SBPW3 Propagation Workshop sBOOM Updated · 2020-02-05 · Sriram K. Rallabhandi Aeronautics...

Sriram K. Rallabhandi

Aeronautics Systems Analysis Branch

NASA Langley Research Center

Hampton, VA 23681

SBPW3: Propagation Workshop Results using sBOOM

5th January, 2020, Orlando, FL, USAAIAA SciTech 2020

SBPW3: sBOOM results 2

• Summary of Cases Analyzed • Boom Propagation Code Details • Cases

• Ground Signatures • Loudness metrics

• Highlights • Summary

Outline

5 January 2020


Summary of Cases Analyzed

5 January 2020

• NASA trimmed low-boom concept - C25P

– Required runs with measured atmospheric profiles

– Lateral cut-off analysis – Optional focus boom simulations


Summary of Cases Analyzed

5 January 2020

• NASA trimmed low-boom concept - C25P

– Required runs with measured atmospheric profiles

– Lateral cut-off analysis – Optional focus boom simulations

• NASA-Lockheed Low-Boom Flight Demonstrator (LBFD): A variant of X-59 QueSST

• Required runs with measured and standard atmospheres


sBOOM • Propagation based on lossy Quasi-1D Burgers equation

Propagation Prediction Code: sBOOM

5 January 2020

𝜕𝑝𝜕𝜎

=𝜕𝐵𝜕𝜎

𝐵𝑝 +

𝛽Ω2𝜌0𝑐3

0 ( 𝑐0

𝑣𝑔 ) 𝜕𝑝2

𝜕𝜏+

𝛿Ω2

2𝜌0𝑐30 ( 𝑐0

𝑣𝑔 ) 𝜕2𝑝𝜕𝜏2

+ ∑𝜈

𝑚𝜈

2𝑐0

𝑡𝜈Ω2

1 + 𝑡𝜈Ω𝜕𝜕𝜏

( 𝑐0

𝑣𝑔 ) 𝜕2𝑝𝜕𝜏2

𝐵 =𝜌𝑐𝑆0𝐷2

0

𝜌0𝑐0𝑆𝐷2

𝑐𝑣𝑔0

𝐷0𝑐0𝑣𝑔

𝐷

, 𝑣𝑔 = 𝑐 . �̄� + �̄� , D = 1 +�̄� . �̄�

𝑐, Ω =

1𝐷

𝑑𝑥𝑑𝑡

= �̄� + 𝑐2𝑞𝐷𝑑𝑞𝑑𝑡

= − [ ∇𝑐𝑐𝐷

+ 3

∑𝑖=1

𝑞𝑖 ∇𝑤𝑖] 𝑞 =�̄�

𝑐 + �̄� . �̄�

• Ray Path Equations:


sBOOM • Propagation based on lossy Quasi-1D Burgers equation

Propagation Prediction Code: sBOOM

sBOOM is under active development. Contact [email protected] to get a copy of sBOOM

• Features and capabilities • Under-track, off-track signatures with

winds • Acceleration, turn-rates, climb-rates,

maneuvers and focus predictions by interfacing with Lossy Nonlinear Tricomi Equation (LNTE)

• Design friendly sensitivities and adjoint error estimates

5 January 2020

𝜕𝑝𝜕𝜎

=𝜕𝐵𝜕𝜎

𝐵𝑝 +

𝛽Ω2𝜌0𝑐3

0 ( 𝑐0

𝑣𝑔 ) 𝜕𝑝2

𝜕𝜏+

𝛿Ω2

2𝜌0𝑐30 ( 𝑐0

𝑣𝑔 ) 𝜕2𝑝𝜕𝜏2

+ ∑𝜈

𝑚𝜈

2𝑐0

𝑡𝜈Ω2

1 + 𝑡𝜈Ω𝜕𝜕𝜏

( 𝑐0

𝑣𝑔 ) 𝜕2𝑝𝜕𝜏2

𝐵 =𝜌𝑐𝑆0𝐷2

0

𝜌0𝑐0𝑆𝐷2

𝑐𝑣𝑔0

𝐷0𝑐0𝑣𝑔

𝐷

, 𝑣𝑔 = 𝑐 . �̄� + �̄� , D = 1 +�̄� . �̄�

𝑐, Ω =

1𝐷

𝑑𝑥𝑑𝑡

= �̄� + 𝑐2𝑞𝐷𝑑𝑞𝑑𝑡

= − [ ∇𝑐𝑐𝐷

+ 3

∑𝑖=1

𝑞𝑖 ∇𝑤𝑖] 𝑞 =�̄�

𝑐 + �̄� . �̄�

• Ray Path Equations:


Run Parameters

5 January 2020

• All azimuthal angles run in parallel • Computing platform:

• OSX running macOS Mojave (10.14.6) • CPU: 2.5 GHz i7 • RAM: 16GB, 1600 MHz DDR3

• NASA Langley mid-range computing facility • Single node of SGI ICE Altix Cluster

• No pre-processing of near-field data • Computational run times

• Typical run times for edge-to-edge carpet predictions • ~30 seconds wall-time @ sampling frequency = 100 KHz (16 azimuths) • ~130 seconds wall-time @ sampling frequency = 200 KHz (16 azimuths)

• Sampling frequency determined by adjoint-error correction approach by continuously embedding uniformly refined grid

• 100 KHz sufficient to resolve loudness BSEL to within 0.1 dB • 400 KHz sufficient to resolve loudness BSEL to within 0.02 dB


Case1: Ground Signatures

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Case1: Loudness Metrics

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Measured Atmosphere



5 January 2020

Standard Atmosphere



5 January 2020

Standard Atmosphere

For the measured atmosphere, carpet widths are larger by:

• 28.17 nm on +ve side • 14.03 nm on –ve side


Case2: Loudness Metrics

5 January 2020


• = (1.4121, 0.015681, 0.000359) • Diffraction boundary layer thickness (𝜹) = 682.45m

(𝑀, �̇�, �̈�)Case1: Optional Focus Analysis

5 January 2020

Flight Altitude

𝜹-tangent ray

caustic-tangent ray

(𝑀, �̇�, �̈�)(𝑀𝑛, �̇�𝑛, �̈�𝑛)

caustic




5 January 2020

Flight Altitude

𝜹-tangent ray

caustic-tangent ray

(𝑀, �̇�, �̈�)(𝑀𝑛, �̇�𝑛, �̈�𝑛)

Near-field (Given)

caustic




5 January 2020

Flight Altitude

𝜹-tangent ray

caustic-tangent ray

(𝑀, �̇�, �̈�)(𝑀𝑛, �̇�𝑛, �̈�𝑛)

Near-field (Given)

𝜹

caustic




5 January 2020

Flight Altitude

𝜹-tangent ray

caustic-tangent ray

(𝑀, �̇�, �̈�)(𝑀𝑛, �̇�𝑛, �̈�𝑛)

Computational domain of Lossy NTE

Near-field (Given)

𝜹

caustic


Case1: Optional Focus Analysis

5 January 2020

𝜕2𝑃

𝜕�̄�2 − �̄�𝜕2𝑃𝜕𝜏2

+𝜇2

𝜕2𝑃 2

𝜕𝜏2+ [ 𝛼

𝜀2+ ∑

𝜈

𝜃𝜈 /𝜀2

1 + 𝜏𝜈𝜕 /𝜕𝜏 ] 𝜕3𝑃𝜕𝜏3

= 0

𝜇 = 2𝛽𝑃𝑎𝑐

𝜌0𝑐20 ( 𝑅𝑡𝑜𝑡𝑓𝑎𝑐

2𝑐0 )2/3

𝜀 = ( 2𝑐0

𝑅𝑡𝑜𝑡𝑓𝑎𝑐 )2/3

𝑅𝑡𝑜𝑡 ≈ 𝑅𝑐𝑎𝑢 =2𝛿3𝑓2

𝑎𝑐

𝑐20

Lossy NTE Model Equation as developed by Joe Salamone for the NASA Scamp Project



5 January 2020

𝜕2𝑃

𝜕�̄�2 − �̄�𝜕2𝑃𝜕𝜏2

+𝜇2

𝜕2𝑃 2

𝜕𝜏2+ [ 𝛼

𝜀2+ ∑

𝜈

𝜃𝜈 /𝜀2

1 + 𝜏𝜈𝜕 /𝜕𝜏 ] 𝜕3𝑃𝜕𝜏3

= 0



2𝑐0 )2/3

𝜀 = ( 2𝑐0



𝑎𝑐

𝑐20


Incoming waveform

𝑃𝑎𝑐 = 50.05 Pa𝑓𝑎𝑐 = 6.32 Hz



5 January 2020

𝜕2𝑃

𝜕�̄�2 − �̄�𝜕2𝑃𝜕𝜏2

+𝜇2

𝜕2𝑃 2

𝜕𝜏2+ [ 𝛼

𝜀2+ ∑

𝜈

𝜃𝜈 /𝜀2

1 + 𝜏𝜈𝜕 /𝜕𝜏 ] 𝜕3𝑃𝜕𝜏3

= 0



2𝑐0 )2/3

𝜀 = ( 2𝑐0



𝑎𝑐

𝑐20


Incoming waveform

𝑃𝑎𝑐 = 50.05 Pa𝑓𝑎𝑐 = 6.32 Hz

Zbar=0.0: PL = 97.8 dB

Zbar=0.05: PL = 106.8 dB

Zbar=1.0: PL = 101.0 dB



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• Lossy vs Lossless propagation • Signature Evolution • Modeling Non-linearity • Loudness build-ups • Loudness Gradients

Highlights

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Highlights: Lossless vs Lossy

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Phi = 00



5 January 2020

Phi = 00Phi = -400



5 January 2020

Phi = 00Phi = -400Phi = 400



5 January 2020

Phi = 00Phi = -400Phi = 400

Losses account for significant (~10-12 dB) reduction in loudness metrics


Highlights: Signature Evolution

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Scaling factor: 1𝑃

Vertical Distance from Cruise AltitudeAircraft Length

Under-track



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Under-track

Near-field character maintained over long

distances



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Phi = 400


Highlights: Modeling Non-linearity

5 January 2020

Acoustic Potential formulation vs Poisson Implementation



5 January 2020


“Numerical Simulation of Shock Wave Focusing at Fold Caustics, with application to Sonic Boom”, Marchiano, R., Coulouvrat, F., Grenon, R., JASA, 114, 1758 (2003), doI: 10.1121/1.1610459



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Standard Atmosphere



5 January 2020



Standard Atmosphere

As loudness levels get lower, significant impact of numerical implementation under windy conditions


Highlights: Modeling Wind

5 January 2020

• Based on provided data, there is a large tailwind at the cruise altitude • Tailwind accounts for almost 10% of the speed of sound


Highlights: Modeling Wind

5 January 2020

• Based on provided data, there is a large tailwind at the cruise altitude • Tailwind accounts for almost 10% of the speed of sound

Significant potential for input error


Highlights: Loudness Build-up

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Highlights: Loudness Build-up

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Loudness build-up plots show dominant portion to go after for OML shaping


Highlights: Loudness Gradients

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Highlights: Loudness Gradients

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Adjoint gradients provide a snapshot of what portions of the

near-field are important to minimize boom carpet loudness


Summary• Near-field waveforms propagated using sBOOM • Lateral cut-off azimuths using standard atmospheres are usually quite different

from measured/realistic atmospheres • Lateral cut-off rays in realistic atmospheres can travel far • Could have low grazing angles

• Focus predictions show much higher loudness values than cruise booms (as expected)

• Different implementation of the underlying mechanisms seem to change the underlying characteristics of the ground signatures

• Poisson vs. Acoustic Potential solutions • Wind considerations • As loudness levels get lower, there is potential for numerical noise to

increase • Loudness build-up plots can localize the loudness dominating portions of the

signatures • Loudness gradients provide a snapshot to allow optimization of the OML

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• NASA Commercial Supersonic Technology (CST) Project • Boom prediction workshop organizing committee

Acknowledgments

5 January 2020

SBPW3: sBOOM results 5 January 2020

SBPW3 Propagation Workshop sBOOM Updated · 2020-02-05 · Sriram K. Rallabhandi Aeronautics...

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Transcript of SBPW3 Propagation Workshop sBOOM Updated · 2020-02-05 · Sriram K. Rallabhandi Aeronautics...