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排序方式: 共有121条查询结果,搜索用时 15 毫秒
71.
抬举湍流H2/N2射流火焰的PDF模拟 总被引:2,自引:0,他引:2
采用数值目的研究了一个高温燃烧产物环境中的抬举湍流H2/N2射流火焰,对火焰的自然和抬举特性进行了研究.采用标量联合概率密度函数(PDF)目的处理详细的化学动力学过程,而湍流流场采用一个多时间尺度(MTS)k-ε湍流模型计算.计算中结合了一套描述氢气氧化的详细化学反应动力学机理.计算结果和实验数据进行了对比,表明所采用的模型可以精确的模拟火焰抬举高度和自然的过程. 相似文献
72.
Reliability sensitivity by method of moments 总被引:1,自引:0,他引:1
Based on the available methods of moments for structural system reliability assessment and point estimate methods for the first few moments of performance functions, an effective method is proposed to analyze reliability sensitivity of a structural system. The proposed method for analyzing reliability sensitivity includes two steps. Firstly, the reliability sensitivity, usually measured by partial differential of the failure probability Pf with respect to distribution parameter θ of the basic random variable is derived according to the moment based reliability assessment. The derived expression of ∂Pf/∂θ is related to the derivative of the performance function moment α with respect to θ. Secondly, by using the integral formulation between α and the probability density function (PDF) of the basic random variable, ∂α/∂θ could be derived as an expectation of a transformed performance function, and the expectation could be approximated by the point estimate methods. Through the two steps above, the reliability sensitivity can be obtained easily. The obvious advantages of the proposed method include independence of the explicit expression of the performance function, no limitations on the types of PDF of the basic random variables, wide applicability for multiple failure modes and high efficiency for low and medium dimensional problem, which are illustrated by the given examples. However, the efficiency of this method decreases as the dimension of the basic random variables increase, therefore, it is not suitable for the high dimensional problems. 相似文献
73.
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75.
基于PDF-LES模型的凹腔支板火焰稳定器模拟 总被引:1,自引:0,他引:1
航空发动机加力燃烧室有进口气体温度高、速度高、湍流度大的特点,是极为典型的湍流与燃烧相互耦合的工况。大涡模拟(LES)兼具高精度与合理计算量两个特点,概率密度函数模型(PDF)适用于湍流与复杂化学反应相互耦合的问题。本文在基于PDF-LES的Aero Engine Combustor Simulation Code(AECSC)程序基础上,对凹腔支板火焰稳定器进行数值模拟。使用气相版本对有无凹腔支板结构分别进行三个速度入口条件下的甲烷湍流燃烧模拟,并用两相版本对带凹腔支板结构进行设计工况下煤油喷雾的模拟。结果表明:凹腔结构的火焰稳定性要优于无凹腔结构;凹腔支板结构对于液相燃料的控制能力较气相更强。 相似文献
76.
Hai-Wen Ge Min-Ming Zhu Yi-Liang Chen Eva Gutheil 《Flow, Turbulence and Combustion》2007,78(2):91-109
A hybrid unsteady Reynolds-averaged numerical simulation (U-RANS) and probability density function (PDF) method is developed
for turbulent non-reactive and reactive flows. The resulting modeled equations are solved by a consistent hybrid finite volume
and Lagrangian Monte-Carlo particle method. Both turbulent non-reactive and reactive flows in a rectangular channel containing
a triangular-shaped bluff-body are simulated. One-step and two-step mechanisms for propane/air combustion are used for the
reactive case. The time-averaged results are compared with both experimental data and numerical results from the literature
using large eddy simulation (LES) and steady RANS. The results of the present method are in good agreement with the experimental
data, and they improve the numerical results available in the literature. 相似文献
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78.
Vibration energy harvesting has emerged as a promising method to harvest energy for small-scale applications. Enhancing the performance of a vibration energy harvester(VEH) incorporating nonlinear techniques, for example, the snap-through VEH with geometric non-linearity, has gained attention in recent years. A conventional snap-through VEH is a bi-stable system with a time-invariant potential function, which was investigated extensively in the past. In this work, a modified snap-through VEH wit... 相似文献
79.
A spray pyrolysis of a water solution of iron, manganese and iron nitrates is applied to prepare Zn0.5Mn0.5Fe2O4 single-phase ferrite with a spinel-type structure. The samples are characterized by means of differential scanning calorimetry, scanning and transmission electron microscopy, X-ray diffraction, infrared and 57Fe Mössbauer spectroscopy. The mass magnetization σ and the magnetic susceptibility 1/χ of the ferrites are measured as a function of temperature over the range of 78–728 K. The obtained sample contains nanoparticles with an average diameter d ∼7 nm possessing MnxZnyFe3−(x+y)O4 spinel-type structure with a uniform distribution of manganese and zinc atoms over the ferrite lattice. The Curie temperature is determined to be 375 ÷ 380 K. 相似文献
80.
The joint scalar PDF method, as implemented in FLUENT, was used to simulate the autoignition of a jet of hydrogen in a turbulent co-flow of heated air. While the autoignition phenomenon is intermittent in the experiment, ensemble-averaged data on the effect of the flow on ignition length are available, which enables us to compare them with the steady state calculations.Results of sensitivity tests showed that the choice of chemical mechanism affects the calculation more than the mixing model and model constants. Further calculations for different initial conditions (i.e. temperature and velocity of the jet T jet and U jet and the co-flow T air and U air) have been done using a set of parameters selected after the sensitivity study. Scatter plots and conditional scalar profiles confirmed that the ignition is always initiated in lean mixture fractions. The ignition length was predicted with good accuracy for the case of U jet>U air but not so well for the case of U jet≈U air. For the equal velocity case, increasing the velocity resulted in delayed autoignition time (defined as the ignition length divided by the mean velocity), in agreement with the experimental trend. The results give credence to the use of the joint scalar PDF method for autoignition in non-premixed flows. 相似文献