1、NASA Technical Paper 1301A Correlation of Mixing NoiseFrom Coannular Jets WithInverted Flow ProfilesS. Paul PaoAPRIL 1979NASAProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA Technical Paper 1301A Correlation of Mixing NoiseFrom Coannular Jets Wit
2、hInverted Flow ProfilesS. Paul PaoLangley Research CenterHampton, VirginiaNASANational Aeronauticsand Space AdministrationScientific and TechnicalInformation Office1979Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-CONTENTSSUMMARY 1INTRODUCTIONSYMBO
3、LS 2STATIC MIXING NOISE 4Static Data BaseEquivalent Jet 5Analysis of Sound Power 7Directivity 10Spectral Characteristics 11FORWARD FLIGHT EFFECTS 4Wind-Tunnel Data Base 4Correlation Methods 5Method I 15Method II 6CONCLUDING REMARKS 7REFERENCES 9TABLES 21FIGURES 40iii Preceding Page BlankProvided by
4、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SUMMARYThis report correlates data for jet mixing noise from coannular jets withinverted flow velocity profiles (IVPs). The acoustic performance of coannularjets is measured against a hypothetical single jet with t
5、he same mass flow,thrust, and total enthalpy flow as the coannular jet. Coannular jets with veloc-ity ratios greater than 1.2 were found to have lower overall sound power levelsthan their equivalent jets. The study shows that the magnitude of the soundpower reduction was a function of both equivalen
6、t jet velocity and velocityratio and that optimum noise reduction of coannular jets in the data set occurswithin a range of equivalent velocities between 500 and 700 meters per secondand velocity ratios between 1.6 and 2.3. If the expected sound power level ofthe single equivalent jet is used as the
7、 basis for comparison, the maximum soundpower reduction is about 4 decibels.The jet mixing noise data have been analyzed for directivity and spectra.Directivity indices for coannular jets in different equivalent jet velocityranges were derived from the data correlation. A special set of spectralcurv
8、es have been developed to describe the characteristic double peak spectraof coannular jet noise. These spectral curves depend on directivity angle,equivalent jet velocity, and velocity ratio. The combination of empiricalcurves for overall acoustic power, directivity, and spectra is used to developa
9、prediction method for aircraft noise from coannular jets. The temperatureratio between the inner and outer streams has not been found to be importantin this acoustic correlation. However, the mean temperature effect has beenincluded in the computations of sound pressure levels.Since the nozzles unde
10、r consideration are limited in variety, effectsof geometric parameters such as radius ratio and area ratio on the acousticproperties of coannular jets are not covered in this study.INTRODUCTIONVariable-cycle engine designs have been proposed for the advanced super-sonic transport. These engine conce
11、pts are intended for achieving high effi-ciency in both subsonic and supersonic flight operations. For a typical design,the jet temperature and velocity in the secondary (outer) stream may be substan-tially higher than those in the primary (inner) stream at take-off conditions.Such an exhaust flow s
12、ystem is different from that for a conventional coaxialjet where the primary stream has a higher velocity than the fan stream; thus,this system has acquired the name of coannular jet with an inverted velocityprofile (IVP).The NASA Lewis Research Center has sponsored a sequence of experimentalprogram
13、s to establish the acoustic properties of the coannular jet. In refer-ences 1 and 2, extensive acoustic measurements are presented for several basiccoannular jet nozzle configurations over a large matrix of flow conditions.Provided by IHSNot for ResaleNo reproduction or networking permitted without
14、license from IHS-,-,-The size and quality of these data sets are comparable to the best availabledata sets on single circular jets.The original data analyses reported in references 1 and 2 showed thatcoannular jets with IVPs produce less noise than expected; however, theamount of noise reduction and
15、 its dependence on jet operating parametersremain controversial. The controversy is due, in part, to the basis fornoise comparison which was used in these earlier data analyses.The purpose of this report is to correlate the data from references 1and 2 from a unified point of view. Recent publication
16、s (refs. 3, 4, and 5)agree that the noise characteristics of the coannular jet should be comparedto those of a fully mixed equivalent jet. This equivalence is a hypotheticalsingle circular jet which has the same mass flow, thrust, and total enthalpyflow as the coannular jet. The equivalent jet is un
17、iquely defined for a givencoannular jet flow condition and is a reasonable standard for noise comparison.Several objectives are accomplished by this data correlation. First, thedependence of noise reduction, measured here in terms of overall acoustic power,on key parameters (such as the equivalent j
18、et velocity and the velocity ratio)is established. This objective may be achieved with confidence because of thelarge size of the data sets. Second, this correlation provides the basis foran interim noise prediction procedure for coannular jets. Third, key trendsare useful in understanding the origi
19、n and dynamic process of coannular jetnoise emission.The analysis of the data begins with the static data sets, and correlationcurves are developed for the overall acoustic power generated by a coannularjet on a static test stand. Then the directivity index and spectral shapes aredeveloped. After eq
20、uations for the noise from a nonmoving jet source are estab-lished, wind-tunnel data are analyzed for the effect of forward velocity on thecoannular jet noise.SYMBOLSA area, m2Ae nozzle exit area defined for equivalent jet, m2Aref reference area for sound power correlation, 1.00 m2C convection facto
21、r, equation (17)C2 convection factor, equation (18)ca ambient speed of sound, m/sDe diameter of equivalent jet, mD(6) directivity factorProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-f one-third-octave band center frequency, HzI acoustic intensity,
22、W/m2Iav average acoustic intensity, W/m2m forward velocity exponentm mass flow rate, kg/sme mass flow rate of equivalent jet, kg/sm- mass flow rate of primary stream, kg/sn2 mass flow rate of secondary stream, kg/sNg e Strouhal number as defined in equation (15)Ng peak peak Strouhal number for a giv
23、en spectrumOASPL overall sound pressure level, dB re 2 * 10“ N/m2PWL sound power level, dB re 1012 Wp acoustic pressure, N/m2p2 mean-square sound pressure, N2/mpa atmospheric pressure, N/m2pt i total pressure of primary stream, N/m2Pt 2 total pressure of secondary stream, N/m2R spherical radius, mNg
24、 i peak Strouhal number for first spectral componentNS 2 peak Strouhal number for second spectral componentSPL one-third-octave band sound pressure level, dB re 2 x 10“ N/m2Ta atmospheric temperature, KTe total temperature of equivalent single jet, KT-j total temperature of primary stream, KT2 total
25、 temperature of secondary stream, KV velocity, m/sProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Va forward velocity, m/sVe velocity of equivalent single jet, m/sV-j velocity of primary stream, m/sV2 velocity of secondary stream, m/sVQ jet velocity
26、as defined in equation (14), m/sW corrected sound power, WW0 sound power, WY ratio of specific heats6 directivity angle from inlet axis, degp density of air, kg/mpa density of ambient air, kg/m-*Pe density of equivalent single jet, kg/nPw jet density exponentSTATIC MIXING NOISEStatic Data BaseThe re
27、search programs described in references 1 and 2 were initiated underNASA Lewis Research Center sponsorship to determine noise characteristics ofduct-burning turbofan engines. Nozzle configurations studied in these programsincluded the basic coannular nozzles and a large variety of coannular nozzlesw
28、ith noise suppression devices. The present report correlates the acousticdata for the basic coannular nozzle configurations shown in figures 1 to 5 only(these configurations are named in this report as models 1 to 5, respectively).Models 1 to 3 were used in reference 1. Model 1, a circular convergen
29、tnozzle, was used for calibration throughout the test series. The primary ductfairing (illustrated in fig. 1) within the nozzle did not have any adverseeffect on the performance of the convergent nozzle. Models 2 and 3 are coan- .nular nozzles with area ratios 0.75 and 1.20, respectively. The second
30、ary orfan stream and the primary stream exit planes were offset in the axial direc-tion. In both models 2 and 3, the secondary nozzle was convergent and theprimary nozzle was convergent-divergent.The total temperature for both streams was limited to 1100 K or less. Themaximum nozzle pressure ratio w
31、as approximately 4.0, while the primary streamnozzle pressure ratio was fixed at 1.53 for most run conditions. The acousticdata obtained with models 1 , 2, and 3 covered 30 one-third-octave bands, fromProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1
32、00 Hz to 80 kHz, and nine (nominal) directivity angles ranging from 60to 165 relative to the inlet axis. The acoustic data were corrected to removeatmospheric attenuation effects in accordance with the SAE ARP 866 procedure(ref. 6). The acoustic tests were conducted in an outdoor facility with a pol
33、ararray of microphones at a radius of 4.57 m away from the primary nozzle exit.Ground effect was not significant for directivity angles greater than 90 inthis test facility because the jets exited vertically upward with respect tothe ground.Models 4 and 5 (figs. 4 and 5) were used in reference 2. Mo
34、del 4 iscoannular and has a centerbody within the primary nozzle. Model 5 is a simplecoannular nozzle with coplanar fan and primary stream exits. The total temper-ature for either stream was again limited to 1100 K or less. The primary jetpressure ratio was fixed at either 1.55 or 1.75, while the fa
35、n pressure ratiovaried from approximately 1.2 to 3.9. The acoustic data obtained with models 4and 5 covered 30 one-third-octave bands, from 50 Hz to 40 kHz, and coverednominal directivity angles in 10 increments from 30 to 160 relative to theinlet axis. The acoustic tests were conducted in an outdoo
36、r facility with apolar array of microphones at a radius of 12.2 m from the nozzle exit referencepoint. The data have been corrected for atmospheric attenuation effects accord-ing to SAE ARP 866 and for ground effects using a method described in refer-ence 2. The published data have also been adjuste
37、d for spherical divergence toshow sound pressure levels at a reference radius of 45.7 m from the nozzle exit.Over 200 flow conditions are included in these static model acoustic measure-ments from references 1 and 2. The flow conditions for models 1 to 5 are sum-marized in tables I to V, respectivel
38、y.Equivalent JetIn replacing the coannular jet with a single equivalent jet, quantitiesto be conserved are mass flow, thrust, and total enthalpy flow. The total basearea of the jet exhaust is also an important consideration in aircraft perfor-mance. However, only three constraints can be imposed for
39、 constructing a sin-gle equivalent jet. Conditions of equal mass flow, thrust, and exit area areoften chosen (refs. 3 and 4). In the present report, the conditions selectedfor constructing the single equivalent jet are equal mass flow, thrust, andtotal enthalpy flow. In most of the jet exhaust flow
40、conditions covered inthis report, the change of total computed nozzle exit area as a result of theconversion is much less than 10 percent. The single jet thus defined is some-times referred to as the fully mixed equivalent jet because, in theory (assum-ing no wall friction losses), it can be obtaine
41、d by actually mixing togetherthe secondary stream and the primary stream by mechanical devices.For a given coannular jet, the condition of mass flow equivalence givesme = m-| + iii2 (1)The conditions of equivalence of mass flow and thrust giveProvided by IHSNot for ResaleNo reproduction or networkin
42、g permitted without license from IHS-,-,-ve = (2)wherem = pAV (3)and the equivalence of mass flow and energy flow givesTe = (4)mewhere the specific heat for constant pressure is assumed to be a constant. Theequivalent jet density is then found by the condition that the jet static pres-sure is equal
43、to the ambient static pressure. The perfect gas law gives= P;-1(5)The equivalent jet exit area is then found fromAe = (6)e eand the diameter is(7)This single equivalent jet and its acoustic properties provide a reference basisfor correlating the overall jet noise power, directivity, and spectral pro
44、per-ties of coannular jets.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Typical acoustic spectral data for each of the five model configurationsare shown in figures 6 to 10. In each case the measured one-third-octave soundpressure levels are shown
45、 at four different angles. The data are shown by sym-bols for easy identification. Predicted sound pressure levels for the corre-sponding single equivalent jets, computed according to the SAE ARP 876 procedure(ref. 7), are shown as continuous curves. The acoustic data shown in figure 6are obtained f
46、rom model 1. It can be seen that the measured data and the pre-diction agree with each other because model 1 is a single circular jet. Theacoustic data in figures 7 to 10 are typical of coannular jets. The measuredsound pressure level is, in general, lower than the predicted equivalent jetsound pres
47、sure level. At large angles from the inlet, the coannular jet noisespectrum exhibits a double hump structure which is quite different from a typi-cal circular jet noise spectrum. Hence, it is clear that the SAE circular jetnoise prediction method is not capable of describing the acoustic propertieso
48、f coannular jets.Analysis of Sound PowerComparison of the noise level of a coannular jet with that of its singleequivalent jet is done on the basis of overall sound power in this report. Thenoise levels can also be compared on the basis of maximum sound pressure level(refs. 3, 4, and 5). Comparison
49、on the basis of maximum sound pressure levelis convenient because the maximum sound pressure level can be obtained directlyfrom the measured data record and can be directly related to perceived noiselevel for full-scale conditions. However, the sound pressure level comparisonis more sensitive to error because its maximum
