ASTM D5096-02(2011)
(Test Method)Standard Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometer
Standard Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometer
SIGNIFICANCE AND USE
This test method will provide a standard for comparison of rotating type anemometers, specifically cup anemometers and propeller anemometers, of different types. Specifications by regulatory agencies (4-7) and industrial societies have specified performance values. This standard provides an unambiguous method for measuring Starting Threshold, Distance Constant, Transfer Function, and Off-Axis Response.
SCOPE
1.1 This test method covers the determination of the Starting Threshold, Distance Constant, Transfer Function, and Off-Axis Response of a cup anemometer or propeller anemometer from direct measurement in a wind tunnel.
1.2 This test method provides for a measurement of cup anemometer or propeller anemometer performance in the environment of wind tunnel flow. Transference of values determined by these methods to atmospheric flow must be done with an understanding that there is a difference between the two flow systems.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D5096 − 02 (Reapproved 2011)
Standard Test Method for
Determining the Performance of a Cup Anemometer or
Propeller Anemometer
This standard is issued under the fixed designation D5096; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope axis of rotation vertical, and the normal position for propeller
anemometers is with the axis of rotation aligned with the
1.1 This test method covers the determination of the Start-
direction of flow. Note that if the anemometer axis is not
ing Threshold, Distance Constant, Transfer Function, and
aligned with the direction of flow, the calculated wind speed
Off-Axis Response of a cup anemometer or propeller anemom-
component parallel to the anemometer axis is used to deter-
eter from direct measurement in a wind tunnel.
mine starting threshold.
1.2 This test method provides for a measurement of cup
3.2.2 distance constant (L, m)—the distance the air flows
anemometer or propeller anemometer performance in the
past a rotating anemometer during the time it takes the cup
environment of wind tunnel flow. Transference of values
wheel or propeller to reach (1−1⁄e) or 63% of the equilib-
determinedbythesemethodstoatmosphericflowmustbedone
riumspeedafterastepchangeinwindspeed (1). Theresponse
with an understanding that there is a difference between the
ofarotatinganemometertoastepchangeinwhichwindspeed
two flow systems.
increases instantaneously from U =0toU=U is (2):
f
1.3 This standard does not purport to address all of the
2t/τ
~ !
U 5 U 1 2 e (1)
~ !
t f
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
where:
priate safety and health practices and determine the applica-
U = is the instantaneous indicated wind speed at time t in
t
bility of regulatory limitations prior to use.
m/s,
U = is the final indicated wind speed, or wind tunnel speed,
f
2. Referenced Documents
in m/s,
t = is the elapsed time in seconds after the step change
2.1 ASTM Standards:
occurs, and
D1356Terminology Relating to Sampling and Analysis of
τ = is the time constant of the instrument.
Atmospheres
D3631Test Methods for Measuring Surface Atmospheric
DistanceConstantis:L 5 U τ (2)
f
Pressure
3.2.3 transfer function (Û = a + bR, m/s)—the linear rela-
f
tionship between wind speed and the rate of rotation of the
3. Terminology
anemometer throughout the specified working range. Û is the
f
3.1 For definitions of terms used in this standard, refer to
predicted wind speed in m/s, a is a constant, commonly called
Terminology D1356.
zero offset, in m/s, b is a constant representing the wind
passageinm/rforeachrevolutionoftheparticularanemometer
3.2 Definitions of Terms Specific to This Standard:
cup wheel or propeller, and R is the rate of rotation in r/s. It
3.2.1 startingthreshold(U ,m/s)—thelowestwindspeedat
o
should be noted that zero offset is not the same as starting
which a rotating anemometer starts and continues to turn and
threshold. In some very sensitive anemometers the constant a,
produce a measurable signal when mounted in its normal
zero offset, may not be significantly greater than zero. The
position. The normal position for cup anemometers is with the
constantsaandbmustbedeterminedbywindtunnelmeasure-
ment for each type of anemometer (3).
This test method is under the jurisdiction of ASTM Committee D22 on Air
3.2.4 off-axis response (U/(U cos θ))—the ratio of the
f
Quality and is the direct responsibility of Subcommittee D22.11 on Meteorology.
indicated wind speed (U ) at various angles of attack (θ)tothe
Current edition approved Oct. 1, 2011. Published October 2011. Originally
indicated wind speed at zero angle of attack (U) multiplied by
approved in 1990. Last previous edition approved in 2007 as D5096-02(2007).
f
DOI: 10.1520/D5096-02R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5096 − 02 (2011)
thecosineoftheangleofattack.Thisratiocomparestheactual 4.4 Transfer Function (Û =a+bR, m/s) is determined by
f
off-axis response to a cosine response. measuring the rate of rotation of the anemometer at a number
of wind speeds throughout the specified working range. In the
3.3 Symbols:
range of wind speeds where the anemometer response is
non-linear (near threshold) a minimum of five data points are
a (m/s) = zero offset constant
b (m/r) = wind passage (apparent pitch) constant or
recorded. A minimum of five additional data points are
calibration constant recorded within the working range of the anemometer and
L (m) = distance constant
windtunnelbutabovethenon-linearthresholdregion(seeFig.
r (none) = a shaft revolution
2). Measurements are recorded for each data point with the
R (r/s) = rate of rotation
wind tunnel speed ascending and descending. The values of a
τ(s) = time constant
and b are determined by least-squares linear regression of the
t (s) = time
individual data points.
U (m/s) = starting threshold
o
4.5 Off-Axis Response may be measured at a number of
U (m/s) = indicated wind speed (used in off-axis test)
wind speeds but must include 5 m/s, and 10 m/s.
U (m/s) = final indicated wind speed or wind tunnel
f
4.5.1 Cup Anemometers—A measurement is made of the
speed
output signal when the anemometer is inclined into the wind
U (m/s) = anemometer application range
max
U (m/s) = instantaneous indicated wind speed at time t (representing a down-draft) and away from the wind (repre-
t
Û (m/s) = predicted wind speed
sentinganupdraft),whilethewindtunnelisrunningatasteady
f
θ (deg) = off-axis angle of attack
speed.Theoutputsignalismeasuredwiththeanemometeraxis
at 5° intervals from vertical to plus and minus 30° from
4. Summary of Test Method
vertical. The measured signal is then converted to a ratio for
4.1 This test method requires a wind tunnel described in each interval by dividing by the normal signal measured with
Section 6, Apparatus.
the anemometer axis in the normal, or vertical, position.
4.5.2 Vane Mounted Propeller Anemometers—A measure-
4.2 Starting Threshold (U , m/s) is determined by measur-
o
ment is made of the output signal when the anemometer’s axis
ingthelowestspeedatwhicharotatinganemometerstartsand
of rotation is inclined downward into the wind (representing a
continues to turn and produce a measurable signal when
down-draft)andinclinedupwardintothewind(representingan
mounted in its normal position.
updraft), while the wind tunnel is running at a steady speed.
4.3 Distance Constant (L, m) may be determined at a
The output signal is measured at 5° intervals from a horizontal
number of wind speeds but must include 5 m/s, and 10 m/s. It
axis of rotation to 630° from the horizontal. The measured
iscomputedfromthetimerequiredfortheanemometerrotorto
signal is then converted to a ratio for each interval by dividing
accelerate(1–1/e)or63%ofastepchangeinrotationalspeed
by the normal signal with the anemometer in the normal, or
after release from a restrained, non-rotating condition. The
horizontal position.This test may be conducted either with the
final response, U, is the wind tunnel speed as indicated by the
f
vaneinplaceorwiththevaneremovedandtheaxisofrotation
anemometer. In order to avoid the unrealistic effects of the
fixed in the down-tunnel direction.
restrained condition, as shown inFig. 1, the time measurement
4.5.3 Fixed Axis Propeller Anemometer—Ameasurement is
should be made from 0.30 of U to 0.74 of U. This interval in
f f
made of the output signal when the anemometer is rotated in
secondsisequaltoonetimeconstant(τ)andisconvertedtothe
the air stream throughout the complete 360° angle of attack.
Distance Constant by multiplying by the wind tunnel speed in
The signal is measured at a number of angles but must include
meters per second (m/s).
10° intervals with additional measurements at 85, 95, 265, and
275°. The measured signal for each angle of attack is then
FIG. 1 Typical Anemometer Response Curve FIG. 2 Typical Anemometer Calibration Curve
D5096 − 02 (2011)
converted to a ratio by dividing by the signal measured at 0° minimum of 50% of the application range of the anemometer
angle of attack (axial flow).Additionally, the stall angle of the under test. The speed control should maintain the flow rate
propeller is measured by orienting the anemometer at 90° and within 60.2 m/s.
slowly rotating into and away from the air flow until the 6.3.3 Calibration—The mean flow rate must be verified at
propeller starts rotating continuously. Stall angle is the total the mandatory speeds by use of transfer standards which have
contained angle within which the propeller does not continu- been calibrated at the National Institute of Standards and
ously rotate. The procedure is repeated at 270°. Technology or by a fundamental physical method. Speeds
below2m/sforthethresholddeterminationmustbeverifiedby
5. Significance and Use
a sensitive anemometer or by some fundamental time and
5.1 Thistestmethodwillprovideastandardforcomparison distance technique, such as measuring the transition time of
smoke puffs, soap bubbles, or heat puffs between two points
of rotating type anemometers, specifically cup anemometers
and propeller anemometers, of different types. Specifications separated by known distance. A table of wind tunnel blower
rpmorsomeotherindexrelatingmethodofcontroltoflowrate
by regulatory agencies (4-7) and industrial societies have
specified performance values. This standard provides an un- shouldbeestablishedbythistechniqueforspeedsof2m/sand
below.
ambiguousmethodformeasuring Starting Threshold, Distance
6.3.4 The wind tunnel must have a relatively constant
Constant, Transfer Function, and Off-Axis Response.
profile (known to within 1%) and a turbulence level of less
6. Apparatus
than 1% throughout the test section.
6.3.5 Environment(9-11).Differencesofgreaterthan3%in
6.1 Measuring System:
the density of the air within the test environment may result in
6.1.1 Rotation—The relationship between the rate of rota-
poor intercomparability of independent measurements of start-
tionoftheanemometershaftandthetransduceroutputmustbe
ing threshold (U ) and distance constant (L) since these values
determined. The resolution of the anemometer transducer
o
are density dependent. The temperature and pressure of the
limits the measurement. The resolution of the measuring or
environment within the wind tunnel test section, and the
recordingsystemmustrepresenttheindicatedwindspeedwith
ambient air pressure (Test Methods D3631) shall be reported
a resolution of 0.02 m/s.
for each independent measurement.
6.1.2 Time—The resolution of time must be consistent with
the distance accuracy required. For this reason the time
7. Sampling
resolution may be changed as the wind tunnel speed is
7.1 Starting Threshold—The arithmetic mean on ten con-
changed. If one wants a distance constant measurement to 0.1
secutive tests is required for a valid starting threshold mea-
meter resolution one must have a time resolution of 0.05 s at 2
surement.
m/s and 0.01 s at 10 m/s. If timing accuracy is based on 50 Hz
or 60 Hz power frequency it will be at least an order of
7.2 Distance Constant—The arithmetic mean of ten tests is
magnitude better than the resolution suggested above.
required for a valid measurement at each speed. The results of
6.1.3 Angle of Attack—The resolution of the angle of attack
the measurements at two or more speeds are averaged to a
(θ)mustbewithin0.5°.Anordinaryprotractorofadequatesize
single value for distance constant.
with 0.5° markings will permit measurements with sufficient
7.3 Transfer Function—Two measurements of U and R are
f
resolution.Afixture should be constructed to permit alignment
recorded for each data point, one with the wind tunnel speed
of the anemometer to the off-axis angles while the wind tunnel
ascendingandonewiththewindtunnelspeeddescending.The
is running at a steady speed.
values are then tabulated for each data point.
6.2 Recording Techniques:
7.4 Off-Axis Response—The results of the measurement at
6.2.1 Digital recording systems and appropriate reduction
two or more speeds are averaged to a single value for each
programswillbesatisfactoryifthesamplingrateisatleast100
angle of attack. The averaged values are tabulated for each
samples/s. Exercise care to avoid electronic circuits with time
angle of attack.
constants which limit the proper recording of anemometer
performance. Oscilloscopes with memory and hard copy capa- 8. Procedure
bility may also be used. Another simple technique is to use a
8.1 Starting Threshold (U ):
o
fast-response strip chart recorder (flat to 10 Hz or better) with
8.1.1 Provide a mechanical method for holding the an-
enough gain so that the signal produced by the anemometer
emometer in its normal position (see 3.1) and for releasing the
whenthewindtunnelisrunningat2m/sissufficienttoprovide
anemometerfromarestrained,ornon-rotatingcondition,while
full scale pen deflection on the recorder. The recorder chart
the wind tunnel is running at the test speed. Test the release
drive must have a fast speed of 50 mm/s or more.
mechanism with the wind tunnel off to verify that the release
6.3 Wind Tunnel (8): method does not move the anemometer rotor when activated.
6.3.1 Size—The wind tunnel must be large enough so that 8.1.2 Set the wind tunnel to a speed that is lower than the
the projection of the cup wheel or propeller, sensor, and starting threshold. Slowly increase the wind tunnel speed until
support apparatus, is less than 5% of the cross sectional area the cup wheel or propeller continues to rotate and produce a
of the tunnel test section. measurable signal.
6.3.2 Speed Range—The wind tunnel must have a speed 8.1.3 Repeattheprocedureof8.1.2tentimesandrecordthe
control which will allow the flow rate to be varied from 0 to a results.
D5096 − 02 (2011)
NOTE 1—Vibration caused by the wind tunnel or by other sources can
air flow. See 4.5.1. Divide each value by the value in the
cause erroneous measurements of starting threshold. Care must be
normal position times the cosine of the tilt angle.
exercised to eliminate any vibrat
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