1、Designation: D6011 96 (Reapproved 2015)Standard Test Method forDetermining the Performance of a Sonic Anemometer/Thermometer1This standard is issued under the fixed designation D6011; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the dy-namic performance of a sonic anemometer/thermometer w
3、hichemploys the inverse time measurement technique for velocityor speed of sound, or both. Performance criteria include: (a)acceptance angle, (b) acoustic pathlength, (c) system delay, (d)system delay mismatch, (e) thermal stability range, (f) shadowcorrection, (g) velocity calibration range, and (h
4、) velocityresolution.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this stand
5、ard 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:2C384 Test Method for Impedance and Absorption of Acous-tical Materials by Impedance Tube MethodD1356 Terminology Relating to Sa
6、mpling and Analysis ofAtmospheresD5527 Practices for Measuring Surface Wind and Tempera-ture by Acoustic MeansIEEE/ASTM SI 10 American National Standard for MetricPractice3. Terminology3.1 DefinitionsFor definitions of terms related to this testmethod, refer to Terminology D1356.3.2 Definitions of T
7、erms Specific to This Standard:3.2.1 axial attenuation coeffcienta ratio of the free streamwind velocity (as defined in a wind tunnel) to velocity along anacoustic propagation path (vt/vd) (1).33.2.2 critical Reynolds number (Rc)the Reynolds numberat which an abrupt decrease in an objects drag coeff
8、icientoccurs (2).3.2.2.1 DiscussionThe transducer shadow corrections areno longer valid above the critical Reynolds number due to adiscontinuity in the axial attenuation coefficient.3.2.3 Reynolds number (Re)the ratio of inertial to viscousforces on an object immersed in a flowing fluid based on the
9、objects characteristic dimension, the fluid velocity, and vis-cosity.3.2.4 shadow correction (vdm/vd)the ratio of the truealong-axis velocity vdm, as measured in a wind tunnel or byanother accepted method, to the instrument along-axis windmeasurement vd.3.2.4.1 DiscussionThis correction compensates
10、for flowshadowing effects of transducers and their supporting struc-tures. The correction can take the form of an equation (3) or alookup table (4).3.2.5 speed of sound (c, (m/s)the propagation rate of anadiabatic compression wave:c 5 P/!s0.5(1)where:P = pressure = density, = specific heat ratio, an
11、ds = isentropic (adiabatic) process (5).3.2.5.1 DiscussionThe velocity of the compression wavedefined along each axis of a Cartesian coordinate system is thesum of propagation speed c plus the motion of the gas alongthat axis. In a perfect gas (6):c 5 R*T/M!0.5(2)The approximation for propagation in
12、 air is:cair5 403 T 110.32 e/P!#0.55 403 Ts!0.5(3)1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved April 1, 2015. Published April 2015. Originallyapproved in 1996. Last prev
13、ious edition approved in 2008 as D6011 96 (2008).DOI: 10.1520/D6011-96R15.2For 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 page onthe
14、ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.6 system clockthe clock used for timing acousticwavefront travel between
15、a transducer pair.3.2.7 system delay (t, s)the time delay through thetransducer and electronic circuitry (7).3.2.7.1 DiscussionEach path through every sonic arrayaxis can have unique delay characteristics. Delay (on the orderof 10 to 20 s) can vary as a function of temperature anddirection of signal
16、 travel through the transducers and electroniccircuitry. The average system delay for each axis in an acousticarray is the average of the delays measured in each directionalong the axis:t 5 t11t2!/2 (4)3.2.8 system delay mismatch (tt, s )the absolute differ-ence in microseconds between total transit
17、 times ttin eachdirection (tt1, tt2) through the system electronics and transduc-ers.3.2.8.1 DiscussionDue principally to slight differences intransducer performance, the total transit time obtained with thesignal originating at one transducer can differ from the totaltransit time obtained with the
18、signal originating at its pairedtransducer. The manufacturer should specify the system delaymismatch tolerance.tt5?tt12 tt2 ?(5)3.2.9 thermal stability range (C)a range of temperaturesover which the corrected velocity output in a zero windchamber remains at or below instrument resolution.3.2.9.1 Dis
19、cussionThermal stability range defines a rangeof temperatures over which there is no step change in systemdelay.3.2.10 time resolution (t, s)resolution of the internalclock used to measure time.3.2.11 transit time (t, s)the time required for an acousticwavefront to travel from the transducer of orig
20、in to thereceiving transducer.3.2.11.1 DiscussionTransit time (also known as time offlight) is determined by acoustic pathlength d, the speed ofsound c, the velocity component along the acoustic propaga-tion path vd, and cross-path velocity components) vn(8):t 5 dc22 vn2!0.56Vd#/c22 vd21vn2!# (6)The
21、 transit time difference between acoustic wavefrontpropagation in one direction (t1, computed for + vd) andthe other (t2, computed for vd) for each transducer pairdetermines the magnitude of a velocity component. Theinverse transit time solution for the along-axis velocity is(9):vd5d2F1t121t2G(7)The
22、 total transit times tt1and tt2, include the sum ofactual transit times plus system delay through the electron-ics and transducers in each direction along an acousticpath, t1and t2. System delay must be removed to calcu-late vd, that is:t15 tt12 t1(8)t25 tt22 t2(9)3.2.11.2 DiscussionProcedures in th
23、is test method includea test to determine whether separate determinations of t1andt2are needed, or whether an average t can be used. Therelationship of transit time to speed of sound is:c25Fd2S1t111t2DG21vn2(10)and the inverse transit time solution for sonic tempera-ture in air is as follows (5):Ts5
24、Sd21612D F1t111t2G21vn2403(11)3.2.12 velocity calibration range (Ucto Us, (m/s)therange of velocity between creeping flow and the flow at whicha critical Reynolds number is reached.3.2.12.1 DiscussionThe shadow correction is valid over arange of velocities where no discontinuities are observed in th
25、eaxial attenuation coefficient.3.2.13 velocity resolution (v, (m/s)the largest change inan along-axis wind component that would cause no change inthe pulse arrival time count.3.2.13.1 DiscussionVelocity resolution defines the small-est resolvable wind velocity increment as determined fromsystem cloc
26、k rate. For some systems, v defined as the standarddeviation of system dither can also be reported.3.3 Symbols:c = speed of sound, m/s,Cp= specific heat at constant pressure, J/(kgK),Cv= specific heat at constant volume, J/(kgK),e = vapor pressure, Pa,d = acoustic pathlength, m,f = compressibility f
27、actor, dimensionless,M = molecular weight of a gas, g/mol,P = pressure, Pa,R* = universal gas constant, 8.31436 J/(molK),RH = relative humidity, %,t = transit time, s,tt= total transit time, s,T = absolute temperature, K,Ts= sonic absolute temperature, K,Uc= upper limit for creeping flow, m/s,Us= cr
28、itical Reynolds number velocity, m/s,vd= velocity component along acoustic propagation path,m/s,vdm= tunnel velocity component parallel to the array axis(vt, cos ), m/s,vn= velocity component normal to an acoustic propagationpath, m/s,vt= free stream wind velocity component (unaffected bythe presenc
29、e of an obstacle such as the acoustic array),m/s,t = system delay, s,tt= system delay mismatch, s,t = clock pulse resolution, s, = acceptance angle, degree, = specific heat ratio (Cp/Cv), dimensionless,v = velocity resolution, m/s, = array angle of attack, degree, and = gas density, kg/m3.D6011 96 (
30、2015)23.4 UnitsUnits of measurement are in accordance withIEEE/ASTM SI 10.4. Summary of Test Method4.1 Acoustic pathlength, system delay, and system delaymismatch are determined using the dual gas or zero windchamber method. The acoustic pathlength and system clockrate are used to calculate the velo
31、city resolution. Thermalsensitivity range is defined using a zero wind chamber. Theaxial attenuation coefficient, velocity calibration range, andtransducer shadow effects are defined in a wind tunnel. Windtunnel results are used to compute shadow corrections and todefine acceptance angles.5. Signifi
32、cance and Use5.1 This test method provides a standard method for evalu-ating the performance of sonic anemometer/thermometers thatuse inverse time solutions to measure wind velocity compo-nents and the speed of sound. It provides an unambiguousdetermination of instrument performance criteria. The te
33、stmethod is applicable to manufacturers for the purpose ofdescribing the performance of their products, to instrumenta-tion test facilities for the purpose of verifying instrumentperformance, and to users for specifying performance require-ments. The acoustic pathlength procedure is also applicable
34、forcalibration purposes prior to data collection. Procedures foroperating a sonic anemometer/thermometer are described inPractices D5527.5.2 The sonic anemometer/thermometer array is assumed tohave a sufficiently high structural rigidity and a sufficiently lowcoefficient of thermal expansion to main
35、tain an internal align-ment to within the manufacturers specifications over itsdesigned operating range. Consult with the manufacturer for aninternal alignment verification procedure and verify the align-ment before proceeding with this test method.5.3 This test method is designed to characterize th
36、e perfor-mance of an array model or probe design. Transducer shadowdata obtained from a single array is applicable for all instru-ments having the same array model or probe design. Somenon-orthogonal arrays may not require specification of trans-ducer shadow corrections or the velocity calibration r
37、ange.6. Apparatus6.1 Zero Wind Chamber, sized to fit the array and accom-modate a temperature probe (Fig. 1) used to calibrate the sonicanemometer/thermometer. Line the chamber with acousticfoam with a sound absorption coefficient of 0.8 or better (TestMethod C384) to minimize internal air motions c
38、aused bythermal gradients and to minimize acoustic reflections. Installa small fan within the chamber to establish thermal equilibriumbefore a zero wind calibration is made.6.2 Pathlength ChamberSee Fig. 2.6.2.1 Design the pathlength chamber to fit and seal an axisof the array for acoustic pathlengt
39、h determination. Constructthe chamber components using non-expanding, non-outgassingmaterials. Employ O-ring seals made of non-outgassing mate-rials to prevent pressure loss and contamination. Design thechamber for quick and thorough purging. The basic pathlengthchamber components are illustrated in
40、 Fig. 2.6.2.2 Gas Source and Plumbing, to connect the pathlengthchamber to one of two pressurized gas sources (nitrogen orargon). Employ a purge pump to draw off used gases. Requiredpurity of the gas is 99.999 %.6.3 Temperature Transducer (two required), with minimumtemperature measurement precision
41、 and accuracy of 60.1Cand 60.2C, respectively, and with recording readout. One isrequired for the zero wind chamber and one for the pathlengthchamber.6.4 Wind Tunnel:6.4.1 Size, large enough to fit the entire instrument arraywithin the test section at all required orientation angles. Designthe tunne
42、l so that the maximum projected area of the sonicarray is less than 5 % of tunnel cross-sectional area.6.4.2 Speed Control, to vary the flow rate over a range of atleast 1.0 to 10 m/s within 60.1 m/s or better throughout the testsection.FIG. 1 Sonic Anemometer Array in a Zero Wind ChamberFIG. 2 Path
43、length Chamber for Acoustic Pathlength Determina-tionD6011 96 (2015)36.4.3 CalibrationCalibrate the mean flow rate using trans-fer standards traceable to the National Institute of Standardsand Technology (NIST), or by an equivalent fundamentalphysical method.6.4.4 Turbulence, with a uniform velocity
44、 profile with aminimum of swirl at all speeds, and known uniform turbulencescale and intensity throughout the test section.6.4.5 Rotating Plate, to hold the sonic transducer array invarying orientations to achieve angular exposures up to 360,as needed. The minimum plate rotation requirements are 660
45、in the horizontal and 615 in the vertical, with an angularalignment resolution of 0.5.NOTE 1Design the plate to hold the array at chosen angles withoutdisturbing the test section wind velocity profile or changing its turbulencelevel.6.5 Measuring System:6.5.1 Counter, to log the anemometer velocity
46、componentreadings, with a count resolution equaling or exceeding theclock rate of the sonic anemometer/thermometer.6.5.2 Recorder, with at least a 10 Hz rate and a resolutioncomparable to instrument resolution, for recording onto mag-netic or optical media the anemometer velocity componentreadings.6
47、.6 Calipers, for transducer separation distancemeasurements, with minimum tolerance of 0.1 mm.6.7 Ancillary MeasurementsAncillary pressure (60.5hPa) and relative humidity measurements (610 %) are neededfor sonic temperature and acoustic pathlength determination ifthe ambient vapor pressure is greate
48、r than 20 Pa. Thesemeasurements can be obtained from on-site instruments orestimated from nearby data sources.7. Precautions7.1 Exercise care while using gas pressurized containers.Procedures for handling pressurized gas cylinders shall beposted and observed. Perform all testing with pressurized gas
49、esin a well-ventilated room. Use of the buddy system is recom-mended.7.2 Maintain chamber temperatures and pressures close tolaboratory temperature and pressure to minimize gradients thatcould cause convection within the chamber, but use sufficientover-pressure to prevent contamination from extraneous gases.7.3 Ascertain that acoustic reflections and apparatus vibra-tions are not contaminating results.NOTE 2Noise and vibrations generated during wind tunnel operationare potential in
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