Acoustic absorption of micro-perforated panels
22
Acoustic absorption of micro-perforated panels Muttalip Temiz Mico Hirschberg Ines Lopez Arteaga
Transcript of Acoustic absorption of micro-perforated panels
Acoustic absorption of
micro-perforated panels
Muttalip Temiz
Mico Hirschberg
Ines Lopez Arteaga
Overview
• What is a micro-perforated panel?
• Why micro-perforated panels in TANGO?
• How does it work?
• History of MPP: from Kirchhoff to Maa
• TANGO results
• Future steps
Micro-perforated panels
What is an MPP?
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Sound absorber made of metal.
Small holes (ø ~ 1 mm ), low
porosity (σ ~ 1%)
Heat and clog resistant.
Why MPPs in TANGO
In a thermoacoustic system, interaction between heat
release and acoustics leads to a feedback mechanism.
Heat
Release
Oscillations
Acoustic
Oscillations
Flow and
Mixture
Perturbations
Results:
• Stability problems
• Efficiency problems
• Noise problems
Possible Solution:
• Minimize the effect of
acoustic oscillations
Why MPPs in TANGO?
• Classical absorbing materials are
impractical.
• Fibrous structure (Flammable),
• Effective at high frequencies (>3000 Hz).
• Micro-Perforated materials are made of
metals.
• Durable,
• Non-flammable,
• Effective at low frequencies,
• Increasing damping characteristics with
flow.
Glass wool
Rock wool
Circular
MPP
Slit MPP
How does an MPP work?
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Oscillating Viscous
Boundary Layers
Acoustic wave
How does an MPP work?
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Viscous Shear
Between Boundary
Layers
Sound Attenuation
How does an MPP work?
Different hole diameters result with different absorption / reflection values.
dp/2 δv
Increasing frequency
Shear number, Sh, proportional to ratio dp/δv
Increasing Shear number
How does an MPP work?
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dp tp
Back Cavity
D
σ=dp2/D2
History
Maa’s impedance model for MPP
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Kirchhoff: harmonically
oscillating flows inside of
a circular tube.
Ingard: harmonically
oscillating flows outside
of a circular tube.
+ =
Maa combined Kirchhoff
and Ingard’s ideas to
model a single perforation.
History
Analytical Expression for Transfer Impedance of MPPs
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Zt= jwtr
01-
2
Sh - j
J1
Sh - j( )J
0Sh - j( )
é
ë
êêê
ù
û
úúú
-1
+2aRS+ jdwr
0
dp
2
Inside the hole Resistive
E.C.
Reactive
E.C.
History
Analytical Expression for Transfer Impedance of MPPs
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Zt= jwtr
01-
2
Sh - j
J1
Sh - j( )J
0Sh - j( )
é
ë
êêê
ù
û
úúú
-1
+2aRS+ jdwr
0
dp
2
Resistive
End-Correction
Coefficient
α=2 or 4
Reactive
End-Correction
Coefficient
δ=1.64
History
Analytical Expression for Transfer Impedance of MPPs
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Zt= jwtr
01-
2
Sh - j
J1
Sh - j( )J
0Sh - j( )
é
ë
êêê
ù
û
úúú
-1
+2aRS+ jdwr
0
dp
2
MAIN PROBLEM: The
value of α changes from
one sample to another*.
* Allam S., Åbom M. Journ. Vib. Acoust.,
133 (3), 2861-2866, 2011
Reactive
End-Correction
Coefficient
δ=1.64
Resistive
End-Correction
Coefficient
α=2 or 4
Example of TANGO Results
Impedance Tube Setup
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D/A
Converter
A/D
Analyzer
DAQ
Card
• Multi-Microphone Method
• Open End Ref. Coef. Measurements
Example of TANGO Results
MPP Samples
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Samples dp [mm] tp [mm] σ [%]
A 0.3 1.0 0.76
B 0.8 1.0 0.74
C 1.6 1.6 0.72
A
B C
Example of TANGO Results
Measurement Procedure
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ZR
= r0c
0
1+ ROE
1- ROE
ZP
= r0c
0
1+ RP
1- RP
Z
t= Z
P- Z
R
Measure Ref. Coef. Translate into Transfer Impedance
Sample
Example of TANGO Results
Non-Dimensional Parameters
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Zt= jwtr
01-
2
Sh - j
J1
Sh - j( )J
0Sh - j( )
é
ë
êêê
ù
û
úúú
-1
+2aRS+ jdwr
0
dp
2
d =Á Z
t{ }- Á Zt{ }
th
wr0d
p2
a =Â Z
t{ }- Â Zt{ }
th
2RS
Sh= dp
w /4n
OBJECTIVE: Estimate α and
δ in terms of non-
dimensional parameters
Example of TANGO Results
Resistive End-Correction Coefficient
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Sample A
Sample B
Sample C
Numerical Fit
Example of TANGO Results
Reactive End-Correction Coefficient
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Sample A
Sample B
Sample C
Numerical Fit
Conclusions & Future Work
Conclusions
α and δ depend only Sh for sharp edge limit.
Limit values of both resistive and reactive end corrections for
high Sh agree with earlier results.
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Conclusions & Future Work
Current work
• Different edge geometries,
(Fillets, chamfers, punched holes, etc.)
• Different hole geometries,
(MPPs with slits)
• Effect of non-linearity.
(High amplitude excitation)
Future work
• Effect of panel flexibility on sound absorption MPP
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Acoustic absorption of
micro-perforated plates
Muttalip Temiz
Mico Hirschberg
Ines Lopez Arteaga
