Quasi-direct numerical simulations of the flow characteristics of a thermal plasma reactor with counterflow jet

Three-dimensional quasi-direct numerical simulations have been performed to investigate a thermal plasma reactor with a counterflow jet. The effects of the momentum flux ratio and distance between the counterflow jet and the thermal plasma jet on the flow characteristics are addressed. The numerical results show that the dimensionless location of the stagnation layer is significantly affected by the momentum flux ratio, but it is not dependent on the distance.Specifically, the stagnation layer is closer to the plasma torch outlet with the increase of the momentum flux ratio. Furthermore, the flow regimes of the stagnation layer and the flow characteristics of the thermal plasma jet are closely related to the momentum flux ratio. The characteristic frequencies associated with the different regimes are identified. The deflecting oscillation flow regimes are found when the momentum flux ratio is low, which provokes axial velocity fluctuations inside the thermal plasma jet. By contrast, for cases with a high momentum flux ratio, flapping flow regimes are distinguished. The thermal plasma jets are very stable and the axial velocity fluctuations mainly exist in the stagnation layer.

Modeling Study of Hydrogen/Oxygen and n-alkane/Oxygen Counterflow Diffusion Flames

A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffusion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH4 to C16H34. The basic diffusion flame structures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The detailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory （LLNL） are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H2 has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.

Drag Reduction Effect for Hypersonic Lifting-Body Vehicle with Counterflowing Jet

This study takes the novel approach of using a counterflowing jet positioned on the nose of a lifting-body vehicle to explore its drag reduction effect at a range of angles of attack.Numerical studies are conducted at a freestream Mach number of 8 in standard atmospheric conditions corresponding to the altitude of 40 km.The effects of jet pressure ratio and flying angles of attack on drag reduction of the model are systematically investigated.Considering the reverse thrust generated from the counterflowing jet,the drag on the nose at hypersonic speeds could be reduced up to 66%.The maximum lift-to-drag ratio of the model is obtained at 6°;meanwhile,the counterflowing jet produces a drag reduction of 8.8%for the whole model.In addition to the nose,the counterflowing jet influences the drag by increasing the pressure drag of the model and reducing the skin friction drag of the first cone within 8°.The results show that the potential of the counterflowing jet as a means of active flow control for drag reduction is significant in the engineering application on hypersonic lifting-body vehicles.

Self-organized phenomena of pedestrian counterflow through a wide bottleneck in a channel

The pedestrian counterflow through a bottleneck in a channel shows a variety of flow patterns due to self-organization.In order to reveal the underlying mechanism,a cellular automaton model was proposed by incorporating the floor field and the view field which reflects the global information of the studied area and local interactions with others.The presented model can well reproduce typical collective behaviors,such as lane formation.Numerical simulations were performed in the case of a wide bottleneck and typical flow patterns at different density ranges were identified as rarefied flow,laminar flow,interrupted bidirectional flow,oscillatory flow,intermittent flow,and choked flow.The effects of several parameters,such as the size of view field and the width of opening,on the bottleneck flow are also analyzed in detail.The view field plays a vital role in reproducing self-organized phenomena of pedestrian.Numerical results showed that the presented model can capture key characteristics of bottleneck flows.

Mixing of A Non-Circular Jet into A Counterflow

An elliptic jet and a square jet flowing into a counterflow with different jet-to-current velocity ratios are investigated by using realizable Ice model. Some computed mean velocity and scalar features agree reasonably well with experimental measurements, and more features are obtained by analyzing the computed results. After fluid issues from a nozzle, it entrains ambient fluid, and its velocity and concentration on the centerline decay with the distance downstream from the potential core （10）. The decay ratio increases with the decreasing jet-to-current velocity ratio a. For an elliptic jet, the evolution of the excess velocity half-width b and the concentration half-width be merely remains constant near the jet exit on major-axis plane while they increase linearly on the minor-axis plane. However, the half-widths on the major-axis and minor-axis plane become proportional to the axial distance downstream after equaling each other. For a square jet, b and bc increase linearly with the distance downstream from the jet exit, but the spread ratio is larger on the middle plane than that on the diagonal plane before they equal each other. The radial extent of the dividing streamline r~ or the mixing boundary rs~ increases linearly downstream, and decreases exponentially after reaching a peak at Xb. The ratio on the minor-axis plane is larger than that on the major-axis plane for an elliptic jet. The characteristics are the same for the square jet. b, be, rs, and rsc on two corresponding planes become equal to each other more rapidly for the square jet than for the elliptic jet, because the sharp comer of the square nozzle induces secondary structures that are more intense. The distributions of the excess axial velocity and scalar concentration exhibit self-similarity for either the elliptic jet or square jet in the region of 10 〈 x 〈 xb. On the cross section, four counter-rotating pairs of vortices, which enhance the entrainment between the jet and counterflow, form at the four comers of the square jet or at the two ends of the major-axis plane of the elliptic jet. The recirculation pattern formed by these axial vortices is more complex for the square jet than that for the elliptic jet. The turbulent kinetic energy k have large value in the region near the jet exit and stagnation point. The maximum value ofk for the square jet is larger than that of the elliptic jet near the jet exit. This results in the square jet mixing more strongly than the elliptic jet.

Experimental and Numerical Studies of Paraguayan Chaco Natural Gas in a Counterflow Diffusion Flame

Combustion is a chemical phenomenon in which a multitude of elementary chemical reactions take place, resulting in the overall process of fuel oxidation. Natural gas fuel has been explored for a few decades and extracted for a few years in the region of Paraguayan Chaco, near Bolivia border. Currently, natural gas is not very important in Paraguay＇s energy matrix, however it could be in the near future if higher volumes are extracted and transported to the most populated cities, specially to the capital. In order to improve Paraguayan natural gas combustion performance, an understanding of its fundamental properties and the combustion pathways is required. This study presents new data for Paraguayan Chaco natural gas combustion in a laminar counterflow diffusion flame configuration at atmospheric pressure. Visible chemiluminescence of excited radicals CH＊ and C2^＊ is employed experimentally. 1D numerical simulation was carried out using Paraguayan Chaco natural gas chemical composition and a standard kinetic mechanism, to which we added CH＊ and C] reactions. Typical flame structures resulting from simulation are presented and a validation of the model is realized comparing experimental and numerical CH＊ and C~ radicals profiles.

Effects of dimethyl ether and ethanol additions on soot transition in ethylene counterflow diffusion flames

This paper investigates the effect of blending dimethyl ether(DME)and ethanol on the soot transition periods in ethylene counterflow diffusion flames by using a novel optical diagnostic method.The soot critical transition point in different conditions is identified experimentally and numerically.Two kinds of flames are carried out to gain the soot critical transition point in counterflow diffusion flames by changing oxygen fraction(Xo)and changing volume flow rates of fuel and oxidizer(Qv).The red-green-blue(RGB)ratio method is used to precisely identify the soot critical transition point,and chemical kinetic simulations are performed to analyze the detailed reaction paths.The results show that compared to the ethylene flame,the soot critical transition point occurs at a higher Xoand a lower Qvwhen DME or ethanol is blended.The addition of DME and ethanol can inhibit soot formation,due to the degree of soot formation reaction being lower than the degree of the oxidation reaction in the blending flames.

从逆、热、郁探讨经方在胃食管反流病中的运用

胃食管反流病与《伤寒杂病论》中部分方证相近,表现出“逆、热、郁”的病机特点。以“逆”为病机的证型有气虚痰逆、阴虚气逆、脾伤饮逆、肝寒浊逆等4型,旋覆代赭汤、麦门冬汤、苓桂术甘汤、吴茱萸汤等方分别治之;以“热”为病机的证型有热郁胸膈、上热下寒等2型,栀子豉汤、黄连汤等方分别治之;以“郁”为病机的证型有邪郁少阳、痰(水)气互阻、痰热互结、阳微阴弦等4型,小柴胡汤、半夏厚朴汤(射干麻黄汤)、小陷胸汤、枳实薤白桂枝汤等方分别治之。应用仲景学说的相关思想可以指导胃食管反流病的治疗。

李素云从“聚于胃,关于肺”辨治胃食管反流性咳嗽思想探析

胃食管反流性咳嗽(gastroesophageal reflux cough,GERC)属于呼吸系统疾病,是慢性咳嗽的三大类型之一,多呈间断发作,缠绵难愈,影响生活质量。李素云教授临证多年,根据“五脏六腑皆令人咳”提出治病求本;病机方面,基于“聚于胃,关于肺”理论,提出肺气上逆为标,肝胃气逆为本。临证治疗该病主张不离于肺胃,亦不止于肺胃,以脏腑辨证为纲,审证求因,以“泄、清、补、疏”四字为法,每获佳效。该文就“聚于胃,关于肺”理论在该病中的运用及其辨治GERC的经验进行探讨,以期对该病的临床治疗思路有所补充。

超临界CO_(2)印刷电路板换热器热工水力特性研究

对于超临界CO_(2)布雷顿循环中的印刷电路板换热器,其复杂结构与工作介质的特殊物理性质将导致集总参数方法出现较大的计算误差。为提升印刷电路板换热器的换热参数的计算精度,本文基于Modelica语言,采取分节点建模方法,开发了印刷电路板换热器的热工水力特性计算程序,对其稳态运行时的换热参数进行了分析。结果表明:印刷电路板换热器的通道内超临界CO_(2)的对流换热系数沿流动方向发生显著变化。与设计值相比,分节点计算程序的最大相对误差小于3%,计算精度相比于集总参数方法显著提升,因此有必要采取分节点计算方法以提高计算精度。研究结果可为超临界CO_(2)布雷顿循环系统中印刷电路板换热器的设计和仿真提供参考。

Numerical exploration on jet oscillation mechanism of counterflowing jet ahead of a hypersonic lifting-body vehicle

Numerical investigation of a supersonic jet from the nose of a lifting-body vehicle opposing a hypersonic flow with the freestream Mach number being 8.0 at 40 km altitude was carried out by solving the three-dimensional, time-accurate Navier-Stokes equations with a hybrid meshes approach. Based on the analysis of the flow field structures and aerodynamic characteristics, the behaviours relevant to the LPM jet were discussed in detail, including the drag reduction effect, the periodic oscillation and the feedback loop. The obtained results show that the flow oscillation characteristic of the LPM jet is low-frequency and high-amplitude while that of the SPM jet is high-frequency and low-amplitude. Compared with the clearly dominant frequencies of the LPM jet, the SPM jet exhibits a broad-band structure. The LPM jet can sustain drag reduction effect until the angle of attack is 8°, and the lift-to-drag ratio of the vehicle is effectively improved by 6.95% at angle of attack of 6°. The self-sustained oscillation process was studied by a typical oscillating cycle of the drag force coefficient and the variation of the instantaneous pressure distribution,which reveals an off-axial flapping motion of the conical shear layer. The variation of the subsonic recirculation zone ahead of the vehicle nose strengthens the understanding of the jet behavior including the source of instability in the long penetration mode and the mechanism of the feedback loop. The aim of this paper is to advance the technology readiness level for the counterflowing jet applied as an active control technology in hypersonic flows by gaining a better insight of the flow physics.

Large eddy simulation of a round jet into a counterflow

A round jet into a counterflow under different jet-to-current velocity ratios was investigated using large eddy simulation.The results agree well with experimental measurements from laser-Doppler anemometry and laser-induced fluorescence that include velocity and mean concentrations along the centerline and radial direction.Vortex rings appear in the region near the jet exit and large-scale vortex structures still occur near the stagnation point.The flow becomes more chaotic and three-dimensional with the presence of these structures.In particular,their presence near the stagnation point results in large velocity fluctuations that enhance the mixing process and dilution.These fluctuations are described by probability density functions that deviate from Gaussian distribution.The three-dimensional streamlines indicate that the jet not only oscillates in three directions but also rotates about the jet axis and around the vortex.The second and third moments of the velocity or scalar fluctuations identify that the mixing processes are greater in the region before the stagnation point.

常克教授从冲脉论治过敏性紫癜经验总结

本文总结常克教授从冲脉辨治过敏性紫癜的临床经验,明析其关于平逆冲脉,调理气血治疗过敏性紫癜的学术观点。常克教授根据冲脉的循行部位及其与阳明胃、少阴肾之间生理病理联系,从冲脉致病的角度出发,诠释过敏性紫癜的疾病特点及发病规律,进而提出阴虚血燥,瘀血内阻为该病病情反复的始动因素;热伏冲脉,气血失调为该病的关键病机。进而提出从冲脉治疗,首辨气血,明析病位,分期论治结合脏腑辨治。早期重视解表利咽,凉血安冲;中期重视清胃泻火,平冲降逆;晚期重视消补并举,通利冲脉。

赵杨基于“阴阳相交生风”论治帕金森病经验

赵杨教授认为“阴阳相交生风”指的是阴阳失衡、相交生风的病理状态,风以阳气为本,阴阳失衡,阳气变动则生内风。帕金森病的病机关键即为“阴阳相交生风”,风既可以作为致病因素内扰清窍,又可作为病理产物影响清窍功能。根据阳气波动情况,帕金森病在不同病程可见阳气亢逆生风、阳气郁滞生风、阳气虚衰生风等病机,临床治疗应以调和阴阳平衡为要,分别治以滋阴潜阳息风、宣阳通郁宁风、温阳养血散风。附验案1则。

油气回收气相管防逆流装置的设计与应用

针对石油库公路下装发油作业油气回收气相鹤管在气体压力变化及下装接头密封不严的情况下,相邻未进行装卸作业的气相鹤管会出现油气逆流逸散的问题,提出了在气相管接口部位加装夹片式止回阀的解决方案,为解决石油库公路发油下装气相鹤管油气逆流逸散问题提供了参考。

王小奇基于六郁理论治疗难治性反流性食管炎经验介绍

介绍王小奇主任医师治疗难治性反流性食管炎的临床经验。王小奇认为难治性反流性食管炎属中医吐酸疾病范畴,强调肝气郁滞为当代吐酸病之核心病机,肝气郁滞既可横逆犯胃,直接影响胃气通降功能,又能变生热(火)郁、痰(湿)郁、食郁、血郁,加重胃气上逆,故以六郁理论为基础,提出理气为本、兼顾他郁、和胃为旨的总治则。理气为本重在疏肝理气,兼顾他郁则遵循热(火)郁者清热泻火,痰(湿)郁者化痰祛湿,食郁者消食和胃,血郁者行气化瘀的原则对症治疗,和胃为旨则是通过配合抑酸降逆药物达到治疗的最终目标。

用于生物气溶胶质谱检测的泵送逆流虚拟切割器研究

单颗粒气溶胶质谱仪(SPAMS)可以提供高时间分辨率和高灵敏度的颗粒物粒径分布和质谱数据组成,广泛应用于大气气溶胶检测和大气科学研究领域。大气环境中的微米级大颗粒数浓度远小于亚微米级小颗粒物,在单颗粒气溶胶质谱的检测中,颗粒经空气动力学加速赋能后,小颗粒物的飞行速度大于大颗粒物,导致生物气溶胶等大颗粒的检测几率大幅度降低。该研究设计了一种泵送逆流虚拟切割器(PCVI),通过3D建模、计算流体动力学(CFD)仿真、实际实验测试以及对实际样品藻类气溶胶的检测,详细介绍了PCVI的实现原理、数据仿真、性能验证与实际应用。PCVI与SPAMS联用,可形成对小颗粒物具有切割能力的PC⁃VI-SPAMS系统,对藻类生物气溶胶的检测证实,所研制的PCVI可以有效去除2μm粒径以下的颗粒,成功对小颗粒背景进行切分,获得了符合预期的效果。

Numerical study of the flow and dilution behaviors of round buoyant jet in counterflow

Pollutants are usually discharged into the receiving water bodies in the form of a turbulent jet or plume, and the presence of a counterflow enhances the initial dilution of the jet effluent. To understand the behaviors of jets in actual situations, a round buoyant jet issued horizontally into a uniform counterflow is simulated for different combinations of densimetric Froude number and jet-to-current velocity ratio. A two-phase mixture model is used to simulate this flow, and the renormalization group k - ε model is used to address the flow turbulence. The inter-phase interactions are described in terms of the relative slip velocity between phases. The jet features, including the trajectory of the jet centerline and the decay of the centedine velocity and the concentration, are investigated. The length scale analysis reveals the relationships between the distance and the centerline dilutions, and different flow mechanisms are revealed before and after the penetration point.

Hysteresis and Multi-state Behavior of Counterflow Flame in a Blowing Cylindrical Burner

This study focuses on flame hysteresis over a porous cylindrical burner. The hysteresis results from different operation procedure of the experiment. Gradually increasing inflow velocity can transform the envelope flame into a wake flame. The blow-off curve can be plotted by determining every critical inflow velocity that makes an envelope flame become a wake flame at different fuel-ejection velocities. In contrast, decreasing the inflow veiocity can transform the wake or lift-off flame into an envelope one. The reattachment curve can be obtained by the same method to explore the blow-off curve, but the intake process is reverse. However, these two curves are not coincident, except the origin. The discrepancy between them is termed as hysteresis, and it results from the difference between the burning velocities associated with both curves. At the lowest fuel-ejection velocity, no hysteresis exists between both curves owing to nearly no burning velocity difference there. Then, raising the fuel-ejection velocity enhances hysteresis and the discrepancy between the two curves. However, as fuel-ejection velocity exceeds a critical value, the intensity of hysteresis almost keeps constant and causes the two curves to be parallel to each other.

考虑行人摔倒和受伤的斜坡相向流社会力模型

行人在斜坡上运动时,其受力情况、运动速度及心理状态均与在平地运动时不同,难以应用现有社会力模型进行有效仿真.为此,考虑斜坡上行人的运动特征,提出一个改进的社会力模型,此模型基于过往实证数据对行人在斜坡上的期望速度进行了校准,并提出了推搡行为下行人摔倒的概率计算方法,同时,结合行人体重、运动加速度、承受压力及等待时间等实时状态实现了对行人摔倒、受伤及不耐烦心理的模拟.斜坡相向行人流场景仿真结果表明:坡度、行人初始密度的升高会延长人群运动时间,使人均意外发生率上升最高至38.0%;不耐烦心理有助于车道效应的形成,但会降低人群运动效率;行人流基本图中,高坡度下流量-密度关系趋势不如平地明显,各坡度行人平均速度比较接近.