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Modeling and testing of a thermal transient anemometer

Description: The Thermal Transient Anemometer (TTA) is a fluid mass flow measuring device which utilizes a thermocouple as a probe. The probe is periodically heated by an electric current pulse through the thermocouple junction, and the measured rate of cooling between pulses is related to the local mean flow velocity. The standard thermocouple sensor provides an inexpensive flow probe which is durable, rugged, and capable of satisfactory operation in hostile environments. The TTA was developed and patented in prototype form by Instrument Development for Applied Physics (IDAP), a small US company. IDAP has tested the TTA and shown that the measurement principle is valid. However, there is a need to refine the prototype so that the TTA becomes a commercially viable instrument. The main concern is to reduce the heating current to the TTA so that battery-powered operation is possible. To do this, a probe needs to be developed such that only the region local to the thermocouple junction is heated, rather than the entire length of the wire. There area number of ways that this might be done, and IDAP has worked with ARi Industries, a thermocouple manufacturer, to develop probe designs that would have this characteristic, and at the same time would retain the ruggedness and ease of manufacture of a standard thermocouple. The purpose of this CRADA was to investigate these designs with a view to their possible commercial development. The starting point was to develop a computer model of the TTA as it currently exists, i.e., the prototype configuration, and to compare the results with experimental data. Good agreement between model and data was obtained, thus allowing new designs to be analyzed with some confidence.
Date: October 1, 1996
Creator: Page, R.J.
Partner: UNT Libraries Government Documents Department

Evaluation of a new sonic anemometer for routine monitoring and emergency response applications

Description: Recently, several new sonic anemometers have become available for routine wind measurements. Sonic anemometers avoid many problems associated with the traditional rotating anemometer and vane sets- inertia of moving parts, bearing wear, contamination from dust and ice, frequent maintenance. Without a starting threshold, the sonic anemometer also produces more accurate measurements of wind direction and sigma theta at very low wind speeds. We illustrate these advantages by comparing 20 days of observations from a new sonic anemometer with data from existing cup and vane sensors at the 10-m level of Lawrence Livermore National Laboratory`s meteorological tower.
Date: February 1, 1997
Creator: Gouveia, F.J & Baskett, R.L.
Partner: UNT Libraries Government Documents Department

Interfacial Refraction Through Curved and Plane-Layered Media

Description: Two laser beam tracing codes, AXIAL and CYLINDER, have been written to determine a laser beam path through plane and cylindrical interfaces. For cylindrical interfaces, an equation set was derived which describes the path of the laser beam. For plane interfaces, it was not possible to derive a single equation set. Instead, it was necessary to divide the domain up into small elements or regions. The laser beam path was then determined by calculating the path of the laser beam through each region. AXIAL and CYLINDER can be used to determine where an LDA should be positioned so that velocity measurements can be made at a specified point.
Date: July 17, 2001
Creator: Kehoe, A.B.
Partner: UNT Libraries Government Documents Department

The Long-Term Inflow and Structural Test Program

Description: The Long-term Inflow and Structural Test (LIST) program is collecting long-term, continuous inflow and structural response data to characterize the extreme loads on wind turbines. A heavily instrumented Micon 65/13M turbine with SERI 8-m blades is being used as the first test turbine for this test program. This turbine and its two sister turbines are located in Bushland, TX a test site that exposes the turbines to a wind regime that is representative of a Great Plains commercial site. The turbines and their inflow are being characterized with 60 measurements: 34 to characterize the inflow, 19 to characterize structural response, and 7 to characterize the time-varying state of the turbine. The primary characterization of the inflow into the LIST turbine relies upon an array of five sonic anemometers. These three-axis anemometers are placed approximately 2-diameters upstream of the turbine in a pattern designed to describe the inflow. Primary characterization of the structural response of the turbine uses several sets of strain gauges to measure bending loads on the blades and the tower and two accelerometers to measure the motion of the nacelle. Data from the various instruments are sampled at a rate of 30 Hz using a newly developed data acquisition system that features a time-synchronized continuous data stream that is telemetered from the turbine rotor. The data, taken continuously, are automatically divided into 10-minute segments and archived for analysis. Preliminary data are presented to illustrate the operation of the turbine and the data acquisition and analysis system.
Date: October 17, 2000
Creator: SUTHERLAND,HERBERT J; JONES,PERRY L. & NEAL,BYRON A.
Partner: UNT Libraries Government Documents Department

LIST/BMI Turbines Instrumentation and Infrastructure

Description: In support of two major SNL programs, the Long-term Inflow and Structural Test (LIST) program and the Blade Manufacturing Initiative (BMI), three Micon 65/13M wind turbines have been erected at the USDA Agriculture Research Service (ARS) center in Bushland, Texas. The inflow and structural response of these turbines are being monitored with an array of 60 instruments: 34 to characterize the inflow, 19 to characterize structural response and 7 to characterize the time-varying state of the turbine. The primary characterization of the inflow into the LIST turbine relies upon an array of five sonic anemometers. Primary characterization of the structural response of the turbine uses several sets of strain gauges to measure bending loads on the blades and the tower and two accelerometers to measure the motion of the nacelle. Data are sampled at a rate of 30 Hz using a newly developed data acquisition system. The system features a time-synchronized continuous data stream and telemetered data from the turbine rotor. This paper documents the instruments and infrastructure that have been developed to monitor these turbines and their inflow.
Date: June 1, 2001
Creator: JONES,PERRY L.; SUTHERLAND,HERBERT J. & NEAL,BYRON A.
Partner: UNT Libraries Government Documents Department

Effects of axial heat conduction and material properties on the performance characteristics of a thermal transient anemometer probe

Description: This paper describes an investigation of the axial heat transfer within a thermal transient anemometer probe. A previous study, evaluated the performance characteristics of a thermal transient anemometer system. The study revealed discrepancies between a simplified theory and test results in the development of a universal calibration curve for probes of varying diameters. Although the cause of these discrepancies were left uncertain due to an inadequate theoretical model, the study suggested that axial conduction within the probe could account for the deviations. In this paper, computer simulations are used to further investigate axial heat conduction within the probes. The effect on calibration of axial variations of material properties along the probes is also discussed. Results from the computer simulation are used in lieu of the theoretical model used in the previous study to develop a satisfactory universal calibration curve. The computer simulations provide evidence that there is significant axial heat conduction within the probes, and that this was the cause of the discrepancies noted in the previous study.
Date: July 1, 1995
Creator: Bailey, J.L.; Page, R.J. & Acharya, M.
Partner: UNT Libraries Government Documents Department

Subcooled Boiling Near a Heated Wall

Description: Experimental measurements of void fraction, bubble frequency, and velocity are obtained in subcooled R-134a flowing over a heated flat plate near an unheated wall and compared to analytical predictions. The measurements were obtained for a fixed system pressure and mass flow rate (P = 2.4 MPa and w = 106 kg/hr) at various inlet liquid temperatures. During the experiments, electrical power was applied at a constant rate to one side of the test section. The local void fraction data, acquired with a hot-film anemometer probe, showed the existence of a significant peak near the heated wall and a smaller secondary peak near the unheated wall for the larger inlet subcoolings. Local vapor velocity data, taken with the hot-film probe and a laser Doppler velocimeter, showed broad maxima near the centerline between the heated and unheated plates. Significant temperature gradients near the heated wall were observed for large inlet subcooling. Bubble size data, inferred from measurements of void fraction, bubble frequency and vapor velocity, when combined with the measured bubble chord length distributions illustrate the transition from pure three dimensional spherical to two-dimensional planar bubble flow, the latter being initiated when the bubbles fill the gap between the plates. These various two-phase flow measurements were used for development of a multidimensional, four-field calculational method; comparisons of the data to the calculations show reasonable agreement.
Date: October 27, 2000
Creator: Trabold, T.A.; Maneri, C.C.; Vassallo, P.F. & Considine, D.M.
Partner: UNT Libraries Government Documents Department

Wind measurement systems and wind tunnel evaluation of selected instruments

Description: The Pacific Northwest Laboratory has conducted wind tunnel tests of seven relatively inexpensive wind measurement systems as part of a program to evaluate the accuracy and reliability of instruments for use in small wind energy conversion system siting studies. This report discusses wind measurement systems and documents the results of the wind tunnel studies. Documentation consists of graphs and tables relating system and system component performance to wind speed. The results describe instrument system performance under ideal conditions; tests in the atmosphere are required to evaluate performance under realistic conditions.
Date: May 1, 1981
Creator: Ramsdell, J.V. & Wetzel, J.S.
Partner: UNT Libraries Government Documents Department

Effects of Temporal Wind Patterns on the Value of Wind-GeneratedElectricity at Different Sites in California and the Northwest

Description: Wind power production varies on a diurnal and seasonal basis. In this paper, we use wind speed data from three different sources to assess the effects of wind timing on the value of electric power from potential wind farm locations in California and the Northwestern United States. By ''value'', we refer to either the contribution of wind power to meeting the electric system's peak loads, or the financial value of wind power in electricity markets. Sites for wind power projects are often screened or compared based on the annual average power production that would be expected from wind turbines at each site (Baban and Parry 2001; Brower et al. 2004; Jangamshetti and Rau 2001; Nielsen et al. 2002; Roy 2002; Schwartz 1999). However, at many locations, variations in wind speeds during the day and year are correlated with variations in the electric power system's load and wholesale market prices (Burton et al. 2001; Carlin 1983; Kennedy and Rogers 2003; Man Bae and Devine 1978; Sezgen et al. 1998); this correlation may raise or lower the value of wind power generated at each location. A number of previous reports address this issue somewhat indirectly by studying the contribution of individual wind power sites to the reliability or economic operation of the electric grid, using hourly wind speed data (Fleten et al.; Kahn 1991; Kirby et al. 2003; Milligan 2002; van Wijk et al. 1992). However, we have not identified any previous study that examines the effect of variations in wind timing across a broad geographical area on wholesale market value or capacity contribution of those different wind power sites. We have done so, to determine whether it is important to consider wind-timing when planning wind power development, and to try to identify locations where timing would have a more positive or ...
Date: August 4, 2006
Creator: Fripp, Matthias & Wiser, Ryan
Partner: UNT Libraries Government Documents Department

Final Report for the Joint Urban 2003 Atmospheric Dispersion Study in Oklahoma City: Lawrence Livermore National Laboratory participation

Description: The Joint Urban 2003 (JU2003) field study was designed to collect meteorological and tracer data resolving atmospheric dispersion at scales-of-motion ranging from flows in and around a single city block, in and around several blocks in the downtown Central Business District (CBD), and into the suburban Oklahoma City area a few km from the CBD. Indoor tracer and flow measurements within four downtown study buildings were also made in conjunction with detailed outdoor measurements investigating the outdoor-indoor exchange rates and mechanisms. The movement of tracer within the study buildings was also studied. The data from the field experiment is being used to evaluate models that are being developed for predicting dispersion of contaminants in urban areas. These models may be fast-response models based on semi-empirical algorithms that are used in real-time emergencies, or highly sophisticated computational fluid dynamics models that resolve individual building faces and crevices. The data from the field experiment, together with the models, can then be used to develop other advanced tools that are especially valuable in the efforts to thwart terrorists. These include tools for finding location and characteristics of a contaminant source; tools that can be used for real-time response or for forensic investigation. The tools will make use of monitoring networks for biological agents that are being established in several sensitive cities throughout the nation. This major urban study was conducted beginning June 28 and ending July 31, 2003. It included several integrated scientific components necessary to describe and understand the physical processes governing dispersion within and surrounding an urban area and into and within building environments. The components included characterizing: (1) the urban boundary layer and the development of the urban boundary layer within the atmospheric boundary layer, (2) the flows within and downwind of the tall-building core, (3) the flows within a ...
Date: October 12, 2005
Creator: Leach, M J
Partner: UNT Libraries Government Documents Department

Automation&Characterization of US Air Force Bench Top Wind Tunnels - Summary Report

Description: The United States Air Force Precision Measurement Equipment Laboratories (PMEL) calibrate over 1,000 anemometer probes per year. To facilitate a more efficient calibration process for probe-style anemometers, the Air Force Metrology and Calibration Program underwent an effort to modernize the existing PMEL bench top wind tunnels. Through a joint effort with the Department of Energy's Oak Ridge National Laboratory, the performance of PMEL wind tunnels was improved. The improvement consisted of new high accuracy sensors, automatic data acquisition, and a software-driven calibration process. As part of the wind tunnel upgrades, an uncertainty analysis was completed, laser Doppler velocimeter profiling was conducted to characterize the velocities at probe locations in the wind tunnel, and pitot tube calibrations of the wind tunnel were verified. The bench top wind tunnel accuracy and repeatability has been measured for nine prototype wind tunnel systems and valuable field experience has been gained with these wind tunnels at the PMELs. This report describes the requirements for the wind tunnel improvements along with actual implementation strategies and details. Lessons-learned from the automation, the velocity profiling, and the software-driven calibration process will also be discussed.
Date: March 23, 2006
Creator: Hardy, J.E.
Partner: UNT Libraries Government Documents Department

ROUGHNESS LENGTHS FOR THE SAVANNAH RIVER SITE

Description: Surface roughness values for the areas surrounding the H, D and N-Area meteorological towers were computed from archived 2010 meteorological data. These 15-minute-averaged data were measured with cup anemometers and bidirectional wind vanes (bivanes) 61 m above the surface. The results of the roughness calculation using the standard deviation of elevation angle {sigma}{sub E}, and applying the simple formula based on tree canopy height, gave consistent estimates for roughness around the H-Area tower in the range of 1.76 to 1.86 m (95% confidence interval) with a mean value of 1.81 m. Application of the {sigma}{sub E} method for the 61-m level at D and N-Areas gave mean values of 1.71 and 1.81 with confidence ranges of 1.62-1.81 and 1.73-1.88 meters, respectively. Roughness results are azimuth dependent, and thus are presented as averages over compass sectors spanning 22.5 degrees. Calculated values were compared to other methods of determining roughness, including the standard deviation of the azimuth direction, {sigma}{sub A}, and standard deviation of the wind speed, {sigma}{sub U}. Additional data was obtained from a sonic anemometer at 61-m on the H-Area tower during a period of a few weeks in 2010. Results from the sonic anemometer support our use of {sigma}{sub E} to calculate roughness. Based on the H-Area tower results, a surface roughness of 1.8 m using is recommended for use in dispersion modeling applications that consider the impacts of a contaminant release to individuals along the Site boundary. The canopy surrounding the H-Area tower is relatively uniform (i.e., little variance in roughness by upwind direction), and data supplied by the U.S. Forest Service at Savannah River show that the canopy height and composition surrounding the H-Area tower is reasonably representative of forested areas throughout the SRS reservation. For dispersion modeling analyses requiring assessments of a co-located worker within the ...
Date: March 28, 2012
Creator: Hunter, C.
Partner: UNT Libraries Government Documents Department

Atmospheric Stability Impacts on Power Curves of Tall Wind Turbines - An Analysis of a West Coast North American Wind Farm

Description: Tall wind turbines, with hub heights at 80 m or above, can extract large amounts of energy from the atmosphere because they are likely to encounter higher wind speeds, but they face challenges given the complex nature of wind flow and turbulence at these heights in the boundary layer. Depending on whether the boundary layer is stable, neutral, or convective, the mean wind speed, direction, and turbulence properties may vary greatly across the tall turbine swept area (40 to 120 m AGL). This variability can cause tall turbines to produce difference amounts of power during time periods with identical hub height wind speeds. Using meteorological and power generation data from a West Coast North American wind farm over a one-year period, our study synthesizes standard wind park observations, such as wind speed from turbine nacelles and sparse meteorological tower observations, with high-resolution profiles of wind speed and turbulence from a remote sensing platform, to quantify the impact of atmospheric stability on power output. We first compare approaches to defining atmospheric stability. The standard, limited, wind farm operations enable the calculation only of a wind shear exponent ({alpha}) or turbulence intensity (I{sub U}) from cup anemometers, while the presence at this wind farm of a SODAR enables the direct observation of turbulent kinetic energy (TKE) throughout the turbine rotor disk. Additionally, a nearby research meteorological station provided observations of the Obukhov length, L, a direct measure of atmospheric stability. In general, the stability parameters {alpha}, I{sub U}, and TKE are in high agreement with the more physically-robust L, with TKE exhibiting the best agreement with L. Using these metrics, data periods are segregated by stability class to investigate power performance dependencies. Power output at this wind farm is highly correlated with atmospheric stability during the spring and summer months, while atmospheric ...
Date: February 22, 2010
Creator: Wharton, S & Lundquist, J K
Partner: UNT Libraries Government Documents Department

CHARACTERIZATION OF AIRFLOWS NEAR THE EXIT OF HVAC REGISTERS USING LASER DOPPLER VELOCIMETRY (LDV).

Description: A facility to characterize the airflow at the exit of HVAC registers was designed and fabricated. The objective of this work is to obtain velocity and turbulence data at the exit of registers, which can then be used as an input boundary condition in a modern Computational Fluid Dynamics (CFD) code to predict the velocity and temperature distribution in an enclosure, and also the register performance parameters such as throw. During the course of this work, two commonly used registers were tested. Both registers were 8 inch x 4 inch sidewall registers. Laser Doppler Velocimetry was used to measure the axial and vertical components of the velocity vector at various locations across the face of the registers. For the two cases of registers studied here, the results suggest that the velocity field at the very exit of each of these registers scales with the flow rate through the registers. This means that, in the mode of operation in which the supply fan (of an HVAC system) has a ''High'' and ''Low'' setting, similar velocity scaling would result for the type of registers tested here.
Date: March 13, 2003
Creator: TUTU,N.K.; KRISHNA,C.R.; ANDREWS,J.W. & BUTCHER,T.A.
Partner: UNT Libraries Government Documents Department

Comparison of data from co-located sensor packages and implications for dispersion modeling: An in situ case study of rugged versus low-threshold anemometers and natural-versus forced-ventilation solar shields

Description: We compared 27 days of 15-minute-average data from two sets of co-located wind and temperature sensors at 10- and 40-m levels on a tower at Lawrence Livermore National Laboratory. One anemometer set was rugged and the other was more sensitive with a lower threshold. At moderate winds (2<U<10 m/s) wind speed and direction between the two sets of sensors were strongly correlated. At low winds (U<2 m/s), the two sets produced small discrepancies due to different thresholds and calibration methods for the wind speed sensors. Stability class (Modified Sigma Theta method) was the same for each sensor package for 76% of the study period and within one stability class for 94% of the time. We also compared temperature data from the naturally aspirated solar shields with data from fan-aspirated shields. The tendencies were expected and quantified: large temperature differences when the wind speed was low and insolation was great. Temperature difference was greater than 1{degrees}C about 15% of the study period and greater than 0.5{degrees}C about 39% of the time.
Date: April 1, 1996
Creator: Gouveia, F.J. & Baskett, R.L.
Partner: UNT Libraries Government Documents Department

Hot-film anemometer measurements in adiabatic two-phase flow through a vertical duct

Description: A hot-film anemometer (HFA) probe was used to obtain local measurements of void fraction and bubble frequency in a vertically oriented, high aspect ratio duct containing R-134a under selected adiabatic two-phase flow conditions. Data were obtained along a narrow dimension scan over the range 0.03 {le} {bar Z} {le} 0.80, where {bar Z} is the distance from the wall normalized with the duct spacing dimension. The void fraction profiles displayed large gradients in the near-wall regions and broad maxima near the duct centerline. The trends in the bubble frequency data generally follow those for the local void fraction data. However, the relatively large number of bubbles at higher pressure implies a larger magnitude of the interfacial area concentration, for the same cross-sectional average void fraction. For the two annular flow conditions tested, analysis of the HFA output voltage signal enabled identification of three distinct regions of the flow field; liquid film with dispersed bubbles, interfacial waves, and continuous vapor with dispersed droplets.
Date: June 1, 1997
Creator: Trabold, T.A.; Moore, W.E. & Morris, W.O.
Partner: UNT Libraries Government Documents Department

Wind Turbine Wake Measurements in the Operating Region of a Tail Vain

Description: In conjunction with the National Renewable Energy Laboratory's (NREL's) Unsteady Aerodynamics Experiment (UAE) at NASA Ames, we measured the wake of an upwind 10-meter (m) diameter wind turbine in the typical region of a tail vane. The experiment was performed in a 24.4-by-36.6-m wind tunnel. We placed two sonic anemometers 0.58 rotor diameters downwind of the rotor at hub height. One was positioned nominally behind the nacelle at 9% radius and the second was placed 2-m outboard at 49% radius. The tunnel wind speed was varied from 5 to 25 meters per second (m/s) and the turbine rotor speed was held at 72 revolutions per minute (rpm). We varied yaw from 0{degree} to 60{degree}. The data showed unsteadiness in the wake due to the nacelle wake. Also, the unsteadiness increased with the onset of blade stall. The axial induction factor in the wake showed that the turbine was operating within the windmill brake state of actuator disk momentum theory. Little variation in unsteadiness was shown under yawed conditions. We also discovered that lateral velocity behind the nacelle was negative and would result in an unfurling normal force on a tail vane. The vertical velocity was shown to change sign under yawed conditions, conceivably as a result of the opposing blade root vortex.
Date: January 22, 2001
Creator: Larwood, S.
Partner: UNT Libraries Government Documents Department

Wind Climate Analyses for a 61-M Tower in the Southeast

Description: The Savannah River Technology Center's (SRTC) Atmospheric Technologies Group (ATG) has operated nine 61-m tower sites including the Central Climatology (CC) tower which is located near the center of the Savannah River Site (SRS) since 1985. Data from the weather instruments on this tower have provided answers to questions involving risk analyses, dose studies, forecast verifications, and wind/temperature conditions during extreme events and planned tests. Most recently, data from these towers are being used for initial and boundary conditions for computationally intensive numerical simulations using mesoscale forecasting models that are run on a three-hourly basis by ATG for SRS and the surrounding vicinity. We found that a series of wind roses based on relatively short time scales (from two weeks to one hour) were a convenient method to depict the predominant wind speeds and directions at anemometer sites in the Southeast operated by the NWS. That report also revealed some interesting spatial and temporal relationships among thirteen NWS stations in the Carolinas, Georgia, and Florida. Our study here will focus on the CC tower to show changes in the wind speed and direction distributions with height during diurnal and annual cycles. This study will concentrate on mean wind speed and direction statistics.
Date: November 24, 2003
Creator: Weber, A.H.
Partner: UNT Libraries Government Documents Department

Measurement of Turbulent Wind Velocities Using a Rotating Boom Apparatus

Description: The present report covers both the development of a rotating-boom facility and the evaluation of the spectral energy of the turbulence measured relative to the rotating boom. The rotating boom is composed of a helicopter blade driven through a pulley speed reducer by a variable speed motor. The boom is mounted on a semiportable tower that can be raised to provide various ratios of hub height to rotor diameter. The boom can be mounted to rotate in either the vertical or horizontal plane. Probes that measure the three components of turbulence can be mounted at any location along the radius of the boom. Special hot-film sensors measured two components of the turbulence at a point directly in front of the rotating blade. By using the probe rotated 90/sup 0/ about its axis, the third turbulent velocity component was measured. Evaluation of the spectral energy distributions for the three components of velocity indicates a large concentration of energy at the rotational frequency. At frequencies slightly below the rotational frequency, the spectral energy is greatly reduced over that measured for the nonrotating case measurements. Peaks in the energy at frequencies that are multiples of the rotation frequency were also observed. We conclude that the rotating boom apparatus is suitable and ready to be used in experiments for developing and testing sensors for rotational measurement of wind velocity from wind turbine rotors. It also can be used to accurately measure turbulent wind for testing theories of rotationally sampled wind velocity.
Date: April 1, 1984
Creator: Sandborn, V. A. & Connell, J. R.
Partner: UNT Libraries Government Documents Department

Measured and predicted rotor performance for the SERI advanced wind turbine blades

Description: Measured and predicted rotor performance for the SERI advanced wind turbine blades were compared to assess the accuracy of predictions and to identify the sources of error affecting both predictions and measurements. An awareness of these sources of error contributes to improved prediction and measurement methods that will ultimately benefit future rotor design efforts. Propeller/vane anemometers were found to underestimate the wind speed in turbulent environments such as the San Gorgonio Pass wind farm area. Using sonic or cup anemometers, good agreement was achieved between predicted and measured power output for wind speeds up to 8 m/sec. At higher wind speeds an optimistic predicted power output and the occurrence of peak power at wind speeds lower than measurements resulted from the omission of turbulence and yaw error. In addition, accurate two-dimensional (2-D) airfoil data prior to stall and a post stall airfoil data synthesization method that reflects three-dimensional (3-D) effects were found to be essential for accurate performance prediction. 11 refs.
Date: February 1, 1992
Creator: Tangler, J.; Smith, B.; Kelley, N. & Jager, D.
Partner: UNT Libraries Government Documents Department

A discussion of the results of an in-situ comparison of three full-vector anemometers

Description: Extensive field measurements and the numerical modeling of dynamic responses associated with wind turbine rotor blades have pointed to strong interactions with coherent turbulent structures in the turbine inflow. These interactions are thought to be a major source of high-cycle fatigue in the primary structural components of wind turbines. The sources of such turbulent structures are not only natural terrain features but also the wakes from upwind turbines. Many unsteady aerodynamic processes are excited by turbulent eddies ranging in size from several rotor diameters down to the dimensions of the mean blade chord. These processes are responsible for inducing large, fluctuating loads on the turbine rotor blades. For the wind turbine generators now in use, this encompasses a spatial range of about 0.1 to 300 m. To assess our ability to measure the coherent properties of inflow turbulence over such a wide range of spatial range, we performed a study to compare three full-vector anemometers. We believe that to identify the dominant fluid dynamic properties of such flows, the instrumentation used must be capable of good fidelity measurements over the desired spatial range. The sonic anemometer is a primary candidate; we also wanted to compare the results associated with a well-designed mechanical instrument which is available at considerably less cost. Two sonic designs and as propeller-bivane were exposed to turbulent flows downstream of both extremely complex and moderately rolling terrain. This paper discusses some of the results of these comparisons with an emphasis on the measurements of turbulent fluctuations.
Date: October 1, 1990
Creator: Kelley, N.D.; Scott, G.N. & Allread, J.S.
Partner: UNT Libraries Government Documents Department