ASTM E2459-05(2011)
(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
SIGNIFICANCE AND USE
All noise control features associated with the inlet or exhaust of large industrial fans and gas turbines are, or should be, based upon inlet or exhaust sound power levels in octave bands of frequency. Sound power levels are not directly measurable, however, so they must be calculated indirectly, using estimated or measured duct interior sound pressure levels.
Estimated in-duct sound pressure level may be obtained by measuring exterior airborne sound pressure levels and applying a transfer function representing the transmission loss of the duct wall. Significant uncertainties are associated with such a procedure, suggesting the need for this guide.
Estimated in-duct sound pressure level may be obtained by measuring exit plane sound pressure levels and applying a transfer function consisting of the insertion loss through the gas path, including the insertion loss of any silencers. Significant uncertainties are associated with such a procedure, suggesting the need for this guide.
This guide purports to measure the in-duct sound pressure level directly using type 1 instrumentation per ANSI S1.4 or S1.43. It is limited, however, to the determination of the sound pressure level at the location of the port only and will include the effects of duct acoustical modes, as well as an unknown degree of turbulence and other flow related effects. Methodologies may be devised by the user to minimize such effects. As a rule, the larger the number of test ports used, the better will be the averaged data. Although not prescribed by this guide, cross-channel coherence analysis is also available to the analyst, using ports at different locations along the duct axis, which may yield improvements in data quality.
This guide is intended for application to equipment in-situ, to be applied to large fans and gas turbines having inlet or exhaust ducts whose cross sectional areas are approximately four (4) square meters, or more, and are therefore not amenable to laboratory testing. Al...
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.
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. 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(Reapproved 2011)
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 2.2 ANSI Standards:
S1.4Specification for Sound Level Meters
1.1 Thisguideisintendedtoprovideasimpleandconsistent
S1.43Specification for Integrating Averaging Sound Level
procedure for the in-situ field measurement of in-duct sound
Meters
pressure levels in large low pressure industrial air ducts, such
as for gas turbines or fans, where considerations such as flow
3. Terminology
velocity, turbulence or temperature prevent the insertion of
sound pressure sensors directly into the flow. This standard 3.1 Definitionsoftheacousticaltermsusedinthisguideare
guide is intended for both ambient temperature intake air and
given in Terminology C634.
hot exhaust gas flow in ducts having cross sections of four (4)
3.2 Definitions of Terms Specific to This Standard:
square meters, or more.
3.2.1 anechoic tube—a constant diameter tube of sufficient
1.2 Thedescribedprocedureisintendedtoprovidearepeat- length that a sound wave reflected from the far end of the tube
ableandreproduciblemeasureofthein-ductdynamicpressure
termination arrives at the microphone position sufficiently
levelattheinletorexhaustofthegasturbine,orfan.Theguide attenuated that it will not appreciably affect the microphone
is not intended to quantify the “true” sound pressure level or
reading.
sound power level. Silencers, as well as Waste Heat Boilers,
3.2.2 dynamic pressure—the total instantaneous pressure
must be designed using the in-duct sound power level as the
incident upon the opening of the test port, including the
basis. Developing the true sound power level based on in-duct
influence of convective turbulence, local tangential modes,
measurements of true sound pressure within a complete oper-
localized boundary layer effects at the test port and the
atingsystemiscomplexandproceduresaredevelopmentaland
indeterminate effects of all duct acoustical modes.
often proprietary.
3.2.3 fixture—the apparatus containing the microphone fit-
1.3 This standard does not purport to address all of the
ting which locates the microphone flush with the inside
safety concerns, if any, associated with its use. It is the
diameteroftheanechoictube,thenecessaryfittingspermitting
responsibility of the user of this standard to establish appro-
airtight connection of the fixture and anechoic tube to the test
priate safety and health practices and determine the applica-
port, and the anechoic tube.
bility of regulatory limitations prior to use. Extreme caution is
3.2.4 probe microphone—a commercially available micro-
mandatory when working near hot exhaust gas systems and
diameter microphone probe that is inserted into the anechoic
appropriate safety precautions such as the installation of quick
termination near the test port connection. Some probes require
acting isolation valves are recommended.
a pressure compensation connection. Use and installation shall
2. Referenced Documents follow manufacturer’s procedures/instructions.
3.2.5 test port—the hole in the duct wall to which the
2.1 ASTM Standards:
anechoic tube is connected and whose diameter is equal to the
C634Terminology Relating to Building and Environmental
inside diameter of the anechoic tube. In general the term test
Acoustics
port,asusedherein,willusuallyincludeanysemi-permanently
installed hardware in the wall of the duct permitting closure of
This guide is under the jurisdiction ofASTM Committee E33 on Building and
EnvironmentalAcousticsandisthedirectresponsibilityofSubcommitteeE33.08on
the test port when not in use (ball valve and threaded pipe cap,
Mechanical and Electrical System Noise.
or both) as well as the pipe elements permitting attachment of
Current edition approved April 1, 2011. Published August 2011. Originally
the fixture and the anechoic tube.
approved in 2005. Last previous edition approved in 2005 as E2459–05. DOI:
10.1520/E2459-05R11.
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, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2459 − 05 (2011)
4. Summary of Guide mount a protective screen covering the inside duct wall
opening, such screen shall not materially influence the sound
4.1 Key features of this guide:
pressure measurements, or a means of quantifying and ac-
4.1.1 Athrough-walltestportopening,25.4mm(nominally,
counting for such influence shall be included in the test
1 in.) or less, to which is connected the fixture, having a
protocol. (Be aware that such screens can become fouled with
constant inside diameter tube, to which the anechoic tube is
particles.)
connected.Thetestportopeningisflushwiththeinsidesurface
4.1.9 The inner duct wall opening shall be the same inside
of the duct wall. No apparatus are inserted into the flow path.
diameter as the inside diameter of the anechoic tube. That is,
4.1.2 The microphone sensor is mounted in the fixture
thisguidedoesnotpermittheanechoictubetobeinsertedinto,
(3.2.3) outboard of the duct wall, with the microphone axis
or positioned within a duct wall port of larger size, unless
oriented normal to the centerline of the anechoic tube.
means are provided to ensure that the inner wall surface at the
4.1.3 The tip of the microphone, usually with a protective
test port is restored to a reasonable semblance of a smooth
grid, is positioned flush with, or more accurately tangential to,
continuous wall surface.
the inner wall of the fixture and as close to the duct wall as
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-
5.1 All noise control features associated with the inlet or
nuities or changes in diameter that might create reflections or
exhaust of large industrial fans and gas turbines are, or should
standing waves within the tube. It is important to avoid any
be, based upon inlet or exhaust sound power levels in octave
protrusion of the apparatus into the gas flow path.
bands of frequency. Sound power levels are not directly
4.1.7 The anechoic termination may be achieved by loosely
measurable, however, so they must be calculated indirectly,
packing the “cold” end of the tube with mineral wool or steel
using estimated or measured duct interior sound pressure
wool. The tube end should be sealed airtight unless forced air
levels.
is to be used to ensure adequate cooling of the anechoic tube.
4.1.8 The inner duct wall opening shall be as smooth as 5.2 Estimated in-duct sound pressure level may be obtained
practicable, with a minimum of turbulence producing discon- by measuring exterior airborne sound pressure levels and
tinuities at the duct wall inner surface. If the user chooses to applying a transfer function representing the transmission loss
NOTE 1—Showing a typical Fixture (see Fig. 2) installed in an insulated duct wall. Note the stem of the Fixture extends all the way to the inner duct
wall surface, occupying a hole in the duct wall only slightly larger than the tube stem O.D.
FIG. 1 Typical Fixture
E2459 − 05 (2011)
NOTE 1—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
of the duct wall. Significant uncertainties are associated with developing this guide has been on gas turbine ducts having
such a procedure, suggesting the need for this guide. temperatures between ambient and 700°C.
5.3 Estimated in-duct sound pressure level may be obtained
6. Operating Conditions
by measuring exit plane sound pressure levels and applying a
transferfunctionconsistingoftheinsertionlossthroughthegas 6.1 Whenever possible, equipment under test shall be oper-
ated in a mode or modes acceptable to all parties to the test.
path, including the insertion loss of any silencers. Significant
uncertainties are associated with such a procedure, suggesting Otherwise, operating conditions must at least be monitored in
order that the test results are properly qualified in terms of the
the need for this guide.
parameters most likely to affect the measurements.
5.4 This guide purports to measure the in-duct sound
pressure level directly using type 1 instrumentation per ANSI
7. Apparatus
S1.4 or S1.43. It is limited, however, to the determination of
7.1 Description of the Apparatus—Seesection4.1andFigs.
thesoundpressurelevelatthelocationoftheportonlyandwill
include the effects of duct acoustical modes, as well as an 1 and 2.
unknown degree of turbulence and other flow related effects.
7.2 Permissible Range ofAnechoic Tube Diameter,6to25.4
Methodologies may be devised by the user to minimize such
mm ( ⁄4 to 1 in.).
effects.As a rule, the larger the number of test ports used, the
7.3 Permissible Range of Microphone Sizes—Maximum
better will be the averaged data. Although not prescribed by
microphone diameter is nominal 25.4 mm (1 in.). Probe
thisguide,cross-channelcoherenceanalysisisalsoavailableto
microphones are permissible.
the analyst, using ports at different locations along the duct
axis, which may yield improvements in data quality. 7.4 Minimum Anechoic Tube Length—The minimum ratio
of the length of the anechoic tube to the tube inner diameter
5.5 This guide is intended for application to equipment
shall be one hundred (L/d > 100). Note that at low frequencies
in-situ,tobeappliedtolargefansandgasturbineshavinginlet
the tube connection is not anechoic. The ⁄4 wavelength
orexhaustductswhosecrosssectionalareasareapproximately
determines the lower usable data range.
four(4)squaremeters,ormore,andarethereforenotamenable
to laboratory testing.All of the field experience on the part of 7.5 Types of Materials—All steel pipe fittings, and metal
task group members developing this guide has been on gas tube for anechoic tube are preferred. Other materials such as
turbineductshavingcrosssectionsinexcessoften(10)square common garden hose could be used for the anechoic tube if it
meters. is shown to be adequate in terms of ambient noise calibration.
5.6 This guide has no known temperature limitations.All of 7.6 Use of shutoff ball valves is highly recommended,
the field experience on the part of task group members especially for hot gas applications.
E2459 − 05 (2011)
7.7 Guides for Creating Anechoic Terminations—Any L 5 L 1TF (1)
PId PMd
acoustically absorptive material such as mineral wool or steel
where:
wool is sufficient.The end of the anechoic tube shall be sealed
TF = L – L = the transfer function,
PRc PMc
airtight for all hot gas applications, or may be fitted with a
L = reference in-duct pressure level, cold,
PRc
pressurized air injection system.
L = measured pressure level, cold,
PMc
7.8 Guidelines for Forced Air Insertion into the Anechoic
L = in-duct pressure level, dynamic, and
PId
Tube—In the event pressurized air injection system is used, L = measured pressure level, dynamic.
PMd
additional tests shall be performed demonstrating no interfer-
8.2.1 If the object is to determine the transfer function
ence results from the sound of the injection system or flow
relative to the mean duct cross-sectional average sound pres-
velocity across the microphone.
surelevel,thenthereferencesoundpressurelevelmustconsist
7.9 Frequency Ranges of Interest—Unless otherwise agreed
of a spatially averaged sound pressure level measured in
tobythepartiestothetest,thefrequencyrangeofinterestshall
sufficient detail over the entire interior duct cross section.
be 16 Hz to 10000 Hz. For low frequency applications ensure
8.2.2 If the object is to determine the transfer function
thatthe ⁄4wavelengthoftheanechoicterminationisbelowthe
strictly in regard to the in-duct sound pressure level in the
range of interest. immediate vicinity of the test port, then the reference sound
pressure level will consist only of the level in the immediate
8. Procedure
vicinityofthetestportitself.Thedistancefromthetestportto
8.1 Selection of Measurement Positions—Location of test
the reference microphone must be specified and, if applicable,
ports shall be at the discretion of the user. To the maximum
the extent of any spatial averaging achieved by moving the
extent practicable, the plane of the duct at which test ports are
microphone while recording the reference signal.
installed should be a region of relatively uniform flow both
8.2.3 If the object is to determine the transfer function
upstream and downstream; that is, a straight portion of duct,
strictly in regard to the full at-wall sound pressure level at the
andlowvelocity.Ifthereareanumberofdiscontinuitiesinthe
port face, then the reference sound pressure is determined by
duct cross sectional area, it would be advisable to locate test
inserting a microphone into the test port so that the micro-
ports at midpoints between the discontinuities. For any given
phone’s protective grid, or probe opening, is flush with the
planeoftestportlocations,experiencehasshownbetterresults
inner wall surface.
when the ports are located away from duct corners. If strong
8.2.4 The artificial sound source used for any of the above
duct acoustical modes are present and the mode shapes are
transferfunctiondeterminationsmaybeahornorloudspeaker.
kn
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