Abstract
This study investigates the uncertainty of the A/D converter when measuring multi-scale turbulence fluctuations using a hot-wire anemometer. The flow is generated in a low-speed wind tunnel, ...the turbulence is generated by a turbulence grid and the fluctuations are measured. A compact hot-wire anemometer was used and a high accuracy A/D converter was introduced for the measurements. Methods to minimise the influence of noise were also incorporated and measurements were carried out in two situations, one with and one without turbulence. The experimental results showed that measurements under a specific condition (Case 1 in this study) had the sufficienty reproducibility of turbulence fluctuations and the least effect of noise. The results showed that the high frequency characteristics of the turbulence could also be accurately measured under this condition. In conclusion, it is clear that the choice of a suitable A/D converter and the optimisation of the measurement environment are critical for turbulence measurements with a hot-wire anemometer.
•Monitoring of wind speed at different elevations with LiDAR technology.•Analyzing the characteristics of wind at a site in the Lake Erie area.•Determination of wind turbine capacity factor from ...LiDAR monitored wind data.•Comparison of estimated wind turbine capacity factor with that based on monitoring data.
Wind energy potential assessment is crucial for proper wind farm siting. Typically, this involves installation of tall and costly meteorological masts with anemometers. New technology such as Light Detection and Ranging (LiDAR) is an alternative mobile technology that serves such purpose. This paper describes the principle of LiDAR technology and presents case studies of its applications to evaluate the energy output potentials at the site near Lake Erie in northern Cleveland, Ohio, USA. A ZephIR® LiDAR system is used to monitor one-year of vertical wind data profile (at 30m and 70m height) from May 2011 to April 2012, from which the wind statistics are determined. These include the monthly average of wind speed, turbulence intensity, Weibull shape and scale factor, wind compass rose, and wind power density, etc. The wind speed data is used to evaluate the wind power capacity factors for prototype wind turbines that are subsequently installed in 2012. The data of power output by the turbines between 2013 and 2015 is used to compare with those predicted based on wind speed model derived from LiDAR measurement. The results show that the estimated wind turbine’s capacity factor from LiDAR data is satisfactory after excluding the maintenance days. This research demonstrates the potential of LiDAR technology as a cost effective way in providing reliable evaluation of wind energy potential.
Spirometry is the most commonly used pulmonary function test. The aim of this comparative study was to evaluate four commercially available spirometers with different measurement principles ...(turbine-, ultrasound-, differential pressure- and hot-wire anemometer). In particular, the measurement accuracy in breathing manoeuvres with low flow rates was investigated, which is highly relevant for paediatric use. Among the tested devices the hot-wire based spirometer showed the highest measurement accuracy at low flows whilst fully complying with the ATS/ERS standards.
An assembled hot wire anemometer design Yao, Xingxing; Shen, Fanhao; Zheng, Yuan ...
Journal of Measurements in Engineering,
03/2024, Letnik:
12, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The hot wire anemometer is a widely utilized device in laboratory settings for measuring air speed. This paper investigates the relationship between air speed and hot wire temperature across various ...air speed ranges, employing the theory of thermal equilibrium. We designed a measurement circuit and hot wire shape based on the hot wire anemometer principle, and validated the linear relationship between current and temperature at different air speeds within an adjustable air speed field. The measured current serves as a representative of air speed. Experimental validation of the designed hot wire anemometer demonstrates accurate measurement results that align with theoretical values across different air speed ranges. Finally, we determined the sensitivity of the anemometer in various measurement ranges, considering the instrument's uncertainty and measurement formula.
We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic ...energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.
The effect of drops in the rotation wheel of the opto-electronic system of a commercial anemometer (Thies First Class Advanced) was studied. The output voltage of this anemometer was measured at ...different wind speeds during its calibration process, at 25 kHz sampling frequency along 25 s. The output frequency was calculated both ways: by counting pulses (CP) and by carrying out a Fast Fourier Transform (FFT). The errors of the anemometers transfer function based on both procedures are given in relation to the official (MEASNET) calibration. The effect of the sampling frequency is also analyzed together with the presence of oil drops. No effect of the oil drops was observed on calibrations carried out by extracting the anemometers transfer function with FFT. When using CP, results showed great differences between calibrations affected and not affected by the presence of oil drops in the rotation wheel of the opto-electronic system.
•Dirt accumulation in cup anemometer output signal generators may produce wrong wind speed measurements.•Cup anemometer CP- (counting pulses) and FFT-calibrations have been compared.•FFT-calibrations are most reliable in case of dirt accumulation in the output signal generators.
Recent studies on observed wind variability have revealed a decline (termed “stilling”) of near-surface wind speed during the last 30–50years over many mid-latitude terrestrial regions, particularly ...in the Northern Hemisphere. The well-known impact of cup anemometer drift (i.e., wear on the bearings) on the observed weakening of wind speed has been mentioned as a potential contributor to the declining trend. However, to date, no research has quantified its contribution to stilling based on measurements, which is most likely due to lack of quantification of the ageing effect. In this study, a 3-year field experiment (2014–2016) with 10-minute paired wind speed measurements from one new and one malfunctioned (i.e., old bearings) SEAC SV5 cup anemometer which has been used by the Spanish Meteorological Agency in automatic weather stations since mid-1980s, was developed for assessing for the first time the role of anemometer drift on wind speed measurement. The results showed a statistical significant impact of anemometer drift on wind speed measurements, with the old anemometer measuring lower wind speeds than the new one. Biases show a marked temporal pattern and clear dependency on wind speed, with both weak and strong winds causing significant biases. This pioneering quantification of biases has allowed us to define two regression models that correct up to 37% of the artificial bias in wind speed due to measurement with an old anemometer.
•Degradation of anemometer bearings lead to substantial wind speed dependent biases.•Large biases were mainly detected under weak or strong winds.•Regression models minimized the wind speed bias due to bearing ageing.
This article concerns airflow-based odometry for estimating MAV flight speed from airflow measurements provided by a set of thermal anemometers. Our approach relies on a Gated Recurrent Unit (GRU) ...based deep learning approach to extract deep features from noisy and turbulent measurement signals of triaxial thermal anemometers, in order to establish the underlying mapping between the airflow measurement and the flight speed. The proposed solution is validated on a multi-rotor MAV. The results show that the GRU-based model can effectively extract noise features and perform denoising, and compensate for induced velocity effects along the propellers’ rotation axis. As a consequence, robust prediction of the flight speed is performed, including during takeoff and landing that induce ground effects and strong variations of vertical airflow.
The subject matter of the article concerns velocities/flow rate measurements in the area of disturbed flows-behind the 90° bend. They were conducted by means of an ultrasonic flowmeter with clamp-on ...sensors on pipeline, for water and two different Reynolds numbers of 70,000 and 100,000, corresponding to two velocities of approximately 1.42 m/s and 2.04 m/s. The tests were carried out at 12 distances from the disturbance. Sensors on the circumference of the pipeline were mounted 30° each. The correction factor values were calculated for the given measurement geometry. The measurements have shown that the values of this coefficient are always greater than 1, which means that the ultrasonic flow meter understates the speed values. They also showed that already at a distance of 8 nominal diameters from the disturbance, the correction factor does not exceed 1.02, so the measurement errors are within the maximum permissible error (MPE) of a typical ultrasonic flow meter. For distances less than eight nominal diameters from the disturbance, not taking the correction factor value into the account can lead to systematic errors of up to 10.8%. Studies have also proved that in each measurement plane behind the disturbance there are two mounting angles for the ultrasonic sensors, 60° and 240° respectively, for which the correction factor values are minimal. Additionally, using the laser Doppler anemometry (LDA) method, velocity solids were determined at individual distances from the disturbance, and the projections of velocity blocks on the appropriate plane represented velocity profiles and indicated the distances from the disturbance at which these profiles stabilise.
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•Friction between air/cups modifies the value of wind speed provided by cup anemometer.•Wind speed, anemometer rotation and air viscosity describe a hyperbolic paraboloid.•By changing ...the calibration process of cup anemometers highly improves AEP assessment.•Considering a constant wind speed, tests show Reynolds is linearly related to TSR.•Cup anemometers measures depends on air density changes regarding calibration tunnel.
The Annual Energy Production (AEP) estimations are crucial to analyze the potential of wind energy projects. To calculate the AEP of a wind farm, it is necessary to accurately measure the wind speed, because small errors in these measures lead to significant deviations in the wind turbine power curve. In-field wind speed is usually measured by means of cup anemometers, which are calibrated within wind tunnels. In-field ambient conditions differ from those at the laboratory, which increases the uncertainty of the wind speed measures performed at the location of the turbine. The present work is focused on analyzing the effect of the following ambient parameters on the cup anemometer behavior: temperature, humidity and atmospheric pressure. In order to reach this target, experimental tests in a wind tunnel were performed, which allows minimizing the effect of the rest of influence parameters: turbulence, average flow inclination angle and flow direction. With this work it is determined how flow air viscous forces affect the cup anemometers, changing its rotation frequency. This explanation concludes that a variation on air temperature, humidity and/or pressure modifies moist air kinematic viscosity, which leads to change the friction between air and cups and, consequently, the cup anemometers rotational frequency. In most cases, the kinematic viscosity is inversely proportional to the air density and therefore, higher in-field densities, compared to those at the laboratory where the anemometer was calibrated, lead to underestimate the wind speed, and vice versa. The fact that this effect has been quantified during the calibration process is quite important, since it allows removing the influence of the environmental parameters studied; so that by modifying the calibration methodology, the accuracy of cup anemometers would be optimized. In order to clarify how the moist air kinematic viscosity influences the calibration curve, the calibration measurements of a real cup anemometer are mapped into a new dimensionless abacus, with the Tip Speed Ratio (TSR) and the Reynold’s number as coordinates. The key idea is that the rotation frequency of the cup anemometer is related to both wind speed and moist air kinematic viscosity. This relation is mathematically described by the equation of a hyperbolic paraboloid surface up to a value of wind speed of 15.3 m/s.
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