Selected Final Results...CEAS BBN Workshop 2008, Bilbao wall flush mounted microphones +1 ref....

1CEAS BBN Workshop 2008, Bilbao EU Framework 6 Research

PROBAND: Improvement of Fan Broadband Noise Prediction: Experimental investigation

and computational modelling

- Selected Final Results -

Lars Enghardt, DLR BerlinProject Coordinator

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CEAS BBN Workshop 2008, Bilbao

EU FP6, Call 2, STREP PROBAND

Consortium:DLR - Deutsches Zentrum für Luft und Raumfahrt (DE) RR - Rolls-Royce plc (UK)SnM - Snecma Moteurs (FR)ECL - Ecole Centrale de Lyon (FR)Flu - Fluorem SAS (FR)ONERA - Office National d’Études et Recherches Aérospatiales (FR)UPMC - Université Pierre et Marie Curie (FR)ISVR - Institute of Sound and Vibration Research (UK) UCAM - University of Cambridge (UK)TUB - Technische Universität Berlin (DE)VKI - Von Karman Institute (BE)UR3 - Università Roma Tre (IT)KTH - Kungliga Tekniska Högskolan (SW)NLR - Nationaal Lucht- en RuimtevaartLaboratorium (NL)ACAT - Anecom Aerotest (DE)

• Budget: 5 M€• Project start: 1. April 2005 • Duration: 3,75 years

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Motivation: Broadband Fan Noise Sources

Interaction mechanism between

• The blade-tip of the rotor fan and the turbulent boundary layer on the inlet-duct (rotor boundary layer interaction noise)

• Turbulent eddies convected in the rotor boundary layer and the rotor trailing edge (rotor self noise)

• The rotor wake and the downstream outlet guide vanes (OGV interaction noise)• Turbulent eddies convected in the vane boundary layer and the vane trailing edge

(OGV self noise)

Rotor boundary layer interaction noise OGV self noise

Rotor self noise OGV interaction noise

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Project Structure

WP1: Co-ordination, specifications

WP2: Single source studies and model development

WP3: Laboratory scale fan rig test : Development of novel

measurement and CFD prediction techniques

WP4: Industrial Fan-OGV noise: Methods Validation

and Demonstration

WP1: Assessment, exploitation

WP2

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WP2: Single source studies and modeldevelopment

Objective• Develop and assess improved existing and future broadband

noise prediction tools

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Features• NACA5510: c =200 mm ; span: 200mm • High lift: 5% camber and 15o AoA• Gap: h~ 10 mm= 5% c • U0= 70 m/s (M~0.2; Rec~9.3 105)• Low turbulence inflow (0.7%)• Incoming TBL: d~ 1.8h (99% thickness)

Variations of parameters: U0 , AoA and h

• TE noise• Tip/casing noise

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1.5

-1

-0.5

0

0.5

1

1.5

2

x/c

-CP

a = 5°

a = 10°

a = 15°

Cp at mid span

Measurements

• PIV, LDA, HWA • Wall pressure• Far field • Combined measurements

Single Airfoil experiment (ECL)

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Implementation

B& K “low cost” ICP -microphones Pressure tube

HW probeGapPin hole

Single Airfoil experiment, unsteady pressure measurements (ECL)

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Steady Flow in gap region : mid-gap sectionU0 = 70 m/s ; a= 15o ; h= 10 mm ;

Single Airfoil experiment, PIV and HWA (ECL)

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Velocity spectra (HWA); gap=10 mmx/c=0.95 ; mid gap

Hump between 1 and 3 kHz and global amplification above 500 Hz

10370

75

80

85

90

95

100

105

110

115

120

PS

D (d

B -

ref 4×

10-1

0 Pa2 )

frequency (Hz)

AoA = 15 deg - U0= 70 m/s : spectra for probe: 29

gap 0gap 1gap 2gap 3gap 5gap 10

Frequency (Hz)

PSD

(dB

–re

f10−

10Pa

2 )

pressure spectrax/c=0.95 ; 1.5 mm from tip

Single Airfoil experiment, unsteady velocity/pressure spectra (ECL)

TIP flowPress. side

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BBN modeling: TE noise model (ECL)

• Mechanism: Pressure perturbations are scattered as acoustic waves at the TE

• The far-field sound pressure PSD is related to the wall-pressure statistics closely upstream of the trailing-edge

• For a large aspect ratio airfoil, this relation comes down to

Convection speed

Wall-pressure spec. Spanwisecoherence scale

Analytical response function

Input from exp. and/or CFD

New: Wall pressure spectrum can be inferred from RANS computed TBL properties [Rozenberg et al (2008)]

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Wall pressure spec. predicted from RANS

Exp. data: Far field

TE model

BBN modeling: Application (ECL)

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Wall pressure spec. predicted from RANS

Exp. data: Far field

TE model

BBN modeling: Application (ECL)

today

tomorrow

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Wavelet analysis of pressure fluctuations (UR3, ECL)

Conditional statistics of pressure or velocity based on localized pressure events extracted using wavelet indicators

Local Intermittency Measure:equivalent to a 2D representation of the Fourier auto-spectrum

(Camussi et al., AIAA 2007-3685, Grilliatet al., AIAA 2008-2845 )

Cross-Wavelet: equivalent to a 2D representation of the Fourier cross-spectrum(Camussi et al., JFM 2008 )

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Averaged signatures (UR3, ECL)

• Oscillations are due to the gap• Event duration scales with U0

1/2

• Potential point-vortex model: pressure induced by co-rotating vortices

• Events are originated at about 50-60% the chord length

• Results confirmed from the far-field pressure conditioning: noise source?

Averaged PIV signatures

Averaged wall-pressure signatures

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Averaged signatures (UR3, ECL)

• Oscillations are due to the gap• Event duration scales with U0

1/2

• Potential point-vortex model: pressure induced by co-rotating vortices

• Events are originated at about 50-60% the chord length

• Results confirmed from the far-field pressure conditioning: noise source?

Averaged PIV signatures

Averaged wall-pressure signatures

today

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• Simulation of boundary layer broadband noise with IDDES

CFD on Selfnoise (TUB)

• grid: 5.3 million cells• 40 cells in span wise

• span wise extent 1cm (d/c = 0.05) • LES like grid on suction side

• dx = 2*dz = 0.5 mm

• coarser grid on pressure side

Vortex structures colored with velocity magnitude (λ2),on slice: visualization of radiated sound (dp/dt)

Grid slice

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→ Simulation shows fully attached resolved boundary layer

– RANS/LES blending inside turbulent boundary layer

→ Interaction of turbulent boundary structures with TE generates broadband noise in the far field

→ broadband noise directivity shows typical dipol directivity

broadband noise directivity in dB from 100 Hz to 30 kHz

Boundary layer analysis at x/c=0.25red: u+- y+ plotblack: blending function RANS/LES(lines – averaged, symbols - instanteneous)


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→ Simulation shows fully attached resolved boundary layer

– RANS/LES blending inside turbulent boundary layer

→ Interaction of turbulent boundary structures with TE generates broadband noise in the far field

→ broadband noise directivity shows typical dipol directivity

broadband noise directivity in dB from 100 Hz to 30 kHz

Boundary layer analysis at x/c=0.25red: u+- y+ plotblack: blending function RANS/LES(lines – averaged, symbols - instanteneous)


today

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LES of a Fan-Tip with gap: characteristics (FLU)

10 mm gap

NACA 5510 : 200 mm chord & height

70 m/s

• Single airfoil configuration with gap,representative of an engine fan-tip / turbulent boundary layer interaction, generator of broadband noise

• 3D N.S. compressible simulation realized at Fluorem with Turb'Flow®

≈ 3 000 000 grid nodesMultiblock structured finite volume Jameson centered spatial scheme 4th orderExplicit 3 steps Runge Kutta of Wray time marching, Δt = 2 10-9 sLES filtered structure function turbulence model (following Ducros, Comte and Lesieur) ‏Computations realized on 16 CPU cores (AMD Opteron® @2400 Mhz) ‏

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• A fully unsteady configuration• Time-averaging of aerodynamic fields• Large tip-vortex flow interaction with incoming

boundary layer + TE vortex shedding: associated to broadband noise sources

LES of a Fan-Tip with gap: aerodynamics (FLU)

Velocity profiles :Mean and ...

Flow

str

uctu

re :

The

tip v

orte

x flo

w... fluctuations(e.g. Ptgap15) ‏

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ListenerProp

agati

on

Different integration surfaces

• Ffowcs Williams and Hawkings (FWH) acoustic analogy associated with a retarded time formulation

• FWH pressure surfaces time series, recorded during

LES of a Fan-Tip with gap: acoustics (FLU)

Surface 0 Surface 1

Surface 3Surface 2

LES computation– Observers

placed on a 2D circle

– Example :

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WP3: Laboratory scale fan rig test : Development of novel measurement and CFD prediction techniques

• Objectives• provide a parametric study on broadband noise sources in a

laboratory-scale fan rig • develop advanced measurement techniques on this fan rig • evaluate the predictions of the broadband noise of the laboratory

fan rig using the RANS/semi-analytic methods and validated LES/DES models

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Low speed scalefan rig (DLR Berlin)

24-blade rotor

16-vanestator

D = 0.5 mMtip = 0.22Re = 220 000

Setup of laboratory scale experiment (DLR)

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Rotor shaft extension to increase rotor-stator gap

32-vanestator


Grid for increased inflow turbulence

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wall flush mountedmicrophones

+1 ref. microphone

inlet

inter-stagesection

pressure side

microphone rakes+ 1 ref. microphone

24-blade rotor 16/32-vane stator

Anechoic termination

throttle

X hot-wire probesrotor & stator

pressure sensors

wall staticpressure sensors

- performance measurements- hot-wire velocity measurements- acoustic measurements- blade unsteady pressure measurements


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Effects on acoustic spectra:

Max. levels near Blade PassingFrequency

Nearly constant decay

Increasing levels with increasing speed

Experimental result: Effect of fan speed (DLR)outlet duct

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0 10 20 30 40 50 60 70 80 90 100 110 120 130engine order

PSD

[dB/

eo]

100% speed 85% speed75% speed65% speed50% speed

Total broadband power vs fan speed

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80

85

90

95

1,65 1,70 1,75 1,80 1,85 1,90 1,95 2,00 2,05

log( fan speed [%] )

PWL

[dB

]

measuredpower fit

2.5tipBBN UP ∝

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Effects on acoustic spectra:

Max. levels near Blade PassingFrequency

Nearly constant decay

Increasing levels with increasing speed

Experimental result: Effect of fan speed (DLR)outlet duct

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50

55

60

65

70

0 10 20 30 40 50 60 70 80 90 100 110 120 130engine order

PSD

[dB/

eo]

100% speed 85% speed75% speed65% speed50% speed

Total broadband power vs fan speed

75

80

85

90

95

1,65 1,70 1,75 1,80 1,85 1,90 1,95 2,00 2,05

log( fan speed [%] )

PWL

[dB

]

measuredpower fit

2.5tipBBN UP ∝

tomorrow

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RANS Calculations for DLR Low Speed Fan (RR)

Centrebody added upstream of rotor blade

RANS study of effect of including upstream centrebody as part of the CFD mesh

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Axial Velocity at plane X2, Downstream of Rotor

Original k-ω/SST k-ω/SST with Centrebody


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Turbulence Energy at plane X2, Downstream of Rotor

Original k-ω/SST k-ω/SST with CentrebodyExperiment


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(Semi)analytical modelling (ISVR)

Upstream PWL Downstream PWL

The broadband noise model was fed with Tu-levels from theexperiments and with the outcome of a RANS calculation.

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(Semi)analytical modelling (ISVR)

Upstream PWL Downstream PWL

The broadband noise model was fed with Tu-levels from theexperiments and with the outcome of a RANS calculation.

today

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LES computations (DLR)

Multi-block structure of the LES mesh

Domain:– Resolves 1 rotor passage and 1

stator passage– Upper and lower boundaries

directly connected (flowassumed periodic)

– Extends 1 rotor chordlengthupstream/downstream of stage

Mesh:– 100x106 cells over 1100 blocks– Span resolved with 600 cells– Tip resolved with 45 cells– Low-Reynolds

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Iso-surfaces of the axial component of vorticity in rotor system.

Rotor leading edge

Rotor tip vortex

Rotor wake region

Stator leading edge

Successive rotor wakes

Iso-surfaces of the axial component of vorticity in stator system.

Rotor trailing edge

Stator trailing edge

LES computations (DLR)

Computed turbulent flow structures

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Rotor-stator interactionClose view of

blade-vane interaction

Iso-surface of Q colored by entropy

LES computations (ONERA)

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Far-field acoustic radiation

0 1 2 3 4 5 67 8 9 10

015

3045

6075

90

05

1015202530354045505560

Frequency (kHz)on Angle (deg)

SP

L (d

B/H

z, re

. 20

µPa)

Radiation Angle (deg)

Input: LES data on OGV


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60

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70

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0 2000 4000 6000 8000 10000Frequency (Hz)

PW

L (d

B/H

z, re

. 1 p

W)

Broadband (test)Mean spectrumAnalytic spectrumCoherent sources

PSD of in-duct sound power


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0 2000 4000 6000 8000 10000Frequency (Hz)

PW

L (d

B/H

z, re

. 1 p

W)

Broadband (test)Mean spectrumAnalytic spectrumCoherent sources

PSD of in-duct sound power


today

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WP4: Industrial Fan-OGV noise: Methods Validation and Demonstration

Objective• Validation and demonstration of the computational methods

developed and assessed in WP2 and WP3

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Setup of industrial fan experiment (ACAT, RR, VKI)

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Pressure measurements on OGV (DLR)

5 dB

Pressure sensor arragement on stator vane surfaces

Variation of total broadband surface autopower levels for five working lines

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stator

intake array

bypass array

rotor

Induct Beamforming (NLR)

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stator

intake array

bypass array

rotor

Induct Beamforming (NLR)

tomorrow

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Fan Blade

High Fan Speed (transonic flow)

k-ω/SST RANS

Wake data extracted on OGV “leading edge plane” Noise Models

Turbulence Energy, k (m2/s2)

Industrial Test Rig RANS result (RR)

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Radius

OGV Leading Edge Peak Turbulence Energy (m2/s2)

Fan Working Line Variation

Hub Casing


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Radius

OGV Leading Edge Peak Turbulence Energy (m2/s2)

Fan Working Line Variation

Hub Casing


today

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CFD of FAN-OGV-ESS: characteristics (FLU)

• Industrial test rig, including rotating fan and two stator vanes (bypass and core ducts) ‏

• Number of blades: FAN=20, OGV=44 modelled by a 1:2 ratio

• 3D N.S. compressible simulation realized at Fluorem with Turb'Flow® :

High fan speed (transonic flow) ‏≈ 6500000 grid nodes, Multiblock structured finite volumeUpwind spatial scheme 3rd order with limiters (because flow field with shocks)‏Explicit 5 steps Runge Kutta time marching with 1500000 Δt per 360° rotation Rotor-stator interactions modeled by a sliding mesh technique using DFTHybrid RANS-Wilcox / LES-WALE (Wall Adapting Large Eddy following Nicoudand Ducros, Flow turbulence and combustion 62:183-200, 1999) ‏Computations realized on 24 CPU cores (AMD Opteron® @2400 Mhz) ‏

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CFD of FAN-OGV-ESS: Mean meridian flow (FLU)

Sample hyb. RANS-LES results :

Azimuthal and temporal averagesof aerodynamic fields

Locations of experimentalmeasurement sectionsin the x-r meridian mesh

Meridian mean total velocities

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CFD of FAN-OGV-ESS: Acoustics (FLU)

Instantaneous velocity divergence

Wake visualizations (entropy) ‏

Pres

sure

and

Vel

ocity

spec

tra

at th

e st

ator

inle

t

Next steps :• Characterization of near field acoustic

sources• Far field noise propagation

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Summary: Final results

• PROBAND enables improved physical understanding of the source mechanisms of self noise, interaction noise, and tip clearance noise. The fundamental experiments provide, in conjunction with advanced CFD, a deeper insight into the flow physics in the source regions.

• PROBAND has developed new tools allowing large scale advanced CFD, and validated them in a realistic experimental environment.

• PROBAND delivers an improved prediction capability for broadbandnoise that will be exploited by the European engine industry to develop low broadband noise fan concepts.

Selected Final Results...CEAS BBN Workshop 2008, Bilbao wall flush mounted microphones +1 ref....

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