Aeromechanics Analysis of a National Aeronautics and Space ...€¦ · Project (Dr. Michael...

1 Aeromechanics Analysis of a Boundary Layer Ingesting Fan!

National Aeronautics and Space Administration!

www.nasa.gov!

Aeromechanics Analysis of a Boundary Layer Ingesting Fan"

presented by!Dr. Milind Bakhle NASA Glenn Research Center!

AIAA-2012-3995 co-authors:!Dr. T. S. R. Reddy (NASA GRC / University of Toledo)!Dr. Gregory P. Herrick (NASA Glenn Research Center)!Dr. Aamir Shabbir and Dr. Razvan V. Florea (United Technologies Research Center)!

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference Atlanta, Georgia, July 29 – August 1, 2012!

https://ntrs.nasa.gov/search.jsp?R=20150010397 2020-06-23T17:44:54+00:00Z


Acknowledgements"

•  This presentation summarizes work performed at NASA Glenn Research Center (GRC) in collaboration with United Technologies Research Center (UTRC)!–  Thanks to Mr. David Arend (Team Lead, Robust Design

of Embedded Engine Systems) and Dr. 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)!

•  Thanks to Ms. Rula Coroneos (NASA GRC) for her support of this task with Nastran finite element analysis!

Aeromechanics Analysis of a Boundary Layer Ingesting Fan!


Outline"

•  Background!•  Fan CFD Analysis – TURBO-AE Code!•  Fan Performance – Clean Inflow, Distorted Inflow!•  Structural Dynamics, Aeroelastic Formulation!•  Inlet Distortion Forced Response, Dynamic Stress!•  Blade Vibrations – Flutter Stability!

–  Clean Inflow!–  Distorted Inflow!

•  Summary and Future Work!



Background"

•  “Wake Ingestion Propulsion Benefits,” L. H. Smith, AIAA Journal of Propulsion and Power, 1993.!

•  Boundary Layer Ingestion (BLI) Propulsion has the potential for significant reduction (5-10%) in Aircraft Fuel Burn!

•  Previous system studies:!Daggett, et al., NASA-CR-2003-212670 !Kawai, et al., NASA-CR-2006-214534 !Plas, et al., AIAA 2007-450 !Nickol, NASA-TM-2008-215112 !Nickol and McCuller, AIAA 2009-931!

•  Recent system studies:!Tillman, et al., AIAA invited pres., 2011!Hardin, et al., AIAA-2012-3993!

4


Technical Challenges"

•  The potential benefits of Boundary Layer Ingestion (BLI) Propulsion can be diminished if key parameters do not meet their targets!–  Inlet total pressure loss!–  Fan efficiency reduction!–  Fan stall margin reduction!

–  Fan aeromechanics requirements(dynamic stresses and flutter stability)!

5


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!


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


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 !

1.05

1.15

1.25

1.35

1.45

1000 1100 1200 1300

Tot

al p

ress

ure

ratio

Inlet corrected mass flow rate, lbm/s

0.60

0.70

0.80

0.90

1.00

1000 1100 1200 1300

Adi

abat

ic e

ffic

ienc

y

Inlet corrected mass flow rate, lbm/s


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!


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)!


Periodicity of Flowfield Around the Rotor"

•  Total pressure ratio for various blade passages!

Variation of total pressure ratio in different blade passages shows flowfield is converged to periodicity

1.30

1.35

1.40

1.45

1.50

1.55

29400 30400 31400 32400 33400 34400

passage 1passage 5passage 10passage 15average

Tot

al p

ress

ure

ratio

Time step counter

1 rotorrevolution


Periodicity of Flowfield Around the Rotor"

•  Total pressure ratio for various blade passages!

Inlet Distortion causes variations in mass flow rate and pressure ratio around the fan rotor

1.30

1.35

1.40

1.45

1.50

1.55

55 60 65 70 75

passage 1passage 5passage 10passage 15average

Tot

al p

ress

ure

ratio

Passage mass flow rate, lbm/s


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


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


Time history over one rotor revolution!

Modal Force"

1,800 time steps per revolution

-4000

-2000

0

2000

4000

0 600 1200 1800

mode 1mode 2mode 3mode 4

Mod

al fo

rce,

lbf

Time step counter


Modal Force"

Fourier components!

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10


Mod

al fo

rce

mag

nitu

de, l

b f

Harmonic number


Campbell Diagram"

EO = engine order

mode 4 close to

7 EO

mode 2 close to

3 EO


0

100

200

300

400

500

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Freq

uenc

y, H

z

Non-dimensional rotational speed

1 EO

2 EO

3 EO

4 EO

8 EO

7 EO

6 EO

5 EO

mode 1

mode 2

mode 3

mode 4

mode 5


Modal Force"

Fourier components!

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10


Mod

al fo

rce

mag

nitu

de, l

b f

Harmonic number

mode 4 close to 7 EO

mode 2 close to 3 EO


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

characteristics (Goodman diagram)!

€

qnr{ } = Kn[ ] −ωr2 Mn[ ][ ]−1 ADnr{ } 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 0.000

0.002

0.004

0.006

0.008

1 2 3 4

qn1qn2qn3qn4

qn5qn6qn7qn8

Gen

eral

ized

dis

plac

emen

t

Mode number


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!


0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12

all bladesaverage

Aer

odyn

amic

dam

ping

, %

Vibration cycle number

no flutter

Flutter Stability with Clean Inflow"

•  Design operating speed, mode 1, 0 nodal diameter pattern (all blades in-phase), 18 blade passages (full rotor)!

mode 1


0

1

2

3

4

5

-9 -6 -3 0 3 6 9

Aer

odyn

amic

dam

ping

, %

Nodal diameter

no flutter


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

mode 1

mode 1



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

odyn

amic

Dam

ping

(%)


mode 1

no flutter


0

1

2

3

4

5

-9 -6 -3 0 3 6 9

near peak efficiencynear stall

Aer

odyn

amic

dam

ping

, %

Nodal diameter

no flutter



mode 3

mode 3


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!



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




0.0

0.4

0.8

1.2

1.6

2.0

0 2 4 6 8 10

0 nodal diameter, all bladesaverage

Aer

odyn

amic

dam

ping

, %


0.0

0.4

0.8

1.2

1.6

2.0

0 3 6 9 12 15 18

0 nodal diameter, all cyclesaverage

Aer

odyn

amic

dam

ping

, %

Blade number




0.0

0.4

0.8

1.2

1.6

2.0

0 3 6 9 12 15 18

1 nodal diameter, all cyclesaverage

Aer

odyn

amic

dam

ping

, %

Blade number

0.0

0.4

0.8

1.2

1.6

2.0

0 2 4 6 8 10

1 nodal diameter, all bladesaverage

Aer

odyn

amic

dam

ping

, %



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 !


Future Work"

•  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!

•  Perform aeromechanical analysis on updated fan stage design including non-axi-symmetric exit guide vanes!

•  Develop inlet-fan coupled aeroelastic analysis capability!


Questions?"

Aeromechanics Analysis of a National Aeronautics and Space ...€¦ · Project (Dr. Michael...

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