Full-scale Wind Research Articles

Shake Table Testing of a Utility-Scale Wind Turbine

AbstractShake table tests were undertaken on a full-scale wind turbine (65-kW rated power, 22.6-m hub height, and 16-m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Structural response characteristics and modal parameters are presented for base shaking imparted in two configurations, both parallel (configuration 1) and perpendicular (configuration 2) to the axis of rotation of the rotor. Results are summarized for a series of progressively stronger motions imparted in configuration 1, with analysis identifying damage sources leading to an overall loss in stiffness. Two sources of observed softening are identified and quantified: (1) degradation of grout at the tower base, and (2) loss of bolt torque at the connections between tower segments. Results showed that the two configurations had little difference in structural response and demand parameters. For the tested turbine, with appropriate con...

Design and Finite Element Modal Analysis of 48m Composite Wind Turbine Blade

We currently notice a substantial growth in the wind energy sector worldwide. This growth is expected to be even faster in the coming years. This means that a massive number of wind turbine blades will be produced in the forthcoming years. There is a large potential for materials savings in these blades. The analysis of designed blade is done in dynamic loading. Five types of spars cross-section are taken in this work. The blade and spar are of composite material. The Finite element modal analysis of designed blade is done in ABAQUS. The scope of the present work is to investigate the structural modal analysis of full-scale 48m fiberglass composite wind turbine blades for 5MW horizontal axis wind turbine and through this to assess the potential for materials savings and consequent reductions of the rotor weight. The entire wind turbine can benefit from such weight reductions through decreased dynamics loads and thus leave room for further optimization. A numerical work has been used to address the most adequate spar shape and to get an understanding of the complex structural behavior of wind turbine blades. Five different types of structural reinforcements helping to prevent undesired structural elastic mechanisms are presented. Comparisons of the eigenfrequencies observed in the full-scale tests are presented and conclusions are drawn based on the mechanisms found.

Full-Scale Wind Turbine Near-Wake Measurements Using an Instrumented Uninhabited Aerial Vehicle

In this paper, the first-ever measurements of the wake of a full-scale wind turbine using an instrumented uninhabited aerial vehicle (UAV) are reported. The key enabler for this novel measurement approach is the integration of fast response aerodynamic probe technology with miniaturized hardware and software for UAVs that enable autonomous UAV operation. The measurements, made to support the development of advanced wind simulation tools, are made in the near-wake (0.5D–3D, where D is rotor diameter) region of a 2 MW wind turbine that is located in a topography of complex terrain and varied vegetation. Downwind of the wind turbine, profiles of the wind speed show that there is strong three-dimensional shear in the near-wake flow. Along the centerline of the wake, the deficit in wind speed is a consequence of wakes from the rotor, nacelle, and tower. By comparison with the profiles away from the centerline, the shadowing effects of nacelle and tower diminish downstream of 2.5D. Away from the centerline, the deficit in wind speed is approximately constant ≈ 25%. However, along the centerline, the deficit is ≈ 65% near to the rotor, 0.5D–1.75D, and only decreases to ≈ 25% downstream of 2.5D.

Experimental investigation of structure vulnerabilities to firebrand showers

Attempting to experimentally quantify the vulnerabilities of structures to ignition from firebrand showers has remained elusive. The coupling of two facilities has begun to unravel this difficult problem. The NIST Firebrand Generator (NIST Dragon) is an experimental device that can generate a firebrand shower in a safe and repeatable fashion. Since wind plays a critical role in the spread of WUI fires in the USA and urban fires in Japan, NIST has established collaboration with the Building Research Institute (BRI) in Japan. BRI maintains one of the only full scale wind tunnel facilities in the world designed specifically for fire experimentation; the Fire Research Wind Tunnel Facility (FRWTF). The present investigation is aimed at extensively quantifying firebrand penetration through building vents using full scale tests. A structure was placed inside the FRWTF and firebrand showers were directed at the structure using the NIST Dragon. The structure was fitted with a generic building vent, consisting of only a frame fitted with a metal mesh. Six different mesh sizes openings were used for testing. Behind the mesh, four different materials were placed to ascertain whether the firebrands that were able to penetrate the building mesh assembly could ignite these materials. Reduced scale test methods afford the capability to test new vent technologies and may serve as the basis for new standard testing methodologies. As a result, a new experimental facility developed at NIST is presented and is known as the NIST Dragon's LAIR (Lofting and Ignition Research). The NIST Dragon's LAIR has been developed to simulate a wind driven firebrand attack at reduced scale. The facility consists of a reduced scale Firebrand Generator (Baby Dragon) coupled to a bench scale wind tunnel. Finally, a series of full scale experiments were conducted to visualize the flow of firebrands around obstacles placed downstream of the NIST Dragon. Firebrands were observed to accumulate in front of these obstacles at a stagnation plane, as was observed when the structure was used for firebrand penetration through building vent experiments, due to flow recirculation. The accumulation of firebrands at a stagnation plane presents a severe threat to ignitable materials placed near structures.

Sail pressures from full-scale, wind-tunnel and numerical investigations

The main results of a two-year project aimed at comparing full-scale tests, wind tunnel tests, and numerical analysis predictions are presented. Pressure measurements were obtained from both full-scale tests and wind tunnel tests, in upwind and downwind conditions. The upwind wind tunnel test condition was modelled using a Vortex Lattice code, while the downwind wind tunnel test was modelled using a Navier–Stokes code. The pressures obtained from the three different methods are compared on three horizontal sections of the headsail, mainsail and asymmetric spinnaker. In general the pressure from the three experiments showed good agreement. In particular, very good agreement was obtained between the numerical computations and the wind tunnel test results. Conversely, the results from the downwind full-scale pressure measurements showed less similarity due to a slightly tightened trim being used for the spinnaker in the on-water tests. Full-scale tests allow the action of unsteadiness due to the wind, wave and yacht movements to affect the results. This unstable environment caused the asymmetric spinnaker to move around, and a tightened trim was required to prevent the spinnaker from collapsing.

An Experimental Investigation of Automobile Interior Wind Noise Using a Production Vehicle

Based on the analysis of automobile aerodynamic noise generation mechanisms and the components of interior wind noise, the spectra characteristics and spatial distribution rule of sound level of interior wind noise were investigated at first, then the frequency characteristics and noise level under different wind speeds, different yaw angles in SAWTC full-scale aeroacoustic wind tunnel were studied. The results show that: the interior noise level was nearly symmetric on vehicle left and right side, noise level of outboard ear was normally higher than that of inboard ear. The frequency characteristics under different wind speeds were almost the same, the linear OASPL of interior noise increased at about 4.4th power and A-weighted OASPL at about 5.5th power of wind speed. In addition, the acoustic power increased as yaw angle rose up, and noise level by leeward side was normally higher than that by windward under the same yaw angle.

Shape-dependent characteristics of full-scale wind profiles

Numerical investigations on vortex excitation of tall and slender structures, like guyed masts or towers oscillating with higher eigenmodes, indicate that it can be beneficial to account for realistic shapes of the mean wind speed profile. In order to use shape-dependent profile characteristics for a prospective stochastic vibration analysis of structures subjected to vortex excitation, the occurrence of different profile shapes is derived from full-scale wind data, which has been continuously recorded at the 344 m measurement mast Gartow since 1989. After the shape-dependent classification of the profile data with an artificial neural network, the classified wind speed profiles and the corresponding turbulence characteristics are described statistically. The classification shows that the frequency of occurrence of constant profile shapes is only 18.4%. Since these are usually used to analyze the vortex-induced fatigue, accounting for realistic wind speed profiles in a vortex excitation analysis can enhance the predicted fatigue safety for structures that oscillate with multiple modal nodes. For such an analysis, the shape-dependent profile characteristics can be well represented independently of the wind direction with Weibull and Gaussian statistics, where the latter is a reasonable approximation for the conditions at the measuring site. For the turbulence intensity, common models apply within each profile class.

Numerical Simulation and Wind Tunnel Studies of the Wind Load on Wind Turbine Structures

This paper investigated the structural responses of the wind turbine due to wind loads by performing the wind tunnel test and the Computational Fluid Dynamics, (CFD). The base shear force and the base moment of the wind turbine measured by the wind tunnel test were compared with the numerical simulation results. Both the numerical dynamic mesh and sliding mesh models were selected for the numerical simulations. The results showed that the dynamic mesh model was better than the sliding model by comparing to the wind tunnel test result. In the case of the k-epsilon RNG turbulence model, the prediction of the bending moment affecting by acrossswind was more than 50%, and the prediction of the force affecting by acrosswind was less than 3%. The both simulation results of the prototype and the full scale wind turbine were obtained by CFD model. The comparisons of the result showed that the error of Fxwas about 15% and Mywas about 13.5%.

A Test Protocol to Quantify the Uplift Resistance of Adhesive Applied Roofing Specimens Subjected to Tensile Loading

Abstract Adhesive applied roofing systems (AARS), a new generation of built-up roofs, are gaining popularity in North American low slope application. AARS uses no fasteners and all components (e.g., deck, vapour barrier, insulation board, and membrane) are integrated by the use of adhesives. As there are no metal fasteners, AARS can offer an advantage of reduction in condensation and thermal bridges for the roof assemblies. Even though, AARS have been in use, there have been no standard that exists to quantify its wind uplift performances. An industries-university-Canadian government collaborative research project, “Development of Wind Uplift Standard for Adhesive Applied Low Slope Roofing System,” has been initiated with three major tasks: Experimental investigation, formulation of a numerical model and development of wind design guide and standards. This paper documents a standardized small scale laboratory test method for the quantification of uplift resistance subject to tensile loading. As part of Task 1 of the project, this systematic investigation focuses on three key parameters: Loading rate, specimen size and end condition. The investigations were completed by constructing over 400 specimens. Both the maximum uplift resistance and the consistence in the failure plane are equally considered during the test method standardization. The data from this small scale testing can facilitate roofing industries to optimize the material combinations such that the uplift resistance data can be used as an indicator before performing a full-scale wind uplift testing.

계통 연계형 풍력 발전 시스템의 LVRT 제어 전략

본 논문은 계통 전압 사고 상황에서 계통 연계형 풍력 발전 시스템이 만족시켜줘야 할 LVRT(Low Voltage Ride Through) 제어 전략을 제안한다. LVRT 규정은 계통 전압 사고 시 풍력 발전 시스템이 지켜야 할 부분들을 전압 감소율과 사고 시간에 대해 나타내고 있다. 특히 전압 감소율이 10% 이상일 경우에는 풍력 발전 시스템은 규정된 무효 전류를 전력 계통에 제공하여 계통 전압 확보에 이바지해야 한다. 본 논문에서의 LVRT 규정은 세계적으로 가장 엄격한 규정인, 독일 계통 연계 규정(German Grid Code)을 기준으로 하고 풀 스케일(Full-scale) 가변 속도 전력 변환 시스템을 고려하여 제어 전략을 수립한다. 본 LVRT 제어 전략은 계통 사고 시 LVRT 규정을 모두 만족시킴과 동시에 직류단 전압 제어의 추가적인 알고리즘으로 직류단 전압의 제어를 통하여 전체 풍력 발전 시스템의 전력 균형을 기할 수 있다. 3상 전압 지락 사고의 경우 계통으로의 전력 제어가 불가능하여 계통 측 컨버터가직류단 전압을 제어할 수 없으므로, 전력 제어의 기능을 발전기 측 인버터로 이행 시켜 상황에 따라 유연한 직류단 전압 제어가 가능함을 보였다. 시뮬레이션과 실험을 통해 LVRT 제어 전략의 타당성을 검증하였다. This paper proposes a LVRT (Low Voltage Ride Through) control strategy which should be satisfied by grid-connected wind power system when grid faults occur. The LVRT regulation indicates rules or actions which have to be executed according to the voltage dip ratio and the fault duration. Especially the wind power system has to support the grid with specified reactive current to secure the grid stability when voltage reduction ratio is over 10%. The LVRT regulation in this paper is based on the German Grid Code and full-scale variable speed wind power conversion system is considered for LVRT control strategy. The proposed LVRT control strategy satisfies not only LVRT regulation but also makes power balance between wind turbine and power system through additional DC link voltage regulation algorithms. Because it is impossible to control grid side power when the 3-phase to ground fault occurs, the DC link voltage is controlled by a generator side inverter using the DC link voltage control strategy. Through the simulation and experiment result, the proposed LVRT control strategy is evaluated and its effectiveness is verified.

Seven-Sensor Fast-Response Probe for Full-Scale Wind Turbine Flowfield Measurements

The unsteady wind profile in the atmospheric boundary layer upstream of a modern wind turbine is measured. The measurements are accomplished using a novel measurement approach that is comprised of an autonomous uninhabited aerial vehicle (UAV) that is equipped with a seven-sensor fast-response aerodynamic probe (F7S-UAV). The autonomous UAV enables high spatial resolution (∼6.3% of rotor diameter) measurements, which hitherto have not been accomplished around full-scale wind turbines. The F7S-UAV probe developed at ETH Zurich is the key-enabling technology for the measurements. The time-averaged wind profile from the F7S-UAV probe is found to be in very good agreement to an independently measured profile using the UAV. This time-averaged profile, which is measured in moderately complex terrain, differs by as much as 30% from the wind profile that is extrapolated from a logarithmic height formula; therefore, the limited utility of extrapolated profiles, which are commonly used in site assessments, is made evident. The time-varying wind profiles show that at a given height, the velocity fluctuations can be as much as 44% of the time-averaged velocity, therefore indicating that there are substantial loads that may impact the fatigue life of the wind turbine’s components. Furthermore, the shear in the velocity profile also subjects the fixed pitch blade to varying incidences and loading. Analysis of the associated velocity triangles indicates that the sectional lift coefficient at midspan of this modern turbine would vary by 12% in the measured time-averaged wind profile. These variations must be accounted in the structural design of the blades. Thus, the measurements of the unsteady wind profile accomplished with this novel measurement system demonstrate that it is a cost effective complement to the suite of available site assessment measurement tools.

Numerical Simulation of Wind Pressure Distribution on Structure Roofs with Suspension Solar Panels

This paper presents the results of full-scale numerical wind tunnel tests of wind pressure on structure roofs with suspension solar panels. Solar roof project is popularized in this century. Solar panels are suspended above the structure roof. So the wind load effect on the structure roof is varied. The wind tunnel experiments are often expensive. A 3D model is introduced and solved using ADINA. The wind pressure distribution coefficients are calculated.

Experimental study of the effect of tower shadow on anemometer readings

Meteorological (met) tower measurements are the industry standard for wind resource assessment for wind farm siting. Towers have many potential geometries such as lattice towers but this study concentrated on solid cylindrical towers. Horizontal booms were used to hold cup anemometers at defined distances from the tower. Anemometers are subjected to winds from all directions. At times, the anemometers are located in the wake of the tower or “shadow” and therefore yield measurements which are under-representative of the true wind speed. Relying on a single anemometer at any given elevation can result in significant discrepancies between the measured and actual wind conditions. This experiment investigated the effects of tower “shadowing” on cup anemometer wind speed readings in the wake of common met tower geometries. The objective of this study was to quantify the decrease in measured wind speed with varying wind direction experimentally using full-scale wind facility testing. The results indicate a significant wind speed deficit up to 35% velocity reduction when the anemometer is located in the wake of the tower. The width of the affected area and the magnitude of the effect are functions of wind speed. Additionally, the effect is not greatest when the centreline of the anemometer is directly inline with the centreline of the tower, but rather when the anemometer is located approximately 2∘–5∘ from the centerline due to the geometry of the cup anemometer.

Aerodynamic loads on buses due to crosswind gusts: extended analysis

The objective of this work is to use inverse simulations on measured vehicle data in order to estimate the aerodynamic loads on a bus when exposed to crosswind situations. Tyre forces, driver input, wind velocity and vehicle response were measured on a typical coach when subjected to natural crosswind gusts. Based on these measurements and a detailed MBS vehicle model, the aerodynamic loads were estimated through inverse simulations. In order to estimate the lift force, roll and pitch moments in addition to the lateral force and yaw moment, the simulation model was extended by also incorporating the estimation of the vertical road disturbances. The proposed method enables the estimation of aerodynamic loads due to crosswind gusts without using a full scale wind tunnel adapted for crosswind excitation.

Simulated tropical cyclonic winds for low cycle fatigue loading of steel roofing

Low rise building roofs can be subjected to large fluctuating pressures during a tropical cyclone resulting in fatigue failure of cladding. Following the damage to housing in Tropical Cyclone Tracy in Darwin, Australia, the Darwin Area Building Manual (DABM) cyclic loading test criteria, that loaded the cladding for 10000 cycles oscillating from zero to a permissible stress design pressure, and the Experimental Building Station TR440 test of 10200 load cycles which increased in steps to the permissible stress design pressure, were developed for assessing building elements susceptible to low cycle fatigue failure. Recently the ‘Low-High-Low’ (L-H-L) cyclic test for metal roofing was introduced into the Building Code of Australia (2007). Following advances in wind tunnel data acquisition and full-scale wind loading simulators, this paper presents a comparison of wind-induced cladding damage, from a “design” cyclone proposed by Jancauskas, et al. (1994), with current test criteria developed by Mahendran (1995). Wind tunnel data were used to generate the external and net pressure time histories on the roof of a low-rise building during the passage of the “design” cyclone. The peak pressures generated at the windward roof corner for a tributary area representative of a cladding fastener are underestimated by the Australian/New Zealand Wind Actions Standard. The “design” cyclone, with increasing and decreasing wind speeds combined with changes in wind direction, generated increasing then decreasing pressures in a manner similar to that specified in the L-H-L test. However, the L-H-L test underestimated the magnitude and number of large load cycles, but overestimated the number of cycles in the mid ranges. Cladding elements subjected to the L-H-L test showed greater fatigue damage than when experiencing a five hour “design” cyclone containing higher peak pressures. It is evident that the increased fatigue damage was due to the L-H-L test having a large number of load cycles cycling from zero load (R=0) in contrast to that produced during the cyclone.

Analysis of full-scale wind and pressure measurements on a low-rise building

Significance of full-scale experiments, analyzing wind and pressure fields in the proximity or on low-rise buildings, is evident from the attention that has been dedicated by researchers to these programs in the recent past. In the south and southeastern regions of US this problem is of particular relevance due to the presence of hurricanes and high-speed winds. This paper presents some recent results derived from a three-year monitoring of a structure located near the coast of North Carolina. In the first part of this study, attention is devoted to the characterization of the wind field around an instrumented house; a comprehensive investigation on wind velocity and turbulence characteristics during the passage of three tropical storms and other significant events is summarized. In the second part, results associated with the meteorological studies are used to assist the interpretation of pressure time histories related to such extreme events. Analyses associated with the derivation of normalized pressure coefficients were concentrated on the identification of direction-dependent pressure characteristics, correlation among consecutive taps and potential effects of the wind unsteadiness on the maximum and minimum values. Building geometry and local topography effects had an important and direct influence on these analyses.

Experimental study on natural ventilation performance of a two-sided wind catcher

Experimental wind tunnel and smoke visualization testing was conducted to investigate the performance of a two-sided wind catcher. This type of wind catcher is divided internally into two halves for the purposes of air supply and extract. In this study, the two-sided wind catcher model was constructed of two similar one-sided wind catcher models, which were attached back to back. These one-sided models are 1: 40 scale models of Kharmani's School wind catcher in the city of Yazd. Experimental investigations were carried out using an open-circuit wind tunnel, and both the induced volumetric airflow into the building and the pressure coefficients around all surfaces of the wind catcher model were measured at various wind angles. Additional experimental tests and computational fluid dynamics simulation of the wind catcher in the wind tunnel were also conducted in order to assess the accuracy of measurement procedures and the uncertainty of experimental results. To evaluate the stack effects on the natural ventilation performance of a two-sided wind catcher system, the results were compared to the corresponding results of a one-sided one. As a result of placing urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined experimentally. The experiments were performed when the wind catcher model with an adjoining house was placed in the wake of upstream objects, resembling neighbouring buildings. It was found that for an isolated two-sided wind catcher model, maximum efficiency is achieved at an air incident angle of 90°, and this can only be explained by the domination of a stack effect rather than dynamic pressure. At this air incident angle the wind catcher efficiency is ≈20 per cent more than the one at zero angle. The results show that the approaching air incident angles, the presence of an object upstream of the structure, and the blowing of atmospheric wind, influence phenomena such as pressure coefficients, induced airflow rate, and the airflow pattern of the two-sided wind catcher. The results show the potential of the two-sided wind catcher as a passive device for providing natural ventilation in buildings.

Effect of wind direction on greenhouse ventilation rate, airflow patterns and temperature distributions

The effect of wind direction, relative to a multi-span naturally ventilated greenhouse, on the airflow patterns and air temperature distribution inside the house and at the openings is investigated in the present study, in a greenhouse with vertical roof openings. Experiments in a full-scale greenhouse, CFD (Computational Fluid Dynamics) full-scale simulations and wind tunnel tests on a small-scale model were carried out. The results showed a significant effect of the wind direction on the flow patterns both inside the house and at the roof openings. Furthermore, wind direction significantly affected the ventilation rate and the air and crop temperature distributions. A reasonable qualitative agreement was achieved between the experiments, numerical simulations and wind tunnel tests with respect to flow patterns through the openings. Quantitatively, the numerically predicted ventilation rates are in reasonable agreement with estimates of ventilation rates obtained by a model given in the literature. However, numerically predicted air velocities at the greenhouse openings differ from the measured values and possible reasons for the differences are highlighted and discussed.

Computational Prediction of Nose-Down Control for F/A-18E at High Alpha

Computational fluid dynamics was used to predict the longitudinal stability and control characteristics of the preproduction F/A-18E Super Hornet configuration with neutral and full nose-down control at high angle of attack, subsonic conditions. Such data contribute to an analysis of the ability of the pilot to recover from extreme angles of attack and are usually obtained and extrapolated from wind-tunnel tests. The current computational study was intended to be an exploratory study of the usefulness of computational fluid dynamics to aid the designer and analysts in predictions of flight behavior. The calculations were made for Mach 0.082 at a Reynolds number of 1.15 x 10 6 based on mean aerodynamic chord at angles of attack between 0 and 60 deg. The F/A-18E was modeled with 34-deg leading-edge flaps, 4-deg trailing-edge flaps, 0-deg aileron deflection, a rudder deflection of 30 deg, a spoiler deflection of 60 deg, and horizontal-tail deflections of 0 and 20 deg. The flow conditions and configuration corresponded to those used in tests of a 15%-scale F/A-18E wind-tunnel model tested at the 30- by 60-ft full-scale wind tunnel at the NASA Langley Research Center in Hampton, Virginia. The flow solver used during this project was USM3D, which was developed by the NASA Langley Research Center. The forces and moments predicted by USM3D compared well to the wind-tunnel data for angles of attack between 0 and 40 deg. For angles of attack from 40 to 60 deg, however, the results from USM3D differed from the wind-tunnel data. These differences are attributed to the unsteady nature of the flow and turbulence effects not adequately captured by the computations.

Experimental investigation of wind turbine noise

Broadband noise is nowadays the major contribution to the total spectrum of noise generated by wind turbines. The mechanisms that generate airfoil self‐noise have been studied through years and many authors agree that dominant noise comes from inflow turbulence, and interaction between turbulent boundary layer and trailing edge of the airfoil. This study presents results from combined experimental techniques in order to better identify and predict noise issuing from a NACA 0012. Noise from trailing edge is most investigated in a 2D configuration in an anechoic wind tunnel, using microphone array (far field measurements), wall pressure fluctuations, hot wire. The data base turns out to be useful in order to improve extensions of Amiet and Brooks models. Some aspects of noise mechanisms and their characteristics are better identified and refined when wind tunnel results are compared to measurements of noise on full scale wind turbines. Measurements in situ achieved with a microphone array of 30 meters wide are used to provide complementary informations on 3D rotating source in terms of localisation and specific directivity.