Viscous Aerodynamic Shape Optimization with ...

National Aeronautics and Space Administration

Viscous Aerodynamic Shape Optimization with Installed Propulsion Effects Christopher M. Heath & Jonathan A. Seidel NASA GRC – Cleveland, OH

Sriram K. Rallabhandi NASA LaRC – Hampton, VA

AIAA Aviation Conference Denver, CO June 5-9, 2017

Research Motivation Overland sonic boom challenges supersonic aircraft viability 3-D CFD

Near%Field% Mid%Field% Far%Field%

1-D Burgers’ Eq.

Goal < 74 PLdB

Far%Field%

State-of-the-Art Low-Boom Design Strategies: •

Aero-optimization to match low-boom feasible pressure waveform target

•

Shielded engine installation to minimize impact on sonic boom

Drawbacks: •

Low-boom aero-optimization sacrifices engine performance to meet loudness objective

•

Propulsion integration compromises engine, airframe and/or low-boom performance

2

Research Objectives 1. Perform propulsion-airframe integration, coupling installed inlet performance with engine operation 2. Use aero-propulsion shape optimization to recover sonic boom loudness compromised by engine integration

Approach:

Point of Departure

•

RANS-CFD to design, optimize and characterize inlet performance (1).

•

Computationally install (i.e. airflow match) inlet w/engine cycle (1).

Government Ref. Vehicle – 25D

•

Use installed engine performance to compute throttle setting and nozzle conditions (1).

Ref. airframe (25D) designed w/Euler adjoint-based shape optimization to achieve under-track loudness 160 full-vehicle RANS CFD computations used to generate inlet map

Engine elevated above thick boundary layer along fuselage at Mach 1.6 Figure 8. Near-operating point total pressure recovery plots at various conditions over the flight envelope.

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Inlet Off-Design Analysis & Operation (Step 3) Supersonic Operation (Aux. Doors Closed, ~1.5% Bypass at Mach = 1.6 ) 1.00 Mach = 1.0

Total Pressure Recovery

0.99

Mach = 1.1

0.98

Mach = 1.2

0.97

Mach = 1.3

0.96

Mach = 1.4

0.95

Mach = 1.5

0.94

Mach = 1.6 Engine Operating Pt.

0.93 0.92 0.91 0.90 0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

WActual/WIdeal

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Inlet Off-Design Analysis & Operation (Step 3) Subsonic Operation (Aux. Doors Closed vs. Aux. Doors Open) 1.00

Total Pressure Recovery

0.99 Mach = 0.40, Closed Mach = 0.45, Closed Mach = 0.50, Closed Mach = 0.60, Closed Mach = 0.70, Closed Mach = 0.80, Closed Mach = 0.90, Closed Mach = 1.00, Closed Mach = 0.40, Open Mach = 0.45, Open Mach = 0.50, Open Mach = 0.60, Open Engine Operating Pt.

0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.90 0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

WActual/WIdeal Transition from aux. open to closed possible with comparable recovery

Transition from aux. open to closed severely limits engine mass flow & recovery

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Drag-Constrained Low-Boom Optimization (Step 4) Parameterized Region

Design Vars. – 48 Total

Removed Vertical Tail

§ § § §

Vertical Tail Fairing – 9 DVs Engine OML – 9 DVs Nozzle Plug – 5 DVs Horizontal Tail – 21 DVs § Planform § Camber § Twist § X-Section § Fuselage – 4 DVs

Optimization Problem *

Minimize:

&+,

∗ ) &

Local pressure Target pressure ratio ratio

s.t.:

0.0 < $Mid-Field Pressure Waveforms % < $%,'()(*

Optimizer

(5 Body Lengths Undertrack) 0.004

5 Body Lengths Undertrack 0.003 0.002

Minimize SSE

0.001

ΔP/P0

§ Gradient-Based à SNOPT § Leverage adjoint-based design approach § Provide analytic surface derivatives

! =

$ $ − $% &

%$0 -0.001 -0.002

Low-Boom Target

-0.003

Local Pressure Field

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-0.004 180

190

200

210

220

230

240

250

260

Low-Boom Optimization Results (Step 4) Mid-Field Sonic Boom Grid

Optimized

Baseline

h/L = 1 (1 Body Length)

h/L = 2 (2 Body Lengths)

•

Mach-aligned extruded grid generated using Inflate tool out to 6 body lengths

•

Grid converted to all tetrahedral elements for design

•

Grid size ~165 million cells

Suppressed Suppressed expansion feature expansion in aft signature feature

Result § Converged after 18 major iterations §Figure Merit function 34.8% 15. Baseline (Left) vs.reduced low-boom optimized (Right) Mach number contour plots at cruise. § Optimality decreased ~5 orders of magnitude § Drag constraint active (1.5% CD compromise) § 2.8% decrease in airframe cruise L/D § 2.9 PLdB reduction in undertrack ground loudness

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Mid-field and Propagated Ground Signatures (Step 4) Mid-Field Pressure Waveforms (5 Body Lengths Undertrack)

Propagated Ground Signatures Propagated Ground Signatures 0.5

0.004

Suppressed waveform

0.002

Pressure Change (psf)

0.001

ΔP/P0

0.004

0

0.003

-0.001

0.002

Nearfield Low-Boom Target

ΔP/P0

-0.002 0.001

Baseline

-0.003 0

0.2 0.1 0.0 -0.1 -0.2

0.2

Optimized (75.0 PLdB) Front = 73.12 PLdB, Aft = 71.96 PLdB

0.1 0.0 -0.1 -0.2 -0.3 0

Optimized

-0.001

Baseline (Total = 77.9 PLdB) Front = 73.12 PLdB, Aft = 76.39 PLdB

0.3

0.3

Nearfield Pressure Waveforms (5 Body Lengths Undertrack)

Target (Total = 72.7 PLdB)

0.4

0.4

Pressure Change (psf)

0.003

0.5

50

180

-0.002

190

200

210

220

230

240

250

260

0

50

-0.004 180

Horizontal tail shear, 190 200 210 220 230 240 250 twist, camber added & Axial Distance Along Sensor (m) tip deflected

260

Optimized

100

150

200

Tail fairing nearly removed

Plug nozzle slightly less expanded

Baseline

200

Axial Distance (m)

Axial Distance Along Sensor (m)

-0.003

150

Axial Distance (m)

-0.3

-0.004

100

Subtle expansion & compression features introduced to fuselage

Aft signature perceived loudness reduced by 4.43 dB Forward signature becomes dominant loudness source 13

Conclusions

Ø Viscous aerodynamic shape optimization demonstrated to reduce perceived loudness of a NASA low-boom conceptual aircraft by 2.9 dB Ø Leveraged propulsion effects within the low-boom optimization process

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Conclusions

Ø Applied adjoint-based design to minimize spillage & increase installed inlet cruise recovery by 1.8% Ø Demonstrated multi-fidelity inlet/engine cycle coupling – reducing uncertainty in sonic boom prediction from propulsion effects Ø Limited compromise in airframe CD (~1.5%) and L/D ratio (~2.8%) tolerated to achieve low-boom design 15

Future Work

Ø Re-integrate vertical tail to ensure re-introduction does not significantly compromise propagated loudness Ø Apply adjoint-based anisotropic mesh refinement to initial and final solutions to reduce spatial discretization errors Ø Extend design optimization to include wing and forward fuselage components to better match front end target signature 16

Acknowledgements

NASA’s Commercial Supersonic Technology (CST) Project

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