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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
National Aeronautics and Space Administration!
www.nasa.gov!
High-Fidelity Analysis of a Boundary Layer Ingesting Fan"Dr. Milind Bakhle
Aerospace Engineer"NASA Glenn Research Center"
2012 Technical Conference NASA Fundamental Aeronautics Program !Subsonic Fixed Wing Project!Cleveland, OH, March 13-15, 2012!
Dr. T. S. Reddy (NASA GRC / University of Toledo)"Dr. Gregory Herrick (NASA GRC)"Ms. Rula Coroneos (NASA GRC)"Dr. Razvan Florea, Dr. Aamir Shabbir, Dr. Steve Lozyniak, Dr. Dmytro Voytovych, and Mr. Mark Stucky (United Technologies Research Center)"
https://ntrs.nasa.gov/search.jsp?R=20150010396 2020-06-23T17:42:40+00:00Z
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Acknowledgements"
• This presentation summarizes work performed at NASA Glenn Research Center (GRC) in collaboration with United Technologies Research Center (UTRC)!– Thanks to David Arend (Team Lead, Robust Design of
Embedded Engine Systems) and Gregory Tillman (UTRC Team Lead)!
• This work was supported by the Subsonic Fixed Wing Project (Dr. Michael Hathaway, Tech Lead for Efficient Propulsion and Power) and by the Environmentally Responsible Aviation Project (Dr. Kenneth Suder, Propulsion Sub-project Manager)!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Outline"
• Background & Technical Challenges!• Goals and Objectives!• Fan CFD Analysis – TURBO-AE Code!• Fan Performance – Clean Inflow, Distorted Inflow!• Aeroelastic Formulation!• Structural Dynamics!• Inlet Distortion Forced Response, Dynamic Stress!• Blade Vibrations – Flutter Stability!
– Clean Inflow!– Distorted Inflow!
• Summary and Future Work!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Background"
• Boundary Layer Ingestion (BLI) Propulsion has the potential for significant reduction in Aircraft Fuel Burn (5-10%)!
• Previous studies referenced in 2011 FAP presentation by Razvan Florea:!
Bangert, et al., NASA-CR-3743 (1983) !Daggett, et al., NASA-CR-2003-212670 !Berrier, NASA-TP-2005-213766 !Campbell, AIAA 2005-0459 !Kawai, et al., NASA-CR-2006-214534 !Carter, AIAA JOA 2006, Vol 43, No. 5 !Plas, MIT PhD Thesis 2006 !Plas, et al., AIAA 2007-450 !Kawai, NASA-CR-2008-215141 !Nikol, NASA-TM-2008-215112 !Drela, AIAA 2009-3762 !Nikol, McCuller, AIAA 2009-931 !
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Technical Challenges"
• The potential benefits of Boundary Layer Ingestion (BLI) Propulsion can be diminished by considerations of!– Inlet total pressure loss!– Fan efficiency reduction!– Fan stall margin reduction!– Fan aeromechanics
(dynamic stresses and flutter stability)!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Optimization-Based Parametric Inlet Design"
Aerodynamic Interface Plane (AIP) total pressure contours
• Inlet excess pressure loss reduced ~4-5x relative to original Inlet A starting point • Dominant distortion harmonic amplitudes reduced ~30-50% relative to original
Inlet A starting point
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fan Efficiency with Distortion-Optimized Inlet"
Inlet significantly improves fan interaction with incoming distortion
Inlet enables fan to meet performance
target
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Excursions in Fan Blade Leading Edge Relative Incidence from Clean Inflow
Fan Efficiency Reduction (%)
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fan CFD Analysis – TURBO Code"
• Implicit, finite-volume solver!• Reynolds-Averaged Navier Stokes equations!• Structured multi-block code!• Multi blade-row code!• k-epsilon turbulence model!• Inlet distortion boundary condition!• Throttle exit boundary condition!
• Dynamic grid deformation for blade vibration!• Prescribed harmonic blade vibrations with energy method
to evaluate flutter stability!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fan Computational Domain"
• Analysis of an Aero Design Iteration (not the Final Design)!
• H, O, and C blocksof mesh generated by UTRC!
Fan rotor blade
Core-bypass splitter
case
hub Inlet boundary
Exit boundary
Exit boundary
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fan Performance – Clean Inflow"
• TURBO code (RANS solver) used with radial inlet profile of total pressure, total temperature, and flow angles!
• Speedline traversed by setting exit throttle condition and converging flow solutions !
1.25
1.30
1.35
1.40
1.45
1000 1100 1200 1300
Tota
l Pre
ssur
e R
atio
Inlet Corrected Mass Flow Rate (lbm/s)
TURBO
84%
88%
92%
96%
1000 1100 1200 1300
Adi
abat
ic E
ffici
ency
Inlet Corrected Mass Flow Rate (lbm/s)
TURBO
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Inlet Flowfield Provides Distortion Pattern"
• Inlet flow computations were performed at UTRC for an inlet design iteration (not final design) and the flowfield results were provided to NASA!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fan Computation with Inlet Distortion"
• Inlet distortion is prescribed as boundary condition at inlet boundary of the fan computational domain (18-blade fan rotor and splitter)!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Periodicity of Flowfield Around the Rotor"
• Total pressure ratio for various blade passages!
Time Step Counter
Tota
l Pre
ssur
e R
atio
1 rotor revolution
Variation of total pressure ratio in different blade passages shows flowfield is converged to periodicity
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Periodicity of Flowfield Around the Rotor"
• Total pressure ratio for various blade passages!
Mass Flow Rate (lbm/s)
Tota
l Pre
ssur
e R
atio
Inlet Distortion causes variations in mass flow rate and pressure ratio around the fan rotor
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Aeroelastic Formulation"
• Blade structural dynamics modal equations with aerodynamic load!
€
ADi =r δ i ⋅ pd
r A ∫
{AD} is the motion-independent aerodynamic load vector – Modal Force
€
q{ } = K[ ] −ω 2 M[ ][ ]−1
AD{ } Forced Response
€
M[ ] ˙ ̇ q { } + K[ ] q{ } = AD{ }
Modal Force computation requires unsteady pressure and modal displacements
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Structural Dynamics Model & Results"
Blade structural model created based on aero design iteration (structural design is in progress)!• 8-node brick elements!• 9,782 elements, 15,096 nodes!• 222 nodes at the root constrained!
mode 1 63.5 Hz
mode 2 156.6 Hz
mode 3 224.8 Hz
mode 4 346.6 Hz
Blade Vibration Modes or Modal Displacements
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Time history over one rotor revolution!
Time Step Counter
Forc
e, lb
f
1,800 time steps per revolution
Modal Force"
1,800 time steps per revolution
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Modal Force"
Fourier components!
0
100
200
300
400
500
600
700
1 2 3 4 5 6 7 8 9 10
mode 1mode 2mode 3mode 4
leve
l
Harmonic Number
Mag
nitu
de, l
b f
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Campbell Diagram"
EO = engine order
mode 4 close to
7 EO
mode 2 close to
3 EO
Freq
uenc
y (H
z)
Non-dimensional Rotational speed
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Modal Force"M
agni
tude
, lb f
0
100
200
300
400
500
600
700
1 2 3 4 5 6 7 8 9 10
mode 1mode 2mode 3mode 4
leve
l
Harmonic Number
mode 4 close to 7 EO
mode 2 close to 3 EO
Fourier components!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Forced Response – Vibration Amplitude and Dynamic Stresses"• Dynamic stresses are required to determine fatigue
characteristics (Goodman diagram)!
€
qnr{ } = Kn[ ] −ωr2 Mn[ ][ ]−1 ADnr{ }
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for nth mode, rth harmonic
€
σ r = Σnsnqnr where sn is the modal stress dynamic stress
harmonic or engine order
vibration amplitude (inch) at tip t.e.
dynamic stress amplitude (psi)
1 5.5 x 10-2 273 2 3.0 x 10-2 290 3 1.9 x 10-2 666 4 3.1 x 10-3 308 5 2.6 x 10-3 169 6 2.7 x 10-4 33 7 7.0 x 10-4 427 8 6.0 x 10-5 19
€
qnr
1 2 3 4
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Flow Chart for Flutter Stability Computation"
• Aerodynamic damping computation using TURBO-AE!
Configuration!€
X = X0ei(ωt+ φ )Prescribe Blade Motion
Calculate Aerodynamic Damping
γ = −W8πKE
€
W = − p.d A→
surface∫∫ • (∂ X
→
∂t)dt
Calculate Work!(for all ω and φ of interest)
Mode Shape!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Flutter Stability with Clean Inflow"
• Design operating speed, mode 1, 0 nodal diameter pattern (all blades in-phase), 18 blade passages (full rotor)!
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12
aedamp_15185_1p0_18psgs
bladesaverage
% a
ero
dam
ping
cycleVibration Cycle Number
Aer
o D
ampi
ng (%
)
mode 1
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
0%
1%
2%
3%
4%
5%
-9 -6 -3 0 3 6 9
Aer
o D
ampi
ng
Nodal Diameter (ND)
Flutter Stability with Clean Inflow"
• Design operating speed, 18 blade passages (full rotor)!• Phase angle of vibration = 360 * Nodal Diameter / 18!
mode 1
mode 1
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
• Design operating speed, 18 blade passages (full rotor)!• Phase angle of vibration = 360 * Nodal Diameter / 18!
0
0.5
1
1.5
2
-3 -2 -1 0 1 2 3
throttle conditions: (15,185);(15,155)split O used
aero
dyna
mic
dam
ping
, %
Nodal Diameter
(15,185)
(15,155)Decreasing Mass Flow Rate along Speedline
Nodal Diameter
Aer
o D
ampi
ng (%
)
Flutter Stability with Clean Inflow"
mode 1
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
0%
1%
2%
3%
4%
5%
-9 -6 -3 0 3 6 9
Aer
o D
ampi
ng
Nodal Diameter (ND)"
Flutter Stability with Clean Inflow"
• Design operating speed, 18 blade passages (full rotor)!• Phase angle of vibration = 360 * Nodal Diameter / 18!
mode 3
Low Mass Flow Rate
mode 3
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Fast-Running Aeroelastic Analysis"
• Harmonic Balance CFD Method!• Fourier series expansion
substituted into governing equations and solved for each harmonic component [Hall, 2000]!
• Lax-Wendroff method!• 2nd and 4th order smoothing for stability!• Non-reflecting boundary conditions!• Spalart-Allmaras turbulence model!• Eigenvalue analysis to calculate aerodynamic damping!
€
U(x,t) ≈ ˆ U n (x)e jnωt
n=−N
N
∑
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
0 1 2 3 4 5
Aer
odyn
amic
Dam
ping
Nodal Diameter
Harmonic Balance Results – Clean Inflow"
Decreasing Mass Flow Rate along Speedline
mode 1
design speed
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Flutter Stability with Distorted Inflow"
Various Approaches"• Circumferentially average the distorted inflow to obtain an
equivalent radial profile; use work-per-cycle analysis!• Select a portion of the inlet distortion to represent a “worst-
case” inflow condition that is used at all circumferential locations; use work-per-cycle analysis!
• Prescribe blade vibrations and distorted inflow; use work-per-cycle analysis; average the results over all blades, and over multiple blade vibration cycles!
• Use tightly-coupled aeroelastic analysis with distorted inflow; blade vibrations are determined as part of the computations; post-process time history to estimate average damping over all blades and multiple vibration cycles!
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Flutter Stability with Distorted Inflow"
Current Preferred Approach"• Prescribe blade vibrations and distorted inflow!• Use work-per-cycle analysis!• Average the results over all blades, and over multiple blade
vibration cycles!
€
Work = −p.d A→
surface∫cycle∫ • (∂ X→
∂t) dt
Unsteady pressure includes effect of 1) inlet distortion 2) blade vibration isolate this component to
assess flutter stability
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Flutter Stability with Distorted Inflow"
• Design operating speed, mode 1, 0 nodal diameter pattern (all blades in-phase), 18 blade passages (full rotor)!
mode 1
Vibration Cycle Number
Aer
o D
ampi
ng (%
)
clean inflow distorted inflow
no flutter
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Summary"
• Created structural model based on aero design iteration and computed structural dynamics characteristics!
• Performed aeromechanical analysis of design iteration!• Performed fan flutter analysis with clean inflow at design
speed – no flutter encountered at conditions analyzed; additional work needed at part-speed conditions!
• Performed distorted inflow analysis for forced response vibrations to determine dynamic stress at design speed – additional work needed at on-resonance conditions near design speed!
• Performed initial analysis with blade vibrations and distorted inflow to estimate flutter stability – additional flutter analyses needed for other vibration modes and operating conditions !
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Fundamental Aeronautics Program!Subsonic Fixed Wing Project!
Future Work"
• Extend computational domain to include fan exit guide vanes in the unsteady aerodynamics analysis!
• Perform aeromechanical analysis on updated fan stage design with non-axi-symmetric exit guide vanes!
• Perform aeromechanical analysis on final inlet-fan design to ensure safe wind-tunnel test!
• Develop tightly-coupled aeroelastic analysis capability in TURBO for more detailed analysis of blade vibrations with distorted inflow!
• Develop inlet-fan coupled aeroelastic analysis capability!