谈谈流体中微粒的“功”与“过”

介绍了流体中掺杂的微小悬浮颗粒对人类健康和工程技术的影响,同时介绍了利用流体中微小悬浮颗粒增强混合,加快反应速度,提高传热效率等工程应用,最后介绍了利用流体中微小悬浮颗粒的跟随性和激光多普勒效应测量流体流动速度的激光多普勒测速技术（laser Doppler velocime-try,LDV）和粒子图像测速技术（particle image velocime-try,PIV）.     

亚微米颗粒在汇作用下运动机理的实验研究

当前,城市空气质量的不断恶化,引起了公众的普遍性关注.空气中的悬浮颗粒物,是城市大气环境重要污染源之一,其分布、运动及扩散规律已成为科学领域的研究热点.与连续流体不同,大气中的悬浮颗粒物是离散的,确定颗粒运动的模型是研究大气细微颗粒污染问题的关键.本文拟研究小空间静稳空气中亚微米级颗粒在汇作用下的运动规律,并构建其运动模型.在密闭实验空间中通过燃烧生成亚微米颗粒,利用静电吸附装置模拟颗粒汇,并通过粒子图像测速(particle image velocimetry,PIV)实验和激光多普勒测速仪(lasser Doppler velocimeter,LDV)实验技术测量分析不同空间内亚微米颗粒在大气中的热运动速度和在汇作用下的运动规律,并推导出颗粒物的速度分布经验公式.结果显示:粒子在汇作用下的运动与连续流体汇运动规律类似,但在小空间内颗粒的运动不满足流体连续方程;说明在无气流夹带输运情况下,利用汇作用及颗粒的扩散而发展的颗粒净化技术是可行的.     

全场测速技术进展

速度场测量技术的研究在流体力学和空气动力学中具有极高的学术意义和实用价值．文中归纳介绍了近十多年来人们积极探索的各种全场测速新技术,特别是激光诱导荧光高速流场测试技术、二维粒子跟踪和粒子图象测试技术以及三维测速的最新进展      

实验流体力学的粒子成像技术

<正> 1 引言 现代实验流体力学的一个重大成就是,发明并发展了整个标量场和矢量场的瞬态测量技术.这些技术包括测量标量的层析摄影干涉测量法(tomographic interferometry)(Hessetink1988)和平面激光诱发荧光法(Hassa et al 1987),以及测量速度场的核磁共振成像法(Leeet al 1987),平面激光诱发荧光法,激光散斑测速法,粒子跟踪测速法,分子跟踪测速     

光束穿越不同介质时LDV的测试及其误差分析

本文应用平面几何及光学原理,从理论和实践上分析了应用激光多普勒测速仪(LDV)进行实际测量时,在有窗口的情况下应该注意的几个问题,并给出了测量点位置偏差修正的定量公式以及光轴方向上测速精度相对误差的评估方程,省略了繁琐的理论推导.     

粒子图像测速技术研究进展

粒子图像测速技术(PIV)作为一种全新的无扰、瞬态、全场速度测量方法,在流体力学及空气动力学研究领域具有极高的学术意义和实用价值.本文对PIV技术的原理、分类作了简要地介绍,详细归纳和评述了现有的各种速度信息的提取方法,并对拓扑图论、神经网络、遗传算法、模糊聚类等新技术在PIV中的应用以及三维PIV技术、两相流PIV测试技术进行了介绍.指出当前PIV技术除了向三维和多相流方向发展外,如何提高PIV的测量精度以及缩短计算时间仍然是目前研究的主要目标.PIV技术随着计算机技术、激光技术和CCD性能的发展,必将取得更大的发展与突破      

激光测速数字相关信号处理器的研制

激光多普勒测速是当代流速测量技术中最具有实用价值和得到广泛应用的技术。多普勒信号处理器在整套测速系统中起着十分关键的作用。为赶超国际先进水平，本文作者独立研制开发出一种新型信号处理器。该处理器采用数字相关原理，对每个多普勒波群直接完成波群检测和自相关处理，得到其频率值。处理器与微机组成一体，各种参数的设置和控制全部采用软件。实测和应用表明，该信号处理器具有抗噪声能力强、功能完善、结构紧凑、成本低等优点，为实现智能化的信号处理和数据处理结合的激光测速系统创造了条件。     

超高速小弹丸激光片光测速系统的研制及应用

为满足轻气炮实验中对超高速小弹丸的测速需求,研制了一套激光片光测速系统.系统采用片光压缩技术、光谱滤光技术以及电路滤波和宽带放大技术,解决了超高速小弹丸测速成功率低和易受干扰的问题,测速信号具有较高的信噪比.在轻气炮实验中,该系统实现了对高速小弹丸的速度测量,与激光光束遮断法对比,测量结果的不一致性小于1％,系统的测量...     

弯曲槽道中湍流脉动的双点激光多普勒相关测量

应用双点激光多普勒测速装置对弯曲槽道中充分发展的湍流进行了相关测量，流动的雷诺数为５０００左右（以槽道中心速度为特征速度，以半槽宽为特征长度）．通过同时测量双点的瞬时流速，得到流向脉动速度沿流向、展向、横向的空间相关系数曲线，并应用条件采样技术（ＶＩＴＡ）对实验数据进行了分析     

INS／ESGM／Doppler组合导航系统中的Kalman滤波方法

根据战略核潜艇对水下组合导航系统的战术要求及可能的配备,建立了INS/ESGM/Doppler组合导航系统的工作模式,推导了该组合系统的集中式Kalman滤波算法,通过数字仿真将INS/ESGM/Doppler组合导航系统与INS/ESGM组合导航系统的性能进行了详细的比较,说明将多普勒测速系统引入组合导航系统并应用Kalman滤波技术,可有效地分别改善ESGM系统、INS系统及单纯的INS/ESGM组合系统的精度。     

Assessment of camera models for use in planar velocimetry calibration

The performance of three implementations of pinhole-based camera models for use in common light-sheet imaging arrangements is investigated on the background of application to particle image velocimetry (PIV) and Doppler global velocimetry (DGV). Calibration data obtained from translated planar calibration targets was found to yield camera attitude within 0.1° on four different test cases with object distance varying as little as 2% depending on the choice of camera model. Camera calibration using data from a single image of coplanar points is considered a viable alternative to manual triangulation of camera positions but is restricted to off-normal viewing directions.

Measurements of the gas and particle flow within a converging-diverging nozzle for high speed powdered vaccine and drug delivery

A unique system has been developed based upon the concept of accelerating pharmaceutical agents in particle form with a gas flow to attain sufficient momentum to enter the epidermis of human skin and achieve a pharmacological endpoint. This paper presents an experimental investigation of the transient gas and particle dynamics within a transonic converging-diverging nozzle prototype. The primary gas flow regimes are identified through Pitot-static pressure surveys and schlieren images with a high frame rate. The action of the gas flow-field in imparting momentum to the drug particles is investigated through schlieren imaging and time-resolved Doppler global velocimetry (DGV).Abbreviations DGV Doppler global velocimetry - CCD Charge coupled device - CST Contoured shock tube M.A.F Kendall and N.J. Quinlan contributed equally to this paper. Some of this work was originally presented at the 22nd International Symposium on Shock Waves, Imperial College, London, UK.     

Application of Doppler global velocimetry in cryogenic wind tunnels

A specially designed Doppler global velocimetry system (DGV, planar Doppler velocimetry) was developed and installed in a high-speed cryogenic wind tunnel facility for use at free stream Mach numbers between 0.2 and 0.88, and pressures between 1.2 bar and 3.3 bar. Particle seeding was achieved by injecting a mixture of gaseous nitrogen and water vapor into the dry and cold tunnel flow, which then immediately formed a large amount of small ice crystals. Given the limited physical and optical access for this facility, DGV is considered the best choice for non-intrusive flow field measurements. A multiple branch fiber imaging bundle attached to a common DGV image receiving system simultaneously viewed a common area in the flow field from three different directions through the wind tunnel side walls. The complete imaging system and fiber-fed light sheet generators were installed inside the normally inaccessible pressure plenum surrounding the wind tunnels test section. The system control and frequency-stabilized laser system were placed outside of the pressure shell. With a field of view of 300×300 mm², the DGV system acquired flow maps at a spatial resolution of 3×3 mm² in the wake of simple vortex generators as well as in the wake of different wing-tip devices on a half-span aircraft model. Although problems mainly relating to light reflections and icing on the observation windows significantly impaired part of the measurements, the remotely controlled hardware operated reliably over the course of three months.     

Heterodyne Doppler global velocimetry

Doppler Global Velocimetry (DGV) is an imaging flow measurement technique which allows the measurement of the velocity distribution in a plane. In DGV the frequency shift of scattered light from moving particles within the flow is used to determine the local flow velocity. Heterodyne Doppler Global Velocimetry (HDGV) is a new approach which combines the imaging and geometrical characteristics of DGV with the measurement principles of reference beam laser Doppler anemometry. The frequency shifted scattered light from the flow tracers is heterodyned with a reference beam from the same light source. Due to interference the result of this superposition is a harmonic intensity modulated signal. This signal is detected using a smart pixel detector array to obtain the velocity distribution. Two different experiments are presented. The first experiment compares the measured velocity distribution of a rotating disk with its actual velocity. The second experiment demonstrates the capability of the technique to measure a real flow.     

Laser Doppler measurements of flow in a cone-and-plate rheometer and the effect of cone misalignment

Laser Doppler velocimetry (LDV) is used to measure the flow profile of a Newtonian fluid in a cone-and-plate rheometer. The primary and secondary flow patterns are measured in the ideal geometry. The results confirm prior predictions of flow patterns. Flow profiles are also measured in the misaligned geometry in which the cone axis of rotation is tilted slightly off the perpendicular with the plate surface. Numerical predictions of these flow patterns (Dudgeon and Wedgewood, 1994) are also confirmed.     

Some tests of constitutive equations for entangled polymers based on planar-extension flow histories in a periodically constricted channel

Stress and velocity were determined locally by birefringence measurements and laser Doppler velocimetry for a mildly entangled polystyrene solution flowing at steady state in a rectangular channel with sinusoidally varying wall spacing. Having measured both the velocity and stress fields, we were able to test constitutive equations locally, i.e., without solving the equations of motion for the entire flow. Four were examined for the periodic planar extensions on the channel centerplane: the Newtonian model, the Lodge network model, the Doi-Edwards tube model, and the Wagner-Schaeffer modification of Doi-Edwards. High enough Weissenberg and Deborah numbers were reached to produce sizable departures from the Newtonian predictions. The Doi-Edwards model underpredicted the stress, as did Wagner-Schaeffer, although to a lesser extent. Predictions of the Lodge model were best of all, a surprising result in view of its inadequacy for simple shear deformations. The predictions of the Lodge model, without parameter adjustment, agreed remarkably well with the planar extension data over the accessible range for our apparatus: Deborah numbers up to 2.0, extensional Weissenberg numbers up to 6.5, and a maximum extension ratio of about 2.3.     

Imaging laser Doppler velocimetry

Imaging laser Doppler velocimetry (ILDV) is a novel flow measurement technique, which enables the measurement of the velocity in an imaging plane. It is an evolution of heterodyne Doppler global velocimetry (HDGV) and may be regarded as the planar extension of the classical dual-beam laser Doppler velocimetry (LDV) by crossing light sheets in the flow instead of focused laser beams. Seeding particles within the flow are illuminated from two different directions, and the light scattered from the moving particles exhibits a frequency shift due to the Doppler effect. The frequency shift depends on the direction of the illumination and the velocity of the particle. The superposition of the two different frequency-shifted signals on the detector creates interference and leads to an amplitude modulated signal wherein the modulation frequency depends on the velocity of the particle. This signal is detected using either a high-speed camera or alternatively a smart pixel imaging array. This detector array performs a quadrature detection on each pixel with a maximum demodulation frequency of 250 kHz. To demonstrate the feasibility of the technique, two experiments are presented: The first experiment compares the measured velocity distribution of a free jet using ILDV performed with the smart pixel detector array and a high-speed camera with a reference measurement using PIV. The second experiment shows an advanced setup using two smart pixel detector arrays to measure the velocity distribution on a rotating disk, demonstrating the potential of the technique for high-velocity flow measurements.     

Two-color particle image velocimetry technique for an internal combustion engine

A two-color particle image velocimetry (PIV) technique has been applied to a single-cylinder motored research engine. Two-color PIV is a quantitative planar velocity measurement technique that can unambiguously determine the velocity magnitude and direction.

The work includes the development of an interrogation system, a series of computer simulations to determine the performance of the technique under various conditions, the comparison of these results to similar ones obtained for an autocorrelation PIV system, and a test of the technique by reconstructing the velocity field of a uniform jet flow.

The technique was then applied to the in-cylinder flow field of a motored single-cylinder, cup-in-head, research engine. A total of 27 instantaneous velocity fields were obtained at a single measurement plane for a single operating condition of the engine. The data were analyzed to yield ensemble-averaged velocity and velocity fluctuation.     

Planar flow field measurements in atmospheric and pressurized combustion chambers

The investigation of velocity fields in complex combustor flows is an important and necessary subject of propulsion technology. A persisting problem in computational fluid dynamics (CFD) modeling is that current numerical design tools have a number of deficiencies in accurately predicting the complex combustor flow. Using planar techniques such as planar Doppler velocimetry (PDV) or particle image velocimetry (PIV) it is possible to provide detailed information of the flow field inside the combustor. This paper reports on the applicability of PIV in combustor flows at realistic operating conditions.     

Single-camera Doppler global velocimetry based on frequency modulation techniques

The main advantage of the described Doppler global velocimeter (DGV) systems based on frequency modulation (FM) or frequency shift keying (FSK) is that no reference detector is required. The frequency variation of the laser light during one modulation period additionally allows an on-line calibration of the complete DGV system. Thus, the new method has the potential to reduce the uncertainty of conventional DGV velocity measurements since time resolved velocity field measurements on a spinning disc have shown standard deviations down to 0.02 m/s. On investigating flow fields, velocity components notably less than 0.5 m/s were resolved.