National Aeronautics and Space Administration High ...€¦ · National Aeronautics and Space...

1

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

2


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)!

3


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!

4


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 !

4

5


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)!

5

6


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

7


Fan Efficiency with Distortion-Optimized Inlet"

Inlet significantly improves fan interaction with incoming distortion

Inlet enables fan to meet performance

target

7

Excursions in Fan Blade Leading Edge Relative Incidence from Clean Inflow

Fan Efficiency Reduction (%)

8


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!

9


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

10


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

11


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!

12


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)!

13


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

14


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

15


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

16


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

17


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

18


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

19


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

20


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!

21


Forced Response – Vibration Amplitude and Dynamic Stresses"•  Dynamic stresses are required to determine fatigue

characteristics (Goodman diagram)!

€

qnr{ } = Kn[ ] −ωr2 Mn[ ][ ]−1 ADnr{ }

21

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

22


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!

23


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

24


0%

1%

2%

3%

4%

5%

-9 -6 -3 0 3 6 9

Aer

o D

ampi

ng

Nodal Diameter (ND)


•  Design operating speed, 18 blade passages (full rotor)!•  Phase angle of vibration = 360 * Nodal Diameter / 18!

mode 1

mode 1

no flutter

25



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 (%

)


mode 1

no flutter

26


0%

1%

2%

3%

4%

5%

-9 -6 -3 0 3 6 9

Aer

o D

ampi

ng

Nodal Diameter (ND)"



mode 3

Low Mass Flow Rate

mode 3

no flutter

27


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

∑

28


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

29


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!

30



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

31



•  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

32


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 !

33


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!

34


Your Title Here 34

Date post:	16-Jun-2020
Category:	Documents
Upload:	others
View:	8 times
Download:	1 times

National Aeronautics and Space Administration High ...€¦ · National Aeronautics and Space...

Documents