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Optimizing progress variable definition in flamelet-based dimension reduction in combustion

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Applied Mathematics and Mechanics(English Edition) 2015年第11期36卷 1481-1498页

作者： Jing CHEN minghou liu Yiliang CHEN Department of Thermal Science and Energy Engineering University of Science and Technology of China

An automated method to optimize the definition of the progress variables in the flamelet-based dimension reduction is proposed. The performance of these optimized progress variables in coupling the flamelets and flow solver is presented. In the proposed method, the progress variables are defined according to the first two principal components （PCs） from the principal component analysis （PCA） or kernel-density-weighted PCA （KEDPCA） of a set of flamelets. These flamelets can then be mapped to these new progress variables instead of the mixture fraction/conventional progress variables. Thus, a new chemistry look-up table is constructed. A priori validation of these optimized progress variables and the new chemistry table is implemented in a CH4/N2/air lift-off flame. The reconstruction of the lift-off flame shows that the optimized progress variables perform better than the conventional ones, especially in the high temperature area. The coefficient determinations （R2 statistics） show that the KEDPCA performs slightly better than the PCA except for some minor species. The main advantage of the KEDPCA is that it is less sensitive to the database. Meanwhile, the criteria for the optimization are proposed and discussed. The constraint that the progress variables should monotonically evolve from fresh gas to burnt gas is analyzed in detail.

关键词： principal component analysis (PCA),oprogress variable flamelet-basedmodel dimension reduction

Study on micronozzle flow and propulsion performance using DSMC and continuum methods

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Acta Mechanica Sinica 2006年第5期22卷 409-416页

作者： minghou liu Xianfeng Zhang Genxuan Zhang Yiliang Chen Department of Thermal Science and Energy Engineering University of Science and Technology of China Hefei 230027 China

In this paper, both DSMC and Navier-Stokes computational approaches were applied to study micronozzle flow. The effects of inlet condition, wall boundary condition, Reynolds number, micronozzle geometry and Knudsen number on the micronozzle flow field and propulsion performance were studied in detail. It is found that within the Knudsen number range under consideration, both the methods work to predict flow characteristics inside micronozzles. The continuum method with slip boundary conditions has shown good performance in simulating the formation of a boundary layer inside the nozzle. However, in the nozzle exit lip region, the DSMC method is better due to gas rapid expansion. It is found that with decreasing the inlet pressure, the difference between the continuum model and DSMC results increases due to the enhanced rarefaction effect. The coefficient of discharge and the thrust efficiency increase with increasing the Reynolds number. Thrust is almost proportional to the nozzle width. With dimension enlarged, the nozzle performance becomes better while the rarefaction effects would be somewhat weakened.

关键词： Micronozzle DSMC Continuum model Slip boundary condition Thrust efficiency

Numerical simulation on micromixer based on synthetic jet

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Acta Mechanica Sinica 2008年第6期24卷 629-636页

作者： minghou liu Chen Xie Xiangfeng Zhang Yiliang Chen Department of Thermal Science and Energy Engineering. USTC. Hefei 230027 China

This paper studied a concept of micromixer with a synthetic jet placed at the bottom of a rectangular channel. Due to periodic ejections from and suctions into the channel, the fluids are mixed effectively. To study the effects of the inlet velocity, the jet intensity and frequency, and the jet location on the mixing efficiency, 3-D numerical simulations of the micromixer have been carried out. It has been found that when the jet intensity and the frequency are fixed, the mixing efficiency increases when Re 〈 50, and decreases when Re 〉 50 with the best mixing efficiency achieved at Re = 50. When the ratio of the jet velocity magnitude to the inlet velocity is taken as 10 and the jet frequency is 100 Hz, the mixing index reaches the highest value. It has also been found that to get better mixing efficiency, the orifice of the synthetic jet should be asymmetrically located away from the channel＇s centerline.

关键词： Micromixer Synthetic jet Mixing index

Size distributions of major elements in residual ash particles from coal combustion

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Chinese Science Bulletin 2009年第6期54卷 958-964页

作者： YU DunXi XU minghou YAO Hong liu XiaoWei State Key Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074 China

Combustion experiments for three coals of different ranks were conducted in an electrically-heated drop tube furnace. The size distributions of major elements in the residual ash particles (>0.4μm) such as Al, Si, S, P, Na, Mg, K, Ca and Fe were investigated. The experimental results showed that the con-centrations of Al and Si in the residual ash particles decreased with decreasing particle size, while the concentrations of S and P increased with decreasing particle size. No consistent size distributions were obtained for Na, Mg, K, Ca and Fe. The established deposition model accounting for trace element dis-tributions was demonstrated to be applicable to some major elements as well. The modeling results indicated that the size distributions of the refractory elements, Al and Si, were mainly influenced by the deposition of vaporized elements on particle surfaces. A dominant fraction of S and P vaporized during coal combustion. Their size distributions were determined by surface condensation, reaction or adsorption. The partitioning mechanisms of Na, Mg, K, Ca and Fe were more complex.

关键词：煤燃烧过程粉煤灰颗粒粒度分布剩余燃烧实验微量元素沉积模式大小分布

Effective identification of the three particle modes generated during pulverized coal combustion

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Chinese Science Bulletin 2008年第10期53卷 1593-1602页

作者： YU DunXi XU minghou YAO Hong liu XiaoWei ZHOU Ke State Key Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074 China

Based on the mass fraction size distribution of aluminum (Al),an improved method for effectively identifying the modes of particulate matter from pulverized coal combustion is proposed in this study. It is found that the particle size distributions of coal-derived particulate matter actually have three modes, rather than just mere *** ultrafine mode is mainly generated through the vaporization and condensation *** coarse mode is primarily formed by the coalescence of molten minerals, while the newly-found central mode is attributed to the heterogeneous condensation or adsorption of vaporized species on fine residual ash *** detailed investigation of the mass fraction size distribution of sulfur(S) further demonstrates the rationality and effectiveness of the mass fraction size distribution of the Al in identifying three particle *** results show that not only can the number of particle modes be identified in the mass fraction size distributions of the Al but also can their size boundaries be more accurately defined. This method provides new insights in elucidating particle formation mechanisms and their physico-chemical characteristics.

关键词：煤炭燃烧颗粒模式元素尺寸分布结构机理

Continuum-based slip model and its validity for micro-channel flows

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Chinese Science Bulletin 2006年第9期51卷 1130-1137页

作者： ZHANG Genxuan liu minghou ZHANG Xianfeng YE Taohong CHEN Yiliang WANG Lu Thermal Science & Energy Engineering Department University of Science & Technology of China Hefei 230027 China The 38th Research Institute of CETC Hefei 230031 China

In this paper, the low Mach number he- lium and nitrogen flows in micro-channels are inves- tigated numerically with variations of inlet to outlet pressure ratios, aspect ratios, out pressures and fluid mediums by using different continuum-based slip models. Theoretical solutions based on perturbation expansions of the Navier-Stokes equations have been developed under different order slip conditions. The validity of slip models has been examined by the corresponding experiments and the DSMC method at different Knudsen numbers. Simulations have shown good predictions of the compressibility, rarefaction and thermal creep effects on micro-channel flows with the present slip models. The higher order slip models relatively decrease the rarefaction effects comparing with a first-order slip model. Both of the Knudsen number and the Reynolds number have been identified as key parameters, which govern the rarefaction effects and thermal creep effects, respec- tively. The present slip models have been also dem- onstrated to be appropriate for micro-channel nitro- gen flows with the Knudsen number less than 0.15, and the higher order slip conditions improve the Na- vier-Stokes predictions in the slip flow regime with Kn<0.08. However, the continuum-based slip models significantly under-predict the rarefaction effects in the transitional flow regime as the Knudsen number exceeds 0.2.

关键词：微通道滑移模型扰动分析稀疏效应克努森数

Physicochemical properties and potential health effects of nanoparticles from pulverized coal combustion

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Chinese Science Bulletin 2009年第7期54卷 1243-1250页

作者： YU DunXi XU minghou YAO Hong liu XiaoWei ZHOU Ke WEN Chang LI Lin State Key Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074 China

Nanoparticles are thought to induce more severe health impacts than larger particles. The nanoparticles from coal-fired boilers are classified into three size fractions with a 13-stage low pressure impactor. Their physicochemical properties are characterized by the high-resolution field emission scanning electron microscope and X-ray fluorescence spectrometer (XRF). The results show that coal-derived nanoparticles mainly consist of individual primary particles of 20―150 nm and their aggregates. Inor-ganic nanoparticles primarily contain ash-forming elements and their aggregates have a dense struc-ture. Organic nanoparticles are dominated by the element carbon and their aggregates have a loose structure. Nanoparticles from the same boiler have a similar composition and are primarily composed of sulfur, refractory elements and alkali/alkaline elements. Some transition and heavy metals are also detected. For different boilers, greater differences are observed in the production of the nanoparticles and their composition, possibly due to the use of low-NOx burners. Coal-derived nanoparticles have a small size, large specific surface area and complicated chemical composition, and thus are potentially more harmful to human health.

关键词：无机纳米粒子煤粉燃烧健康影响理化性质场发射扫描电子显微镜 X射线荧光光谱仪 X射线荧光光谱法燃煤锅炉

Dimensional Analysis and Dissipation Rate Estimation in the Near Wake of a Circular Cylinder

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Journal of Applied Mathematics and Physics 2014年第6期2卷 431-436页

作者： Xintai Zhang Wei Wei Zhong Jiangzhi Yang minghou liu Department of Thermal Science and Energy Engineering University of Science and Technology of China Hefei Anhui 230027 China

A particle image velocimetry (PIV) experiment is performed for dissipation rate estimation in the near wake behind a circular cylinder with diameter D of 12 mm and corresponding Reynolds number of 7100. Considering the limitation of PIV resolution, a large eddy PIV method based on idea of large eddy simulation (LES), is used for more accurate estimation of dissipation rate. Based on the dynamic equilibrium assumption in the inertial subrange, the dissipation rate of the subgrid scales is approximated by the subgrid scale (SGS) flux, computed from PIV velocity fields and Smagorinsky model for SGS stress. A dimensional analysis about the integral length scale and the Kolmogorov length scale is discussed firstly to verify whether the dynamic equilibrium assumption holds or not.

关键词： Cylinder Near Wake Large Eddy PIV Dissipation Rate

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不朽的《培尔·金特》在上海

戏剧（中央戏剧学院学报） 2008年第S1期 141-148页

作者：刘明厚上海戏剧学院戏剧文学系

挪威戏剧家易卜生曾对中国的话剧事业产生过重大影响,中国学者、艺术家在"易卜生年"的时候表现出极大的热情与敬意。仅在上海,2006年和2007年两年中就有3台易卜生的《培尔.金特》不同形式的演出。易卜生在这部戏剧里大量采用象征和隐喻... 详细信息

挪威戏剧家易卜生曾对中国的话剧事业产生过重大影响,中国学者、艺术家在"易卜生年"的时候表现出极大的热情与敬意。仅在上海,2006年和2007年两年中就有3台易卜生的《培尔.金特》不同形式的演出。易卜生在这部戏剧里大量采用象征和隐喻的手法,塑造了一个扑朔迷离的梦幻境界。这些特点恰恰使这一剧作具有可以颠覆性解读的文本基础,符合了中国戏曲灵活性与假定性的传统美学,从而使《培尔.金特》这部开放式结构的戏剧以京剧的形式和环境戏剧的形式得到了最大效果的发挥,赢得了年轻一代对易卜生这部不朽的剧作《培尔.金特》的喜爱。

关键词：《培尔·金特》音乐戏剧京剧环境戏剧