1、Designation: D 5741 96 (Reapproved 2002)e1Standard Practice forCharacterizing Surface Wind Using a Wind Vane andRotating Anemometer1This standard is issued under the fixed designation D 5741; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorially added a new Reference item in October 2002.1. Scope1.1 This practice covers a method for c
3、haracterizing surfacewind speed, wind direction, peak one-minute speeds, peakthree-second and peak one-minute speeds, and standard devia-tions of fluctuation about the means of speed and direction.1.2 This practice may be used with other kinds of sensors ifthe response characteristics of the sensors
4、, including theirsignal conditioners, are equivalent or faster and the measure-ment uncertainty of the system is equivalent or better thanthose specified below.1.3 The characterization prescribed in this practice willprovide information on wind acceptable for a wide variety ofapplications.NOTE 1This
5、 practice builds on a consensus reached by the attendeesat a workshop sponsored by the Office of the Federal Coordinator forMeteorological Services and Supporting Research in Rockville, MD onOct. 2930, 1992.1.4 This standard does not purport to address all of thesafety concerns, if any, associated w
6、ith its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1356 Terminology Relating to Sampling and Analysis ofAtmosphere
7、sD 5096 Test Method for Determining the Performance of aCup Anemometer or Propeller AnemometerD 5366 Test Method for Determining the Dynamic Perfor-mance of a Wind Vane3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 aerodynamic roughness length (z0, m)a characteris-tic length
8、representing the height above the surface whereextrapolation of wind speed measurements, below the limit ofprofile validity, would predict the wind speed would becomezero (1).3It can be estimated for direction sectors from alandscape description.3.1.2 damped natural wavelength (ld, m)a characteristi
9、cof a wind vane empirically related to the delay distance and thedamping ratio. See Test Method D 5366 for test methods todetermine the delay distance and equations to estimate thedamped natural wavelength.3.1.3 damping ratio (h, dimensionless)the ratio of theactual damping, related to the inertial-
10、driven overshoot of windvanes to direction changes, to the critical damping, the fastestresponse where no overshoot occurs. See Test Method D 5366for test methods and equations to determine the damping ratioof a wind vane.3.1.4 distance constant (L, m)the distance the air flowspast a rotating anemom
11、eter during the time it takes the cupwheel or propeller to reach (1 1/e) or 63 % of the equilibriumspeed after a step change in wind speed. See Test MethodD 5096.3.1.5 maximum operating speed (um, m/s)as related toanemometer, the highest speed as which the sensor will survivethe force of the wind an
12、d perform within the accuracyspecification.3.1.6 maximum operating speed (um, m/s)as related towind vane, the highest speed at which the sensor will survivethe force of the wind and perform within the accuracyspecification.3.1.7 standard deviation of wind direction (su, degrees)the unbiased estimate
13、 of the standard deviation of winddirection samples about the mean horizontal wind direction.The circular scale of wind direction with a discontinuity at1This practice is under the jurisdiction of ASTM Committee D22 on Samplingand Analysis of Atmospheres and is the direct responsibility of Subcommit
14、teeD22.11 on Meteorology.Current edition approved May 10, 1996. Published July 1996.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary p
15、age onthe ASTM website.3The boldface numbers in parentheses refers to the list of references at the endof this standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.north may bias the calculation when the direction oscillatesabout
16、 north. Estimates of the standard deviation such assuggested by (2, 3) are acceptable.3.1.8 standard deviation of wind speed (su, m/s)theestimate of the standard deviation of wind speed samples aboutthe mean wind speed.3.1.9 starting threshold (u0, m/s)as related to anemom-eter, the lowest speed at
17、which the sensor begins to turn andcontinues to turn and produces a measurable signal whenmounted in its normal position (see Test Method D 5096).3.1.10 starting threshold (u0, m/s)as related to system, theindicated wind speed when the anemometer is at rest.3.1.11 starting threshold (u0, m/s)as rela
18、ted to wind vane,the lowest speed at which the vane can be observed ormeasured moving from a 10 offset position in a wind tunnel(see Test Method D 5366).3.1.12 wind direction (u, degrees)the direction, refer-enced to true north, from which air flows past the sensorlocation if the sensor or other obs
19、tructions were absent. Thewind direction distribution is characterized over each 10-minperiod with a scalar (non-speed weighted) mean, standarddeviation, and the direction of the peak 1-min average speed.The circular direction range, with its discontinuity at north,requires special attention in the
20、averaging process. A unitvector method is an acceptable solution to this problem.3.1.12.1 DiscussionWind vane direction systems provideoutputs when the wind speed is below the starting threshold forthe vane. For this practice, report the calculated values (see 4.3or 4.4) when more than 25 % of the p
21、ossible samples are abovethe wind vane threshold and the standard deviation of theacceptable samples, su, is 30 or less, otherwise report lightand variable code, 000.3.1.13 wind speed (u, m/s)the speed with which air flowspast the sensor location if the sensor or other obstructions wereabsent. The w
22、ind speed distribution is characterized over each10-min period with a scalar mean, standard deviation, peak 3-saverage, and peak 1-min average.3.2 For definitions of additional terms used in this practice,refer to Terminology D 1356.4. Summary of Practice4.1 Siting of the Wind Sensors:4.1.1 The wind
23、 sensor location will be identified by anunambiguous label which will include either the longitude andlatitude with a resolution of1sofarc(about 30 m or less) ora station number which will lead to that information in thestation description file. When redundant sensors or microscalenetwork stations (
24、for example, airport runway sensors) areavailable, they will have individual labels which unambigu-ously identify the data they produce.4.1.2 The anemometer and wind vane shall be located at a10-m height above level or gently sloping terrain with an openfetch of at least 150 m in all directions, wit
25、h the largest fetchpossible in the prevailing wind direction. Compromise isfrequently recognized and acceptable for some sites. Obstaclesin the vicinity should be at least ten times their own heightdistant from the wind sensors.4.1.3 The wind sensors shall preferably be located on top ofa solitary m
26、ast. If side mounting is necessary, the boom lengthshould be at least three times the mast width. In the undesirablecase that locally no open terrain is available and the measure-ment is to be made above some building, then the wind sensorheight above the roof top should be at least 1.5 times the le
27、sserof the maximum building height and the maximum horizontaldimension of the major roof surface. In this case, the stationdescription file shall indicate the height above ground level(AGL) of the highest part of the building, the height of thewind sensors above ground, AGL, and the height of the wi
28、ndsensors above roof level. Site characteristics shall be docu-mented in sectors no greater than 45 nor smaller than 30 inwidth around the wind sensors. The near terrain may becharacterized with photographs, taken at wind sensor height ifpossible, aimed radially outward at labeled central angles, wi
29、threspect to true north.Average roughness of the nearest 3 km ofeach sector shall be characterized according to the roughnessclass as tabulated above (4). The z0numbers in Table 1 aretypical and not precise statements.4.1.4 Important terrain features at distances larger than 3 km(hills, cities, lake
30、s, and so forth, within 20 km) shall beidentified by sector and distance. Additional information, suchas aerial photographs, maps, and so forth, pertinent to the site,is recommended to be added to the basic site documentation.NOTE 2Cameras using 35-mm film in the landscape orientation willhave the f
31、ollowing theoretical focal length to field angle relationships:50 mm yields 4040 mm yields 4828 mm yields 66TABLE 1 Characterizations Extracted from Wieringa, J. (4)No. z0, m Landscape Description1: 0.0002 Sea Open sea or lake (irrespective of the wave size), tidal flat, snow-covered flat plain, fea
32、tureless desert, tarmac and concrete, with afree fetch of several kilometres.2: 0.005 Smooth Featureless land surface without any noticeable obstacles and with negligible vegetation; for example, beaches, pack ice withoutlarge ridges, morass, and snow-covered or fallow open country.3: 0.03 Open Leve
33、l country with low vegetation (for example, grass) and isolated obstacles with separations of at least 50 obstacle heights; forexample, grazing land without windbreaks, heather, moor and tundra, runway area of airports.4: 0.10 Roughly open Cultivated area with regular cover of low crops, or moderate
34、ly open country with occasional obstacles (for example, low hedges,single rows of trees, isolated farms) at relative horizontal distances of at least 20 obstacle heights.5: 0.25 Rough Recently developed young landscape with high crops or crops of varying heights, and scattered obstacles (for example
35、, denseshelter-belts, vineyards) at relative distances of about 15 obstacle heights.6: 0.5 Very rough Old cultivated landscape with many rather large obstacle groups (large farms, clumps of forest) separated by open spaces of about10 obstacle heights. Also low-large vegetation with small interspaces
36、, such as bushland, orchards, young densely planted forest.7: 1.0 Closed Landscape totally and quite regularly covered with similar-size large obstacles, with open spaces comparable to the obstacle heights;for example, mature regular forests, homogeneous cities, or villages.8: 2 Chaotic Centers of l
37、arge towns with mixture of low-rise and high-rise buildings. Also irregular large forests with many clearings.D 5741 96 (2002)e12Prints or transparencies may not utilize the total theoretical width of theimage. It is desirable to label known angles in the photograph. Forexample, a 45 sector photogra
38、ph could have a central label of 360 withmarker flags located at 337.5 and 022.5 true.4.2 Characteristics of the Wind SystemsThere are twocategories of sensor design within this practice. Sensitivedescribes sensors commonly applied for all but extreme windconditions. Ruggedized describes sensors int
39、ended to functionduring extreme wind conditions. The application of this prac-tice requires the starting threshold (u0) of both the wind vaneand the anemometer to meet the same operating range cat-egory.4.2.1 Operating Range:Category Starting Threshold, u0Maximum Speed, umSensitive 0.5 m/s 50 m/sRug
40、gedized 1.0 m/s 90 m/s4.2.2 Dynamic Response CharacteristicsDynamic re-sponse characteristics of the measurement system may includeboth the sensor response and a measurement circuit contribu-tion. The specified values are for the entire measurementsystem, including sensors and signal conditioners (5
41、).Itisexpected that the characteristics of the sensors, which can beindependently determined by the referenced Test MethodsD 5096 and D 5366, will not be measurably altered by thecircuitry.Anemometer Distance constant, L 0.3Wind vane Damped natural wavelength, ld10 m/s 5 % of readingWind direction D
42、egrees of arc to true north 65 (see Note 5)NOTE 3The relative accuracy of the position of the vane with respectto the sensor base should be less than 63 for averaged samples. The biasof the sensor base alignment to true north should be less than 62.4.2.4 Measurement Resolution:Average Standard De-vi
43、ationWind speed 0.1 m/s 0.1 m/sWind direction 1 0.14.2.5 SamplingPeriods of time, specified as the averagingintervals, are fixed clock periods and not running or overlap-ping intervals, except for the three-second gust. Outputs mustbe continuously and uniformly sampled during the reportingperiod. In
44、complete data must be identified.Wind speed 1 to3s(seeNote 4)Winddirection 1to3s(seeNote 5)NOTE 4A true 3-s average wind speed results from counting theoutput pulses of the anemometer transducer for 3 s. If a pulse-generatingtransducer is not used, a suitable sampling rate and averaging method isreq
45、uired to produce a true 3-s average.NOTE 5A sample of the wind direction may be used ONLY when thesample of wind speed is at or above the wind direction starting threshold.4.3 Standard Data Output for ArchivesTime labels shoulduse the ending time of the interval. If a different labelingmethod is con
46、sistently used, it must be defined. The dataoutputs are listed as follows:4.3.1 Ten-minute scalar averaged wind speed.4.3.2 Ten-minute unit vector or scalar averaged wind direc-tion.4.3.3 Fastest 3-s gust during the 10-min period.4.3.4 Time of the fastest 3-s gust during the 10-min period.4.3.5 Fast
47、est 1-min scalar averaged wind speed during the10-min period (fastest minute).4.3.6 Average wind direction for the fastest 1-min windspeed.4.3.7 Standard deviation of the wind speed samples (1 to 3s) about the 10-min mean speed (su).4.3.8 Standard deviation of the wind direction samples (1 to3 s) ab
48、out the 10-min mean direction (su).4.4 Optional Condensed Data Output for ArchivesSomenetworks will not be able to save eight 10-min data sets (48values plus time and identification) each hour. For those cases,an abbreviated or condensed alternative is provided. When thecondensed output is employed
49、the following outputs arerequired.4.4.1 Sixty-minute scalar averaged wind speed.4.4.2 Sixty-minute unit vector or scalar averaged winddirection.4.4.3 Fastest 3-s gust during the 60-min period.4.4.4 Wind direction for the fastest 3-s gust.4.4.5 Fastest 1-min scalar averaged wind speed during the60-min period.4.4.6 Average wind direction for the fastest 1-min windspeed.4.4.7 Ending time of the fastest 1-min wind speed.4.4.8 Root-mean-square of six 10-min standard deviationsof the wind speed samples about their 10-min mean speeds.4.4.9 Root-mean-sq
