penn state leverton 1 cd 2013

8/12/2019 Penn State Leverton 1 CD 2013

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Penn State August 2013Leverton Associates International

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



NOISINESSUnit of NOYS used as basisfor EPNdB



WEIGHTING CURVES



WEIGHTINGCURVES



SOUND PRESURE LEVEL (SPL)FREQUENCY & PERIOD

SPL ( Sound Pr essure Level ) = 10 log P 2 = 20 log PPref 2 P ref



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)



Summation ofTwo Sources



Noise Reduction with Distance

6 dB per

doubling orhalving ofdistance

SPL = 20 log (d/d ref)

Doubling of Distance = + 6 dB



Wavelengths

Wavelengths in Air undernormal conditions



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 .



L A MAXL A




1/3 Octave Bands / Octave Bands



PNdB ~PNL

See Handout forNoise Certification

PNL/EPNdBCalculation

Noise

CertificationEPNdB



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



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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


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 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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Flyover Noise High Tail Rotor Noise


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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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Penn State August 2013Leverton Associates InternationalBlade Tip Mach Number

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)


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)


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)


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

penn state leverton 1 cd 2013

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