Wind Field Measurements Research Articles

Lidar Scanning of Induction Zone Wind Fields over Sloping Terrain

Scanning lidar instrumentation in the form of two synchronized ground-based WindScanners and a nacelle-mounted SpinnerLidar were deployed to measure wind fields in a vertical plane in the induction zone from 0.2 to 3 rotor diameters (D) in front of a Vestas V52 test turbine (D = 52 m) situated at DTU Risø Campus. First, the two ground-based WindScanners accurately reproduced the vertical profiles of horizontal mean wind speed when compared to measurements from a reference met-mast installed 2.2D upwind in the prevailing wind direction. The vertical plane scanned wind field measurements within in the induction zone were also compared with the vertical wind profiles measured at 1D by a nacelle-mounted scanning DTU SpinnerLidar. The vertical plane wind field as measured by the two ground-based WindScanners shows that the wind field in the induction zone is influenced by the turbine as well as by the slope of the terrain.

Double-wedge Sagnac lateral shearing interferometer for measuring the upper atmospheric wind field

The double-wedge Sagnac lateral shearing interferometer was put forward as a novel device for the upper atmospheric wind field measurement, and its shearing principle was presented. Using the geometrical optics, the exact expression of the optical path difference (OPD) within the range of the whole field was calculated when the incident ray with arbitrary directions arrived at the incoming plane. In order to analyze and discuss the influences of different parameters on the OPD, the computer simulations were performed for two moveable directions (the hypotenuse and right angle side) of the moving wedge prism. The OPD of the double-wedge Sagnac lateral shearing interferometer was changed by the moving wedge prism, which could enlarge the field of view be as much as possible for a specific OPD. These works provided an important theoretical guidance for improving the detecting precision of the upper atmospheric wind field, and had great practical value for the development of the double-wedge Sagnac lateral shearing interferometer apparatus.

Validations of three-dimensional wake models with the wind field measurements in complex terrain

This paper aims to validate the analytical three-dimensional wake models by the wind data measured at a complex-terrain hilly wind farm in China. The wake models take into account the variation of wind speed in the vertical direction. The profiles of wind speeds were scanned by two moveable lidars. Two scanning modes were adopted to obtain the profiles of wind speed in vertical and horizontal directions, respectively. When validating the wake model for a single wind turbine in the vertical direction, the model can predict the wind speeds with acceptable accuracy, especially at positions beyond 10D downstream distance or above 100 m height. Some large errors were found at positions less than 40 m height. Wind speeds in two symmetrical side sections showed different distributions at the same downwind positions. When validating the wake model for multiple wind turbines in horizontal direction, the model also had a reliable accuracy at the far wake positions and near the inflow measuring site, but it cannot predict the wind deficits before an operating wind turbine and was not accurate in some complex-terrain situations. Suggestions and factors were given to be considered for improving the wake models in the future.

1.55-μm pulse coherent LIDAR with 10-km detection range

Recently, a 1.55-μm pulsed coherent Doppler LIDAR system using all fiber optical components was developed to achieve real-time measurements of wind fields. The system employs 100-μJ pulse energy at 10 kHz pulse repetition rate. In addition, the system consists of a fiber-based optical transceiver unit, a two-axis scanner, and a multicore digital signal processor (DSP) for real-time signal processing. With compact and mobile design, the LIDAR is easy to transport and deploy for different field campaigns. For a different application of LIDAR, the range resolution can change manually. A horizontal detection range of 10 km is achieved with the temporal and spatial resolution of 1 s and 30 m, respectively. Field experiments compared with an anemometer show that correlation coefficient of the different wind speed measurements is 0.953; the correlation coefficient for wind direction values is 0.967. Continuous wind profiles of the planetary boundary layer are presented to demonstrate the stability of the system.

Intricate features in the lifetime and deposition of atmospheric aerosol particles

The advection of particles emanated, e.g., from volcano eruptions or other pollution events exhibits chaotic behavior in the atmosphere. Due to gravity, the particles move downward on average and remain in the atmosphere for a finite time. The number of particles not yet deposited from the atmosphere decays exponentially after a while characteristic to transient chaos. The so-called escape rate describes the rapidity of the decrease, the reciprocal of which can be used to estimate the average lifetime of the particles. Based on measured wind field data, we follow aerosol particles and demonstrate that the geographical distribution of the individual lifetime of the particles distributed over the globe at different altitudes shows a filamentary, fractal distribution, typical for chaos: the lifetime of particles may be quite different at very nearby geographic locations. These maps can be considered as atlases for the potential fate of volcanic ash clouds or of particles distributed for geoengineering purposes. Particles with similar lifetime deposit also in filamentary structures, but the deposition pattern of extremely long-living particles covers more or less homogeneously the Earth. In general, particles emanated around the equator remain in the atmosphere for the longest time, even for years, e.g., for particles of 1μm radius. The escape rate does not show any considerable dependence on the particles' initial altitude, indicating that there exists a unique chaotic saddle in the atmosphere. We reconstruct this saddle and its stable and unstable manifolds on two planar slices and follow its time dependence.

New Test Method of Wind Pressure Coefficient Based on CAARC Standard Model Determined Using Vehicle Driving Wind

The driving characteristics of a vehicle, combined with a wind tunnel test and field measurement, can produce wind. This study proposes a transiting test method of building wind pressure under ideal road conditions via theoretical derivation and field testing. In this work, the basic theory of the transiting test was formulated, and the transiting test of a physical test platform was designed and assembled, and a software test system was established. The test data processing method was investigated and adopted for testing the mean wind pressure coefficient of the CAARC standard model’s typical measuring points. The influence of different speeds on the mean wind pressure coefficient was studied, and the difference of the mean wind pressure coefficient of repeated tests with the same speed was analyzed. Results showed the accuracy of the theoretical formula of the proposed transiting test, and the hardware and software systems were acceptable. The mean wind pressure coefficient of the typical measuring points of the standard model agreed well with the wind tunnel test results from relevant literature. Moreover, different speeds minimally affected the mean wind pressure coefficient. Thus, the technique is feasible under ideal road conditions. The transiting test method proposed in this study provides a new test technique for structural wind resistance research.

Characteristics of intense winds in mountain area based on field measurement: Focusing on thunderstorm winds

With the development of mountain areas, more wind-sensitive infrastructures are constructed. In the design of these infrastructures, the wind loading cannot be accurately obtained from the code based on the flat area. Hence, it is of great importance to study the mountain wind characteristics. In this study, the wind field measurement was initiated in a mountain area of western China. After the examination of the measured data, two typical wind events including the thunderstorm wind and thermally developed wind are highlighted. To extract and separate these wind events, an automatic classification method is proposed. The thunderstorm wind is analyzed in order to capture the rapid variation of its maximum wind speed, mean temperature and mean humidity through the boxplot method while the analysis of thermally developed winds relies on the correlation between the mean wind speed and mean temperature. Since the thunderstorm wind is relatively more important for wind engineering, its wind characteristic is focused hereafter and analyzed in detail based on the ultrasonic anemometer data. The characteristics of the thermally developed wind and other wind will be the matter of further studies and investigations. Results show that the characteristics of the thunderstorm wind measured in the mountainous area have no significant difference in comparison with those in the flat area. Due to the limited data, the above results deserve further investigations when more measurements become available.

Wind field simulation over complex terrain under different inflow wind directions

Accurate numerical simulation of wind field over complex terrain is an important prerequisite for wind resource assessment. In this study, numerical simulation of wind field over complex terrain was further carried out by taking the complex terrain around Siu Ho Wan station in Hong Kong as an example. By artificially expanding the original digital model data, Gambit and ICEM CFD software were used to create high-precision complex terrain model with high-quality meshing. The equilibrium atmospheric boundary layer simulation based on RANS turbulence model was carried out in a flat terrain domain, and the approximate inflow boundary conditions for the wind field simulation over complex terrain were established. Based on this, numerical simulations of wind field over complex terrain under different inflow wind directions were carried out. The numerical results were compared with the wind tunnel test and field measurement data for land and sea fetches. The results show that the numerical results are in good agreement with the wind tunnel data and the field measurement data which can verify the accuracy and reliability of the numerical simulation. The near ground wind field over complex terrain is complex and affected obviously by the terrain, and the wind field characteristics should be fully understood by numerical simulation when carrying out engineering application on it.

基于相关计算的激光雷达二维风场探测

基于相关计算的激光雷达二维风场探测

Estimation of winter time NOx emissions in Hefei, a typical inland city of China, using mobile MAX-DOAS observations

In this paper, we present a quantitative determination of the NOx emission in Hefei using mobile Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements. The measurements were carried out during winter time from December 2016 to February 2017. The measured NO2 vertical column densities (VCDs) show a strong spatial gradient with higher values within the city center, indicating the majority of NOx emission sources are located at the city center. A significant “holiday effect” was found by comparing measurements taken during weekdays and weekend. The weekend reduction is more significant in the suburban (∼28%) compared to the city center (∼13%). Mobile measurements of NO2 vertical column densities (VCDs) were analyzed together with meteorological data to determine the NOx emission by applying the loop-integral method. Detailed error analysis of the NOx emission shows the variation of wind field and large measurement gap dominated the total error of NOx emission calculation. The result shows the NOx emission in Hefei during winter time varies in a wide range from 10 × 1024 to 40 × 1024molecs−1 with an average of 18.44 × 1024molecs−1. Our estimation is about 43% lower than the number reported in the previous emission inventory in 2012. The reduction of NOx emission reflects the successful implementation of emission control measures in recent years. Our result also shows about 73% of the total NOx in the city were transported from outside of the city during winter. The impacts of transported NOx are especially large when air masses originated from heavily polluted regions, i.e. North China Plain and Yangtze River Delta. The result presented provides a better understanding of the impacts of local emissions and transportation of pollutants on the local air quality of Hefei.

Comparison of simulations and wind tunnel measurements for the improvement of design tools for Vertical Axis Wind Turbines

As wind turbines are getting larger and cost reductions through up-scaling are reaching a limit, there is increasing pressure to reduce their installation and operating costs, making the business case for Vertical Axis Wind Turbines (VAWTs) more interesting again. However, in order to properly assess the economic potential of large-scale VAWTs, improved design tools are required. As the research budget for VAWT projects is generally too small to carry out expensive large-scale wind tunnel tests and field measurements, alternative methods are required. In this work, the application of small-scale, lower budget methods for improving VAWT design tools is assessed. It is shown that (a) currently available tools for VAWT design have not been sufficiently validated, (b) lower budget, small-scale wind tunnel tests can be effective for examining VAWT performance in terms of average power coefficient vs. tip speed ratio as well as the dynamics of the torque, and (c) Detached Eddy Simulations on small-scale VAWTs can be effective for examining their performance in terms of average power coefficient vs. tip speed ratio as well as the forces on the blades. Based on these results, a process for the transfer of the results of lower budget, small-scale measurements and simulations into recommendations for improved design tools is being developed.

Identification of wind loads on super-tall buildings by Kalman filter

An inverse method based on the discrete time Kalman filter is developed to simultaneously estimate the unknown wind-induced responses and wind loads of high-rise buildings using limited response measurements. The accuracy and effectiveness of the presented estimation method are assessed based on both wind tunnel test results and field measurements of wind effects on a super-tall building. The wind-induced responses obtained by wind tunnel test are used to identify the wind loads on the super-tall building and evaluate the effects of crucial factors, such as covariance matrix of noise, initial estimation error, noise in measurements, modelling errors of structural dynamic properties and number of vibration modes, on the identification results. In addition, the wind loads are also estimated based on the field measured displacements during Typhoon Neoguri. Comparisons between the identified wind loads from the field measured displacements and the wind tunnel test results are made to verify the applicability of the inverse technique. The results of this study illustrate that the proposed inverse method is an efficient tool for predicting the wind loads on super-tall buildings from limited measurements of structural responses.

Measuring Ocean Surface Wind Field Using Shipborne High-Frequency Surface Wave Radar

Extraction of ocean surface wind field from data collected by shipborne high-frequency surface wave radar (HFSWR) is an ongoing challenge because of the inherent directional ambiguity and the effect of complicated platform motion on radar Doppler spectra. Here, a method for extracting the wind direction and speed from the spreading first-order radar Doppler spectra is first presented. First, the mathematical model of the wind direction versus a variable spreading parameter is developed. Moreover, based on the spreading characteristic of the first-order spectra, an approach for simultaneously determining the unambiguous wind direction and the unique spreading parameter with a single receiving antenna is presented. Furthermore, the relationship between the wind speed and the spreading parameter is derived on the basis of the relationship between the drag coefficient and the spreading parameter, and the wind speed can be determined. Therefore, the wind field of ocean area covered by shipborne HFSWR can be measured by sequentially exploiting the presented method, which is more beneficial for shipborne HFSWR because of smaller installation space and less cost. Simulation results and discussions of basic applications show the feasibility of wind field measurement in shipborne HFSWR. Experimental results validate the presented method and evaluate the detection accuracy and distance limit. The range for wind field measurement is up to 120 km, which is the range for which the signal-to-noise ratio typically exceeds about 11 dB in the relevant first-order portions of the backscatter spectra. Comparisons between the radar-measured and forecasting or buoy-measured results show good agreement.

A comparative analysis of built environment and open terrain wind data by higher order statistics and performance evaluation of 5 kW HAWT using FAST

Small wind turbines (SWT) that are designed as per the IEC 61400-2 standard suffer structural and operational complexities when operating in the built environment, because such environments impose stochastic variations in wind speed and turbulence. The wind conditions in flat terrain of Östergarnsholm (OG) Island, Sweden and built environment of Port Kennedy (PK), Australia are compared for turbulence intensity (TI) and intermittency. The TI of the PK wind field was 24% at mean wind speed of 15 m/s, which was higher than the Normal Turbulence Model (NTM) indicated in IEC 61400-2. The TI in the open terrain was below 18% for all mean wind speeds. Similarly, for three chosen wind speed bins within a SWT’s operating range, the urban wind field had higher intermittency for smaller timescales but resulted in smaller intermittency as the time lag increased. The effect of these measured wind fields on the performance and loading of a turbine was studied at the three chosen wind speed bins using an aeroelastic model of a 5 kW SWT that was developed in FAST. The predicted output statistics using measured wind fields were compared with the assumed wind fields in the IEC 61400-2 standard. The rotor thrust and blade flapwise bending moment with PK wind data were higher than that of the IEC standard due to the increased turbulence in the inflowing wind indicating the inadequacy in the current wind standard applied for such SWTs for urban installations.

Evaluation of the LINCOM wind field reconstruction method with simulations and full-scale measurements

The LINCOM method is a set of linearised flow equations that enables the reconstruction of a 3D wind field from a large set of non-parallel radial wind speed measurements. An evaluation of the model is performed with both simulated and full-scale boundary layer wind field measurements. The model is first tested on deterministic wind fields to evaluate its performance under simple conditions. Afterwards, line-of-sight measurements are extracted from a virtual SpinnerLidar placed in an LES wind field and then the LINCOM method is applied and compared to it. Finally, the methodology is experimentally evaluated with lidar measurements from the IRPWIND joint experiment SCANFLOW campaign, where SpinnerLidar line-of-sight inflow measurements from the nacelle of a test turbine were used to reconstruct 3D wind fields. These reconstructed wind fields are then compared with simultaneously measured independent full-scale 3D short-range WindScanner data. It was seen that the LINCOM model is able to accurately reconstruct the deterministic wind fields. For the analysis with the LES wind fields, the LINCOM model is able to obtain an R2 coefficient of 0.72 with no significant correlation found for the v- and w-components. The cosine de-projection of the line-of-sight speeds onto the main direction yields R2 = 0.834. For the full field measurements, the LINCOM model was able to predict the longitudinal component with a low standard error, but the v- and w-components deviate significantly. The results suggest the suitability of the model to reconstruct only the mean characteristics of 3D fields under low turbulent conditions, and give a reasonable estimate of the fluctuations of the u-component.

Inflow characterization using measurements from the SpinnerLidar: the ScanFlow experiment

We present a preliminary analysis of inflow measurements performed with a SpinnerLidar on a turbine’s nacelle and those from three grounded-based short-range continuous- wave lidars (WindScanners) during the ScanFlow experiment. After proper filtering for blade contamination and hub/nacelle shading of the beam, the SpinnerLidar measurements capture the structure of the inflow in detail. The WindScanners’ 3D measurements provide estimations of the three wind speed components without any flow assumptions. These 3D wind field measurements are used as reference to evaluate SpinnerLidar reconstructed winds. A wind reconstruction methodology for the SpinnerLidar measurements is evaluated against a numerical wind inflow simulation successfully. An intercomparison between reconstructed longitudinal velocity components from the WindScanners and the Spinnerlidar shows good agreement (no bias and high correlation) at hub height and close to zero biases for all vertical levels measured by the SpinnerLidar.

Measurement uncertainty of IR thermographic flow visualization measurements for transition detection on wind turbines in operation

The application of thermographic flow visualization on wind turbines in operation differs from the well-established application in wind tunnel experiments. The necessary temperature difference between the rotor blade and the flow only relies on the absorbed solar radiation, which often leads to a low signal-to-noise ratio. Furthermore, a large distance of up to 400 m exists between the rotor blade and the thermographic camera for ground based measurements, mainly due to the height of the wind turbine. This results in a poor spatial resolution as well as a small numerical aperture, which means a small detectable radiant power further degrades the signal-to-noise ratio. In order to determine the limits of measurability for the localization of the laminar-turbulent transition, the fundamental effects on the measurement uncertainty are investigated. For this purpose, the measurement uncertainty budgets for three signal processing algorithms are derived and validated with wind tunnel experiments and field measurements on a 1.5 MW wind turbine under sunny and cloudy weather conditions. As a result, the achievable standard uncertainty of the laminar-turbulent transition position for a temperature difference of 2 K amounts to 0.16 pixels in this case, which corresponds to 0.17% chord length. In addition, the measurement uncertainty is currently not limited by the measurement system (detector noise and fixed pattern noise of the camera), but by flow induced temperature fluctuations and fluctuations of the laminar-turbulent transition position itself. Hence, the field measurements on wind turbines in operation are still limited by the flow characteristics, i.e., the measurement object itself. Finally, one of the presented signal processing methods allows a robust, automated flow characterization for wind turbines in operation with subpixel accuracy in all of the presented measurements.

Experimental and theoretical investigation of tower shadow impacts on anemometer measurements

The tower supporting an anemometer modifies the local wind field and anemometer measurements. In wind energy resource assessment, tower-induced flow modification contributes a non-negligible amount of uncertainty to the wind resource assessment. The effect of wind speed averaging period on anemometer measurement errors was investigated using high resolution sonic measurements from two sonic anemometers on a tubular tower. Measurements were post-processed into equivalent datasets that differed only by averaging periods. Averaging period only impacted the measured magnitude of the wake, while little effect was seen outside the wake region for data averaging periods between 15 s and 1 h. A model is proposed to remove tower shadow effects from anemometer data using a potential flow solution in the region outside the tower wake and assuming the tower wake is Gaussian and turbulent. An untuned version of the model reproduced the main features of tower-induced flow modification including the turbulent wake, but was not accurate enough to provide a useful correction for wind resource assessment purposes. Fitting model parameters using measured data was found to be a practical way to partially correct wind data from a pair of anemometers in which one fails or becomes unreliable.

Wind characteristics at a long-span sea-crossing bridge site based on monitoring data

Six years of wind data are used to investigate the statistical characteristics of general and strong winds acting on the Donghai Bridge, a sea-crossing bridge in China. The general wind at the bridge site shows a relatively stable annual repeatability, and the discrepancies are found between the measured wind field parameters and those suggested by the design code. For strong winds, both the 10-min mean wind speed and the turbulent variance greatly exceed those of general winds, while the turbulence intensity, integral length scale, and gust factor do not exhibit any noticeable quantitative trends. The measured wind spectra of both general and strong winds show a shift toward the high-frequency range compared with Simiu’s spectrum (along-wind direction). The wind measurements at the bridge site are easily interfered with the bridge structure itself, resulting in a greater turbulence along the bridge axis and a higher turbulent kinetic energy in the high-frequency range, which needs to be considered in designing structural health monitoring systems in the future. This study provides field evidence for the wind-resistant design and evaluation of long-span sea-crossing bridges.

Turbidity in response to wind speed, wind direction and wind duration in Gonghu Bay, Lake Taihu

水体浊度是影响水下光场及营养盐循环的关键要素之一，其变化过程与水生生态环境演变关系密切.基于2015-2016年7个时段于太湖贡湖湾内外的金墅和上山村两站点的水体浊度及东山气象站的逐时风场数据，利用分位统计等方法，探讨了风速、风向及时间累积效应对水体浊度的影响.结果表明：在以风场驱动为主要动力来源的大型浅水湖泊中，春、秋两季水体浊度的变化频率高于夏、冬两季，且春季变率更为突出；冬季风场和水体浊度的变率均较夏季明显.风场（包括风速、风向及其累积时间）是影响水体浊度变化的关键因素.其中风速是主要决定性因子；风向对水体浊度有较明显的影响，其通过对风速效应的修正进而影响水体浊度，该修正作用可用三角函数表征；水体浊度变化同时还受前期风场累积的影响，其前期时间累积效应的有效时段为2~10 h.该研究给出了风速、风向及风场累积效应的耦合对水体浊度的影响模型，有助于弄清风场对水体浊度变化的影响机制.;Turbidity is one of the key factors that affect the underwater light climate and nutrient circulation, and its change is closely related to the evolution of aquatic ecosystem. Based on the turbidity data at the two sites near Jinshu and Shangshan Village in Gonghu Bay of Lake Taihu from 2015 to 2016 and the hourly wind field measurement in Dongshan weather station, the effects of wind speed, wind direction and wind duration on turbidity was analyzed with quantile regression technique. The results show as follows. In large shallow lakes where wind as the primary driving force, the turbidity change frequency in spring and autumn is higher than that in summer and winter, with spring as the most prominent. The change of water turbidity in winter is more obvious than that in summer. The variability of wind field (the speed, direction and duration), particularly the wind speed, is the key factor regulating turbidity. The wind direction can affect the turbidity by the correction of the wind speed. The correction can be characterized by a trigonometric function. The turbidity was mainly affected by the northern wind, and followed by the east-west wind. The influence of the south wind is the weakest. The change of turbidity is influenced by the wind field preceding measurement time, and the valid wind duration is about 2-10 hours. This study developed a model elucidating the influence of wind speed, wind direction and wind duration on the turbidity, which is helpful to clarify the mechanism on turbidity variation in Lake Taihu.