Cross-correlation Doppler global velocimetry (CC-DGV)

A flow velocimetry method, cross-correlation Doppler global velocimetry (CC-DGV), is presented as a robust, simplified, and high dynamic range implementation of the Doppler global/planar Doppler velocimetry technique. A sweep of several gigahertz of the vapor absorption spectrum is used for each velocity sample, with signals acquired from both Doppler-shifted scattered light within the flow and a non-Doppler shifted reference beam. Cross-correlation of these signals yields the Doppler shift between them, averaged over the duration of the scan. With presently available equipment, velocities from 0 ms⁻¹ to over 3000 ms⁻¹ can notionally be measured simultaneously, making the technique ideal for high speed flows. The processing routine is shown to be robust against large changes in the vapor pressure of the iodine cell, benefiting performance of the system in facilities where ambient conditions cannot be easily regulated. Validation of the system was performed with measurements of a model wind turbine blade boundary layer made in a 1.83 m by 1.83 m subsonic wind tunnel for which laser Doppler velocimetry (LDV) measurements were acquired alongside the CC-DGV results. CC-DGV uncertainties of ±1.30 ms⁻¹, ±0.64 ms⁻¹, and ±1.11 ms⁻¹ were determined for the orthogonal stream-wise, transverse-horizontal, and transverse-vertical velocity components, and root-mean-square deviations of 2.77 ms⁻¹ and 1.34 ms⁻¹ from the LDV validation results were observed for Reynolds numbers of 1.5 million and 2 million, respectively. Volumetric mean velocity measurements are also presented for a supersonic jet, with velocity uncertainties of ±4.48 ms⁻¹, ±16.93 ms⁻¹, and ±0.50 ms⁻¹ for the orthogonal components, and self-validation done by collapsing the data with a physical scaling.     

Measurement of absolute flow velocity vector using dual-angle, delay-encoded Doppler optical coherence tomography

Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.     

固体火箭发动机羽流流速TDLAS测量方法研究

针对现有对固体火箭发动机推进剂燃烧时产生的羽流流速测量方法的不足,提出了将可调谐半导体激光吸收光谱（TDLAS）技术应用于羽流流速的测量方法,通过测量燃烧产物中H₂O分子位于1 392 nm处的单根吸收谱线特征,根据多普勒效应建立的光谱频移和分子速度之间的关系来获得气流流速,解决了接触式测量方法会干扰羽流场和传统非接触式测量中示踪粒子不均匀的问题,并且取得了有效试验数据,通过对试验数据进行分析处理,得到了发动机的羽流流速。     

Effect of wall scattering on SNR in off-axis differential-type laser Doppler velocimetry

Though various properties and applications of laser Doppler velocimetry have been extensively studied in the past decade, there is little discussion on the effect of light scattering from the surface of a cell on Doppler beat signals or on methods of reducing it. In this paper, the effect of light scattering from the surface of the cell is treated as a background noise and is studied theoretically and experimentally on the detecting process of Doppler beat signals in off-axis differential-type laser Doppler velocimetry. Laser Doppler velocimetry of an off-axis type is verified to be effective for measurement of the flow velocity in the vicinity of a scattering wall. The effect of the light scattered from the wall surface on the signal-to-noise ratio (SNR) of Doppler beat signals is discussed in detail. The minimum distance, which is close to the wall and at which good Doppler beat signals can be obtained, is defined and determined quantitatively. This minimum distance is found to be strongly affected by the off-axis angle of the detecting optical system.     

光学相干层析多普勒成像功能拓展研究

光学多普勒成像(Optical Doppler tomography,ODT)是一种结合了光学相干层析成像技术(Opticalcoherence tomography,OCT)和多普勒流速仪的非侵入、非接触的成像技术,能够实现对高散介质组织内部的血管分布和血液流速的探测。阐述了基于数字希尔伯特变换的相位分离多普勒光学相干层析成像技术的工作原理,并且通过对玻璃毛细管和生物芯片微通道管中聚苯乙烯溶液流速的实验测量,准确测量管内微粒缓慢移动时的多普勒频移量,获得了玻璃管内和生物芯片微通道管中流速分布曲线,证实了所提方法的可行性。获取的多普勒图像具有较高的空间分辨力和速度分辨力,在未来的临床应用中有潜在的应用价值。     

Extrinsic fibre-optic sensors for remote measurement: Part two

The impact of incorporating fibre optic components into well established optical techniques such as laser Doppler velocimetry, non-contact vibration measurement, holography and light scattering, is discussed in the two sections of this paper. The possibilities range from simply including a fibre ‘optic link’ in a conventional system to facilitate measurements in difficult or remote areas, to the realization of entirely new optical configurations in which virtually all of the conventional optical components have been replaced by their fibre-optic equivalents. In part two laser velocimetry, vibration measurement, holography and scattering are discussed.     

Simultaneous 2D flow velocity and gas temperature measurements using thermographic phosphors

In this paper a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented. The phosphoric particles respond to the temperature changes in the flow while acting as tracers for velocity mapping. The temperature sensitive particles were seeded into a heated flow and were excited by a pulsed UV laser. The subsequent red shifted emission was detected and analyzed to infer temperature using calibration procedures for lifetime and emission spectra against temperature. The diameter of the temperature sensitive particles, usually in the range of 1–10 μm, makes them useful for velocity measurements using particle image velocimetry (PIV). As such, simultaneous measurement of temperature and flow velocity of a gaseous flow were performed and presented. PACS  42.62.-b; 47.80.Cb; 47.80.Fg     

In vivo bidirectional color Doppler flow imaging of picoliter blood volumes using optical coherence tomography

We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-microm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.     

Digital Holographic Particle Tracking Velocimetry for 3-D Transient Flow around an Obstacle in a Narrow Channel

Digital holographic particle tracking velocimetry (PTV) is developed by single high-speed camera and single double pulsed laser with high frequency pulses. This system can directly capture 1000 hologram fringe images for 1 second through a camera computer memory. The 3-D particle location is made of the reconstruction by using a computer hologram algorithm in a personal computer. This system can successfully be applied to instantaneous 3-D velocity measurement in the water flow with a square obstacle, and can obtain an average of 300 instantaneous velocity vectors.     

基于可调谐半导体激光吸收光谱技术的高速气流流速测量方法研究

以激光Doppler效应为原理,结合可调谐半导体激光吸收光谱技术的窄线宽、可调谐优势, 可实现高速气流流速的实时在线检测.介绍了流速测量的基本原理和方法,搭建了双光路流速测量系统, 利用DFB激光器对位于1398 nm处的水汽吸收线进行10 kHz快速扫描,获得高速气流的实时光谱信息, 并根据两路吸光度曲线之间的Doppler频移来反演气流流速.介绍了频率标定和Doppler频移测量的方法. 在风洞上进行了流速测量验证性实验,将流速测量结果与理论计算结果进行了对比,二者之间符合得较好, 初步证明了该方法的可行性.分析了系统的性能及可能引起流速测量误差的因素,以便系统进一步优化.     

Doppler angle and flow velocity mapping by combined Doppler shift and Doppler bandwidth measurements in optical Doppler tomography

Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information.     

组合时延估计及人工时延方法用于脉冲相干多普勒测速去模糊

提出了一种改进的脉冲相干多普勒测速的速度模糊消除方法,将待测速度空间以两倍最大可测速度的间隔划分为一系列速度区间,使得对任意速度的测量转化为对速度区间的确定和区间内速度偏移量的测量,通过"相关-相位"组合法进行精确时延估计,实现无模糊速度测量;提出"人工时延"的方法,消除在速度区间边界值附近可能存在的速度跳变;与传统的速度解模糊方法相比,该方法仅需要对多次人工时延的方案进行计算,无需多次测量,且理论上不受流速范围的限制;通过仿真和实验对该方法的有效性进行了验证。      

相关时延及频谱不对称对声学多普勒测速偏差影响

研究了复协方差频移估计测速下相关时延及接收信号频谱幅值不对称对声学多普勒测速偏差的影响.不考虑测速公式简化误差,复协方差频移估计测速偏差可以简化为多普勒频移测量偏差.经推导,不考虑发射信号波束开角的窄带测频无偏、宽带测频有偏;考虑波束开角的窄带测频和宽带测频均有偏.相关时延不准确且频谱不对称是该偏差的重要来源.仿真分析...     

全光纤速度干涉仪设计及应用

针对冲击波物理与爆轰物理等研究领域中对高速运动物体进行连续速度测量的需求,设计了一种全光纤速度干涉仪.该干涉仪采用单模光纤作为光传输和延迟元件,对t和t-τ两个时刻由于速度变化而引起的多普勒差拍信号进行检测.由于两个时刻的两束光信号对应的待测物体速度变化不大,因而两者几乎有相等的频移量,从而大大降低了差拍信号频率.并且,通过光纤长度的改变,灵活调节条纹常量（τ值）,使差拍信号频率不超过记录系统的带宽,从原理上解决记录系统响应带宽受限问题,拓展测速的上限.单模光纤的采用,对漫反射光起到了较好的选模作用,使干涉仪实现了对漫反射靶的测量.实验设计了1.5 m·s-1和150 m·s-1两种条纹常量,对低速过程的霍普金森杆实验和高速过程的激光驱动实验分别进行了测试,取得较好结果,证明了该干涉测试技术的有效性.     

Doppler velocimetry in a supersonic jet by use of frequency-modulated filtered light scattering

A new nonintrusive velocimetry diagnostic that combines the sensitivity of frequency-modulated (FM) absorption spectroscopy techniques and the spectral discrimination afforded by atomic-vapor absorption filters is presented. Doppler-shifted light from a FM Ti:sapphire laser scattered from a supersonic flow is imaged through a potassium-vapor cell and is detected by FM spectroscopy. The difference between the potassium resonance frequency and the laser frequency when the scattered light is in resonance is the flow-induced Doppler shift.     

波束开角对多普勒测频结果的影响*

具有不同波束开角的声学多普勒测速设备未标定的测速结果存在偏差。基于水底椭圆散射模型研究了波束开角对声学多普勒测速结果的影响,对提高声学测速性能具有实际意义。水底椭圆散射模型下,足印上不同方位传播损失和散射强度存在差异,导致频谱不对称,测频结果偏小。利用不对称系数量化频谱不对称程度,若波束开角增大,方位不对称系数随之增大,测频偏差增大,推导了波束开角导致的测频偏差解析式。分析仿真和外场试验数据测频结果可知,不同多普勒频移下测频偏差和理论计算值相符,不同波束开角下实际测频偏差与理论公式计算的测频偏差均随波束开角增大而增大。     

The influence of correlation delay and spectral asymmetry on acoustic Doppler velocimetry bias

The influence of correlation delay and spectral amplitude asymmetry of the received signal on acoustic Doppler velocimetry bias with the complex covariance approach are studied.Neglecting the simplifying error of the velocimetry formula,the velocimetry bias is simplified to the Doppler shift measurement bias.It is deduced that if not considering the beam angle,the narrowband frequency measurement is unbiased while the broadband frequency measurement is biased;and if considering the beam angle,th...     

Imaging and quantifying transverse flow velocity with the Doppler bandwidth in a phase-resolved functional optical coherence tomography

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT.     

Intracavity Rayleigh-Mie scattering for multipoint, two-component velocity measurement

A simultaneous multipoint, two-component Doppler velocimeter is described. The system uses two optical cavities: a Fabry-Perot etalon and an optical cavity for collecting and recirculating the Rayleigh-Mie-scattered light that is collected from the measurement volume in two parallel but opposite directions. Single-pulse measurements of two orthogonal components of the velocity vector in a supersonic free jet were performed to demonstrate the technique. The recirculation of the light rejected by the interferometer input mirror also increased the signal intensity by a factor of 3.5.     

Doppler radial velocity detection based on Doppler asymmetric spatial heterodyne spectroscopy technique for absorption lines

Doppler asymmetric spatial heterodyne spectroscopy(DASH) technique has developed rapidly in passive Dopplershift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift sensitivity,compact,and rugged structure,DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work.Unlike atmospheric emission lines,almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars,so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established.According to the analysis of the components of the interferogram received by the detector array,we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines.In the end,numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out.The simulation results show that the relative errors of the retrieved speeds are less than 0.7% under ideal conditions,proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.