Low-resistance acoustic lining panel based on crescent inclined holes and design method thereof

Abstract

The invention discloses a low-resistance acoustic lining panel based on crescent inclined open pores and a design method thereof, the structure adopts a perforated plate with crescent inclined open pores to replace a circular perforated plate of an original acoustic lining, the crescent opening direction is consistent with the airflow direction, and by reducing the size of the open pores in the flow direction and reducing the airflow entering a cavity, the low-resistance acoustic lining panel is formed. Therefore, the flow resistance of the acoustic liner is reduced, the sectional area of the opening is kept unchanged, and the acoustic performance of the acoustic liner is ensured to be unchanged.

Description

Technical Field

[0001] This invention relates to the field of aircraft engine nacelles, and more specifically to a low-resistivity acoustic liner panel based on crescent-shaped inclined openings and its design method. Background Technology

[0002] "Low noise" has long been a key goal pursued by large civil aircraft, and reducing engine noise is crucial to reducing the overall noise level of the aircraft. Currently, the most effective method for reducing engine noise is to install sound-absorbing linings on the inner walls of the engine nacelle. For example... Figure 1 As shown, an acoustic liner typically consists of a perforated plate, a honeycomb core, and a rigid backing plate. Essentially, it can be viewed as an array of regularly arranged Helmholtz resonant cavities. Noise generated by the engine during operation passes through the acoustic liner surface. When the sound wave frequency approaches the resonant frequency corresponding to the acoustic liner, a violent pressure fluctuation is generated at the perforation openings of the perforated plate, thus converting sound energy into internal energy and achieving noise reduction. However, the perforated plate also introduces a "side effect" of increased drag during sound absorption, thereby increasing the aircraft's overall drag and consequently increasing fuel consumption. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a low-resistance acoustic liner panel based on crescent-shaped inclined openings and its design method. The perforated panel is provided with a uniformly arranged array of crescent-shaped inclined openings. The drag reduction mechanism of this invention is achieved by reducing the size of the openings along the flow direction and reducing the airflow entering the cavity, while maintaining a constant opening area, thereby ensuring that acoustic performance is not affected. The specific technical solution is as follows:

[0004] A low-resistivity acoustic liner panel based on crescent-shaped inclined openings includes a perforated plate, wherein the crescent-shaped inclined openings are evenly distributed in an array on the perforated plate, and the positions of the crescent-shaped inclined openings in two adjacent rows are staggered, such that the crescent-shaped inclined openings in the middle row can form an equilateral triangle with the center lines connecting the left and right adjacent crescent-shaped inclined openings in the row before and the row after.

[0005] The crescent-shaped inclined hole is inclined in the opposite direction to the airflow direction, and the crescent-shaped opening faces the airflow direction.

[0006] Furthermore, the specific shape of the crescent-shaped inclined hole is as follows: the outer arc of the crescent shape is a semicircle with the two endpoints of the crescent shape as diameters, and the inner arc of the crescent shape is an arc with the two endpoints of the crescent shape as chords and a central angle of 90°.

[0007] Furthermore, the radius of the circle corresponding to the arc with the two endpoints of the crescent shape as chords and a central angle of 90° is...

[0008]

[0009] Where d is the diameter of the circular opening under the same acoustic performance conditions.

[0010] Furthermore, the inclination angle of the crescent-shaped inclined hole is α, and 45° < α < 90°.

[0011] A design method for a low-resistivity acoustic liner panel based on crescent-shaped inclined openings includes the following steps:

[0012] Step 1: Determine the diameter d of the circular hole when the perforated plate has a circular opening, according to the design requirements;

[0013]

[0014] Where r is the target design acoustic impedance, σ and t are the perforation rate and thickness of the perforated plate, respectively, ρ, c, and μ are the density, sound velocity, and viscosity of air, respectively, K is the perforation constant, and f is the incident sound wave frequency.

[0015] Step 2: Based on the diameter d of the circular hole and the known perforation rate σ, the side length L of the equilateral triangle is obtained by solving the following formula:

[0016]

[0017] according to Obtain the radius R corresponding to the inner arc of the crescent shape. 内 ;

[0018] according to The radius R corresponding to the inner arc of the crescent shape is calculated. 外 ;

[0019] Step 3: Based on the R of the crescent-shaped inclined opening obtained in Step 2 内 R 外 A hole is made in the perforated plate with the side length L of the equilateral triangle distribution and the inclination angle α of the crescent-shaped inclined opening.

[0020] The beneficial effects of this invention are as follows:

[0021] The acoustic liner panel of the present invention changes the opening shape of the perforated plate from the original circular shape to a crescent-shaped inclined opening, which can reduce the flow resistance coefficient of the acoustic liner without changing the overall acoustic performance of the acoustic liner, that is, achieve a considerable drag reduction effect, thereby helping the aircraft to reduce fuel consumption. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an acoustic liner structure with a perforated plate with circular holes in the prior art.

[0023] Figure 2 This is a partial top view of a low-resistivity acoustic liner panel with a crescent-shaped opening, according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the tilt angle of a crescent-shaped tilting hole according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of a crescent-shaped inclined hole design according to an embodiment of the present invention.

[0026] Figure 5 This is a comparative experimental verification diagram of the drag reduction effect of the present invention (α=60°).

[0027] Figure 6 This is a comparative diagram of the acoustic characteristics experimental verification of an embodiment of the present invention (α=60°).

[0028] Figure 7 This is a comparison chart of numerical simulation results of drag reduction effect in an embodiment of the present invention (α=75°). Detailed Implementation

[0029] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0030] like Figure 1 As shown, the existing acoustic liner structure is a sandwich structure, with a perforated plate 1-1 at the top, the openings being circular with a diameter of d; a thin-walled hexagonal honeycomb layer 1-2 in the middle; and a rigid solid wall 1-3 at the bottom. This invention only modifies the shape of the perforated plate 1-1, while keeping the rest of the structure unchanged. The drag reduction mechanism of this invention is to reduce the size of the perforated plate openings along the flow direction while maintaining the opening area unchanged, thereby ensuring that the acoustic performance is not affected.

[0031] like Figure 2 The diagram shown is a top view of the perforated plate with crescent-shaped inclined openings according to the present invention. The crescent-shaped inclined openings are evenly distributed in an array on the perforated plate, and the positions of the crescent-shaped inclined openings in two adjacent rows are staggered, so that the crescent-shaped inclined opening in the middle row can form an equilateral triangle with the center line connecting the crescent-shaped inclined openings on the left and right sides of the row before and after it. The side length of the equilateral triangle is L.

[0032] like Figure 3 As shown, the inclination angle of the crescent-shaped inclined hole is α, and 45° < α < 90°. Assuming the airflow flows parallel to the surface of the acoustic liner panel, the crescent-shaped opening faces the direction of the airflow.

[0033] Figure 4 This is a schematic diagram of the crescent-shaped inclined hole design. Specifically, a circle is drawn with point O as the center and radius r. Further, two points A and C are taken on the circumference such that the angle θ between line segments AO and CO is 90°. Then the length of the chord AC is... Furthermore, with the midpoint B of line segment AC as the center, construct semicircle two, the diameter of which is... By subtracting the arc-shaped region with a central angle of 90° from the second semicircle, we can obtain a crescent shape, such as... Figure 4 The shaded area shown.

[0034] The area S of the crescent shape is given below. c The expression:

[0035] Where S1 is the area of ​​semicircle ABC:

[0036]

[0037] S2 is the area corresponding to the segment ABC:

[0038] S2 = S3 - S4

[0039] Where S3 and S4 are the areas corresponding to sector AOC and triangle AOC, respectively, that is:

[0040]

[0041] In summary, the area of ​​the crescent shape is:

[0042]

[0043] During the design process, the initial circular hole diameter d is first calculated. While maintaining the opening area constant, we have:

[0044]

[0045] Another embodiment of the present invention provides a design method for a low-resistivity acoustic liner panel based on a crescent-shaped inclined opening, comprising the following steps:

[0046] Step 1: Determine the diameter d of the circular hole when the perforated plate has a circular opening, according to the design requirements;

[0047]

[0048] Where r is the target design acoustic impedance, σ and t are the perforation rate and thickness of the perforated plate, respectively, ρ, c, and μ are the density, sound velocity, and viscosity of air, respectively, K is the perforation constant, and f is the incident sound wave frequency.

[0049] Step 2: Based on the diameter d of the circular hole and the known perforation rate σ, the side length L of the equilateral triangle is obtained by solving the following formula:

[0050]

[0051] according to Obtain the radius R corresponding to the inner arc of the crescent shape.内 ;

[0052] according to The radius R corresponding to the inner arc of the crescent shape is calculated. 外 ;

[0053] Step 3: Based on the R of the crescent-shaped inclined opening obtained in Step 2 内 R 外 The side length L of the equilateral triangle distribution and the tilt angle α of the crescent-shaped inclined opening are used to make holes in the perforated plate.

[0054] Below is a comparison of the experimental results for the drag coefficients of two types of acoustic liners: a crescent-shaped inclined opening and a circular opening, when the tilt angle α is 60°. Figure 5 As shown, the horizontal axis represents the Mach number of the airflow, ranging from 0.1 to 0.6. It can be seen that under the studied operating conditions, the drag coefficient of the crescent-shaped orifice acoustic liner is significantly smaller than that of the circular orifice acoustic liner.

[0055] Figure 6 This chart compares the experimental results of acoustic parameters for two types of acoustic liners. For the acoustic liner, the acoustic impedance is determined by the perforated plate, and the acoustic impedance by the back cavity. Only the acoustic impedance results are compared here. At the target frequency of 1500Hz, the acoustic impedances of both are almost equal, indicating that the acoustic parameters of the acoustic liners remain almost unchanged. Therefore, when α = 60°, the use of a crescent-shaped inclined perforation acoustic liner achieves a reduction in the flow resistance coefficient without affecting the acoustic performance of the liner, resulting in a considerable drag reduction effect.

[0056] Figure 7 Numerical simulation results comparing the drag coefficients of two types of acoustic liners, crescent-shaped inclined opening and circular opening, are presented when the tilt angle α is 75°. It can be seen that at Mach numbers of 0.1 and 0.3, the drag coefficient of the crescent-shaped inclined opening acoustic liner is lower than that of the circular opening acoustic liner.

[0057] Using an inclined hole can reduce the amount of fluid entering the acoustic liner back cavity, thereby further reducing the acoustic liner drag. However, if the inclination angle α is too small, it will cause processing difficulties and affect the acoustic performance of the acoustic liner. Usually, it is taken as 45° < α < 90°.

[0058] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A low-resistivity acoustic liner panel based on crescent-shaped inclined openings, characterized in that, The perforated plate includes crescent-shaped inclined holes that are evenly distributed in an array on the perforated plate, and the positions of the crescent-shaped inclined holes in two adjacent rows are staggered, so that the crescent-shaped inclined holes in the middle row can form an equilateral triangle with the center lines connecting the left and right adjacent crescent-shaped inclined holes in the row before and the row after. The crescent-shaped inclined hole is inclined in the opposite direction to the airflow direction, and the crescent-shaped opening faces the airflow direction.

2. The low-resistivity acoustic liner panel based on crescent-shaped inclined openings according to claim 1, characterized in that, The specific shape of the crescent-shaped inclined hole is as follows: the outer arc of the crescent shape is a semicircle with the two endpoints of the crescent shape as diameters, and the inner arc of the crescent shape is an arc with the two endpoints of the crescent shape as chords and a central angle of 90°.

3. The low-resistivity acoustic liner panel based on crescent-shaped inclined openings according to claim 2, characterized in that, The radius of the circle corresponding to the arc with the two endpoints of the crescent shape as chords and a central angle of 90° is... Where d is the diameter of the circular opening under the same acoustic performance conditions.

4. The low-resistivity acoustic liner panel based on crescent-shaped inclined openings according to claim 1, characterized in that, The inclination angle of the crescent-shaped inclined hole is α, and 45° < α < 90°.

5. A design method for a low-resistivity acoustic liner panel based on crescent-shaped inclined openings as described in any one of claims 1 to 3, comprising the following steps: Step 1: Determine the diameter d of the circular hole when the perforated plate has a circular opening, according to the design requirements; in, r is the target acoustic impedance, J and t are the perforation rate and thickness of the perforated plate, respectively, ρ, c, and μ are the density, sound velocity, and viscosity of air, respectively, K is the perforation constant, and f is the incident sound wave frequency. Step 2: Based on the diameter d of the circular hole and the known perforation rate J, the side length L of the equilateral triangle is obtained by solving the following formula: according to Obtain the radius R corresponding to the inner arc of the crescent shape. 内 ; according to The radius R corresponding to the inner arc of the crescent shape is calculated. 外 ; Step 3: Based on the R of the crescent-shaped inclined opening obtained in Step 2 内 R 外 A hole is made in the perforated plate with the side length L of the equilateral triangle distribution and the inclination angle α of the crescent-shaped inclined opening.

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