Constant-bandwidth constant-temperature hot-wire anemometer

A constant-temperature anemometer (CTA) enables the measurement of fast-changing velocity fluctuations. In the classical solution of CTA, the transmission band is a function of flow velocity. This is a minor drawback when the mean flow velocity does not significantly change, though it might lead to dynamic errors when flow velocity varies over a considerable range. A modification is outlined, whereby an adaptive controller is incorporated in the CTA system such that the anemometer's transmission band remains constant in the function of flow velocity. For that purpose, a second feedback loop is provided, and the output signal from the anemometer will regulate the controller's parameters such that the transmission bandwidth remains constant. The mathematical model of a CTA that has been developed and model testing data allow a through evaluation of the proposed solution. A modified anemometer can be used in measurements of high-frequency variable flows in a wide range of velocities. The proposed modification allows the minimization of dynamic measurement errors.     

An alternative mathematical model of vane anemometers based on the balance of power

Anemometers based on the exchange of momentum between the flow and rotating measuring element comprise an important class of instruments used in flow metrology, especially in meteorological and ventilation measurements. In these instruments, overvaluation of the measured average velocity, caused by the inertia of their rotors, takes place. To analyse this phenomenon and the dynamics of the measurement process, as well as to estimate and minimize the measurement uncertainty, it is required to be acquainted with the mathematical model of the anemometer. In this study, the model of the vane anemometer based on the equation of motion of its rotor available in the literature is analysed, and a new model based on the power balance is proposed. Model testing and a comparison of both models has also been performed.     

基于最小二乘法的旋转风速仪误差校正研究

旋转风速仪测量误差会导致风电场发电机组发电量损失、电能质量下降。通过测量实验对比三杯式风速仪和超声波风速仪,得出误差产生的主要因素是3.5 m/s以上三杯式风速仪的"过高效应"。该文提出一种风速测量校正方法,基于最小二乘法对三杯式风速仪的测风误差进行校正,能有效减小风电场测风系统测量误差。     

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry technique flow are presented. The hot-wire calibration is based on the determination of the acoustic velocity reference value through an acoustic pressure measurement and their relationship using a linear acoustic model. In this model, an analytical approach involving the coupling between the sound source and the resonant cavity effects and the viscous and the thermal effects in the boundary layers is used. The amplitude and phase calibrations are reported for the first time, simultaneously, either by varying the sound source input voltage for a fixed frequency, or by varying the frequency for a given source input voltage. The amplitude calibration is detailed by using a filtering technique to eliminate either the acoustic streaming effects or the anemometer basic electric voltage variations effects. This provides a simple way to an amplitude calibration with good accuracy when measuring an average of a stationary oscillating velocity. The phase calibration is proposed here by considering the phase difference between the microphone and the hot-wire anemometer output signals. The results obtained by using a simple fluid-filled resonant cavity are encouraging on the feasibility of this method to carry out a first-order acoustic velocity measurement. However, the complexity of the dynamic calibration due to that of the heat transfer mechanism around the hot-wire probe in various frequency ranges clearly merits more investigation.     

Digital technique for the simultaneous measurement of velocity and temperature

A computer-oriented, hot-wire anemometer technique for the simultaneous measurement of velocity and temperature in heated turbulent flows is described. This technique involves conversion of analogue anemometer voltage signals into digital forms and processing of these latter on a digital computer, in accordance with the anemometer response equations, to obtain instantaneous temperature and velocity. The technique was tested with a heated plane jet and found to be satisfactory.     

A high-linearity DC planar Ionic anemometer

A high-linearity DC planar ionic anemometer which can measure the airflow velocity of boundary-layers near a surface was constructed and tested. The differential anemometer described in this paper includes two symmetrical cathodes and one anode with a sharp tip. High voltage is applied to the anode to generate a symmetrical ionic discharge, and then the airflow deflects the symmetrical ion distribution and produces a differential current between the two cathodes. It can detect bidirectional airflow velocity and is more crash-resistant than traditional hot-wire anemometers. It has minimum impact on the airflow profile because of its thin-shape design and achieves high measurement accuracy. A series of tests have been done for the static characteristics and dynamic performance by changing structural parameters such as cavity depth, gap width, anode tip angle, cathode width and length. The results show that the cavity depth is the most important structural parameter since it has the greatest effect on the stability of the gas discharge, which is affected by ion mobility and friction between ions and the bottom of cavity. The gap width plays a decisive role in the current and sensitivity values. Besides, the uncertainties of the tests have been analyzed by introducing the error bars and the testing errors are in reasonable ranges. The anemometer is cost-effective and offers the possibility of building a MEMS version in the future.     

Measurement range expansion of continuous wave ultrasonic anemometer

This study was conducted to expand the measurement range of a continuous wave ultrasonic anemometer (CWUA) that uses phase difference measurement. A CWUA has a narrower measurement range than conventional ultrasonic anemometers because it can measure the phase difference up to the half-cycle of the used ultrasonic signals. In this study, a method of expanding the measurable range of the phase difference using a phase delay circuit and a frequency divider was developed. Through experiments, it was found that this method doubled or quadrupled the measurement range when the method was used. Furthermore, an algorithm for determining the validity of the measurement data by comparing them with the previous data was implemented with a wind velocity measurement error of less than ±1 μs to solve the problem caused by the use of the frequency divider and to produce a stable measurement system.     

基于Zigbee技术的矿用无线智能便携式风速表

为解决目前煤矿风速检测工作中存在的问题,采用基于Zigbee技术的无线微控器CC2430设计了具有无线通信功能的便携式智能风速表.给出了风速表总体结构,并介绍了详细的软硬件设计.在通风仿真实验室环境下进行了风速测量及无线通信试验,结果显示该风速表提高了风速检测的准确性,完成了数据的传输功能并实现了对检测人员的跟踪.该风...     

Potential accuracy of methods of laser Doppler anemometry in the single-particle scattering mode

Potential accuracy of methods of laser Doppler anemometry is determined for the singleparticle scattering mode where the only disturbing factor is shot noise generated by the optical signal itself. The problem is solved by means of computer simulations with the maximum likelihood method. The initial parameters of simulations are chosen to be the number of real or virtual interference fringes in the measurement volume of the anemometer, the signal discretization frequency, and some typical values of the signal/shot noise ratio. The parameters to be estimated are the Doppler frequency as the basic parameter carrying information about the process velocity, the signal amplitude containing information about the size and concentration of scattering particles, and the instant when the particles arrive at the center of the measurement volume of the anemometer, which is needed for reconstruction of the examined flow velocity as a function of time. The estimates obtained in this study show that shot noise produces a minor effect (0.004–0.04%) on the frequency determination accuracy in the entire range of chosen values of the initial parameters. For the signal amplitude and the instant when the particles arrive at the center of the measurement volume of the anemometer, the errors induced by shot noise are in the interval of 0.2–3.5%; if the number of interference fringes is sufficiently large (more than 20), the errors do not exceed 0.2% regardless of the shot noise level.     

A Superheterodyne Three-Component Laser Doppler Anemometer

The design, method of tuning, and operating principle of a three-component laser Doppler anemometer with a symmetrical heterodyning optical system are described. The use of an optical frequency modulator with a 100% modulation factor and its possibility of continuously changing the light frequency allows the anemometer to operate in a superheterodyne mode. The range of measured velocities is from 1 mm/s to 50 m/s. The relative error of the velocity measurements in a multiparticle regime is at most 5%. The methodological capabilities of the instrument are demonstrated for an example of measuring the gas velocity field in a prototype of a vortex tube. It is pointed out that the anemometer can operate under forward and backward laser-light scattering conditions.     

一种基于最小均方差算法的散斑图像微位移测量系统

为了满足微位移量的实时、非接触测量的需要,研制了基于散斑图像的一种嵌入式微位移测量系统,它是基于最小均方差法和DSP处理器(TMS320DM642)设计的.重点阐述软件系统和实验系统的设计与实现方法,并在不同运动速度和表面粗糙度的条件下,对其测量系统进行实验和数据分析.实验结果表明,该测量系统是可行有效的.     

组合热膜式流速矢量传感器

针对在微型飞行器上测量空气流速矢量的需要,提出了一种比空速管轻巧、比热线式流速传感器抗干扰能力强的微型热膜式流速传感器及其组合系统.与热线式流速传感器相似,热膜流速传感器仅输出电阻值信息,对流速和流向均敏感.将多个传感器按照一定规律组合,可实现对一定角度范围内的流速矢量的测量,从而拓展其应用.结合试验推导了组合传感器测...     

高精度超声风速测量系统设计与实现

时差法是超声风速风向测量系统的基本方法.文中首先对影响时差法测量精度的因素进行分析,针对这些影响因素,在超声换能器设计、阵型设计、电路系统设计和信号处理算法等方面提出了提高系统精度的设计方案,并制成样机.实验测试表明,文中所实现的系统已经基本达到国际尖端产品的测量精度,且具有体积小、可靠性高等优点,具有很高的实际应用价值.     

Experimental study on acoustic vector tomography of 2-D flow field in an experiment-scale furnace

An experiment study is performed on acoustic measurement of 2-D dynamic fields in a cold experimental scale furnace. By the acoustic method, the velocity field is restored with the vector tomography from the reciprocal acoustic travel time data measured. Regarding the measuring system, piezoelectric speakers and pickups are used as transmitters and receivers, which can stimulate powerful acoustic signal resource and receive the acoustic signal stimulated from long distance respectively. A high-pass digital FIR filter is designed for the signal filtering, and the signal correlation analysis by correlation coefficient is performed to obtain accurate acoustic transit time data from the filtered simulated and received acoustic signals. In the experiments, two different cases are tested, respectively symmetric and asymmetric flow fields. To validate the flow field recovered by the acoustic method, under the same conditions, the symmetric velocity field is measured by a hot-wire anemometer at some points and simulated with CFD software, and the asymmetrical velocity field is simulated. It is proved that the flow fields recovered by the acoustic method are reasonable and reliable. As a whole, from the experiment results, the acoustic measuring system and method developed in this paper is applicable in measuring the 2-D flow field in a cold experimental set-up and similarly in cold large-scale industrial furnaces. Additionally, the extension of the method to hot furnaces is discussed too.     

Determination of the velocity and size of bubbles in two-phase flows by using a laser doppler anemometer

Natural oscillations of a spherical interface between a gas and a liquid in a bubble are registered. A possibility of measuring the geometric parameters of stationary and moving particles of the disperse phase by a laser Doppler anemometer is demonstrated. A method for simultaneous determination of the size and velocity of a bubble or a droplet in a two-phase flow is developed. The mean sizes of a group of bubbles settled on a ruler are compared: the results are obtained by two independent methods, i.e., by analyzing the image and by processing the Doppler signal containing information about the natural oscillations of the spherical interface between the media. A possibility of using a laser Doppler anemometer for simultaneous measurements of the velocity and size of bubbles or droplets in a two-phase flow is confirmed.     

Systematic investigation of pipe flows and installation effects using laser Doppler anemometry—Part II. The effect of disturbed flow profiles on turbine gas meters—a describing empirical model

For systematic investigations of installation effects and for finding efficient ways to minimise these effects, a research project was initiated at the PTB. It covers the design of an automated test facility using a laser Doppler anemometer, the measurement of velocity profiles downstream of several pipe configurations and flow conditioners, as well as the measurement of the change in the gas meter behaviour, namely the shift of the error curve due to the disturbed velocity profiles.

Part I of this paper (presented in this issue) describes the test facility for the investigation of installation effects and shows the relation between pipe configuration and disturbed flow profile for a wide variety of pipe configurations and flow conditioners.

The second part compares the error shift of turbine meters with the characteristic of disturbed flow profiles. For this, three flow field parameters are used to quantify the disturbances of the velocity profiles such as the swirl intensity, flatness and asymmetry of the profile. Considering this, an empirical model is presented to explain the error shift of a turbine meter as a function of these three flow field parameters. The model will be verified for three types of turbine meters and the results will be discussed.     

Investigation on the determination of flow direction using two parallel cylindrical hot film sensors

Measurement of instantaneous air flow velocity with high frequency can be carried out by using a hot wire anemometer (HWA). HWA works on the basis of heat transfer rate from hot wire to the fluid flow, therefore directional identification of the air flow using hot wire anemometer is a difficult task. By using two parallel cylindrical hot film sensors a probe was built. By considering the wake and heat effect of the upstream sensor on the downstream sensor, direction of the air flow can be identified. In this work, the wake and heat effect resulting from the upstream sensor to the velocity measurement, by the downstream sensor was studied. This measured velocity is dependent of the following factors namely; air velocity, upstream sensor overheat ratio, distance between the two sensors and turbulence intensity of the flow. As a result it was found that the manufactured probe with sensor distance of 1 mm apart is capable of measuring reverse flow measurements of up to 20 m/s for a moderate turbulent flow.     

Analysis of acoustic Doppler current profiler mean velocity measurements in shallow flows

Acoustic Doppler current profilers (ADCPs) are commonly used instruments for measurement of natural streamflow and flow in manmade channels. Velocities measured in a profile by the instrument are used to estimate the discharge in a channel. A Teledyne RD Instruments StreamPro ADCP was used to measure the mean velocity simultaneously with a laser Doppler anemometer (LDA) in a laboratory flume. An average of 3.9% under-prediction of the mean velocity measured by the ADCP occurred when compared to the measurements of the LDA. Moreover, this study shows that the sampling duration of the measurements significantly impacts the mean point velocities measured by up to 50%.     

Reproduction of air velocity in the entrance region of the test pipe in a wind tunnel

The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.     

气枪喷嘴除尘除水效率的实验研究

利用图像处理的方法对小尺度气枪喷嘴冲击射流的除尘除水效率进行研究,实现了对喷嘴除尘除水效率的定量测量。利用该方法对影响气枪喷除尘除水效率的各种因素进行研究,并将实验结果与用热线风速仪测量的结果进行了比较,得到了关于喷嘴工作最佳工况的一些结论。这些结论可对了解喷嘴的除尘除水工作原理及对气枪喷嘴进一步改进和优化提供帮助。