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

The perceived noisiness of an aircraft flyover depends on the

frequency content, relative to the ear’s response, and on the duration. The

perceived noisiness is measured in NOYs (unit of perceived noisiness) and

is plotted as a function of sound pressure level and frequency for random

noise in Fig. 4.1.


Figure 4.1 Perceived noisiness as a function of frequency and sound

pressure level

Pure tones (frequencies with pressure levels much higher than that of the

neighboring random noise in the sound spectrum) are judged to be more

annoying than an equal sound pressure in random noise, so a “tone

correction” is added to their perceived noise level. A “duration

correction” represents the idea that the total noise impact depends on the

integral of sound intensity over time for a given event.

The 24 one-third octave bands of sound pressure level (SPL) are

converted to perceived noisiness by means of a noy table.


Figure 4.2 Perceived noise level as a function of NOYs

Conceptually, the calculation of EPNL involves the following steps.

1. Determine the NOY level for each band and sum them by the relation


where k denotes an interval in time, i denotes the several frequency

bande, and n(k) is the NOY level of the noisiest band. This reflects

the “masking” of lesser bands by the noisiest.

2. The total PNL is then PNL(k) = 40 + 33.3 log10N(k).

3. Apply a tone correction c(k) by identifying the pure tones and adding

to PNL an amount ranging from 0 to 6.6 dB, depending on the frequency

of the tone and its amplitude relative to neighboring bands.

4. Apply a duration correction according to EPNL = PNLTM + D, where PNLTM

is the maximum PNL for any of the time intervals. Here


where (t = 0.5 sec, T = 10 sec, and d is the time over which PNLT

exceeds PNLTM – 10 dB. This amounts to integrating the sound pressure

level over the time during which it exceeds its peak value minus 10

dB, then converting the result to decibels.

All turbofan-powered transport aircraft must comply at certification with

EPNL limits for measuring points which are spoken about in the next


5 Noise Certification

The increasing volume of air traffic resulted in unacceptable noise

exposures near major urban airfields in the late 1960s, leading to a great

public pressure for noise control. This pressure, and advancing technology,

led to ICAO Annex 16, AP-36, Joint Aviation Regulation Part 36 (JAR-36) and

Federal Aviation Rule Part 36 (FAR-36), which set maximum take-off, landing

and “sideline” noise levels for certification of new turbofan-powered

aircraft. It is through the need to satisfy this rule that the noise issue

influences the design and operation of aircraft engines. A little more

general background of the noise problem may be helpful in establishing the

context of engine noise control.

The FAA issued FAR-36 (which establishes the limits on take-off,

approach, and sideline noise for individual aircraft), followed by ICAO

issuing its Annex 16 Part 2, and JAA issuing JAR-36. These rules have since

been revised several times, reflecting both improvements in technology and

continuing pressure to reduce noise. As of this writing, the rules are

enunciated as three progressive stages of noise certification. The noise

limits are stated in terms of measurements at three measuring stations, as

shown in Fig. 5.1: under the approach path 2000 m before touchdown, under

the take-off path 6500 m from the start of the take-off roll, and at the

point of maximum noise along the sides of the runway at a distance of 450



Figure 5.1 Schematic of airport runway showing approach, take-off, and

sideline noise measurement stations.

The noise of any given aircraft at the approach and take-off stations

depends both on the engines and on the aircraft’s performance, operational

procedures, and loading, since the power settings and the altitude of the

aircraft may vary.

The sideline station is more representative of the intrinsic take-off

noise characteristics of the engine, since the engine is at full throttle

and the station is nearly at a fixed distance from the aircraft. The actual

distance depends on the altitude the aircraft has attained when it produced

maximum noise along the designated measuring line. Since FAR-36 and

international rules set by the International Civil Aviation Organization

(ICAO annex 16, Part 2) which are generally consistent with it have been in

force, airport noise has been a major design criterion for civil aircraft.

Stricter noise pollution standards for commercial aircraft,

established by the International Civil Aviation Organization, came into

effect worldwide on 1 April. Most industrialized countries, including all

EU states, enforced the new rules and the vast majority of airliners flying

in those states already meet the more stringent requirements. But some

Eastern European countries are facing a problem, especially Russia. Eighty

percent of its civilian aircraft fall short of the standards, meaning it

will not be able to apply the new rules for domestic flights. Even more

worrisome for Moscow is the fact that Russia could find many of its planes

banned from foreign skies. Enforcement of the new rules could force Russia

to cancel 11,000 flights in 2002, representing some 12 percent of the

country's passenger traffic.

The new rules have been applied only to subsonic transports, because

no new supersonic commercial aircraft have been developed since its


5.1 Noise Limits

As mentioned above, all turbofan-powered transport aircraft must

comply at certification with EPNL limits for the three measuring stations

as shown in Fig. 5.1. The limits depend on the gross weight of the aircraft

at take-off and number of engines, as shown in Fig. 5.2. The rule is the

same for all engine numbers on approach and on the sideline because the

distance from the aircraft to the measuring point is fixed on approach by

the angle of the approach path (normally 3 deg) and on the sideline by the

distance of the measuring station from the runway centerline.


Figure 5.2 Noise limits imposed by ICAO Annex 16 for certification of


On take-off, however, aircraft with fewer engines climb out faster, so they

are higher above the measuring point. Here the “reasonable and economically

practicable” principle comes into dictate that three-engine and two-engine

aircraft have lower noise levels at the take-off noise station than four-

engine aircraft.

There is some flexibility in the rule, in that the noise levels can

be exceeded by up to 2 EPNdB at any station provided the sum of the

exceedances is not over 3 ENPdB and that the exceedances are completely

offset by reductions at other measuring stations.

6 Noise Level Calculations

17 Tupolev 154M Description

For most airlines in the CIS, the Tupolev Tu-154 is nowadays the

workhorse on domestic and international routes.


Figure 6.1 Tupolev 154M main look

It was produced in two main vesions: The earlier production models

have been designated Tupolev -154, Tupolev -154A, Tupolev -154B, Tupolev

-154B-1 and Tupolev -154B-2, while the later version has been called

Tupolev -154M. Overall, close to 1'000 Tupolev -154s were built up to day,

of which a large portion is still operated.

Table 6.1 Tupolev 154M main characteristics

|Role | |Medium range passenger aircraft |

|Status | |Produced until circa 1996, in wide |

| | |spread service |

|NATO Codename | |Careless |

|First Flight | |October 3, 1968 |

|First Service | |1984 |

|Engines | |3 Soloviev D-30KU (104 kN each) |

|Length | |47.9 m |

|Wingspan | |37.5 m |

|Range | |3'900 km |

|Cruising Speed | |900 km/h |

|Payload Capacity | |156-180 passengers (5450 kg) |

|Maximum Take-off | |100'000 kg |

|Weight | | |

The Tu-154 was developed to replace the turbojet powered Tupolev Tu-

104, plus the Antonov - 10 and Ilyushin - 18 turboprops. Design criteria in

replacing these three relatively diverse aircraft included the ability to

operate from gravel or packed earth airfields, the need to fly at high

altitudes 'above most Soviet Union air traffic, and good field performance.

In meeting these aims the initial Tupolev -154 design featured three

Kuznetsov (now KKBM) NK-8 turbofans, triple bogey main undercarriage units

which retract into wing pods and a rear engine T-tail configuration.

The Tupolev -154's first flight occurred on October 4 1968. Regular

commercial service began in February 1972. Three Kuznetsov powered variants

of the Tupolev -154 were built, the initial Tupolev -154, the improved

Tupolev -154A with more powerful engines and a higher max take-off weight

and the Tupolev -154B with a further increased max take-off weight. Tupolev

-154S is a freighter version of the Tupolev -154B.

Current production is of the Tupolev -154M, which first flew in 1982.

The major change introduced on the M was the far more economical, quieter

and reliable Solovyev (now Aviadvigatel) turbofans. The Tupolev - 154M2 is

a proposed twin variant powered by two Perm PS90A turbofans.

6.2 Noise Calculaions

Noise level at control points is calculated using the Noise-Power-

Distance (NPD) relationship. In practice NPD-relationship is used in the

parabolic shape:


where coefficients А, В, С are different for different aircraft types and

engine modes. For Tupolev-154M the coefficients А, В, С are shown in the

table 6.2 in respect to Tupolev-154.

Table 6.2 Noise-Power-Distance coefficients of similar aircraft.

| |Tupolev-154 |Tupolev-154M |

|Weight, kg |80000 |76000 |72000 |68000 |68000 |

|Vapp, m/s |74,8 |72,91 |70,964 |68,965 |66,91 |

|Thrust, kg |8445,63 |8024,67 |7601,88 |7179,66 |6758,58 |

|LA, dBA |96,74 |96,05 |95,35 |94,66 |93,97 |

|EPNL, EPNdB |112,17 |111,32 |110,48 |109,64 |108,79 |

|?LA, dBA |0 |0,69 |0,7 |0,69 |0,69 |

|?EPNL, EPNdB |0 |0,85 |0,84 |0,84 |0,85 |

|SQRT (Wing |21,082 |20,548 |20 |19,437 |18,856 |

|Load) | | | | | |

|Thrust To |0,10557 |0,105588 |0,105582 |0,105583 |0,105603 |

|Weight rt. | | | | | |

Tupolev 154M has the same aerodynamics as Tupolev 154, thus the

necessary thrust for both of them during approach is almost the same.

Tupolev 154M has more powerful engines and it can carry more payload. Its

maximum landing weight is 2 tons greater than that one of 154. Noise

parameters are different for these aircraft (table 6.2), and the calculated

noise levels slightly differ as well.

7 Noise Suppression

7.1 Suppression of Jet Noise

Methods for suppressing jet noise have exploited the characteristics

of the jet itself and those of the human observer. For a given total noise

power, the human impact is less if the frequency is very high, as the ear

is less sensitive at high frequencies. A shift to high frequency can be

achieved by replacing one large nozzle with many small ones. This was one

basis for the early turbojet engine suppressors. Reduction of the jet

velocity can have a powerful effect since P is proportional to the jet

velocity raised to a power varying from 8 to 3, depending on the magnitude

of uc. The multiple small nozzles reduced the mean jet velocity somewhat by

promoting entrainment of the surrounding air into the jet. Some attempts

have been made to augment this effect by enclosing the multinozzle in a

shroud, so that the ambient air is drawn into the shroud.

Certainly the most effective of jet noise suppressors has been the

turbofan engine, which in effect distributes the power of the exhaust jet

over a larger airflow, thus reducing the mean jet velocity.

In judging the overall usefulness of any jet noise reduction system,

several factors must be considered in addition to the amount of noise

reduction. Among these factors are loss of thrust, addition of weight, and

increased fuel consumption.

A number of noise-suppression schemes have been studied, mainly for

turbofan engines of one sort or another. These include inverted-temperature-

profile nozzles, in which a hot outer flow surrounds a cooler core flow,

and mixer-ejector nozzles. In the first of these, the effect is to reduce

the overall noise level from that which would be generated if the hot outer

jets are subsonic with respect to the outer hot gas. This idea can be

implemented either with a duct burner on a conventional turbofan or with a

nozzle that interchanges the core and duct flows, carrying the latter to

the inside and the former to the outside. In the mixer-ejector nozzle, the

idea is to reduce the mean jet velocity by ingesting additional airflow

through a combination of the ejector nozzles and the chute-type mixer.

Fairly high mass flow ratios can be attained with such arrangements, at the

expense of considerable weight.

The most promising solution, however, is some form of “variable cycle”

engine that operates with a higher bypass ratio on take-off and in subsonic

flight than at the supersonic cruise condition. This can be achieved to

some degree with multi-spool engines by varying the speed of some of the

spools to change their mass flow, and at the same time manipulating

throttle areas. Another approach is to use a tandem-parallel compressor

arrangement, where two compressors operate in parallel at take-off and

subsonically, and in series at a supersonic conditions.

7.1.1 Duct Linings

It is self evident that the most desirable way to reduce engine noise

would be to eliminate noise generation by changing the engine design. The

current state of the art, however, will not provide levels low enough to

satisfy expected requirements; thus, it is necessary to attenuate the noise

that is generated.

Fan noise radiated from the engine inlet and fan discharge (Fig. 7.1)

of current fan jet airplanes during landing makes the largest contribution

to perceived noise.


Figure 7.1 Schematic illustration of noise sources from turbofan


Figure 7.2. shows a typical farfield SPL noise spectrum generated by a

turbofan engine at a landing-approach power setting. Below 800 Hz, the

spectrum is controlled by noise from the primary jet exhaust. The spectrum

between 800 and 10000 Hz contains several discrete frequency components in

particular that need to be attenuated by the linings in the inlet and the

fan duct before they are radiated to the farfield.


Figure 7.2 Engine-noise spectrum

The objective in applying acoustic treatment is to reduce the SPL at

the characteristic discrete frequencies associated with the fan blade

passage frequency and its associated harmonics. Noise reductions at these

frequencies would alleviate the undesirable fan whine and would reduce the

perceived noise levels.

A promising approach to the problem has been the development of a

tuned-absorber noise-suppression system that can be incorporated into the

inlet and exhaust ducts of turbofan engines. An acoustical system of this

type requires that the internal aerodynamic surfaces of the ducts be

replaced by sheets of porous materials, which are backed by acoustical

cavities. Simply, these systems function as a series of dead-end

labyrinths, which are designed to trap sound waves of a specific

wavelength. The frequencies for which these absorbers are tuned is a

function of the porosity of flow resistance of the porous facing sheets and

of the depth or volume of the acoustical cavities. The cavity is divided

into compartments by means of an open cellular structure, such as honeycomb

cells, to provide an essentially locally reacting impedance (Fig. 7.3).

This is done to provide an acoustic impedance almost independent of the

angle of incidence of the sound waves impinging on the lining.

The perforated-plate-and-honeycomb combination is similar to an array

of Helmholtz resonators; the pressure in the cavity acts as a spring upon

which the flow through the orifice oscillates in response to pressure

fluctuations outside the orifice.


Figure 7.2 Schematic of acoustic damping cavities in an angine duct. The

size of the resonators

is exaggerated relative to the duct diameter.

The attenuation spectrum of this lining is that of a sharply tuned

resonator effective over a narrow frequency range when used in an

environment with low airflow velocity or low SPL. This concept, however,

can also provide a broader bandwidth of attenuation in a very high noise-

level environment where the particle velocity through the perforations is

high, or by the addition of a fine wire screen that provides the acoustic

resistance needed to dissipate acoustic energy in low particle-velocity or

sound-pressure environments. The addition of the wire screen does, however,

complicate manufacture and adds weight to such an extent that other

concepts are usually more attractive.


Figure 7.3 Acoustical lining structure.

Although the resistive-resonator lining is a frequency-tuned device

absorbing sound in a selected frequency range, a suitable combination of

material characteristics and lining geometry will yield substantial

attenuation over a frequency range wide enough to encompass the discrete

components and the major harmonics of most fan noise.

7.1.2 Duct Lining Calculation

First we have to determine the blade passage frequency:


where z is number of blades, n is RPM.

Blade passage frequencies for different engine modes are given in table 7.1

Next we determine the second fan blade passage harmonic frequency, which is

two times greater than the first one: [pic].

Table 7.1 Fan blade passage frequencies for different engine modes.

|Take-off |Nominal |88%Nom |70%Nom |60%Nom |53%Nom |Idle | |RPM |10425

|10055 |9878 |9513 |9315 |8837 |4000 | |1st harmonic freq., Hz |5386,25







| |2nd harmonic freq., Hz |10772,5







| |

Using experimental data, we determine lining and cell geometry:

For the first harmonic, parameters will be:

. Distance between linings 28.5 cm;

. Lining length 45 cm;

. Lining depth 2.5 cm;

. Cell length 2 cm..

For the second harmonic, parameters will be the following:

. Distance between linings 4.5 cm;

. Lining length 5 cm;

. Lining depth 2.5 cm;

. Cell length 0.4 cm.

Figure 7.4 shows the placement of the lining in engine nacelle.


Figure 7.4 Lining placement in the nacelle.

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