JPS6010168B2 - Sound absorption duct with asymmetrical sound absorption treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sound-absorbing duct, and more particularly to a sound-absorbing fan having asymmetrical or circumferentially discontinuous acoustic treatment.

As a typical application, the present invention relates to an asymmetrical noise-suppressing sound-absorbing lining for an aircraft engine fan inlet. BACKGROUND OF THE INVENTION Sound absorbing materials used as linings in sound absorbing ducts are usually used symmetrically with respect to the axis of the duct.

That is, the sound absorbing material is circumferentially continuous in any track direction or longitudinal position. For example, an acoustic lining in the inlet passage of a jet engine fan is used throughout 3600 of the inner surface of the fan cowling or casing. This is US Patent No. 35421
It is shown in No. 52. The sound absorbing material in this patent is
It is a honeycomb-shaped panel with a tuned resonant cavity structure to absorb wide range noise. Both the sound absorbing panel itself and the cowling are provided with means for draining intruding liquid. "Configuration and Effects of the Invention" Although the improved asymmetric sound absorption treatment technology of the present invention is advantageous for the above applications,
It can be used in various other applications, such as mufflers for industrial gas turbines, etc. It can also be applied to modify the directivity pattern of acoustic horns.

An asymmetrical or circumferentially discontinuous sound absorbing liner for absorbing sound generated within a sound absorbing duct selectively directs the sound emitted from one end of the duct depending on its position and extent in the circumferential direction. I learned that I have the ability to change.

By changing the directivity of the generated sound or noise, the sound suppression effect can be selectively strengthened at a predetermined angle of the directivity pattern of the sound or noise. In the present invention, even in a sound absorbing duct for a gas turbine engine with a sound absorbing lining attached to the inner surface, the sound absorbing lining extends in the longitudinal direction so as to cover a part of the circumferential surface of the duct or a plurality of opposing parts. The sum of the lengths in the direction of the sound absorption duct is shorter than all the stations of the sound absorption duct.As a result of this configuration, the sound suppression effect is obtained only in the necessary angle range, and the sound absorption lining is omitted in the unnecessary angle range. As a whole, the same sound suppression effect can be obtained as with one that has been completely sound-absorbed.

``Sound-absorbing materials can be selected based solely on the sound-absorbing effect for areas where sound-absorbing lining is applied, but air resistance can be reduced and water treatment effects improved in areas where sound-absorbing lining is not applied. The fan noise generated in the duct is selectively suppressed in the angular castle generally below the fan duct inlet by treating only the upper portion of the duct interior surface.

It is also possible to use fiber sound-absorbing materials with relatively high sound absorption coefficients and, for example, 0.5%. In the case of the semi-cylindrical sound absorbing lining, the amount of noise suppression for ground observers is almost the same as in the case of the 36Qo all-round treatment. The advantage is thus that less sound-absorbing material or weight is required, or conversely, that it is more effective for the same throughput.The rationale is that the rigidity or untreated It is believed that this has something to do with the relatively good sound reflection by the lower inner surface.
e) This is an asymmetrically treated sound absorbing duct for suppressing weaving ~ This is 1
It includes an acoustic lining having a pair of opposing acoustic strips. Each sound piece is also effective in selectively suppressing the opposite side lobe in the directional pattern, that is, in lateral sound absorption. This illustrates the versatile applicability of asymmetrically arranging sound-absorbing materials in a sound-absorbing field to obtain desired selective effects. According to the invention, "a second sound-absorbing lining is also used to treat all or part of the remaining inner surface of the fan or other sound-absorbing duct.

That is, "a first sound-absorbing lining is installed asymmetrically with respect to the axis of the duct on a part of the inner surface of a relatively rigid hard-walled duct extending in the vertical direction in the longitudinal direction to the remaining part of the inner surface of the duct in the local direction. A second sound-absorbing lining is attached to the lining.The first and second sound-absorbing linings are combined and continuous in the vertical direction. 1st
The sound absorption coefficient of the second sound absorption lining is higher than the sound absorption coefficient of the second sound absorption lining.
As a result of such a configuration, which creates an asymmetric directivity pattern, for example, the first sound-absorbing lining may be selected for its durability and good drainage of liquid that has entered the duct, but the second sound-absorbing lining may be By selecting a combination of low cost, storage, and sound absorption coefficient, the overall performance of the sound absorption duct can be improved.

In other words, the balance between sound suppression and duct function can be determined over a wide range. An example of an application detailed in relation to the figures is asymmetrical or circumferential continuous sound absorbing linings for aircraft jet engine inlet ducts to reduce the level of noise that can be combated on the ground during takeoff or landing.

Figure 1 also shows a general data fan type turbojet engine. The engine body has an annular streamlined fan casing and an air passageway, which is formed by an annular cowling or fan casing with a streamlined section and a suitable engine nacelle structure body extending into the cowling. Only the forward portion of the nacelle structure is shown in outline and houses a suitable compressor, combustor and turbine. This turbine drives a fan as part of its function. .Fan Gunkame'
The air passage between the front end of the curling electric bonito and the nacelle mechanical gymnastic shaft drives the air flowing in the direction of the nacelle to provide propulsive force to the engine, and also directs air into the second inlet air passage 15. to supply air to the compressor. The majority of the fan airflow exits through an annular exhaust nozzle opening 16 formed by the inner surface of the cowling 12 and the outer surface of the gas generator pot casing 17. A compressor inlet air passage 15 is formed between an inlet casing 17 and a forwardly projecting teardrop-shaped fan mounting and drive structure 18 . The outer surface of the casing 17 is covered with the aforementioned honeycomb-shaped resonance chamber sound absorbing panel 19.
properly lined with. For more information regarding this type of turbofan jet engine, reference may be made to U.S. Pat. No. 3,540,682.As clearly shown in FIG. installed.

In this embodiment of the invention, the trining 20 covers only the upper half of the inner surface. This structure is hereinafter referred to as an asymmetrically processed fan duct. By applying a 180o sound absorption treatment to the top half of the fan duct, the noise suppression to ground observers is much or nearly the same as with known 360o sound absorption treatments. To further illustrate this, the directionality of the noise emitted by the fan 14 is varied such that suppression of noise pressure levels is preferentially enhanced in a predetermined direction, in this case generally below the source of the sound. Fan 14 produces a wide range of noise and is the main noise source for jet engines. Although a variety of acoustical lining materials may be used, such as the honeycomb-shaped resonant chamber acoustical panels disclosed in the aforementioned US Pat. Since the acoustical lining only covers the upper half of the fan duct, the need for the use of materials capable of drainage of intruding fluids is reduced, if not virtually eliminated.Suitable textile acoustical materials are e.g. Glass fiber "stainless steel wire, hard wire for the high temperature section of the duct, etc.The advantages of 50% or asymmetrically treated fan ducts are obvious.

This is because it provides virtually the same noise suppression benefits as traditional 360o processing, but at half the cost and weight. In addition to minimizing processing weight, these and other fibrous acoustical materials can have a cost per square foot less than that of honeycomb resonant chamber acoustical panels. Alternatively, if the processing weight is kept the same, the noise suppression effect will increase. moreover,
Improved airflow over smooth untreated duct surfaces may reduce airflow losses within the fan duct. The modified asymmetric directivity pattern of noise emanating from the inlet end of a semi-cylindrical 50% treatment fan duct is shown in FIG.

The upper half of the experimental fan duct 21 has a sound-absorbing treated semi-cylindrical shape, while the lower half is an untreated semi-cylindrical shape.Measurements were made in an anechoic chamber using a one-third scale model of a General Electric CF6 jet engine fan. The fan was operated at 90% design speed. As a basis of comparison ~
The symmetrical directivity patterns of an untreated fan duct and a 3600 all-round treated fan duct using the same sound-absorbing material are shown by dotted lines and dashed lines, respectively. Immediately below the duct entrance, the reduction in sound pressure generated by full-circle sound absorption treatment is approximately . The asymmetric directivity pattern obtained by applying the novel 180o processing is shown by a solid line. As shown, over a wide angle range generally below and in front of the duct inlet, the amount of noise suppression using the 180o treatment is approximately the same as with the 3600 treatment. According to the measurement data, compared to the case of all-round processing, 18
The noise reduction with the 00 treatment is nearly the same over an angular range of 50° to 110° measured down to the forward extension axis of the duct. Immediately before the duct entrance, the noise suppression effect is not as good as the effect of all-around treatment. However, there is relatively little need to worry about noise suppression in these spaces. This is because the primary purpose of sound absorption treatments is to reduce the amount of noise that is felt by humans on the ground. Immediately above the duct entrance, the noise suppression effect of ~180o treatment is about half that of 360o treatment. Although the asymmetric sound absorption treatment is illustrated for axisymmetric noise sources, the redirection of noise achieved by this asymmetric treatment is independent of the type of sound absorption material employed. It will be appreciated that the circumferential position of the asymmetric treatment will generally determine the direction in which selective noise suppression is provided. Therefore, when reducing fan noise in other applications, applying sound absorption treatment to the lower half of the fan duct instead of the upper half will selectively increase the noise suppression effect above the duct entrance rather than below. Although the theoretical interpretation of the directional deflection of sound emanating from asymmetrically treated fan ducts or other sound-absorbing ducts is uncertain, it is believed that it can be explained by the reflection of sound by the internal surface of the duct.

The wide-range noise generated by the axially symmetrically installed fan is radiated in all directions; some of the waves are incident on the treated semi-cylindrical duct surface, and the other part is incident on the untreated semi-cylindrical duct surface. Some of it is incident on the duct surface, and another part of it emanates directly from the end of the fan duct. Part of the sound that impinges on the treated upper half is absorbed and the other part is reflected. On the other hand, almost all of the sound incident on the untreated lower half of the t-duct is reflected because the untreated lower half is lined with a smooth sheet metal panel. Some of the sound reflected by the untreated lower half of the duct is incident on the treated upper half where it is partially absorbed. Conversely, some of the sound reflected by the treated upper half is directed toward the lower half, where it is reflected again and directed toward the absorbing treated upper half.In the end, the unabsorbed sound energy dissipates out of the duct entrance. .
However, as will be readily appreciated, the energy of the relatively high sound pressure bell reflected from the untreated lower half near the duct entrance will generally diverge upwardly, while the energy reflected from the treated upper half out of the duct entrance. The energy of a relatively low sound pressure bell is generally dissipated downward. Therefore, the directional pattern is asymmetric, and the selective damping enhancement is determined by the circumferential position of the sound-absorbing material. It is generally applicable to arcuate asymmetric treatments with ranges greater or less than 180o, the limits of which are determined by practical considerations and the desired application on either side, taking into account the cost of the sound-absorbing material for the desired amount of selective noise suppression. Furthermore, the present invention is generally applicable to sound absorbing ducts having cross sections other than circular, such as rectangular or square.Another embodiment shown in FIG. Two different sound absorbing lining materials are used to achieve this.

This is particularly well exemplified in the case of fan ducts for aircraft jet engines. According to this embodiment, the upper half of the inner surface of the curling force 2 is lined with a sound-absorbing lining 28 of textile sound-absorbing material, and the lower half thereof is lined with the sound-absorbing lining 22 of the aforementioned honeycomb-shaped resonant chamber sound-absorbing structure panel. The second acoustic lining 22 has the advantages of durability and good drainage of intruding liquids, while the acoustic treatment material of the first acoustic lining 20 is selected to obtain a combination of low cost and high sound absorption coefficient. It is desirable.Sound absorbing lining 2
2 is made of or has a face plate of a suitable rigid material, such as metal or plastic, and reflects sound more easily than an acoustic lining 20 of textile acoustic material. This all-around treatment of the fan duct improves the overall directional pattern, resulting in better noise reduction above and in front of the duct entrance, as well as better sound-absorbing material in the upper half of the duct. A high noise reduction effect generally below the duct inlet due to the use of the duct is also ensured in this case. Instead of continuous treatment in the circumferential direction as shown, a gap may be provided between the two types of sound-absorbing treatment materials. Another embodiment of the present invention, shown in FIG.
A case in which the method is applied to suppressing ``erobe'' will be exemplified.

The duct 23 in this case is a hard wall acoustic duct suitable for use in other applications such as industrial gas turbine mufflers or acoustic horn structures. To explain the principle, in the case of an application to a gas turbine noise muffler, it would be desirable to divert noise away from an occupied area.
24b is used. The duct 23 has a length that is at least equal to or greater than its diameter, and the sound absorbing pieces 24a, 24b are axially distributed over the entire length of the duct or a specific portion thereof. Assuming a noise source that generates a symmetrical directivity pattern with side lobes, the effect of the asymmetric left sound absorbing piece 24a is to suppress the side lobe on the right side of the directivity pattern. The effect of piece 24b is to suppress the sidelobes on the left side of the directional pattern.As a result, the directional pattern changes so that there is selective noise suppression on both sides. is the same as that of the fan duct (see Fig. 4), and does not need to be described again. The use of sound-absorbing materials improves the overall noise reduction.It will be appreciated that the sidelobe-suppressing sound-absorbing strips 24a, 29b are made of a material with a relatively high sound absorption coefficient. Asymmetric sound-absorbing linings for suppressing sound or noise originating from ducts have the advantage, or conversely In other words, it provides a higher effect for the same throughput.Furthermore, although the sound absorption duct for reducing jet engine fan noise on the ground and suppressing side lobes has been described, various other applications are possible.
Although several preferred embodiments of the present invention have been described above, their aspects and details can be modified in various ways without departing from the concept of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the forward part of a ducted fan aircraft jet engine having a fan duct with an asymmetrical semi-cylindrical sound-absorbing lining according to the invention, the forward part being partially shown in longitudinal section. FIG. 2 is a vertical cross-sectional view of only the inlet fan duct or casing taken along line 2--2 of FIG. 1, illustrating a 180° asymmetric sound absorption treatment for selective noise suppression to ground observers.
FIG. 3 shows three types of directivity patterns obtained in experiments when a cylindrical jet engine fan duct is not subjected to sound absorption treatment, when it is subjected to 360o sound absorption treatment, and when it is subjected to 180o sound absorption treatment. FIG. 4 is a cross-sectional view similar to FIG. 2, illustrating another embodiment of the invention using two different acoustic lining materials to optimize economic and noise suppression effects. FIG. 5 is a sectional view of a sound absorbing duct subjected to asymmetrical treatment to suppress side lobes. In the figure, 12 represents a fan casing, and 20 represents an asymmetric sound absorbing lining. Yutaku J Takanashi 2 Fake 8 Grandchild 4 Grandchild Yu

Claims (1)

[Claims] 1. In a sound-absorbing duct for a gas turbine engine having a sound-absorbing lining attached to the inner surface, the sound-absorbing lining extends in the longitudinal direction so as to cover a part of the circumferential surface of the duct or a plurality of opposing parts, A sound absorbing duct characterized in that the total circumferential length thereof is shorter than the entire circumference of the sound absorbing duct. 2. A first sound absorbing lining is attached to a circumferential portion of the inner surface of an axially extending relatively steel hard-walled duct asymmetrically with respect to the axis of the duct, and a first sound absorbing lining is attached to the circumferential remainder of the inner surface of the duct. A second acoustic lining is attached and the first
and a second sound-absorbing lining are circumferentially continuous in combination, each of the sound-absorbing linings being axially and circumferentially continuous and substantially uninterrupted; Asymmetric directivity characterized in that the sound absorption coefficient is higher than the sound absorption coefficient of the second sound absorption lining, and the directivity of sound emitted from the end of the duct is changed to strengthen sound suppression in a predetermined angular range as necessary. A sound-suppressing sound-absorbing duct designed to create a pattern.