1、Designation: E2459 05 (Reapproved 2011)Standard Guide forMeasurement of In-Duct Sound Pressure Levels from LargeIndustrial Gas Turbines and Fans1This standard is issued under the fixed designation E2459; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he 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 guide is intended to provide a simple and consistentprocedure for the in-situ fi
3、eld measurement of in-duct soundpressure levels in large low pressure industrial air ducts, suchas for gas turbines or fans, where considerations such as flowvelocity, turbulence or temperature prevent the insertion ofsound pressure sensors directly into the flow. This standardguide is intended for
4、both ambient temperature intake air andhot 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 repeat-able and reproducible measure of the in-duct dynamic pressurelevel at the inlet or exhaust of the gas turbine, or f
5、an. The guideis not intended to quantify the “true” sound pressure level orsound power level. Silencers, as well as Waste Heat Boilers,must be designed using the in-duct sound power level as thebasis. Developing the true sound power level based on in-ductmeasurements of true sound pressure within a
6、complete oper-ating system is complex and procedures are developmental andoften proprietary.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 pract
7、ices and determine the applica-bility of regulatory limitations prior to use. Extreme caution ismandatory when working near hot exhaust gas systems andappropriate safety precautions such as the installation of quickacting isolation valves are recommended.2. Referenced Documents2.1 ASTM Standards:2C6
8、34 Terminology Relating to Building and EnvironmentalAcoustics2.2 ANSI Standards:S1.4 Specification for Sound Level Meters3S1.43 Specification for Integrating Averaging Sound LevelMeters33. Terminology3.1 Definitions of the acoustical terms used in this guide aregiven in Terminology C634.3.2 Definit
9、ions of Terms Specific to This Standard:3.2.1 anechoic tubea constant diameter tube of sufficientlength that a sound wave reflected from the far end of the tubetermination arrives at the microphone position sufficientlyattenuated that it will not appreciably affect the microphonereading.3.2.2 dynami
10、c pressurethe total instantaneous pressureincident upon the opening of the test port, including theinfluence of convective turbulence, local tangential modes,localized boundary layer effects at the test port and theindeterminate effects of all duct acoustical modes.3.2.3 fixturethe apparatus contain
11、ing the microphone fit-ting which locates the microphone flush with the insidediameter of the anechoic tube, the necessary fittings permittingairtight connection of the fixture and anechoic tube to the testport, and the anechoic tube.3.2.4 probe microphonea commercially available micro-diameter micr
12、ophone probe that is inserted into the anechoictermination near the test port connection. Some probes requirea pressure compensation connection. Use and installation shallfollow manufacturers procedures/instructions.3.2.5 test portthe hole in the duct wall to which theanechoic tube is connected and
13、whose diameter is equal to theinside diameter of the anechoic tube. In general the term testport, as used herein, will usually include any semi-permanentlyinstalled hardware in the wall of the duct permitting closure ofthe test port when not in use (ball valve and threaded pipe cap,or both) as well
14、as the pipe elements permitting attachment ofthe fixture and the anechoic tube.4. Summary of Guide4.1 Key features of this guide:1This guide is under the jurisdiction of ASTM Committee E33 on Building andEnvironmentalAcoustics and is the direct responsibility of Subcommittee E33.08 onMechanical and
15、Electrical System Noise.Current edition approved April 1, 2011. Published August 2011. Originallyapproved in 2005. Last previous edition approved in 2005 as E245905. DOI:10.1520/E2459-05R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servi
16、ceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harb
17、or Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 Athrough-wall test port opening, 25.4 mm (nominally,1 in.) or less, to which is connected the fixture, having aconstant inside diameter tube, to which the anechoic tube isconnected.The test port opening is flush with the in
18、side surfaceof the duct wall. No apparatus are inserted into the flow path.4.1.2 The microphone sensor is mounted in the fixture(3.2.3) outboard of the duct wall, with the microphone axisoriented normal to the centerline of the anechoic tube.4.1.3 The tip of the microphone, usually with a protective
19、grid, is positioned flush with, or more accurately tangential to,the inner wall of the fixture and as close to the duct wall astemperature or access limitations permit.4.1.4 The diameter of the microphone shall always be lessthan or equal to the inside diameter of the anechoic tube.4.1.5 The positio
20、n of the microphone is critical for hightemperature ducts, so as to limit the maximum temperature onthe microphone during testing.4.1.6 The anechoic tube shall have no inner wall disconti-nuities or changes in diameter that might create reflections orstanding waves within the tube. It is important t
21、o avoid anyprotrusion of the apparatus into the gas flow path.4.1.7 The anechoic termination may be achieved by looselypacking the “cold” end of the tube with mineral wool or steelwool. The tube end should be sealed airtight unless forced airis to be used to ensure adequate cooling of the anechoic t
22、ube.4.1.8 The inner duct wall opening shall be as smooth aspracticable, with a minimum of turbulence producing discon-tinuities at the duct wall inner surface. If the user chooses tomount a protective screen covering the inside duct wallopening, such screen shall not materially influence the soundpr
23、essure measurements, or a means of quantifying and ac-counting for such influence shall be included in the testprotocol. (Be aware that such screens can become fouled withparticles.)4.1.9 The inner duct wall opening shall be the same insidediameter as the inside diameter of the anechoic tube. That i
24、s,this guide does not permit the anechoic tube to be inserted into,or positioned within a duct wall port of larger size, unlessmeans are provided to ensure that the inner wall surface at thetest port is restored to a reasonable semblance of a smoothcontinuous wall surface.4.2 A sketch of a typical T
25、est Port is shown in Fig. 1.Asketch of a typical Fixture is shown in Fig. 2. Only the initialportion of the otherwise very long Anechoic Tube is depictedin each figure.5. Significance and Use5.1 All noise control features associated with the inlet orexhaust of large industrial fans and gas turbines
26、are, or shouldbe, based upon inlet or exhaust sound power levels in octavebands of frequency. Sound power levels are not directlymeasurable, however, so they must be calculated indirectly,using estimated or measured duct interior sound pressurelevels.5.2 Estimated in-duct sound pressure level may be
27、 obtainedby measuring exterior airborne sound pressure levels andapplying a transfer function representing the transmission lossNOTEShowing 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 wallsurface, occupying a
28、hole in the duct wall only slightly larger than the tube stem O.D.FIG. 1 Typical FixtureE2459 05 (2011)2of the duct wall. Significant uncertainties are associated withsuch a procedure, suggesting the need for this guide.5.3 Estimated in-duct sound pressure level may be obtainedby measuring exit plan
29、e sound pressure levels and applying atransfer function consisting of the insertion loss through the gaspath, including the insertion loss of any silencers. Significantuncertainties are associated with such a procedure, suggestingthe need for this guide.5.4 This guide purports to measure the in-duct
30、 soundpressure level directly using type 1 instrumentation per ANSIS1.4 or S1.43. It is limited, however, to the determination ofthe sound pressure level at the location of the port only and willinclude the effects of duct acoustical modes, as well as anunknown degree of turbulence and other flow re
31、lated effects.Methodologies may be devised by the user to minimize sucheffects. As a rule, the larger the number of test ports used, thebetter will be the averaged data. Although not prescribed bythis guide, cross-channel coherence analysis is also available tothe analyst, using ports at different l
32、ocations along the ductaxis, which may yield improvements in data quality.5.5 This guide is intended for application to equipmentin-situ, to be applied to large fans and gas turbines having inletor exhaust ducts whose cross sectional areas are approximatelyfour (4) square meters, or more, and are th
33、erefore not amenableto laboratory testing. All of the field experience on the part oftask group members developing this guide has been on gasturbine ducts having cross sections in excess of ten (10) squaremeters.5.6 This guide has no known temperature limitations.All ofthe field experience on the pa
34、rt of task group membersdeveloping this guide has been on gas turbine ducts havingtemperatures between ambient and 700C.6. Operating Conditions6.1 Whenever possible, equipment under test shall be oper-ated in a mode or modes acceptable to all parties to the test.Otherwise, operating conditions must
35、at least be monitored inorder that the test results are properly qualified in terms of theparameters most likely to affect the measurements.7. Apparatus7.1 Description of the ApparatusSee section 4.1 and Figs.1 and 2.7.2 Permissible Range of Anechoic Tube Diameter,6to25.4 mm (14 to 1 in.).7.3 Permis
36、sible Range of Microphone SizesMaximummicrophone diameter is nominal 25.4 mm (1 in.). Probemicrophones are permissible.7.4 Minimum Anechoic Tube LengthThe minimum ratioof the length of the anechoic tube to the tube inner diametershall be one hundred (L/d 100). Note that at low frequenciesthe tube co
37、nnection is not anechoic. The14 wavelengthdetermines the lower usable data range.7.5 Types of MaterialsAll steel pipe fittings, and metaltube for anechoic tube are preferred. Other materials such ascommon garden hose could be used for the anechoic tube if itis shown to be adequate in terms of ambien
38、t noise calibration.7.6 Use of shutoff ball valves is highly recommended,especially for hot gas applications.NOTEShowing a shutoff (ball) valve, a tee connection in which to mount the microphone and various fittings which will maintain a constant insidediameter through the tee connection to the anec
39、hoic tube. The example shown uses a ” microphone attached to a ” ID anechoic tube. Note that if theorientation of the microphone is vertical, as shown, there is less likelihood of accumulating condensation on the microphone from hot exhaust gases.FIG. 2 Typical FixtureE2459 05 (2011)37.7 Guides for
40、Creating Anechoic TerminationsAnyacoustically absorptive material such as mineral wool or steelwool is sufficient. The end of the anechoic tube shall be sealedairtight for all hot gas applications, or may be fitted with apressurized air injection system.7.8 Guidelines for Forced Air Insertion into t
41、he AnechoicTubeIn the event pressurized air injection system is used,additional tests shall be performed demonstrating no interfer-ence results from the sound of the injection system or flowvelocity across the microphone.7.9 Frequency Ranges of InterestUnless otherwise agreedto by the parties to the
42、 test, the frequency range of interest shallbe 16 Hz to 10 000 Hz. For low frequency applications ensurethat the14 wavelength of the anechoic termination is below therange of interest.8. Procedure8.1 Selection of Measurement PositionsLocation of testports shall be at the discretion of the user. To t
43、he maximumextent practicable, the plane of the duct at which test ports areinstalled should be a region of relatively uniform flow bothupstream and downstream; that is, a straight portion of duct,and low velocity. If there are a number of discontinuities in theduct cross sectional area, it would be
44、advisable to locate testports at midpoints between the discontinuities. For any givenplane of test port locations, experience has shown better resultswhen the ports are located away from duct corners. If strongduct acoustical modes are present and the mode shapes areknown, avoidance of the acoustica
45、l nodes is clearly necessary.It is always advisable to have more than one test port at a givenmeasurement plane and, if possible, ports on at least two sidesof the duct. In the event cross channel coherence studies are tobe included in the test program, it is recommended that thechannels involved in
46、 the analysis consist of test ports occupy-ing two different planes along the flow path, separated by aminimum of one-half (12) the larger duct dimension.8.2 Transfer FunctionSince the sound pressure level mea-sured at the microphones position within the anechoic tubewill differ from the sound press
47、ure level in the duct, a systemcorrection factor must be determined for the test apparatus. Thesystem correction factor so determined shall be referred to asthe transfer function.The transfer function shall be added to themeasured sound pressure level. The transfer function shall bethe difference in
48、 decibels when the measured sound pressurelevel is subtracted from the reference in-duct sound pressurelevel, as given in Eq 1. The transfer function test shall beperformed as a static (no flow) test, using an artificial soundsource, while the machine is off, permitting access to theinterior of the
49、duct. If multiple test ports on a given duct arefitted with identical apparatus, differing only in the successivere-mounting of the fixture and anechoic tube to the valved testport, a single transfer function test will suffice for each type ofapparatus used. The transfer function shall be determined foreach one-third octave band of interest, and shall be applied tothe data in the subsequent analysis. The specific guide ofperforming the transfer function or applying a correction factorshall be unambiguously specified or described in the testreport.LPId5 LPM
