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1
Summary and Statistical Analysis of the First AIAA Sonic Boom Prediction Workshop!Mike Park!Computational AeroSciences Branch!NASA Langley Research Center !
2
Overcoming the Barriers to Practical High Speed Vehicles!
Efficient Vehicles • Efficient airframe and
propulsion throughout flight envelope
Sonic Boom • Design for low noise sonic boom • Understand Community Response
Airport Noise • Noise levels not louder than subsonic
aircraft at appropriate airports
High Altitude Emissions • No or minimal long term impact
at supersonic cruise altitudes
Light Weight, Durable Vehicles • Low airframe and propulsion weight in a
slender flexible vehicle operating at supersonic cruise temperatures
Efficient Operations • Airspace-Vehicle interaction for
full utilization of high speed
Environmental Barriers
Efficiency Barriers
Solutions to Barriers Drive the Selection of NASA Research Themes
3
Modeling of Atmospheric Effects
Modeling of Transmission into
Structures
Modeling of Human Response to Booms
Design for Low Boom
Overland Supersonic Flight !• Most significant barrier to
opening new markets for supersonic civil aircraft!– FAA: No flight at Mach > 1.0!– ICAO: No sonic boom
disturbance!• Rule change driven by
improved technology and industry interest!
• International cooperation is required!
• NASA has a long history of low boom research and a clear role in the technology and science behind a rule change as a national laboratory!
4
Background on Mitigation!
• Sonic waves from existing aircraft coalesce into an N-wave sonic boom!• Durations less than a second!
– Impulsive noise!
Time Domain
5
Background on Mitigation!
• N-waves have significant energy at frequencies that humans perceive well!
Frequency Domain
6
Frequency (Hz)
Gai
n (d
B)
101 102 103 104 105-60
-50
-40
-30
-20
-10
0
10
Background on Noise Measures!
• Multiple models have been developed and evaluated in experiments!• Humans perceive noises to be louder if they are 600 Hz to 10,000 Hz !
Frequency (Hz)
Ga
in (
dB
)
101
102
103
104
105-60
-50
-40
-30
-20
-10
0
10
A-Weighted Sound Exposure Level
Stevens JASA (1971) Perceived Loudness (PL)
7
Background on Mitigation!
• Current low-boom designs prevent coalescence!
Time Domain
8
Background on Mitigation!
• Which significantly reduce energy at these important frequencies!
Frequency Domain
Important Frequencies
9
Prediction of Loudness (Annoyance)!
• Generation of the acoustic disturbances!
• Propagation through real atmosphere!
– Winds, temperature variation, molecular relaxation, and maneuvering aircraft !
• Atmospheric turbulence!• Response of structures
(typically below 10 Hz)!• Perception of noise and
annoyance correlated to noise measures through experiments !
[image: Mathias Wintzer]
10
First AIAA Sonic Boom Workshop!
• Assess state-of-the-art near-field CFD as part of sonic boom prediction!
• One-day workshop before American Institute of Aeronautics and Astronautics (AIAA) SciTech January 2014 conference!
• Impartially compare relevant measures of near-field signatures to each other and wind tunnel measurements!
• Following successful AIAA workshop model!
[image: Mathias Wintzer]
11
AIAA Sonic Boom Workshop Participants!
• 19 groups!– Individuals and collaborations of up to 5 people!– 13 US, 3 France, and 3 Japan!– 10 Government, 5 Companies, 4 University!
Boeing'4%'
Dassault'4%' Gulfstream'
4%'INRIA'4%'
JAXA'14%'
Lockheed'MarAn'9%'
NASA'Ames'14%'
NASA'LaRC'18%'
ONERA'9%'
Sanko'SoHware'
5%'
Standford'U'5%'
Tokyo'U'5%'
U.'of'Miami'5%'
Organiza(ons+
12
AIAA Sonic Boom Workshop Models!
Flat-top signature axisymmetric SEEB-ALR
Simple Delta Wing Body
LM1021 Full Configuration
[image: Aftosmis, Nemec AIAA-2014-558]
13
SEEB-ALR Near-Field Pressure!
• Axisymmetric body designed by Lockheed Martin for the validation of a flat-top signature design method!
– Seebass and George with aft lift relaxation!• 18in long, examining at H=21.2in, 42.0in !• Mach 1.6 !• 64 extracted signatures submitted!
14
All SEEB-ALR Near-Field Signatures!
Near-Field Signatures Computed with Each Participants' Finest Grid
All Participant Signatures
Wind Tunnel Mean and Uncertainty from an Ensemble of Measurements
15
Fine-Grid SEEB-ALR Near-Field Signatures!
Near-Field Signatures Computed with Each Participants' Finest Grid
16
Fine-Grid SEEB-ALR Ground Signatures!
Near-Field Signatures Propagated to Ground Through Standard Atmosphere
17
Statistical Method!
• Goal is to identify “different” results, not “correct” or “wrong”!• Median +/- (1.7 coverage factor)*(standard deviation)!
– Assume a uniform distribution!• Small sample size with correlated results (same person, same code,
different grid)!• Used by other AIAA workshops (e.g., Drag Prediction, High Lift)!
18
All SEEB-ALR Perceived Level!
Sample
PL (d
B) f
rom
21.
2in
0 10 20 30 40 50 60 7088
89
90
91
92
93
94
MedianLimitsParticipantsExperiments
All Participant Signatures
19
Finest-Grid SEEB-ALR Perceived Level!
Sample
PL (d
B) f
rom
21.
2in
0 10 20 30 40 50 60 7088
89
90
91
92
93
94
MedianLimitsParticipantsExperiments
Near-Field Signatures Computed with Each Participants' Finest Grid
20
Expected Grid Convergence!
• Consistent methods should approach a value as the grid is refined to “zero” h!
Characteristic Grid Length (h)
Second-order
First-order
21
SEEB-ALR Perceived Level Grid Convergence!
h
PL (d
B)
0.000 0.002 0.004 0.006 0.008 0.01091.0
92.0
93.0StructuredTetrahedralMixed
22
Validation Metric!
• Integral of the absolute value of the difference between the submitted signatures and wind tunnel measurement!– Inherently imperfect (measurement is not “truth”)!– Used in validation exercises and the First AIAA Shock
Boundary Layer Interaction Workshop!
23 h
V
0.000 0.002 0.004 0.006 0.008 0.0100.0000
0.0002
0.0004
0.0006
0.0008
0.0010StructuredTetrahedralMixed
SEEB-ALR Validation Metric!
24
AIAA Sonic Boom Workshop Models!
Flat-top signature axisymmetric SEEB-ALR
Simple Delta Wing Body
LM1021 Full Configuration
[image: Aftosmis, Nemec AIAA-2014-558]
25
Sample
PL (d
B) f
rom
21.
2in
0 10 20 30 40 50 60 7088
89
90
91
92
93
94
MedianLimitsParticipantsExperiments
Sample
PL (d
B) f
rom
H=2
4.8i
n
0 10 20 30 40 50 60 7092
93
94
95
96
97
98
MedianLimitsParticipantExperiment
Delta Wing Body!
• Very similar statistics to the SEEB-ALR!• Uniform grid refinement did not converge to as tight a range!
– Stronger stocks!
SEEB-ALR fine-grid PL! Delta Wing Body fine-grid PL!
26
Delta Wing Body!
• Very similar statistics to the SEEB-ALR!• Uniform grid refinement did not converge to as tight a range!
– Stronger stocks!
27
AIAA Sonic Boom Workshop Models!
Flat-top signature axisymmetric SEEB-ALR
Simple Delta Wing Body
LM1021 Full Configuration
[image: Aftosmis, Nemec AIAA-2014-558]
28
LM1021 (Lockheed-Martin)!
• Developed for NASA by Lockheed-Martin under contract!• Complex configuration with wing, body, tails, and nacelles examined
at 2.1 degree angle of attack!• 22.4in long, 4in half span!• Mach 1.6!• Wind tunnel Reynolds number and blade sting mount increase
loudness!– Full-scale free-flight has a typical carpet of 85 PL (dB)!
• 11 sets of extracted signatures (optional case)!
[image: Cliff, et al.]
29
LM1021 Pressure on Centerline!
30
LM1021 Ground, R/(b/2)=7.9, Centerline!
All submissions!Euler, laminar, and turbulent simulations!Workshop and participant provided grids!
31
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
Phi (degrees)
PL (d
B)
0 10 20 30 40 50 6084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
PL extracted at different H/L! PL extracted at different phi!
From R/(b/2)=7.9 At centerline
32
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
Phi (degrees)
PL (d
B)
0 10 20 30 40 50 6084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
From R/(b/2)=7.9 At centerline
PL extracted at different H/L! PL extracted at different phi!
33
Examine Size of Variation Sources!
• Physical model!• Far-field multipole correction!• Signature close-out reconstruction!• Contribution of each shock (i.e., nose and tail shocks)!• Extraction distance!• Off-track!
34
LM1021 Signatures, R/(b/2)=7.9, Centerline!
35
LM1021 Ground, R/(b/2)=7.9, Centerline!
36
Multipole Far-Field Correction!
• Page and Plotkin AIAA-91-3275!• Corrects for diffraction of acoustic sources in span wise direction!
– Mitigate sampling near-field pressure too close to the configuration!– Correction is configuration dependent and decreases to zero with distance!
37
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Far-Field (Multi-Pole) correction!
[AIAA-2014-2006] At centerline
PL extracted at different H/L! Multi-pole correction!
38
Phi (degrees)
PL (d
B)
0 10 20 30 40 50 6084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Far-Field (Multi-Pole) correction!
[AIAA-2014-2006] From R/(b/2)=7.9
PL extracted at different phi! Multi-pole correction!
39
Tail closure!
• LM1021 wind tunnel model aft signature must be recreated to remove the mounting sting from the measurements and simulation!
Near-field!(full-scale)!
Step, Whitham, !and ramp tail!closures!
40
Tail closure!
• The steepness of the aft shock of this model is sensitive to the aft signature reconstruction method!
Step, Whitham, !and ramp tail!closures!
41
Tail closure!
• Higher frequencies are impacted by tail shock steepness!
Step closure 4 PL (dB)!louder than ramp!(ramp was used at workshop)!
Ground!spectra!
42
Frequency (Hz)
Gai
n (d
B)
101 102 103 104 105-60
-50
-40
-30
-20
-10
0
10
Background on Noise Measures!
• Humans perceive noises to be louder if they are 600 Hz to 10,000 Hz !• Measures have been evaluated in experiments (PL best loudness
correlation)!• ASEL is a good surrogate for PL and is a continuous weighting!
Frequency (Hz)
Ga
in (
dB
)
101
102
103
104
105-60
-50
-40
-30
-20
-10
0
10
A-Weighted Sound Exposure Level
Stevens JASA (1971) Perceived Loudness (PL)
43
ASEL (dB)
PL
(d
B)
69 70 71 72 73 74 75 76 77 78 79 8084
85
86
87
88
89
90
91
92
93
94
95
A-Weighted Sound Exposure Level (ASEL) and PL!
Range of both axes is 11 dB Line has unity slope
with offset of 14.5 dB Scatter of about 2 dB
All participants On and off centerline
All extraction distances
44
Time Domain A-Weighted Filter!
• Continuous weighting of ASEL enables time domain filtering !• Integrated to yield ASEL as a function of position!
– See the contribution of each ground signature feature to the total!
45
LM1021 Ground Signature!
46
LM1021 A-Filtered Pressure and Ground Signature!
47
LM1021 ASEL and A-Filtered Pressure!
48
LM1021 Ground and ASEL!
49
LM1021 Ground Signature!
50
LM1021 Ground Signature and ASEL!
51
LM1021 Ground Signature and ASEL!
52
LM1021 Ground Signature and ASEL!
69-72 dB 70-73.5 dB 71-80 dB
53
LM1021 Ground Signature and ASEL!
69-72 dB 70-73.5 dB 71-80 dB
54
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
PL extracted at different H/L! Near-field extracted at diff. H/L!
At centerline At centerline
55
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
At centerline At centerline
PL extracted at different H/L! Ground extracted at diff. H/L!
56
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
At centerline At centerline
PL extracted at different H/L! Ground extracted at diff. H/L!
57
R/(b/2)
PL (d
B)
0 5 10 15 20 25 3084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Background and Motivation!
At centerline At centerline
PL extracted at different H/L! ASEL extracted at diff. H/L!
58
Phi (degrees)
PL (d
B)
0 10 20 30 40 50 6084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Phi = 50 Degrees!
H/L=25, phi=50 degrees
PL extracted at different H/L! Ground signature!
59
LM 1021 Phi = 50 Degrees Ground!
60
Phi (degrees)
PL (d
B)
0 10 20 30 40 50 6084
85
86
87
88
89
90
91
92
93
94
95
1A2B3C4C5C6C7E8M9O10Q11Q
LM 1021 Phi = 50 Degrees!
ASEL!
H/L=25, phi=50 degrees
61
LM 1021 Phi = 50 Degrees ASEL!
64.5-79.5 dB 69-80 dB
62
Conclusions!
• Successful first workshop with international participation that includes government agencies, industry, and academia!
• The simpler required configurations each had 60+ submissions!• The optional full-configuration case had 11 submissions!• SEEB-ALR: 91.8 PL (dB) median, 0.3 dB standard deviation!• Delta Wing Body on centerline: 95.5 PL (dB) median, 0.2 dB
standard deviation!• LM1021 wind tunnel configuration: large 85 PL (dB) to 95 PL (dB)
variation and small sample size (no statistics)!• Exclusion of coarser grids in the uniform grid refinement study had a
negligible effect on median and limits for SEEB-ALR and Delta Wing Body!
63
Conclusions!
• LM1021 signature was more sensitive to inviscid and viscous simulations than simpler configurations (tail shock) but did not produce clear trends in Perceived Level (PL)!
• Multiple sources of variation for LM1021 PL and ASEL!– Centerline ground noise measures are dominated by the tail shock!– Both bow and tail shocks contribute to the 50 degree off-track ground noise
measures!• A-weighted Sound Exposure Level (ASEL) is a useful surrogate for
Perceived Level (PL)!• ASEL is continuous and can be applied in both the frequency and
time domains!
64
Recommendations!
• Design for reduced PL and ASEL sensitivity to small localized signature changes!
• Identify the sensitive portions of the signal (and model) to target for adequate grid refinement!
• A uniform grid refinement study may have provided insight into the LM1021 PL sensitivity!
• Minimize the variation introduced during reconstruction of aft pressure signature for models with sting or extend aft boundary for free-flight models!
• Apply far-field (multipole) correction into participant evaluations in a more consistent manner to quantify the impact of extraction distance!
• Use A-weighted filter and ASEL with PL for compiling statistics!
65
Participate!
• Visit http://lbpw.larc.nasa.gov for !– Presentations and references!– Geometry, grids, submitted data, and derived data are available:
independent analysis encouraged!!– Sign up for the low-traffic announcement e-mail list!
• See you for the next workshop!– AIAA SciTech 2017, 7-8 January 2017, Grapevine, Texas, USA!– Lower PL configurations from 90s to 70s!– Expand participation to include propagation and noise metric experts!– Include propulsion effects for optional case!– Provide uniformly refined grids for all cases!
66
Flight Demonstration Concept Formulation & Planning!
Requirements!• Demonstrate that noise from sonic booms
can be reduced to a level acceptable to the population residing under future supersonic flight paths.!
• Create a community response database that supports an International effort to develop a noise based rule for supersonic overflight!
Recent Technical progress has created an opportunity for a new effort to overcome the sonic boom barrier
Supersonic Low Boom Flight Demonstration Concept !
Approach!• Build on recent NASA progress to prepare for a future flight demonstration!• Partner with regulatory agencies and communities to create a roadmap for community
response study and rule development!• Revitalize the excitement of manned X-Planes using a focused and cost-effective
approach to design and operate a low boom research aircraft!• Flight demonstration project is under consideration as a new project!
67
Acknowledgements!
• Peter Coen provided the project and potential demonstrator overview!
• Fellow organizers and participants of the First AIAA Sonic Boom Prediction Workshop!
• Mathias Wintzer, Michael Aftosmis and Susan Cliff, NASA Ames, for contributing diagrams of the models and analysis process!
• Sriram Rallabhandi, National Institute of Aerospace, and Joe Salamone, formerly Gulfstream Aerospace, provided the suggestion of A-weighted filter for time domain analysis!
!
68
Focus& …2010& 2011& 2012& 2013& 2014& 2015& 2016& 2017…& …2020&
Formulate&Standards&&Apply%methodologies%&%%protocols%for%cer3fica3on%scheme%based%on%R&D%findings%
Metrics&Studies&• Jury%boom%simulator%tests%• Boom%vibro>acous3cs%tests%• Full%building%response%tests%%
Propaga>on&&&Flight&Effects&&&• Atmospheric:%Temp,%RH,%
turbulence%influences%• Terrain,%geographic,%clima3c%&%
seasonal%effects%• Test%flight%procedures%• Focus%&%Secondary%Boom%• Cut>off%Mach%No.%%
Research&AircraE&Design&&&Fabrica>on&
Community&Exposure&Tests&
Sta>s>cal&Extrapola>on&&&Acceptability&Criteria&
PSU:&Atmospheric&&Turbulence&filters&
ICAO&SSTG:&&Metrics&selec>on&&
%ICAO&SSTG:&&Formulate&
&“Preliminary”&standards&
Small&jet&low&boom&a/c&design&
%PreWdemonstrator&community&survey&W&protocol&&&best&prac>ces&
Ini>al&indoor&simulator&&&outdoor&boom&metric&R&D&studies&&
9& 10& CAEP&8&
%ICAO&SSTG:&&Monitor&R&D&progress&&&&State&of&Art&for&sonic&boom&
mi>ga>on&
NASA:&Focus&Boom&Predic>on&&&Valida>on&(SCAMP&project)&
NASA:&Ini>al&community&survey&tools&and&data&
collec>on&&(WSPR&Project)%
Preliminary&route&simula>on&exposure&modeling&
Correla>on&&&assessment&&of&data&&&&“Prelim”&standards&&
PSU:&Terrain&effects&model&
NASA:&Carpet&edge&and&Mach&cutoff&boom&study&(FaINT&proj.)&&
&DWSEND&(ph&2)&&
NASA:&Predic>ve&model&of&building&response&
NASA:&Turbulence&effects&on&low&boom&signatures&
11&
JAXA:&DWSEND&(ph&1)&test&& NASA&Low&Boom&Flight&Demonstra>on&(Business&and&Small&Airliner&Class&a/c)& %1st&
community&test&~2020&
May%2013%version%
Demonstrator(s)&rolls&out&
Demonstrator&&1st&flight&in&~2018&
Small&jet&low&boom&a/c&fabrica>on&
%ICAO&SSTG:&&Validate&&
“Preliminary”&standards&
ICAO&SSTG:&&Metrics&&&thresholds&
ICAO&SSTG:&&Noise&test&flight&procedures&development&
ICAO/FAA Notional Roadmap for!Sonic Boom Noise Standard!
69
Typical Mission Boom Carpet!
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