Multiple mapping conditioning of velocity in turbulent jet flames

Multiple mapping conditioning (MMC) has emerged as a new approach to model turbulent reacting flows. This study revises the standard MMC closure for velocity in turbulent jet flows from linearity in the reference space to linearity in the composition space. This modeling amendment ensures that the standard velocity model in conditional moment closure studies can now be used for MMC computation as well. A simplified model for the velocity-dependence of MMC drift coefficients is derived without loss of generality and is implemented for the revised velocity closure. Modeling results have been corroborated against the Direct Numerical Simulation database of a spatially evolving, planar turbulent jet flame. The revised model shows marked improvement over standard MMC closure in predicting velocity statistics close to the nozzle.     

Laminar flame speeds and extinction limits of conventional and alternative jet fuels

Experimental results of laminar flame speeds and extinction stretch rates for the conventional (Jet-A) and alternative (S-8) jet fuels are acquired and compared to the results from our earlier studies for neat hydrocarbon surrogate components, including n-decane and n-dodecane. Specifically, atmospheric pressure laminar flame speeds are measured using a counterflow twin-flame configuration for Jet-A/O₂/N₂ and S-8/O₂/N₂ mixtures at preheat temperatures of 400, 450, and 470 K and equivalence ratios ranging from 0.7 to 1.4. The flow field is recorded using digital particle image velocimetry. Linear extrapolation is then applied to determine the unstretched laminar flame speed. Experimental data for the extinction stretch rates of the nitrogen diluted jet fuel/oxidizer mixtures as a function of equivalence ratio are also obtained. In addition, the experimental data of Jet-A are compared to the computed values using a chemical kinetic mechanism for a kerosene surrogate reported in literature. A sensitivity analysis is further performed to identify the key reactions affecting the laminar flame speed and extinction stretch rate for this kerosene surrogate.     

提高活性染料固着率的冷染工艺

冷染工艺是在原有的喷射溢流染色机的工艺基础上，用适合的中温型染料在低温高ｐＨ值下染棉针织物。只要染料选择适当，该工艺可以达到节资降本，减少污染效果。     

某喷漆机库改造项目电气防爆设计介绍

结合工程实例,介绍飞机喷漆工艺,依据国内外标准关于爆炸危险区域划分的原则,适当划分喷漆机库爆炸危险区域,并采取相应的防范措施。     

Longitudinal tunnel ventilation control. Part 1: Modelling and dynamic feedforward control

Road tunnels exceeding a certain minimum length are equipped with a ventilation system. In case of a fire it is used to achieve a predefined air flow velocity in the tunnel by adequately controlling the installed jet fans in order to ensure sufficient visibility for persons to safely follow the escape routes. As the dynamics of the air flow in road tunnels strongly depend on the tunnel length, short tunnels with longitudinal ventilation systems pose a challenging control task. In this paper, non-linear dynamic feedforward control is proposed for longitudinal ventilation control in case of an emergency. For this purpose, an analytical non-linear zero-dimensional model of the air flow is feedback linearised. Due to its special properties, which are presented and analysed, two different versions of feedforward control are proposed: One is focused on performance, the other on robustness. Finally, the beneficial behaviour of the presented two-degrees-of-freedom control approach is demonstrated by its application to an Austrian motorway tunnel.     

Nonlinear eddy viscosity modeling and experimental study of jet spreading rates

Indoor airflow pattern is strongly influenced by turbulent shear and turbulent normal stresses that are responsible for entrainment effects and turbulence‐driven secondary motion. Therefore, an accurate prediction of room airflows requires reliable modeling of these turbulent quantities. The most widely used turbulence models include RANS‐based models that provide quick solutions but are known to fail in turbulent free shear and wall‐affected flows. In order to cope with this deficiency, this study presents a nonlinear k‐ε turbulence model and evaluates it along with linear k‐ε models for an indoor isothermal linear diffuser jet flow measured in two model rooms using PIV. The results show that the flow contains a free jet near the inlet region and a wall‐affected region downstream where the jet is pushed toward the ceiling by entrainment through the well‐known Coanda effect. The CFD results show that an accurate prediction of the entrainment process is very important and that the nonlinear eddy viscosity model is able to predict the turbulence‐driven secondary motions. Furthermore, turbulence models that are calibrated for high Reynolds free shear layer flows were not able to reproduce the measured velocity distributions, and it is suggested that the model constants of turbulence models should be adjusted before they are used for room airflow simulations.     

An experimental study of the autoignition characteristics of conventional jet fuel/oxidizer mixtures: Jet-A and JP-8

Ignition delay times of Jet-A/oxidizer and JP-8/oxidizer mixtures are measured using a heated rapid compression machine at compressed charge pressures corresponding to 7, 15, and 30 bar, compressed temperatures ranging from 650 to 1100 K, and equivalence ratios varying from 0.42 to 2.26. When using air as the oxidant, two oxidizer-to-fuel mass ratios of 13 and 19 are investigated. To achieve higher compressed temperatures for fuel lean mixtures (equivalence ratio of ∼0.42), argon dilution is also used and the corresponding oxidizer-to-fuel mass ratio is 84.9. For the conditions studied, experimental results show two-stage ignition characteristics for both Jet-A and JP-8. Variations of both the first-stage and overall ignition delays with compressed temperature, compressed pressure, and equivalence ratio are reported and correlated. It is noted that the negative temperature coefficient phenomenon becomes more prominent at relatively lower pressures. Furthermore, the first-stage-ignition delay is found to be less sensitive to changes in equivalence ratio and primarily dependent on temperature.     

三峡一期土石围堰设计与运用

三峡工程采用“三期导流，明渠通航，三期碾压混凝土围堰挡水发电”的施工导流方案。一期土石围堰主要用于保护导流明渠开挖及护坡，护底施工；混凝土纵向围堰基础开挖及混凝土浇筑等，围堰轴线长２５０２．３６ｍ，最大高４２ｍ围护基础７５万ｍ＾２。堰体分茅坪溪段，上浮横向段，纵向段和下游横向段，围堰防冲采用“守点顾线”设计方案，即在上，下游转角处设防冲矶头石体护脚，防渗体采用柔性混凝土防渗上接土工合成材料方案，部     

射流偏转板伺服阀放大级优化设计

鉴于射流偏转板伺服阀在阀类产品相较下的优点以及国内其成品缺乏的现状,提出了其关键结构放大级的优化设计。运用CAD软件对射流偏转板伺服阀放大级流场进行建模,并对其需要设计的尺寸进行多组建模,再运用CFD软件对上一步的模型进行适当的网格划分和流场分析,得到不同尺寸条件以及不同运动情况下的流体压力、速度分布情况。最后将得到的数据进行曲面拟合,并根据分析结果选取良好的工况点,实现参数的优化。     

俄罗斯原油生产3号喷气燃料的探索

介绍了辽阳石化公司作为国内首家全炼俄罗斯原油的石化单位,在对俄油喷气燃料馏分性质和喷气燃料各项指标深入研究的基础上,通过优化生产方案和油品调和,成功生产满足国标要求的3号民用喷气燃料,为国内大规模加工俄罗斯原油提供了良好的借鉴经验。