Pain Threshold: 130 140 dB Sound Pressure Level above 150 dB:
Acoustic Fatigue Continuous Exposition to 75 dB noise: - Stress; -
Hipertension & Heartbeat increase. Noise Introduction to
Aeroacoustics
Slide 5
Aircraft Noise Predictions: - Steady growth rate of 2 3% per
year - From 1990 to 2015 the number of airplanes will double in
number. Necessary to reduce take-off and landing noise. Aircraft
Noise reduction less that Air traffic Increase Aircraft Noise
Introduction to Aeroacoustics
Slide 6
Easy way to reduce noise in aircraft: - Take-off weight
limitation, by reducing number of passengers, payload and/or fuel.
- Less engine powwer and/or speed Flights less profitable (more
fuel stops and less passengers) Efficient Solution: Prediction
Methods of aircraft noise generation during early design phase.
Aircaft Noise Introduction to Aeroacoustics
Slide 7
Noise nuisance depends on its duration, periodicity, etc. Human
response to noise varies with the noise frequency Units used in
Aviation, taking into account the human ear sensibility and the
specific noise characteristics: dBA A weighted decibel Does not
take into account time variations PNdB Perceived Noise decibel Used
to meadure Aircraft Noise (in particular, it considers the high
pitch noise components of jet engines). EPNdB Effective Perceived
Noise decibel Uses as penalty not only the fundamental frequencies
of jet engines, but also the time duration of the Aircaft flight.
Subjective Units of Noise Resposta relativa (em dB) da escala dBA
Introduction to Aeroacoustics
Slide 8
Worldwide, three Organizations can be singled out for aircraft
certification: ICAO International Civil Aviation Organization
United Nations Agency, for international certification FAA Federal
Aviation Agency FAR Federal Aviation Regulations, divided em parts
JAA Joint Aviation Authorities (European Space) JAA Joint Aviation
Requirements EASA European Aviation Safety Agency Replaced the
former JAA Created in 2003; in full operation in 2008 Aircraft
Authority in European Union (as opposed to JAA, that depended on
each European Nation) Aircraft Noise Certification For noise: FAR
36 JAR 36 EASA - Form 45 Introduction to Aeroacoustics
Slide 9
As Aircraft noise become less popular, FAA proposed in the 70s
a noise certification scheme for all Aircraft, later adopted by
ICAO, using three noise certification reference positions: - Noise
under approach flight; - Noise under take-off (also called
flyover); - Sideline noise, with engines at full power. Noise
limits are dependent on aircraft weight and on the number of
engines. Noise could not exceed 108 EPNdB, which was 6 -10 DB less
than the noise generated by the operating aircraft. Noise
Certification Introduction to Aeroacoustics
Slide 10
Current three stages for Noise Certification: -A Stage I
aircraft generates noise levels during take-off, approach and
sideline, that exceed Stage II limits. - A Stage II aircraft obeys
to the limits given by FAR 36 - C36.5 (a) (2), tendo contudo (Noise
levels above those imposed by limites impostos pelo Stage III.) - A
Stage III aircraft generate noise within the limits given by FAR 36
- C36.5 (a) (3). Stage IV has been introduce, which will force
Aircraft to be quieter. Noise Certification Introduction to
Aeroacoustics
Slide 11
Stage 4 Certification Noise Limits, EPNdB Approach Limit: 98.7
dB Sideline Limit: 94.8 dB Takeoff Limit: 89 dB Measured Approach:
89.8 dB Measured Sideline: 89.1 dB Measured Takeoff: 82.4 dB
Cumulative Margin = 21.2 dB Measured Global Express, EPNdB Stage 3
Certification Noise Limits, EPNdB 282.5 dB Total 261.3 dB Total
Approach Max Limit: 98.7 dB Sideline Max Limit: 94.8 dB Takeoff Max
Limit: 89 dB Maximum = 272.5 dB Total Total Reduction = 10 dB
Cumulative Margin =11.2 dB Noise Certification for Stages III and
IV Introduction to Aeroacoustics
Slide 12
Number of current Aircraft Introduction to Aeroacoustics
Slide 13
Aviation currently accounts for 2-3% of mans contribution to
global warming. Air travel is predicted to increase by 4-5% each
year over the next 20 years. Aviation will have to find ways to
meet the growing demand for civil air transport whilst reducing its
environmental impact, specifically to the level of carbon emission.
The International Air Transport Association vision is for: carbon
neutral growth by 2020, 50% absolute reduction in carbon emission
by 2050 and zero-emission aircraft within 50 years. The aviation
industry in Europe has long recognised this challenge. The Green
Aviation Challenge
Slide 14
In 2001 the Advisory Council for Aeronautical Research in
Europe (ACARE) established the following targets for new aircraft
entering service in 2020 compared to those entering service in
2000: reduce fuel consumption and CO 2 emissions by 50% per
passenger kilometre reduce NO x emissions by 80% reduce perceived
noise by 50% (from European Aeronautics: A Vision for 2020, January
2001) EU 2020 targets: Horizon 2020
Slide 15
The Aircraft flight forces the movement of considerable amounts
of air, which generate high noise levels. Noise Sources - Airframe
Noise - Sonic Boom - Propeller noise - Jet Noise - Helicopter Noise
Airframe Noise - Air flow interacts with all aircraft structures: -
Windows structures (dimensions in centimeters) - Wings and Fuselage
(dimensions in meters) - Broad frequency range (broadband noise),
sendo o Significant Noise increase when landing gear is down.
Aircraft Noise Sources Introduction to Aeroacoustics
Slide 16
Sonic Boom - Noise created by Aircraft flying at supersonic
speed. - Nowadays, only used by military Aircraft (Even the Concord
only flew at Mach >1 over the Oceans). - Supersonic flights over
Land are not allowed by most Countries: Even a sonic boom of a
small aircraft, at a long distance, can have a significant impact
on the human and wild welfare. Introduction to Aeroacoustics
Aircraft Noise Sources
Slide 17
Propeller Noise - Although first Propellers were very noisy, it
was no cause for concern untill WWII. - With the increase of
Turbine Propulsion, Jet Noise became much more relevant. - However
the noise restriction increase Brought a new concern in noise
research, when generated by Propeller Engines. - Noise
characterized by well defined harmonics, that are multiple of BPF
(Blade Passing Frequency) - Monopolar Noise (Thickness Noise) and
Dipolar Noise (Loading Noise): Efficient Sound Sources Introduction
to Aeroacoustics Aircraft Noise Sources
Slide 18
Jet Noise Considerable increase in efficiency, as larger
volumes of air are drawn at considerable less speed. - Bypass
cycle: requires 50% more air per unit of Thrust unit, which reduces
the mean exhaust velocity. - Divides the larger entry airflow into
two almost equal streams, using only one to supply a smaller but
more efficient engine core, which then has the same fairly exhaust
as in pure jet. - Turbo-Fan: Another step forward in efficiency by
even higher levels of bypass flow via a large fan. Lighthill Law:
Introduction to Aeroacoustics Aircraft Noise Sources
Slide 19
Jet Noise As bypass ratio rises and jet velocity falls, so the
external jet mixing noise falls also. Introduction to Aeroacoustics
Aircraft Noise Sources
Slide 20
Helicopter Noise Several characteristics that are different
from Aircraft: - The rotor is aligned with the flight direction,
rather than being normal to it. - BVI (Blade Vortex Interaction)
characteristic noise generated by the blade interaction with the
flow coming from the previous blade. - Tail Rotor Noise. -
Asymmetric noise field: substantial difference in relative tipspeed
between the blade on the advancing side and on the retreating side
of the rotor disc plane, with respect to flight direction.
Introduction to Aeroacoustics Aircraft Noise Sources
Slide 21
Number of passengers tends to increase 4% per year. Given the
continuous increase on the aircraft dimensions, we can predict an
increase of 2-3 % per year on the global number of aircraft. Given
the number of flights, noise increases 1 dB each year. However:
Individual Aircraft Noise tends to decrease. Twin-engine Aircraft
have been replacing Four-Engine Aircraft. (The reliability of the
former even led to their use in transatlantic flights.) Future
Perspectives Introduction to Aeroacoustics