Propeller Anemometer Research Articles

A Vertical Propeller Eddy-Covariance Method and Its Application to Long-term Monitoring of Surface Turbulent Fluxes on the Greenland Ice Sheet

On the Greenland ice sheet, the sensible heat flux is the second largest source of energy for surface melt. Yet in atmospheric models, the surface turbulent heat fluxes are always indirectly estimated using a bulk turbulence parametrization, which needs to be constrained by long-term and continuous observations. Unfortunately, such observations are challenging to obtain in remote polar environments, especially over ablating ice surfaces. We therefore test a classical eddy-covariance method, based on propeller anemometers and thermocouple measurements, to estimate the momentum and sensible heat fluxes on the Greenland ice sheet. To correct for the high-frequency attenuation, we experimentally derive the sensor frequency-response characteristics and evaluate the universal turbulence spectra on the ice sheet. We show that the corrected fluxes are accurate and that the sampling interval can be reduced to 4 s to increase the system’s autonomy. To illustrate its potential, we apply the correction to one year of vertical propeller eddy-covariance measurements in the western ablation area of the ice sheet, and quantify the seasonal variability of the sensible heat flux and of the aerodynamic roughness length.

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Aerodynamic drag coefficient over equatorial coastal industrialized and urban areas

Drag coefficient (CD) in the urban roughness sublayer over industrialized and urban equatorial areas under low wind conditions are reported in this paper. An observation tower was set up in (1) the field of the Institusi Teknologi Tunku Abdul Rahman in the middle of the Prai Industrial Park (5°22′N, 100°23′E), employing a Gill UVW propeller anemometer and a temperature sensor placed at a height of 10m above the ground level and (2) on the top of a faculty building in Universiti Sains Malaysia (USM) (5°21′N, 100°18′E), employing a sonic anemometer at 18m above the ground level. Meteorological data were collected for three months in the years 2006 and 2010. Monin–Obukhov similarity theory using local scales was first tested at the sites studied and was found to be applicable. The relationships between CD and mean wind speed, V, local friction velocity, u⁎l, and atmospheric stability, ζl, are also discussed (subscript “l” denotes local). Generally, CD is strongly dependent and increased with u*l for both sites. CD was also confirmed to be influenced by atmospheric stability where it is at its maximum when u*l (and V) is large, which generally occurs in neutral atmospheric conditions. This relationship was seen at both sites, suggesting its generality. Lastly, the measured CDN value obtained was also used to calculate CGN, geostrophic drag coefficient (=1.9×10−3), which is similar to the reported values in the literature.

Deviation of Cup and Propeller Anemometer Calibration Results with Air Density

The effect of air density variations on the calibration constants of several models of anemometers has been analyzed. The analysis was based on a series of calibrations between March 2003 and February 2011. Results indicate a linear behavior of both calibration constants with the air density. The effect of changes in air density on the measured wind speed by an anemometer was also studied. The results suggest that there can be an important deviation of the measured wind speed with changes in air density from the one at which the anemometer was calibrated, and therefore the need to take this effect into account when calculating wind power estimations.

Greenhouse Gas (GHG) Emissions from Mechanically Ventilated Deep Pit Swine Gestation Operation

Emission of greenhouse gases (GHGs) from mechanically ventilated deep pit manure storage was monitored in a swine gestation operation. Air samples were collected from pit exhaust fans at different times of the year (fall, summer, and spring) using a vacuum chamber and Tedlar bags. GHGs concentrations were measured with a greenhouse gas chromatograph (GC) within 24 hours of collection. Air flow rates from exhaust fans were measured using a 160 mm bi-directional Gill propeller anemometer and the ventilation rate was determined as the summation of air flow rates from all fans. The average methane (CH4) concentration was 88±61 ppm and CH4 concentration differences were statistically significant among sampling dates and seasons. The carbon dioxide (CO2) concentration followed the same trend as CH4. The average CO2 concentration was 1105±1063 ppm. Nitrous oxide (N2O) concentrations ranged from 0.02 to 0.66 ppm. Methane emissions varied between 115.94 to 572.18 g d-1 AU-1 and higher methane emission was observed during summer (480.28 g d-1 AU-1). The average carbon dioxide emissions varied from 5.35 to 15.83 kg d-11 AU-1, whereas average N2O emissions varied from 0.06 to 7.30 g d-1AU-1. Significant variation of GHG concentrations and emissions were observed among fall, summer and spring seasons.

Whole Process Wind Characteristics Field Measurements of a Strong Wind

This paper presents field measurement results of boundary layer wind characteristics over typical open country during the passages of typhoon Fung-wong passed by Wenzhou in July 2008. The field data such as wind speed and wind direction were measured from two propeller anemometers placed at the height of about 30m. The measured wind data are analyzed to obtain the information on mean wind speed and direction, turbulence intensity, gust factor, turbulence integral length scale and spectra of wind speed fluctuations. The results clearly demonstrate that the turbulence intensity and gust factor of typhoon Fung-wong are larger than normal, and there is a tendency for the turbulence intensities to decrease with the increase of the mean wind speed, however, there is another tendency for the turbulence integral length scale to increase with the increase of the mean wind speed. The power spectral densities of fluctuating wind speed in longitudinal and lateral directions obtained from the measured wind speed data roughly fit with Von Karman spectra. The results presented in this paper are expected to be of use to researchers and engineers involved in design of low-rise buildings.

Analysis of calibration results from cup and propeller anemometers. Influence on wind turbine Annual Energy Production (AEP) calculations

AbstractThe calibration coefficients of several models of cup and propeller anemometers were analysed. The analysis was based on a series of laboratory calibrations between January 2003 and August 2007. Mean and standard deviation values of calibration coefficients from the anemometers studied were included. Two calibration procedures were used and compared. In the first, recommended by the Measuring Network of Wind Energy Institutes (MEASNET), 13 measurement points were taken over a wind speed range of 4 to 16 m s−1. In the second procedure, 9 measurement points were taken over a wider speed range of 4 to 23 m s−1. Results indicated no significant differences between the two calibration procedures applied to the same anemometer in terms of measured wind speed and wind turbines' Annual Energy Production (AEP). The influence of the cup anemometers' design on the calibration coefficients was also analysed. The results revealed that the slope of the calibration curve, if based on the rotation frequency and not the anemometer's output frequency, seemed to depend on the cup center rotation radius. Copyright © 2010 John Wiley & Sons, Ltd.

Ammonia emission rates from dairy livestock buildings in Eastern Canada

Gaseous ammonia emissions from livestock production are deemed responsible for the acidification of several ecosystems and for the formation of PM 2.5 . The latter induces adverse health effects in humans, mostly respiratory ailments. In this study, ammonia emission rates from two tie-stall commercial dairy buildings were monitored in Canada where little data is currently available. Buildings studied were mechanically ventilated and livestock management practices were typical of Eastern Canada. Ammonia emission measurements made at building A during the months of February and March 2007 ranged from 3.77 to 6.80 g day −1 animal −1 while those performed at building B during summer 2007 ranged from 11.33 to 18.20 g day −1 animal −1 . These values fall within the range of ammonia emission rates found in the literature for studies completed in Western Europe: 0.1625 g day −1 AU −1 to 23.38 g day −1 animal −1 . A titration method, using acid traps, was used at building B to measure average ammonia concentrations while an electrochemical ammonia analyser was used at building A for continuous measurements. Propeller anemometers were developed to measure building ventilation flow rates. The precision of the equipment used to measure building ventilation rates and gaseous ammonia concentrations inside the building were evaluated at both locations.

Improved Wind and Turbulence Measurements Using a Low-Cost 3-D Sonic Anemometer at a Low-Wind Site

A year of data from sonic anemometer and mechanical wind sensors was analyzed and compared at a low-wind site. Results indicate that 15-minute average and peak 1-second wind speeds (u) from the sonic agree well with data derived from a co-located cup anemometer over a wide range of speeds. Wind direction data derived from the sonic also agree closely with those from a wind vane except for very low wind speeds. Values of standard deviation of longitudinal wind speed (σu) and wind direction fluctuations (σø) from the sonic and mechanical sensors agree well for times with u > 2 ms-1 but show significant differences with lower u values. The most significant differences are associated with the standard deviation of vertical wind fluctuations (σw): the co-located vertical propeller anemometer yields values increasingly less than those measured by the sonic anemometer as u decreases from 2.5 approaching 0 ms-1. The combination of u over-estimation and under-estimation of σw from the mechanical sensors at low wind speeds causes considerable underestimation of the standard deviation of vertical wind angle fluctuations (σø), an indicator of vertical dispersion. Calculations of σø from sonic anemometer measurements are typically 5° to 10° greater than from the mechanical sensors when the mechanical instruments indicate that σø < 5° or so. The errors with the propeller anemometer, cup anemometer and wind vane, caused by their inability to respond to higher frequency (smaller scale) turbulent fluctuations, can therefore lead to large (factors of 2 to 10 or more) errors in both the vertical and horizontal dispersion during stable conditions with light winds. The sonic anemometer clearly provides more accurate and reliable wind data than the mechanical wind sensor with u < 2.5 ms-1

Evaluations of the von Kármán constant in the atmospheric surface layer

The von Kármán constant $k$ relates the flow speed profile in a wall-bounded shear flow to the stress at the surface. Recent laboratory studies in aerodynamically smooth flow report $k$ values that cluster around 0.42–0.43 and around 0.37–0.39. Recent data from the atmospheric boundary layer, where the flow is usually aerodynamically rough, are similarly ambiguous: $k$ is often reported to be significantly smaller than the canonical value 0.40, and two recent data sets suggest that $k$ decreases with increasing roughness Reynolds number $Re_{\ast}$. To this discussion, we bring two large atmospheric data sets that suggest $k$ is constant, 0.387$\,{\pm}\,$0.003, for $2\, {\le}\,\hbox{\it Re}_\ast \,{\le} \,100$.The data come from our yearlong deployment on Arctic sea ice during SHEBA, the experiment to study the Surface Heat Budget of the Arctic Ocean, and from over 800 h of observations over Antarctic sea ice on Ice Station Weddell (ISW). These were superb sites for atmospheric boundary-layer research; they were horizontally homogeneous, uncomplicated by topography, and unobstructed and uniform for hundreds of kilometres in all directions.During SHEBA, we instrumented a 20 m tower at five levels between 2 and 18 m with identical sonic anemometer/thermometers and, with these, measured hourly averaged values of the wind speed $U(z)$ and the stress $\tau (z)$ at each tower level $z$. On ISW, we measured the wind-speed profile with propeller anemometers at four heights between 0.5 and 4 m and measured $\tau $ with a sonic anemometer/thermometer at one height. On invoking strict quality controls, we gleaned 453 hourly $U(z)$ profiles from the SHEBA set and 100 from the ISW set. All of these profiles reflect near-neutral stratification, and each exhibits a logarithmic layer that extends over all sampling heights. By combining these profiles and our measurements of $\tau $, we made 553 independent determinations of $k$. This is, thus, the largest, most comprehensive atmospheric data set ever used to evaluate the von Kármán constant.

Measurements of Wake Vortices Interacting with the Ground

Although wake vortices are known to decay more rapidly near the ground than away from the ground, the details of the ground interaction are not well understood. Propeller anemometer arrays located under the approach path have been used to study vortex transport and provide some information about the vortex interaction with the ground, such as the generation of secondary vortices via boundary-layer detachment. A propeller anemometer array at John F. Kennedy International Airport using 8.5-m poles was augmented with 1) a sonic anemometer measuring three-dimensional wind and temperature at 10 Hz and 2) a vertical array of vertical wind and crosswind anemometers, mounted at four additional levels (4.2, 3.2, 1.05, and 0.5 m). The sonic anemometer gave 1) measurements of turbulence inside the vortex flowfield and 2) indications of vertical variations in the ambient headwind and temperature, which were brought down to the measurement level by the descent of the vortex recirculation oval. In general, under conditions of low to moderate turbulence, the turbulence level inside the wake vortex flowfield is greater than that in the ambient wind. The vertical anemometer array showed that the crosswind profile under a wake vortex in ground effect has a very thin boundary layer, much thinner than that of the ambient wind. It also provided some details concerning the wind profile of the secondary vortex.

Evapotranspiration of flood-irrigated pecans

Pecan orchards require more irrigation water to maximize yield than any other crop grown in the Southwest US. This paper reports daily evapotranspiration (Et) measurements for 2001 and 2002 in a 5.1 ha, mature pecan orchard on the Rio Grande floodplain, 7 km south of Las Cruces, NM, USA. The 21-year-old stand had an average tree height of 12.8 m, diameter at breast height of 30 cm, and tree spacing of 9.7 m × 9.7 m. Additional pecan orchards surrounded the study orchard. When the tensiometer reached a suction of 65 kPa at the 45 cm depth, the orchard was flood-irrigated. Sparling meters were installed on the pumps and read before and after each irrigation. The total irrigation amount was 1940 mm in 2001 and 1870 mm in 2002. A walk-up tower was placed in the orchard’s center to support flux sensors at 16 m height. The instrument package included a net radiation (Rn), discs for soil heat flux ( G), and two sets of one-propeller eddy covariance (OPEC) sensors. OPEC systems measure sensible heat flux ( H) with a sensitive, vertically oriented propeller anemometer and a fine-wire thermocouple. Latent heat flux (LE) was obtained as a residual in the surface energy balance LE = Rn − G − H. The maximum daily evapotranspiration was 8 mm/day, and the yearly cumulative evapotranspiration averaged for 2 years was 1420 mm, resulting in a yearly average irrigation application efficiency of 79%. The crop coefficient (daily measured Et/reference Penman Et) ranged from 0.2 to 1.1. Increased evaporation due to irrigation was detected only for the April 9 irrigation in 2001. The seasonal water use was 4% lower in 2001 and 12% lower in 2002 than previously reported values.

Atmospheric Turbulence Decay During the Solar Total Eclipse of 11 August 1999

The studies of turbulence decay were based in the past on measurements carried out in neutrally stratified wind tunnels and, more recently, on large-eddy simulation runs. Here the atmospheric turbulence decay process during the solar total eclipse of 11 August 1999 is examined. Thus a rapid transition from convective boundary-layer turbulence to that of a neutral or slightly stable one is considered. A u-v-w propeller anemometer and a fast response temperature sensor located in northern France on top of a 9-m mast recorded the turbulence observations. The measurements, in terms of turbulent kinetic energy decay with time, were found to be in good agreement with those prescribed by a theoretical model of turbulence decay recently proposed. In particular, it was found that the exponent of the power law describing the decay process has the value -2.

MEASUREMENT OF PARTICULATE MATTER EMISSIONS FROM CORN RECEIVING OPERATIONS WITH SIMULATED HOPPER-BOTTOM TRUCKS

Dust emissions from grain elevator operations can be a safety and health risk as well as a nuisance. Fundamentaldata on air entrainment and dust emission are needed for designing adequate and effective dust emission control methods. Thisstudy measured the amount of entrained air and emitted dust during corn receiving operations at an elevator operated by theUSDA-ARS Grain Marketing and Production Research Center in Manhattan, Kansas. Shelled corn (maize) was unloaded froma storage bin, representing a hopper-bottom truck, to the receiving pit at rates of 17 to 262 kg/s and drop heights of 38 to 56cm. Airflow rates were measured with propeller anemometers. The emission rates of total suspended particulates (TSP) andparticulate matter smaller than 10 .m aerodynamic diameter (PM10) were measured with high-volume particulate samplers.The amount of air entrained per unit volume of grain decreased with increasing grain flow rate (0.26 to 2.07 m3/m3). Theemission rates of TSP (8.3 to 52.1 g/metric ton of grain received) and PM10 (0.6 to 6.1 g/t) decreased with increasing grainflow rate and decreasing drop height.

FAN ASSESSMENT NUMERATION SYSTEM (FANS) DESIGN AND CALIBRATION SPECIFICATIONS

A device for insitu fan airflow measurement, known as the Fan Assessment Numeration System (FANS) device, previously developed and constructed at the USDAARS Southern Poultry Research Laboratory, was refined at University of Kentucky as part of a project for quantifying building emissions from mechanically ventilated poultry and livestock facili- ties. The FANS incorporates an array of five propeller anemometers to perform a realtime traverse of the airflow entering fans of up to 137 cm (54 in.) diameter. Details of the updated design, including hardware, software, and calibration methodolo- gy are presented. An error analysis of the flow rate, and calibration results from ten FANS units, is provided. Sufficient details of fabrication and calibration are presented so that interested readers can replicate a FANS for their use. Full design details are available at www.bae.uky.edu/IFAFS/FANS.htm.

Stable Atmospheric Boundary-Layer Experiment in Spain (SABLES 98): A Report

This paper describes the Stable Atmospheric Boundary Layer Experiment in Spain (SABLES 98), which took place over the northern Spanish plateau comprising relatively flat grass- land, in September 1998. The main objectives of the campaign were to study the properties of the mid-latitude stable boundary layer (SBL). Instrumentation deployed on two meteorological masts (of heights 10 m and 100 m) included five sonic anemometers, 15 thermocouples, five cup anemometers and three propeller anemometers, humidity sensors and radiometers. A Sensitron mini-sodar and a tethered balloon were also operated continuously. A triangular array of cup anemometers was installed to allow the detection of wave events. Two nocturnal periods analysed on 14-15 and 20-21 September are used to illustrate the wide-ranging characteristics of the SBL.

Wind Tunnel And Field Measurements Of Turbulent Flow In Forests. Part I: Uniformly Thinned Stands

Many forest management methods alterstand density uniformly. The effectsof such a change on the wind andturbulence regimes in the forest arecritical to a number of processes governingthe stability of the stand and itsmicroclimate. We measured wind speed andturbulence statistics with a Dantec tri-axialhot-film probe in model forests of variousdensities (31–333 trees m-2), created byremoving whole trees in a regular pattern in awind tunnel, and compared them with similarmeasurements made with propeller anemometers insimilarly thinned plots (156–625 trees ha-1)within a Sitka spruce stand in Scotland. The results agree well, in general, with measurements made inother such studies with diverse canopy types.The systematic variations with density and verticalleaf-area distribution (which differed betweenwind-tunnel and field trees) in our work can explainmuch of the variability shown in scaled profiles ofbasic turbulence statistics reported in theliterature. The wind tunnel and field results are shown to be in good agreement overalldespite the difference in vertical leaf-areadistribution. Within-canopy and isolated-treedrag coefficients in the wind tunnel showthat tree-scale shelter effects increase astree density increases. The measurements indicatethat turbulence in the canopy is dominated bylarge-scale structures with dimensions of the sameorder as the height of the canopy as found inother studies but suggest that inter-tree spacing also modulates the size of these structures. These structures are associated with the sweeps that dominatemomentum exchange in the canopy and it is thisfact that allows the tri-axial probe to operate sowell despite the relatively narrow range of anglesin which the wind vector is correctly measured. Theratio of streamwise periodicity of these structuresto vorticity thickness varies systematically withtree density in the range 2.7–5.1, which spans theexpected range of 3.5–5 found in a laboratorymixing-layer, suggesting that tree spacing imposes another relevant length scale. This test andothers show that the results are in agreement withthe idea that canopy turbulence resembles that of a mixing layer even though they disagree with, and challenge the linear relationship between, streamwise periodicity andshear length scale presented recently in theliterature. The measurements are also in goodoverall agreement with simple drag models presented recently by other researchers.

Behaviour Of An Ultrasonic Anemometer Under Cloudy Conditions

The use of ultrasonic anemometers under cloudy weather conditions is often doubted, even rejected or not discussed in the literature. To investigate the influence of liquid water content on the behaviour of sonic anemometers a small intercomparison experiment using an ultrasonic anemometer, a fast response propeller anemometer, and a Particulate Volume Monitor was performed at the German Environmental Research Station ‘Schneefernerhaus’ near the top of Mt. Zugspitze. The results obtained under different conditions (dry/cloudy) give no significant hint on such an influence.

Recirculating Flow Generated by Line-Source Bubble Plumes

The flow structure in the far field of line-source bubble plumes in shallow water is investigated. Recirculating cells form at both sides of the plume. Cell lengths, as given by other investigators, vary between 2.5 and 7 times the water depth. The variations are caused in part by different definitions of cell length and by the different geometries of the experimental setups. In the present study the influence of the cross-sectional geometry of the channel on the cell structure is investigated experimentally. Experiments have been made in a tank with dimensions 1 × 1 × 40 m. A dividing wall has been used to vary the width of the channel. Flow velocities in the plane of symmetry have been measured by use of a propeller anemometer. These results have been supplemented by measurements with an acoustic Doppler velocimeter. Different criteria for the definition of the cell length have been examined, such as the surface flow rate, the surface velocity, and surface flow patterns. The velocity distributions show a strong influence of the cross-sectional geometry. For values of the depth-to-width ratio higher than unity the cell length is rather short. In a very wide channel three-dimensional effects occur. The aspect ratio is found to be a characteristic parameter for the flow. For an analysis of the flow in the far field, a model based on an analogy of the surface flow with a free (half) jet with counterflow is proposed.

Validation of NCAR 10.6-μm CO2Doppler Lidar Radial Velocity Measurements and Comparison with a 915-MHz Profiler

Abstract The capability of the NCAR 10.6-μm-wavelength CO2 Doppler lidar to measure radial air motion is validated by examining hard-target test data, comparing measurements with those from a two-axis propeller anemometer and a 915-MHz profiling radar, and analyzing power spectra and autocovariance functions of the lidar radial velocities in a daytime convective boundary layer. Results demonstrate that the lidar is capable of measuring radial velocity to less than 0.5 m s−1 precision from 20 laser pulse averages under high signal-to-noise ratio conditions. Hard-target test data and comparisons with other sensors show that the lidar data can be biased by as much as ±2 m s−1 when operating in the coherent oscillator mode and that correlated errors are negligible. Correlation coefficients are as large as 0.96 for 90-min comparisons of horizontal velocities averaged for 1 min from the lidar and anemometer, and 0.87 for 2.5-h comparisons between vertical velocities averaged for 30 s from the lidar and profiler...