A leading-edge serration based airfoil surface cavity flow noise control structure

Abstract

The application discloses a wing surface hole cavity flow noise control structure based on a leading edge sawtooth, and belongs to the technical field of noise control. The structure comprises a spoiler structure sawtooth component arranged at a hole opening leading edge position of a hole cavity, which is used for destroying the spanwise coherence of a hole shear layer and regulating vortex scale. The spoiler structure sawtooth component comprises a plurality of sawtooth units arranged along the hole cavity leading edge in sequence, and the sawtooth unit has a preset tooth shape, wavelength, wave amplitude and upper and lower surface angle. The tooth shape is selected from one or more combinations of a sine wave tooth shape, a triangular wave tooth shape or a composite wave tooth shape. The wavelength, wave amplitude and upper and lower surface angle are matched and set according to the scale distribution characteristics of a vortex in a target hole cavity flow field, so that the spoiler structure sawtooth component can segment, break and guide vortexes of different scales, thereby reducing hole cavity flow noise in a wide frequency band and reducing additional power loss of an original flow field. The application realizes wide frequency band noise suppression while reducing power loss.

Description

Technical Field

[0001] This invention belongs to the field of noise control technology, specifically relating to a noise control structure for airfoil surface cavity flow based on leading-edge serrations. Background Technology

[0002] In engineering fields such as aerospace, wind power, and industrial equipment, fluids flowing through porous structures are prone to generating eddies and turbulence, which in turn induce flow noise. This type of noise not only reduces the comfort of equipment operation and disturbs the surrounding environment, but may also affect the acoustic stealth performance of aircraft and the operating efficiency of equipment.

[0003] Existing cavity noise control technologies mostly employ traditional noise reduction structures, such as sound-absorbing material covering and anechoic cavity design, but these have significant limitations: First, the noise reduction effect is limited, especially in achieving balanced suppression across a wide frequency range; second, energy loss is substantial, altering the original flow field structure and reducing equipment power efficiency; and third, adaptability is poor, requiring separate designs for different cavity types (such as square cavities and airfoil surface cavities), making them difficult to apply universally. Furthermore, existing sawtooth noise reduction structures are mostly installed on the leading and trailing edges of complete airfoils, only controlling external wall-attached flow noise, and are not designed for the cavity flow field of perforated airfoils, making it difficult to suppress cavity fluid self-excited oscillations and sound radiation, thus limiting their application.

[0004] The existing method for suppressing vibration noise in flow-induced orifices disclosed in CN113844629A achieves noise control through frequency shifting and orifice optimization, but it relies on numerical simulation calculations and structural layout adjustments, making the operation process complex, and its effect on equalizing and suppressing noise over a wide frequency band is limited. The wing grating vortex generator proposed in the existing technology CN106080953A can reduce noise by reducing the flow exchange inside and outside the orifice through flow guidance and rectification, but it is only suitable for a narrow range of orifice types and flow velocities, and its noise reduction effect in the high-frequency band needs to be improved.

[0005] Therefore, there is an urgent need for a noise control scheme for airfoil surface cavities that takes into account wide-band noise reduction, low power loss, and high adaptability. Summary of the Invention

[0006] The technical problem to be solved: To avoid the shortcomings of existing technologies, this invention provides a noise control structure for airfoil surface cavity flow based on leading-edge serrations. Based on the biological characteristics of the serrated trailing edge of an owl's wing, a serrated component of a turbulence structure that can be adapted to different cavity structures is designed to achieve wide-band noise suppression while reducing power loss.

[0007] The technical solution of the present invention is: a noise control structure for airfoil surface cavity flow based on leading edge sawtooth, including a turbulence structure sawtooth assembly, wherein the turbulence structure sawtooth assembly is disposed at the leading edge of the cavity opening, and is used to disrupt the spanwise coherence of the orifice shear layer and control the eddy current scale. The turbulence structure sawtooth assembly includes several sawtooth units arranged sequentially along the front edge of the cavity. The sawtooth unit has a preset tooth shape, wavelength λ, amplitude h, and included angle θ between the upper and lower surfaces. The tooth profile is selected from one or more combinations of sinusoidal wave tooth profile, triangular wave tooth profile, or composite wave tooth profile; The wavelength λ, amplitude h, and the angle θ between the upper and lower surfaces are matched and set according to the scale distribution characteristics of the vortex in the target cavity flow field, so that the serrated component of the disturbance structure can divide, break up and guide vortices of different scales, thereby reducing cavity flow noise in a wide frequency band and reducing the additional dynamic loss to the original flow field. A further technical solution of the present invention is: the wavelength λ of the sawtooth unit is in the range of 0.05D~0.4D, the amplitude h is in the range of 0.15D~0.35D, and the included angle θ between the upper and lower surfaces is in the range of 15°~45°, where D is the diameter of the cavity opening.

[0008] A further technical solution of the present invention is: the tooth profile design is as follows: The sinusoidal wave tooth profile is a smooth and continuous curved surface tooth profile with 3 teeth, used to control small-scale vortices ≤0.1D; The triangular wave tooth profile includes a first triangular wave tooth profile with 3 teeth and a second triangular wave tooth profile with 6 teeth. The first triangular wave tooth profile with 3 teeth is used to cut large-scale vortices ≥0.2D, and the second triangular wave tooth profile with 6 teeth is used to cut medium-scale vortices greater than 0.1D and less than 0.2D. The composite wave tooth profile is a composite wave tooth profile with alternating large and small teeth, including a first composite wave tooth profile with 6 large triangular wave tooth profiles and 5 small sinusoidal wave tooth profiles, or a second composite wave tooth profile with 6 large sinusoidal wave tooth profiles and 5 small triangular wave tooth profiles; used to cover the control of eddies across the entire scale.

[0009] A design method for the airfoil surface cavity flow noise control structure based on leading-edge serrations includes the following steps: Step 1: Construct a simulation model of the target cavity; The aperture diameter D, aperture depth H, and inflow velocity U of the cavity were determined, and the scale distribution characteristics of the vortex in the cavity flow field were obtained through simulation analysis. Step 2: Match the tooth shape and initial parameters of the serrations of the turbulence structure according to the scale distribution characteristics of the vortex, wherein large-scale vortices ≥ 0.2D, 0.1D < mesoscale vortices < 0.2D, and small-scale vortices ≤ 0.1D; the initial parameters include wavelength λ, amplitude h, and the angle θ between the upper and lower surfaces; Step 3: Implant the tooth shape and initial parameters determined in Step 2 into the simulation model to simulate the state of the serrated component of the turbulence structure fixed at the front edge of the cavity, and carry out fluid numerical simulation to obtain full-band sound pressure level spectrum data and flow field characteristics; Step 4: Iteratively adjust at least one parameter among tooth profile, wavelength, amplitude, or included angle based on the simulation results; Step 5: Once the simulation results meet the noise reduction requirements across the entire frequency band, lock in the core parameters of the serrated component of the turbulence structure, and formulate a maintenance plan based on the simulation results.

[0010] A further technical solution of the present invention is as follows: In step 2, the rules for determining the wavelength λ and the amplitude h are as follows: If the flow field is dominated by large-scale eddies, the wavelength λ is taken as 0.2D~0.3D, the amplitude h1 of the large tooth wave is taken as 0.25D~0.35D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the large and small-scale eddies in the flow field are uniformly distributed, the wavelength λ is taken as 0.1D~0.2D, the amplitude h1 of the large tooth wave is taken as 0.2D~0.28D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the flow field is dominated by small-scale eddies, the wavelength λ is taken as 0.05D~0.1D, the amplitude h1 of the large tooth wave is taken as 0.18D~0.25D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the proportion of medium-scale eddies in the flow field is relatively high, the wavelength λ is taken as 0.1D~0.15D and the amplitude h is taken as 0.18D~0.28D.

[0011] A further technical solution of the present invention is as follows: In step 2, the rule for determining the angle θ between the tooth profile and the upper and lower surfaces is as follows: For scenarios dominated by large-scale eddies, the first triangular wave tooth shape or the first composite wave tooth shape is preferred, with θ ranging from 15° to 22°. For scenarios with uniform vortex distribution across the entire scale, the first composite wave tooth shape is preferred, with θ ranging from 30° to 38°. For scenarios dominated by small-scale vortices, sinusoidal wave tooth profiles or second composite wave tooth profiles are preferred, with θ ranging from 38° to 45°. For scenarios with a high proportion of medium-scale vortices, the second triangular wave tooth shape is selected, with θ ranging from 22° to 30°.

[0012] A further technical solution of the present invention is: in step 4, the specific strategy for iterative adjustment is as follows: If the noise reduction in the low-frequency band (0-100Hz) is insufficient, replace it with the first triangular wave tooth shape or the first composite wave tooth shape, and increase the wavelength and amplitude. If the sound pressure level in the mid-frequency band of 100~300Hz increases, adjust θ to 22°~30° or change it to the second triangular wave tooth shape; If the noise reduction in the high-frequency band of 300~1000Hz is insufficient, replace it with a sine wave tooth profile or a second composite wave tooth profile, and optimize the amplitude and wavelength of the small teeth. Repeat the iteration until the simulation results meet the requirements of low-frequency noise reduction ≥10dB and high-frequency noise reduction ≥8dB across the entire frequency band (0~1000Hz), thereby determining the final design parameters.

[0013] A method for controlling cavity flow noise based on the aforementioned structure includes the following steps: Step 1: Fix the turbulence structure sawtooth assembly, which is pre-matched according to the opening diameter D of the target cavity and the incoming flow velocity range, at the leading edge of the opening of the cavity, so that the sawtooth units of the turbulence structure sawtooth assembly are arranged sequentially along the leading edge of the cavity. Step 2: During actual operation, acquire the incoming flow velocity and vortex-scale distribution characteristics of the cavity flow field in real time or periodically; If the current flow field is dominated by large-scale vortices, then select or switch to a serrated component of a turbulence structure with triangular wave tooth shape or first composite wave tooth shape. If the proportion of small-scale vortices in the current flow field is high, then select or switch to a serrated component of a sine wave tooth or a second composite wave tooth for the turbulence structure. If the vortices are uniformly distributed across the entire scale in the current flow field, then a serrated component of the turbulence structure with the first composite wave tooth shape should be selected or maintained. If the proportion of medium-scale vortices in the current flow field is high, then the second triangular wave toothed component should be selected or switched. Step 3: Under incoming flow conditions, the spanwise coherence of the orifice shear layer is passively disrupted and the eddy scale is controlled by the sawtooth component of the turbulence structure, so that large-scale eddies are broken up and small-scale eddies are guided and dissipated, and the eddy shedding frequency is dispersed to a wide frequency band, thereby achieving full-band noise suppression without the need for external energy input. Step 4: When the sound pressure level of the cavity radiation noise in a specific frequency band rises above the preset threshold, it is determined that the current sawtooth component is mismatched with the vortex scale of the flow field. Repeat Step 2 to replace the sawtooth component with the corresponding tooth shape and parameters to restore or optimize the noise reduction effect.

[0014] A square cavity structure, comprising: The flow channel is a rectangular parallelepiped. The cavity is a cuboid structure with vertical flow channels. A circular hole is provided in the gap between the flow channel and the cavity, and the center of the circular hole is located on the central axis of the cavity; A noise control structure for airfoil surface cavity flow based on leading-edge sawtooth includes a turbulence structure sawtooth assembly, which is fixedly installed at the leading edge of the circular hole.

[0015] An airfoil structure, comprising: The airfoil body is the NACA0012 airfoil; A central opening, a circular hole located at the midpoint of the surface of the airfoil body; The airfoil surface cavity flow noise control structure based on leading edge sawtooth includes a turbulence structure sawtooth assembly, which is fixedly installed at the leading edge of the central opening.

[0016] Beneficial effects The beneficial effects of this invention are as follows: This invention applies a serrated perforated structure to the leading edge of the cavity, achieving broadband noise reduction through a dual mechanism of spanwise coherence disruption and eddy current scale control; based on eddy current scale distribution matching with various tooth profiles and parameters, passive control without power loss significantly improves the cavity noise suppression effect and adaptability. Specific effects are analyzed as follows: Wideband noise reduction: By breaking the spanwise coherence of the orifice vortex through the serrated turbulence structure, balanced noise reduction is achieved in low frequency (0-100Hz) and high frequency (300-1000Hz), and the sound pressure level noise reduction amplitude in the mid frequency band (100-300Hz) is higher than 6dB, solving the problem of poor frequency band adaptability of traditional technologies.

[0017] Low dynamic loss: All tooth profiles adopt optimized curved surface design and angle parameters, which have little disturbance to the original flow field. The drag coefficient of the airfoil and square cavity structure with added leading edge serrations is not significantly different from that of the structure without added leading edge serrations, and does not affect the original operating efficiency of the equipment.

[0018] High adaptability: By adjusting the parameters of the serrated component of the turbulence structure, it can be adapted to cavity structures of different diameters (20, 100 mm) and different types (square cavity / airfoil cavity), without the need for separate design, thus reducing application costs.

[0019] Easy to maintain: The device has a simple structure, the components are detachable and replaceable, and it is easy to maintain in the later stage. Attached Figure Description

[0020] Figure 1 A schematic diagram of the square cavity model and the position of the leading edge sawtooth hole: showing the installation position of the turbulence structure sawtooth assembly at the leading edge of the square cavity's circular hole, and marking the flow channel and cavity dimensions; Figure 2 Schematic diagram of mesh generation for a square cavity orifice with added leading-edge serrations: This diagram shows the near-wall structure mesh generation at the orifice of a square cavity model with added serration components for a flow-disrupting structure. Figure 3 A schematic diagram of the airfoil model and the location of the leading edge sawtooth hole: showing the installation position of the serrated component of the turbulence structure at the leading edge of the central opening of the NACA0012 airfoil, and marking the external flow field area; Figure 4 A schematic diagram of the mesh generation for the orifice of an airfoil surface cavity structure with added leading-edge serrations: This diagram shows the near-wall structure mesh generation at the orifice of an airfoil surface cavity structure model with added serration components for aerodynamic structure. Figure 5Schematic diagram of the parameters of the sawtooth assembly with different tooth shapes for the turbulence structure: showing five tooth shapes of the sawtooth body, (a) sine wave tooth shape, (b) first triangular wave tooth shape, (c) second triangular wave tooth shape, (d) first composite wave tooth shape, and (e) second composite wave tooth shape; Figure 6 Cross-sectional view at the opening: showing the included angle θ between the upper and lower surfaces of the serrated component of the turbulence structure; Figure 7 The comparison chart shows the changes in sound pressure level and noise reduction of the square cavity structure with the first and second composite wave tooth shapes across the entire frequency band at an incoming flow velocity of 6 m / s. Figure 8 A comparison of the full-frequency noise directivity curves of airfoil surface cavity structures with different waveform leading-edge serrated edges: This shows the flow noise directivity curves of two airfoil surface cavity structures with different opening sizes and different waveform leading-edge serrated edges at a speed of 6 m / s, across the entire frequency band. Figure 9 The graph shows the variation of the total sound pressure level amplitude of the airfoil surface cavity structure with the leading edge sawtooth of the first composite wave tooth at different included angles θ: Compare the variation trend of the total sound pressure level amplitude of the first composite wave tooth with different included angles θ of the upper and lower surfaces at a speed of 6 m / s, and explain the reason for the determination of the range of θ values. Figure 10 Comparison of noise reduction effects of the leading edge sawtooth of composite wave tooth profiles with different parameters at different speeds: Comparison of the noise reduction effects of two composite wave tooth profiles under different parameter conditions; Figure 11 Comparison of noise reduction effects of adding two different sizes of first composite wave tooth airfoil surface cavity structures (100mm hole) at different speeds: full-band sound pressure level spectrum curves (0-1000Hz) of two different sizes of first composite wave tooth structures with similar overall sound pressure level noise reduction effects. Figure 12 A comparison chart of airfoil drag coefficients with and without leading-edge serrations: By comparing the drag coefficients of airfoils with and without serrations, the low dynamic loss of the structure can be verified. Detailed Implementation

[0021] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0022] In the existing technology, the biomimetic noise reduction structure based on the serrated trailing edge of an owl's wing is mainly applied to the trailing or leading edge of an airfoil. Its noise reduction scenario is the interaction between boundary layer turbulence and the trailing / leading edge. The noise reduction mechanism is to destroy the coherent structure of turbulence, suppress vortex shedding, or reduce the leading edge vortex-solid interference, ultimately reducing the aerodynamic noise generated by the airfoil's own flow around it.

[0023] The noise reduction scenario targeted by this invention is completely different: when fluid flows through the cavities (holes) opened on the airfoil surface, the instability of the shear layer at the orifice will excite the self-excited oscillation of the fluid inside the cavity, forming standing wave resonance, and thus radiating strong cavity noise. Although the biomimetic sawtooth leading edge structure of this invention is similar in appearance to the sawtooth edge of an owl's tail, its working mechanism has undergone a fundamental change: through the spanwise coherence disruption effect and the eddy scale control effect, it intervenes in the vortex shearing process of the orifice shear layer, thereby suppressing the self-excited oscillation of the fluid inside the cavity and reducing the sound radiation caused by cavity resonance.

[0024] Therefore, this invention differs fundamentally from existing owl-inspired bionic sawtooth noise reduction technology in the following three dimensions: 1. Different noise reduction scenarios: Existing technologies are used for flow noise around the trailing / leading edge of airfoils; this invention is used for self-excited oscillation noise of airfoil surface cavities.

[0025] 2. Different noise reduction mechanisms: Existing technologies mainly disrupt the vortex coherence structure of the turbulent boundary layer or weaken vortex-solid interference; this invention reduces the self-excited oscillation of the fluid inside the orifice by suppressing the instability of the orifice shear layer.

[0026] 3. Different effects: Existing technologies reduce the noise radiated by the airfoil itself; this invention reduces the sound radiation of the airfoil caused by fluid oscillation within the cavity, while maintaining the original aerodynamic characteristics of the airfoil.

[0027] When fluid flows through a cavity structure, the core source of noise is the eddy shear layer instability at the orifice, which causes eddy shear layer shedding and standing wave resonance in the flow field inside the cavity. Without a control structure, the fluid at the orifice forms a continuous and spanwise coherent shear layer. This shear layer continuously rolls up during the flow to form periodic eddies. When the eddy shedding frequency matches the cavity size and the incoming flow velocity, it will excite the flow field inside the cavity to generate standing wave resonance, thereby radiating strong noise. This noise is particularly significant in specific frequency bands (such as the low frequency band due to the large eddy size and the high frequency band due to eddy breakup).

[0028] The intervention of the sawtooth leading edge of the turbulence structure in this invention breaks the chain reaction of noise generation through two key effects: ① Spanwise coherence disruption effect: The sawtooth divides the continuous shear layer at the orifice into several independent local shear units. The eddy generation, development, and shedding processes of each unit are independent, avoiding the radiated sound amplification caused by synchronous eddy shedding across the entire span, thus weakening the energy basis of noise radiation at the source. ② Eddy scale control effect: The key structural parameters of the sawtooth change the initial disturbance scale of the shear layer, dispersing the eddy shedding frequency across a wide frequency band and reducing the noise peak at a single frequency. At the same time, the smooth curved surface design of the sawtooth can guide some fluid to flow along the sawtooth contour, reducing the impact intensity between the shear layer and the orifice wall, and reducing the high-frequency noise generated by eddy breakup. The specific technical solution is as follows: 1. Turbulence-inducing sawtooth component structure: The cavity noise disturbance control structure component of this invention is based on the serrated structure of the tail edge of an owl's wing, and includes five tooth profiles. The characteristics and design parameters of each tooth profile are as follows: Sine wave tooth profile ( Figure 5 (a) The structure adopts a sinusoidal tooth profile with 3 teeth, which has a smooth and continuous waveform. It has an outstanding effect on breaking and regulating small-scale vortices and can accurately act on small-scale vortices in the flow field. The high-frequency noise generated by vortex breaking is reduced by guiding the curved surface.

[0029] First triangular wave pattern ( Figure 5 (b): This is a triangular wave tooth profile with 3 teeth. The tooth profile is sharp and the structure is simple. It has a significant effect on cutting and breaking large-scale vortices. It can quickly destroy the coherent structure of large-scale vortices and weaken the source of low-frequency noise.

[0030] Second triangular wave pattern ( Figure 5 c): This is a triangular wave tooth profile with 6 teeth. Compared to the first triangular wave tooth profile, it has a higher tooth density and is suitable for scenarios where there are many medium-scale vortices in the flow field. It can more finely divide vortices and broaden the range of adaptability to vortex scale.

[0031] First composite wave pattern ( Figure 5 (d) is a composite wave tooth profile with alternating large and small teeth, consisting of 6 large teeth and 5 small teeth, where the large teeth are triangular waves and the small teeth are sine waves. This tooth profile combines the efficient breaking capability of large-scale eddies by triangular wave teeth with the precise control advantage of small-scale eddies by sine wave teeth. The synergistic effect achieves comprehensive control of eddies across all scales, resulting in optimal noise reduction.

[0032] Second composite wave pattern ( Figure 5 (e): It is also a composite wave tooth shape with alternating large and small teeth, containing 6 large teeth and 5 small teeth. The large teeth are sine waves and the small teeth are triangular waves. It is suitable for flow field environments with a higher proportion of small-scale vortices. The control effect of vortices of different scales is balanced by the wide range guidance of the sine wave large teeth and the fine cutting of the triangular wave small teeth.

[0033] All key structural parameters of the sawtooth pattern (wavelength λ, amplitude h, and angle θ between the upper and lower surfaces) must be precisely matched based on the vortex scale control mechanism, rather than simply taking values. The definition and determination logic of each parameter are as follows: Wavelength λ: The axial distance between the crests (or troughs) of the sawtooth wave. Its value must match the characteristic scale of the dominant vortex in the target cavity flow field. Based on the correlation mechanism between vortex scale and flow coherence, the reasonable range of λ is 0.05D to 0.4D (D is the diameter of the cavity opening). The core logic is to ensure that the sawtooth can effectively cut the vortex clusters and destroy their spanwise coherence by matching λ with the characteristic length of vortices of different scales. For example, when there are large-scale vortices of 10 to 40 mm in the cavity flow field, λ needs to be 0.1 to 0.3 times D to achieve accurate segmentation of such vortices.

[0034] Wave amplitude h: refers to the vertical distance between the crest and trough of the sawtooth wave, ranging from 0.15D to 0.35D. Its design is based on the radial distribution characteristics of the vortex. Large-scale vortices have a wider radial influence range, requiring a larger h value (0.25D to 0.35D) to fully intervene in the vortex development process; small-scale vortices have a narrower radial range, and can be controlled with a smaller h value (0.15D to 0.2D). The composite wave tooth shape can simultaneously cover the radial influence range of both large and small-scale vortices by alternately setting large and small tooth units with different h values.

[0035] Angle θ between the upper and lower surfaces Figure 6 (As shown): The value range is 15° to 45°. Its core function is to regulate the shear layer separation angle. This range is determined based on vortex generation dynamics and the shear layer regulation mechanism. When θ < 15°, the wall is too steep, causing the shear layer to separate too quickly. The fluid rapidly peels away to form an extremely thin shear layer, making it difficult for vortices to diffuse. They easily coalesce into strongly coherent large-scale vortices, radiating low-frequency strong noise and inducing secondary vortices, thus weakening the noise reduction effect. When θ > 45°, the wall is gentle, causing the shear layer to separate too slowly. The vortex clusters develop incompletely and have strong coherence, easily forming continuous vortex bands, leading to increased noise in the mid-frequency range. At the same time, the sawtooth cutting effect is weakened, making it impossible to effectively separate large-scale vortices. The 15° to 45° range can balance the shear layer separation velocity and the vortex cluster dispersion effect. Combined with various tooth-shaped characteristics, it can broaden the vortex scale regulation range and provide a guarantee for noise reduction across the entire frequency band.

[0036] 2. Control methods Based on the above structure, the cavity noise control method of the present invention includes the following steps: Cavity parameter setting: The type of target cavity (square cavity / airfoil surface cavity), opening diameter (D), hole depth (H) and incoming flow velocity (U) are determined by simulation modeling, and key parameters (such as the flow channel length of 1800mm for square cavity, the airfoil is NACA0012 section, etc.) are input into the simulation system. The focus is on analyzing the scale distribution characteristics of vortices in the flow field (such as the dominant range of large-scale vortices and the distribution density of small-scale vortices) to construct a cavity simulation model that matches the actual vortex field.

[0037] Turbulence structure sawtooth parameter matching: Based on the vortex scale distribution results in the simulation model, first select a suitable tooth profile, and then determine the core parameters of the corresponding tooth profile: (1) Determination of h and λ parameters: Based on the vortex size distribution results in the simulation model, and based on the vortex generation dynamics and shear layer control mechanism, the wavelength λ and amplitude h parameters are preferentially matched to ensure that they are accurately adapted to the vortex structure size.

[0038] If the flow field is dominated by large-scale eddies (≥0.2D), the value of λ is set to 0.2D~0.3D. This range is determined because 0.2D corresponds to the minimum characteristic length of large-scale eddies, which can ensure the effective coverage of the eddy core region by the sawtooth, while 0.3D matches the maximum extension range of large-scale eddies, which can fully act on the entire eddy structure. The value of the large tooth h1 is 0.25D~0.35D, where 0.25D meets the depth control requirements of the large radial influence range of large-scale eddies, and 0.35D is adapted to the maximum radial diffusion distance of eddies, ensuring sufficient encapsulation and breaking of large-scale eddies; the value of the small tooth h2 is 0.15D~0.2D, which can take into account the small number of small-scale eddies in the flow field, and will not cause excessive interference to the small-scale flow field due to excessive parameters. 0.15D corresponds to the normal radial range of small-scale eddies, and 0.2D is a reasonable upper limit for intervening in small-scale eddies.

[0039] If the large and small-scale eddies are uniformly distributed in the flow field, λ is set to 0.1D to 0.2D. 0.1D can accurately adapt to the characteristic length of small-scale eddies, while 0.2D can cover the core region of large-scale eddies, achieving a comprehensive match for the characteristic length of eddies across all scales. The large tooth h1 takes a value of 0.2D to 0.28D. 0.2D can adapt to the radial range of medium and large-scale eddies, while 0.28D ensures the control effect while avoiding excessive interference to small-scale eddies. The small tooth h2 takes a value of 0.15D to 0.2D. 0.15D corresponds to the minimum radial range of small-scale eddies, while 0.2D can balance the control effect on small-scale eddies with the stability of the flow field, forming a complementary fit with the large tooth parameters.

[0040] If the flow field is dominated by small-scale vortices (≤0.1D), λ should be between 0.05D and 0.1D. This range can accurately match the characteristic length of small-scale vortices, ensuring that the sawtooth can effectively act on the small-scale vortex structure. The large tooth h1 is between 0.18D and 0.25D, and the small tooth h2 is between 0.15D and 0.2D. 0.15D corresponds to the conventional radial range of small-scale vortices, and 0.2D is a reasonable upper limit for matching the radial distribution of small-scale vortices. The large tooth parameter of 0.18D to 0.25D can take into account the overall stability of the flow field without interfering with the control of small-scale vortices, avoiding control failure due to excessively small parameters.

[0041] If the proportion of medium-scale vortices in the flow field is high, λ is set to 0.1D to 0.15D. This range closely matches the characteristic length of medium-scale vortices, enabling precise cutting and control of them. h is set to 0.18D to 0.28D, which adapts to the radial distribution of medium-scale vortices, ensuring effective intervention without causing new flow field disturbances due to inappropriate parameters. 0.18D serves as the basic control threshold, while 0.28D represents a reasonable upper limit for maximizing the control effect.

[0042] (2) Tooth profile selection and θ parameter determination The determined h and λ parameters are implanted into the corresponding tooth structure, and the range of the angle θ between the upper and lower surfaces is determined based on the control requirements of different vortex scales, so as to achieve parameter synergistic optimization.

[0043] For scenarios dominated by large-scale vortices, the first triangular wave tooth shape or the first composite wave tooth shape is preferred, with θ ranging from 15° to 22°. This angle range is set to enhance the cutting effect on large-scale vortices through a steeper wall angle, quickly destroying the coherent structure of large-scale vortices, while avoiding the problem of strong coherent vortices and secondary vortices caused by too small an angle.

[0044] For scenarios with uniform vortex distribution across all scales, the first composite wave tooth shape is preferred, with θ ranging from 30° to 38°. This angle range can balance the separation velocity and dispersion efficiency of vortices at different scales, ensuring effective cutting of large-scale vortices while precisely controlling the breaking process of small-scale vortices, thus achieving coordinated noise reduction of vortices across all scales.

[0045] For scenarios dominated by small-scale vortices, sinusoidal or second composite wave serrations are preferred, with θ ranging from 38° to 45°. By optimizing the breaking and control of small-scale vortices with a relatively gentle angle, the interference effect of the sawtooth on small-scale vortices can be fully utilized, while avoiding the problem of weakened sawtooth cutting effect and increased vortex coherence caused by excessively large angles.

[0046] For scenarios with a high proportion of medium-scale vortices, the second triangular wave tooth shape is selected, with θ ranging from 22° to 30°. This angle range precisely matches the separation velocity requirements of medium-scale vortices, enabling efficient cutting and dispersion of medium-scale vortices and avoiding an increase in mid-frequency noise peaks.

[0047] Fluid numerical simulations were conducted to simulate different incoming flow velocities, focusing on monitoring changes in vortex-scale distribution, sound pressure level spectrum data, and drag coefficients to ensure precise matching of parameter configurations with vortex structure control requirements. If simulation data showed insufficient noise reduction in the low-frequency band (0–100 Hz), it indicated that the large-scale vortex control effect was not as expected. The vortex shape needed to be replaced with the first triangular wave tooth or the first composite wave tooth, while simultaneously increasing the λ and h values ​​of the corresponding large teeth. Increasing λ further covers the maximum extension range of the large-scale vortex, and increasing h strengthens the ability to envelop and break up the radial distribution of the large-scale vortex, thereby enhancing the low-frequency noise reduction effect. If the sound pressure level increased in the mid-frequency band (100–300 Hz), it indicated an imbalance in the control of the mid-scale vortex. The θ angle could be adjusted to 22°–30° or the vortex shape could be replaced. The second triangular wave tooth profile is used, and this angle range is compatible with the structural characteristics of the second triangular wave tooth profile. It can accurately match the separation velocity requirements of medium-scale vortices, achieving efficient cutting and dispersion of medium-scale vortices and avoiding the increase of mid-frequency noise peaks. If the noise reduction in the high-frequency band (300-1000Hz) is insufficient, it indicates that the control of small-scale vortex breaking is inadequate. It is necessary to replace it with a sinusoidal wave tooth profile or a second composite wave tooth profile, and optimize the h and λ values ​​of the small teeth. By refining the parameter configuration corresponding to the small-scale vortices, the precise intervention of small-scale vortices is strengthened, and the noise suppression effect in the high-frequency band is improved. The parameters are iteratively adjusted repeatedly until the simulation results meet the noise reduction requirements of the entire frequency band (0-1000Hz) (low-frequency noise reduction ≥10dB, high-frequency noise reduction ≥8dB).

[0048] The above technical solution will be further analyzed below with reference to examples and accompanying figures: Example 1: Noise Control of Square Cavity Structure Model establishment: Reference Figure 1As shown, the square cavity model is fixed to a single size and is divided into three regions: flow channel, hole, and cavity body. The flow channel is located on the upper side of the model and is formed by stretching a 200mm × 200mm square face in the side view plane by 1800mm. The cavity body is located 900mm to the left of the flow channel and 5mm perpendicular to the flow channel, and is formed by stretching a 200mm × 200mm square face in the side view plane by 100mm. The hole is located in a 5mm gap between the flow channel and the cavity body. The hole is a circular hole with a diameter of 40mm, and the center of the hole is located on the central axis of the cavity body. According to the flow field simulation analysis, large-scale vortices dominate at the three incoming flow velocities of 4m / s, 6m / s, and 8m / s. The first or second composite wave tooth shape is selected, with parameters set as λ=8~12mm, large tooth h1=10~14mm, small tooth h2=6~8mm, and θ=15°~22°. The parameters of the sawtooth component of the turbulence structure of this specification are implanted into the simulation model of the square cavity structure.

[0049] Grid generation: Refer to Figure 2 As shown, a structured mesh is used for model discretization. Structured meshes offer advantages such as regular element shapes and strong numerical stability, making them suitable for the geometric characteristics of the cavity. ICEM software is used to perform model block subdivision and point-line-surface mapping, achieving a precise association between the geometric model and the mesh model. The mesh node distribution is adjusted to ensure that the mesh element shape in each region is close to a regular hexahedron, avoiding extreme deviations in edge angles and ensuring mesh quality. For key flow regions such as the orifice shear layer, serrated surface, and near-wall surface, a mesh expansion layer is set and refined. The height h of the first boundary layer mesh is determined to be ≤7.3×10 using the wall y+ formula. - The mesh size is 2mm, accurately capturing the details of boundary layer flow under different flow velocities. The final structured mesh has a total of 16,734,175 elements, with over 90% of the mesh quality above 0.7, ensuring the accuracy of flow field and noise simulation under multiple flow velocity conditions.

[0050] Computational Domain Setup: A cuboid flow channel is used as the basis to construct a cubic cavity fluid computational domain. Boundary conditions are precisely configured according to function: a velocity inlet is set on one side of the incoming flow direction, accurately matching three incoming flow velocity conditions of 4m / s, 6m / s, and 8m / s, to realistically reproduce the inlet flow state under different flow velocities; a pressure outlet is set downstream of the external flow field to ensure pressure continuity and flow stability when the fluid flows out; wall boundary conditions are set on the cuboid cavity wall and the sawtooth surface of the turbulence structure, combining the material smoothness characteristics and friction coefficient to accurately simulate the interaction between the fluid and the solid wall at different flow velocities; symmetrical boundary conditions are set on the remaining non-critical surfaces of the computational domain to avoid the interference of wall effects on the flow field and ensure that the simulation results under each flow velocity condition are consistent with the actual flow law.

[0051] Calculation parameter settings: First, the DDES delayed separated vortex model was selected as the turbulence model. This model can accurately characterize the boundary layer flow in the near-wall region of the circular orifice using the RANS mode, and accurately capture the generation, development, and collision processes of vortices at different flow velocities of 4 m / s, 6 m / s, and 8 m / s in the separation zone inside the cavity and downstream of the orifice using the LES mode. This effectively avoids the problem of excessive dissipation or omission of vortex structures in traditional models, ensuring the accuracy of flow field simulation across the entire flow velocity range. Second, a flow field monitoring point was set at a vertical distance of 5 mm above the center of the circular orifice to collect real-time flow field pressure fluctuation data under the three flow velocity conditions. Finally, the calculation step size and sub-iteration parameters were set. Considering the requirement of the target frequency range of 0–1000 Hz, the calculation step size was determined to be 1 × 10⁻⁶. -4 The sub-iteration number is set to 10 steps, and the total number of calculation steps is 4000 steps, ensuring that the frequency resolution of the spectrum analysis meets the noise reduction evaluation requirements under different flow velocities. After completing the parameter settings, the flow field simulation calculation is started.

[0052] Noise reduction effect verification: After the flow field calculation is completed, the pressure pulsation time domain data under the three flow velocity conditions collected by the monitoring points are analyzed by Fast Fourier Transform (FFT) to convert the time domain signal into frequency domain sound pressure level spectrum data. At the same time, the flow field characteristic parameters (velocity distribution, vorticity distribution) corresponding to each flow velocity are combined to carry out a comprehensive evaluation. Simulation results show that: at 4 m / s, the square cavity model with the first composite wave toothed leading edge sawtooth structure achieves a maximum noise reduction of 15 dB in the low-frequency band (0–100 Hz), 8–10 dB in the mid-frequency band (100–300 Hz), and 10–12 dB in the high-frequency band (300–1000 Hz); at 6 m / s, the maximum noise reduction is 14 dB in the low-frequency band, 7–9 dB in the mid-frequency band, and 9–11 dB in the high-frequency band; at 8 m / s, thanks to the efficient adaptation of the first composite wave toothed structure to large-scale vortices, the noise reduction is ≥12 dB in the low-frequency band, 6–8 dB in the mid-frequency band, and 7–9 dB in the high-frequency band. All indicators for the three flow velocity conditions meet the noise reduction requirements across the entire frequency band.

[0053] Example 2: Noise Control of Airfoil Surface Cavities Model establishment: Reference Figure 3As shown, the airfoil surface cavity model is built based on the NACA0012 airfoil. The overall structure includes the airfoil body, the central opening, and the outer flow field region: the airfoil body is set to be 1.4m long and 0.5m high, and adopts the standard NACA0012 cross-sectional profile; the central opening is circular, adaptable to two specifications with diameters of 20mm and 100mm, and the center of the opening is located at the midpoint of the airfoil surface; the outer flow field region is set with dimensional parameters according to simulation requirements to ensure that the incoming flow is not constrained by the boundary and fully restores the flow field environment under actual working conditions. Based on the flow field simulation analysis of different opening diameters, corresponding tooth shapes and parameters were selected respectively: for a diameter of 20mm (small-scale vortex-dominated), the second composite wave tooth shape (λ=2~4mm, large tooth h1=4~7mm, small tooth h2=2~4mm, θ=38°~45°) was selected; for a diameter of 100mm (high proportion of large-scale vortices), the first composite wave tooth shape (λ=10~20mm, large tooth h1=20~35mm, small tooth h2=15~20mm, θ=15°~22°) was selected. The corresponding serrated component of the turbulence structure was implanted into the simulation model of the airfoil surface cavity to simulate the installation state of the serrated component fixed at the leading edge of the opening.

[0054] Grid generation: Refer to Figure 4 As shown, a structured mesh is used for model discretization. Structured meshes offer advantages such as regular element shapes and strong numerical stability, and are well-suited to the geometric characteristics of the airfoil surface cavities. ICEM software is used to perform model block partitioning and point-line-surface mapping, achieving a precise association between the geometric model and the mesh model. The mesh node distribution is adjusted to ensure that the mesh element shape in each region is close to a regular hexahedron, avoiding extreme deviations in edge angles and ensuring mesh quality. For key flow regions such as the orifice shear layer, serrated surfaces, and near-wall surfaces of the airfoil, a mesh expansion layer is set and refined. The height h of the first boundary layer mesh is determined to be ≤4.6×10 using the wall y+ formula. - The mesh size is 2mm, accurately capturing the details of boundary layer flow. The final total number of structured mesh cells meets the simulation accuracy requirements, and more than 90% of the mesh quality is above 0.5, ensuring the accuracy of flow field and noise simulation.

[0055] Computational Domain Setup: The fluid computational domain is constructed with the airfoil and external flow field region as the core. Boundary conditions are precisely configured according to function: a velocity inlet is set on one side of the incoming flow direction, matching five incoming flow velocity conditions of 2m / s, 4m / s, 6m / s, 8m / s, and 10m / s respectively, to reproduce the incoming flow state under different flow velocities; a pressure outlet is set downstream of the external flow field to ensure the pressure continuity and flow stability when the fluid flows out; wall boundary conditions are set on the airfoil surface, the opening wall surface, and the sawtooth surface of the turbulence structure, and the interaction between the fluid and the solid wall is accurately simulated by combining the material smoothness characteristics and friction coefficient; symmetric boundary conditions are set on the other non-critical surfaces of the computational domain to avoid the interference of wall effects on the flow field and ensure that the simulation results fit the actual flow law.

[0056] Calculation parameter settings: First, the DDES delayed separation vortex model was selected as the turbulence model. This model can accurately characterize the viscous sublayer flow in the airfoil near-wall region and orifice boundary layer using the RANS mode, and capture the generation, development, collision, and breakup processes of vortices in the separation zone downstream of the orifice and the vortex region of the external flow field using the LES mode. This effectively solves the problem of excessive dissipation or omission of vortex structures in traditional models, ensuring the accuracy of wide-band flow field simulation. Second, a flow field monitoring point was set at a vertical distance of 5 mm above the center of the circular orifice to collect real-time flow field pressure fluctuation data under different operating conditions. Finally, the calculation step size and sub-iteration parameters were set. Considering the requirement of the target frequency range of 0-1000Hz, the calculation step size was determined to be 5×10. -4 Set the sub-iteration number to 10 steps and the total number of calculation steps to 6000 steps to ensure that the frequency resolution of the spectrum analysis meets the requirements. After completing the parameter settings, start the flow field simulation calculation.

[0057] Noise Reduction Effect Verification: After the flow field calculation was completed, based on the pressure pulsation time-domain data collected from the monitoring points, Fast Fourier Transform (FFT) was used for spectral analysis to convert the time-domain signal into frequency-domain sound pressure level spectrum data. Simultaneously, multi-dimensional comparative analysis and noise reduction effect evaluation were conducted by combining flow field characteristic parameters (velocity distribution, vortex distribution). First, under the same velocity condition, the noise reduction effects of five different tooth profiles—sine wave tooth profile, first triangular wave tooth profile, second triangular wave tooth profile, first composite wave tooth profile, and second composite wave tooth profile—were compared to select the optimal tooth profile type suitable for flow fields with different opening diameters. Second, the total sound pressure level change of the leading-edge sawtooth structure of the first composite wave tooth profile with different upper and lower surface angles θ was compared to clarify the optimal range of θ values ​​under different vortex scales dominating the flow field. Then, for opening sizes of 20mm and 100mm, the noise reduction effects were evaluated separately. The noise reduction effect of composite wave serrations with different parameters on the total sound pressure level across the entire frequency band at different speeds from 2 to 10 m / s was compared, and the matching law of core parameters for different aperture sizes was determined. Finally, the full-frequency sound pressure level spectrum curves of two different parameters with similar noise reduction effects on the total sound pressure level across the entire frequency band in the first composite wave serration were compared. It was found that the parameters λ=10, h1=35, h2=20 had a better suppression effect on low-frequency noise, while the parameters λ=15, h1=35, h2=15 had a better noise reduction effect on high-frequency noise. The comprehensive simulation results under different opening diameters and incoming flow velocities show that: when the diameter is 20mm, the noise reduction is 10-13dB across the entire frequency band at 2m / s; at 4-6m / s, the noise reduction is ≥10dB in the low-frequency band and ≥8dB in the high-frequency band; and at 8-10m / s, the noise reduction is ≥9dB in the low-frequency band. When the diameter is 100mm, the noise reduction is 10-15dB across the entire frequency band at 2m / s; at 4-6m / s, the noise reduction is ≥10dB in the low-frequency band and ≥8dB in the high-frequency band; and at 8-10m / s, the noise reduction is ≥12dB in the low-frequency band. All conditions meet the noise reduction requirements across the entire frequency band.

[0058] To compare the full-band noise reduction capabilities of two types of composite wave tooth profiles on a square cavity structure, and to clarify the suitable scenarios for different tooth profiles, a comparative verification of the noise reduction effects of two different composite tooth profiles was conducted. Figure 7 As shown in the figure, this is a comparison of the noise reduction effects across the entire frequency band of the square cavity structure using three different composite wave tooth profiles at an incoming flow velocity of 6 m / s. The frequency range covers 0-1000 Hz and is divided into low-frequency, mid-frequency, and high-frequency intervals for analysis. The reference structure without serrations has an overall high sound pressure level across the entire frequency band. In the low-frequency region, the shedding and resonance of large-scale vortices create significant noise peaks, which are also the main source of noise in the square cavity flow. After adding the first composite wave tooth profile, the structure shows the most outstanding noise reduction effect in the low-frequency range, with a noise reduction of 12-14 dB, 7-9 dB in the mid-frequency range, and 9-11 dB in the high-frequency range. Relying on the large triangular teeth, it can efficiently break up the dominant large-scale vortices in the flow field, making it highly compatible with the square cavity flow field where large-scale vortices account for a high proportion. The second composite wave tooth profile has slightly weaker low-frequency noise reduction capability, but excellent high-frequency noise reduction performance, achieving a noise reduction of over 10dB in the 300~1000Hz range. The large sinusoidal teeth cause less disturbance to the flow field, and when paired with small triangular teeth, they can precisely cut small-scale vortices, making them more suitable for applications with a high proportion of small- to medium-scale vortices. Both composite wave tooth profiles achieve effective noise reduction across the entire frequency band without any increase in sound pressure level. Both meet the design specifications of at least 10dB low-frequency noise reduction and at least 8dB high-frequency noise reduction. In practical engineering, the appropriate tooth profile can be flexibly selected based on the vortex scale distribution in the flow field.

[0059] Meanwhile, to investigate the influence of different tooth profiles on the spatial radiation characteristics of airfoil cavity noise, noise directivity tests were conducted for two typical apertures. For example... Figure 8As shown in the figure, this is a comparison of the full-frequency noise directivity curves of different waveform leading-edge sawtooth patterns applied to the surface cavities of airfoils with a large aperture of 100mm and a small aperture of 20mm under an incoming flow of 6m / s. The comparison samples include undisturbed structures, sinusoidal wave sawtooth profiles, two types of triangular wave sawtooth profiles, and two types of composite wave sawtooth profiles. The circumferential angle represents the noise radiation direction, and the sound pressure level amplitude represents the noise intensity in the corresponding direction. The undisturbed control group has the highest sound pressure level in all directions, with a wide noise radiation range and concentrated directivity. The fundamental reason is that the spanwise coherence of the orifice vortex is strong, forming strong directional noise. The first triangular wave tooth profile significantly reduces noise in 100mm large-aperture airfoil cavities, greatly weakening directional noise caused by large-scale vortices, but its improvement on the high-frequency noise directivity of 20mm small-aperture cavities is limited. The second triangular wave tooth profile is suitable for medium-scale vortices and can optimize the mid-frequency noise directivity of both types of aperture structures, but it cannot achieve balanced noise reduction across the entire frequency band. The sinusoidal wave tooth profile has outstanding advantages in the 20mm small-aperture condition, effectively dispersing the high-frequency directional radiation generated by small-scale vortices, but its low-frequency noise reduction effect is insufficient when applied to large-aperture structures. Both types of composite wave tooth profiles can comprehensively reduce the noise amplitude in all directions, break the concentrated noise directivity, and make the noise radiation distribution more uniform. The first composite wave tooth profile is suitable for large-aperture airfoil cavities, while the second composite wave tooth profile is more suitable for small-aperture structures. Experimental results show that the leading-edge sawtooth can effectively disrupt the spanwise coherence of vortices and weaken the directional radiation capability of noise. The tooth profile must match the vortex scale corresponding to the aperture diameter to achieve the best noise reduction effect.

[0060] The included angle between the upper and lower surfaces of the sawtooth is a core parameter that controls the separation state of the shear layer and affects the overall noise reduction effect. To determine a reasonable range for this parameter, a simulation experiment with varying angles was conducted. Figure 9As shown in the figure, in a 6 m / s incoming flow environment, the relationship between the angle θ between the upper and lower surfaces of the airfoil cavity with the first composite wave tooth shape and the total sound pressure level amplitude at the monitoring point is shown. The horizontal axis represents the angle value and the vertical axis represents the total sound pressure level, which intuitively reflects the influence of the angle parameter on the overall noise reduction performance. When the included angle θ is less than 15°, the sawtooth wall is too steep, the shear layer separation speed at the orifice is too fast, and secondary vortices and strong coherent vortices are easily generated, resulting in a significant increase in the total sound pressure level and the noise reduction function is basically ineffective. When the included angle is in the range of 15° to 22°, the total sound pressure level remains at a low level, and the noise reduction effect reaches its best. This range is suitable for flow field conditions dominated by large-scale vortices. When the included angle is in the range of 22° to 38°, the total sound pressure level increases steadily and slightly, and the noise reduction effect decreases slightly. This range can be applied to flow fields with uniform distribution of vortices at all scales or a high proportion of medium-scale vortices. When the included angle is in the range of 38° to 45°, the sound pressure level continues to increase slowly, but still has good noise reduction capability, which is suitable for scenarios dominated by small-scale vortices. When θ exceeds 45°, the sawtooth wall tends to be gentle, the cutting effect on vortices is significantly weakened, the coherence of vortices gradually recovers, the total sound pressure level rises sharply, and the noise intensifies again. The curve fully verifies that the 15°~45° included angle range set in this invention is reasonable. Parameters exceeding the range will cause abnormal shear layer separation and increased vortex coherence, resulting in a significant reduction in noise reduction effect. The included angle parameters of different sub-intervals can be specifically matched to flow fields of different vortex scales, which is an important basis for structural parameter design.

[0061] To investigate the adaptation relationship between structural parameters such as wavelength and amplitude and the incoming flow velocity, and to verify the reliability of the parameter design rules across the entire flow velocity range, multiple sets of parameter combinations were set up to conduct variable flow velocity simulation analysis. For example... Figure 10As shown in the figure, this is a comparison of the noise reduction effects of composite wave tooth profiles with different parameter combinations at different inflow velocities from 2 to 10 m / s. It is divided into two sub-figures: one with a 100 mm aperture and the first composite wave tooth profile, and the other with a 20 mm aperture and the second composite wave tooth profile. The horizontal axis represents the inflow velocity, and the vertical axis represents the sound pressure level. Each group includes a undisturbed control group and multiple test samples with different wavelengths and amplitudes. The overall trend shows that as the inflow velocity increases, the sound pressure level of all structures increases synchronously. However, there is always a significant difference between the structure with the sawtooth component and the undisturbed group, proving that this structure can stably reduce noise across the entire velocity range. For the 100 mm large aperture structure, the parameter combination of 10 mm wavelength, 35 mm large tooth amplitude, and 20 mm small tooth amplitude shows the best overall performance, with stable noise reduction across the entire flow velocity range of 2 to 10 m / s and outstanding low-frequency noise suppression capability. Samples with wavelengths and amplitudes deviating from the optimal range show acceptable noise reduction performance at low speeds, but the noise reduction decreases significantly at high speeds. For a 20mm small aperture structure, the parameter combination of 2mm wavelength, 7mm large tooth amplitude, and 2-4mm small tooth amplitude is highly consistent with the characteristics of small-scale vortices, maintaining excellent high-frequency noise reduction capability even at high flow velocities. If the amplitude value is too large, it will additionally disturb the flow field, causing a slight increase in sound pressure level under high-speed conditions. Therefore, the wavelength and amplitude of the sawtooth need to be matched in conjunction with the aperture diameter, incoming flow velocity, and flow field vortex scale. Based on the parameter value rules of vortex scale division, it can meet the engineering application requirements under different working conditions.

[0062] While some parameter combinations may result in similar overall noise reduction, differences exist in noise reduction performance across different frequency bands. To clarify the noise reduction emphasis of different parameters and guide refined selection, a comparative spectral analysis experiment was conducted with the same total noise reduction. For example... Figure 11As shown in the figure, for a 100mm aperture airfoil cavity, two sets of first composite wave tooth profiles with similar overall noise reduction effects but different parameters were selected. The sound pressure level spectrum of the entire frequency band from 0 to 1000Hz was compared under three typical incoming flow velocities of 2m / s, 6m / s, and 10m / s. The two sets of parameters are wavelength 10mm, large tooth amplitude 35mm, small tooth amplitude 20mm, and wavelength 15mm, large tooth amplitude 35mm, small tooth amplitude 15mm, respectively. At a low speed of 2 m / s, the sound pressure level curves corresponding to the two sets of parameters basically overlap, and the difference in noise reduction effect across the entire frequency band is minimal. At a typical medium speed of 6 m / s, the first set of parameters has a lower sound pressure level in the 0-100 Hz low-frequency band and a stronger suppression effect on large-scale eddies, while the second set of parameters performs better in the 300-1000 Hz high-frequency band and has a more prominent ability to control small and medium-scale eddies. When the flow velocity increases to a high speed of 10 m / s, the difference in noise reduction across the frequency bands of the two types of parameters is further amplified. The first set of parameters continues to maintain its advantage in low-frequency noise reduction, while the high-frequency noise reduction performance of the second set of parameters is also more stable. The noise reduction levels of the two in the 100-300 Hz mid-frequency band are basically the same. Experiments show that even if the total noise reduction is similar, different parameter combinations will have different noise reduction focuses. In practical applications, if the equipment is mainly low-frequency noise, parameters with smaller wavelengths and larger differences in amplitude between the large and small teeth can be selected first. If it is necessary to control high-frequency noise, parameters with larger wavelengths and smaller small tooth amplitudes should be selected. The selection can be made flexibly based on the characteristics of the noise frequency band at the site.

[0063] Traditional cavity noise reduction structures generally suffer from large dynamic losses. To verify the impact of the sawtooth structure of this invention on flow field resistance and evaluate the comprehensive application value of the device, drag coefficient comparison tests were conducted. Figure 12 As shown in the figure, this is a comparison of the drag coefficients of the airfoil structure without and with leading-edge serrations at different incoming flow velocities of 2~6 m / s. The horizontal axis represents the incoming flow velocity, and the vertical axis represents the drag coefficient, thus quantifying the additional dynamic loss caused by the serrated structure. Throughout the entire speed measurement range, the two drag coefficient curves almost completely overlap, with minimal numerical difference, indicating that the drag characteristics of the airfoil do not change significantly after adding the leading-edge serrated disturbance structure of this invention. This result confirms that the serrated component designed in this invention, with its optimized curved surface shape and reasonable angle parameters, causes minimal disturbance to the original flow field and does not significantly increase operating drag. It effectively overcomes the shortcomings of traditional noise reduction structures, which suffer from large dynamic losses. While achieving wide-band flow noise control, it fully preserves the original operating efficiency of the equipment, balancing noise reduction performance and dynamic performance.

[0064] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A noise control structure for airfoil surface cavity flow based on leading-edge serrations, characterized in that, It includes a serrated turbulence structure assembly, which is disposed at the leading edge of the orifice opening to disrupt the spanwise coherence of the orifice shear layer and control the eddy current scale. The turbulence structure sawtooth assembly includes several sawtooth units arranged sequentially along the front edge of the cavity. The sawtooth unit has a preset tooth shape, wavelength λ, amplitude h, and included angle θ between the upper and lower surfaces. The tooth profile is selected from one or more combinations of sinusoidal wave tooth profile, triangular wave tooth profile, or composite wave tooth profile; The wavelength λ, amplitude h, and the angle θ between the upper and lower surfaces are matched and set according to the scale distribution characteristics of the vortex in the target cavity flow field, so that the serrated component of the disturbance structure can divide, break up and guide vortices of different scales, thereby reducing cavity flow noise in a wide frequency band and reducing the additional dynamic loss to the original flow field.

2. The airfoil surface cavity flow noise control structure based on leading-edge serrations according to claim 1, characterized in that: The wavelength λ of the sawtooth unit ranges from 0.05D to 0.4D, the amplitude h ranges from 0.15D to 0.35D, and the included angle θ between the upper and lower surfaces ranges from 15° to 45°, where D is the diameter of the cavity opening.

3. The airfoil surface cavity flow noise control structure based on leading-edge serrations according to claim 1, characterized in that: The tooth profile design is as follows: The sinusoidal wave tooth profile is a smooth and continuous curved surface tooth profile with 3 teeth, used to control small-scale vortices ≤0.1D; The triangular wave tooth profile includes a first triangular wave tooth profile with 3 teeth and a second triangular wave tooth profile with 6 teeth. The first triangular wave tooth profile with 3 teeth is used to cut large-scale vortices ≥0.2D, and the second triangular wave tooth profile with 6 teeth is used to cut medium-scale vortices greater than 0.1D and less than 0.2D. The composite wave tooth profile is a composite wave tooth profile with alternating large and small teeth, including a first composite wave tooth profile with 6 large triangular wave tooth profiles and 5 small sinusoidal wave tooth profiles, or a second composite wave tooth profile with 6 large sinusoidal wave tooth profiles and 5 small triangular wave tooth profiles; used to cover the control of eddies across the entire scale.

4. A design method for a cavity flow noise control structure based on leading-edge serrations on an airfoil surface, as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Construct a simulation model of the target cavity; The aperture diameter D, aperture depth H, and inflow velocity U of the cavity were determined, and the scale distribution characteristics of the vortex in the cavity flow field were obtained through simulation analysis. Step 2: Match the tooth shape and initial parameters of the serrations of the turbulence structure according to the scale distribution characteristics of the vortex, wherein large-scale vortices ≥ 0.2D, 0.1D < mesoscale vortices < 0.2D, and small-scale vortices ≤ 0.1D; the initial parameters include wavelength λ, amplitude h, and the angle θ between the upper and lower surfaces; Step 3: Implant the tooth shape and initial parameters determined in Step 2 into the simulation model to simulate the state of the serrated component of the turbulence structure fixed at the front edge of the cavity, and carry out fluid numerical simulation to obtain full-band sound pressure level spectrum data and flow field characteristics; Step 4: Iteratively adjust at least one parameter among tooth profile, wavelength, amplitude, or included angle based on the simulation results; Step 5: Once the simulation results meet the noise reduction requirements across the entire frequency band, lock in the core parameters of the serrated component of the turbulence structure, and formulate a maintenance plan based on the simulation results.

5. The design method according to claim 4, characterized in that: In step 2, the rules for determining the wavelength λ and amplitude h are as follows: If the flow field is dominated by large-scale eddies, the wavelength λ is taken as 0.2D~0.3D, the amplitude h1 of the large tooth wave is taken as 0.25D~0.35D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the large and small-scale eddies in the flow field are uniformly distributed, the wavelength λ is taken as 0.1D~0.2D, the amplitude h1 of the large tooth wave is taken as 0.2D~0.28D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the flow field is dominated by small-scale eddies, the wavelength λ is taken as 0.05D~0.1D, the amplitude h1 of the large tooth wave is taken as 0.18D~0.25D, and the amplitude h2 of the small tooth wave is taken as 0.15D~0.2D; If the proportion of medium-scale eddies in the flow field is relatively high, the wavelength λ is taken as 0.1D~0.15D and the amplitude h is taken as 0.18D~0.28D.

6. The design method according to claim 5, characterized in that: In step 2, the rule for determining the angle θ between the tooth profile and the upper and lower surfaces is as follows: For scenarios dominated by large-scale eddies, the first triangular wave tooth shape or the first composite wave tooth shape is preferred, with θ ranging from 15° to 22°. For scenarios with uniform vortex distribution across the entire scale, the first composite wave tooth shape is preferred, with θ ranging from 30° to 38°. For scenarios dominated by small-scale vortices, sinusoidal wave tooth profiles or second composite wave tooth profiles are preferred, with θ ranging from 38° to 45°. For scenarios with a high proportion of medium-scale vortices, the second triangular wave tooth shape is selected, with θ ranging from 22° to 30°.

7. The design method according to claim 6, characterized in that: In step 4, the specific strategy for iterative adjustment is as follows: If the noise reduction in the low-frequency band (0-100Hz) is insufficient, replace it with the first triangular wave tooth shape or the first composite wave tooth shape, and increase the wavelength and amplitude. If the sound pressure level in the mid-frequency band of 100~300Hz increases, adjust θ to 22°~30° or change it to the second triangular wave tooth shape; If the noise reduction in the high-frequency band of 300~1000Hz is insufficient, replace it with a sine wave tooth profile or a second composite wave tooth profile, and optimize the amplitude and wavelength of the small teeth. Repeat the iteration until the simulation results meet the requirements of low-frequency noise reduction ≥10dB and high-frequency noise reduction ≥8dB across the entire frequency band (0~1000Hz), thereby determining the final design parameters.

8. A method for controlling cavity flow noise based on the leading-edge serrated airfoil surface cavity flow noise control structure according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Fix the turbulence structure sawtooth assembly, which is pre-matched according to the opening diameter D of the target cavity and the incoming flow velocity range, at the leading edge of the opening of the cavity, so that the sawtooth units of the turbulence structure sawtooth assembly are arranged sequentially along the leading edge of the cavity. Step 2: During actual operation, acquire the incoming flow velocity and vortex-scale distribution characteristics of the cavity flow field in real time or periodically; If the current flow field is dominated by large-scale vortices, then select or switch to a serrated component of a turbulence structure with triangular wave tooth shape or first composite wave tooth shape. If the proportion of small-scale vortices in the current flow field is high, then select or switch to a serrated component of a sine wave tooth or a second composite wave tooth for the turbulence structure. If the vortices are uniformly distributed across the entire scale in the current flow field, then a sawtooth component of the turbulence structure with the first composite wave tooth shape should be selected or maintained. If the proportion of medium-scale vortices in the current flow field is high, then the second triangular wave toothed component should be selected or switched. Step 3: Under incoming flow conditions, the spanwise coherence of the orifice shear layer is passively disrupted and the eddy scale is controlled by the sawtooth component of the turbulence structure, so that large-scale eddies are broken up and small-scale eddies are guided and dissipated, and the eddy shedding frequency is dispersed to a wide frequency band, thereby achieving full-band noise suppression without the need for external energy input. Step 4: When the sound pressure level of the cavity radiation noise in a specific frequency band rises above the preset threshold, it is determined that the current sawtooth component is mismatched with the vortex scale of the flow field. Repeat Step 2 to replace the sawtooth component with the corresponding tooth shape and parameters to restore or optimize the noise reduction effect.

9. A square cavity structure, characterized in that, include: The flow channel is a rectangular parallelepiped. The cavity is a cuboid structure with vertical flow channels. A circular hole is provided in the gap between the flow channel and the cavity, and the center of the circular hole is located on the central axis of the cavity; The airfoil surface cavity flow noise control structure based on leading edge sawtooth as described in any one of claims 1-3 includes a turbulence structure sawtooth assembly, wherein the turbulence structure sawtooth assembly is fixedly installed at the leading edge of the circular hole.

10. An airfoil structure, characterized in that, include: The airfoil body is the NACA0012 airfoil; A central opening, a circular hole located at the midpoint of the surface of the airfoil body; The airfoil surface cavity flow noise control structure based on leading edge sawtooth as described in any one of claims 1-3 includes a turbulence structure sawtooth assembly, wherein the turbulence structure sawtooth assembly is fixedly installed at the leading edge of the central opening.

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