A dimple structure for noise reduction of an airfoil surface

Abstract

The present application belongs to the technical field of aircraft body noise reduction, and specifically discloses a pit structure for wing surface noise reduction, which is arranged on a wing and comprises: a layout base surface arranged on the upper surface and the lower surface of the wing and located at the tail of the wing along the axis direction of the fuselage on which the wing is located, the layout base surface has a correlation in length with the wing along the chord length direction, and the layout base surface is located at a preset proportional position of the wing along the chord length direction; and pits distributed on the layout base surface in a preset arrangement mode, which has the following advantages: different from the sawtooth noise reduction structure, the shallow pit structure is directly applied to the rear part of the wing flange, and no additional body effect is generated. Compared with the conventional passive method of applying permeable materials, the total resistance increase caused by the shallow pit structure is small, and only a small amount of aerodynamic loss is generated. Moreover, the impermeability of the shallow pit structure ensures that the noise reduction performance will not be easily changed due to pollution. Compared with the previous noise reduction structure, the present application has better optimization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aircraft body noise reduction, in particular to a pit structure for reducing noise on the surface of a wing. BACKGROUND

[0002] The phenomenon of turbulent boundary layer trailing edge noise is a long-standing problem in the field of aeroacoustics. In addition to this broadband sound mechanism, when turbulent flow interacts with a blunt trailing edge, the resulting vortex shedding can lead to additional tonal noise. The noise reduction research of these two noise phenomena, i.e. broadband "turbulent boundary layer trailing edge noise" and tonal "vortex shedding blunt trailing edge" noise, has been the focus of research in the past decade.

[0003] The application of natural serrations on the trailing edge has successfully reduced noise. The retrofitted serrated appendages can break up the turbulent vortices entering the wake, thus reducing the intensity of the edge scattering. In addition, it has also been found that the serrations will destructively interfere with the radiated sound from the trailing edge. Another popular passive method studied to reduce the above two noise phenomena includes the application of permeable materials on the trailing edge. The application of permeable materials has successfully reduced far-field noise by 5-10 dB. However, the application of porous materials results in a reduction of lift and a significant increase in surface frictional drag. Under operating conditions, this reduced aerodynamic performance must be compensated by higher flight speeds, which in turn increases the "turbulent boundary layer trailing edge noise". Due to this aerodynamic loss, the industrial use of porous materials to reduce noise remains a distant reality. In addition, due to the porosity / permeability, porous materials are easily contaminated by dust or liquids (e.g. de-icing fluids), which can change their noise reduction capabilities. Therefore, it is most important to explore methods that can reduce noise without affecting the airfoil aerodynamic performance.(General defects of prior art)

[0004] In order to solve the problem of body noise, the prior art provides the following scheme: a three-section wing trailing edge side edge noise reduction scheme design with special configuration baffle added in Chinese patent CN115292818A proposes a noise reduction scheme of adding a strip-shaped baffle at the end of the flap towards the main wing root. However, since an appendage needs to be added to the flap, the effect of the appendage may affect the flow field of the airfoil.(Solution of prior art and main problems in the solution)

[0005] A bionic multi-hole noise reduction design method based on owl wings is proposed in a Chinese patent CN06529020A, "Unmanned aerial vehicle capable of landing on any terrain". The main design steps are as follows: on the premise that the reference airfoil geometric parameters do not change, the sound source is determined according to the flow field structure around the reference airfoil, the multi-hole medium equivalent to the owl wing velvet-like covering is attached inside the turbulent boundary layer on the surface of the airfoil, and then the properties, position and distribution of the multi-hole medium are appropriately adjusted by using the results of wind tunnel test and noise test, so as to achieve the purpose of noise reduction. This passive noise reduction method first needs to analyze and determine the source position of noise, and at the same time, the addition of medium on the surface of the wing will increase the frictional resistance of the wing and change the aerodynamic performance, and it is also easy to reduce the noise reduction ability due to pollution and other problems.

[0006] In summary, the passive noise reduction method of the existing technology does not change the wing itself simply to achieve long-term effective noise reduction performance, and cannot reduce noise without increasing the appendage and ensuring the aerodynamic performance of the wing. SUMMARY

[0007] The present application aims to provide a pit structure for reducing noise on the surface of a wing to solve or improve at least one of the above technical problems.

[0008] Therefore, the first aspect of the present application provides a pit structure for reducing noise on the surface of a wing.

[0009] The first aspect of the present application provides a pit structure for reducing noise on the surface of a wing, which is arranged on the wing, and the pit structure comprises: a layout base surface arranged on the upper surface and the lower surface of the wing and located at the end of the wing away from the fuselage, the layout base surface being located at a predetermined proportional position of the wing along the chord length direction of the wing; and pits distributed on the layout base surface in a predetermined arrangement manner.

[0010] Further, the layout base surface comprises a first layout base surface located on the upper surface of the wing and a second layout base surface located on the lower surface of the wing, and the pits have a geometric center; the geometric center of the pit on the first layout base surface is projected on the second layout base surface in the longitudinal direction and located between the pits on the second layout base surface; and / or the geometric center of the pit on the second layout base surface is projected on the first layout base surface in the longitudinal direction and located between the adjacent pits on the first layout base surface.

[0011] Further, the opening depth of the pit is less than the radius of the inner arc surface of the pit.

[0012] Furthermore, the base surface has an axis of symmetry along the chord length direction, and the preset arrangement includes: setting a recess on the base surface along the axis of symmetry, and setting multiple recesses on the base surface along the circumferential direction of the recess; or setting multiple recesses on the base surface along the axis of symmetry, and setting at least one row of recesses towards each end of the wing along the chord length direction, and setting multiple recesses in each row, with the recesses between adjacent rows staggered along the wingspan direction.

[0013] Furthermore, the base surface has a first end and a second end along the chord direction, and the preset proportional position is: the first end is located at 81% to 82% of the wing length along the chord direction from the wing root to the wing tip; and / or the second end is located at 97% to 98% of the wing length along the chord direction from the wing root to the wing tip.

[0014] The beneficial effects of this invention compared to the prior art are as follows:

[0015] The application of pits causes larger eddies to decompose into finer scales towards the trailing edge, and achieves disruption of transverse coherence and reduction of flow-directed convective eddies in the low to mid-frequency range. Power spectral density spectra of surface pressure fluctuations measured at different locations on the pit surface show elimination of tonal eddy shedding noise. Since trailing edge noise is inherently broadband and tonal, the application of pits helps reduce trailing edge noise.

[0016] Unlike serrated noise reduction structures, the shallow concave structure is applied directly to the rear of the wing flange, avoiding additional appendage effects. Compared to traditional passive methods using permeable materials, the increase in total drag caused by the shallow concave structure is minimal, with only a small aerodynamic loss. Furthermore, its non-permeable nature ensures that its noise reduction performance will not easily change due to contamination. This represents a significant improvement over previous noise reduction structures.

[0017] Additional aspects and advantages of embodiments of the invention will become apparent in the following description or may be learned by practice of embodiments of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0019] Figure 1 This is a schematic diagram of the recesses of the present invention being formed on the wing surface;

[0020] Figure 2 This is a schematic diagram showing the depth of the recess in this invention;

[0021] Figure 3 This is a schematic diagram showing the arrangement of the pits in this invention;

[0022] Figure 4 Fig. 1 is a partial view of a wing with a concave structure according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present application clearer, the following will further describe the present application with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0024] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application. However, the present application can also be implemented in other different manners than those described herein, and therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0025] Referring to Fig. 1, the following describes a concave structure for reducing noise on a wing surface according to some embodiments of the present application. Figures 1-4

[0026] Embodiments of the first aspect of the present application provide a concave structure for reducing noise on a wing surface. In some embodiments of the present application, as shown in Fig. 1, a concave structure for reducing noise on a wing surface is provided, which is arranged on a wing, and the concave structure comprises: Figures 1-4

[0027] A layout base surface is arranged on the upper surface and the lower surface of the wing and located at an end of the wing away from the fuselage, and the layout base surface is located at a preset proportion position of the wing along the chord length direction of the wing.

[0028] Concaves are distributed on the layout base surface in a preset arrangement manner.

[0029] In some embodiments, the first layout base surface located on the upper surface of the wing and the second layout base surface located on the lower surface of the wing, and the concaves have a geometric center.

[0030] The projection of the geometric center of the concaves on the first layout base surface on the longitudinal direction is located between the concaves on the second layout base surface; and / or

[0031] The projection of the geometric center of the concaves on the second layout base surface on the longitudinal direction is located between the adjacent concaves on the first layout base surface.

[0032] In some embodiments, the opening depth of the concaves is less than the radius of the inner arc surface of the concaves.

[0033] In some embodiments, the layout base surface has a symmetry axis along the chord length direction, and the preset arrangement manner comprises:

[0034] ​​A pit is arranged on the layout base along the symmetry axis, and a plurality of pits are arranged on the layout base along the circumferential direction of the pit; or

[0035] A plurality of pits are arranged on the layout base along the symmetry axis, and at least one row of pits is arranged on the layout base along the chord length direction to both ends of the wing, and a plurality of pits are arranged in each row, and the pits between adjacent rows are arranged in staggered manner along the wing span direction.

[0036] In some embodiments, the layout base has a first end portion and a second end portion along the chord length direction, and the preset proportion position is:

[0037] The first end portion is located at 81% to 82% of the wing length along the chord length direction from the wing root to the wing end portion; and / or

[0038] The second end portion is located at 97% to 98% of the wing length along the chord length direction from the wing root to the wing end portion.

[0039] The present application provides a pit structure for reducing noise on the surface of a wing. The application of the pit can cause larger vortexes to break down into finer scales towards the trailing edge, and can achieve the destruction of crosswise coherence and the reduction of streamwise convective vortex flow velocity in the medium and low frequency range. The power spectrum density spectrum of the surface pressure fluctuation measured at different positions on the pit surface shows the elimination of tonal vortex shedding noise. The trailing edge noise is essentially broadband and tonal, so the application of the pit helps to reduce the trailing edge noise.

[0040] Unlike the sawtooth noise reduction structure, the shallow pit structure is directly applied to the rear of the wing, and does not produce additional appendage effect. Compared with the traditional passive method of applying permeable material, the total drag increase caused by the shallow pit structure is small, only a small amount of aerodynamic loss. And its impermeability ensures that it will not easily change the noise reduction performance due to pollution. Compared with the previous noise reduction structure, it has better optimization.

[0041] Taking NACA0012 airfoil as an example, the new shallow pit structure is applied to the rear of the airfoil in the "flow alignment" mode.

[0042] NACA airfoil is a series of airfoils developed by the National Advisory Committee for Aeronautics (NACA). The code of each airfoil consists of four letters "NACA" and a string of numbers. The exact shape of the airfoil can be obtained by substituting the geometric parameters described by the string of numbers into a specific equation. NACA0012 airfoil is one of the typical airfoils widely used for theoretical calculation and wind tunnel test research comparison of two-dimensional airfoils at home and abroad. NACA0012 airfoil represents that the relative camber of the airfoil is 0 and the relative thickness is 12%.

[0043] The dimples, when acting as a noise reduction structure, can cause a small increase in drag. Dimples have some inherent advantages: they are very shallow and do not complicate the skin panel or cause new design limitations compared to active systems and laminar flow technology. For the same reason, the geometry of the dimple surface is very smooth and therefore not prone to wear or dust accumulation. As Figure 2 shown in FIG. 9, the dimple size data are: dimple radius R is 0.665, dimple depth d is 0.03333, dimple chamfer radius r is 0.15, first dimple spacing L z is 2.2, second dimple spacing L x is 3.812. All parameters are normalized with the trailing edge boundary layer thickness.

[0044] This design choice is a flow-aligned dimple arrangement. As Figure 3 shown in FIG. 10, a series of dimples are applied to the rear of a NACA0012 airfoil, starting at 81.9% chord and extending to 97.1% chord. The periodicity of the dimple arrangement is guaranteed in the spanwise direction, here spanning 12.7% chord.

[0045] Taking a chord length of 0.3m and a blunt trailing edge thickness of 0.6mm airfoil model as an example, the free stream velocity is 20m / s, so the chord-based Reynolds number Re is 4.2x105. The flow-aligned dimple treatment starts at 81.9% of the chord and extends along the streamwise direction to 97.1% of the chord, the baseline configuration without treatment is referred to as the "smooth wall" configuration, denoted by "SW", while the treated baseline is referred to as the "dimple" configuration, denoted by "DIM".

[0046] Between the second dimple and the trailing edge, the increased wall friction downstream of the dimple compared to the SW case has a dissipative effect on the turbulent structures, which makes the vortex shedding into smaller scales, with energy transfer to higher frequencies. Therefore, the dimple treatment breaks the periodicity of the vortex shedding, resulting in no tonal components at approximately 4.5kHz. Near-field analysis shows that this local application of dimples eliminates the tonal vortex shedding noise that would occur in the reference configuration without dimples.

[0047] Another important parameter that determines the strength of the noise generation is the speed at which the pressure field scatters at the trailing edge, while the pressure disturbances in the far field depend on the convective speed in the boundary layer. Compared to the SW configuration, the vortexes in the DIM case take longer to cross the same distance, which indicates that the turbulent structures are stretched in the streamwise direction by the dimple treatment. This means that the vortexes are subjected to a deceleration process as they pass through the dimples, i.e. the convective speed is reduced, which in turn reduces the trailing edge noise.

[0048] The application of shallow dimples results in the destruction of spanwise coherence in the low and mid frequency range and reduces the convection velocity of the streamwise convection vortex. These effects have a positive impact on the reduction of the trailing edge noise, the total drag increases by 1.8%, which is less than 1 drag count; the far-field sound characteristics show that the dimple treatment results in a total sound pressure level reduction in the downstream radiation direction of ≈5.5dB; therefore, the shallow dimple has great application potential as a new passive noise reduction method

[0049] In the description of the present application, it is to be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0050] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope determined by the claims of the present application.

Claims

1. A recessed structure for noise reduction on an airfoil surface, characterized in that, The recessed structure, disposed on the wing, includes: The base surface is set on the upper and lower surfaces of the wing and located at the end of the wing away from the fuselage. The base surface is located at a predetermined proportional position on the wing along the chord length direction of the wing. The pits are distributed on the substrate in a preset arrangement. The mounting base includes: a first mounting base located on the upper surface of the wing and a second mounting base located on the lower surface of the wing, and the recess has a geometric center; The geometric center of the pit on the first mounting surface projects longitudinally onto the second mounting surface between the pits on the second mounting surface; and / or The geometric center of the pit on the second mounting surface is projected longitudinally onto the first mounting surface between adjacent pits on the first mounting surface.

2. The recessed structure for noise reduction on an airfoil surface according to claim 1, characterized in that, The depth of the recess is less than the radius of its inner arc surface.

3. The recessed structure for noise reduction on an airfoil surface according to claim 1, characterized in that, The base surface has an axis of symmetry along the chord length direction, and the preset arrangement includes: A recess is provided on the base surface along the axis of symmetry, and multiple recesses are provided on the base surface along the circumferential direction of the recess; or Multiple pits are provided on the base surface along the axis of symmetry, and at least one row of pits is provided at each end of the wing along the chord length direction, with multiple pits in each row, and the pits between adjacent rows are staggered along the wingspan direction.

4. A recessed structure for noise reduction on an airfoil surface according to claim 1, characterized in that, The base surface has a first end and a second end along the chord length direction, and the preset proportional position is as follows: The first end portion is located at 81% to 82% of the wing length along the chord direction from the wing root to the wing tip; and / or The second end is located at 97% to 98% of the wing length along the chord direction from the wing root to the wing tip.

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