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根据流体力学相关的理论知识,对采用固体粒子显示气流的跟随特性进行了理论分析, 并选用碱式MgCOfluid experiment;solid tracer element;following characteristic;visualization2011-09-06http://lxsj.cstam.org.cn/CN/10.6052/1000-0879-lxysj2008-3562013-09-03 20:54:18http://lxsj.cstam.org.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=1425852008-07-14根据流体力学相关的理论知识,对采用固体粒子显示气流的跟随特性进行了理论分析, 并选用碱式MgCO$_{3}$白色粉末作为直接投入物,用实验的方法进行了比较和验证,结果表 明：直接投入MgCO$_{3}$粉末来显示气流具有良好的可视性和可记录性,可以很直观地观测 到流体的流动状况,是一种有效的实验方法.     

超声速气流磁流体加速初步实验研究

利用激波风洞, 采用氦气驱动氩气, 在平衡接触面运行方式下得到高温气体,通过在低压段注入电离种子K₂CO₃粉末, 实现高温条件下导电流体的产生, 设计了超声速喷管及磁流体加速实验段, 采用大电容提供电能, 开展了超声速气流磁流体加速初步实验研究. 典型实验条件下, 当喷管入口总压为0.7049MPa、理论平衡温度为8372.8K, 喷管出口马赫数为1.5, 电容充电电压为400V, 磁感应强度为0.5T时, 对电压电流特性、电导率、负载系数、电效率、加速效果等进行了测量或计算, 主要结论有: 磁场作用下的超声速气流的电导率的值大约在150S/m; 磁流体加速通道负载系数约为4, 电效率约为28%, 平均输入功率约198kW; 采用电参数测试方法对磁流体加速效果进行评估, 速度增加约15.7%;超声速气流的电导率对加速通道的电效率及加速效果等有很重要的影响.      

民机机头气动特性的实验研究

在1.2m量级亚跨超声速风洞采用DPIV、测压、油流显示三种实验技术对某型飞机机头模型气动特性进行了实验研究，得到了两个机头模型在巡航马赫数和快速巡航马赫数条件下的气动特性，实验结果表明：在巡航马赫数条件下（Ma=0.785），机头顶端气流速度和压力分布平滑，不存在流动分离和超音速区域；在快速巡航马赫数条件下（Ma=0.820），机头顶端存在局部很小区域的超音速区，强度很小，不存在流动分离；相同马赫数条件下，对于确定模型，随着攻角增大（由3o增加到6o），气流在模型上进入高流速区或超音速区的位置有所提前，位置相差约为半个到一个测压面间距；相同马赫数和相同攻角条件下，气流在两个机头模型上进入高流速区或超音速区的位置存在差异，位置相差约半个测压面间距。三种实验方法结果相互吻合，实验数据符合气动规律，可作为机头气动设计的依据。     

高速气流中横向液体射流雾化研究进展

在涡轮燃烧室和以液态碳氢燃料为工质的超燃冲压发动机中,高速气流中横向液体射流雾化是一个重要而复杂的过程.雾化过程进行的好坏直接关系到燃料的掺混和燃烧,进而影响发动机的性能. 针对高速气流中横向射流雾化的特点,对现阶段的实验和数值模拟研究进展进行了综述.实验方面结合国内外现状,阐明了一次、二次雾化的机理和雾化过程中的波现象,对穿透深度的确定方法及其影响因素进行了概括总结,分析了气液混合区的结构性质, 并列举和分析了常用的测量手段.数值模型研究介绍了现阶段的一次雾化和二次雾化常用的计算模型.最后提出了存在的问题和未来的研究方向.      

微尺度气体流动

了解微尺度气体流动特点是微机电系统设计和优化的基础.有关的研究可以上溯到20世纪初Knudsen的平面槽道流动质量流量的测量和Millikan的小球阻力系数的测量,实验结果揭示了稀薄气体效应即尺度效应对气体运动的重要影响.由于流动特征长度很小,微尺度气流经常处于滑流区甚至过渡领域,流动的相似参数为Knudsen数和Mach数.因此可以考虑利用相似准则,通过增大几何尺寸、减小压力的途径,解决微机电系统实验观测遇到的困难.为解决直接模拟Monte Carlo方法分析微机电系统中低速稀薄气流遇到的统计涨落困难,我们提出了信息保存法(IP),该方法能够有效克服统计散布,并已成功用于多种微尺度气流.      

纳米疏水性SiO2协同作用抑制丁烷爆炸速度与压力的耦合分析

为研究纳米疏水性SiO₂粉末作为阻燃剂和流动增强剂作用下丁烷爆炸速度与压力的耦合规律,在自行设计并搭建的基于LabVIEW控制系统的爆炸测试平台上开展了实验,通过休止角测试、SEM（scanning electron microscope）和EDS（energy dispersive spectrometer）分析了粉末团聚情况,分析了混合粉末抑制爆炸的机理,同时,实验了不同比例和不同浓度下纳米疏水性SiO₂改善CaCO₃粉末流动性并协同其抑制丁烷爆炸的效果,对爆炸火焰速度和压力的耦合关系进行了分析。结果表明,添加疏水性SiO₂可以使混合粉末的休止角降低,流动性增强,改善粉末的扩散效果和贮存能力,改变混合粉末的比例和浓度对燃烧反应有着显著的影响,在一定浓度范围内,粉末通过较大的比表面积和热解结合燃烧区域的自由基,使火焰传播速度和爆炸超压显著下降,但过大的粉末浓度会促进初期的爆炸,并且两种粉末协同对爆炸的抑制效果优于单一粉末。在混合粉末的抑制作用下,爆炸压力达到最大值时速度几乎降至最低,压力波形由持续上升变为单峰曲线。此外,在SiO₂和CaCO₃两种粉末质量比为1∶1混合、粉末质量浓度为106 g/m3时,对丁烷体积分数为4.20%的丁烷-空气混合气体爆炸的抑制效果最佳,火焰传播平均速度和最大爆炸超压的衰减率分别为85.5%和59.6%。     

人体上呼吸道内气流运动特性的数值模拟分析

运用计算流体动力学(CFD)方法对人体上呼吸道内的气流运动特性进行了数值模拟,通过PIV实验对数值模拟结果进行了验证。研究结果表明:气流在咽部外壁、气管外壁发生分离现象,气流在气管内壁形成局部高速区,支气管内的气流在分叉处发生分离,靠近支气管内壁速度较高,并且在支气管边界层的外缘速度达到最大值。气管和支气管内的二次涡流运动和轴向速度的分布使得气管支气管内壁受到的剪应力较大,内壁粘膜更容易受到损伤。     

钨粉爆炸烧结对粉末初始参数依赖关系的研究

本文从粉末爆炸烧结的能量沉积概念出发,提出了粉末爆炸烧结下限概念,讨论了钨粉末的爆炸烧结密度值和硬度分布对粉末初始参数的依赖关系,给出了实验结果。从理论和实验阐述了粉末初始参数在爆炸烧结实验中的重要作用。     

纳米-Al2O3陶瓷粉末的预热爆炸压实实验研究

对纳米-Al2O3陶瓷粉末在预热温度为0.5Tm的条件下,以不同的爆炸压实压力实施了烧结实验。通过X射线衍射分析了烧结体的晶型,并用高分辨率扫描电子显微镜进行了微观组织观察。实验结果表明,纳米-Al2O3陶瓷粉末在爆炸压力为13.1 GPa时可得到晶粒间结合致密且晶粒度在100 nm左右的-Al2O3烧结体;而在爆炸冲击压力为9.35 GPa以下时,烧结体的晶型没有发生转变,仍然是-Al2O3晶型。     

脉冲气流发生器流场的优化实验研究

为了分析脉冲气流发生器在不同喷嘴结构下的脉冲气流特征及其流场的变化规律,利用高速摄影技术, 通过控制闪光光源,得到不同喷嘴结构产生的冲击波及脉冲气流流场的实验图像及其影响。采用多项式拟合的方法获得冲击波超压值、速度随距离变化的衰减规律;通过图像处理技术,获取脉冲气流的有效数据,采用一阶指数衰减方程拟合出脉冲气流位移、速度随时间的变化规律。该实验方法及数据处理技术可以认知不同结构脉冲气流发生器产生的冲击波、脉冲气流的相关参数。     

One-dimensional nonequilibrium air flow

A solution is found for the problem of steady quasi-one-dimensional air flow in a stream tube with nonequilibrium chemical reactions, ionization reactions, and nonequilibrium excitation of the vibrational degrees of freedom in the molecular components. We consider the inverse problem: for a given pressure distribution find the distributions of all the other gas-thermodynamic quantities and the streamtube sections. The use of an implicit scheme for approximating the equations makes it possible to carry out the calculations over the entire range of variation in the degree of nonequilibrium — from the frozen state to equilibrium. We discuss the nature of the variation in temperature, vibrational energies, and component concentrations along the stream tube. A numerical analysis is made of the transition to equilibrium flow.     

Exergy efficiency of a counterflow air/air heat exchanger with vapour condensation

The exergy efficiency of a counterflow hot moist air/ambient air heat exchanger with vapour condensation as a function of the temperature and humidity of the hot moist air, the ratio of ambient air flow rate to hot moist air flow rate and the minimum temperature differences between the flows is determined. The ranges 20 to 120°C and 0.01 to 1.0 kg·kg^–1 for the temperature and humidity ratio of hot moist air respectively are considered. Constant ambient air conditions of 20°C and 0.01 kg·kg^–1 were assumed.

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Exergie-Wirkungsgrad eines Luft/Luft-Gegenstrom-Wärmetauschers mit Dampfkondensation

Zusammenfassung Der Exergie-Wirkungsgrad eines Gegenstrom-Wärmetauschers wird bestimmt für die Kombination: heiße Feuchtluft zu Umgebungsluft mit Dampfkondensation, und zwar als Funktion von Temperatur und Feuchtegrad der heißen Feuchtluft, des Verhältnisses von Umgebungsluft zu heißen Feuchtluftstrom und der minimalen Temperaturdifferenz zwischen beiden Strömen. Die Temperatur des heißen Feuchtluftstroms variiert im Bereich von 20 bis 120°C, sein Feuchtegrad im Bereich 0,01 bis 1,0. Bezüglich der Umgebungsluft wurden konstante Bedingungen angenommen, und zwar 20°C und ein Feuchtegrad von 0,01.

     

Effect of air injection method on the performance of an air lift pump

Air lift pump performance was investigated experimentally for different submergence ratios (the ratio between the immersed length of the riser and its total length) using different air injection footpiece designs. For this purpose an air lift pump with a riser 200 cm long and 2.54 cm in diameter, was designed and tested. Nine different air injection footpiece designs were used at four submergence ratios with different air injection pressures (from 0.2 to 0.4 bar). An area of 10 mm² was chosen and divided into nine injection hole arrangements (1, 2, 3, 4, 6, 15, 25, 34 and 48 holes) to cover the whole experimental range. Four submergence ratios were used for this work: 0.75, 0.7, 0.6 and 0.5. The experimental results showed a marked effect on the pump performance when operated with different types of injectors at different submergence ratios. The results indicated that the disk with three holes (D3) gives the highest efficiency at nearly all submergence ratios. Moreover, it is found that there is a suitable disk design for maximum water flow rate at every submergence ratio. Further, the highest efficiency resulted at the largest used submergence ratio, namely 0.75. The pump capacity and efficiency were found to be functions of air flow rate, lift ratio, and injection pressure.     

A track-laying air cushion vehicle

Almost no previous research has dealt with the design of a track-laying air cushion vehicle. Preliminary estimates indicated that the total power requirement would be high, so means of reducing the likely power consumption were studied. An analysis of the behaviour of three track layouts made it possible to compare their power efficiencies under a wide range of operating conditions. A two track articulated configuration was generally the most efficient. To minimize loss pressurised air the exit gap height between track and side skirt must be small, but an unstable heave motion is prone to develop under these conditions. The heave motion characteristics of a plenum air cushion were, therefore, investigated theoretically and guidelines for design established. These were used in the design of a $\text{3}\text{4}$ scale model of one track of a 20,000 N air track vehicle. The model incorporated a new type of side skirt assembly which can react automatically to vertical motion of the lower track run. The new skirt was stable in heave and was reasonably effective in avoiding local closure of the air exit gap when the track belt was raised on small simulated bumps. It was confirmed that the original estimates of blower power required by an air cushion track were of the right order.     

Statistics of the surface temperature field of an air/water interface under air flow

Experimental results are presented that reveal the relationship between the root mean square of the surface temperature field of an air/water interface (σ) and the heat flux (q′′) emanating from that interface, over a range of wind speeds. Experiments were conducted for wind speeds ranging from 1.0 to 4.0 m/s to determine if and how the σ versus q′′ relationship was affected by wind speed. Consistent surfactant coverage conditions were maintained for wind speeds ranging from 1.0 to 2.6 m/s, and these are the focus of the results presented herein. For wind speeds above 2.6 m/s the surfactant was consistently pushed downstream, resulting in an inhomogeneous surface condition for the air/water interface. For wind speeds less than 2.6 m/s the relationship between σ and q′′ is approximately linear and is weakly dependent on wind speed. The surface temperature field was obtained by infrared (IR) imaging. Sample IR images are presented in addition to the σ versus q′′ data. IR images are presented for surfaces covered with insoluble surfactants (liquid phase and solid phase), a soluble surfactant, and a clean water surface.

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The 2500 kilowatt a-c air arc

Summary During the latter part of 1957 and early 1958, consideration was given by the General Electric Co. toward the development of electric-arc discharge techniques to heat relatively large and continuous mass flows of gas to pressure levels and stagnation enthalpy levels comparable to those encountered in atmospheric flight up to satellite velocities. Such a device is, required for the study of aero-thermodynamic aero-thermoelatic and heat protection problems associated with hypersonic flight conditions. Testing of small models (approximately 1 in. in diameter) with wate-arc and air-arc units (50 to 100 kw dc) is sufficient for mateerials screening purposes, but larger size models (approximately 6 in. in diameter) must be utilized to obtain adequate structural information.Parametric studies were conducted to define facility requirements, model sizes and stagnation propeerties. Two 125,000-kva, 3-phase, 60-cycle a-c flywheel-type generators, located at the Switchger Development Laboratory of the General Electric Co. in South Philadelphia, were utilized to support this program. These generators have the potential of providing a source energy level of 50,000 kw; however, the initial phase of the program concentrated upon development of a unit capable of providing a jet energy level equivalent to 2500 kw. Such a unit can be adapted for use as a low-density wind tunnel capable of simulating free-flight model stagnation properties to Mach 25.Paper was presented at 1959 SESA Spring Meeting heald in Washington, D. C., on May 20–22.     

Self-entrainment of air on stepped spillways

The pseudo-bottom-inception point related to air entrainment is located further upstream on stepped spillways than on smooth spillways, for otherwise identical conditions. Its position is relevant concerning cavitation aspects, flow losses and flow depths. This Paper presents and discusses visual observations made with a high-speed camera and air concentration measurements in the vicinity of the pseudo-bottom air inception point on a stepped model spillway. Insight into the bottom aeration processes is provided, pointing at the effects of dynamic and turbulent air-phase surface troughs instantaneously protruding to the pseudo-bottom. In addition, the measured data were analyzed with regard to the extensions of these surface troughs. The trough bases were found to reach approximately 70–80% of the mixture flow depth upstream of the inception point, to 60–70% at the inception point and to 40–50% at the equilibrium flow region downstream of the inception point. The highly-turbulent character of developed flow is described and the general air transport process specified on the basis of air concentrations and related parameters.     

Convective instability of air in snow

Convective instability of air in the pores between ice crystals in snow is considered. In the Boussinesq approximation, a system of equations that describes the origin of thermal convection within the snow thickness is derived. It is shown that for snow, as for a liquid, there is a criterial number analogous to the Rayleigh number that determines the origin of air instability in snow. The contribution of natural convection of air to the heat- and mass-transfer processes in snow is estimated and possible reasons for the considerable scatter of reported experimental data on the thermal conductivity and diffusivity of snow are discussed. Kabardino-Balkarian State University, Nal'chik 360004. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 54–59, November–December, 1999.