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排序方式: 共有179条查询结果,搜索用时 187 毫秒
71.
A joint probability distribution function of a conservative scalar (mixture fraction) and its gradient is predicted numerically.
Statistical moments of this function are compared to their approximations, direct numerical simulation data, and also to the
results obtained by simplified models for a conditional rate of scalar dissipation, the surface density function, and the
one-point PDF of scalar fluctuation under homogeneous isotropic turbulence. The results allow to evaluate the performance
of existing statistical micromixing models. 相似文献
72.
介绍了利用Office组件Microsoft Office Document Imaging实现图像文件或者PDF文件的文字识别,使不能编辑的图像文字转换为可以编辑的文字的方法。 相似文献
73.
74.
Turbulence modulation model for gas–particle flow based on probability density function approach
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The paper focuses on the turbulence modulation problem in gas–particle flow with the use of probability density function(PDF) approach. By means of the PDF method, a general statistical moment turbulence modulation model without considering the trajectory difference between two phases is derived from the Navier–Stokes equations. A new turbulence production term induced by the dispersed-phase is analyzed and considered. Furthermore, the trajectory difference between two media is taken into account. Subsequently, a new k–ε turbulence modulation model in dilute particle-laden flow is successfully set up. Then, the changes to several terms, including the turbulence production, dissipation, and diffusion terms, are well described consequently. The promoted model provides a more probable explanation for the modification of particles on the turbulence. Finally, we applied the model to simulate a gas–particle turbulence flow case in a wall jet, and found that the simulation results agree well with the experimental data. 相似文献
75.
分别采用标量联合的概率密度函数方法、稳态火焰面模型、Euler非稳态火焰面模型和基于有限体积/Monte Carlo混合算法的完备PDF模型对钝体驻定的Sydney湍流扩散火焰HM1进行数值模拟,以比较不同燃烧模型的性能,并比较标量联合的概率密度函数方法和Euler非稳态火焰面模型对氮氧化物排放预测的差异.计算结果和实验数据的比较表明,采用概率密度函数方法计算化学反应可以得到更好的结果但计算量较大,而用火焰面模型求解计算量较小,在接近完全燃烧的情形下,其计算结果比较合理. 相似文献
76.
The motivation of this study is to investigate the turbulence–chemistry interactions by using probability density function
(PDF) method. A consistent hybrid Reynolds Averaged Navier–Stokes (RANS)/PDF method is used to simulate the turbulent non-reacting
and reacting flows. The joint fluctuating velocity–frequency–composition PDF equation coupled with the Reynolds averaged density,
momentum and energy equations are solved on unstructured meshes by the Lagrangian Monte Carlo (MC) method combined with the
finite volume (FV) method. The simulation of the axisymmetric bluff body stabilized non-reacting flow fields is presented
in this paper. The calculated length of the recirculation zone is in good agreement with the experimental data. Moreover,
the significant change of the flow pattern with the increase of the jet-to-coflow momentum flux ratio is well predicted. In
addition, comparisons are made between the joint PDF model and two different Reynolds stress models.
The project supported by the National Natural Science Foundation of China (50506028), and Action Scheme for Invigorating Education
Towards the twenty-first century. 相似文献
77.
78.
对二维条码PDF417的基本概念、用途、优势作了系统的介绍,着重分析了PDF417条码的具体译码过程,并给出该条码作为多进制码,进行R-S纠错译码时所要注意的有关域运算及模运算。 相似文献
79.
PDF417纠错码原理及实现 总被引:2,自引:0,他引:2
为了促进PDF417这种高效率低成本的条形码在中国的深入研究和推广,介绍了Reed-Solomon纠错码原理和它在PDF417二维条形码中的应用方法.推导了在迦罗华域GF(929)内编译码方法,并通过实例具体说明.提出了一种适用于PDF417纠错编码和译码的查表方法,可以简单确定任意码字在GF(929)内所对应的本原元的幂次.运用该方法可以快速而准确地计算出纠错码生成多项式的系数列以及差错伴随式. 相似文献
80.
Simulations of sooting turbulent jet flames using a hybrid flamelet/stochastic Eulerian field method
The stochastic Eulerian field method is applied to simulate 12 turbulent C1?C3 hydrocarbon jet diffusion flames covering a wide range of Reynolds numbers and fuel sooting propensities. The joint scalar probability density function (PDF) is a function of the mixture fraction, enthalpy defect, scalar dissipation rate and representative soot properties. Soot production is modelled by a semi-empirical acetylene/benzene-based soot model. Spectral gas and soot radiation is modelled using a wide-band correlated-k model. Emission turbulent radiation interactions (TRIs) are taken into account by means of the PDF method, whereas absorption TRIs are modelled using the optically thin fluctuation approximation. Model predictions are found to be in reasonable agreement with experimental data in terms of flame structure, soot quantities and radiative loss. Mean soot volume fractions are predicted within a factor of two of the experiments whereas radiant fractions and peaks of wall radiative fluxes are within 20%. The study also aims to assess approximate radiative models, namely the optically thin approximation (OTA) and grey medium approximation. These approximations affect significantly the radiative loss and should be avoided if accurate predictions of the radiative flux are desired. At atmospheric pressure, the relative errors that they produced on the peaks of temperature and soot volume fraction are within both experimental and model uncertainties. However, these discrepancies are found to increase with pressure, suggesting that spectral models describing properly the self-absorption should be considered at over-atmospheric pressure. 相似文献