ASTM E2459-05
(Guide)Standard Guide for Measurement of In-Duct Sound Pressure Levels from Large Industrial Gas Turbines and Fans
Standard Guide for Measurement of In-Duct Sound Pressure Levels from Large Industrial Gas Turbines and Fans
SCOPE
1.1 This guide is intended to provide a simple and consistent procedure for the in-situ field measurement of in-duct sound pressure levels in large low pressure industrial air ducts, such as for gas turbines or fans, where considerations such as flow velocity, turbulence or temperature prevent the insertion of sound pressure sensors directly into the flow. This standard guide is intended for both ambient temperature intake air and hot exhaust gas flow in ducts having cross sections of four (4) square meters, or more.
1.2 The described procedure is intended to provide a repeatable and reproducible measure of the in-duct dynamic pressure level at the inlet or exhaust of the gas turbine, or fan. The guide is not intended to quantify the "true" sound pressure level or sound power level. Silencers, as well as Waste Heat Boilers, must be designed using the in-duct sound power level as the basis. Developing the true sound power level based on in-duct measurements of true sound pressure within a complete operating system is complex and procedures are developmental and often proprietary.
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. Extreme caution is mandatory when working near hot exhaust gas systems and appropriate safety precautions such as the installation of quick acting isolation valves are recommended.
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Designation: E2459 – 05
Standard Guide for
Measurement of In-Duct Sound Pressure Levels from Large
Industrial Gas Turbines and Fans
This standard is issued under the fixed designation E2459; 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 C634 Terminology Relating to Building and Environmental
Acoustics
1.1 Thisguideisintendedtoprovideasimpleandconsistent
2.2 ANSI Standards:
procedure for the in-situ field measurement of in-duct sound
S1.4 Specification for Sound Level Meters
pressure levels in large low pressure industrial air ducts, such
S1.43 Specification for Integrating Averaging Sound Level
as for gas turbines or fans, where considerations such as flow
Meters
velocity, turbulence or temperature prevent the insertion of
sound pressure sensors directly into the flow. This standard
3. Terminology
guide is intended for both ambient temperature intake air and
3.1 Definitionsoftheacousticaltermsusedinthisguideare
hot exhaust gas flow in ducts having cross sections of four (4)
given in Terminology C634.
square meters, or more.
3.2 Definitions of Terms Specific to This Standard:
1.2 Thedescribedprocedureisintendedtoprovidearepeat-
3.2.1 anechoic tube—a constant diameter tube of sufficient
ableandreproduciblemeasureofthein-ductdynamicpressure
length that a sound wave reflected from the far end of the tube
levelattheinletorexhaustofthegasturbine,orfan.Theguide
termination arrives at the microphone position sufficiently
is not intended to quantify the “true” sound pressure level or
attenuated that it will not appreciably affect the microphone
sound power level. Silencers, as well as Waste Heat Boilers,
reading.
must be designed using the in-duct sound power level as the
3.2.2 dynamic pressure—the total instantaneous pressure
basis. Developing the true sound power level based on in-duct
incident upon the opening of the test port, including the
measurements of true sound pressure within a complete oper-
influence of convective turbulence, local tangential modes,
atingsystemiscomplexandproceduresaredevelopmentaland
localized boundary layer effects at the test port and the
often proprietary.
indeterminate effects of all duct acoustical modes.
1.3 This standard does not purport to address all of the
3.2.3 fixture—the apparatus containing the microphone fit-
safety concerns, if any, associated with its use. It is the
ting which locates the microphone flush with the inside
responsibility of the user of this standard to establish appro-
diameteroftheanechoictube,thenecessaryfittingspermitting
priate safety and health practices and determine the applica-
airtight connection of the fixture and anechoic tube to the test
bility of regulatory limitations prior to use. Extreme caution is
port, and the anechoic tube.
mandatory when working near hot exhaust gas systems and
3.2.4 probe microphone—a commercially available micro-
appropriate safety precautions such as the installation of quick
diameter microphone probe that is inserted into the anechoic
acting isolation valves are recommended.
termination near the test port connection. Some probes require
2. Referenced Documents a pressure compensation connection. Use and installation shall
follow manufacturer’s procedures/instructions.
2.1 ASTM Standards:
3.2.5 test port—the hole in the duct wall to which the
anechoic tube is connected and whose diameter is equal to the
ThisguideisunderthejurisdictionofASTMCommitteeE33onEnvironmental
inside diameter of the anechoic tube. In general the term test
Acoustics and is the direct responsibility of Subcommittee E33.08 on Mechanical
port,asusedherein,willusuallyincludeanysemi-permanently
and Electrical System Noise.
installed hardware in the wall of the duct permitting closure of
Current edition approved Oct. 15, 2005. Published November 2005. DOI:
10.1520/E2459-05. the test port when not in use (ball valve and threaded pipe cap,
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 Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2459 – 05
or both) as well as the pipe elements permitting attachment of 4.1.8 The inner duct wall opening shall be as smooth as
the fixture and the anechoic tube. practicable, with a minimum of turbulence producing discon-
tinuities at the duct wall inner surface. If the user chooses to
4. Summary of Guide
mount a protective screen covering the inside duct wall
4.1 Key features of this guide:
opening, such screen shall not materially influence the sound
4.1.1 Athrough-walltestportopening,25.4mm(nominally,
pressure measurements, or a means of quantifying and ac-
1 in.) or less, to which is connected the fixture, having a
counting for such influence shall be included in the test
constant inside diameter tube, to which the anechoic tube is
protocol. (Be aware that such screens can become fouled with
connected.Thetestportopeningisflushwiththeinsidesurface
particles.)
of the duct wall. No apparatus are inserted into the flow path.
4.1.9 The inner duct wall opening shall be the same inside
4.1.2 The microphone sensor is mounted in the fixture
diameter as the inside diameter of the anechoic tube. That is,
(3.2.3) outboard of the duct wall, with the microphone axis
thisguidedoesnotpermittheanechoictubetobeinsertedinto,
oriented normal to the centerline of the anechoic tube.
or positioned within a duct wall port of larger size, unless
4.1.3 The tip of the microphone, usually with a protective
means are provided to ensure that the inner wall surface at the
grid, is positioned flush with, or more accurately tangential to,
test port is restored to a reasonable semblance of a smooth
the inner wall of the fixture and as close to the duct wall as
continuous wall surface.
temperature or access limitations permit.
4.2 A sketch of a typical Test Port is shown in Fig. 1.A
4.1.4 The diameter of the microphone shall always be less
sketch of a typical Fixture is shown in Fig. 2. Only the initial
than or equal to the inside diameter of the anechoic tube.
portion of the otherwise very long Anechoic Tube is depicted
4.1.5 The position of the microphone is critical for high
in each figure.
temperature ducts, so as to limit the maximum temperature on
the microphone during testing.
5. Significance and Use
4.1.6 The anechoic tube shall have no inner wall disconti-
nuities or changes in diameter that might create reflections or 5.1 All noise control features associated with the inlet or
standing waves within the tube. It is important to avoid any exhaust of large industrial fans and gas turbines are, or should
protrusion of the apparatus into the gas flow path. be, based upon inlet or exhaust sound power levels in octave
4.1.7 The anechoic termination may be achieved by loosely bands of frequency. Sound power levels are not directly
packing the “cold” end of the tube with mineral wool or steel measurable, however, so they must be calculated indirectly,
wool. The tube end should be sealed airtight unless forced air using estimated or measured duct interior sound pressure
is to be used to ensure adequate cooling of the anechoic tube. levels.
NOTE—ShowingatypicalFixture(seeFig.2)installedinaninsulatedductwall.NotethestemoftheFixtureextendsallthewaytotheinnerductwall
surface, occupying a hole in the duct wall only slightly larger than the tube stem O.D.
FIG. 1 Typical Fixture
E2459 – 05
NOTE—Showing a shutoff (ball) valve, a tee connection in which to mount the microphone and various fittings which will maintain a constant inside
diameter through the tee connection to the anechoic tube. The example shown uses a ¼” microphone attached to a ¼” ID anechoic tube. Note that if the
orientation of the microphone is vertical, as shown, there is less likelihood of accumulating condensation on the microphone from hot exhaust gases.
FIG. 2 Typical Fixture
task group members developing this guide has been on gas
5.2 Estimated in-duct sound pressure level may be obtained
by measuring exterior airborne sound pressure levels and turbineductshavingcrosssectionsinexcessoften(10)square
meters.
applying a transfer function representing the transmission loss
of the duct wall. Significant uncertainties are associated with 5.6 This guide has no known temperature limitations.All of
such a procedure, suggesting the need for this guide. the field experience on the part of task group members
developing this guide has been on gas turbine ducts having
5.3 Estimated in-duct sound pressure level may be obtained
temperatures between ambient and 700°C.
by measuring exit plane sound pressure levels and applying a
transferfunctionconsistingoftheinsertionlossthroughthegas
6. Operating Conditions
path, including the insertion loss of any silencers. Significant
uncertainties are associated with such a procedure, suggesting 6.1 Whenever possible, equipment under test shall be oper-
the need for this guide.
ated in a mode or modes acceptable to all parties to the test.
Otherwise, operating conditions must at least be monitored in
5.4 This guide purports to measure the in-duct sound
order that the test results are properly qualified in terms of the
pressure level directly using type 1 instrumentation per ANSI
parameters most likely to affect the measurements.
S1.4 or S1.43. It is limited, however, to the determination of
thesoundpressurelevelatthelocationoftheportonlyandwill
7. Apparatus
include the effects of duct acoustical modes, as well as an
unknown degree of turbulence and other flow related effects.
7.1 Description of the Apparatus—Seesection4.1andFigs.
Methodologies may be devised by the user to minimize such
1 and 2.
effects.As a rule, the larger the number of test ports used, the
7.2 Permissible Range of Anechoic Tube Diameter,6to
better will be the averaged data. Although not prescribed by
25.4 mm ( ⁄4 to 1 in.).
thisguide,cross-channelcoherenceanalysisisalsoavailableto
7.3 Permissible Range of Microphone Sizes—Maximum
the analyst, using ports at different locations along the duct
microphone diameter is nominal 25.4 mm (1 in.). Probe
axis, which may yield improvements in data quality.
microphones are permissible.
5.5 This guide is intended for application to equipment 7.4 Minimum Anechoic Tube Length—The minimum ratio
in-situ,tobeappliedtolargefansandgasturbineshavinginlet
of the length of the anechoic tube to the tube inner diameter
orexhaustductswhosecrosssectionalareasareapproximately shall be one hundred (L/d > 100). Note that at low frequencies
four(4)squaremeters,ormore,andarethereforenotamenable
the tube connection is not anechoic. The ⁄4 wavelength
to laboratory testing.All of the field experience on the part of determines the lower usable data range.
E2459 – 05
7.5 Types of Materials—All steel pipe fittings, and metal each one-third octave band of interest, and shall be applied to
tube for anechoic tube are preferred. Other materials such as the data in the subsequent analysis. The specific guide of
common garden hose could be used for the anechoic tube if it performingthetransferfunctionorapplyingacorrectionfactor
is shown to be adequate in terms of ambient noise calibration. shall be unambiguously specified or described in the test
7.6 Use of shutoff ball valves is highly recommended, report.
especially for hot gas applications.
L 5 L 1 TF (1)
PId PMd
7.7 Guides for Creating Anechoic Terminations—Any
where:
acoustically absorptive material such as mineral wool or steel
TF = L – L = the transfer function,
wool is sufficient.The end of the anechoic tube shall be sealed
PRc PMc
L = reference in-duct pressure level, cold,
PRc
airtight for all hot gas applications, or may be fitted with a
L = measured pressure level, cold,
PMc
pressurized air injection system.
L = in-duct pressure level, dynamic, and
PId
7.8 Guidelines for Forced Air Insertion into the Anechoic
L = measured pressure level, dynamic.
PMd
Tube—In the event pressurized air injection system is used,
8.2.1 If the object is to determine the transfer function
additional tests shall be performed demonstrating no interfer-
relative to the mean duct cross-sectional average sound pres-
ence results from the sound of the injection system or flow
surelevel,thenthereferencesoundpressurelevelmustconsist
velocity across the microphone.
of a spatially averaged sound pressure level measured in
7.9 Frequency Ranges of Interest—Unlessotherwiseagreed
sufficient detail over the entire interior duct cross section.
tobythepartiestothetest,thefrequencyrangeofinterestshall
8.2.2 If the object is to determine the transfer function
be 16 Hz to 10000 Hz. For low frequency applications ensure
strictly in regard to the in-duct sound pressure level in the
thatthe ⁄4wavelengthoftheanechoicterminationisbelowthe
immediate vicinity of the test port, then the reference sound
range of interest.
pressure level will consist only of the level in the immediate
8. Procedure
vicinityofthetestportitself.Thedistancefromthetestportto
the reference microphone must be specified and, if applicable,
8.1 Selection of Measurement Positions—Location of test
the extent of any spatial averaging achieved by moving the
ports shall be at the discretion of the user. To the maximum
microphone while recording the reference signal.
extent practicable, the plane of the duct at which test ports are
8.2.3 If the object is to determine the transfer function
installed should be a region of relatively uniform flow both
strictly in regard to the full at-wall sound pressure level at the
upstream and downstream; that is, a straight portion of duct,
port face, then the reference sound pressure is determined by
andlowvelocity.Ifthereareanumberofdiscontinuitiesinthe
inserting a microphone into the test port so that the micro-
duct cross sectional area, it would be advisable to locate test
phone’s protective grid, or probe opening, is flush with the
ports at midpoints between the discontinuities. For any given
inner wall surface.
planeoftestportlocations,experiencehasshownbetterresults
8.2.4 The artificial sound source used for any of the above
when the ports are located away from duct corners. If strong
transferfunctiondeterminationsmaybeahornorloudspea
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