Inlet channel arrangement for an auxiliary generator for noise reduction.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- GULFSTREAM AEROSPACE CORP
- Filing Date
- 2016-12-05
- Publication Date
- 2026-07-30
AI Technical Summary
Aircraft auxiliary generators generate high-frequency noise that propagates through intake ducts, causing noise pollution both inside and outside the aircraft, particularly affecting passengers and contributing to the aircraft's overall noise signature, with existing noise reduction methods increasing cost, complexity, and weight.
An intake duct assembly with a door equipped with a noise-absorbing component positioned to intercept and absorb noise directly from the auxiliary generator, reducing noise emission without requiring extensive duct modifications.
Significantly dampens noise levels emitted into the surrounding area by redirecting noise through a sound-absorbing component on the intake duct door, achieving noise reduction without adding weight or complexity to the aircraft.
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Abstract
Description
TECHNICAL AREA
[0001] The present invention relates generally to aircraft and in particular to inlet duct arrangements for auxiliary generators which are equipped with door arrangements designed to attenuate noise generated by auxiliary engines. BACKGROUND
[0002] Jet aircraft typically include an auxiliary power unit (APU). An APU primarily provides electrical power to the aircraft when the jet engines are switched off. For example, it is common to run the APU to power the aircraft's systems while passengers are boarding or disembarking.
[0003] An auxiliary generator is a jet engine connected to a generator rather than a propulsion system. Like all jet engines, the auxiliary generator requires an air supply. Because the auxiliary generator is mounted inside the fuselage rather than in an engine bay, it is not exposed to the ambient air around the aircraft and therefore requires a dedicated air intake path and a dedicated exhaust path. The air intake path typically includes an intake duct that connects the auxiliary generator to an opening in the fuselage. This opening is covered by a door that moves between a closed position and one or more open positions. While the door is in the closed position, air is prevented from entering the intake duct. The door remains closed while the auxiliary generator is off.When the door is in an open position, air can enter the intake duct and reach the auxiliary generator. The intake duct door is usually mounted on the upper part of the fuselage. In some cases, the door is positioned near the vertical stabilizer.
[0004] An auxiliary unit generates a considerable amount of noise during operation. The primary intake noise produced by the auxiliary generator has a frequency that corresponds to the number of vanes used in the compressor multiplied by the rotational speed. The higher the frequency of the noise, the more directional it will be. This high-frequency noise propagates upwards in the intake duct in a direction opposite to the airflow and continues outside the intake into the surrounding airspace. Additionally, the high-frequency noise is deflected by solid reflective surfaces it encounters as it exits the intake duct. When this high-frequency, highly directional noise reaches the intake duct door, it is deflected in the same way as a billiard ball striking the bumpers of a billiard table.Anyone standing in the path of the noise being diverted from the door of the entrance channel will hear a continuous and shrill screech.
[0005] The intake duct door typically opens in a direction facing the forward section of the aircraft. If the passenger door to the aircraft is located on the same side of the aircraft as the intake duct door, passengers boarding or deplaneting while the auxiliary generator is operating may experience a noisy environment as the noise from the intake duct reflects off the underside of the door toward them. This can be irritating and may make it difficult to continue a conversation. This is an undesirable situation, particularly in the case of a business jet, where passengers have a high expectation of quiet and there is no enclosed aisle to shield them from the noise as they approach the aircraft.
[0006] Additionally, the auxiliary generator can also be operated during flight. The opening of the air intake door is determined by the airspeed and / or altitude. Noise from the air intake can be radiated to the ground under certain flight conditions and can contribute to the overall noise signature of the aircraft.
[0007] To address these issues, aircraft manufacturers typically line the walls of the intake duct with noise-absorbing material. However, this solution can necessitate an oversized intake duct to accommodate the volume required by the noise-absorbing material. Another method to reduce noise from the intake duct is to add noise-absorbing partial guide vanes that span the duct's cross-section. However, these vanes introduce flow resistance to the intake system and might require a larger duct cross-section to avoid excessively restricting the airflow entering the auxiliary generator. Therefore, these solutions could add significant cost, complexity, and weight to the aircraft.
[0008] It is desirable to provide an improved device for reducing the noise generated during the operation of the auxiliary generator and transmitted through the inlet duct. Furthermore, other desirable features and characteristics will become apparent from the following detailed description and the attached claims, in conjunction with the accompanying drawings and the preceding technical field and background information. SUMMARY
[0009] An improved auxiliary generator inlet arrangement and an auxiliary generator door arrangement for use with an auxiliary generator in an aircraft are disclosed herein.
[0010] In a first non-restrictive embodiment, the auxiliary generator inlet assembly includes, but is not limited to, an inlet duct with a first end and a second end. The first end is configured for coupling to the auxiliary generator. The auxiliary generator inlet assembly further includes, but is not limited to, a door associated with the second end of the inlet duct. The door is configured to move between a first position and a second position. The door closes the second end of the inlet duct when it is in the first position, and allows air to enter the second end of the inlet duct when it is in the second position. The auxiliary generator inlet assembly further includes, but is not limited to, a noise-absorbing component mounted on the door and located near (proximal to) the inlet duct.The noise-absorbing component is positioned at the door so that any noise generated by the auxiliary generator directly impacts the noise-absorbing component.
[0011] In another non-restrictive embodiment, the auxiliary generator door assembly includes a door designed to be mounted on, but not limited to, an inlet duct of an auxiliary generator. The door is designed to move between a first position and a second position when mounted near the inlet duct of the auxiliary generator. The door closes the inlet duct of the auxiliary generator when in the first position, and allows air to enter the inlet duct of the auxiliary generator when in the second position. The auxiliary generator door assembly further includes, but is not limited to, a noise-absorbing component mounted on the door and positioned near (proximal to) the inlet duct of the auxiliary generator when the door is mounted near the inlet duct of the auxiliary generator.The noise-absorbing component is positioned on the door so that any noise generated by the auxiliary generator directly impacts the noise-absorbing component when the door is mounted near the auxiliary generator's inlet duct. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention is described below in conjunction with the following drawings, wherein similar reference numerals denote similar elements, and wherein:
[0013] Fig. 1 a perspective schematic representation which depicts a tail section of an aircraft which is equipped with a non-restrictive auxiliary generator inlet duct arrangement and an inlet duct door arrangement according to the present disclosure;
[0014] Fig. 2 is an extended perspective view, which shows the inlet channel arrangement and the inlet channel door arrangement of the Fig. 1 represents;
[0015] Fig. 3 is an extended fragmentary perspective view, which shows a section of the in Fig. The inlet channel arrangement shown in Figure 2 includes the inlet channel door arrangement arranged in an open position;
[0016] Fig. 4 is a fragmentary perspective view, which shows the section of the in Fig. The inlet channel arrangement shown in Figure 3 includes the inlet channel door arrangement arranged in a closed position;
[0017] Fig. 5 is a fragmentary side sectional view, which shows the section of the inlet duct arrangement and the inlet duct door arrangement of the Fig. 4 shows;
[0018] Fig. 6 is a fragmentary exploded view, which shows the section of the inlet duct arrangement and the inlet duct door arrangement of the Fig. 3 shows;
[0019] Fig. 7 a top view of a grid spacing structure and a noise-absorbing foam material for use with the inlet duct arrangement and the inlet duct door arrangement of the Fig. 1– Fig. 6 is;
[0020] Fig. 8 is a perspective view which shows the inlet channel of the Fig. 2 equipped with a non-restrictive alternative embodiment of a door; and
[0021] Fig. 9 a perspective view of the inlet channel of the Fig. 2 equipped with a non-restrictive alternative embodiment of a noise-absorbing component. DETAILED DESCRIPTION
[0022] The following detailed description is merely exemplary and is not intended to limit the invention, the application, or any uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
[0023] An improved auxiliary generator inlet duct arrangement is disclosed herein. In a non-limiting embodiment, the auxiliary generator inlet duct arrangement includes an inlet duct door arrangement having a noise-absorbing component mounted on a section of the door facing the inlet of the inlet duct arrangement. The noise-absorbing component is positioned such that noise emanating from the inlet of the inlet duct arrangement strikes it and is at least partially absorbed by the noise-absorbing component before being diverted toward the surrounding area. In conventional inlet duct arrangements lacking a noise-absorbing component at the inlet duct door, noise emanating from the inlet strikes the door itself directly and is diverted into the surrounding area without diffusion.By mounting a noise-absorbing component to the underside of the intake duct door and placing it directly in the path of the noise emanating from the intake, the energy of the noise emerging from the intake duct is reduced, and consequently, the level of noise emitted into the immediate surroundings is significantly attenuated. Notably, this reduction in noise level is achieved without complicated and expensive modifications to the intake duct itself, such as lining it with noise-absorbing material or redesigning the intake duct to accommodate such material.
[0024] A better understanding of the auxiliary generator inlet channel arrangement and the inlet channel door arrangement described above may be achieved by reviewing the illustrations accompanying this application together with a review of the following detailed description.
[0025] Fig. Figure 1 is a perspective schematic view of a rear section of an aircraft. 10 , which uses an auxiliary generator 12 is equipped. The auxiliary generator 12 is fluidically coupled to the immediate environment outside the aircraft 10 with an inlet channel arrangement 14 and an outlet channel 16 Ambient air enters the auxiliary generator. 12 through the inlet channel arrangement 14 and is expelled through the exhaust channel after combustion 16 blown out or released into the immediate vicinity.
[0026] The inlet channel arrangement 14includes a door arrangement 20 and an inlet channel 22 The door arrangement 20 is mounted on the aircraft 10 near the end 24 of the inlet channel 22 and is designed to move between an open position and a closed position. The inlet channel 22 and the door arrangement 20 are positioned so that the door arrangement 20 in an upper surface of the hull 26 of the aircraft 10 is integrated. This presents the intake channel 22 access to surrounding air outside the aircraft 10 ready, which is needed when the auxiliary generator 12 is in operation. When the auxiliary generator 12 The door arrangement is in operation 20 opened. If the door arrangement 20 In the open position, it allows surrounding air to enter the inlet duct. 22to penetrate. In some embodiments, the door arrangement may 20 It should be adjustable, meaning it can be opened to a range of different angles and / or positions to allow more or less air into the intake duct. 22 to allow, depending on the air mass flow required to power the auxiliary generator 12 to operate. If the door arrangement 20 When in a closed position, it prevents air from entering the inlet channel. 22 The door arrangement 20 remains closed when the auxiliary generator 12 is not in operation to remove moisture, precipitation and other solid particles from outside the inlet channel. 22 to maintain and the aerodynamics of the aircraft 10 to improve during the flight.
[0027] Fig. Figure 2 is an extended perspective view showing the inlet channel arrangement. 14 represents. Fig. 2 is the door arrangement 20 Shown in an open position. The door arrangement 20 may be opened and closed using any mechanism suitable for the door arrangement 20 to move between an open and a closed position. For example, and without limitation, a hydraulic actuator may be used for this purpose. The mechanism used to move the door arrangement 20 The movement between their open and closed positions has been omitted from the figures for the purpose of illustration and to simplify the object depicted here.
[0028] Further with reference to Fig. 1, if the auxiliary generator 12 is operated while the aircraft 10 As the air approaches the door arrangement, it is in flight. 20 in the direction indicated by the arrow 28 is indicated. If this air is on the door arrangement 20When it hits the air, some of this air is diverted downwards into the intake duct. 22 and to the auxiliary generator 12 directed. To facilitate the capture of this air from the free flow, the door arrangement can be 20 be shaped like a shovel. In such a configuration, the door arrangement would 20 Side walls are included to capture and direct air from the free flow into the intake duct. 22 to support.
[0029] At one end 30 of the inlet channel 22 Two flanges will be used. 32 shown. The flanges 32 are used to end 30 to the inlet port (not shown) on the auxiliary generator 12 (see Fig. 1) to couple. Even if, in this embodiment, the inlet channel arrangement 14When flanges are shown, the expert in the technical field will appreciate that a wide variety of means can be used to finish the end. 30 to the auxiliary generator 12 to couple and that the use of any such alternative means does not represent a deviation from the teaching of the present revelation.
[0030] Fig. 3 is a fragmentary perspective view, which shows the end 24 of the inlet channel 22 the inlet channel arrangement 14 represents. With increasing reference to the Fig. 1– Fig. 2 is Fig. 3 shown from the perspective of the arrow 28 and establishes the door arrangement 20 shown in an open position. From the angle shown, the underside of the door assembly is visible. 20 to see. Here you can see the door arrangement. 20 a door 21and a noise-absorbing component 34 It contains the noise-absorbing component. 34 is on the underside of the door 21 mounted. In the illustrated embodiment, the noise-absorbing component has 34 a rectangular configuration, which essentially corresponds to the rectangular configuration of the internal periphery of the inlet channel 22 This configuration maximizes the surface area of the noise-absorbing component. 34 and accordingly maximizes the ability of the noise-absorbing component 34 , noises emanating from the auxiliary generator 12 were generated, to intercept them as soon as they reach the end 24 emerge. This configuration also allows the noise-absorbing component to 34 completely into the end 24 It fits if the door arrangement 20in the closed position. In other embodiments, the noise-absorbing component may 34 have a smaller configuration without deviating from the teachings of the present disclosure. In other embodiments, the internal periphery of the inlet channel may be 22 have a shape other than rectangular. In such embodiments, the noise-absorbing component may be 34 have a shape which corresponds to such a non-rectangular shape of the internal periphery of the inlet channel 22 This corresponds to other embodiments. In yet other embodiments, the noise-absorbing component may 34 have a periphery which is the internal periphery of the inlet channel 22 does not correspond. In such embodiments, in which the periphery of the noise-absorbing component 34 the internal periphery of the inlet channel 22If this does not correspond, it may be desirable that the periphery of the noise-absorbing component 34 nevertheless completely into the periphery of the inlet channel 22 fits inside to ensure the door arrangement 20 It can be closed without obstruction.
[0031] In general, noise absorption is typically optimized when the acoustic impedance of the material matches the impedance of the air. Therefore, the choice of noise-absorbing material plays a role in the effectiveness of a noise absorber. In the present disclosure, the noise-absorbing component may be 34shall include any suitable noise-reducing material, including but not limited to airflow-resistant materials designed and / or constructed to absorb the high-frequency noise in question. Airflow-resistant materials suitable for auxiliary generator environments shall include but not be limited to matrix metals (felt metal), fiber metals, sintered metals, and wire mesh.
[0032] In some embodiments, the noise-absorbing component may 34 comprise a metallic material. For example, steel, stainless steel, titanium and / or aluminum. In other embodiments, the noise-absorbing component may comprise any suitable woven metallic material.
[0033] In addition to the noise-absorbing components mentioned above, a tuned sound resonance absorber (such as a Helmholtz resonator) may be used as the noise-absorbing component, tuned to absorb the high-frequency sound in question. Such a tuned sound resonance absorber may be made of perforated panels or perforated skin, which are attached to the door. 21 The tuned noise resonance absorber can be made of metals, plastics, or any other suitable material or composite.
[0034] In addition to the choice of sound-absorbing material, its positioning also plays a role in the effectiveness of the sound absorber. Maximum sound absorption at a specific frequency is achieved when the depth of the recess behind the resistive porous material is approximately one-quarter of the wavelength of that frequency. Accordingly, the sound-absorbing material should be positioned away from the door. 21 They should be arranged at a relatively precise distance. Advantageously, this arrangement allows water to drain away. In some applications, however, the recess may also be filled with a second sound-absorbing material.
[0035] Continuing with reference to the Fig. 1– Fig. 3, is Fig. 4. A perspective view of the end 24 of the inlet channel 22 the inlet channel arrangement 14 with the door arrangement 20in a closed position. In this view, it can be observed that the noise-absorbing component 34 closing the door arrangement 20 did not hinder progress and that the noise-absorbing component 34 completely from view from outside the aircraft 10 is hidden when the door arrangement 20 is closed.
[0036] Fig. Figure 5 is a fragmentary side sectional view of the end. 24 of the inlet channel 22 the inlet channel arrangement 14 In this view, the spatial relationship between the noise-absorbing component can be seen. 34 and the underside of the door 21 be perceived. In the illustrated embodiment, the noise-absorbing component 34 in a distanced relationship with reference to the door 21 arranged. The noise-absorbing component 34is at a distance D from the bottom of the door 21 arranged by spacing out the noise-absorbing component 34 from the underside of the door 21 will be a chamber 36 formed. The chamber 36 records sounds emanating from the end 24 of the inlet channel 22 emerge. In some embodiments, the distance D may be approximately one quarter of the wavelength of the high-frequency noise emanating from the inlet channel. 22 emerges. In other embodiments, the distance D may be any distance suitable for separating the end from the 24 to disperse emerging or radiating or emitted noise.
[0037] In the Fig. In the embodiment shown in Figure 5, the noise-absorbing component is 34 held in a position which is from the underside of the door 21 through a spacer component 38is spaced apart (best seen in the Fig. 6 and Fig. 7) The spacing component 38 has a grid-like configuration, the ends of which are in Fig. 5 are visible. In other embodiments, any other configuration for spacer components may be used. 38 to be used which is suitable for the noise-absorbing component 34 at a distance D from the bottom of the door 21 to keep, without deviating from the teachings of the present revelation.
[0038] Continuing with reference to the Fig. 1– Fig. 5, is Fig. 6 a fragmentary exploded view showing the inlet channel arrangement 14 This view shows the arrangement of the essential components of the inlet channel assembly. 14 to be seen. The distancing component 38 is in Fig. 6 to see in its entirety. Even if the distancing component 38 While it has been shown in a three by three configuration, it should be understood that any other configuration suitable for the noise-absorbing component is also possible. 34 in a distanced relationship relative to the door 21 to hold, and which essentially does not prevent the nose from passing through the noise-absorbing component 34 to pass through, which can also be used. The door arrangement 20 may be at the inlet channel 22 be fastened in any suitable manner which allows the door arrangement 20 It allows movement between an open and a closed position. For example, a hinge or joint and a hydraulic actuator can be used to control the door arrangement. 20 to move between an open and a closed position.
[0039] Fig. 7 is a top view showing the spacer component 38 together with a variety of noise-absorbing components 40 shows. With increasing reference to the Fig. 1– Fig. 6 is the use of noise-absorbing components 40 with the door arrangement 20 optional and may have the ability to arrange the doors 20 to absorb the end 24 of the inlet channel 22 the inlet channel arrangement 14 Improve radiated noise. The noise-absorbing components 40 are configured to fit into the spaces of the spacer component 38 to fit and the chamber 36 to fill. The noise-absorbing components 40They may comprise any material suitable for absorbing noise emitted from the inlet duct. In some embodiments, the noise-absorbing components may comprise a foam material or other porous structures that provide or enable viscous damping to reduce the kinetic energy of air molecules. By arranging the noise-absorbing components 40 in the chamber 36 a further reduction of the inlet channel arrangement 14 prominent noise can be achieved.
[0040] Continuing with reference to the Fig. 1– Fig. 7, shows Fig. 8 an inlet channel arrangement 14 with an alternative embodiment of the door 21 (in Fig. 8 is the alternative embodiment identified with the reference numeral 21' As shown, the door contains 21' a pair of spaced-apart walls 42 ,44 , which extend from the underside of the door 21' extend and which are in the direction of the inlet channel 22 are aligned with the flowing air. The inclusion of the pair of spaced walls 42 , 44 It allows the door 21' acting as a scoop, drawing surrounding air from the free flow into the inlet channel 22 It steers. Additionally, the noise-absorbing components... 34' and 34'' each on the internal surface of the spaced walls 42 , 44 mounted to absorb noise through the door arrangement 20 to enable or facilitate. In other embodiments, the door arrangement may employ a single noise-absorbing component designed to act on the internal surface of the spaced walls. 42 and 44 as well as the underside of the door 21'to cover, instead of two additional noise-absorbing components, like the noise-absorbing components 34' and 34'' , to be used. In other embodiments of the door 21' like the spaced-away walls 42 and 44 be free of any noise-absorbing components.
[0041] Continuing with reference to the Fig. 1– Fig. 8, shows the Fig. 9 an inlet channel arrangement 14 , which with an alternative embodiment of the noise-absorbing component 34 is equipped (in Fig. 9 is the alternative embodiment indicated by the reference numeral 46 (displayed). The noise-absorbing component 46 It is a tuned noise resonance absorber, like a Helmholtz resonator. In some embodiments, the noise-absorbing component may 46a perforated plate with an air recess behind it. In some embodiments, the air recess may be assigned to a single perforation, while in other embodiments the air recess is used by some or all of the perforations. In some embodiments, the noise-absorbing component may 46 from the door 21 They must be spaced apart. In some embodiments, the distance may correspond to a quarter of the wavelength of the high-frequency noise emitted by the auxiliary generator. 12 was generated. In further embodiments, the tuned noise resonance absorbers may be attached directly to the door. 21 They can be mounted because they contain an internal recess.
[0042] While at least one exemplary embodiment has been set forth in the preceding detailed description of the invention, it should be borne in mind that a large number of variations exist. It should also be borne in mind that the exemplary embodiment or embodiments are merely examples and are not intended to limit the scope of protection, applicability, or structure of the invention in any way. Rather, the preceding detailed description will provide the person skilled in the art with convenient guidance for implementing an exemplary embodiment of the invention. It should be noted that various modifications may be made to the function and arrangement of the elements described in an exemplary embodiment without thereby departing from the scope of the invention as set forth in the appended claims.
Claims
[1] An auxiliary generator inlet arrangement for use with an auxiliary generator in an aircraft, comprising the auxiliary generator inlet arrangement: an inlet channel with a first end and a second end, the first end being designed for coupling to the auxiliary generator; a door associated with the second end of the inlet duct, wherein the door is configured to move between a first position and a second position, the door closing the second end of the inlet duct when the door is in the first position, and the door allowing air to enter the second end of the inlet duct when the door is in the second position; and a noise-absorbing component which is mounted on the door and located near the inlet duct, wherein the noise-absorbing component is positioned at a location on the door such that a noise generated by the auxiliary generator hits the noise-absorbing component. [2] The auxiliary generator inlet duct arrangement according to claim 1, wherein the door includes a pair of spaced-apart walls which extend transversely from the door and which are oriented in a direction which is substantially aligned with a direction of the airflow entering the second end of the inlet duct. [3] The auxiliary generator inlet arrangement according to claim 2, wherein the noise-absorbing component is further mounted on an inside of each wall of the pair of spaced-apart walls. [4] The auxiliary generator inlet arrangement according to one of the preceding claims, wherein the noise-absorbing component comprises a matrix metal material. [5] The auxiliary generator inlet arrangement according to one of the preceding claims, wherein the noise-absorbing component comprises a tuned noise resonance absorber. [6] The auxiliary generator inlet arrangement according to claim 5, wherein the tuned noise resonance absorber has a perforated plate with an air space arranged at the rear of the perforated plate. [7] The auxiliary generator inlet arrangement according to one of the preceding claims, wherein the noise-absorbing component is mounted to the door in a spaced manner. [8] The auxiliary generator inlet arrangement according to claim 7, wherein the noise-absorbing component is mounted to the door by a spacer component. [9] The auxiliary generator inlet arrangement according to claim 8, wherein the spacer component has a grid structure. [10] The auxiliary generator inlet arrangement according to one of claims 7 to 9, wherein the noise-absorbing component is spaced away from the door by a distance which corresponds to a frequency of the noise generated by the auxiliary generator. [11] The auxiliary generator inlet arrangement according to claim 10, wherein the distance is less than approximately one quarter of a wavelength of the noise produced by the auxiliary generator. [12] The auxiliary generator inlet arrangement according to claim 10, wherein the distance is less than half an inch. [13] The auxiliary generator inlet arrangement according to one of the preceding claims, further comprising a foam material which is arranged between the noise-absorbing component and the door. [14] An auxiliary generator inlet door assembly for use with an auxiliary generator inlet duct of an auxiliary generator in an aircraft, comprising the auxiliary generator inlet door assembly: a door configured for mounting near the auxiliary generator inlet duct, wherein the door is designed to move between a first position and a second position when mounted near the auxiliary generator inlet duct, wherein the door closes the auxiliary generator inlet duct when the door is in the first position, and wherein the door allows air to enter the auxiliary generator inlet duct when the door is in the second position; and a noise-absorbing component which is mounted on the door and which is located near the auxiliary generator inlet duct when the door is mounted near the auxiliary generator inlet duct, wherein the noise-absorbing component is positioned at a location on the door such that a noise generated by the auxiliary generator hits the noise-absorbing component when the door is mounted near the auxiliary generator inlet duct. [15] The auxiliary generator inlet door arrangement according to claim 14, wherein the noise-absorbing component comprises a matrix metal material. [16] The auxiliary generator inlet door arrangement according to claim 14 or 15, wherein the noise-absorbing component comprises a tuned noise resonance absorber. [17] The auxiliary generator inlet door arrangement according to one of claims 14 to 16, wherein the noise-absorbing component is mounted to the door in a spaced manner. [18] The auxiliary generator inlet door arrangement according to claim 16, wherein the noise-absorbing component is spaced away from the door by a distance which is not greater than a quarter of a wavelength of the noise. [19] The auxiliary generator inlet door arrangement according to any one of claims 14 to 18, wherein the door includes a pair of spaced-apart walls which extend transversely from the door and which are oriented in a direction which is substantially aligned with a direction of the airflow entering the second end of the inlet duct. [20] The auxiliary generator inlet door arrangement according to claim 19, wherein the noise-absorbing component is further mounted on an inside of each wall of the pair of spaced-apart walls.