS) of a three-dimensional spatially-developing supersonic lifted hydrogen jet flame has been conducted in this paper. The scalar structure of the lifted flame is investigated through instantaneous images and conditional means of combustion statistics. And then the scalar dissipation rate and its implications on the flamelet-based combustion modeling are analyzed in detail. It can be found that most of the heat release occurs in the subsonic region. However, distributed reaction pockets exist in the sonic mixing layer due to the rolled up vortices. The magnitude of conditional compression or expansion rate of the fluid presents comparable to the corresponding heat release rate, and takes a great influence on the flame temperature in the high speed reacting flow. The probability density functions of mean conditional and unconditional scalar dissipation rate prove to qualitatively agree with the presumed log-normal distribution, while a little skewed to the higher scalar dissipation rate in the sonic mixing layer. The conditional mean scalar dissipation rate presents to be radial dependent at the flame base, especially in the fuel lean mixture. The DNS results show good agreement with the trends of the flamelet calculations; however, the amplitudes of temperature are far lower than the corresponding flamelet statistics due to finite rate reaction and expansion of the high speed reacting flow.     

Numerical investigation on effectiveness of flow separation control in two-dimensional high-load compressor cascade by synthetic jet

The effectiveness of flow separation control in two-dimensional high load cascade by synthetic jet is investigated through numerical simulation of the effect of excitation frequency and amplitude together with the adaptability of synthetic jet to off-design conditions. Test results indicate that synthetic jet can be used to effectively control the large-scale two-dimensional flow separation in compressor cascade. Preferable results can be obtained when excitation frequency is close to or times of the characteristic frequency of original flow field. Excitation amplitude has a more important effect on the effectiveness of flow separation control, and the increase in excitation amplitude can bring about a dramatic decrease in the loss of total pressure. Synthetic jet has also a very good adaptability to off-design conditions. It can therefore be concluded that the incidence sensitivity of compressor cascade can be effectively reduced by synthetic jet.     

Numerical simulation on the behavior of a liquid jet into an air flow

A numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001     

LES of a premixed jet flame DNS using a strained flamelet model

Turbulent premixed flames in the thin and broken reaction zones regimes are difficult to model with Large Eddy Simulation (LES) because turbulence strongly perturbs subfilter scale flame structures. This study addresses the difficulty by proposing a strained flamelet model for LES of high Karlovitz number flames. The proposed model extends a previously developed premixed flamelet approach to account for turbulence’s perturbation of subfilter premixed flame structures. The model describes combustion processes by solving strained premixed flamelets, tabulating the results in terms of a progress variable and a hydrogen radical, and invoking a presumed PDF framework to account for subfilter physics. The model is validated using two dimensional laminar flame studies, and is then tested by performing an LES of a premixed slot-jet direct numerical simulation (DNS). In the premixed regime diagram this slot-jet is found at the edge of the broken reaction zones regime. Comparisons of the DNS, the strained flamelet model LES, and an unstrained flamelet model LES confirm that turbulence perturbs flame structure to leading order effect, and that the use of an unstrained flamelet LES model under-predicts flame height. It is shown that the strained flamelet model captures the physics characterizing interactions of mixing and chemistry in highly turbulent regimes.     

Study on the Characteristics of Supersonic Coanda Jet

INTRoDUCTI0NTheCoandaeffectthatisanimportamconsequence0fthepressurevariati0nperpendiculart0curvdStreanilines,isthetendencyofafiuldjettoattaChitSelftoaconvexsolidb0dyoranadacentsurface.Inrec6Dtyears,theusefulnessoftheCoandaeffectisencowteredinawiderangeofaPplicationfromfiuldicdevicetoaircraftwingSandfiaPdevices[1~22l.Horiietal.I`-s]shOWdthatafocusedandhiglilystablesPiralfiowwasobtainedusinganozzlewithanannularslitconnectedtoaconicalcylinder.Toimprovthrustvectoring,Bevilaquaetal.[16jin…     

喷射火环境下液化气储罐热响应行为数值模拟

应用CFD软件Fluent6.3对液化气（liquefied petroleum gas,LPG）储罐在火灾条件下的热响应过程进行了三维数值模拟。研究了喷射火作用下LPG储罐罐壁温度、内部介质温度和压力响应的特点,分析了液相介质充装率和储罐壁厚对储罐热响应的影响。结果表明,液相介质充装率越高,储罐失效时间越短,并且当充装率为60%~85%时储罐的失效时间下降更加明显;储罐壁厚越厚,火焰作用下升压越慢,当壁厚大于14mm时,壁厚对储罐升压的影响明显变小。据此,可选择合适的充装率和合理的壁厚以减缓储罐的升压速度,为预防和控制液化气储罐事故的发生争取时间。