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  • 1
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    Fan noise and performance (1972)
    In:  CASI
    Details
    Publication Date: 2005-11-30
    Description: Tradeoffs between aerodynamic and acoustic properties of various fan configurations led to the selection of a variety of fans that produce noise levels in the range of 100 to 120 PNdb. Fan configuration and design pressure ratio required for specific mission operations depend in part on the type of mission to be performed. Noise data obtained for single-stage low speed fans, single-stage high speed fans, and two-stage fan engines are presented in table form.
    Keywords: AIRCRAFT
    Type: Aircraft Engine Noise Reduction; p 7-61
    Format: text
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  • 2
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    Multiple pure tone noise generated by fans at supersonic tip speeds (1974)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The existence of clusters of pure tones at integral multiples of shaft speed has been noted for supersonic-tip-speed operation of fans and compressors. A continuing program to explore this phenomenon, often called combination-tone noise, has been in effect for several years. This paper reviews the research program, which involves a wide range of engines, compressor rigs, and special apparatus. Elements of the aerodynamics of the blade-associated shock waves are outlined and causes of blade-to-blade shock inequalities, responsible for the multiple tones, are described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Pennsylvania State Univ. Fluid Mech., Acoustics, and Design of Turbomachinery, Pt. 2; p 435-459
    Format: application/pdf
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  • 3
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    Method for extracting forward acoustic wave components from rotating microphone measurements in the inlets of turbofan engines (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This report describes a procedure for enhancing the use of the basic rotating microphone system so as to determine the forward propagating mode components of the acoustic field in the inlet duct at the microphone plane in order to predict more accurate far-field radiation patterns. In addition, a modification was developed to obtain, from the same microphone readings, the forward acoustic modes generated at the fan face, which is generally some distance downstream of the microphone plane. Both these procedures employ computer-simulated calibrations of sound propagation in the inlet duct, based upon the current radiation code. These enhancement procedures were applied to previously obtained rotating microphone data for the 17-inch ADP fan. The forward mode components at the microphone plane were obtained and were used to compute corresponding far-field directivities. The second main task of the program involved finding the forward wave modes generated at the fan face in terms of the same total radial mode structure measured at the microphone plane. To obtain satisfactory results with the ADP geometry it was necessary to limit consideration to the propagating modes. Sensitivity studies were also conducted to establish guidelines for use in other fan configurations.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-195457 , E-9577 , NAS 1.26:195457
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  • 4
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    Improved methods for fan sound field determination (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Several methods for determining acoustic mode structure in aircraft turbofan engines using wall microphone data were studied. A method for reducing data was devised and implemented which makes the definition of discrete coherent sound fields measured in the presence of engine speed fluctuation more accurate. For the analytical methods, algorithms were developed to define the dominant circumferential modes from full and partial circumferential arrays of microphones. Axial arrays were explored to define mode structure as a function of cutoff ratio, and the use of data taken at several constant speeds was also evaluated in an attempt to reduce instrumentation requirements. Sensitivities of the various methods to microphone density, array size and measurement error were evaluated and results of these studies showed these new methods to be impractical. The data reduction method used to reduce the effects of engine speed variation consisted of an electronic circuit which windowed the data so that signal enhancement could occur only when the speed was within a narrow range.
    Keywords: ACOUSTICS
    Type: NASA-CR-165188 , PWA-5635-43
    Format: application/pdf
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  • 5
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    Investigation of continuously traversing microphone system for mode measurement (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The continuously Traversing Microphone System consists of a data acquisition and processing method for obtaining the modal coefficients of the discrete, coherent acoustic field in a fan inlet duct. The system would be used in fan rigs or full scale engine installations where present measurement methods, because of the excessive number of microphones and long test times required, are not feasible. The purpose of the investigation reported here was to develop a method for defining modal structure by means of a continuously traversing microphone system and to perform an evaluation of the method, based upon analytical studies and computer simulated tests. A variety of system parameters were examined, and the effects of deviations from ideal were explored. Effects of traverse speed, digitizing rate, run time, roundoff error, calibration errors, and random noise background level were determined. For constant fan operating speed, the sensitivity of the method to normal errors and deviations was determined to be acceptable. Good recovery of mode coefficients was attainable. Fluctuating fan speed conditions received special attention, and it was concluded that by employing suitable time delay procedures, satisfactory information on mode coefficients can be obtained under realistic conditions. A plan for further development involving fan rig tests was prepared.
    Keywords: ACOUSTICS
    Type: NASA-CR-168040 , NAS 1.26:168040 , PWA-5846-26
    Format: application/pdf
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  • 6
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    Method of fan sound mode structure determination (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method for the determination of fan sound mode structure in the Inlet of turbofan engines using in-duct acoustic pressure measurements is presented. The method is based on the simultaneous solution of a set of equations whose unknowns are modal amplitude and phase. A computer program for the solution of the equation set was developed. An additional computer program was developed which calculates microphone locations the use of which results in an equation set that does not give rise to numerical instabilities. In addition to the development of a method for determination of coherent modal structure, experimental and analytical approaches are developed for the determination of the amplitude frequency spectrum of randomly generated sound models for use in narrow annulus ducts. Two approaches are defined: one based on the use of cross-spectral techniques and the other based on the use of an array of microphones.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-135293 , PWA-5554-3
    Format: application/pdf
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  • 7
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    Two-stage, low noise advanced technology fan. Volume 3: Acoustic data (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Tabulations and plots of the principal farfield noise characteristics of the fan installed in a special outdoor static noise test facility are presented.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-134829 , PWA-5303-VOL-3
    Format: application/pdf
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  • 8
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    Two-stage, low noise advanced technology fan. 5: Acoustic final report (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The NASA Q2S(quiet two-stage) fan is a 0.836m (32.9 in.) diameter model of the STF 433 engine fan, selected in a 1972 study for an Advanced Technology Transport (ATT) airplane. Noise-control features include: low tip speed, moderate stage pressure rise, large blade-vane spacings, no inlet guide vanes, and optimum blade and vane numbers. Tests were run on the baseline Q2S fan with standard inlet and discharge ducts. Further tests were made of a translating centerbody sonic inlet device and treated discharge ducts. Results were scaled to JT8D and JT3D engine fan size for comparison with current two-stage fans, and were also scaled to STF 433 fan size to compare calculated ATT flyover noise with FAR 36 limits. Baseline Q2S results scaled to JT8D and JT3D engine fan sizes showed substantial noise reductions. Calculated unsuppressed baseline ATT flyovers averaged about 2.5 EPNdB below FAR 36 limits. Using measured sonic inlet results, scaled baseline Q2S fan results, and calculated attenuations for a 1975 technology duct liner, projected flyover noise calculations for the ATT averaged about FAR 36 limits minus 10 EPNdB. Advances in suppression technology required to meet the 1985 goal of FAR 36 limits minus 20 EPNdB are discussed.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-134831 , PWA-5305
    Format: application/pdf
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  • 9
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    Two stage low noise advanced technology fan. 1: Aerodynamic, structural, and acoustic design (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A two-stage fan was designed to reduce noise 20 db below current requirements. The first-stage rotor has a design tip speed of 365.8 m/sec and a hub/tip ratio of 0.4. The fan was designed to deliver a pressure ratio of 1.9 with an adiabatic efficiency of 85.3 percent at a specific inlet corrected flow of 209.2kg/sec/sq m. Noise reduction devices include acoustically treated casing walls, a flowpath exit acoustic splitter, a translating centerbody sonic inlet device, widely spaced blade rows, and the proper ratio of blades and vanes. Multiple-circular-arc rotor airfoils, resettable stators, split outer casings, and capability to go to close blade-row spacing are also included.
    Keywords: FLUID MECHANICS
    Type: NASA-CR-134662 , PWA-5069
    Format: application/pdf
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  • 10
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    Experimental clean combustor program: Noise study (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Under a Noise Addendum to the NASA Experimental Clean Combustor Program (ECCP) internal pressure fluctuations were measured during tests of JT9D combustor designs conducted in a burner test rig. Measurements were correlated with burner operating parameters using an expression relating farfield noise to these parameters. For a given combustor, variation of internal noise with operating parameters was reasonably well predicted by this expression but the levels were higher than farfield predictions and differed significantly among several combustors. For two burners, discharge stream temperature fluctuations were obtained with fast-response thermocouples to allow calculation of indirect combustion noise which would be generated by passage of the temperature inhomogeneities through the high pressure turbine stages of a JT9D turbofan engine. Using a previously developed analysis, the computed indirect combustion noise was significantly lower than total low frequency core noise observed on this and several other engines.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-135106 , PWA-5458
    Format: application/pdf
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