This paper is the last part of a series of four papers characterizing the installation effectsof a typical high bypass ratio engine jet using numerical simulations and particle imagevelocimetry. The global objectives are an improved understanding of the link between thejet flows and the generated noise, the validation of methods for computing the aerodynamicfield and the noise sources for industrial configurations, and the assessment of the benefits ofa serrated nozzle when installed under a wing profile. This paper proposes an evaluation ofthe jet acoustics of under-wing nozzles with experimental and numerical tools. Far-field andnear-field noise is measured in the CEPRA19 anechoic facility. Acoustic maps of jet noisesources are obtained using a beamforming technique. Characteristic effects of jet velocityand flight simulation are observed on measured jet noise in the near-field and far-field,and are related to the flow-field analysis. CFD-CAA tools are able to capture the effect offlight on jet mixing noise. The low-frequency source peak is located by beamforming onexperimental data in the region of intense mixing downstream of the nozzle pylon. Thecross-analysis with CFD, PIV data and numerical tools confirms that the pylon plays amajor role in mixing noise signature. The serrations are found to have a peculiar behavior.Joint papers show that the serrations increase the jet potential core length by an orderof 20 per cent. The mixing rate and the turbulent kinetic energy are reduced over alarge region of the jet. The far-field acoustic signature resembles chevron trends with low-frequency reduction and high-frequency lift. CFD, PIV, beamforming and far-field dataare analyzed together and evidence a significant interaction between serrations and pylonleading to noise reduction. Significant aeroacoustic phenomena seem to take place verynear the nozzle at high frequencies, for round and serrated nozzle. Finally, under-winginstallation effects are analyzed with experimental data. Measured jet-wing interactionnoise admits harmonic frequencies that correlate with the flow velocities, but with ratioshigher than the expected turbulence convection velocity. Serrations reduce the intensityof the aeroacoustic interaction. This lower noise is interpreted by the strong reductionof turbulent energy in the mixing layer downstream the pylon. CFD-CAA tools capturesome trends for serrations impact on mixing noise. Future work will involve numerical andexperimental cross-analysis on the high-quality VITAL database to further assess codes forserrations, propagation and installation effects.
∗Engineer, Aeroacoustics Group, Airbus France, AIAA member.†Engineer, Numerical Acoustics Group, Airbus France, AIAA member.‡Engineer, Acoustics Department, Snecma.§Research engineer, DSNA, ONERA.
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Dmix Mixed (or Equivalent) jet diameter (m)JFI Jet-Flap InteractionJWI Jet-Wing InteractionMa Mach number of the flight streamNPR Nozzle Pressure Ratio: total pressure at exhaust over ambient pressureOASPL Overall Sound Pressure Level (dB)OP Operating Point in the test matrixPIV Particle Image VelocimetrySPL Sound Pressure Level (dB)SNR Signal-to-Noise RatioSt Strouhal numberStC Cross-over Strouhal number (for serration effect)TKE Turbulent Kinetic EnergyVmix Mixed jet velocity (m/s)V R Velocity ratio = VS/VPVa Flight stream velocityVP Primary jet exhaust velocityVS Secondary jet exhaust velocityΨ Polar angle relative to inlet axisρmix Mixed jet density (kg.m−3)Θ Azimuthal angle relative to pylon (0deg facing the pylon)~x Source position vector~y Observer position vector~r Acoustic radius vector~ut(x) Turbulent velocity vector~kn Random wave number of mode n~σn Random velocity direction vectorun Amplitude of mode nΨn Random phase of mode nE(k) Von Karman energy spectrumε Dissipation rateke Wave number corresponding to the maximum value of E(k)kη Kolmogorov wave numberL integral length scale(∗)i ith component of vector (*)(∗)ij line i and row j element of tensor (*)Rij correlation tensorRijn correlation tensor related to mode nTij Lighthill tensor
I. Introduction
Jet noise during takeoff remains a major component of total aircraft community noise for state-of-the-artcommercial aircraft. Engines are more likely to be close-coupled with the wing as their size and bypass
ratios increase. This trend might cause an increase of the acoustic interactions between the jet and theairframe, named jet-related installation effects. This prompts us to increase our effort to understand, modeland evaluate jet noise sources, noise propagation as well as jet-airframe interaction sources, in close-coupledconfigurations.
As part of the VITAL European research project (FP6), an extensive aeroacoustic wind tunnel testcampaign was conducted in the ONERA CEPRA19 facility, with the aim of characterising installationeffects of typical VHBR (Very High Bypass Ratio) engines. VITAL is a four-year project aiming to reduceaircraft engine noise and CO2 emissions, lead by Snecma and including 53 partners gathering all major
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European engine manufacturers: Rolls-Royce plc, MTU Aero Engines, Avio, Volvo Aero, Techspace Aero,Rolls-Royce Deutschland and ITP, and the airframer Airbus. The work in this paper has been performedunder SP7 (Installation).
This paper is the fourth part of a series of four papers presenting the installation effects characterisationof a typical high bypass ratio engine using numerical simulations and particle image velocimetry, aiming at abetter understanding of the link between the jet flows and the generated noise, the validation of the methodsfor computing the aerodynamic field and the noise sources for industrial configurations, and the assessmentof the benefits of a serrated nozzle when installed under a wing profile. The first paper by Vuillemin et al.1
presents the facility and set-up of experiments. The second publication by Davy et al.2 shows the meansand results of Particle Image Velocimetry (PIV) performed on the large-scale jet. The third paper by Dezit-ter et al.3 focuses on the RANS CFD methods to capture the subsonic jet behavior at takeoff conditionsand the validation against PIV data. This paper proposes an evaluation of the acoustics tied to differentnozzles installed under wing with experimental and numerical tools. The first section focuses on the set-upof experiments and the validation of data. The second part of the paper presents an analysis of the testresults. Then numerical codes are used to reconstruct noise sources from CFD solutions. A discussion ofresults follows. Each subsection dedicated on a specific effect puts in perspective the present analysis againstpublished material.
II. Experimental Set-up and Data Validation
This section presents the experimental set-up in the CEPRA19 wind-tunnel anechoic test chamber andthe validation of acquired data. The far-field acoustic measurements are introduced first. The second partof the section deals with the measurements made in the near acoustic field using a microphone array.
The data analysis presents characteristic distances and velocities in terms of the equivalent mixed jet toallow a better comparison with existing data. Dmix is the mixed diameter, Vmix is the mixed jet velocityand St is the Strouhal number based on mixed jet velocity and mixed jet diameter. Vmix and Dmix aredefined in SAE ARP876D by:
Vmix = (WP ∗ VP +WS ∗ VS)/(WP +WS), (1)
Dmix =√
(4 ∗ (WP +WS)/(π ∗ ρmix ∗ Vmix) (2)
St = f ∗Dmix/Vmix (3)
where W is the mass flow rate, f the frequency in Hz, and the subscripts P and S are related respectivelyto primary and secondary jet.
A. Far-field Noise Measurements
This part of the paper describes the VITAL SP7 noise experiments. Both aerodynamic and acoustic ex-periments were conducted in the CEPRA19 wind tunnel test chamber, operated by the ONERA GMTdepartment, and located in Saclay (France). The facility and the general experimental set-up are describedin the first series paper by Vuillemin et al.1. The acoustic measurement procedure is shortly recalled hereand illustrated in Figure 1. Two 6 meter-radius arrays of fixed microphones are oriented at normal incidenceon the secondary exhaust center of the nozzle. Each array is composed of 12 microphones located every 10between 40 upstream to 150 downstream with respect to the nozzle axis at inlet. These arrays of microphonesare located in the flyover plane below the pylon model (Θ = 180deg in the azimuthal arc), and in the sidelineplane (124deg in the azimuthal arc), outside the wind tunnel flow to avoid spurious noise. The spectraldensities are averaged on 300 blocks with a block size of 4096 time samples averages at a sampling frequencyof 204 kHz. Narrowband data with a bin spacing of 50Hz were acquired and synthetized to produce one-thirdoctave spectra, up to a center band frequency of 80 kHz. Measured data are monitored and corrections areapplied on the raw test data for ambient pressure, microphones calibration, background noise, free-jet shearlayer refraction, and atmospheric absorption.
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Figure 1. Far-field acoustic measurements sketch. The sketch also includes the positions of the linear near-fieldantenna.
Nine configurations and four nozzle operating conditions are tested with parametric changes to assessthe different acoustic effects and trends:- Jet power effects: 4 operating conditions,- Flight effects: static case (M = 0 ideally) and M = 0.27- Serrations effects: baseline nozzle, and serrated core and fan nozzle- Installation effects: presence of the airfoil, 2 pylon sizes and 2 flap settings (0deg and 30deg). Figure 2shows views of the round baseline model and the serrated model.
180 degFlyover arc
124 degSideline arc
0 deg
45 deg
(a) Baseline nozzle with pylon simulator (b) Serrated nozzle with pylon in rigging process
Figure 2. HBPR dual-stream nozzles in isolated configuration, looking upstream at the trailing edges of thenozzle. The main values for the azimuthal angle Θ used in this paper are shown in blue boxes.
Figure 3 features pictures of two installed baseline configurations, with the short pylon and with the longpylon. Table 4 present the acoustic test matrix for the nozzle operating conditions achieved in CEPRA19.
The quality of the noise measurements is presented. Whereas the validation of the flow fields is thoroughly
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(a) Baseline installed with short pylon 2 (b) Baseline installed with long pylon 1
Figure 3. Baseline HBPR dual-stream nozzle installed under the wing profile with each of the two pylons
Conditions Cutback (CB) Additional Point1 (Add1) Sideline (SL) High power (HP)
P 1.17 1.32 1.24 1.33S 1.42 1.48 1.50 1.64P K 757 799 799 862S K 331 335 337 346
Vp m/s 256 350 308 370Vs m/s 251 267 273 303
Velocity Ratio Vp/Vs 0.98 0.76 0.88 0.82Mixed Velocity Vm m/s 251 276 276 310
Mixed Temperature Tm K 289 284 288 290Flight Stream Velocity m/s 0, 60, 90 0, 60, 90 0, 60, 90 0, 60, 90
conducted in the joint papers2,3, the validation of the noise measured on the polar arcs in the chamber isdone in this paper. The wind tunnel background noise and repeatability are verified. Figure 5 presents thesignal-to-noise ratio obtained with the lowest jet operating power at two polar angles. The narrowband levelsare presented at each angle for 3 configurations: the isolated nozzle and the installed nozzle with the two flapdeflections, and 2 operating conditions: a nozzle flow matched with the Mach 0.27 flight stream (solid lines),and the Cutback jet operating point with same flight simulation (dash lines). The SNR obtained was verysatisfactory except for the flap deflection at 30 degrees. An anemometer placed on purpose in the chamberindicated a strong recirculation, which led to the hypothesis of a deflection of the flight stream outside therange of the collector at the downstream end of the sphere. The flight velocity was reduced to Mach 0.18to allow valid jet noise measurements with flight stream on and the wing profile in the worst case scenario(flap deployed at 30deg). A reasonable SNR was then achieved. The test points were therefore achievedwith flight simulation at both Mach 0.27 and Mach 0.18 to allow good SNR and cross-comparisons.
The measurements of isolated nozzle builds display classical spectral shapes and directivities for jet noise.Figure 6 presents the OASPL directivity of the measured noise for the baseline nozzle in static condition,at the four operating regimes. The associated measured SPL spectra at the downstream observation angleφ = 133.6deg are also presented. A classical increase of OASPL with polar angle is noted. The sidelinearc lateral to the pylon measures slightly more energy than the flyover arc. This is also typical of nozzlesequipped with pylon simulators, and interpreted as a pylon effect being a reflective and diffractive surface,as well as creating additional mixing in its wake. The SPL spectra are of broadband content and respondto classical jet noise spectral shapes shown by Viswanathan4.
The test of large-size nozzles and wing in open-section anechoic facility has important implications. Thepresented test campaign is a powerful demonstration at different levels. The most striking example is thedeflection of the flight stream and the jet by the lifting wing profile. This deflection is shown by CFD andPIV measurements, see Dezitter et al.3. When the air streams hit the collector, recirculation in the anechoicchamber is likely and the SNR may be severely impacted, as shown in Figure 5. The far-field hypothesis ofthe measurements is assessed. The far-field microphones are located at an average distance of 6m from the
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Figure 5. Measured narrowband spectra for isolated and installed nozzle builds without and with defleectedflaps, at two polar angles. Ma = 0.27. Solid line: Background noise with matched jet. Dashed lines: lowestCutback operating condition.
fan nozzle exit plane as seen in Figure 1. This represents a measurement distance of 23 fan nozzle diameters,or 35 equivalent jet diameters. Viswanathan5 assessed that a minimum distance of 35 nozzle diameterswould be adequate to ensure true far-field measurements on a single-stream jet. Whether the 35 Dmix
distance pertains for coaxial jets with the equivalent jet diameter has not been demonstrated. The VITALmeasurements probably lie at the limit of the true far field. Thanks to the reasonable 35 Dmix distance,the impact of potential near-field effects on EPNL evaluations is expected to be minimal. The fine detailsof the models are also crucial for the data quality. The thickness of the trailing edges of the serrated corenozzle impacted the noise measurements. Figure 7 displays narrowband SPL measurements in the far-fieldat φ = 79.6deg. Broadband humps are evidenced between 60kHz and 90kHz on the serrated nozzle dataonly. Humps peak frequencies increase with increasing polar angle, vary with nozzle operating conditions,but are independent from flight stream condition and nozzle installation under wing. Frequencies correlatewell with the primary jet mean velocity with a ratio of St = 0.17 based on the measured trailing-edgethicknesses: 0.33mm for the baseline nozzle, 0.41mm for the fan serrations, and 0.70 for the core serrations.The core serrations turned out to lie about in the domain indicated by Henderson et al.6. Within thisdomain, trailing-edge noise is potentially generated. This extraneous nozzle trailing-edge noise is identifiedin test data for the serrated nozzle, is attributed to the core lip, and can therefore be accounted for in theanalysis of the serrations effects. Another tonal hump is identified with the serrated nozzle only in isolatedbuild. The peak frequency matches with fan velocity, but not with trailing-edge thicknesses. This suggeststhat the extraneous noise might be due to aerodynamic noise in the fan duct, perhaps due to rigging of thecowls as it disappeared on installed builds.
B. Near-field Noise Measurements
The geometry of the new antenna designed for this test is a linear array instrumented with 43 BK microphones1/4in. The arrangement of the microphones is shown in Figure 8. Four sub-arrays with spacing respectivelyequal to 2.5cm, 5cm, 10cm and 20cm, are designed in order to cover at best the Strouhal number range0.2 - 8.0 Hz relevant to jet mixing noise physics and evaluation for commercial aircraft community noise7.The antenna is about 15 Dmix long and is located facing the jet at a radial distance of 15 Dmix fromthe jet center axis. Two positions of the antenna were investigated. The first position corresponds to the
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Figure 6. Measured SPL at φ = 133.6deg and OASPL directivities versus φ polar angle, for the 4 operatingpoints in static condition. Isolated baseline nozzle.
microphone 1 located in the secondary exhaust plane. The second position corresponds to a translation ofthe whole antenna by 8.5 Dmix downstream. Both positions are illustrated in Figure 1. The near-field datawas acquired during the NACRE test campaign performed in synergy with the VITAL test campaign bothat the CEPRA19 facility. The objective of this instrumentation was to determine the main source locationversus frequency for the isolated jet noise, in order to be taken into account in the numerical simulationperformed by NACRE for the prediction of installation effects.
Up to now, beamforming remains the most robust and established method for jet noise source localisation.As demonstrated in8, the method based on distribution of uncorrelated monopoles applied to jet noise couldlead to strong bias in the results. Advanced methods able to take into account strong source directivities areunder development9,10. This is the rationale for using beamforming within the NACRE projet. This methoddoes not provide access to reconstructed noise spectra but is able to provide valuable sources positions iftheir directivity in the antenna aperture remains ”reasonable”. The assumptions of beamforming implieslimitations for the results analysis, and are recalled now before presenting the results. As already noted, thesource directivity is not taken into account and the sources positions calculated could be affected if serratednozzle strongly modifies the noise sources characteristics. Another cause of bias on the source location is theposition of the focusing axis. The localisation is done on an axis, but the near-field measurements should beinterpreted as the total noise radiated by the axial slice of the jet. Depending on the frequency, the sourcescould be circumferentially distributed in the core/bypass shear layer and in the bypass/flightstream shearlayer. Depending on the observation angle, a slight shift of the true sources position could be induced byparallax effect. This parallax effect is shown in Figure 9. The location of the noise sources is defined asthe point of maximum coherence for a given frequency on the axis where the monopoles are placed a priori.Two axes of focus are set: Y = 0m is on the jet centerline, and Y = -0.133m corresponding to the bypassexhaust radius. With the upstream antenna position, both analyses lead to the same position. There isminimal parallax effect because the antenna faces the sources. The downstream antenna position X = 1.5mhas its first microphone at an axial distance 8.5 Dmix from the nozzle. The antenna is no longer facing themain sources, and a parallax effect is clealy identified when the focus axis is changed. Then, Y = 0m leadsto unrealistic high-frequency source locations upstream of the nozzle exhaust plane. Y = -0.133m improves
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Spectra at φ = 78°
Baseline nozzle Serrated nozzle
M=0.27
Jet Power effect
Tone noise with serrated nozzle only in isolated configuration
Cutback
Additional 1Sideline High power
10
dB
10
dB
Trailing-edge noise due to thickness of serrated fan nozzle model lips
200 40 60 80 200 40 60 80
St St
Figure 7. Narrowband SPL measured at φ = 79.6deg at 4 operating points with flight simulation, for theisolated baseline nozzle (left) and serrated nozzle (right).
Figure 8. Arrangement of the microphones on the linear antenna used for near-field measurements.
the representation of the source location. For the rest of the analysis, the upstream position X = 0m ofthe antenna is used for it introduces minimal parallax effect. As it is well known, the spatial resolution ofbeamforming is proportional to the inverse of the frequency. So in low frequency, the resolution is very poor.Nevertheless, we can determine the position of the peak source and we can also notice general trends ofthe localisation maps in Figure 9: at low frequency, mixing noise is located about four mixed jet diametersdownstream of the secondary exhaust nozzle. The sources location shifts rapidly near the exhaust positionat Strouhal numbers around 1.
0.1
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ix/V
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ix/V
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Yfoc = 0 mmYfoc = -133 mm
(a) Upstream X = 0m antenna position (b) Downstream X = 1.5m antenna position
Figure 9. Influence of the focalisation axis on the location of the exhaust sources
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The last main cause of uncertainty is the convection and refraction effects due to the two coaxial streamsof the jet. In this work, we only consider the convection and refraction induced by the flight stream.Obviously the ray paths are modified during the propagation in the sheared jet streams and mixing layers.This propagation is not accounted for in the beamforming procedure.
III. Analysis of Test Results
This part of the paper analyses the acoustic experimental data in light of the results from aerodynamicstudies performed by Davy et al.2 and Dezitter et al.3. Far-field noise measurements are presented jointlywith beamforming results. The first section presents the effects of nozzle conditions are shown. In a secondpart, the flight stream effect is analyzed. The third part focuses on serrations effect on jet mixing noise. Thelast subsection deals with the installation effects related to the nozzle flow.
A. Effect of Nozzle Operating Condition
This subsection presents the influence of the jet power on measured far-field noise and the peak sourceslocation.
Figure 6 already presents the effect of nozzle operating conditions on OASPL directivities and measuredSPL spectra, at the downstream observation angle φ = 133.6deg. The maximum acoustic energy radiated bythe jet increases from Cutback to Sideline, then Add1 and is highest at High Power. The differences in theinitial conditions are small between Sideline and Add1, Vmix remains equal and Tmix only increases by 4degKelvin, while one notes a slight increase of noise on the low-Strouhal peak. The SAE ARP876D model forcoaxial noise based on Lu11 performs predictions at both OP conditions. The predicted delta noise betweenthe two operating points confirms the experimental trend between Sideline and Add1.
The near-field data were acquired at three operating points Cutback, Sideline and High power. Figure 10shows that the sources positions are shifted downstream when the jet power increases. The sharp transitionregion between downstream sources and exhaust sources is also shifted to higher frequency. The rapidtransition and the trends versus jet velocity are qualitatively very close to data presented by Lee andBridges12 at small scale, and by Brusniak13 on jet noise at full scale. From Figure 10, the influence of thejet power condition is the same in the static case and in the flight cases. The trend is also the same whetherthe nozzle is round or serrated. However large differences in source location appear between the baselinenozzle at the High Power condition seen on Figure 10 (a) and (b), and the other test points. The maximumcoherence for sources at St [1 - 6] is located at [2.5 - 4] Dmix, instead of [0 - 2] Dmix for all the other cases.The shear between the hot primary jet and secondary jet increases from Cutback (VR = 0.98) to Sideline(VR = 0.88) and to High Power (VR = 0.82). At High Power, the source related to the inner mixing layerbetween core flow and fan flow may become measurable and explain changes in beamforming results. Thiscase appears a good candidate for future research with CFD and source models.
The noise peak locations at St around 0.3 are located by beamforming upstream of the expected low-frequency dynamics. For the isolated baseline nozzle at Sideline and Ma = 0.0, Dezitter et al.3 have locatedthat axial mean velocity decays at about 11 Dmix and TKE reaches its maximum value on the jet centerlinearound 13 Dmix. The beamforming shows peak locations at the same test point between [5 - 6] Dmix. PIVand CFD indicate that the region [4 - 6] Dmix is where the maximum value of TKE is located in the wake ofthe pylon (see Figure 18). Davy presents a telling Figure 15 in 2 where TKE values are plotted on three lines;the TKE peak in the outer mixing layer downstream of the pylon is much higher by a factor of 2 and locatedmore upstream than the TKE peak in the outer mixing layer opposite to the pylon, and in turn higher andmore upstream than the TKE peak on the jet centerline. It is possible that the near-field antenna captures astrong acoustic contribution of the mixing behind the pylon at low [0.3 - 0.6] Strouhal numbers. The lineararray was looking to the pylon at an angle of 45deg and could measure this energy without masking by thehot jet. We will consider this zone further in the analysis of serrations in Section C.
B. Effect of Flight Simulation
This paragraph presents the influence of flight simulation around the nozzle on far-field spectra and the peaksources location. Figure 11 displays spectra measured with and without flight simulation at Ma = 0.27 atthe polar angles 90deg and 140deg on the far-field flyover arc, for the baseline and serrated nozzles. Thespectral shape for each angle of observation is characteristic of subsonic jet noise. The energy is maximum
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ix/V
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(a) Baseline nozzle - static case (b) Baseline nozzle - Ma 0.18 case
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ix/V
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Cutback - 2237Sideline - 2238High Power - 2241
(c) Serrated nozzle - static case (d) Serrated nozzle - Ma 0.18 case
Figure 10. Location of the jet noise sources by beamforming on the jet axis, versus axial distance from fannozzle exhaust plane and jet Strouhal number. Baseline and serrated nozzle. Three operating conditions atstatic and flight case.
at St = 0.3 at aft angles, and peaks at St = 0.7 in the perpendicular direction. These values are comparableto findings in previous studies, for example14. When wind is turned on, the reduced shear lowers the SPLby an order of 4 dB at 90deg, and by up to 7 dB on the peak of noise at 140deg. It can be noted that atSt = 10, static SPL are equivalent between 90deg and 140deg, and yet flight simulation is more efficent atreducing aft radiating noise.
VITAL far-field 1-TOB SPL vs St for High Power - measured at 90deg
0.1 1 10 100St
SPL
dB
Baseline - Static
Serrated - Static
Baseline - Flight
Serrated - Flight
VITAL far-field 1-TOB SPL vs St for High Power - measured at 140deg
0.1 1 10 100St
SPL
dB
Baseline - Static
Serrated - Static
Baseline - Flight
Serrated - Flight
(a) SPL measured at 90deg (b) SPL measured at 140deg
Figure 11. Measured one-third-octave band SPL versus Strouhal number for baseline nozzle (clean lines) andserrated nozzle (dotted lines). Static condition (continuous lines) and flight stream Ma = 0.27 (dash lines).OP High Power.
Figure 12 shows the peak sources locations without and with flight simulation at two Mach numbers, Ma
= 0.18 and Ma = 0.27. The sources positions are shifted downstream when the flight Mach number increasesat constant nozzle operating condition. The most dramatic effect is on the sources at frequencies above St =2. These sources have a maximum coherence located very close to the nozzle exit plane in static condition.
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Figure 11 points that the acoustic far-field energy is still significant at St near 2 despite the high-frequencyroll-off. Important noise generation seems to occur in the vicinity of the nozzle in static condition. Thesource location is shifted by almost 1 Dmix when flight stream is turned on. The Strouhal number at whichthe sharp transition region occurs between ”downstream sources” and ”exhaust sources” seen on the serratednozzle at the High Power operating point, is not modified by the flight stream.
0.1
1.0
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100.0
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f.Dm
ix/V
mix
M = 0 - 2219M = 0.18 - 2217M = 0.27 - 2218
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f.Dm
ix/V
mix
M = 0 - 2240M = 0.18 - 2241M = 0.27 - 2242
(a) Baseline nozzle (b) Serrated nozzle
Figure 12. Location of the jet noise sources by beamforming on the jet axis, versus axial distance fromfan nozzle exhaust plane and jet Strouhal number. Baseline and serrated nozzle. Three entrainment Machnumbers for the High-Power nozzle operating point.
C. Effect of Serrations
The reader will refer to the publication by Dezitter et al.3 for a bibliographic review of the effects of chevronson jet mixing and aeroacoustics.
Far-field noise Figure 11 illustrates the effect of serrations on far-field measurements. The reduction ofthe low-frequency part of noise spectra occurs up to StC = 10 in static and StC = 5 in flight. Above thiscross-over Strouhal number, SPL are increased. VITAL far-field noise measurements show that the noisereduction by the serrations is larger in the sideline arc than in the flyover arc. Measurements performed inthe NACRE jet noise test campaign are used to continue the analysis at a more radical azimuth. NACREfar-field data are measured at azimuthal angles Θ = 0deg and Θ = 45deg, whilst VITAL data is taken inthe Flyover arc at Θ = 180deg opposite to the pylon and in the Sideline arc at Θ = 124deg as illustratedin Figure 2. Figure 13 presents dB SPL delta [Serrated - Baseline] at Sideline OP and static condition attwo azimuthal angles Θ = 45deg and Θ = 180deg. The delta obtained with serrations on the jet noise peakat St = 0.7 is near 3 dB SPL at Θ = 45deg, while only 1 dB at Θ = 180deg. This significant differencebetween the two Θ values indicates that serrations have an asymmetric action on radiated noise. Serrationsare therefore increasingly efficient in the region St [0.6 - 4] when the far-field observer turns around the jetfrom the flyover position toward facing the pylon. As it will be shown further in Figure 16, serrations reduceTKE levels by a large extent aft of the pylon.
Continuing with observations in the acoustic far-field, Figure 11 reveals that turning on the flight streamhas a detrimental effect for the low-frequency gain (decrease) and high-frequency penalty (increase) of theserrations. The cross-over Strouhal number StC tends to decrease when the flight steam velocity increases.In the flight case, the serrations act on a lower shear and appear less efficient. Low-noise device efficiencyshall be evaluated with flight stream simulation for a proper estimate of the benefits on aircraft.
Near-field noise Max coherence plots and coherence maps are used to study the effects of serrations withnear-field data. Figure 14 presents the maximum coherence level location on the jet axis for the baseline andserrated nozzles at two nozzle operating conditions and two entrainment Mach numbers. Figure 15 presentsthe complete coherence level map versus the axial distance on the jet axis and the jet Strouhal number, forthe case (a) in Figure 14. For all test points, the peak locations in the high-frequency range St ≥ 4 arenot influenced by the corrugations and remain very close to the exhaust nozzle. The flight stream movesthe peak location 0.5 Dmix downstream. Their coherence is however higher with the serrations comparedto the baseline jet as shown in Figure 15. This is interesting to confront with recent observations at St [5
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B)
VITAL NACRE
Figure 13. Delta SPL dB between baseline and serrations measured at polar angle Φ = 120deg and twoazimuthal angles : Flyover plane (VITAL) and Θ = 45deg (NACRE) facing 45deg to the pylon. Sideline OP.Flight stream Ma = 0.05. A positive delta means noise reduction
- 10] by Kerherve et al.15 on important near-nozzle coherent dynamics in the generation of propagatingpressure fluctuations. In a large intermediate-frequency range at St [0.6− 4], the peak sources locations areshifted upstream with the corrugated nozzle. Sources in this St range undergo a drastic change at the HighPower OP in Figure 14 (c), with peak source locations moved upstream by 2 Dmix. At very low frequenciesSt ≤ 0.6, a consistent trend is difficult to capture. In flight, the serations tend to move the peak sourceupstream by about 0.5 Dmix. In static, the peak source with the serrated nozzle is located slightly moredownstream than for the baseline jet. This static observation is in agreement with a study presented onengine static test with chevron nozzles by Nesbitt16. We are aware that if the serrations change radicallythe directivity of the jet noise sources, this could introduce a bias on the source location. The classicalbeamforming method is however chosen here for its robustness.
Beamforming processing of near-field acoustic data is a useful tool to investigate the effects of serrations.In future works, new methods based on more complex modelling should be investigated in order to determinewith higher accuracy the position, and also in order to provide the amplitude of the source distribution inthe jet. Bulte and Fleury are attempting such work on the same subsonic jet case in 9,10. Also note Michelet al.17 on aeroengine data.
The cross-analysis of aerodynamic and acoustic data is further carried out on the serrations. Figure 16shows a cross-section cuts of CFD solution from Airbus displaying TKE for the baseline nozzle and serratednozzle. The TKE plots confirm that mixing is very intense in the wake of the pylon, and serrations reducethe max TKE value. Figure 17 shows the same cross-section cuts of CFD solution from Airbus with vorticity.The vorticity field for the baseline jet indicates that the pylon modifies the development of the primary jetand large structures develop early in the pylon wake. The serrations reduce the magnitude of the vorticitydownstream of the pylon. Core serrations manage to kill the primary jet mixing structures initially formedby the pylon by creating small jetlets. Overall, the upper part of the jet between [3 - 6] Dmix sees theinfluence of the pylon on mixing between the secondary jet and the ambient air, and the merging of the innerprimary-secondary mixing layer with the outer mixing layer.
Figure 18 provides additional evidence of the intense mixing in the upper part of the jet downstream ofthe pylon. It displays the TKE from PIV data in the symmetry plane of the pylon for four cases: a near-staticcase where Ma = 0.1, a flight case with Ma = 0.27, baseline and serrations. The rationale for the choiceof the cut plane is explaned by Dezitter3. In the static case, serrations shift the max TKE location moredownstream by about 2 Dmix. In the flight case, serrations do not change the location of the max TKE. Themax TKE location follows the same trend as the location of noise sources at St [0.2− 1] in Figure 12 andFigure 14. Serrations shift the low-frequency sources location downstream in the static case, and upstreamin the flight case. Conversely, turning the flight stream on moves the sources upstream in the serrated case,and has virtually no effect on low-frequency source location in the baseline case.
Note that in both static and flight cases, the PIV and CFD data shows that the serrations extend the
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0.1
1.0
10.0
100.0
-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
X/Dmix
f.Dm
ix/V
mix
Baseline - 2215 Low noise - 2239
0.1
1.0
10.0
100.0
-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
X/Dmix
f.Dm
ix/V
mix
Baseline - 2216 Low noise - 2238
(a) OP Sideline - Ma=0.0 (b) OP Sideline - Ma=0.18
0.1
1.0
10.0
100.0
-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
X/Dmix
f.Dm
ix/V
mix
Baseline - 2219 Low noise - 2240
0.1
1.0
10.0
100.0
-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
X/Dmix
f.Dm
ix/V
mix
Baseline - 2218 Low noise - 2242
(c) OP High power - Ma = 0.0 (d) OP High power - Ma = 0.27
Figure 14. Effect of the serrations on the peak sources location. Two Nozzle Operating Points. Static andflight simulation at two velocities Ma 0.18 and Ma 0.27.
jet potential core and mixing regions further downstream. The noise reduction of these serrations cannot beinterpreted by a shorter potential core and reduced volume of sources as in observations on chevron nozzlesby Callender18. Despite the global lengthening effect on aerodynamics, the serrations appear to move noisesources locations for St ≥ 0.6 upstream, from Figure 14 and Figure 15. Another interpretation could bethat serrations kill noise sources downstream of the pylon and exhance high-frequency noise radiation in thenear-nozzle region. This could make the maximum acoustic coherence appear at upstream locations.
On the baseline jet, beamforming locates energetic low St [0.2 - 0.6] noise sources in the region [5 - 7]Dmix where the mixing is most intense. The energetic and organized mixing structures behind the pylonappear to play a role in the generation of propagative energy, perhaps by coupling with the jet structure andradiating low-frequency noise.
On the corrugation effect, Figure 16 points that serrations are able to reduce significantly the mixingintensity in the secondary-ambient shear layer. Furthermore, serrations kill the large structures involved inthe interaction between the primary-secondary and the secondary-ambient mixing layers. Far-field measure-ments azimuthally distributed around the jet have shown that serrations bring a increasingly large noisereduction when observers move on the azimuth from the flyover position to facing the pylon, over a largeSt range [0.6 - 4]. Beamforming shows a dramatic effect of serrations on peak noise sources in the same Strange at the High Power OP. This analysis indicates that the interaction between serrations and pylon maybe significant for both jet mixing behavior and radiated noise.
D. Installation Effects
The acoustic installation effects of the nozzle under the wing profile are presented in this part. Theseinstallation effects are defined as the modification of the noise generation and propagation in the wholepropulsive jet system due to the installation of the nozzle under the wing. These effects can be of differentnature: modification of mixing jet noise sources, generation of new sources like jet-wing interaction (JWI)and jet-flap interaction (JFI), and perturbation of the acoustic propagation by reflection, diffraction andrefraction. On the one hand, the jet mixing noise and the propagation effects may be studied by analyticaland numerical means. On the other hand, few models describe the jet-wing and jet-flap interaction noise
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(a) Baseline nozzle (b) Serrated nozzle
Figure 15. Coherence map as a function of distance on the jet axis, and jet Strouhal number, for the baselinenozzle and the serrated nozzle. OP Sideline - Ma = 0.05. The two vertical black lines point the bypass andcore exhaust planes location.
1
TKE
Baseline
Serrated
1.5Dmix 3.6Dmix 5.7Dmix
Figure 16. Cross-section cuts of CFD solution at Airbus with TKE (colorplots) and streamlines (black lines onright-hand side) for the baseline nozzle and serrated nozzle. Sideline OP. Flight stream Ma = 0.27. Three cutscorrespond to three axial distances from the fan exhaust plane: 1.5, 3.6, 5.7 Dmix. Colorcode shows increasingvalues from blue to red.
sources yet. For this reason, our experimental analysis will focus on characterizing the behaviour of the JWIand JFI phenomena by using parametric changes between experimental configurations, the analysis of flowfield from CFD data.
1. Introduction
Many mechanisms of sound generation have been cited to describe the aeroacoustic jet-wing interaction.As quoted by Mengle et al.19, jet-flap interaction noise has been studied quite well in the literature and
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2
Vorticity
Baseline
Serrated
1.5Dmix 3.6Dmix 5.7Dmix
Figure 17. Cross-section cuts of CFD solution at Airbus with Vorticity (colorplots) and streamlines (blacklines on right-hand side) for the baseline nozzle and serrated nozzle. Sideline OP. Flight stream Ma = 0.27.Three cuts correspond to three axial distances from the fan exhaust plane: 1.5, 3.6, 5.7 Dmix. Colorcode showsincreasing values from blue to red.
1
TKE
SR
BS
SR
BS
Max TKE / Same Location
Max TKE / Location shifted downstream
Ma = 0.27
Ma = 0.10
Figure 18. TKE plots from PIV data in the plane of the pylon for Baseline (BS) and Serrations (SR). Near-static case Ma = 0.1, and flight case Ma = 0.27. Colorcode shows increasing values from blue to red.
several original references can be found in Fink’s review20 on Propulsive Lift Noise. For under the wingconfigurations, Fink lists three mechanisms (see Figure 8 in20): (i) Lift fluctuation noise, (ii) Trailing edgenoise, and (iii) Quadrupole noise from deflected jet (also known as impact noise). The common feature inall of them is that they radiate noise predominantly in the front quadrant due to the deflection of the flapindependent of the type of singularity (dipole, quadrupole, etc.) representing the noise source. When theflaps are not completely immersed in the jet stream as it is the case in the VITAL experiment, the JFI noisecan only be considered as a weak form of propulsive lift noise. The two most dominant mechanisms givingrise to JWI noise may be the diffraction of the hydrodynamic near field of the jet by the trailing edge ofthe wing, as described in21, and the fluctuating lift on the wing as described in22. Both mechanisms are
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associated with convection of turbulence in the jet shear layer past the wing, and neither requires the jet toactually impinge on it. The balance between the two sources is complex, and they are difficult to separateas they are expected to be of similar frequency, since both may depend on the turbulence passing-rate. Theintensity of the diffraction source evolves with the fifth power of the jet velocity, while the intensity of the liftfluctuation source varies with the sixth power. As jet velocity increases, the lift fluctuation noise is expectedto become more dominant. It should also be noted at this point that, because jet noise has an approximateeighth power dependence on jet velocity23, the overall significance of jet-wing interaction noise will reduceas jet velocity increases. This trend has been observed in the VITAL data. In terms of frequency scaling,Sengupta24 suggests that the peak frequency of the jet-wing interaction noise for a static aircraft should begiven by:
f = 0.8 ∗ VS/L (4)
where VS is the secondary jet mean exhaust velocity, and L is the wing chord length. This frequency isessentially the inverse of the time taken for each eddy to pass the wing. The velocity 0.8 ∗ VS can beinterpreted as the convection velocity of the turbulent structures in the outer mixing layer of a jet withoutentrainment. Now with flight simulation, the correction speed in the external shear layer may be expressed asVa + 0.8 ∗ (VS − Va). Recently, Tinney and Jordan25 identified the convection speed of the near-field energyof a coaxial jet at 0.6 (VP + VS) /2. The present investigation means to extract the main characteristicsof JWI and JFI noise, analyze the correlation of its amplitudes and peak frequencies with the installationparameters and the different formulations of convection velocities corresponding to test conditions. We willalso describe the impact of the nozzle lip treatment on JWI and JFI noise.
2. Jet Wing Interaction Noise
The SPL of the JWI source is computed by pressure delta between the installed and isolated configuration.The assumption is that this source is the major cause for the increase of noise in the forward arc, overreflection for instance. It is also most intense at low frequencies, which in turn dominate the source OASPL.JFI noise is defined as the additional component purely due to flap deflection. The OASPL of the JFI sourceis therefore computed by pressure delta between the installed build with flaps deployed and installed build withclean wing. JWI noise is studied at the flight stream Ma = 0.27. For reasons of SNR described in Section A,JFI noise is investigated at the flight stream velocity Ma = 0.18. The velocity dependence of source OASPLis studied with the exponent m defined in the following expression OASPLsource = 10 ·m · log10(V ), with Vthe flow velocity most relevant to the studied interaction noise source.
Figure 19 displays SPL spectra for the isolated baseline nozzle and the corresponding installed build withpylon 2 and clean wing. The JWI noise extracted from measurements also appear on the graph as log delta.The peak observed at the lowest Strouhal number St = 0.35 also has the highest dB amplitude. This appearsto be the fundamental harmonic of the JWI. It is noteworthy to mention that the following three harmonicsare clearly seen and indicated in Figure 19 by the orange arrows. The peak Strouhal numbers correspond toexact multiples of 0.35: 0.70, 1.05 and 1.40. The green arrow points to another peak seemingly due to JWIaround St = 0.6 therefore outside the scope of the harmonics. This peak around St = 0.6 was seen for otherconfigurations and at other angles. We note the lesser significance of the St = 0.6 peak in terms of energy,relatively to the other orange JWI peaks identified.
The peak frequencies of the JWI are successfully correlated with the eddy-passing frequency under theclean wing. However, the frequencies measured fit the Sengupta frequencies calculated with a convective ratioof 1.0 instead of a more usual 0.7 to 0.8 ratio. This surprising ratio will be discussed further in Sub-section 3dedicated to JFI noise.
The JWI source OASPL correlate well with the relative mixed jet velocity Vrel = Vmix - Va, and exhibita dependence with exponent m between 4.5 and 5. The exponent is lower for static conditions than in flightby about 1. This indicates that the balance between mechanisms responsible for the noise generation instatic and in flight may differ. The increase of the exponent when the flight stream is turned on might inferthat lift fluctuation mechanisms characterized in the literature by a higher exponent of 6 come into playwhen the flight stream is on. Diffraction of the jet near-field pressure may dominate at static condition.
3. Jet Flap Interaction Noise
This sub-section examines the characteristics of measured JFI noise. The noise increase caused by JFInoise is seen preferentially in the forward arc. The source is most intense at polar angles around 40deg to
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Narrowband SPL dB for isolated and installed baseline builds47deg polar angle - Flyover arc
0.1 1 10 100St
SPL
dB
Isolated nozzle
Installed nozzle
log delta
5dB
Figure 19. Narrowband SPL dB for isolated and installed baseline builds. Ψ = 47deg, Flyover arc. OP Sideline,Ma = 0.27.
60deg. Figure 20 presents the evolution of the JFI spectra and dB delta with polar angle for the baselinenozzle. The JFI source radiates clearly preferentially at forward angles. The arrows mark the peaks thatare assumed to be harmonics seen at St 0.25, 0.50, 0.75 and 1.0. The fundamental JFI frequency fits wellwith the Sengupta relation when taking into account a convection ratio of 1.0 and the full chord of the wingwith the deployed flaps. It is difficult to identify whether the flap itself responds independently by properfrequencies because the eddy-passing frequency under the flap is estimated at St = 1 for the condition ofFigure 20, which is itself a harmonic of the eddy-passing frequency under the full wing with deployed flaps.The fundamental frequency found in this analysis indicates that the characteristic noise frequencies relateto the overall average chord. The wing with deployed flaps interacts acoustically with the jet as a singleobject. The convection ratio of 1.0 is coherent with the behaviour of JWI. However this ratio can hardlybe explained by physics of convected turbulence. The convection speed of the structures depends on theirsize and the radial position in the shear layer. The convection velocity ratio of large-scale structures is oftenfound experimentally around 0.65. The measured JWI peak frequencies do not match the evolution of theconvection velocity found by Tinney et al.25.
Narrowband SPL dB JFI SOURCE (Flaps-Deployed - Clean builds)Baseline nozzle - Flyover arc - at various fwd polar angles
0.1 1 10Strouhal number
SPL
dB 47.8
53.9
61.4
69.4
78.1
87.5
5 dB
Figure 20. Narrowband SPL dB for JFI noise for the baseline nozzle at different forward Ψ polar angles.Flyover arc Θ = 180deg, OP Sideline, Ma = 0.18.
The JFI noise intensity is higher at flyover arc than at the sideline direction. This higher level at flyoveris observed for both baseline and serrated nozzles. This may be explained by the directivity of the interactionnoise source, documented as dipole-type in26. The dipole is oriented perpendicular to the flap chord plane.Logically, the intensity of the noise radiated directly below the flap is higher than at the lateral angles. The
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most energetic wavelengths of JWI noise are much larger than the primary hot jet diameter. For this reasonwe may suppose that the hot jet blockage may not affect the JWI and JFI.
The velocity dependence is investigated now similarly to the JWI. The best fit between the four operatingpoints is found with the relative velocity Vmix - Va. The relative velocity exponent is found around 6. Thisis coherent with the lift-fluctuation mechanism, chosen by Mengle et al.19 to model the JFI noise source.According to Mengle, the lift fluctuations on the flaps are then diffracted by the wing trailing edge. Thiscould explain why we observe a higher dispersion for the JFI velocity exponent with observation angles thanfor JWI.
4. Effect of Serrations on Jet Interaction Noise
Figure 21 presents the effects of serrations on the JFI noise source extracted from measurements. NarrowbandSPL dB are charted versus St, for the baseline case and serrated nozzle at Sideline OP and Ma = 0.18. Theequivalent jet mixing noise from the isolated baseline nozzle is also represented for comparison of SPLamplitude. The difference between baseline and serrated cases is unambiguous. The serrations reduce theamplitude of all JFI peaks. Peak frequencies might be slightly modified. The noise reduction is verified assystematic; at both flyover and sideline, and all forward polar angles. The comparison with the isolatedjet noise points that the global jet-surface interaction noise can reach amplitudes 20 dB above the peak ofpure jet noise energy at forward angles. In this experimental case the flap trailing edge is located in thegeometrical plane of the fan nozzle trailing edge, therefore it is expected very close to the mixing layer. CFDstudies within VITAL predict that the jet is deflected by the wing and there is no jet impingement onto theflap.
Figure 21. Narrowband SPL for the JFI source with the baseline nozzle and the serrated nozzle installed withpylon 2. The equivalent isolated jet noise spectra is shown for relative comparison of levels. Ψ = 47deg. Θ =180deg. OP Sideline, Ma = 0.18.
There is a large dispersion in the literature on effects of chevrons on JWI/JFI noise. Some high-BPRchevron nozzles configurations have brought benefits to the Propulsion-Airframe Aeroacoustics in installedconfigurations27. The VITAL PIV data show that serrations lead to an increased jet cone length, thinnermixing layers, and lower levels of TKE shortly downstream of the exhaust and especially so in the wake ofthe pylon. It is possible to interpret the decrease of JWI and JFI by the VITAL serrations by the decreasethe TKE levels near the wing trailing edges. Serrations reduce the turbulent fluctuations responsible for thevery energetic near-jet pressure field. This may in turn lead to lower magnitudes of the acoustic jet-winginteractions.
An objective of VITAL SP7 is to describe how the under-wing installation of high-bypass-ratio enginesimpact the efficiency of low-noise nozzle devices. Loheac et al.28 have shown that medium-BPR core chevronsmay see their acoustic efficiency reduced by under-wing installation. Figure 22 shows the SPL delta betweenbaseline and serrated nozzles for three configurations. Serrations reduce JWI noise in the clean wing con-figuration since the delta remains constant, and JWI noise is shown to dominate at these forward angles.Serrations are even superior at reducing JFI noise up at St ≤ 2 when flap is deflected. Above St ≥ 2, theincreased noise reflection under the wing surfaces leads to a lower efficiency of the serrations. The fact thatVITAL serrations are able to reduce JWI and JFI noise may allow them to maintain their noise mitigation
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-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0.1 1.0 10.0 100.0
St mix
Del
ta S
PL (d
B)
Isolated Installed Flap 30 Installed Flap 00
Figure 22. One-third-octave band SPL delta [Baseline - Serrated] for isolated and installed nozzles with pylon2. Ψ = 60deg. Θ = 180deg. OP Sideline, Ma = 0.18. Positive values correspond to noise reduction byserrations.
efficiency in the global balance of noise sources and propagation effects.
This section has linked observations on VITAL installed jet aeroacoustics to literature and commonunderstanding of the phenomena involved. However many trends and sensitivities in the data highlight thelack of consensus on the noise generation mechanisms of jet-wing interaction noise. The energy involvedis considerable, with SPL above the peak of jet noise by orders of 20 dB for least favorable configurations.Jordan29 talks about the near pressure field of the jet being a well of non-propagating, reactive (or ”trapped”)fluctuation energy. Any obstacle or surface present in this field has the potential to release some of thistrapped fluctuation energy by shifting it into radiating modes. OASPL levels measured in the irrotationalnear field of co-axial jets noted around 140 dB by Tinney et al.25 signify the depth of this well. Moreresearch is required on the understanding and modeling of the jet-surface interaction noise.
IV. Numerical Evaluations and Comparison with Experiments
In the present paragraph, RANS-CFD based acoustic models are presented together with their applicationin the framework of VITAL in order to assess their capability to predict realistic jet noise trades. Threeacoustic numerical approaches are investigated by the authors.First, at Airbus Acoustics Department, two complementary approaches are considered. On the one hand, ananalytical code inspired by the Jet3D frequency-domain tool initially developed at NASA Langley is used.As the latter is based on the free field radiation equation of Lighthill, it is not expected to model propagationthrough inhomogeneous flow and installation effects. That is why Airbus, in partnership with Onera, hasdeveloped a model capable of generating jet sources in the time domain and likely to be coupled with a CAApropagation code. The resulting source reconstruction tool named sArA (for Synthesized Acoustic fromRans Aerodynamic) and its application through VITAL are presented in the second part of the chapter. Asthe interfacing process between sArA and CAA codes is still under investigation, this paper will not dealwith the numerical prediction of acoustic installation effects.In the third and last part, a Snecma method based on Tam and Auriault’s theory using an updated analyticaldirectivity is applied to assess serration effects, and highlights the weakness of the method in installedconfigurations.
A. Presentation of the Codes
1. Jet3D-Airbus code
Jet3D-Airbus is an Airbus in-house code strongly based on the work by Hunter30 who derivated a jet noiseprediction analytical model from the Ribner’s ”Theory of Two-Point Correlation of Jet Noise”31.First a mathematical manipulation of Lighthill’s equation yields the following expression for the pressure-pressure 2-point correlation:
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¯p2(~x, τ) =rirj rmrn16π2c40r
2
∫ ∫∂4
∂t4¯TijT ′mnd~ηd~Y (5)
By following the assumption that the Lighthill tensor can be written as a single shear term Tij = ρuiuj ,splitting the velocity into its mean and fluctuating parts, assuming a steady density medium, and neglectingthe triple correlation terms, Hunter writes the 2-point time delayed correlation of the Lighthill source termas follows:
∂4
∂t4¯TijT ′mn = ρρ′
∂4
∂t4[4VjV ′n ¯viv′m + ¯vivjv′mv
′n
](6)
The first term of the right-hand side component of Equation 6 relates to a mixed contribution of meanand fluctuating velocities and is commonly known as the shear-noise source term. The second term involvessolely turbulent velocities and is referred to as the self-noise source.
Mathematical considerations and postulated space and time correlations allow to rewrite Equation 6 asa function of the Reynolds stress tensor and the dissipation rate provided by a steady CFD computation.
2. sArA Code - Airbus-Onera
a) Source reconstruction in sArA.
sArA code was developed during an Airbus-Onera PhD studentship focusing on fast jet noise numericalprediction. It is based on two main modules.First, a volume source model based on the Stochastic Noise Generation and Radiation approach (SNGR)initially proposed by Bailly32 is used to compute turbulent velocities. The latter are then used to determinea source term that fits Lighthill analogy and are radiated in the far field. This computation procedure issuitable for isolated jet and its extension to installed nozzles using a sArA-Euler coupling, is still underinvestigation.
The SNGR approach derives from the early investigations of Kraichnan who initially proposed to generatea stochastic turbulent field in order to study the diffusion of particles. For a homogeneous turbulence, aspatial turbulent field that matches a given spatial correlation distribution is provided by the following sumof random Fourier modes:
~u(x) = 2.N∑n=1
uncos( ~kn.~x+ ψn) ~σn (7)
In the latter expression, a synthesized spatial turbulent velocity is described by a sum of mode, each modebeing characterized by a wave vector, a random phase and a velocity direction. Omais et al.33 publishedadditional details on the method.
Once the entire random variables have been generated, one should focus on the quantitative determinationof the velocity amplitude un in such a way that the synthesized velocity field fits the required spatialcorrelation function. This step is achieved by considering the Von Karman turbulent kinetic energy spectrumE(k) of which the first and second order momentum respectively represents the flow kinetic energy ktand dissipation rate ε. The knowledge of these two turbulent quantities is thus sufficient to define thecorresponding energy spectrum :
E(k) = α2Kt
3ke
( kke)4
(1 + ( kke)2)17/6
exp(−2(k
kν)2) (8)
In Equation 8, ke, kν and L are defined using the turbulent characteristics provided by a RANS com-putation. In order to determine the amplitude of the stochastic field, the basic definition of the turbulentkinetic energy is used. In a second step, a temporal filter is applied to recover a space-time correlated signal.
b) Noise radiation in sArA.
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It is clear that the use of a stochastic approach to predict aerodynamic noise is mainly justified by thecoupling possibilities with CAA codes as the sources are generated in the temporal domain. However asa preliminary validation step, the acoustic computation has been performed using an analytical methodfor CPU reasons. In what follows, far field acoustic spectra were estimated by the use of the temporalformulation of Lighthill integration over the source region:
p′(−→x , t) =1
4π
∫ ∫ ∫1r
∂2Tij∂yi∂yj
(−→y , t− r/c∞)d−→y (9)
As sArA does not deal with the tricky determination of the velocity-pressure correlations in turbulentfield, the so-called entropy terms are neglected in the Lighthill tensor:
Tij = ρuiuj (10)
This is a quite strong hypothesis in the case of a hot single jet as it is known that the noise contributionsfrom entropy and shear sources are highly correlated. In the case of a dual-stream engine, entropy sourcesare expected to be less influent in terms of acoustics considering the high mass-flow rate of the cold externalshear layer. Nevertheless, this assumption should be assessed in the future, for instance by using full andtruncated source terms from an unsteady CFD computation.
To account for the significant effect of source convection in the jet, a moving observer related to eachpoint of the sArA grid is considered. Let us consider an elementary source volume inside the jet convectedwith a local velocity Uc. In the source frame, a fixed observer outside the jet region is considered to moveat the velocity −Uc. In the present approach, the acoustic contribution of each elementary source at a fixedobserver point is computed independently as if the considered observer was advected at the source oppositevelocity. A single integration over the whole source volume provides the total acoustic contribution outsidethe jet.
Refraction effects are modelled according to the Snell and Descartes’ law: a so-called ”zone of silence”is identified and a rough approximation consisting in neglecting sources radiating in the zone of silence ismade.
3. TAPIR Code - Snecma
The TAPIR code is a Snecma in-house version of the Tam and Auriault34 theory, which predict fine scaleturbulence noise. This method is applied to k − ε RANS CFD mean flow and turbulent fields to evaluatethe acoustic power spectral density of fine scale turbulence STA as:
STA (x, ω) = 4π(
π
log 2
)3/2 ∫∫∫q2s l
3s
c2τs|pa (x2,x, ω)|2
exp{−ω2l2s/4u
2c log 2
}[1 + ω2τ2
s (1− uc cos θ/a∞)2]dx2 (11)
with pa the adjoint pressure, uc convection velocity, τs = cτkt/ε et ls = clk3/2t /ε the time and space turbulent
scales and q2s/c2 = A2 (2/3ρkt)
2 the elementary source intensity. Here, kt stands for the turbulent kineticenergy and ε for the turbulent dissipation rate.
The determination of pa needs to resolve the adjoint problem. However Tam35 and Morris36 noticed thatthe adjoint pressure for 90◦ radiation has an analytical form leading to:
|pa (x2,x, ω)|2 =ω2
64π4c40 |x− x2|2(12)
To simplify the methodology, the exact solution is computed for 90◦ radiation and the angular evolutionis taken into account thanks to a directivity factor (1 −Mc cos θ)−3 proposed initially by Goldstein37 andused by Morris36. This simplication is however not valid in the cone of silence, where refraction effectsbecome dominant.
B. Applications and Analysis
Based on the isolated RANS k − ε computations performed in the Airbus Aerodynamics Department3, theprediction capabilities of Airbus in-house jet noise prediction tools are assessed regarding flight and pyloneffects. In addition to these isolated nozzles studies, Snecma investigates the capability of the TAPIR code
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to account for the effect of serrations in the case of installed nozzles. Considering the free-field hypothesiscontained in the Tam and Auriault model, only aerodynamic installation effects are included in this compu-tation; reflection and diffraction due to the presence of the wing are not considered.In the framework of this numerical tools assessment study, five jet configurations are considered and sum-marized in the following table:
• An isolated baseline nozzle with pylon at Mach 0.27 (CFD computed at Airbus aerodynamic depart-ment)
• An isolated baseline nozzle with pylon at Mach 0 (CFD computed at Airbus aerodynamic department)
• An isolated axisymmetric baseline nozzle (without pylon) at Mach 0.27 (CFD computed at Airbusaerodynamic department)
• An installed (pylon + wing) baseline nozzle at Mach 0.27 (computed at Snecma aerodynamic depart-ment)
• An installed (pylon + wing) serrated nozzle at Mach 0.27 (computed at Snecma aerodynamic depart-ment)
Figure 23. Isosurfaces of the turbulent velocity colored by the total velocity (sArA computation)
1. Flight Effects
As explained by Dezitter et al.3, decreasing flight velocity yields an increase of the mixing layer spreadingrate leading to a shorter potential core length and higher turbulent kinetic energy (TKE). Dezitter plots theTKE profiles in the symmetry plane from 3.6 Dmix to 18 Dmix downstream the fan exhaust from CFD andexperimental results. It was highlighted that despite a slight global underestimation of the flight effect inthe computation, the qualitative dynamic behavior was quite well predicted.
Using above-mentioned CFD data, the characteristic frequency and length scales used in sArA have beencomputed and analyzed. Figure 24 features their axial evolutions against the TKE profile in the mixing layer.
First, one can notice that, according to empirical laws, flight effect in the characteristic length scales areincreasingly significant as sources are located farther downstream from the nozzle exit. Considering the linkbetween spatial correlations and radiated sound level, sources responsible for the acoustic flight effect shouldbe located downstream. However, provided the differences in TKE levels that can be observed in the vicinityof the nozzle lips, one should also expect the presence this part of the jet to contribute to the acoustic flighteffect.
As it could be expected, Figure 24 also shows that the characteristic frequency in the near field is higher forthe flight case, which is coherent with the exhibited lower mixing layer spreading rate. However, it appears
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that the turbulence frequency decreases very quickly in the vicinity of the nozzle exit. Hence, the peakfrequency structures seem to contain very little energy and are not expected to behave as significant noisesources.
Figure 24. Flight effect on TKE, length scale and time scale in the jet external mixing layer
sArA computations have been performed over 1600 iterations using a time step of 45.e-6s. Figure 25features the acoustic delta spectra between a static and a flight case for an observer located at 90deg fromthe jet axis. One can notice that the qualitative acoustic flight effect is quite well predicted as the peakfrequency and the plateau at high frequency are recovered by the model. Moreover, it is noticeable that theacoustic delta remains positive in a wide range of frequencies, which is in accordance with the fact that noisesources responsible for the acoustic delta may be located in an extended portion of the jet.
Figure 25. Flight acoustic effect at Ψ = 90deg. sArA computations vs measurements.
2. Pylon Effects
As no axisymetric mock-up has been tested in VITAL, the pylon effect on the azimuthal directivity of thebaseline nozzle was investigated by using a set of azimuthal microphones located in the downstream direction.
Figure 27 displays (a) the measured spectra from VITAL and NACRE experiments with Θ = 0deg takenat the pylon side and Θ = 180deg at the opposite side, and (b) sArA results. The polar angle is Ψ = 146deg inthe downstream direction. According to Figure 27 (a), the pylon essentially affects Strouhal numbers above0.5 with a noise increase close to 3 dB. Based on results presented by Dezitter et al., Figure 26 features theturbulent characteristics of a baseline jet with and without pylon. According to empirical laws, the presenceof the pylon increases the energy level and frequency of the sources located near the nozzle lips whereas it
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reduces the energy of sources located at more than 2 D from the nozzle exit. Figure 27 (b) presents theresults from sArA computations for radiated noise at the same two observers. The difference captured bythe code above St = 0.5 is fairly small. The use of the Lighthill analogy for sound propagation modelingleads to the fact that upper and lower shear layers radiate nearly the same acoustic energy at every spatialdirection. Hence, as the sound level decreases as 1/r2 and provided that the nozzle diameter is very smallcompared to r, the far-field directivity resulting from the Lighthill equation is nearly axisymmetric. In otherwords, the result may not illustrate a proper pylon effect but rather the omni-directional radiation of theshear layers inherent to the Lighthill formulation.
Figure 26. Pylon effect on TKE, length scale and time scale in the jet external mixing layer.
Figure 27. Pylon effect on the azimuthal directivity. Narrowband SPL spectra computed for Θ = 0deg and Θ= 180deg. OP Sideline, Ma = 0.27, Ψ = 146deg. Left (a): Measurements. Right (b): sArA computation.
To further refine the assessment of sArA capabilities to predict the pylon effect on jet noise, the jet fora baseline nozzle without pylon is computed by CFD with computational techniques analogous to thosepresented in3. The resulting acoustic delta between the computed axisymmetric nozzle and the nozzle with
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pylon features the same behavior as the azimuthal delta measured in the test campaign, as illustrated inFigure 28. The acoustic delta is more significant this time, and closer to measured values.
Figure 28. Acoustic effect of the pylon predicted by sArA. Narrowband SPL spectra computed for Θ = 0degwith the pylon, and without the pylon. OP Sideline, Ma = 0.27, Ψ = 146deg
The same cases have been studied using Jet3D-Airbus tool. Considering the similarities between sArAand Jet3D-Airbus radiation processes, the results from the two approach was expected to feature a similarbehavior. This point is confirmed by Figure 29.
Figure 29. Acoustic effect of the pylon predicted by Jet3D-Airbus. Left: Narrowband SPL spectra computedfor Θ = 0deg and Θ = 180deg with pylon. Right: Narrowband SPL spectra computed for Θ = 0deg with pylon,and without pylon. OP Sideline, Ma = 0.27, Ψ = 146deg
3. Serrations Effects
Snecma computed the flow-fields for two installed nozzle configurations with the elsA CFD solver using a k-εturbulence model, and post processed the CFD solutions with the TAPIR code. The two configurations arethe baseline nozzle and the serrated nozzle installed with the short pylon 2 under the EUROPIV wing with0deg flap setting. We do not expect the mixing source reconstruction code to capture Jet-Wing Interactionnoise. The computational effort will capture the effects of serrations on the jet mixing noise sources in theinstalled configuration. In other terms, the CFD-TAPIR procedure may be able to capture the aerodynamiceffect of installation on the jet mixing noise sources, but not the acoustic installation effects like acousticreflection, refraction or interaction noise. Serrations have been shown to affect the aero-acoustic interactionbetween the jet turbulence and the lifting surfaces in Section 4, also see27. The effect of serrations in installedbuilds will be difficult to validate on the noise measurements. Nevertheless, results of the CFD-TAPIRcomputational procedure are presented in Figure 30 and Figure 31. Figure 30 presents SPL spectra versusSt for measurements and CFD-TAPIR computation at the upstream angle Ψ = 60 degrees. A serration effectis predicted with noise attenuation at low frequencies, and noise level increase at high frequencies. Howeverthe cross-over frequency as well as the levels of the benefit and the high-frequency penalty are not fully
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satisfactory. The comparison at upstream angles is blurred by the jet-wing interaction. An extra benefit dueto the serrations is identified between St 0.1 and 0.65 in the upstream microphone measurements. Figure 31presents SPL dB delta between serrated and baseline cases, versus St for measurements and CFD-TAPIRcomputation at the downstream angle Ψ = 120 degrees. At this angle, the JWI noise is weaker and the trendsbetween numerical and experimental results are more consistent. Nevertheless, at all angles the CFD-TAPIRchain tends to over-estimate the impact of the serrations: a larger benefit below the crossover frequency,and higher noise increases above the cross-over frequency. The crossover is sharp, whereas the experimentaltrend is smoother.
Figure 30. One-third-octave band SPL predicted by TAPIR (blue) and measured (red) with the baselinenozzle (solid lines) and the serrated nozzle (dash lines). Nozzles are installed with pylon 2 and flap 0deg. Ψ =60deg, Θ = 180deg. OP Sideline, Ma = 0.27.
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2
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Figure 31. One-third-octave band SPL delta between [serrated - basline] predicted by TAPIR (blue) andmeasured (red). Nozzles are installed with pylon 2 and flap 0deg. Ψ = 120deg, Θ = 180deg. OP Sideline, Ma= 0.27. Negataive values correspond to noise reduction.
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V. Conclusions and Perspectives
We conclude this paper with a summary of the investigations performed within the framework of theVITAL research project. The VITAL WP7.2 study has allowed to build a large experimental and numericaldatabase of high quality on jet aerodynamics and acoustics with industrial high-BPR nozzle configurations.The jet mixing noise was described for realistic high-bypass ratio nozzles with pylon simulator and installedunder wing. Experimental acoustic data in the far-field and in the near-field are analyzed jointly with theresults from two joint papers on PIV and CFD. On top of this analysis, three numerical codes are used toreconstruct the mixing noise sources from CFD solutions.
Characteristic effects of jet velocity are observed on measured mixing noise. Beamforming on experimentaldata captures low-frequency St [0.2 - 0.6] peak noise sources where mixing is most intense behind the pylonbetween 5 and 7 Dmix downtream of the fan nozzle exit plane. This range of location is relatively upstreamfrom the expected end of the ”potential core”. Aerodynamic data, far-field and near-field acoustic analysesand sArA numerical predictions confirm the importance of the pylon for creating an asymmetric jet noiseradiation, with higher energy measured when facing the pylon. Coherent high-frequency St ≥ 4 sourceactivity is located very close to the nozzle within 1 Dmix. An additional source region at mid Strouhalranges appears in the jet noise maps at [2 - 4] Dmix when the nozzle switches to the highest operatingpoint with the largest primary/secondary shear. Classical flight effects are measured in the far-field for bothbaseline and serrated nozzles. The numerical code sArA manages to capture acoustic relative deltas due tothe flight effects on baseline nozzle.
Jet-wing and jet-flap interaction noise is analyzed from the experimental data and linked to literature.The energy radiated by this interaction can be considerable, up to 20 dB SPL above the peak of jet noisein the forward arc. Exponents for the dependence of JWI/JFI OASPL to jet velocities in static and flightconditions are globally coherent with diffraction and lift fluctuations noise mechanisms. Interaction noisepeaks emerge at harmonic frequencies. The fundamental peak frequency appears to correlate to the jetflow velocities. However the ratio to the mean jet velocity is found around 1 and is much higher than theturbulence convection speed in the jet mixing layers. More research is required on the understanding andmodeling of the jet-surface interaction noise.
The serrations are found to have a peculiar behavior. Joint papers2,3 have shown that the serrationsincrease the jet potential core length by an order of 20 per cent. The mixing rate and the turbulent kineticenergy are reduced over a large region of the jet. The far-field acoustic signature resembles chevron trendswith low-frequency reduction and high-frequency lift. Because of the atypical flowfield created by serrations,their acoustic effect cannot be paralleled with classical chevron nozzles. CFD, PIV, beamforming and far-field data are analyzed together and evidence a significant interaction between serrations and pylon, leadingto noise reduction. This combined effects make serrations more efficient at reducing noise on the pylon sidethan in the opposite flyover arc. The max TKE location behind the pylon follows roughly the same trend asthe location of noise sources at St [0.2 - 1]. Serrations shift the low-frequency sources location downstream inthe static case, and upstream in the flight case. Further, aerodynamic data shows that serrations annihilatelarge structures involved in the interaction between the primary-secondary and the secondary-ambient mixinglayers. This may be linked to beamforming results telling us that serrations have a drastic effect on the mid-Strouhal sources located at [2 - 4] Dmix for the largest primary/secondary shear. Serrations also increase thenoise source coherence in beamforming sense close to the nozzle exit plane. The application of TAPIR codeshows a potential to capture some trends of serrations on mixing noise. Experiments with installed nozzlesshow that serrations may reduce the intensity of jet-surface interaction by acting on the turbulent energy inmixing layers near the wing.
The three acoustic codes sArA, JET3D-Airbus and TAPIR have shown the capabilities of fast numericaltools to predict flight effects, pylon effects and some trends of serrations for jet mixing noise from realisticnozzles. The presented results are a starting point in our assessment of the RANS-based acoustic tools.Future work will consist in running the different aeroacoustic codes on CFD for isolated nozzles to improvethe assessment whether codes may capture the aeroacoustic effects of the serrations. The need for a couplingwith a proper propagation tool is underlined. This coupling should enable a better characterization of thesound propagation in the shear layers and the acoustic installation effects.
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Acknowledgments
The authors would like to thank Olivier Piccin and the technical team at CEPRA19 facility for theirdedication toward a successful test. Many thanks to the VITAL and NACRE coordinators for their supportin the review and publication of test results. J. H. and M. O. authors are grateful to Fabien Dezitter atAirbus Aerodynamics Method group for fruitful discussions on fluid dynamics and the link with aeroacoustics.
VITAL is a collaborative research project, running for five years, which aims to significantly reduceaircraft engine noise and CO2 emissions. It has a total budget of 91 million euros, including 51 million eurosin funding from the European Commission. The work in this paper above was performed under WP 7.2”Optimisation of aero-acoustic nozzle concepts” and AIRBUS FRANCE, SNECMA and ONERA specificallycontributed to the work presented in the paper.
Part of the work presented was funded by the European Commission under the FP6 integrated projectNACRE. Contributions from ONERA, SNECMA and AIRBUS FRANCE partners are acknowledged.
References
1Vuillemin, A., Piccin, O., and Davy, R., “Installation Effects Characterization of VHBR Engines: 1. ExperimentalSetup and Wind Tunnel Improvements,” 1st CEAS European Air and Space Conference, Berlin Germany, CEAS paper 363,September 2007.
2Davy, R., “Installation Effects Characterization of VHBR Engines: 2. Experimental Study Using Particle Image Ve-locimetry,” 15th AIAA/CEAS Aeroacoustics Conference, Miami FL, AIAA Paper 2009-3253, May 2009.
3Dezitter, F., Bezard, H., de Saint Victor, X., Zeggai, K., Britchford, K., Joubert, G., and Puigt, G., “Installation EffectsCharacterization of VHBR Engines: 3. CFD Assessment for Jet Mixing,” 15th AIAA/CEAS Aeroacoustics Conference, MiamiFL, AIAA Paper 2009-3253, May 2009.
4Viswanathan, K., “Analysis of the Two Similarity Components of Turbulent Mixing Noise,” AIAA journal , Vol. 40,No. 9, 2001, pp. 1735–1744.
5Viswanathan, K., “Instrumentation Considerations for Accurate Jet Noise Measurements,” AIAA journal , Vol. 44, No. 6,2004, pp. 1137–1149.
6Henderson, B., Kinzie, K., and Haskin, H., “The Effect of Nozzle Trailing Edge Thickness on Jet Noise,” AIAA paper ,10th AIAA/CEAS Aeroacoustics Conference and Exhibit, 2004-2948.
7Huber, J. and Illa, S., “Jet Noise Assessment and Sensitivity at Aircraft Level,” 13th AIAA/CEAS Aeroacoustics Con-ference, Roma Italy, AIAA Paper 2007-3728, May 2007.
8Elias, G., “Reseau microphonique pour la caracterisation des sources acoustiques en position et densite spectrale a l’aided’un modele de sources monopolaires correlees,” Tech. rep., ONERA Report 1/09276 DSNA, October 2004.
9Bulte, J. and Fleury, V., “Determination of Acoustic Directivity from Microphone Array Measurements using CorrelatedMonopoles,” 14th AIAA/CEAS Aeroacoustics Conference, Vancouver BC , AIAA Paper 2008-2855, May 2008.
10Bulte, J. and Fleury, V., “Estimation of Acoustic Directivity from Microphone Array Measurements using ParametricModels,” 15th AIAA/CEAS Aeroacoustics Conference, Miami FL, AIAA Paper 2009-3124, May 2009.
11Lu, H. Y., “An Empirical Model for Prediction of Coaxial Jet Noise in Ambient Flow,” AIAA, AIAA 1986-1912, 1986.12Lee, S. S. and Bridges, J., “Phased-Array Study of Dual-Flow Jet Noise: Effect of Nozzles and Mixers,” 12th AIAA/CEAS
Aeroacoustics Conference, Cambridge MA, AIAA20062647, May 2006.13Brusniak, L., Underbrink, J. R., and Nesbitt, E., “Phased Array Measurements of Full-Scale Engine Exhaust Noise,”
13th AIAA/CEAS Aeroacoustics Conference, Roma, Italy, AIAA Paper 2007-3612, May 2007.14Viswanathan, K., “Does a Model-Scale Nozzle Emit the Same Jet Noise as a Jet Engine?” AIAA journal , Vol. 46, No. 2,
2008, pp. 336–355.15Kerherve, F., Guitton, A., Jordan, P., Delville, J., Fortune, V., Gervais, Y., and Tinney, C., “Identifying the Dynam-
ics Underlying the Large-scale and Fine-scale Jet Noise Similarity Spectra,” 14th AIAA/CEAS Aeroacoustics Conference,Vancouver BC , AIAA Paper 2008-3027, May 2008.
16Nesbitt, E., Brusniak, L., Underbrink, J., Lynch, D., and Martinez, M., “Effects of Chevrons on Engine Jet NoiseStructure,” 13th AIAA/CEAS Aeroacoustics Conference, Roma Italy, AIAA Paper 2007-3597, May 2007.
17Michel, U. and Funke, S., “Noise Source Analysis of an Aeroengine with a New Inverse Method SODIX,” 14thAIAA/CEAS Aeroacoustics Conference, Vancouver BC , AIAA Paper 2008-2860, May 2008.
18Callender, B., An Investigation of Innovative Technologies for Reduction of Jet Noise in Medium and High Bypass RatioTurbofan Engines, Ph.D. thesis, University of Cincinnati, 2004.
19Mengle, V. G., Stoker, R. W., Brusniak, L., and ans R. H. Thomas, R. E., “Flaperon Modification Effect on Jet-FlapInteraction Noise Reduction for Chevron Nozzles,” 13th AIAA/CEAS Aeroacoustics Conference, Roma, Italy, AIAA 2007-3666,May 2007.
20Fink, M. R., “Propulsive Lift Noise,” Aeroacoustics of Flight Vehicles: Theory and Practice, Volume 1: Noise Sources,Vol. 1, H. H. Hubbard, Aug. 1991, pp. 219–240.
21Ffowcs-Williams, J. E. and Hall, L. H., “Aerodynamic Sound Generation by Turbulent Flow in the Vicinity of a ScatteringHalf Plane,” Journal of Fluid Mechanics, Vol. 40, No. 4, 1970, pp. 657–670.
22Curle, N., “The Influence of Solid Boundaries upon Aerodynamic Sound,” Proceedings 231A, the Royal Society of London,London, UK, 1955, pp. 505–517.
28 of 29
American Institute of Aeronautics and Astronautics
23Viswanathan, K., “Mechanisms of Jet Noise Generation: Classical Theories and Recent Developments,” InternationalJournal of Aeroacoustics, Vol. 8, No. 4, 2009, pp. 355–408.
24SenGupta, G., “Analysis of Jet-Airframe Interaction Noise,” AIAA, AIAA Paper 1983-0783, October 1983.25Tinney, C. E. and Jordan, P., “The Near Pressure Field of Co-axial Subsonic Jets,” Journal of Fluid Mechanics, Vol. 611,
2008, pp. 175–204.26Head, R. W. and Fisher, M. J., “Jet/surface interaction noise: analysis of far-field low-frequency augmentation of jet
noise due to the presence of a solid shield,” AIAA, AIAA Paper 1976-0502, July 1976.27Mengle, V. G., Elkoby, R., Brusniak, L., and Thomas, R. H., “Reducing Propulsion Airframe Aeroacoustic Interactions
with Uniquely Tailored Chevrons: 2. Installed Nozzles,” 12th AIAA/CEAS Aeroacoustics Conference, Cambridge MA, AIAAPaper 2006-2434, May 2006.
28Loheac, P., Julliard, J., and Dravet, A., “CFM56 Jet Noise Reduction with the Chevron Nozzle,” 10th AIAA/CEASAeroacoustics Conference, Manchester, UK , AIAA Paper 2004-3044, May 2004.
29Jordan, P., private communication, April 2009.30Hunter, C. A. and Thomas, R. H., “Development of a Jet Noise Prediction Method for Installed Jet Configurations,”
AIAA, AIAA Paper 2003-3169, May 2003.31Ribner, H. S., “Theory of Two-point Correlations of Jet Noise,” Nasa tn-d-8330, NASA, May 1995.32Bailly, C. and Juve, D., “A Stochastic Approach to Compute Subsonic Noise using Linearized Euler’s Equations,” AIAA
Paper 1999-1872, 1999.33Omais, M., Caruelle, B., Redonnet, S., Manoha, E., and Sagaut, P., “Jet Noise Prediction Using RANS CFD Input,”
14th AIAA/CEAS Aeroacoustics Conference, Vancouver BC , AIAA Paper 2008-2938, May 2008.34Tam, C. K. W. and Auriault, L., “Jet mixing noise from fine scale turbulence,” AIAA journal , Vol. 37, No. 2, 1999,
pp. 145–152.35Tam, C. K. W., “Dimensional analysis of jet-noise data,” AIAA journal , Vol. 44, No. 3, 2006, pp. 512–522.36Morris, P. J. and Farassat, F., “Acoustic Analogy and Alternative Theories for Jet Noise Prediction,” AIAA Journal ,
Vol. 40, 2002, pp. 671–680.37Goldstein, M., Aeronautics, McGraw-Hill, New York, 1976.
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