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Phased Array TechnologyApplied to Aeroacoustics
Bob DoughertyPresident, OptiNav, Inc.
15th AIAA/CEAS Aeroacoustics Conference(30th AIAA Aeroacoustics Conference)
13 May 2009Miami, Florida
• Problems• History• Beamforming algorithms• Airframe Noise• Fan Noise• Engine Noise• Jet Noise• Dipole Study from the OptiNav
Aeroacoustic Facility• Conclusions• Postscript (added after the presentation)
Outline
Flap side-edgenoise
Gearnoise
Slat edge noiseSlat gapnoise
Inlet noise:fan, lowpressurecompressor
Aft fan, turbine,combustor andjet noise
Problems:• Locate and isolate the sources• Understand them• Reduce them• Predict the results
History
The Telescope
Hans Lippershey 1608
also
Galileo Galilei 1609
source: Wikipedia
The Radio Telescope
source: WikipediaKarl Guthe Jansky 1931
Astronomical Interferometry
source: Wikipedia
Ryle, M. & Vonberg, D., 1946
VLA: inaugurated in 1980
The Acoustic Telescope J. Billingsley and R. Kinns, “The acoustic telescope”Journal of Sound and Vibration, 48, (4) 485-510, 1976.
Computer: CA1 LSI-2, 48 kilobytes
AIAA JOURNAL VOL. 14, NO. 4, 489-497, APRIL 1976
Laufer, Schlinker, and Kaplan
Jet engine noise source location: The polar correlation techniqueM.J. Fisher, M. Harper-Bourne, and S.A.L. GleggJSV 51(1), 23-54, 8 March 1977.
Fisher, Harper-Bourne and Glegg
Polar Correlation Technique in Context
J. Billingsley, “A comparison of the sourcelocation techniques of the acoustic telescopeand polar correlation,” JSV 61(3), 419-425,1978.
More History• Linear arrays
- Soderman and Nobel, 1974- Billingsley and Kinns, 1976
• Directional mirror microphones, 1976- Grosche, et al, Kendall, Schlinkler,
• Polar correlation technique- Fisher, Harper-Bourne, and Glegg, 1977
• Advanced algorithms- CLEAN: Högbom, 1974- Maximum likelihood: El-Behery & MacPhie, 1978- MUSIC: Schmidt, 1986- Robust adaptive beamforming: Cox, et al, 1987, Gramann & Mocio, 1993- Making cross arrays work: Elias, 1995- DAMAS: Brooks & Humphreys, 2004- CLEAN-SC: Sijtsma, 2007
• Flyover testing-Michel, et al, 1997
• Wind tunnel techniques (spiral arrays, diagonal deletion, ignoring reflections)- Dougherty & Underbrink, 1994
Beamforming Algorithms
Optical Beamforming
Acoustics Beamforming
Time Domain
pn(t) = time-domain pressure at microphone n,n = 1,…, N. (real)
1 2 ... N
Dataacquisitionsystem
noise
Loopthroughgrid points
Delay
Array sum
Color contour plot
Integrate square
n n
Delay
Array data Array data in emission time
( )jn
t !r
"+
!
t
j!r
Case of one source at
Frequency domain
un( t) = pn
!" / 2
" / 2
# (t + t ' )ej$ t'
dt'
narrowbandcomplexpressure
τ = block length ˜ 1-100 ms
1/τ = bandwidth
1 2 ... N
r u t( ) =
u1
t( )
u2
t( )
u3
t( )
...
uN
t( )
!
"
# # # # # #
$
%
& & & & & &
Dataacquisitionsystem
Digital filter
noise
A =
v u
v u
†time average
f (t) =1
Tf (t)dt
0
T
!
T ˜ 20 seconds (limited by disk storage or source motion)
Cross-spectral matrix
Frequency domain data model
v u t( ) =
v C
m
m=1
M
! Sm
t( ) +r n t( ) = C
v S (t) +
r n t( )
Q =
v S (t )
v S
†(t)
ICQCA n
2† !+=
If
and integration is long enough, then
where
Frequency domain beamforming
mmCACmb !!=!vv
†)(
Array design goal
mmmmCC !! " #vv
†
ideally
mmQmb !!=!)(
Nature of a Beamform Map
Nature of a Beamform Map
7 dB dynamic range 20 dB dynamic range
7 dB dynamic range 20 dB dynamic range
1/3 OctaveBands (Toowide fornarrowbandbeamforming)
20 dBdynamicrange
7 dB dynamic range 20 dB dynamic range
1/3 OctaveBands (Toowide fornarrowbandbeamforming)
7 dB dynamicrange
Problem Cases: Two Sources
7 dB dynamic range 20 dB dynamic range
Weaker Source(10 dB down)
Coherent Source
Problem Case: Extended Source
7 dB dynamic range 20 dB dynamic range
Weaker Source Coherent Source
DAMAS, Eigenvalues, CLEAN-SC and TIDY
Goal: explain these buttons
CLEAN IdeaDirty map (initially regular beamforming) Clean map (initially blank)
• Find peak• Move it to clean map• Remove contribution from data and dirty map (removes sidelobes too)
• • •
• Iterate until dirty map is empty• Clean map now contains real sources
- No sidelobes- No peak spreading
Final clean map (result)Final dirty map (empty)
(Högbom, 1974)
Mutually Incoherent Sources
!
A = Qm
r C
m
r C
m
†
m=1
M
" +#n
2I
!
r "
1
!
r "
2
!
r " M map
!
r "
!
r x
1
!
r x
2
!
r x
n
!
r x
N
!
r C
n
r " ( )
Point Spread Function
Array
Beamform Grid
Consider the steering vector as a function of the beamform grid point
!
r C
n
r " ( )
Point Spread Function
!
b (r " )=
1
N2
v C
†r " ( ) A
v C
r " ( )Beamform map:
Assume incoherent sources
!
b (r " )= Qm psf
r " ,
r " m( )
m=1
M
#
where
!
psfr " ,
r " m( )=
v C
†r " ( )
r C m
2
DAMAS
!
Amm'= psf
r m ,
r m'( )=
v C
†r m( )
r C m '
2
!
r x =
Q1
.
.
.
QM map
"
#
$ $ $ $ $ $
%
&
' ' ' ' ' '
!
r y =
br "
1( ).
.
.
br " M map( )
#
$
% % % % % %
&
'
( ( ( ( ( (
!
r y = A
v x
(A is not the CSM on this slide …)
(Brooks and Humphreys)
About DAMAS
• Important advancement in beamforming
• Assumes incoherent sources
• Narrow band
• Requires good estimate of psf
• Very slow in its pure form
• Closely related to other deconvolution methods used in image processing
Effect of DAMAS: Incoherent SourceConventional12 dB dynamic range
Weakersource
Weakersource
DAMAS212 dB dynamic range
Effect of DAMAS: Coherent SourcesConventional
Coherentsource
DAMAS2
Coherentsource
Eigenvalues
!
A = Qm
r C
m
r C
m
†
m=1
M
" +#n
2I
!
A = "n
r V
n
r V
n
†
n=1
N
#
(Schmidt, 1986)
Eigenvalues: Incoherent, First EVConventional
Weakersource
First EV
Weakersource
Eigenvalues: Incoherent, Second EVConventional
Weakersource
Second EV
Weakersource
Eigenvalues: Incoherent, Third EVConventional
Weakersource
Thrid EV
Weakersource
Eigenvalues: Coherent, First EVConventional
Coherentsource
First EV
Coherentsource
Second EV is 27 dB
Move Away from the Assumptionof Mutually Incoherent Sources
CLEAN-SC(Sijtsma)
h is determined so that
!
C j ACmax
= C jGCmax
for all steering vectors Cj.
!
"CSM = Qmax
hh
TIDY(Dougherty 2009)
Similar to CLEAN-SC, but operates in the time domainusing the cross correlation matrix instead of the crossspectral matrix. Wide band.
!
bFD
xm( ) =
1
N2
r C
†x
m( )Ar C x
m( ) =1
N2
Ci
*x
m( )AikC
kx
m( )k= 0
N"1
#i= 0
N"1
#
( ) ( ) ( )!! "= tptpR kiik
!
bTD
xm( ) =
1
N2
s "im( )Rik
t( )s #" km( )k= 0
N#1
$i= 0
N#1
$t= 0
TD, FD relationship for beamforming
!
s "( ) f t( ) = f t # "( )Shift operator
Effect of TIDY: Incoherent SourceConventional12 dB dynamic range
Weakersource
Weakersource
TIDY12 dB dynamic range
Effect of TIDY: Coherent SourcesConventional
Coherentsource
TIDY
Coherentsource
Effect of TIDY: Extended Source
Weaker Source Coherent Source
Conventional TIDY
Bandwidth too large for DAMAS
Other Deconvolution Algorithms
Coherent Source
Conventional TIDY
Bandwidth too large for DAMAS
• Richardson-Lucy and NNLS (image processing)See Ehrenfried & Koop AIAA 2006-2711
• DAMAS-C (Brooks & Humphreys)
• LORE (Ravetta)
• Generalized inverse beam-forming (Suzuki)
Airframe Noise
Wind tunnel testing: setup for a closed jet test
phased array
noise
phased arrays
phased arrayflow
noise
flow
RWS
13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) AIAA 2007-3448A Preliminary Study of Landing Gear Noise in Low-Speed Wind Tunnel
Hiroki URA, Takeshi ITO, Toshimi FUJITA, Akihito IWASAKI, Norihisa ANDO and Jun SATO
URA, ITO, FUJITA,IWASAKI, ANDO and SATO
6.3 kHz7 dB range
Wind tunnel testing: setup for an open jet test
phased array
phased array
free jet nozzle
free jet nozzle
flow
noise
flow
noise
Michel, U., Barsikow, B.,Helbig, J., Hellmig, M., andSchüttpelz, M., “Flyover noisemeasurements on landingaircraft with a microphonearray," AIAA Paper 98-2336,1998,
Michel, U., Barsikow, B.,Helbig, J., Hellmig, M., andSchüttpelz, M., “Flyover noisemeasurements on landingaircraft with a microphonearray," AIAA Paper 98-2336,1998,
AIAA Paper 98-2336, 1998
767 737
Doughery, R. P. , F. W. Wang, E. R. Booth, M. E. Watts, N. Fenichel,and R. E. D’Errico, “Aircraft wake vortex measurements at DenverInternational Airport,” AIAA Paper. 2004-2880, May, 2004.
Fan Noise
Boeing/GE LSAF Test 1993
Boeing/Rolls Royce
Boeing/Pratt&Whitney ICD Array, 1999
-40 -30 -20 -10 0 10 20 30 40
70
75
80
85
90
Spinning order, m
2800 Hz
-40 -30 -20 -10 0 10 20 30 40
68
70
72
74
76
Spinning order, m
2708 Hz
Co-rotating mode Counter-rotating mode
13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) AIAA 2007-3696
Feasibility of In-Duct BeamformingPieter Sijtsma
Sijtsma
Sijtsma
Virtual Rotating Microphone Imaging of Broadband Fan NoiseRobert P. Dougherty and Bruce E. Walker
AIAA-2009-3121
Dougherty and Walker
Dougherty and Walker
Baseline Modified
Dougherty and Walker
Phased Array Noise Source Localization MeasurementsMade on a Williams International FJ44 Engine
Gary G. PodboyNASA Glenn Research Center
Cleveland, OhioU.S.A.
Csaba HorvathASRC Aerospace Corporation
Cleveland, OhioU.S.A.
Presented by Daniel L. Sutliff at15th AIAA/CEAS Aeroacoustics Conference
Miami, FloridaMay 12, 2009
3000 lbf (12500 N) thrust class
16 fan blades
2 spools LP: fan, 3-stage axial comp, 2-stage axial turbine HP: single-stage centrifugal comp, single-stage axial turbine
The Williams FJ44 Engine
Podboy and Horvath
OptiNav Array 48 Phased Array System
48 flush-mounted electretmicrophones
1m x 1m Al plate
Log spiral arrangement
Data reduction options-conventional beamforming-deconvolution methods
Podboy and Horvath
OptiNav Array 48 Phased Array System
Software overlays acoustic source location data on top of photo taken with the camera.
Podboy and Horvath
Peak
Peak – 7
(dB)
10 kHz 1/3rd Octave Beamform Map for Engine at 100% Speed
Podboy and Horvath
1/3rd Octave Beamform Maps for 3 Engine SpeedsPodboy and Horvath
Engine Noise
Noise Source Analysis of an Aeroengine with a New Inverse Method SODIX
Ulf Michel and Stefan Funke
AIAA-2008-2860
Michel and Funke
NASA/Honeywell EVNERT 2006
Phased Array Beamforming with 100-foot Polar Arc Microphones in a Static Engine Noise Test
46th AIAA Aerospace Sciences Meeting and Exhibit 7 - 10 January 2008, Reno, Nevada AIAA 2008-51
Robert P. Dougherty and Jeff M. Mendoza
Dougherty and Mendoza
60% Power, 5° High Frequency Array
dB
Dougherty and Mendoza
Jet Noise
Boeing/Honeywell Cage Array, 1999
800 Hz630 Hz500 Hz
400 Hz250 Hz125 Hz
Cage Array, Baseline Configuration
11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference) 23 - 25 May 2005, Monterey, California AIAA 2005-2842
Phased-array Measurements of Single Flow Hot JetsSang Soo Lee and James Bridges
LOCALIZATION OF MULTIPLE TYPES OF JET NOISE SOURCES
12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference) 8 - 10 May 2006, Cambridge, Massachusetts AIAA 2006-2644
Dimitri Papamoschou and Ali Dadvar
Papamoschou and Dadvar
Supersonic With ShocksImproved Phased Array Imaging of a Model Jet
Robert P. Dougherty and Gary G. Podboy
AIAA-2009-3186
90˚ 40˚Condition 2
Mj = 0.89, Ma = 1.46
St = 0. 071 - 0.14
St = 0.14 - 0.29
St 0.29 - 0.57
St = 0.57 - 1.15
St = 1.15 - 2.30
St = 2.30 - 4.60
40˚
90˚
Condition 2Mj = 0.89, Ma = 1.46
CF (kHz) BF Peak (dB) Array Ave. (dB) TIDY Integ. (dB) Source Loc (diam.)
1 100.0 101.1 101.4 9.2
2 103.5 106.1 105.6 6.6
4 103.1 108.3 107.5 5.4
8 98.9 108.0 106.8 3.5
16 91.3 106.0 104.2 1.8
32 78.2 98.3 92.7 0.8
OASPL 113.6 112.6
CF (kHz) BF Peak (dB) Array Ave. (dB) TIDY Integ. (dB) Source Loc (diam.)
1 119.4 118.5 119.9 8.4
2 122.4 122.3 122.8 5.3
4 122.1 122.5 122.7 3.6
8 115.3 117.5 117.0 2.2
16 105.7 110.9 109.0 1.1
32 90.4 100.7 97.2 0.1
OASPL 126.9 127.3
90˚ 40˚Mj = 1.81, Ts = TambRobert P. Dougherty and Gary G. Podboy
St = .058-.12
St = .12-.23
St = .23-.46
St = 46-.93
St =. 93-1.86
St = 1.86-3.72
Conventional
TIDY
Conventional
TIDY
Underexpanded, Supersonic CaseRobert P. Dougherty and Gary G. Podboy
Dipole Noise StudyOptiNav Aeroacoustic FacilityMay, 2009
OptiNav Aeroacoustic Facility
Vortex SheddingTIDY
Vortexshedding
Shearlayerturbulence
Shop vac noise
Vortex Shedding: Dipole Sound
Vortex Shedding: Dipole Parallel to Array
TIDYConventional
Dipole Beamforming
TIDY, dipoleConventional, dipole
Option in Beamform Interactive
See also: papers by Liu, Quayle and Dowling (and Sijtsma); Suzuki
Shear Layer Noise
N1 = 127 Hz (7620 RPM)dstring = 1.7 mmrHub = 4 cmrTip = 20 cmMtip = 0.46
String TrimmerNoise
!
f =c
c + vs
f0
Receding string
Approaching string
!
vs
31.9 m/s
159.6 m/s
- 31.9 m/s
- 159.6 m/s
Assume c = 344 m/s, St = 0.21
13,467 Hz
3605 Hz
4342 Hz
36,779 Hz
Frequencies14,518 Hz
VortexSheddingFrequency
Doppler ShiftedFrequency
1 2 34Shaft order
StringSpeed
!
f0
= Stvs
d
3940 Hz
19,715 Hz
19,715 Hz
3940 Hz
Conventional
TIDY
X-Dipole
TIDY X-Dipole
Component Models:TIDY Integral
Freq1 Freq2 Time1 Time2 z(m) Mic_Med. Peak_BF Integral xPeak yPeak
6120.6 6491 0 8.3 0.5 71.6 60.9 57.8 98 82
6491 6890.4 0 8.3 0.5 72.6 64.1 63.1 98 78
6890.4 7314.5 0 8.3 0.5 73.7 64.8 64.8 95 75
7314.5 7764.6 0 8.3 0.5 75.4 68.6 68 97 67
7764.6 8226.3 0 8.3 0.5 77.5 73.5 72.9 97 67
8226.3 8698.2 0 8.3 0.5 78.7 72.5 72.2 96 63
8698.2 9197.3 0 8.3 0.5 80.4 73.4 72.6 96 56
9197.3 9724.9 0 8.3 0.5 82.1 75.3 74.1 96 54
9724.9 10282.9 0 8.3 0.5 83.7 76.5 75.7 97 47
10282.9 10872.8 0 8.3 0.5 86.7 81.7 80.9 97 36
10872.8 11496.6 0 8.3 0.5 89.8 84.4 83.4 97 33
11496.6 12156.2 0 8.3 0.5 93.1 87.3 87.2 97 21
12156.2 12891.7 0 8.3 0.5 95.8 91.3 88.7 98 17
12891.7 13712.4 0 8.3 0.5 96 85.2 82.2 98 13
In-Plane String Trimmer Noise(String Components, 1Hz levels)
Approaching,Dipole
Receding,Dipole
Approaching,Monopole
Conclusion
Phased Array Technology is
• Well suited to aeroacoustics
• Nearly indispensable
• Continuously evolving
• Quite practical at this point
PostscriptNotes added after the presentation
• Brian Tester and Ulf Michel have both noted that flyover measurements were reported in: G.P. Howell, A.J. Bradley, M.A. McCormick, and J.D. Brown, “De-Dopplerization and acoustic imaging of aircraft flyover noise measurements,” Journal of Sound and Vibration 105(1) 151-167, 1986.
• Another source of good examples is: L. Brusniak, J.R. Underbrink, and R.W. Stoker, “Acoustic imaging of aircraft noise sources using large aperture phased arrays,” AIAA 2006-2715
