ASTM_D_5366_-_96_2011.pdf

Designation:D536696(Reapproved 2011)Standard Test Method forDetermining the Dynamic Performance of a Wind Vane1This standard is issued under the fixed designation D5366;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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 startingthreshold,delay distance,and overshoot ratio of a wind vanefrom direct measurements in a wind tunnel.This test method isapplicable only to wind vanes having measurable overshoot.1.2 This test method provides for determination of theperformance of a system consisting of a wind vane and itsassociated position-to-output transducer in wind tunnel flow.Use of values determined by this test method to describeperformance in atmospheric flow of a wind direction measur-ing system incorporating the vane must be done with anunderstanding of the differences between the two systems andthe two environments.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 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Terminology2.1 Definitions:2.1.1 delay distance(D)the distance the air flows past awind vane during the time it takes the vane to return to 50%of the initial displacement.2.1.2 overshoot(un)the amplitude of a deflection of awind vane as it oscillates about uBafter release from an initialdisplacement.2.1.3 overshoot ratio(V)the ratio of two successiveovershoots,as expressed by the equation:V 5 un11!/un(1)where unand u(n+1)are the n and n+1 overshoots,respec-tively.In practice,since deflections after the first(to the sideopposite the release point are normally small,the initial re-lease point(that is,the n=0 deflection)and the first deflec-tion after release(n=1)are used in determining the over-shoot ratio.2.1.4 starting threshold(Uo)the lowest speed at which thevane can be observed or measured moving from a 10 offset ina wind tunnel.2.2 Symbols:D(m)delay distanceUo(m/s)starting thresholdV(none)overshoot ratioh(none)damping ratiold(m)damped natural wavelengthun(degrees)overshoot;maximum angular excursionuo(degrees)reference directionuB(degrees)vane equilibrium positionuB uo(degrees)dynamic vane bias2.3 Calculated or Estimated Values:2.3.1 damping ratio(h)calculated from the overshootratio(1,2).2h 5ln1/V!p21ln1/V!#2!0.5(2)2.3.2 damped natural wavelength(ld)at sea level in theU.S.Standard Atmosphere,damped natural wavelength isrelated to delay distance and damping ratio by the empiricalexpression(1,2).2ld5D6.02 2.4h!1 2 h2!0.5(3)3.Summary of Test Method3.1 Reference Direction(uo,degrees)is the indicated angu-lar position of the vane when aligned along the centerline of thewind tunnel.3.2 Vane Equilibrium Position(uB,degrees)is the finalresting position of the vane after motion in response to aninitial displacement.Ideally,uB=uo.3.3 Dynamic Vane Bias(uB uo,degrees)is the displace-ment of the vane from the wind tunnel centerline at 5 m/s.Thismeasurement will identify wind vanes with unbalanced aero-dynamic response because of damage(for example,bent tail)or poor design.3.4 Starting Threshold(Uo,m/s)is determined by observingor measuring the lowest speed at which the vane,released from1This 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 Oct.1,2011.Published October 2011.Originallyapproved in 1993.Last previous edition approved in 2007 as D5366-96(2007).DOI:10.1520/D5366-96R11.2The 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 States1 a 10 offset position in a wind tunnel,moves toward uB.Movement must be distinguishable from vibration.3.5 Delay Distance(D,m)may be determined at a numberof wind speeds but shall include 5 m/s and 10 m/s.It iscomputed from the time required for the vane to reach 50%ofthe initial displacement from 10 off uB.This time in secondsis converted to delay distance by multiplying by the windtunnel speed in metres per second.Tests shall include an equalnumber of displacements to each side of uB.3.6 Overshoot Ratio(V)may be determined at the sametime as the delay distance.The maximum angular excursion onthe opposite side of uBfrom the initial 10 displacementfromuBis measured.This value is divided by the initialdisplacement to obtain V.4.Significance and Use4.1 This test method will provide a standard for comparisonof wind vanes of different types.Specifications by regulatoryagencies and industrial societies(3-5)have stipulated perfor-mance valu