Aftosmis, Michael

Nemec, Marian

Spurlock, Wade

English

NASA Technical Reports Server

National Aeronautics and Space Administration
www.nasa.gov 
Minimizing Sonic Boom Through 
Simulation-Based Design: 
 The X-59 Airplane
Computational Aerosciences Branch 
NASA Advanced Supercomputing Division 
Ames Research Center
SC19, Denver, CO 
Nov 17-22, 2019
Marian Nemec      Michael Aftosmis      Wade Spurlock
NASA Ames Science & Technology CorpNASA Ames
https://ntrs.nasa.gov/search.jsp?R=20200000307 2020-03-11T13:32:25+00:00Z
• Vision for Commercial Supersonic Flight is a future 
where fast air travel is available to a broad spectrum 
of the traveling public 
• Biggest challenge is sonic boom 
- Civil supersonic flight operations are prohibited over 
many parts of the world 
- Currently, U.S. law prohibits flight in excess of Mach 1 overland 
• Supersonic En-Route Noise standard is required  
- Must be accepted internationally (ICAO, FAA, EASA, TCCA) 
• Additional barriers include airport noise, high-altitude emissions, efficiency, and many more
Motivation
2SC19, 17-22/11/2019
Overcoming the Barrier to Overland Supersonic Flight
Credit: Lockheed Martin
www.nasa.gov
Sonic Boom Physics
SC19, 17-22/11/2019 3
Sound heard
Sound generated
Ra
y 
Pa
th
Mach > 1
Acoustic Frame of Reference
Simulation-based analysis must reliably predict ground noise
Acoustic Propagation
Aerodynamic Frame of Reference
Simulation-based design must reliably determine aircraft shape to minimize ground noise
Goals
µ = sin 1
✓
1
Mach
◆
Mach = 1 → 767 mph or 1,235 km/h (at sea level)
SC19, 17-22/11/2019 4
Sonic Boom Noise
Pe
rc
eiv
ed
 L
ou
dn
es
s
70 Car doorclosing
80
Car on 
freeway 
@ 25ft 
90 SubwayPlatform
100
105 ConcordeSonic Boom
Helicopter 
@ 100ft
(dB)
2x
4x
8x
(Heineck et. al., NASA) 
Atmospheric 
Propagation
Ground Signature
Al
tit
ud
e 
(~
10
 m
ile
s)
Boom sound characteristics are a function of the ground 
pressure signature 
•Classical signatures are N-waves
•Low-boom designs exploit shaped signatures

-Strategy is to increase rise time, decrease amplitude, 
increase duration and smooth recovery

-Requires designing aircraft with nearfield signatures 
that do not coalesce into N-waves
∆p
Time
Rise Time
Zero-Peak

Amplitude
Positive-Phase

Duration
Negative-Phase

Duration
Pressure 
Recovery
Schlieren photograph 
of a supersonic aircraft 
SC19, 17-22/11/2019 5
Sonic Boom Noise
Pe
rc
eiv
ed
 L
ou
dn
es
s
70 Car doorclosing
80
Car on 
freeway 
@ 25ft 
90 SubwayPlatform
100
105 ConcordeSonic Boom
Helicopter 
@ 100ft
(dB)
2x
4x
8x
(Heineck et. al., NASA) 
Atmospheric 
Propagation
Ground Signature
Al
tit
ud
e 
(~
10
 m
ile
s)
Boom sound characteristics are a function of the ground 
pressure signature 
•Classical signatures are N-waves
•Low-boom designs exploit shaped signatures

-Strategy is to increase rise time, decrease amplitude, 
increase duration and smooth recovery

-Requires designing aircraft with nearfield signatures 
that do not coalesce into N-waves
Schlieren photograph 
of a supersonic aircraft 
∆p
Time
∆p = 2 lb/ft2

Duration = 0.25 s
Sonic Boom Footprint
6SC19, 17-22/11/2019
BOOM CARPET
Sonic boom characterization requires prediction of the primary boom carpet
• Influenced by several factors, some with significant  uncertainties
Aircraft shape and

operating conditions
Atmospheric conditions

(wind, temperature, humidity)
Local terrain
Additional factors

• Aircraft acceleration and maneuvers, focus booms

• Secondary boom carpets 
Low-Boom Flight Demonstration
7SC19, 17-22/11/2019
Pe
rc
eiv
ed
 L
ou
dn
es
s
70 Car doorclosing
80
Car on 
freeway 
@ 25ft 
90 SubwayPlatform
100
105 ConcordeSonic Boom
Helicopter 
@ 100ft
(dB)
2x
4x
8x
X-59
Community 
Response Surveys
Co
mm
un
ica
tio
ns 
& A
DS
-B 
U.S. 
National Air 
Space
X-59 QueSST
GPS
Mobile Operations 
Facility
Typical 
Community
Limited Ground
Microphones
Meteorological 
Data (balloon)
Meteorological 
Data (ground)
•NASA mission to support development of an En-Route noise standard 
- Aircraft is a supersonic-acoustic-signature-generator with characteristics representative 
of a commercial supersonic transport 
•Design Mach number is 1.4 
•Design sonic boom sound level is 75 PLdB (Perceived Level) 
- Roughly a factor of eight quieter than the boom 
generated by Concorde 
- Near ambient noise level of a city 
- Similar to a rumble from a distant thunderstorm 
•Goal is to perform multiple overflights of 
representative communities and climate across the 
US to collect noise response data 
•Deliver community response data to ICAO
X-59 Aircraft
SC19, 17-22/11/2019 8
www.nasa.gov/aero/x-59-quesst-overview
Role of High-Fidelity Simulations and HPC
9SC19, 17-22/11/2019
NASA Dryden 
Aeronautical Test Range
F-15 Probe Aircraft
LBFD Aircraft
Meteorological 
Data (ground)
GPS
Air Traffic Control
and Communications
Mission Control
and Telemetry
NASA Operations and 
Ground Facilities
Hangar Edwards 
Air Force Base
Tel
em
etr
y &
  C
om
mu
nic
atio
nsAir-to-Air 
Position Data
Meteorological 
Data (balloon)
TG-14 with 
Microphone
Microphone Arrays 
(ground)
ConOps Composite
Community Surveys
_ _ _ _ _ Near-field _ _ _
_ _ _ _ _ Mid-field _ _ _
_ _ _ _ _ Far-field _ _ _ 
_ _ _ _ Ground-level _ _ _ 
Schlieren Imaging
(airborne)
Schlieren Imaging
(ground)
Community 
Response Surveys
Co
mm
un
ica
tio
ns 
& A
DS
-B 
U.S. 
National Air 
Space
X-59 QueSST
GPS
Mobile Operations 
Facility
Typical 
Community
Limited Ground
Microphones
Meteorological 
Data (balloon)
Meteorological 
Data (ground)
•High-fidelity CFD simulations are a major contributor to X-59 
- All aspects of aerodynamic design and acoustic analysis 
- Wind-tunnel hardware verification and test support 
- Uncertainty quantification 
•Ongoing pre-test analysis to support acoustic validation flights 
•Near-real-time prediction capability for community test planning 
•Suite of new prediction tools for certification of supersonic aircraft
Acoustic Validation 
Flights
Community Response Overflights
Sonic Boom Analysis
SC19, 17-22/11/2019 10
Ground Signal
CFD Domain
Near-field
Signal
Altitude Atmospheric
Propagation
Nearfield 
3D effects (aircraft shape and plume)
Use CFD
Propagation 
Atmospheric variability
Absorption
Use Ray Tracing and 
quasi-1D PDE
(~10 miles)
Flight p
ath
Ray Tracing
Core Solver: Cart3D
SC19, 17-22/11/2019 11
• Multilevel embedded-boundary Cartesian mesh

‣ Cut-cells at boundary

‣ Handles arbitrarily complex vehicle shapes
Meshing
• Inviscid flow assumption (Euler equations)

• Second-order spatial and temporal discretization

‣ Fully conservative finite-volume method

‣ Dual time-stepping for unsteady flows

• Calorically perfect and equilibrium gas models

• Runge-Kutta time marching with multigrid acceleration

Flow Solver
Pressure  
Signature 
Error
Core Solver: Cart3D
SC19, 17-22/11/2019 12
• Mesh automatically refined in locations with most impact on user selected outputs (pressure 
signatures, lift, drag, moments, …)

‣ Method of adjoint weighted residuals

‣ Used for every simulation
Error Estimation and Goal-Oriented Mesh Adaptation
Pressure  
Signature Location
Near-body region of adapted mesh around LBFD aircraft 
for pressure sensor output (Cp contours) Adaptation Convergence History
Parallel Performance
SC19, 17-22/11/2019 13
Excellent scalability through use of domain decomposition based on space-filling curves
Cascade Lake Engineering Workstation
1 2 4 8 16 32 64 128
Number of Cores
1
2
4
8
16
32
64
No
rm
al
ize
d 
Ex
ec
ut
io
n 
Ti
m
e Compact
Scatter
• Intel(R) Xeon(R) Gold 6252 CPU

• 2 sockets, 24 physical cores per socket

• Hyper-Threading and TurboBoost ON

• icc, version 19.0.4.243
KMP Affinity
OpenMP Performance
OpenMP and MPI fully supported 
HECC Supercomputing Systems
Example Results
14SC19, 17-22/11/2019
NASA Dryden 
Aeronautical Test Range
F-15 Probe Aircraft
LBFD Aircraft
Meteorological 
Data (ground)
GPS
Air Traffic Control
and Communications
Mission Control
and Telemetry
NASA Operations and 
Ground Facilities
Hangar Edwards 
Air Force Base
Tel
em
etr
y &
  C
om
mu
nic
atio
nsAir-to-Air 
Position Data
Meteorological 
Data (balloon)
TG-14 with 
Microphone
Microphone Arrays 
(ground)
ConOps Composite
Community Surveys
_ _ _ _ _ Near-field _ _ _
_ _ _ _ _ Mid-field _ _ _
_ _ _ _ _ Far-field _ _ _ 
_ _ _ _ Ground-level _ _ _ 
Schlieren Imaging
(airborne)
Schlieren Imaging
(ground)
Acoustic Validation Flights
1. Nearfield Flow Solutions 
2. Nearfield Signatures 
3. Ground Signatures 
4. Ground Noise Level 
Nearfield
15SC19, 17-22/11/2019
(Heineck et. al., NASA, 2016) (Heineck et. al., NASA, 2019) 
•Schlieren photographs are a well-established experimental technique

-Visualization of density gradients, excellent for shocks

•New capability in Air-to-Air Background Oriented Schlieren (AirBOS) imaging

-Allows schlieren imagery of aircraft in flight

-Emerging technique for validating simulations through comparison with computational schlierens
Schlieren Flow Visualization
Photographs from flight tests in the Supersonic Corridor 
near Armstrong Flight Research Center
Flight-Matching Computation
16SC19, 17-22/11/2019
Computational schlieren 
image from Cart3D simulation
Flight TestCart3D Simulation
Computational schlieren
Mach number = 1.05

Angle of Attack = 1.15°

T-38 Aircraft
AirBOS image 
Photographed 2,000 feet from the aircraft 
Shock-Shock Interactions
17SC19, 17-22/11/2019
Supersonic Formation Flight
Computational schlieren
AirBOS image 
Photographed 2,000 feet from the aircraft 
Mach number = 1.05

Angle of Attack = 1.15°

T-38 Aircraft
Preliminary work toward flight-matching simulations and future acoustic validation flights 
18SC19, 17-22/11/2019
Computational schlieren

• Dark lines are shockwaves

• White regions are expansions

• Perspective projection
Mach number = 1.05 
Angle of Attack = 1.15° 
T-38 Aircraft (wingtip separation ~13’)
19SC19, 17-22/11/2019
Mach number = 1.05 
Angle of Attack = 1.15° 
T-38 Aircraft (wingtip separation ~13’)
Computational schlieren

• Dark lines are shockwaves

• White regions are expansions

• Perspective projection
X-59 Nearfield Predictions
20SC19, 17-22/11/2019
Ground Signal
CFD Domain
Near-field
Signal
Altitude Atmospheric
Propagation
Challenging simulations:

•Fine geometric detail (probes, vortex generators, flaps, 
ailerons, stabilator, t-tail, …)

•Many secondary-air systems, in addition to the main engine

•Requires accurate prediction of a complex system of 
shockwaves far from the aircraft in addition to standard 
aerodynamic performance coeﬃcients
Shockwaves at Cruise
21SC19, 17-22/11/2019
• Significant influence of nozzle exhaust

• Shaped pressure signature below aircraft
Computational schlieren

• Dark lines are shockwaves

• White regions are expansions

• Perspective projection
Mach number = 1.4 
Angle of Attack = 2.05°
0 5 10 15 20 25 30 35 40
Distance along sensor
-0.0075
-0.005
-0.0025
0
0.0025
0.005
0.0075
0.01
Δ
p/
p ∞
SC19, 17-22/11/2019 22
Nearfield Pressure Signature
h
L
= 1
(⇡ 30m)
h
L
= 2
(⇡ 60m)
(⇡ 90m)
h
L
= 3
Mach number = 1.4 
Angle of Attack = 2.05°
On-track Nearfield 
Pressure Signature
Nearbody refinement in streamwise 
and crossflow directions: 
• Typical mesh size 50 million cells 
• Fine mesh size 100—500 million cells
Coefficient of pressure on mid-plane 
• White: freestream 
• Yellow-Red: above freestream 
• Blue: below freestream
SC19, 17-22/11/2019 23
∆p
/p
∞
No
rm
al
ize
d 
PD
F
Distance
10% 
Quantiles
1.4 1.51.3
Mach Number 
Uncertainty
Low uncertainty 
region 
200 220 240 260x
-0.002
0
0.002
0.004
Δ
p/
p ∞
Error Estimate
Nearfield Pressure Signature
0 5 10 15 20 25 30 35 40
Distance along sensor
-0.0075
-0.005
-0.0025
0
0.0025
0.005
0.0075
0.01
Δ
p/
p ∞
Nominal Conditions
Mach=1.4, α=2.05°
Uncertainty Quantification
Local Discretization 
Error Estimates
Distance long sensor
Distance along sensor
Signature 
Probability 
Density 
Function
Nearfield Pressure Cylinders
SC19, 17-22/11/2019 24
0 5 10 15 20 25 30 35 40
Distance along sensor (m)
-0.01
-0.0075
-0.005
-0.0025
0
0.0025
0.005
0.0075
0.01
Δ
p/
p ∞
φ =  0º
φ = 20º
φ = 40º
Free Polar Graph Paper from
 http://incom
petech.com
/graphpaper/polar/
50°
20°
30°
40°
10°Φ = 0° off-tr
ack 
angl
e
• Recall that goal is to compute the boom carpet on the ground 
- This requires computation of the nearfield pressure cylinder, not just the on-track signature
BOOM CARPET
Example nearfield pressure              
cylinders below the   
aircraft
• Adaptively refined mesh for many sensor locations

- In practice, we take full advantage of mesh alignment

- Separate into several cases with sensors at similar oﬀ-track angles
Pressure signatures at 
diﬀerent oﬀ-track angles
Atmospheric Propagation and Ground Signatures
SC19, 17-22/11/2019 25
ϕ = -45°ϕ = 0°
ϕ = + 45°
Flight 
path (+
x )
67 sec112 sec
112 sec
Propagation & Ray Tubes
0 20 40 60 80 100 120 140
Time Miliseconds  (ms)
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Ov
er
pr
es
su
re
 (p
sf)
φ =   0°
φ = 10°
φ = 20°
φ = 30°
φ = 40°
Propagation altitude, 55076 ft
Ground Signatures
0 5 10 15 20 25 30 35 40
Distance along sensor (m)
-0.01
-0.0075
-0.005
-0.0025
0
0.0025
0.005
0.0075
0.01
Δ
p/
p ∞
φ =  0º
φ = 20º
φ = 40º
Ground waveforms
Nearfield 
signatures
• Propagate nearfield signature through atmosphere to ground 
• Numerical analysis via sBOOM: 
1.Ray tracing (path and arrival time) 
2.Quasi-1D propagation (signature morphology) 
• Includes relaxation loses, stratification, spreading and 
non-linear propagation
Sonic Boom Carpet
SC19, 17-22/11/2019 26
-50 -40 -30 -20 -10 0 10 20 30 40 50
Off-Track Angle (deg)
56
58
60
62
64
66
68
70
72
74
76
78
No
is
e 
M
et
ric
 (d
B)
PLdB
ASEL
Free Polar Graph Paper from
 http://incom
petech.com
/graphpaper/polar/
Track Width (70+ miles!)
  = off-track angle
Altitude 
(~10 miles)
cutoff angle
Noise target is 75 PLdB

• Current design is quieter than target over the 
full carpet 

• Holds for most atmospheric conditions
Convert ground waveform to level of noise for each oﬀ-track angle 
up to cutoﬀ

• Perceived level (PLdB) is the primary metric

• ASEL, BSEL & CSEL also used 
0 20 40 60 80 100 120 140
Time Miliseconds  (ms)
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Ov
er
pr
es
su
re
 (p
sf)
φ =   0°
φ = 10°
φ = 20°
φ = 30°
φ = 40°
Propagation altitude, 55076 ft
Ground noise
Importance of High-End Computing
27SC19, 17-22/11/2019
Pleiades

-Broadwell
Aitken

-Cascade Lake
Endeavour

-Sandy Bridge 
Electra

-Skylake 
Challenges of simulating low-boom aircraft

-Propagation of weak shocks over several aircraft lengths 
‣Difficult to reap benefits of advanced higher-order schemes 
‣Highly susceptible to attenuation by discretization error 
-Wide range of scales: complex flow & aircraft geometry 
‣Large grids even with adaptive mesh refinement 
- Many engineering cases 
‣Operating conditions, flaps, ailerons, stabilator, T-tail, engine settings 
‣Fast turn-around critical (4—8 hours per case) 
‣Each case fits on 1—4 nodes, but may need several 100 nodes to fill databases efficiently
Acknowledgements
28SC19, 17-22/11/2019
• NASA High-End Computing (HEC) Program 
through the NASA Advanced Supercomputing 
(NAS) Division

‣ SciCon in-house performance monitoring 
and debug tools

• NASA's ARMD Commercial Supersonic 
Technology and LBFD/X-59 Projects


Minimizing Sonic Boom Through Simulation-Based Design: The X-59 Airplane

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server