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4、A) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR5303AEROSPACEINFORMATIONREPORTAIR5303 Issued 2010-02Infrasound Phenomenon in Engine Test Cel
5、ls RATIONALEThe rationale behind this document is to provide background information on the subject of infrasound as it pertains to the use of gas turbine engines in indoor test cells. Little information exists as to the driving mechanisms behind this phenomenon, but it can cause significant problems
6、 for a test cell operator, thus it was considered important to educate the test cell owner about the possible presence of such a condition, and to the possible solutions that may be used to solve an infrasound problem. INTRODUCTIONAs gas turbine engine technology advances, the size and power of each
7、 new engine generation has increased significantly. While the energy output of modern engines has doubled in the last twenty years, the size of the facilities used to test these engines has not. The phenomenon known as infrasound, has been known for many years in the medical and oceanographic fields
8、. However, its appearance in the gas turbine testing field has not been widely known or accepted until relatively recently. The major reason for this is the inability to easily measure and quantify the phenomenon. Infrasound is a term given to sub-audible noise in the 1 to 20 Hz range. Since it is g
9、enerally not heard, infrasound surfaces mostly in anecdotal accounts of problems associated with vibration and rattling of windows and other equipment in buildings some distance away from the engine test facility. In addition increasing pressure from airport authorities and other regulatory agencies
10、 requires that infrasound limits be added to the specifications to be met when a new test facility is built. Thus a better understanding of the factors leading to this aero-acoustic problem is certainly needed by both the test cell operator and the test cell designer. The purpose of this paper is to
11、 identify the infrasound phenomenon, including its possible cause(s), relate the various types based on the source, and describe some of the typical “fixes” that have been used to try and solve the problem. Work on a complete solution for infrasound problems associated with gas turbine test faciliti
12、es in on-going by many facility designers, so this paper is really an introduction to those who are unfamiliar with the phenomenon or who may suspect that that have an infrasound problem. SAE AIR5303 Page 2 of 111. SCOPE This SAE Aerospace Information Report (AIR) has been written for individuals as
13、sociated with the ground level testing of large turbofan and turbojet engines, and particularly those who are interested in infrasound phenomena. 2. REFERENCES The following is a list of some applicable references and documents used in the preparation of this information report: 1. James C. Battis a
14、nd Francis A. Crowley, Forecasting Hush House Induced Vibro-acoustics, AFGL-TR-87-0221, 14 July, 1987. 2. D. G. Mabey, Reduction of Infrasound from the Auxiliary Compressors of a large Wind Tunnel, Journal of Sound and Vibration, Vol. 63, March 8, 1979. 3. S. D. Noel and R. W. Whitaker, Comparison o
15、f Noise Reduction Systems, Report No. DE91-015318, LA-12008-MS. Los Alamos National Lab., 1991. 4. R. W. Whitaker, S. D. Noel, and W. R. Meadows, Infrasonic Observations and Modeling of the Minor Uncle High Explosion Devise, Report No. LA-UR-94-2771; Conf-9406244-1, August 1999. 5. M. L. S. Vercamme
16、n, Setting Limits on Low Frequency Noise, Journal of Low Frequency Sound, Vol. 8, No.4, 1989. 6. H. Pawlaczyk and M. Luszcznska, An Application of a Three Element Microphone Measuring Method for Locating Distant Sources of Infrasonic Noise, Journal of Low Frequency Noise and Vibration, Vol. 15, No.
17、2, 1996. 7. H. Onusic and V. S. Mizutani, Infrasonic Pressure Levels in Commercial Vehicles, SAE Brazil 1993 Mobility Technology Conference and Exhibit, Sao Paulo, Brasil, October 1993. 8. T. Yoshinaga, K. Fuji, and S. Nagai, Suppression of Infrasonic Noise Emanating from NAL 1mX1m Supersonic Wind T
18、unnel, AIAA97-0664. 9. Laurence J. Heldelberg and Elliot B. Gordon, Acoustic Evaluation of the Helmoltz Resonator Treatment in the NASA Lewis 8- by 6-Foot Supersonic Tunnel, NASA Technical Memorandum 101407, January 1989. 10. Allan J. Whitten, Vibrational Impact of Hush House Operation, Proceedings
19、of the 1988 Joint CSCE-ASCE National Conference, Vancouver, July 1988 11. V. R. Miller, et al. “Investigation if Acoustic Characteristics of Aircraft/Engines Operating in the Dry-Cooled Jet EngineMaintenance Facility”. The Shock and Vibration Bulletin, Naval Research Laboratory, 1983. 12. I. L. Ver
20、and D. W. Anderson, “Report on the Infrasound and Vibration Study at Luke AFB, Phoenix, Arizona”. Bolt, Beranek and Newman, Inc. Project No. 05558. 13. A. J. Witten and M. Lessen, “Low Frequency Acoustic Emissions from Jet Engine Test Facilities”. Journal of AIAA. 14. A. L.Kafka and J. I. Blaney, “I
21、nfrasonic Emissions from the Otis AFB Hush House”, Geophysics Laboratory/Earth Science Division/LWH, Report No. GL-TR-90-0225, September 1990. 15. N. Doelling and R. H. Bolt, “Noise Control for Aircraft Engine Test cells and Ground Run-Up Suppressors” WADC Tech Report 58-202, November 1961. 16. R. J
22、.Freuler and K. A.Montgomery, “Reducing Large Pressure Fluctuations in an Engine Test Cell by Modifying the Exhaust Blast Basket End Configuration”, CEAS/AIAA 95-128, June, 1995. SAE AIR5303 Page 3 of 113. INFRASOUND ANECDOTES After the construction of a new large test cell, the operator experienced
23、 the windows of a nearby building severely rattled whenever the cell was in operation. Installing a ring diffuser and replacing the exhaust basket with a diffuser grid reduced the magnitude of the effect but did not stop the windows from rattling. The eventual solution was adding caulk to the window
24、s to stop them from rattling in their frames. When a new JT8D test cell was put into service, the owner started receiving telephone calls from residential neighbors more than a half mile distant. One neighbor complained he was in the shower and his guts vibrated so badly he thought he was having a h
25、eart attack. Another neighbor reported dishes rattling off their shelves and windows rattling. A third neighbor reported that they thought a train was passing by. Their young son, who loved watching the trains, started to cry when the “train” turned out to be a phantom caused by the test cell. In a
26、large test cell, whenever a JT8D engine with a QEC flight nozzle was tested, the main cell door pulsed and shook at a 0.5 Hz rate. Whenever the slave nozzle was used no pulsing was noticed. The QEC flight nozzle had a slight cant in thrust angle while the slave nozzle was true axial flow. The asymme
27、trical flow in the augmentor somehow cased the infrasound pressure waves. The problem was solved by the installation of a ring diffuser. Near an engine test site, farmers as far as 5 miles away reported their cows were giving less milk and chickens stopped laying eggs whenever the site was in operat
28、ion. The farmers reported everything returned to normal, after the test site made a monetary settlement with the farmers. A test cell complex with a ramp in the exhaust stack to direct exhaust flow, reported that adjacent building roofs were rattling and pulsing at a 0.5 Hz rate. The entire building
29、 roof could be seen to visibility flex. The problem was solved by replacing the deflector ramp with a diffusing grid. 4. CHARACTERISTICS Infrasound is the low frequency emission with peaks under 20 Hz, with the majority of the phenomenon occurring in the 4 to 16 Hz range. Measurements have shown tha
30、t infrasound behaves as a near monopole source located near the rear of the test facility. Infrasound emissions generally increase with engine power although there are several cases where the infrasound was much stronger at a power setting below maximum. It has been suggested that infrasound emissio
31、ns are coupled to the surrounding buildings by one or more resonant modes of the test cell itself. One theory suggests that infrasound originates in the high speed portion of the engine exhaust gas flow as a result of aero-acoustic mechanisms, known as acoustic Cherenkov radiation. Acoustic Cherenko
32、v radiation is similar to a shock wave and occurs when a hot gas is moving at supersonic speed in the surrounding air. Perception of infrasound is contingent on a persons hearing and the amount of vibration present. Vibration capable of inducing perception will occur only at high pressure levels, 20
33、 to 40 dB above the threshold of auditory perception. The threshold for perception is 65 dB 32 Hz, 95 dB 16 Hz, 120 dB 3 Hz, and 140 dB 1 Hz. When infrasound becomes loud enough, it is annoying. Infrasound can affect the human body, especially the hormonal and central nervous systems. It may damage
34、the semicircular canals of the middle ear, which control balance, and may affect the inner ear, and excite resonant frequencies ranging from 0.1 to 25 Hz in particular parts of the body, such as the abdomen, chest or throat. While infrasound does not usually produce and dramatic health effects durin
35、g short exposure periods, it certainly causes disturbance and annoyance to most individuals. SAE AIR5303 Page 4 of 115. INFRASOUND SOURCES Generally there are three classes of infrasound sources: (1) the engine itself, (2) the test facility with the engine as the driver, or (3) the facility dimensio
36、ns produce a trigger effect causing infrasound by toggling the engine exhaust plume between two stable flow states. 5.1 The Engine Source Most engine manufacturers do not generally measure acoustic frequencies below 32 Hz since even the largest 100K class engines show a pronounced monotonic decrease
37、 in dBA from 100 down to 32 Hz. But recent data (Figure 1) taken with flat response pressure instrumentation shows a slow increase of 10 dB from 32 Hz down to 1 Hz. This data taken in an outdoor test facility with the engine centerline 15 ft above the ground and at 115 degrees (directly in front of
38、engine is zero) shows no peaks indicative of a strong resonance generated by the engine itself. Also the level of 90 dB is significantly lower than the 130 dB or higher that is typical of measurements in a test cell engine room adjacent to the exhaust pipe. The initial conclusion is that infrasound
39、generation requires instabilities in the engine exhaust plume relatively far downstream, or an interaction with the ground plane or other structure in the area. 5.2 The Facility Source with Engine as Driver If the engine by itself cannot produce the level of infrasound indicated by actual data, then
40、 the test facility geometry must be a critical part of the mechanism which allows energy to be extracted from the engine exhaust plume. To date analysis and scale model tests to determine the aero-acoustic coupling details have not produced useful results. There are many side to side, rotational, an
41、d axial modes of engine jet oscillation that could provide the necessary coupling, but these modes may not be the same in each test cell and engine combination. 5.3 The Engine source with Facility Trigger This mode of operation is characterized by the engine exhaust plume deflecting towards one surf
42、ace of the exhaust tube initially caused by the Coanda effect with an acoustic wave traveling forward to the cell inlet. This pressure wave reflected from the inlet travels back to the exhaust tube and triggers a shift of the engine exhaust plume, attaching it to the opposite side of the exhaust tub
43、e. This process continues at a primary frequency with timing determined by the length of the test cell inlet system. The pressure in the engine room will approximate a square wave made up of the primary frequency plus odd harmonics. 6. TEST EVALUATION TECHNIQUES There are three test techniques (Refe
44、rence 15) that may be used to evaluate and aid in determining a solution to an engine test cell infrasound problem: (1) full scale engine test, (2) loudspeaker and variable frequency amplifier, (3) explosive or impulsive noise source. Scale model testing is a fourth technique that may prove useful t
45、o compare proposed solutions prior to full scale implementation. 6.1 Full Scale Engine Test The most obvious and realistic approach is to install acoustic instrumentation at problem locations in both the near and far field as appropriate, and record data while running an engine at a power level know
46、n to be a problem. The objective would be to obtain dB levels and associated frequency spectrums that would identify critical dimensions or lengths in test cell inlet, engine room, augmentor or exhaust stack that contributed to the infrasound. For example a sound attenuation panel with a length that
47、 corresponded to a frequency peak in the acoustic spectrum. The solution may then be to add a support to restrain the vibration of this panel or panels. However the complexity of the spectrum and harmonics will typically cause a degree of uncertainty and several attempts may be required finally isol
48、ate and correct the problem. The primary disadvantage of this approach lies in the cost of required engine runs, availability of an engine known to cause an infrasound problem and test cell scheduling and down time. SAE AIR5303 Page 5 of 116.2 Loudspeaker An alternative procedure that can be effecti
49、ve for internal and near field infrasound is to install a high power loudspeaker in the engine room, generally at the engine location and facing aft towards the cell exhaust tube. A high power variable frequency amplifier drives the speaker over a range of test frequencies while acoustic data is recorded at various locations within and surrounding the test facility. The data obtained will identify elements of the air
