基于CompactRIO的风洞喷管执行器位置监测系统开发

针对大型超声速风洞喷管设备,采用Compact RIO模块化仪器架构和LabVIEW开发平台,通过传感器、数据采集卡及上/下位机软件实现了对喷管执行器位置数据的采集、状态显示、分析、存储和预警等功能。利用该系统对2米超声速风洞喷管执行器进行监测分析,实验表明,该系统能实时显示喷管型面工作状态,及时判断故障产生的位置和超限情况,满足了执行器位置监测的实际需求,为操作者提供了有效的监测工具,提高了风洞喷管运行的安全性和可靠性。     

一种流场温度的测量方法

纹影技术可以测量流场的平均温度,对流场温度作定量计算。分析了流场温度定量计算的公式和原理,设计了一套透射式纹影测量装置。采用纹影图像分析法对温度进行标定。为了减小试验环境变化引起的纹影图像灰度不均匀对测量精度的影响,取图像中某一区域的平均灰度值代替某一点的灰度值作标定曲线。采用温度可控加热金属板作为测量对象,选取一系列温度点,同时利用纹影仪和Pt100对每一组温度值进行测量和记录。试验结果表明,对于加热金属板表面温度,纹影仪测量的温度值和Pt100测量的温度值具有较好的一致性;利用纹影仪对流场温度进行定量计算是可行的方法。     

白光纹影的流场检测及信息处理

介绍白光纹影流场检测系统的组成,测量原理和计算分析,并以酒精灯火焰和电吹风作为测试段的扰动场得到实验结果。纹影法的原理是用刀口在焦点处去切割光源像,把光线受流场的扰动转变为记录平面上的光强分布,从而对流场进行显示和测量。     

叶栅纹影试验图像增强及流场密度处理探讨

叶栅纹影图像的背景噪声和流场结构信息接近,给识别流场结构和获取定量信息带来了困难。采用加权L₀梯度平滑和伪彩色技术,提高纹影图像中关键流场结构的识别度。并探讨了通过标定纹影图像灰度与光线偏移量（刀口切割量）的函数关系,反演试验流场中的密度分布。研究结果表明,采用上述方法获得的流场纹影图像质量良好,叶栅通道内激波、尾迹和膨胀波的分辨率高,流场信息可读性强。验证了纹影图像及密度处理程序的可行性,但流场密度的准确测量需要在试验件加工装配、试验前光学调校和图像灰度标定等多方面开展细致的准备工作。     

超音速巡航导弹用轴对称进气道设计与研究

针对设计马赫数为4的超音速巡航导弹用进气道的特点,选取混压式超声速轴对称冲压进气道,进气道外罩唇口的内型面采用椭圆形的型面设计.给出了设计方法.采用k-ω湍流模型,数值求解雷诺时均N-S方程,模拟得到了在不同飞行马赫数和不同反压条件下的流场结构、流动特征、设计参数和计算结果.有效地模拟了马赫数为4时设计工况与非设计工况条件下的流场性能,并给出了高马赫数内、外混合复杂流动的计算结果,可为弹用超声速巡航进气道的设计提供参考.     

计算流动显示——概念,原理及实现

计算流动显示是近年来在流体领域出现的一个新的研究方向,是计算流体力学、实验流体力学和科学计算可视化等领域的结合。本文介绍了其概念和原理,描述了一种简单高效的基于光线投射方法的光线跟踪方法,用于构造计算流场的干涉图、阴影图和纹影图,并给出了计算与实验结果的比较。     

超声速轴对称进气道稳定工作范围研究

基于二维轴对称N-S方程,利用一阶迎风格式和k-ε湍流模型,对超声速轴对称外压式单/双锥进气道流场进行了数值模拟.所得流场结构清晰.研究结果表明:在设计马赫数为2.5时,对于长度相等且具有同等扩压特性的进气道而言,双锥进气道的总压恢复系数比单锥进气道高,且其稳定丁作范围更宽,然而,其出口马赫数比单锥进气道高.在超临界状态下,随着进气道出口反压的提高,结尾正激波向喉道方向移动,结尾激波损失减小,总压恢复系数提高,进气道出口流场畸变程度降低.     

小型轴流风扇内外部流场的数值研究

小型轴流风扇的性能及降噪研究建立在流场研究的基础之上。通过对风扇VD8025的Fluent数值模拟,展开了其内外部流场的分析研究,结论如下：在叶片吸力面（非工作面）侧存在主要由边界层分离引起的分离涡,在叶片压力面（工作面）侧顶部间隙存在二次流引起的叶顶间隙涡,沿轴向存在有限叶高诱导双旋涡。对风扇内部流场的速度分布进行了定量分析,分析的结果说明了上述旋涡等流动情况的存在。由风扇出口管道速度分布的定量分析可得,对于所研究的风扇,距离风扇出口120 mm处为排风最佳位置。     

锤击实验台冲击盘三维流场数值仿真

在锤击实验台控制优化的设计中,引信的性能直接影响到弹丸发射的精确性,通过测试引信性能的锤击实验台高速旋转受到空气阻力的作用,对冲击盘有重要影响,从理论上分析锤击实验台冲击盘的外流场非常重要。通过数值仿真,可以大大缩短冲击盘的改进设计周期,减少研制经费。建立了实验台冲击盘的三维计算模型,采用Navier-Stokes理论、以AN-SYS/FLOTRAN流场计算软件为平台对实验台冲击盘进行了三维流场数值仿真。得到了冲击盘外流场的速度及压力的分布图并对其进行了分析,仿真结果为实验台冲击盘的优化设计和三维旋转物体的流场模拟提供了理论参考。     

硬球-拟颗粒耦合模拟超声速流动

超声速流动广泛存在于航天航空和能源动力等领域,其中连续介质假设往往不再适用,需要充分考虑介质的离散性质。但传统上基于软球模型的分子动力学(MD)方法对于流动过程的模拟计算量过大,难以实际应用。本文利用硬球-拟颗粒耦合方法克服了软球MD方法计算量大和硬球MD方法可扩展性差的缺点,高效实现了超声速流动的微观离散模拟。通过超声速单球绕流和充气式返回舱实验装置等算例表明了该方法模拟含激波等剧烈变化的流场的可行性,以及在航空航天等工程领域的应用前景。     

Influence of numerical and viscous dissipation on shock wave reflections in supersonic steady flows

Numerical simulations are investigated to describe precisely the shock wave reflections in supersonic steady air flow field. The main objectives are to study the influence of the wedge trailing edge corner angle, of the numerical methods and of the viscous effects on the shock wave reflections and on the hysteresis behavior. The computations are done with different MUSCL-TVD finite volume schemes and the corresponding results are compared. The flow viscosity is also taken into account and comparisons are made between inviscid and viscous flow simulations. The results display the non-negligible influence of the numerical scheme accuracy on the results, mainly on the position and height of the Mach stem, and the relatively weak influence of the flow viscosity on these parameters. Comparisons between numerical results and experimental data have also been done and a good agreement is only observed for small wedge angles mainly due to the three-dimensional effects in the experimental setup.     

Electron‐optics of the Fast Intelligent Tracking (F!T) tube: A CRT without a shadow mask

Abstract— In this paper, we describe the electron‐optics involved in realizing a maskless CRT based on tracking the electron beams along horizontally aligned phosphor lines. We discuss the boundary conditions in order for the system to function. Emphasis is placed on the requirements of color purity, beam current, and spot size. A dedicated electron gun has been designed and tested. Results indicate that the spot‐size requirements for the feasibility of the concept can be met. The depth of focus, in terms of the allowed mismatch of the dynamic focusing voltage, is small. Inter‐beam space‐charge repulsion turns out to be unproblematic. The cathode drive is shown to lead to beam displacements that cannot be corrected. Consequently, a grid‐1 drive has to be used.     

用VC++开发Protel原理图显示库

电路原理图的显示是开发电路故障诊断等软件中的关键技术.利用Visual C 6.0和面向对象方法开发了Protel99原理图显示库.在分析Protel99原理图文件的格式的基础上,详细描述了显示库的主要的类和方法函数的设计原理.显示库在某电源测试台软件中得到成功的应用,稍作修改,便可用于其它矢量图形的显示,如AutoCAD图形.     

Aggregate growth and breakup in particulate suspension flow through a micro-nozzle

A computational study is reported on the growth of aggregates in flow of a particulate suspension through a micro-nozzle. The study employs a soft-sphere discrete element method (DEM) with van der Waals adhesion force between the particles in two-dimensional, incompressible channel flow. A new computational approach for particle transport in complex domains is developed which uses a background Cartesian grid for efficient flow field interpolation at the particle locations, together with a level-set method to represent the nozzle boundaries in the particle computation. Three mechanisms for the growth or breakup of particulate aggregates in the micro-nozzle are examined: (1) enhanced particle collision due to lateral compression as fluid elements pass through the nozzle, (2) stretching of aggregates due to axial stretching of fluid elements, and (3) collision and intermittent adhesion of particles to the nozzle wall. The first of these mechanisms leads to aggregate growth, and the second to aggregate breakup. The wall collision and adhesion mechanism can enhance either aggregate growth or breakup, but it is found in most cases to be a primary agent in the breakup of incident aggregates as part of the aggregate attaches to the nozzle wall and is torn from the remainder of the aggregate due to the high shear near the walls. Simplified models for these processes are developed and used to interpret the trends observed in the DEM simulations. The effects of particle adhesion parameter, particle size and density, particle concentration, and nozzle geometry are examined. It is found that passage of a particulate suspension through a nozzle can lead to either a substantial decrease in aggregate size or a modest increase under different conditions, depending in part on the size of the incident aggregates.     

整流型加油枪在柴油加注过程中的数值模拟与试验研究

应用计算流体力学软件Fluent,基于多相流VOF模型,进行加油枪加油时有、无整流管两种状态的模拟,得出的油箱内油气体积分数云图表明：加装整流管加注时油箱内流场更加稳定,产生的气泡更少。通过柴油加注试验,对比分析加油枪有、无整流管两种情况,得到不同加油阶段油液状态的图像,由此表明整流管有较好的整流效果,可有效减少油液面上油沫的产生。最后总结研究结论并对整流管的使用提出了建议。     

液体冲压发动机仿真模型研究

发展了一种弹用液体冲压发动机仿真模型.利用小偏离线性化理论和分段集总参数法,分别研究了超声速进气道、燃烧室和可调收敛喷管的建模方法.以正激波作为上边界,燃油流量的小变化作为扰动方程,喷管作为下边界,从而建立了液体冲压发动机仿真模型.根据所建立的仿真模型,对冲压发动机系统进行了仿真实验.仿真结果验证了仿真模型的有效性和合理性.该模型可用于液体冲压发动机控制系统的研究.     

Nano‐emissive display technology for large‐area HDTV

Abstract— Using nano‐emissive display (NED) technology, Motorola labs has successfully developed 5‐in. full‐color display prototypes. Carbon‐nanotube‐based field‐emission displays with a pixel size of 0.726 mm for a 42‐in. HDTV exhibit video image quality comparable to CRT displays and demonstrate a luminance of 350 cd/m². These novel low‐drive‐voltage NEDs take advantage of selective growth of CNTs to obtain the desired electron‐emission performance while maintaining inexpensive manufacturing due to a simple self‐focusing and self‐regulating planar structure. Improved video image quality and color purity are achieved with very low power consumption and without the need for an expensive focusing grid.     

Numerical investigation of air suction through the louvers of a funnel due to high velocity air jet

The present investigation predicts the suction flow rate from the atmosphere through the louvers of a funnel (used in naval and merchant ships) when the high velocity exhaust comes out from a nozzle or a set of nozzles placed inside the funnel. Conservation equations of mass and momentum have been solved for the funnel with a surrounding computational domain so that the suction can take place at the louvers entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two equation k-ε turbulence model. It has been found from the computation that the air suction rate into the funnel increases with the increase in louvers opening area, nozzle flow rate and height of the funnel. There exists optimum protrusion of the nozzle into the funnel for which maximum suction of air can be achieved with a prescribed nozzle flow rate and all other parameters of the funnel remaining fixed. Similarly there also exists optimum funnel diameter where the suction rate of air becomes the highest with all other parameters remaining fixed. There also exists optimum louver opening area on the funnel where the suction rate becomes the maximum as a function of the funnel diameter. The inclination of the funnel with respect to the vertical has no effect on mass ingress of air into it. An optimum nozzle diameter could be decided for a particular funnel diameter by considering the funnel suction rate and the back pressure developed by the nozzle per meter length of the pipe containing the nozzle (intersection of the two curves gives the optimum point of operation).     

Study of subsonic�Csupersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

We use an extended direct simulation Monte Carlo (DSMC) method, applicable to unstructured meshes, to numerically simulate a wide range of rarefaction regimes from subsonic to supersonic flows through micro/nanoscale converging–diverging nozzles. Our unstructured DSMC method considers a uniform distribution of particles, employs proper subcell geometry, and follows an appropriate particle tracking algorithm. Using the unstructured DSMC, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number on the flow field in micro/nanoscale nozzles. If we apply the back pressure at the nozzle outlet, a boundary layer separation occurs before the outlet and a region with reverse flow appears inside the boundary layer. Meanwhile, the core region of inviscid flow experiences multiple shock-expansion waves. In order to accurately simulate the outflow, we extend a buffer zone at the nozzle outlet. We show that a high viscous force creation in the wall boundary layer prevents any supersonic flow formation in the divergent part of the nozzle if the Knudsen number exceeds a moderate magnitude. We also show that the wall boundary layer prevents forming any normal shock in the divergent part. In reality, Mach cores would appear at the nozzle center followed by bow shocks and expansion region. We compare the current DSMC results with the solution of the Navier–Stokes equations subject to the velocity slip and temperature jump boundary conditions. We use OpenFOAM as a compressible flow solver to treat the Navier–Stokes equations.