用求解概率密度函数输运方程的方法模拟湍流自由射流

用求解概率密度函数输运方程的方法模拟湍流自由射流周向阳，郑楚光，马毓义（华中理工大学煤燃烧国家重点实验室武汉４３００７４）关键词概率密度函数；湍流；自由射流１前言和通常的湍流统计矩模型（如ｋ－ε模型或Ｒｅｙｎｏｌｄｓ应力模型等）相比，用求解速度和标量...     

湍流空气自由射流引射特性的比较研究

对商用CFD软件中的四种湍流模型给出的湍流空气自由射流引射特性计算结果进行了比较,并将采用四种湍流模型计算获得的射流引射量计算数据与文献报道的采用多孔壁技术获得的射流引射量实验数据进行了对比,结果表明：在四种湍流模型中,标准K—ε湍流模型给出的湍流空气自由射流引射规律与实验数据较好符合。本文还选用标准K—ε湍流模型对欠...     

湍流射流与扩散火焰大涡拟序结构的波动特性研究

１前言湍流射流扩散燃烧方式提供了射流火焰与涡团相互作用的最基本形式,对研究在湍流射流剪切边界层内的反应物的卷吸混合、热量及动量的输运及湍流射流结构方面具有其特殊的意义。Ｋａｔｔａ［１］利用浮力与单步反应机理模型对Ｎ２－Ｈ２射流扩散火焰进行了直接数值模...     

边界条件对径向湍流射流的影响的计算研究

本文对径向湍流自由射流作了计算，研究了边界条件的不同取法对计算结果的影响，与文献发表的计算结果和实验结果作了比较，再次证明上游湍流结构的边界条件对射流的渐近扩张速率及雷诺应力等流场参数有明显的影响．     

气膜冷却计算中湍流黏性系数的修正

燃气轮机高温叶片气膜冷却中的复杂涡系结构使得流动传热很难被准确预测.本文基于平板气膜冷却数值和实验研究结果,指出雷诺平均算法中常用的湍流模型在射流侧向输运和二次涡的捕捉上具有相当的局限性.文中对湍流黏性系数提出了各向异性对数率涡黏模型(ALEV模型)修正,基于ALEV模型修正后的湍流模型增强了射流的侧向输运,减弱了二次...     

径向湍流旋转射流的计算研究

本文对径向湍流旋转射流作了计算研究,考察了边界条件的不同取法对计算结果的影响,并与过去国外学者发表的实验结果作了比较讨论,再次证明边界条件的适当改变,对射流的渐近扩张速率有明显的影响,也有助于流场其它参数（如雷诺应力,脉动速度）预测的改善。同时我们也看到:（1）由于实验数据的误差;（2）也由于流场上游的边界条件不是实验测量的,除了湍流结构系数Y12F是作者凭经验估计的以外都是用的文献[2]的计算结果; （3）由于平均流动定常的假定;湍流应力的预测,特别是左边半幅和uw,还不理想。     

受限湍流射流扩散火焰的PDF模拟

采用k-ε双方程模型和概率密度函数(PDF)相结合的办法,研究受限条件下的湍流射流扩散火焰,着重考虑受限条件下固体壁面、压力梯度等因素对速度场和标量场求解的影响,并在此基础上对两个不同尺寸的受限湍流燃烧场进行计算,分别研究了受限湍流射流扩散火焰的流场结构、火焰结构和火焰形状.最后给出结果,定性分析,并得出结论.     

双时间尺度湍流模型的应用

双时间尺度湍流模型的应用蔡晓丹，陈义良（中国科技大学工程热物理系合肥２３００２６）关键词：双时间尺度，湍流模型一、引言流动的分离现象是自然界最常见的现象之一。在工程应用中，对流动分离的控制往往是我们关心的焦点。二维后台阶流动（图正），是一种典型的有回...     

三维自由射流缩流及扩散的数值研究

由于非定常多相流特性,大气下水自由射流的水力性能相当复杂.本文依据弯管二次流机理确定的最优湍流模型,以六喷嘴冲击式水轮机最术端的喷嘴射流作为研究对象,进行了三维非定常自由射流的数值模拟解析.定量分析了三维自由射流在不同空间方向沿程变化的两相流流态.能量构造及射流形状,为水斗提供了真实的入流条件,确认了最未端喷嘴射流水力效率较差的原因:由于最末端喷管的急剧弯道使得射流产生了大幅度的膨胀扩散.     

受限空间狭缝射流传热特性数值模拟研究

狭缝冲击射流是一种高效的换热形式,传统湍流模型无法准确预测其换热规律。采用常用的k-ε系列湍流模型和k-ω系列湍流模型,结合Kato-Launder模型、剪切流修正模型、间歇转捩模型和横流效应修正模型,对受限空间狭缝射流开展了数值模拟研究。结果表明,标准k-ω湍流模型结合Kato-Launder模型和剪切流修正模型可在两种典型冲击距离下都成功预测壁面传热特性,间歇转捩模型对SST k-ω剪切应力输运湍流模型预测能力的改善作用极其有限,而Kato-Launder模型可以极大改善SST k-ω湍流模型在较小冲击距离下的传热预测能力,但在较大冲击距离下,Kato-Launder模型会预测出更为显著的努塞尔数伪第二峰值。     

有旋湍流场中湍流模型应用的研究

本文通过对三种双时间尺度湍流模型的理论分析，选择出最合理的模型，并在其基础上引入非线性Reynolds应力─应变关系式及梯度Richardson数修正，对有旋湍流场进行计算，其结果表明，双时间尺度模型能较好地预测出复杂湍流场中平均物理量的分布，尤其对回流区大小和强度的预测较常规k-ε模型结果有很大改进。因此，本文将双时间尺度模型应用于旋流燃烧器中气体颗粒两相流动的计算。     

PDF calculations of piloted premixed jet flames

A series of piloted premixed jet flames with strong finite-rate chemistry effects is studied using the joint velocity-turbulence frequency-composition PDF method. The numerical accuracy of the calculations is demonstrated, and the calculations are compared to experimental data. It is found that all calculations show good agreement with the measurements of mean and rms mixture fraction fields, while the reaction progress is overpredicted to varying degrees depending on the jet velocity. In the calculations of the flame with the lowest jet velocity, the species and temperature show reasonable agreement with the measurements, with the exception of a small region near the centerline where products and temperature are overpredicted and fuel and oxidizer are underpredicted. In the calculations of the flame with the highest jet velocity, however, the overprediction of products and temperature and underprediction of fuel and oxidizer is far more severe. An extensive set of sensitivity studies on inlet boundary conditions, turbulence model constants, mixing models and constants, radiation treatment, and chemical mechanisms is conducted to show that any parameter variation offers little improvement from the base case. To shed light on these discrepancies, diagnostic calculations are performed in which the chemical reactions are artificially slowed. These diagnostic calculations serve to validate the experimental data and to quantify the amount by which the base case calculations overpredict reaction progress. Improved calculations of this flame are achieved only through artificially slowing down the chemical reaction by a factor of about 10. The mixing model behavior in this combustion regime is identified as a likely cause for the observed discrepancy in reaction progress.     

炉顶平焰炉供热负荷变化对流场的影响

１引言平焰燃烧器自六十年代问世以来,已广泛使用在各种加热炉上。它具有较多的优点,诸如温度场均匀,压力场均匀,可显著降低炉膛高度等。但平焰燃烧器的供热负荷与加热炉的炉型参数的匹配关系,仍是许多设计人员感到棘手的问题之一［１］,有必要从理论上对其进行研究...     

Mean and fluctuating velocity fields of a diamond turbulent jet

The present paper reports the first investigation on a turbulent jet issuing from a diamond orifice(hereafter termed a "diamond jet") with an aspect ratio of 1.7.Velocity measurements were conducted in the transitional region,and the exit Reynolds number of the jet was 50000.For comparison,a round jet with identical normalized boundary conditions was also measured.It is shown that the diamond jet decays and spreads faster than the round jet does over the measured flow region.The axis-switching phenomenon is observed in the diamond jet.Although both jets display primary coherent structures in the near field,these structures are found to break down more rapidly in the diamond jet,due to the higher three-dimensionality of the flow.Moreover,the streamwise components of the Reynolds normal stress and all the shear stresses reach their maxima around the location of the maximal mean shear while the maxima of the lateral components of the Reynolds normal stresses occur around the centreline of the jet.     

Numerical study of the effect of turbulence on rate of reactions in the MILD combustion regime

In this paper, the importance of fluctuations in flow field parameters is studied under MILD combustion conditions. In this way, a turbulent non-premixed CH₄+H₂ jet flame issuing into a hot and deficient co-flow air is modeled using the RANS Axisymmetric equations. The modeling is carried out using the EDC model to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H₂/methane jet flame. Results illustrate that although the fluctuations in temperature field are small and the reaction zone volume are large in the MILD regime, the fluctuations in temperature and species concentrations are still effective on the flow field. Also, inappropriate dealing with the turbulence effect on chemistry leads to errors in prediction of temperature up to 15% in the present flame. By decreasing of O₂ concentration of hot co-flow air, the effect of fluctuations in flow field parameters on flame characteristics are still significant and its effect on species reaction rates does not decrease. On the other hand, although decreasing of jet inlet Reynolds number at constant inlet turbulence intensity addresses to smaller fluctuations in flow filed, it does not lead to lower the effect of turbulence on species distribution and temperature field under MILD combustion conditions.     

高斯-谢尔模光束在大气湍流中传输的相干特性研究

文章分析了高斯-谢尔光束在大气湍流中传输时相干长度的变化, 并与真空传输做比较, 真空传输相干长度的变化只与光源参数有关, 大气湍流中传输相干长度的变化受光源参数和湍流的共同影响. 真空传输光束扩展造成相干长度增大; 大气湍流中, 传输距离较短时, 相干长度由于光源扩展而增加, 当传输距离较大时, 湍流效应增强引起相干长度下降. 因此, 单纯从相干长度方面分析大气湍流带来的影响不够完备. 为排除光源扩展影响, 利用相干长度与光斑尺度的比值进行分析, 发现大气湍流会造成比值的下降. 在数值仿真的基础上对上述结果给出了解释. 关键词： 部分相干 大气湍流 高斯-谢尔模 光束扩展     

LES based investigation of autoignition in turbulent co-flow configurations

The impact of turbulence on the autoignition of a diluted hydrogen jet in a hot co-flow of air is studied numerically. The LES combustion model used is successfully validated against experimental measurements and 3D DNS. Parametric studies are then carried out by separately varying turbulent intensity and integral length scale in the co-flow, while keeping all other boundary conditions unchanged. It is found that the impact of turbulence on the location of autoignition is non-trivial. For weak to mild turbulence, with a turbulent time scale larger than the minimum ignition delay time, autoignition is facilitated by increased turbulence. This is due to enhanced mixing between fuel and air, creating larger most reactive mixture fraction regions. On the other hand, for turbulent time scales smaller than the ignition delay time, the increased scalar dissipation rate dominates over the effect of increased most reactive mixture fraction regions, which leads to a rise in the autoignition length. Turbulence–chemistry interaction mechanisms are analysed in order to explain these observations.