NEAT Consulting

On Aircraft Trailing Edge Noise

Yueping Guo NEAT Consulting, Seal Beach, CA 90740 USA

and Russell H. Thomas NASA Langley Research Center, Hampton, VA 23681 USA

Future Aircraft Design and Noise Impact 22nd Workshop of the Aeroacoustics Specialists Committee of the CEAS 6 – 7 September 2018 Netherlands Aerospace Centre – Amsterdam Acknowledgments NEAT Consulting • Aircraft Noise Reduction (ANR) Subproject of the Advanced Air Transport Technology (AATT) Project for funding this research

2 Outline NEAT Consulting • Introduction • Trailing edge noise data • Prediction methods • Estimate of HWB trailing edge noise • Summary

3 Introduction NEAT Consulting • Significant noise reduction opportunities for future aircraft have been investigated for the major airframe noise sources • Is trailing edge noise the noise floor? – Need reliable data and/or prediction tool to assess its relative importance • Objectives of this presentation – Review currently available data and prediction methods – Illustrate importance of trailing edge noise for future aircraft by preliminary estimate for the Hybrid-Wing- Body (HWB) aircraft

4 Airframe Noise Reduction NEAT Consulting • Thomas R. H., Burley C.L. and Guo Y. P., “Potential for Landing Gear Noise Reduction on Advanced Aircraft Configurations,” AIAA 2016-3039 • Thomas R. H., Guo Y. P., Berton J. J. and Fernandez H., “Aircraft Noise Reduction Technology Roadmap Toward Achieving the NASA 2035 Noise Goal,” AIAA 2017-3193 • Guo Y. P., Thomas R. H., Clark I.A. and June J.C., “Far Term Noise Reduction Roadmap for the Mid-Fuselage Nacelle Subsonic Transport,” AIAA 2018-3126

Krueger Dual Use Fairing  -8 dB

CML on Simple Flap Design  -10 dB Pod Gear  -12 dB

5 Trailing Edge Noise Measurement NEAT Consulting • Challenges – Wind tunnel background noise – Other noise components – Flight test at engine idle for cruise configuration – Noise floor may also contain other components such as wing tip, fuselage boundary layer, aileron, and residual engine noise • Useful techniques – Phased array: subdomain integration to extract trailing edge noise when it is not significantly lower than other sources

6 Trailing Edge vs Slat NEAT Consulting • Guo Y. P., Yamamoto K. J. and Stoker R. W., “A Component Based Empirical Model for High Lift System Noise Prediction,” J. Aircraft 40(5), 914-922, 2003 • Conventional Aircraft: 4.7% MD-11 Model 80 • Data from phased array measurements • M = 0.24, 90 degrees emission angle

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1 Trailing Edge

50 2 3 4 10 10 10 7 Full Scale Frequency (Hz) Trailing Edge vs Flap NEAT Consulting • Stoker R. and Guo Y. P., “Airframe Noise of a Full-Scale 777 and Comparison with Past Model-Scale Tests,” NASA Contract Report, Contract NAS1-97040, February 2002 100

• Average difference about 8 dB 95 for all angles

90   8 dB

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L 85

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A O 80 Flap Setting 1, Gear Up Flap Setting 25, Gear Up 75 Flap Setting 30, Gear Up

70 40 60 80 100 120 140 Emission Angle (Deg) 8 Trailing Edge vs Landing Gear NEAT Consulting • Average difference about 8 dB below 1000 Hz • Engine noise contamination above 1000 Hz • Difference expected to be more than 8 dB above 1000 Hz when 150 engine noise is corrected (green dashed curve) • Kipersztok O. and Sengupta, G., 145 “Flight Test of the 747-JT9D for Airframe Noise,” Journal of Aircraft,

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B Vol. 19, No. 12, December, 1982

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120 102 103 104 Frequency (Hz) 9 Component Noise NEAT Consulting

Landing Gear Flap Slat Current Level above 8 8 6 TE Noise (dB) Potential Noise -12 -10 -8 Reduction (dB) Potential Level -4 -2 -2 above TE Noise (dB) Worst case because of other noise components in the noise floor and the potential of trailing edge noise reduction for advanced aircraft • With advanced noise reduction, trailing edge noise can potentially hold up the noise floor • Order of estimate only and need more accurate quantitative study – Detailed study for existing database in aircraft type, directivity, etc. – Extract other components and engine residual noise • Even without noise reduction, trailing edge noise may increase for particular aircraft configurations (see HWB example later) 10 Prediction Method NEAT Consulting • Source mechanisms well studied • Prediction formulation for noise spectrum  L (  ,x )cos( Au ,2 V )(223 MDFM ,) 0 r 2 • Need local turbulent kinetic energy k, convection velocity V, and boundary layer thickness 

A = empirical constant

0 = mean density 2 u = turbulent velocity (u  k) Turbulent Boundary Layer V = convection velocity M = flight Mach number L = trailing edge length  = boundary layer thickness r = far field distance  = sweep angle Sound D = directivity F = spectral function

11 Fink Method NEAT Consulting • Approximate all local flow quantities by an empirical constant S  (,)(x ,)(,) AMDFM5 FINKFINK r 2 – S = wing surface area

– AFINK = empirical constant defined for two classes of aircraft (“aerodynamically clean” or otherwise) • Database only include old aircraft pre 1977 • Variations in current and future aircraft not likely to fit into an empirical constant • Empirical approximation no longer necessary because local flow quantities can be derived by CFD

12 HWB Trailing Edge Noise Estimate NEAT Consulting • Estimate source flow quantities in reference to conventional aircraft by using a generic two-element high lift system – 4o angle of attack for tube-and-wing (T+W) aircraft – 15o angle of attack for HWB • Estimate noise variations due to changes in – turbulent kinetic energy k – convection velocity V – trailing edge length L – boundary layer thickness  • Effect of flight Mach number not considered because it affects all components U

Noise 13 Turbulent Kinetic Energy NEAT Consulting

kHWB/ kT+W = 1.33

3 HWB T+W

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i t 1.5 o e  = 15

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T Turbulent Kinetic Energy Kinetic Energy Turbulent 0 0 2 4 6 8 10 Distance From Wing (% of Chord)

14 Convection Velocity at Trailing Edge NEAT Consulting

0.24

0.22

0.2 Outside BL 0.18 4% Chord From Wing 0.16

Mach Number

0.14 20 T+W HWB 0.12 ) 18 o d  = 2 r o 2 4 6 8 10 12 15

o

h  = 4 16 o C  = 6 AOA (Degrees)

f o 14  = 8o

% o ( 12  = 10 g o n V / V = 1.154 i  = 12 HWB T+W 10 o W  = 15 m 8

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D 2 0 0 0.04 0.08 0.12 0.16 0.2 0.24 Mach Number 15 Boundary Layer Thickness NEAT Consulting 12 % of Total Pressure 99.90% 99.80% 99.70% 10

(% of Chord) (% of 8

Boundary Layer Thickness T+W HWB 6 2 4 6 8 10 12 15 AOA (Degrees)

Total Pressure (%) 99.9 99.8 99.7

HWB/ T+W 1.28 1.27 1.23

Average Value of  /  = 1.26 HWB T+W 16 HWB Trailing Edge Noise Estimate NEAT Consulting

SPL = 10  log(kHWB/ kT+W) Turbulent Kinetic Energy

+ 20  log(VHWB/ VT+W) Convection Velocity

+ 10  log(HWB/ T+W) Boundary Layer Thickness

+ 10  log(LHWB/ LT+W) Trailing Edge Length Estimate:

kHWB/ kT+W = 1.33

VHWB/ VT+W = 1.15

HWB/ T+W = 1.26

LHWB/ LT+W= 1.2

SPL = 4.3 dB

Question: Does this increase make TE noise important?

17 Extrapolation to HWB NEAT Consulting • Assume the same slat noise for HWB and T+W aircraft (green circles) • Trailing edge noise increases 4 dB from T+W (blue diamonds) to HWB (black curve)

80 Comparable at Low Frequencies

Good Margin at

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1 T+WTrail iTEng Edge HWBHWB TE

50 2 3 4 10 10 10 18 Full Scale Frequency (Hz) Preliminary Observations NEAT Consulting • Because of the potential reduction of other noise components, trailing edge noise may become the noise floor for future aircraft • Trailing edge noise itself can increase for some aircraft such as HWB and truss braced wing aircraft, increase the importance of trailing edge noise in reference to other components • Current prediction method is outdated and has been used only because trailing edge noise is more than 8 dB lower than other components for current aircraft • More accurate and robust prediction tools are feasible by computing the local flow quantities

19 NEAT Consulting

Thank you