Porous bionic model design method based on Helmholtz resonant cavity

Abstract

The invention discloses a porous bionic model design method based on a Helmholtz resonant cavity, and belongs to the technical field of fluid noise control, and the method specifically comprises the following steps: determining the position area of a porous bionic structure on a model according to the flow field and pulsating pressure characteristics of the model; porous bionic structure parameters are designed based on a Helmholtz resonant cavity principle; optimizing the parameters of the porous bionic structure on the basis of S1 and S2; a porous bionic part is introduced on the basis of a reference model based on the Helmholtz resonator principle, pulsating pressure distribution on the surface of the model can be adjusted, the characteristics of a space flow field can be changed, flow noise and flow-induced noise of the model can be reduced to a certain degree, and the effect on line spectrum discrete noise is especially obvious. According to the technical invention, the noise level of a moving object in air or a water medium can be reduced, and a low-noise sound stealth technology is provided.

Description

Technical Field

[0001] The invention relates to the technical field of fluid noise control, and in particular to a porous bionic model design method based on a Helmholtz resonance cavity. Background Art

[0002] At present, some research work on the application of porous bionic structures in fluid and noise control has been carried out at home and abroad, mainly introducing the bionic concepts of organisms such as owls and humpback whales. For example, application number CN201610982241.X uses a porous structure equivalent to pigeon wing velvet feathers to adhere to the inside of the turbulent boundary layer, achieving the purpose of low-noise bionic airfoil; application number 201811559956 uses a gradient porous bionic structure on the trailing edge of the airfoil to address the problem of prominent noise at the trailing edge of the airfoil, which reduces the phenomenon of sudden changes in the flow characteristics at the trailing edge and ultimately achieves the purpose of noise reduction; the microscopic scale structure on the surface of butterfly wings is introduced into the design of the porous material surface to change the propagation direction and energy distribution of the sound waves, thereby improving the noise reduction performance of the material itself; in terms of cylindrical flow and noise control, related studies have adopted the design idea of ​​a structured porous covering layer to control the flow field and noise control of the cylinder in a uniform flow field; in terms of controlling multiphase transport, i.e., gas-liquid-solid interface and flow control, some studies have used honeycomb water transport structures to simulate the transpiration of plants, providing ideas and methods for the study of porous bionic structures in fluid control.

[0003] Some typical bionic structure design methods are given above, which have achieved certain noise reduction effects. The present invention proposes another method, namely a porous bionic model design method based on the Helmholtz resonance cavity. The Helmholtz resonance cavity principle has been mostly used in acoustic control in the past, and the purpose of noise suppression is achieved by controlling the amplitude of sound waves. The characteristic of the method adopted by the present invention is that the porous structure is designed in a targeted manner according to the flow field and pulsating pressure characteristics of the model, and the surface porous structure is designed and optimized in combination with fluid mechanics and acoustic principles, which is different from the acoustic principle of the Helmholtz resonance cavity. Among them, the porous bionic structure includes parameters such as pore shape, pore size and depth, and whether each pore is internally connected, so as to ultimately suppress the pulsating pressure amplitude and thus reduce fluid noise and flow-induced noise. Summary of the invention

[0004] The purpose of the present invention is to propose a porous bionic model design method based on the Helmholtz resonance cavity on the basis of the prior art, to design the porous structure in a targeted manner according to the flow field and pulsating pressure characteristics of the model, and to design and optimize the surface porous structure in combination with fluid mechanics and acoustic principles, so as to ultimately suppress the pulsating pressure amplitude and thereby reduce fluid noise and flow-induced noise.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A porous bionic model design method based on a Helmholtz resonance cavity comprises the following steps: S1: Determine the location of the porous bionic structure on the model according to the flow field and pulsating pressure characteristics of the model; S2: Design parameters of porous bionic structure based on the Helmholtz resonance cavity principle; S3: Optimize the parameters of the porous bionic structure based on S1 and S2.

[0006] In the above technical solution, the region of the model where the porous bionic structure is located is determined mainly based on the computational fluid dynamics method (i.e., CFD method), and the boundary layer attachment area and separation area of ​​the model are determined. The method for determining the location region of the porous bionic structure on the model includes the following steps: S11: Determine the location of the separation area where the larger vortex reflow appears on the model, and judge whether it is the entire area or the local area of ​​the tail. The specific method is as follows: First, determine the separation point of the separation area, that is, at this time (At this time, the normal velocity gradient of the model wall is zero); Secondly, when a fluid adverse pressure gradient appears after the separation point, that is, through Eq. The separation position can be determined where: is the dimensionless pressure gradient parameter, is the length from the front edge, is the velocity outside the boundary layer, is the velocity gradient outside the boundary layer in the incoming flow direction, is the density of the fluid medium, is the pressure gradient outside the boundary layer in the direction of the incoming flow.

[0007] S12: According to the actual working conditions of the model, the incoming flow velocity and the model angle of attack are given, and one of the turbulence models, the detached eddy simulation DES or the large eddy simulation LES, is selected to verify the position of the separation zone and determine the spatial flow field characteristics. The specific method is as follows: (1) When the detached eddy simulation DES method is selected, the boundary layer is simulated using the following method:

[0008] in: and are the time average velocities in the incoming flow direction and the incoming flow normal direction, respectively. and They represent the spatial position of the incoming flow direction and the incoming flow normal direction respectively. It means that the average value of the instantaneous velocity has nothing to do with the spatial position of the incoming flow direction. represents the time-average velocity changing with time, is the transient speed, is the Reynolds stress, which is determined by the following formula:

[0009] in: is the turbulent kinetic energy per unit fluid mass, is the turbulent viscosity coefficient, is the turbulent dissipation rate.

[0010] At this time, the model boundary layer flow separation and long-range flow field information are processed by the LES method. Through this method, low-frequency noise source information can be obtained.

[0011] (2) When the LES method is selected, the spatial flow field characteristics information can be obtained through the following equation:

[0012] in: is the large-scale part of the velocity field after filtering, is the large-scale part of the pulsating pressure after filtering To solve the above equation, we need to give and , respectively represent Leonard stress and sub-grid Reynolds stress. Considering There is a high probability that it will be covered by numerical errors, so this invention ignores this item. It is determined by the following equation: in: is the Smagorinsky coefficient, a dimensionless constant.

[0013] At this time, this method can be used to solve all pulsating signals larger than the filtering scale, and can solve the noise source information with higher frequencies.

[0014] Which of the above methods to use should be determined based on the frequency range and solution efficiency.

[0015] S13: The separation area on the model is designed as a replaceable component to replace the porous bionic structure. In this way, the bionic configuration can be compared with the spatial flow field and pulsating pressure signal of the reference configuration. The specific method is as follows: First, the connection between the replaceable parts and other parts should be tangent, and no artificial adverse pressure gradient steps should be formed; Secondly, the replaceable components should be equipped with multiple pulsating pressure measuring points at corresponding positions to detect pulsating pressure signals.

[0016] In the above technical solution, the parameters of the porous bionic structure are determined by combining the pulsating pressure characteristics of the turbulent boundary layer separation zone and the Helmholtz resonance cavity principle, including the following steps: S21: Determine the pulsating pressure characteristics of the model, especially the frequency range of the main energy of the line spectrum type power spectrum density, using the same method as S12 above; S22: The porous bionic structure is designed as a Helmholtz open cavity configuration so that the noise source frequency formed by the pulsating pressure and the open cavity configuration are in the same resonance band, which can achieve a better noise reduction effect. The specific method is as follows: in: is the acoustic capacity of the cavity configuration, is the acoustic impedance of the cavity configuration, It is the air pulsation mass at the opening of the cavity configuration.

[0017] S23: Based on S21 and S22, the porous bionic structure is designed into a periodic structure or a honeycomb structure according to the frequency range.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: The present invention introduces a porous bionic component based on the benchmark model based on the principle of the Helm resonance cavity, which can adjust the pulsating pressure distribution on the surface of the model, change the spatial flow field characteristics, and reduce the flow noise and flow-induced noise of the model to a certain extent, especially the line spectrum discrete noise. The technical invention described in the invention can reduce the noise level of moving objects in air or water media, and provide a low-noise acoustic stealth technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 Benchmark model flow separation and pulsating pressure characteristics; Figure 2 Schematic diagram of replaceable parts of the model; Figure 3 The noise reduction effect of pulsating pressure at the model monitoring point; Among them: 1 is the replaceable part, 2 is the model. DETAILED DESCRIPTION

[0020] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0021] Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0022] According to the above technical solution, in this embodiment, the SUBOFF submarine hull is selected as the reference model. First, the boundary layer attachment area and separation area of ​​the model are determined. At this time, the model working conditions are: angle of attack , flow velocity , inlet width According to the S11 method in the invention, the distance from the inlet to the separation point is about 342 mm, and the upper limit of the distance between the separation point and the leading edge of the model is about 686 mm. Therefore, according to theoretical calculations, the boundary layer will separate at a distance of 342 mm to 686 mm from the leading edge of the model.

[0023] According to the technical solution of the invention, in this embodiment, the separation position and spatial flow field characteristics of the model are simulated by selecting the DES numerical simulation method. According to the analysis, the separation position is about 600mm, and the separation point is within the range of theoretical calculation results. At the same time, it is found that a large number of vortex shedding and airflow vortex phenomena appear in the tail area of ​​the separation zone. These phenomena lead to the appearance of obvious line spectrum pulsating pressure signals, with concentrated frequency. In the low frequency range, such as Figure 1 shown.

[0024] According to the technical solution of the invention, Figure 2 As shown, the area after the separation point of model 2 is designed as a replaceable component 1, and the interior of the area after the separation point of model 2 is designed as a hollow structure. The replaceable component 1 is used to fill the hollow structure, and the replaceable component 1 is tangent to the surface of the connection area of ​​model 2. A number of holes arranged in an array are provided on the surface of the replaceable component 1, and all the holes are designed as open cavity structures. All the holes can be designed to be interconnected inside the model 2. When the replaceable component 1 is installed on the model 2, all the holes are evenly contacted with the fluid medium, and pulsating pressure measurement points are arranged at the positions corresponding to different holes for testing.

[0025] According to the technical solution of the invention, in this embodiment, a porous open cavity bionic structure is designed in combination with the line spectrum frequency characteristics of the pulsating pressure. Through the above DES analysis, it is found that a relatively obvious line spectrum pulsating pressure appears in the frequency range of 462.5Hz. After the porous bionic configuration design is performed, the line spectrum noise can be significantly suppressed, and the noise reduction effect is obvious. Figure 3 shown.

[0026] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A porous bionic model design method based on a Helmholtz resonance cavity, characterized in that The following steps are involved: S1: Determine the location of the porous bionic structure on the model according to the flow field and pulsating pressure characteristics of the model; S2: Design parameters of porous bionic structure based on the Helmholtz resonance cavity principle; S3: Optimize the parameters of the porous bionic structure based on S1 and S2.

2. The porous bionic model design method based on the Helmholtz resonance cavity according to claim 1 is characterized in that In S1, the method for determining the location area of ​​the porous bionic structure on the model comprises the following steps: S11: determine the location area where the separation zone of the larger vortex reflow appears on the model; S12: Determine the incoming flow velocity and the model angle of attack according to the actual working conditions of the model, select a turbulence model in the detached eddy simulation or large eddy simulation, verify the position of the separation zone and determine the spatial flow field characteristics; S13: The separation area on the model is designed as a replaceable part for replacing the porous bionic structure.

3. The porous bionic model design method based on the Helmholtz resonance cavity according to claim 2 is characterized in that In S11, the method for determining the location area includes the following steps: Determine the separation point of the separation region, that is, the normal velocity gradient of the model wall is zero. When a fluid adverse pressure gradient appears after the separation point, by: Determine the separation location, where: is the dimensionless pressure gradient parameter, is the length from the front edge, is the velocity outside the boundary layer, is the velocity gradient outside the boundary layer in the incoming flow direction, is the density of the fluid medium, is the pressure gradient outside the boundary layer in the direction of the incoming flow.

4. The porous bionic model design method based on the Helmholtz resonance cavity according to claim 1 is characterized in that The porous bionic structure parameters are determined by combining the pulsating pressure characteristics of the turbulent boundary layer separation zone and the Helmholtz resonance cavity principle, including the following steps: S21: Determine the pulsating pressure characteristics of the model and obtain the frequency range of the main energy of the power spectrum density of the line spectrum type; S22: The porous bionic structure is designed as a Helmholtz open cavity configuration, so that the frequency of the noise source formed by the pulsating pressure and the open cavity configuration are in the same resonance band; S23: Based on S21 and S22, the porous bionic structure is designed into a periodic structure or a honeycomb structure according to the frequency range.

5. The porous bionic model design method based on the Helmholtz resonance cavity according to claim 4 is characterized in that The Helmholtz opening cavity is configured to open toward the fluid region.

6. A porous bionic model design method based on a Helmholtz resonance cavity according to any one of claims 1 to 5, characterized in that The geometric configuration of the porous bionic structure can be adjusted according to the spatial flow field characteristics and pulsating pressure distribution characteristics of the model.

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