Tupolev 154M noise asesment (Анализ шумовых характеристик самолёта Ту-154М)

Tupolev 154M noise asesment (Анализ шумовых характеристик самолёта Ту-154М)

Contents

The Noise Problem

Effects of Noise

1. Hearing Loss

2. Noise Interference

3. Sleep Disturbance

4. Noise Influence on Health

Noise Sources

5. Jet Noise

6. Turbomachinery Noise

Noise Measurement and Rules

7. Noise Effectiveness Forecast (NEF)

8. Effective Perceived Noise Level (EPNL)

Noise Certification

9. Noise limits

Calculations

10. Tupolev 154M Description

11. Noise calculations

1. Take-off Noise Calculation

2. Landing Approach Noise Claculation

Noise Suppression

12. Jet Noise Suppression

13. Duct Linings

1. Duct Lining Calculation

1 The Noise Problem

Though long of concern to neighbors of major airports, aircraft noise

first became a major problem with the introduction of turbojet-powered

commercial aircraft (Tupolev 104, Boeing 707, Dehavilland Comet) in the

late 1950s. It was recognized at the time that the noise levels produced by

turbojet powered aircraft would be unacceptable to persons living under the

take-off pattern of major airports. Accordingly, much effort was devoted to

developing jet noise suppressors, with some modest success. Take-off noise

restrictions were imposed by some airport managements, and nearly all first-

generation turbojet-powered transports were equipped with jet noise

suppressors at a significant cost in weight, thrust, and fuel consumption.

The introduction of the turbofan engine, with its lower jet velocity,

temporarily alleviated the jet noise problem but increased the high-

frequency turbomachinery noise, which became a severe problem on landing

approach as well as on take-off. This noise was reduced somewhat by

choosing proper rotor and stator blade numbers and spacing and by using

engines of the single-mixed-jet type.

2 Effects Of Noise

Noise is often defined as unwanted sound. To gain a satisfactory

understanding of the effects of noise, it would be useful to look briefly

at the physical properties of sound.

Sound is the result of pressure changes in a medium, caused by

vibration or turbulence. The amplitude of these pressure changes is stated

in terms of sound level, and the rapidity with which these changes occur is

the sound's frequency. Sound level is measured in decibels (dB), and sound

frequency is stated in terms of cycles per second or Hertz (Hz). Sound

level in decibels is a logarithmic rather than a linear measure of the

change in pressure with respect to a reference pressure level. A small

increase in decibels can represent a large increase in sound energy.

Technically, an increase of 3 dB represents a doubling of sound energy, and

an increase of 10 dB represents a tenfold increase. The ear, however,

perceives a 10-dB increase as doubling of loudness.

Another important aspect is the duration of the sound, and the way it

is distributed in time. Continuous sounds have little or no variation in

time, varying sounds have differing maximum levels over a period of time,

intermittent sounds are interspersed with quiet periods, and impulsive

sounds are characterized by relatively high sound levels and very short

durations.

The effects of noise are determined mainly by the duration and level

of the noise, but they are also influenced by the frequency. Long-lasting,

high-level sounds are the most damaging to hearing and generally the most

annoying. High-frequency sounds tend to be more hazardous to hearing and

more annoying than low-frequency sounds. The way sounds are distributed in

time is also important, in that intermittent sounds appear to be somewhat

less damaging to hearing than continuous sounds because of the ear's

ability to regenerate during the intervening quiet periods. However,

intermittent and impulsive sounds tend to be more annoying because of their

unpredictability.

Noise has a significant impact on the quality of life, and in that

sense, it is a health problem. The definition of health includes total

physical and mental well-being, as well as the absence of disease. Noise is

recognized as a major threat to human well-being.

The effects of noise are seldom catastrophic, and are often only

transitory, but adverse effects can be cumulative with prolonged or

repeated exposure. Although it often causes discomfort and sometimes pain,

noise does not cause ears to bleed and noise-induced hearing loss usually

takes years to develop. Noise-induced hearing loss can indeed impair the

quality of life, through a reduction in the ability to hear important

sounds and to communicate with family and friends. Some of the other

effects of noise, such as sleep disruption, the masking of speech and

television, and the inability to enjoy one's property or leisure time also

impair the quality of life. In addition, noise can interfere with the

teaching and learning process, disrupt the performance of certain tasks,

and increase the incidence of antisocial behavior. There is also some

evidence that it can adversely affect general health and well-being in the

same manner as chronic stress.

2.1 Hearing Loss

Hearing loss is one of the most obvious and easily quantified effects

of excessive exposure to noise. Its progression, however, is insidious, in

that it usually develops slowly over a long period of time, and the

impairment can reach the handicapping stage before an individual is aware

of what has happened.

Prolonged exposure to noise of a certain frequency pattern can cause

either temporary hearing loss, which disappears in a few hours or days, or

permanent loss. The former is called temporary threshold shift, and the

latter is known as permanent threshold shift.

Temporary threshold shift is generally not damaging to human’s ear

unless it is prolonged. People who work in noisy environments commonly are

victims of temporary threshold shift.

[pic]

Figure 2.1 Temporary threshold shift for rock band performers.

Repeated noise over a long time leads to permanent threshold shift.

This is especially true in industrial applications where people are

subjected to noises of a certain frequency.

There is some disagreement as to the level of noise that should be

allowed for an 8-hour working day. Some researchers and health agencies

insist that 85 dB(A) should be the limit. Industrial noise level

limitations are shown in the Table 2.1.

Table 2.1 Maximum Permissible Industrial Noise Levels By OSHA

(Occupational Safety and Health Act)

|Sound Level, dB(A) |Maximum Duration |

| |During Any |

| |Working Day |

| |(hr) |

|90 |8 |

|92 |6 |

|95 |4 |

|100 |2 |

|105 |1 |

|110 |Ѕ |

|115 |ј |

Noise-induced hearing loss is probably the most well-defined of the

effects of noise. Predictions of hearing loss from various levels of

continuous and varying noise have been extensively researched and are no

longer controversial. Some discussion still remains on the extent to which

intermittencies ameliorate the adverse effects on hearing and the exact

nature of dose-response relationships from impulse noise. It appears that

some members of the population are somewhat more susceptible to noise-

induced hearing loss than others, and there is a growing body of evidence

that certain drugs and chemicals can enhance the auditory hazard from

noise.

Although the incidence of noise-induced hearing loss from industrial

populations is more extensively documented, there is growing evidence of

hearing loss from leisure time activities, especially from sport shooting,

but also from loud music, noisy toys, and other manifestations of our

"civilized" society. Because of the increase in exposure to recreational

noise, the hazard from these sources needs to be more thoroughly evaluated.

Finally, the recent evidence that hearing protective devices do not perform

in actual use the way laboratory tests would imply, lends support to the

need for reevaluating current methods of assessing hearing protector

attenuation.

2.2 Noise Interference

Noise can mask important sounds and disrupt communication between

individuals in a variety of settings. This process can cause anything from

a slight irritation to a serious safety hazard involving an accident or

even a fatality because of the failure to hear the warning sounds of

imminent danger. Such warning sounds can include the approach of a rapidly

moving motor vehicle, or the sound of malfunctioning machinery. For

example, Aviation Safety states that hundreds of accident reports have many

"say again" exchanges between pilots and controllers, although neither side

reports anything wrong with the radios.

Noise can disrupt face-to-face and telephone conversation, and the

enjoyment of radio and television in the home. It can also disrupt

effective communication between teachers and pupils in schools, and can

cause fatigue and vocal strain in those who need to communicate in spite of

the noise. Interference with communication has proved to be one of the most

important components of noise-related annoyance.

Interference with speech communication and other sounds is one of the

most salient components of noise-induced annoyance. The resulting

disruption can constitute anything from an annoyance to a serious safety

hazard, depending on the circumstance.

Criteria for determining acceptable background levels in rooms have also

been expanded and refined, and progress has been made on the development of

effective acoustic warning signals.

It is now dear that hearing protection devices can interfere with the

perception of speech and warning signals, especially when the listener is

hearing impaired, both talker and listener wear the devices, and when

wearers attempt to locate a signal's source.

Noise can interfere with the educational process, and the result has been

dubbed "jet-pause teaching" around some of the nation's noisier airports,

but railroad and traffic noise can also produce scholastic decrements.

2.3 Sleep Disturbance

Noise is one of the most common forms of sleep disturbance, and sleep

disturbance is a critical component of noise-related annoyance. A study

used by EPA in preparing the Levels Document showed that sleep interference

was the most frequently cited activity disrupted by surface vehicle noise

(BBN, 1971). Aircraft none can also cause sleep disruption, especially in

recent years with the escalation of nighttime operations by the air cargo

industry. When sleep disruption becomes chronic, its adverse effects on

health and well-being are well-known.

Noise can cause the sleeper to awaken repeatedly and to report poor

sleep quality the next day, but noise can also produce reactions of which

the individual is unaware. These reactions include changes from heavier to

lighter stages of sleep, reductions in "rapid eye movement" sleep,

increases in body movements during the night, changes in cardiovascular

responses, and mood changes and performance decrements the next day, with

the possibility of more serious effects on health and well-being if it

continues over long periods.

2.4 Noise Influence on Health

Noise has been implicated in the development or exacerbation of a

variety of health problems, ranging from hypertension to psychosis. Some of

these findings are based on carefully controlled laboratory or field

research, but many others are the products of studies that have been

severely criticized by the research community. In either case, obtaining

valid data can be very difficult because of the myriad of intervening

variables that must be controlled, such as age, selection bias, preexisting

health conditions, diet, smoking habits, alcohol consumption, socioeconomic

status, exposure to other agents, and environmental and social stressors.

Additional difficulties lie in the interpretation of the findings,

especially those involving acute effects.

Loud sounds can cause an arousal response in which a series of

reactions occur in the body. Adrenalin is released into the bloodstream;

heart rate, blood pressure, and respiration tend to increase;

gastrointestinal motility is inhibited; peripheral blood vessels constrict;

and muscles tense. Even though noise may have no relationship to danger,

the body will respond automatically to noise as a warning signal.

3 Noise Sources

All noise emanates from unsteadiness – time dependence in the flow. In

aircraft engines there are three main sources of unsteadiness: motion of

the blading relative to the observer, which if supersonic can give rise to

propagation of a sequence of weak shocks, leading to the “buzz saw” noise

of high-bypass turbofans; motion of one set of blades relative to another,

leading to a pure-tome sound (like that from siren) which was dominant on

approach in early turbojets; and turbulence or other fluid instabilities,

which can lead to radiation of sound either through interaction with the

turbomachine blading or other surfaces or from the fluid fluctuations

themselves, as in jet noise.

3.1 Jet Noise

When fluid issues as a jet into a stagnant or more slowly moving

background fluid, the shear between the moving and stationary fluids

results in a fluid-mechanical instability that causes the interface to

break up into vortical structures as indicated in Fig. 3.1. The vortices

travel downstream at a velocity which is between those of the high and low

speed flows, and the characteristics of the noise generated by the jet

depend on whether this propagation velocity is subsonic or supersonic with

respect to the external flow. We consider first the case where it is

subsonic, as is certainly the case for subsonic jets.

[pic]

Figure 3.1 A subsonic jet mixing with ambient air, showing the mixing layer

followed by the fully developed jet.

For the subsonic jets the turbulence in the jet can be viewed as a

distribution of quadrupoles.

3.2 Turbomachinery Noise

Turbomachinery generates noise by producing time-dependent pressure

fluctuations, which can be thought of in first approximation as dipoles

since they result from fluctuations in force on the blades or from passage

of lifting blades past the observer.

It would appear at first that compressors or fans should not radiate

sound due to blade motion unless the blade tip speed is supersonic, but

even low-speed turbomachines do in fact produce a great deal of noise at

the blade passing frequencies.

4 Noise Measurement and Rules

Human response sets the limits on aircraft engine noise. Although the

logarithmic relationship represented by the scale of decibels is a first

approximation to human perception of noise levels, it is not nearly

quantitative enough for either systems optimization or regulation. Much

effort has gone into the development of quantitative indices of noise.

4.1 Noise Effectiveness Forecast (NEF)

It is not the noise output of an aircraft per se that raises

objections from the neighborhood of a major airport, but the total noise

impact of the airport’s operations, which depends on take-off patterns,

frequencies of operation at different times of the day, population

densities, and a host of less obvious things. There have been proposals to

limit the total noise impact of airports, and in effect legal actions have

done so for the most heavily used ones.

One widely accepted measure of noise impact is the Noise

Effectiveness Forecast (NEF), which is arrived at as follows for any

location near an airport:

1. For each event, compute the Effective Perceived Noise Level (EPNL) by

the methods of ICAO Annex 16, as described below.

2. For events occurring between 10 PM and 7 AM, add 10 to the EPNdB.

3. Then NEF = [pic], where the sum is taken over all events in a 24-hour

period. A little ciphering will show that this last calculation is

equivalent to adding the products of sound intensity times time for

all events, then taking the dB equivalent of this. The subtractor 82

is arbitrary.

4.2 Effective Perceived Noise Level (EPNL)

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