penn state leverton 1 cd 2013
TRANSCRIPT
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August 2008
Dr John W LevertonLeverton Associates
International
August 2013
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SOUND MEASUREMENTS
METRICS FOR MEASUREMENTAND ANALYSIS OF AIRCRAFT
NOISE
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HearingResponse
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LoudnessPhons
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Equal Loudness Curves ISO 226
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Relationship between loudness in Sonesand loudness level in Phons.
LOUDNESS
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NOISINESSUnit of NOYS used as basisfor EPNdB
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WEIGHTING CURVES
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WEIGHTINGCURVES
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SOUND PRESURE LEVEL (SPL)FREQUENCY & PERIOD
SPL ( Sound Pr essure Level ) = 10 log P 2 = 20 log PPref 2 P ref
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sPL = 10 log (P 2/P ref 2) Sound I ntensi ty or Energy
= 10 log (P/P ref )2
= 20 log (P/P ref )
If Two Equal Sources . Sources SPL = 10 log (P/P ref )2 + 10 log (P/P ref )2
= + 3 dB
If Pressure Doubled
SPL = 20 log (2 x P/P ref )
= + 6 dB
SOUND PRESSURE LEVEL (SPL)
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Summation ofTwo Sources
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Noise Reduction with Distance
6 dB per
doubling orhalving ofdistance
SPL = 20 log (d/d ref)
Doubling of Distance = + 6 dB
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Wavelengths
Wavelengths in Air undernormal conditions
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L A MAXL A
Sound Exposure Level - SEL (L AE )
Often r eferenced:
Single Event Level
Sound Event Level
.... there is also a Single Event Noise Exposure Limit (SENEL) used in California State .
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L A MAXL A
Sound Exposure Level - SEL (L AE )
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Sound Exposure Level - SEL (L AE )
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1/3 Octave Bands / Octave Bands
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PNdB ~PNL
See Handout forNoise Certification
PNL/EPNdBCalculation
Noise
CertificationEPNdB
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EPNdBdB(A)max/dBA M
SEL/L AE
Max Level
10dB
10dB
Measured Noise Levels
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Community Noise Levels
Rotorcraft Flyover
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Ground Reflection of Sound
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Sound Reflection due to Wind
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Sound Reflection due to Temperature
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TypicalNoise / Sound Levels
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TypicalNoise / Sound
Levels
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Flyover Noise / Typical Ambient Noise
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Amplitude vs. Time and Frequency
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VARIATION OF NOISEWITH
TEMPERATUREAND
RELATIVE HUMIDITY
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Variation of 1/3 Octave Spectrum with Distance
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Variation of 1/3 Octave Spectrum with Distance
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ACOUSTIC CHARACTERISTICS
OF ROTORCRAFT
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dB
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Helicopter Noise Sources
Approach
BVI/Blade Slap
can be higherand dominate
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Flyover
+
Takeoff
Helicopter Noise Sources
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Helicopter Noise Sources
Flyover BVI/Blade Slap* not indicate
BVI/Blade Slap = Main Rotor/Main Rotor Tip Vortex Interaction
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MAIN ROTOR TIP VORTEX TRAJECTORIESDURING HOVER AND FORWARD FLIGHT - LYNX
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Narrowband, Frequency or Spectrum Analysis
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Narrowband,Frequency
or SpectrumAnalysis
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Narrowband,
Frequencyor SpectrumAnalysis
BVI/Blade Slap
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Pressure TimeHistory
BVI/Blade Slap
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Hovering Wessex Impact of Wind
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Time History BVI/Blade Slap
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Flyover Time History
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Generalized dB(A) Flyover Time History
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Helicopter with no HSI, no BVI, no TRIand low Tail Rotor (TR) Noise
HSI High Speed Impulsive Noise / Thickness Noise
Generalized dB(A) Flyover Time History
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Helicopter with High Levels of HSI, BVI,Tail Rotor (TR) and/or TRI Noise
TRI or Tail Rotor (TR) Noise
Helicopter with no HSI, no BVI, no TRIand low Tail Rotor (TR) Noise
HSI High Speed Impulsive Noise / Thickness NoiseBVI Blade Vortex Interaction (Blade Slap)
TRI - Tail Rotor (Main Rotor Wake) Interaction
Flyover Noise
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Helicopter with High Levels of HSI, BVI,Tail Rotor (TR) and/or TRI Noise
TRI or Tail Rotor (TR) Noise
Helicopter with no HSI, no BVI, no TRI
and low Tail Rotor (TR) Noise
Flyover Noise High HSI/Thickness Noise or BVI/Blade Slap
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Helicopter with High Levels of HSI, BVI,Tail Rotor (TR) and/or TRI Noise
TRI or Tail Rotor (TR) Noise
Helicopter with no HSI, no BVI, no TRIand low Tail Rotor (TR) Noise
Flyover Noise High Tail Rotor Noise
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Helicopter with High Levels of HSI, BVI,Tail Rotor (TR) and/or TRI Noise
TRI or Tail Rotor (TR) Noise
Helicopter with no HSI, no BVI, no TRIand low Tail Rotor (TR) Noise
Flyover Noise Public Acceptance
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ROTOR NOISE GENERATION
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ROTATIONAL NOISE
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FUNDAMENTAL (1st Harmonic)
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Rotational NoiseHarmonic Level (SPL)
vs. Thrust
* 160 RPM - 461 ft/sec 205 RPM - 593 ft/sec
230 RPM 670 ft/sec
260 RPM 758 ft/sec
T 2 = (Thrust) 2
T 2 = (Thrust) 2
T 0 = Independent of Thrust
160 RPM461 ft/sec
260 RPM758 ft/sec
FUNDAMENTAL (1st Harmonic)
5th Harmonic
10th Harmonic
20th Harmonic
30th Harmonic
2 BLADED S-55 ROTOR
Rotational Noise
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Rotational NoiseHarmonic Level (SPL) vs. Rotor Tip Speed
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Rotational NoiseHarmonic Level (SPL) vs. Rotor
Tip Speed
o 0 lbs
700 lbs
+ 1850 lbs
x 3050 lbs
2 BLADED S-55 ROTOR
V12
V6
758
0 lbs
3050 lbs
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Main Rotor Rotational Noise Harmonic ;Fall- off
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Rotational Noise
Directivity
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LOW FREQUENCYBROADBAND NOISE
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Broadband Noise Spectra
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Low Frequency Broadband Noise Analysis Model
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Low Frequency
Broadband Noise
Flat SPL vs. Thrust
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Low FrequencyBroadband Noise
Flat SPL vs. Tip Speed
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Low FrequencyBroadband Noise
and
Total (Overall)
Rotor NoiseNoise Directivi ty
2 Bladed (S55) Rotor250 ft radius
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ROTOR ACOUSTICSTHEORETICAL ASPECTS
Acoustics Theory
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Lighthill (1952)
redefined by Ffowcs-Williams and Hawkings (1969)
Acoustics Theory
Acoustics Theory
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Lighthill (1952)
redefined by Ffowcs-Williams and Hawkings (1969)
Acoustics Theory
Aerodynamic Sound = Monopole + Dipole + Quadrupole Sources
Monopole blade volume or thickness noise
Dipole blade ( fluctuating ) force or lift noise
Quadrupole - high speed effect s: transonic compressibility
flow, shock and viscous flow
Acoustics Theory
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Lighthill (1952)
redefined by Ffowcs-Williams and Hawkings (1969)
Acoustics Theory
Dipole Source
where: r = distance from observer to sourceco = speed of sound
Fi = fluctuating force(t-r/c o) = retarded time
Acoustics Theory
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Lighthill (1952)
redefined by Ffowcs-Williams and Hawkings (1969)
Acoustics Theory
Dipole Source far field
where: Ls = loading per unit spanxn = coordinate normal to the span.
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BladeLoading
Blade Loading
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R i l N i P di i
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Rotational Noise Prediction
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BladeLoading(Force)
NoisePredictions
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Directivity Moving Dipole
Rotor Wake Calculation
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Rotor Wake Calculation
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MAIN ROTOR TIP VORTEX TRAJECTORIESDURING HOVER AND FORWARD FLIGHT - LYNX
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Wake Modeling
Fluctuating Load and Acoustic Pressure Calculations
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Fluctuating Load and Acoustic Pressure Calculations
[Westland H elicopters Ltd]
BVI/Blade Slap Calculations
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Peak Pressure Directivity6 descent/ 70 knots
Forward Speedvs.
Descent Angle
Thickness Noise
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Thickness Noise
Thickness Noise
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Thickness Noise
Prediction
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ThicknessNoise
Predictions
HSI/Thickness Noise - Directivity
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S / c ess o se ect v ty
Peak Acoustic Pressure
143 knot level flight
0
10
20
30
40
50
60
70
80
90
100
centreline
Vertical Directivity
P di ti A
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Prediction Accuracy