A noise reduction structure for aircraft landing gear based on longitudinal corrugated strut design

Abstract

The present invention discloses an aircraft landing gear noise reduction structure based on a longitudinal corrugated strut design. The landing gear consists of five parts: a wheel, a main strut, an auxiliary strut, a coupling shaft and a torsion bar. The upper end of the main strut is connected to the aircraft body, and the lower end of the main strut is connected to the landing gear coupling shaft. The main strut is a combination structure of a variable diameter section and a constant diameter section in the longitudinal direction. The variable diameter section is a corrugated section, including one or more corrugations; and the corrugated section and the constant diameter section have a smooth transition. The corrugated strut of the present invention can effectively suppress the periodic vortex structure in its wake, and also improve the flow around other components, so that the overall radiation noise of the landing gear is weakened at the sound source, thereby reducing the far-field radiation noise, and can also suppress the flow-induced vibration problem caused by the periodic wake vortex structure of the landing gear structure. The structure is simple, the performance is reliable, and it is easy to implement in various aircraft construction and simple in daily maintenance.

Description

Technical Field

[0001] The invention belongs to the field of flow control technology and aviation aerodynamic noise, and specifically relates to an aircraft landing gear noise reduction structure based on a longitudinal corrugated strut design, which can be used to reduce flow-induced vibration of the aircraft landing gear structure and reduce the aerodynamic noise of the aircraft landing gear. Background Art

[0002] With the rapid development of civil aviation transportation, aircraft noise has become a key concern of the aviation industry. The main noise sources of modern large aircraft include engine noise and fuselage noise. With the widespread application of large bypass ratio turbofan engines in civil aircraft and the implementation of a series of engine noise reduction projects, engine noise has dropped significantly. Especially during the take-off and landing phases of the aircraft, the landing gear is lowered and the lift-enhancing device is turned on, and the engine is in a low-power state. At this time, the aerodynamic noise generated by the landing gear, lift-enhancing device and other fuselage components is at the same level as the aircraft engine noise, or even exceeds the engine noise. Studies have shown that when the engine is idling and the lift-enhancing device is not turned on, the landing gear noise accounts for more than 25% of the total aircraft noise. Therefore, landing gear aerodynamic noise is a key issue that needs to be solved in the aviation industry.

[0003] The generation of landing gear noise is related to its complex shape. Landing gear noise is mainly broadband noise, and its generation mechanism includes two categories: one is blunt body separation noise, that is, the noise radiated by flow phenomena such as flow separation and reattachment when the airflow flows through the blunt body parts of the landing gear; the other is interference noise, that is, the noise generated by the unsteady turbulent wake of the upstream parts acting on the downstream parts. In addition to broadband noise, discrete noise is another important part of landing gear noise. Discrete noise is mainly generated by the acoustic excitation phenomenon of some small hole structures in the landing gear configuration and the cavity structures that may exist inside and outside the wheels. The location of the main noise source of the landing gear and the far-field noise characteristics are closely related to the configuration of the landing gear. The number of landing gear wheels will affect the size of the low-frequency and high-frequency noise of the landing gear at the same time; the real landing gear will generate additional high-frequency noise due to the presence of small-sized and small parts; the installation effect of the real landing gear will cause it to differ from the noise measured in the wind tunnel experiment. The directional characteristics of the total noise of the landing gear are most similar to the directional characteristics of the wheel noise, which is a dipole directional characteristic.

[0004] Since the early 1970s, researchers have conducted a lot of experimental research on the aerodynamic noise of landing gear. Heller and Dobrzynski conducted flight tests of medium-complexity 2-wheel and 4-wheel landing gear models, obtained the noise data of the two models and compared them for the first time. After that, Fink established a noise prediction model based on the experimental data of the two. Guo conducted noise tests on the front and main landing gears of the Boeing 737 and proposed an empirical model for noise prediction of the landing gear; NASA conducted wind tunnel tests and flight tests on the aerodynamic noise of the full-size main landing gear of the Boeing 787 in the QTDⅡ technical research in 2005; the European Union carried out experiments and simulations on the design of low-noise landing gear in the EU SILENCE program. Liu Peiqing and others from the Beijing University of Aeronautics and Astronautics conducted a lot of research on the noise mechanism through experiments and numerical simulations. Liu Xingqiang and others from the China Aircraft Strength Research Institute conducted a lot of research on the front landing gear of a certain type of aircraft; Long Shuangli and others from Nanjing University of Aeronautics and Astronautics also carried out related work on noise tests and simulations of landing gear components. Zhao Kun and others from the China Aerodynamics Research and Development Center also conducted a series of experimental studies on landing gear aerodynamic noise and explored related noise reduction measures.

[0005] After a large number of experiments and numerical studies, scholars have obtained a series of results related to the characteristics and mechanisms of landing gear aerodynamic noise, and based on this, have proposed many methods and measures to reduce aircraft landing gear aerodynamic noise.

[0006] Currently, the methods for landing gear noise reduction are divided into active noise reduction methods and passive noise reduction methods.

[0007] (1) Active noise reduction method

[0008] Plasma noise reduction is one of the active noise reduction methods. This method uses a plasma actuator to ionize the air and generate a directional jet under the action of the electric field force. The directional jet induced by the plasma actuator is used to control the airflow passing through the landing gear surface, reduce flow separation and pressure pulsation, and thus reduce the aerodynamic noise and vibration on the landing gear surface.

[0009] Another active noise reduction method is the air curtain method. The principle is: add extra laminar flow to the cylindrical surface of the landing gear. The extra laminar flow is called "air curtain". The air film generates laminar flow around and behind the landing gear, which moves the turbulence separation point backward, significantly reduces the turbulence area, and greatly reduces the noise generated by turbulence, that is, reduces the blunt body flow noise of the landing gear.

[0010] In addition, there is a noise reduction method based on edge jets for the interference noise and strut noise caused by the mutual position of landing gear structural parts. This method applies vertical airflow to the edge of the leeward surface of the torque arm, thereby forming a closed space between the torque arm, the jet plane and the strut, which can effectively improve the flow separation condition on the rear side of the torque arm, reduce the pressure pulsation caused by the tail vortex shedding caused by the torque arm and the impact on the strut, and achieve the purpose of reducing the intensity of the sound source. At the same time, the edge jet also effectively reduces the intensity of the blunt body flow noise, which significantly reduces the strut noise.

[0011] (2) Passive noise reduction method

[0012] Reducing the length of the landing gear is the simplest and most direct passive noise reduction method. Since the noise of the landing gear mainly comes from the struts, reducing the length of the landing gear can effectively reduce the range of noise generation, thereby achieving the purpose of noise reduction.

[0013] Another passive noise reduction method is to optimize the shape of the landing gear, that is, to install fairings, fairing nets, fairing shells, etc. The complex geometric shape of the landing gear and the interaction of aerodynamics will form a complex airflow field structure. Optimizing the shape of the landing gear to make it more streamlined can reduce the complexity of the flow field, reduce airflow separation, reduce pressure pulsation on the landing gear surface, and reduce the noise of the landing gear to a certain extent.

[0014] In addition, covering and filling the landing gear cavity structure is also an effective noise reduction measure. The landing gear cavity may produce some strong pure sound noise due to the self-excited oscillation of the cavity. Therefore, filling and covering the landing gear cavity structure can reduce the landing gear pure sound noise.

[0015] The above landing gear noise reduction method has the following main shortcomings:

[0016] (1) Active noise reduction methods can achieve effective control of flow and noise without changing the overall aerodynamic shape. However, this method not only requires additional energy input, but also requires the coordinated work of corresponding sensors, controllers, actuators, etc., which increases the complexity of the system and reduces reliability.

[0017] (2) In passive noise reduction methods, due to the increasing diameter of the nacelle of high bypass ratio engines and the design requirements for the landing gear height during aircraft takeoff, reducing the length of the landing gear is not applicable in engineering practice. Optimizing the shape of the landing gear is a popular method, but this method usually requires the installation of fairings around the landing gear structure, which will significantly increase the structural weight and lead to a reduction in payload. The presence of the fairing will also place higher requirements on the space of the landing gear compartment. Some cavity structures of the landing gear may have other functions and usually cannot be simply filled or covered.

[0018] Therefore, how to effectively reduce landing gear noise while not increasing the complexity of the system and not reducing system reliability is a problem that urgently needs to be solved. Summary of the invention

[0019] In order to solve the above problems existing in the prior art, the present invention proposes an aircraft landing gear noise reduction structure based on a longitudinal corrugated strut design.

[0020] The present invention can be achieved through the following technical solutions:

[0021] The invention discloses an aircraft landing gear noise reduction structure based on a longitudinal corrugated strut design. The landing gear is composed of five parts: a wheel, a main strut, an auxiliary strut, a connecting shaft and a torsion bar. The upper end of the main strut is connected to the aircraft body, and the lower end of the main strut is connected to the landing gear wheel. The main strut is a combination structure of a variable diameter section and a constant diameter section in the longitudinal direction. The variable diameter section is a corrugated section including one or more corrugations; and the corrugated section and the constant diameter section have a smooth transition.

[0022] Furthermore, the corrugation shape is a single waveform or a combination of multiple waveforms.

[0023] Furthermore, the landing gear body is a single-wheel, two-wheel or four-wheel landing gear model.

[0024] Furthermore, the corrugated sections and the equal diameter sections are realized by integral molding, segmented joining or installation of additional layers.

[0025] Furthermore, the type of the corrugation is one of a sine waveform, a cosine waveform, a half-sine waveform, a cosine waveform, a square wave, a triangular waveform, and a triangular waveform with rounded corners, or a combination of two or more thereof.

[0026] Furthermore, the specific position of the main pillar corrugated section starts from the connection end between the main pillar and the aircraft body, and the length of the corrugated section is determined according to the wavelength and wave number of the corrugation. The wave height range of the corrugation is A=0.05-02D, and the wavelength is λ=0.5-2D, where D is the average diameter of the main pillar.

[0027] Furthermore, the maximum diameter of the main pillar is the average diameter D of the main pillar plus twice the wave height, and the minimum diameter is the average diameter D of the main pillar minus twice the wave height.

[0028] Furthermore, the wave height and wavelength parameters of the main support corrugated section are combined and distributed, and different wave height and wavelength parameters are used in the same corrugated section.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention belongs to the noise reduction technology of fluid mechanics wave-vortex interaction. Compared with various existing noise control technologies, such as reducing the height of the landing gear, fairing devices, serrated trailing edges and cavity filling, the corrugated strut noise control starts from the flow and sound generation mechanism of the landing gear, and based on the research and analysis of the boundary vortex flow and boundary pseudo-vortex energy flow of vortex dynamics, the inherent relationship and development between the flow structure and the noise source, and the far-field radiation noise is established, so the noise reduction effect is very significant; this corrugated structure does not need to significantly change the outer structure of the landing gear, and will hardly affect the installation layout of other structures of the landing gear, and there is no need to redesign related structures such as the landing gear compartment; in addition, the corrugated strut structure has the advantages of simple installation and stable operation. The invention improves the vortex shedding behavior of the landing gear strut wake, thereby reducing the interference effect of the wake on downstream components, thereby achieving the purpose of reducing the landing gear noise, and will not increase the resistance of the landing gear components, which is easy to implement and maintain in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a typical two-wheel landing gear

[0032] Figure 2 Schematic diagram of the corrugated strut landing gear described in this article

[0033] Figure 3-1 , 3-2 are schematic diagrams of typical two-wheel and four-wheel landing gears respectively

[0034] Figure 4 Schematic diagram of the combination of ripple segments and equal value segments

[0035] Figure 5 Schematic diagram of various waveforms

[0036] Figure 6 Schematic diagram of minimum corrugation diameter

[0037] Figure 7 Installation diagram of corrugated section

[0038] Figure 8 Schematic diagram of corrugation segments with different corrugation parameter combinations DETAILED DESCRIPTION

[0039] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0040] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] The present invention provides a corrugated strut that can be used for landing gear noise reduction. Compared with a traditional landing gear strut system, the corrugated strut of the present invention can significantly reduce the aerodynamic noise generated by the landing gear during takeoff and landing of an aircraft, thereby reducing the noise pollution to the crew and residents around the airport.

[0042] The present invention takes the front landing gear of a certain type of aircraft as an example to introduce a landing gear noise reduction structure based on the longitudinal corrugated strut design, so that those skilled in the art can better understand the present invention and implement it. The landing gear consists of five parts: wheels, main struts, auxiliary struts, connecting shafts and torsion bars. Figure 1 As shown: 1-main strut, 2-auxiliary strut, 3-wheel, 4-torque arm, 5-coupling. The upper end of the main strut 1 is connected to the aircraft body, and the lower end of the main strut 1 is connected to the landing gear coupling 5.

[0043] The present invention improves the landing gear strut component from a traditional equal-diameter columnar structure to a combination of a variable-diameter section and an equal-diameter section. The variable-diameter section is a corrugated section including one or more corrugations. The corrugated section can be any waveform and smoothly transition with the equal-diameter section. The corrugated shape can be a single waveform or a combination of multiple waveforms.

[0044] The specific implementation contents of using longitudinal corrugated struts to reduce landing gear noise are as follows:

[0045] Implementation content 1: Combination Figure 2 As shown, the aircraft landing gear noise reduction structure based on longitudinal corrugated struts described in this embodiment has a simple structure of the corrugated section of the strut, which can be formed in an integral manner or by an additional layer. Therefore, this embodiment is easy to implement in engineering applications.

[0046] Implementation content 2: Combination Figure 3-1 As shown in 3-2, the main landing gear of the corrugated strut described in this embodiment can be a single-wheel, two-wheel or four-wheel landing gear model.

[0047] Implementation content three: Combination Figure 4 As shown, the main strut described in this embodiment is a landing gear strut with one or more corrugations arranged longitudinally. The main strut is a segmented structure, including two sections, the first section is a corrugated section a, and the second section is a constant diameter section b. The corrugated section a is mainly distributed at the upper end that does not affect other components, and the constant diameter section b is distributed in the remaining position where it is not easy to arrange corrugations. The corrugated section a and the constant diameter section b can be realized by integral molding, segmented joining or installation of additional layers. The connection position of the corrugated section a and the constant diameter section b is tightly fitted, and the transition is smooth.

[0048] Implementation content 4: Combination Figure 5As shown, the types of corrugations of the main pillars described in this embodiment are one or a combination of two or more of a sine wave, a cosine wave, a half-sine wave, a cosine wave, a square wave, a triangular wave, and a triangular wave with rounded corners.

[0049] Implementation content five: Combination Figure 6 As shown, the minimum diameter of the corrugated strut of the landing gear described in this embodiment is equal to or greater than the average diameter D of the main strut.

[0050] Implementation content six: Combination Figure 5 , as shown in FIG7 , the specific position of the corrugated section of the corrugated support described in this embodiment is the start of the connection end between the landing gear support and the fuselage P, and the length of the corrugated section is specifically determined according to the wavelength and wave number of the corrugation, in principle without affecting other components. The wave height of the corrugation ranges from A=0.05-0.2D, and the wavelength is λ=0.5-2D, where D is the average diameter of the main support.

[0051] Implementation content seven: Combination Figure 8 As shown, the corrugated section parameters of the corrugated support in this embodiment can be combined and distributed, and different wave height and wavelength parameters are used in the same corrugated section. The wave height of corrugated section 1 (C in the figure) and the wave height of corrugated section 2 (D in the figure) take different values ​​respectively.

[0052] Example:

[0053] Taking a simplified front landing gear of a certain type of aircraft as an example, the landing gear height is H=2.3m, the wheel diameter is Dw=0.72m, the strut diameter is Ds=0.18m, and the typical flight speed condition Ma=0.15-0.25 during takeoff and landing of the aircraft is adopted. Computational fluid dynamics is used to perform numerical optimization on the corrugation. By setting three corrugations with a wavelength of λ=2D and a wave height of A=0.1D starting from the connecting section between the landing gear strut and the fuselage, the best noise reduction effect is achieved, the total noise will be lower than 3-4dB, and the landing gear resistance will not be significantly increased. In addition, the present invention is also applicable to the noise suppression of landing gears of other structural types.

[0054] The principle of the present invention is:

[0055] The aerodynamic noise control technology of the corrugated landing gear strut is based on the wave-vortex interaction theory of vortex dynamics: waves and vortices always coexist in turbulent flow fields. When low-speed flow separates, nonlinear unstable waves prepare for the generation of separation vortices, and the vortex structure that has been formed creates shear in the flow field, creating conditions for a new level of unstable waves. The periodic change of the cylinder diameter in the span direction to obtain a corrugated cylinder can effectively reduce the pulsation of the resistance and lift of the cylinder and reduce the distribution of turbulent vortices in the cylindrical flow field. The boundary vorticity flow and boundary pseudo-vortex energy flow represent the rate at which the wall vorticity diffuses into the flow field and the interaction between the flow field vorticity and the wall vorticity, respectively. The corrugated cylinder changes the distribution of the boundary vorticity flow and boundary pseudo-vortex energy flow on the surface of the cylinder, resulting in a decrease in the vorticity generated by the wall and diffused into the flow field, thereby reducing the vortex structure of the flow field.

[0056] According to the vortex sound theory: under low-speed conditions, the vortex is the sound of flow. If the vortex is controlled, the source of the sound is controlled. There are a large number of cylindrical structures in the landing gear structure, such as pillars, couplings, etc. The corrugated pillar method proposed in the present invention can not only effectively reduce the radiated noise of the landing gear, but also reduce the resistance. After a large number of scientific research experiments and numerical calculations in the early stage, the present invention has proved that the spanwise corrugated cylinder has a significant inhibitory effect on noise; and the noise source of the landing gear is analyzed, and it is found that the main source is a large number of turbulent vortex structures in the wake of the pillar and the wheel component. The turbulent vortex of the main pillar wake will also interfere with the downstream components (such as the auxiliary pillar) to generate a lot of noise, indicating that the pillar component is the most important noise source of the landing gear. Therefore, the noise control of the landing gear can be achieved by the modified design of the longitudinal corrugated pillar, and the structural strength requirements are considered when designing the corrugated pillar, so that the minimum diameter of the corrugated pillar is greater than the original landing gear pillar diameter. The corrugated pillar method proposed in the present invention can not only effectively reduce the radiated noise of the landing gear, but also reduce the resistance. Through the modified design of the corrugated strut, the turbulent vortex intensity of the landing gear strut wake is weakened, and the originally strong periodic flow is suppressed. At the same time, the introduction of the longitudinal corrugations optimizes the turbulent wake and reduces the radiation noise of the main strut components. The reduction of the turbulent vortex in the wake of the main landing gear strut reduces the interference with the auxiliary strut, resulting in a reduction in the noise generated. The corrugated strut has basically no effect on the remaining components, thereby reducing the overall noise radiated by the landing gear. Under the creative idea of ​​the present invention, technicians in this field can make various changes and improvements to the above-mentioned structure and shape, including other combinations of these features. These deformations and / or combinations all fall within the technical field involved in the present invention and fall within the scope of protection of the claims of the present invention.

Claims

1. An aircraft landing gear noise reduction structure based on a longitudinal corrugated strut design, the landing gear consists of five parts: a wheel, a main strut, an auxiliary strut, a connecting shaft and a torsion bar, the upper end of the main strut is connected to the aircraft body, and the lower end of the main strut is connected to the landing gear connecting shaft, characterized in that: The main strut is a combination structure of a variable diameter section and a constant diameter section in the longitudinal direction, the variable diameter section is a corrugated section including one or more corrugations; and the corrugated section has a smooth transition with the constant diameter section; the specific position of the main strut corrugated section starts from the connection end of the main strut and the aircraft body, and the length of the corrugated section is determined according to the wavelength and wave number of the corrugation, the wave height of the corrugation ranges from A=0.05~0.2D, and the wavelength is λ=0.5-2D, wherein D is the average diameter of the main strut; the maximum diameter of the main strut is the average diameter D of the main strut plus 2 times the wave height, and the minimum diameter is the average diameter D of the main strut minus 2 times the wave height; the wave height and wavelength parameters of the corrugated section of the main strut are combined and distributed, and different wave height and wavelength parameters are used in the same corrugated section.

2. The aircraft landing gear noise reduction structure based on the longitudinal corrugated strut design according to claim 1 is characterized in that: The corrugation shape is a single waveform or a combination of multiple waveforms.

3. The aircraft landing gear noise reduction structure based on the longitudinal corrugated strut design according to claim 1, characterized in that: The landing gear body is a single-wheel, two-wheel or four-wheel landing gear model.

4. The aircraft landing gear noise reduction structure based on the longitudinal corrugated strut design according to claim 1, characterized in that: The corrugated sections and the equal diameter sections are realized by integral molding, segmented joining or installation of additional layers.

5. The aircraft landing gear noise reduction structure based on longitudinal corrugated strut design according to claim 1, characterized in that: The type of the corrugation is one of a sine waveform, a cosine waveform, a half-sine waveform, a cosine waveform, a square wave, a triangle waveform, and a triangle waveform with rounded corners at the tip, or a combination of two or more thereof.

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