Noise propagation model design method based on whale fin-like wave front fan blade

Abstract

The application discloses a kind of based on the noise propagation model design method of whale fin imitated wave front fan blade, in method, based on wave front shape control equation, the three-dimensional model of whale fin imitated wave front fan blade is established;Based on the three-dimensional model of the whale fin imitated wave front blade, the computational domain model of flow turbulence and whale fin imitated wave front fan rotor interference is established;Based on large eddy simulation turbulence model, full three-dimensional compressible Naiver-Stoke flow field control equation is solved, the vortex distribution in flow field is calculated, and the vortex structure position is identified;Based on vortex structure position, the control surface including vortex structure is established, and the equivalent sound source on control surface is solved;Based on the surface of whale fin imitated wave front fan blade, different boundary element grid is divided in sparseness, to control surface on the equivalent sound source as incident noise, grid independence verification is carried out, and whale fin imitated wave front fan rotor noise propagation model is established.

Description

Technical Field

[0001] This invention belongs to the field of aero-acoustics technology for aero-engines, and in particular, it is a design method for a noise propagation model based on a whale fin-inspired wave-leading edge fan blade. Background Technology

[0002] Compared to the total energy contained in the flow field, the noise component propagating to the far field in the form of sound waves is negligible. Due to the assumptions made by turbulence models to address the underdeterminacy of the Navier-Stokes equations, and the limitations of current computational capabilities, accurately predicting the noise of high-bypass-ratio engine fans has long been a highly challenging problem. Furthermore, to simplify the analysis process, sound sources are often simplified to compact sources, and the sound wave equations are solved using the free-field Green's function. This neglects physical phenomena such as reflection and scattering caused by interference between the sound waves and the engine fan during propagation. Exploring the impact of these physical phenomena on far-field noise during sound propagation is a key scientific issue in predicting broadband fan noise.

[0003] Based on the accurate acquisition of flow field information of aero-engine fan rotor, the surface of the simulated whale fin wave leading edge fan rotor is discretized, and a boundary element model of the fan rotor is established. Using the FW-H acoustic analogy equation, the equivalent noise source in the flow field is calculated and used as the incident sound wave of the boundary element model to achieve coupling between CFD simulation and boundary element model, and to predict the far-field noise of the simulated whale fin wave leading edge fan rotor. The influence of reflection, scattering and other phenomena caused by the interference between the sound wave and the novel simulated whale fin wave leading edge fan rotor on the noise propagation process is investigated. The characteristic information of the incoming noise source and the far-field noise is extracted to reveal the mapping relationship between the two during the sound propagation process.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a noise propagation model design method based on a whale fin wave-leading fan blade. The method discretizes the surface of the whale fin wave-leading fan rotor, establishes a boundary element model of the fan rotor, and calculates the equivalent aerodynamic noise source on the control surface of the whale fin wave-leading fan rotor deviating from the rotor using the FW-H equation. This source serves as the incident sound wave in the boundary element model, predicting the far-field noise of the whale fin wave-leading fan rotor. This allows for the investigation of the influence of reflection and scattering phenomena caused by the interference between sound waves and the novel whale fin wave-leading fan rotor on the noise propagation process.

[0006] The objective of this invention is achieved through the following technical solution: a noise propagation model design method based on a whale fin wave-leading edge fan blade includes:

[0007] In the first step: a three-dimensional model of a whale fin-shaped wave-leading fan blade is established based on the wave-leading shape control equation;

[0008] In the second step: Based on the three-dimensional model of the whale fin wave-leading blade, a computational domain model of the interference between the incoming turbulence and the whale fin wave-leading fan rotor is established. The computational domain model is meshed with preset mesh quality parameters, the fluid flow velocity is calculated with a predetermined Reynolds number, and the boundary conditions of the computational domain are set.

[0009] In the third step: Based on the large eddy simulation turbulence model, solve the full three-dimensional compressible Naiver-Stoke flow field control equations, calculate the vorticity distribution in the flow field, and identify the location of vortex structures.

[0010] In the fourth step: Based on the location of the vortex structure, a control surface containing the vortex structure is established, and the equivalent sound source on the control surface is solved based on the FfowcsWilliams-Hawkings acoustic analogy equation.

[0011] In the fifth step: Based on the surface of the imitation whale fin wave leading edge fan blade, boundary element meshes of different densities are divided to control the equivalent sound source on the surface as incident noise, mesh independence is verified, and a noise propagation model of the imitation whale fin wave leading edge fan rotor is established.

[0012] In the noise propagation model design method based on the wave-leading fan blades inspired by whale fins, the first step, the governing equation for the wave-leading shape, is:

[0013]

[0014] Where c(z) is the distribution function of the chord length of the leading edge blade of the whale fin wave pattern along its span. The average chord length of the leading edge blades is denoted as h, where h is the amplitude from the crest to the trough of the wavy leading edge, λ is the wavelength of the wavy leading edge, and x is the average chord length of the leading edge blades, which mimic the wave shape of a whale fin. s x represents the abscissa of the cross-sectional control curve at different z positions of the wavy leading-edge blade. w The position of the wavy leading-edge blade curve along the mid-arc line, y s y represents the thickness of the reference blade along the mid-arc line. w The thickness of the wavy leading edge blade along the mid-arc line.

[0015] In the noise propagation model design method based on the simulated whale fin wave-leading edge fan blade, the second step involves establishing a cuboid computational domain that represents the interference between the incoming turbulence and the rotor of the simulated whale fin wave-leading edge fan. The origin of the computational domain coincides with the origin of the control curves for different cross-sectional shapes of the wave-shaped leading edge. The width of the computational domain is equal to the span of the simulated whale fin wave-leading edge blade. s The same applies to the distance from the origin of the computational domain at the entrance of the computational domain. Distance of the computation domain exit from the computation domain origin The upper and lower boundaries of the computational domain are both at a distance from the origin of the computational domain. The dimensionless distance y of the boundary layer mesh wall of the wave-leading blade of the whale fin + Satisfy y + <1. The mesh height growth rate perpendicular to the blade wall does not exceed 1.2, and the mesh skewness is less than 0.5 are the preset mesh quality parameters. The mesh type is structured mesh. The computational domain model is meshed according to the predetermined Reynolds number. Calculate the average flow velocity of the fluid Where v is the kinematic viscosity coefficient; and the boundary conditions at the entrance of the computational domain are set as velocity inlet, the boundary conditions at the exit of the computational domain are set as pressure outlet, the left and right sides are set as cyclic boundary conditions, and the top and bottom sides are set as symmetrical boundary conditions.

[0016] In the noise propagation model design method based on the wave-leading edge fan blades of a whale fin, the third step of the fully three-dimensional compressible Naiver-Stoke equation is:

[0017]

[0018] Where T is the fluid temperature, p is the fluid pressure, and ρ is the fluid density. For differential operators, The matter derivative is defined as follows: U is the fluid flow velocity vector, S M Let e ​​be the momentum source term, k be the internal energy per unit fluid, Φ be the thermal conductivity, and S be the dissipation function. e Let μ be the internal energy term and μ be the dynamic viscosity coefficient. Based on the distribution of various variables in the flow field, calculate the second invariant Q of the standardized velocity gradient tensor. n Identify the location of the main vortex structures in the flow field, Q n Defined as:

[0019]

[0020] in, For vortex tensor, Let x be the deformation rate tensor. i With x j U is the coordinate in the Cartesian coordinate system. i For velocity U at x i Components in direction.

[0021] In the noise propagation model design method based on the wave-leading edge fan blades of a whale fin, the fourth step involves solving for the equivalent monopole, dipole, and quadrupole noise sources on the control surface based on the FW-H acoustic analogy equation. The FW-H acoustic analogy equation is as follows:

[0022]

[0023] Where ρ′ represents far-field noise and c0 represents the speed of sound. For the Laplace operator, T ij For Lighthill stress tensor, T ij =ρU′ i U j ′,U′ i For velocity fluctuations U′ in x i The components in the direction, f is the wall function, and H(f) is the Herveyd function:

[0024]

[0025] δ(f) is the Dirac function, F i =ρU i (U n -v n )+ρn i -τ ij n j For an equivalent dipole noise source, where U n For the fluid velocity perpendicular to the control surface, v n To control the surface velocity, n i n j x represents the vertical normal vector of the blade surface, respectively. i x j Directional component, τ ij For fluid stress tensor; Q = ρU n -(ρ-ρ0)v n For an equivalent monopole sound source, ρ0 is the initial density of the fluid.

[0026] In the noise propagation model design method based on the simulated whale fin wave-leading edge fan blade, in the fifth step, based on the surface of the simulated whale fin wave-leading edge fan blade, boundary element meshes of different densities are divided, and boundary element mesh independence is verified. The noise generated by equivalent monopole, dipole, and quadrupole noise sources on the surface is used as incident noise. The sound pressure in the entire computational domain is calculated based on the boundary element method integral formula, establishing the simulated whale fin wave-leading edge fan rotor noise propagation model. The boundary element method integral formula is:

[0027]

[0028] Where C is the surface shape function and G is the free-space Green's function. The sound pressure at frequency ω and These are the frequency domain representations of the Lighthill stress tensor, the dipole equivalent sound source, and the monopole equivalent sound source, respectively. i is the imaginary unit, Ω is the control surface, and V is the computational domain.

[0029] The noise propagation model design method based on the wave-leading edge fan blades of a whale fin includes the following steps for verifying the independence of the boundary element mesh:

[0030] S501. Based on the surface shape of the leading edge of a whale fin wave, divide the surface into 3 to 5 sets of structural meshes with different densities using predetermined mesh parameters.

[0031] S502. Calculate the Lighthill stress tensor, dipole equivalent sound source, and monopole equivalent sound source on the FW-H control surface using the FW-H formula. and The expression,

[0032] S503. Using the aforementioned 3 to 5 sets of structural meshes with different densities, calculate the sound pressure distribution throughout the entire computational domain based on the boundary element method integral formula. Specify a point within the computational domain and calculate the noise sound pressure level at that point.

[0033] S504. Compare the far-field noise sound pressure level calculation results based on grids of different densities. If the error does not exceed 5%, retain a grid with a suitable density. Otherwise, repeat steps S501, S502 and S503 until the calculation error does not exceed 5%.

[0034] In the noise propagation model design method based on the wave-leading edge fan blades of the whale fin, the predetermined grid parameters are: each grid must contain more than 6 sound wave wavelengths at the frequencies of interest.

[0035] Compared with existing technologies, the present invention has the following advantages: The noise propagation model design method based on the simulated whale fin wave leading edge fan blade described in the present invention, by accurately obtaining the flow field information of the aero-engine fan rotor, discretizing the surface of the simulated whale fin wave leading edge fan rotor, establishing the boundary element model of the fan rotor, and calculating the equivalent noise source in the flow field based on the FW-H equation as the incident sound wave of the boundary element model, realizes the coupling of CFD simulation and boundary element model. Compared with traditional noise prediction models, the present invention provides a method to predict the far-field noise of the simulated whale fin wave leading edge rotor, and can further explore the influence of reflection, scattering and other phenomena generated by the interference of sound waves with the novel simulated whale fin wave leading edge fan rotor on the noise propagation process. Attached Figure Description

[0036] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0037] In the attached diagram:

[0038] Figure 1 This is a flowchart illustrating a noise propagation model design method based on a simulated whale fin wave leading edge fan blade according to an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of a three-dimensional model of a fan blade with a wave-like leading edge, based on a noise propagation model design method for a fan blade with a wave-like leading edge, according to an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of the vortex structure generated by the interference between the simulated whale fin wave leading edge fan blade and the flow field, based on the noise propagation model design method of the simulated whale fin wave leading edge fan blade according to an embodiment of the present invention.

[0041] Figure 4 This is a schematic diagram illustrating the process of verifying the independence of the boundary element mesh in a noise propagation model design method based on a simulated whale fin wave leading edge fan blade according to an embodiment of the present invention.

[0042] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0043] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0044] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0045] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0046] To better understand, such as Figures 1 to 4 As shown, the design method for a noise propagation model based on a whale fin-inspired wave-leading fan blade includes,

[0047] In the first step (S1): a three-dimensional model of a whale fin-shaped wave-leading fan blade is established based on the wave-leading shape control equation;

[0048] In the second step (S2): Based on the three-dimensional model of the imitation whale fin wave leading edge blade, a computational domain model of the interference between the incoming turbulence and the imitation whale fin wave leading edge fan rotor is established. The computational domain model is meshed with preset mesh quality parameters, the fluid flow velocity is calculated with a predetermined Reynolds number, and the boundary conditions of the computational domain are set.

[0049] In the third step (S3): Based on the large eddy simulation turbulence model, solve the full three-dimensional compressible Naiver-Stoke flow field control equations, calculate the vorticity distribution in the flow field, and identify the location of vortex structures;

[0050] In the fourth step (S4): Based on the location of the vortex structure, a control surface containing the vortex structure is established, and the equivalent sound source on the control surface is solved based on the Ffowcs Williams-Hawkings acoustic analogy equation.

[0051] In the fifth step (S5): Based on the surface of the imitation whale fin wave leading edge fan blade, boundary element meshes with different densities are divided to control the equivalent sound source on the surface as incident noise, mesh independence verification is performed, and a noise propagation model of the imitation whale fin wave leading edge fan rotor is established.

[0052] In a preferred embodiment of the noise propagation model design method based on the wave-leading fan blades inspired by whale fins, in the first step (S1), the wave-leading shape control equation is:

[0053]

[0054] Where c(z) is the distribution function of the chord length of the leading edge blade of the whale fin wave pattern along its span. The average chord length of the leading edge blades is denoted as h, where h is the amplitude from the crest to the trough of the wavy leading edge, λ is the wavelength of the wavy leading edge, and x is the average chord length of the leading edge blades, which mimic the wave shape of a whale fin. s x represents the abscissa of the cross-sectional control curve at different z positions of the wavy leading-edge blade. w The position of the wavy leading-edge blade curve along the mid-arc line, y s The thickness of the reference blade along the mid-arc line, y w The thickness of the wavy leading edge blade along the mid-arc line.

[0055] In a preferred embodiment of the noise propagation model design method based on a whale-fin wave-leading edge fan blade, in the second step (S2), a cuboid computational domain is established to represent the interference between the incoming turbulence and the rotor of the whale-fin wave-leading edge fan. The origin of the computational domain coincides with the origin of the control curves for different cross-sectional shapes of the wave-shaped leading edge, and the width of the computational domain is equal to the span of the whale-fin wave-leading edge blade. s Similarly, the distance from the computational domain entrance to the computational domain origin is the same. Distance of the computation domain exit from the computation domain origin The upper and lower boundaries of the computational domain are both at a distance from the origin of the computational domain. The dimensionless distance y of the boundary layer mesh wall of the wave-leading blade of the whale fin + Satisfy y + <1. The mesh height growth rate perpendicular to the blade wall does not exceed 1.2, and the mesh skewness is less than 0.5 are the preset mesh quality parameters. The mesh type is structured mesh. The computational domain model is meshed according to the predetermined Reynolds number. Calculate the average flow velocity of the fluid Where v is the kinematic viscosity coefficient; and the boundary conditions at the entrance of the computational domain are set as velocity inlet, the boundary conditions at the exit of the computational domain are set as pressure outlet, the left and right sides are set as cyclic boundary conditions, and the top and bottom sides are set as symmetrical boundary conditions.

[0056] In a preferred embodiment of the noise propagation model design method based on the wave-leading edge fan blades inspired by whale fins, in the third step (S3), the fully three-dimensional compressible Naiver-Stoke equation is:

[0057]

[0058] Where T is the fluid temperature, p is the fluid pressure, and ρ is the fluid density. The differential is calculated at, The matter derivative is defined as follows: U is the fluid flow velocity vector, S M Let e ​​be the momentum source term, k be the internal energy per unit fluid, Φ be the thermal conductivity, and S be the dissipation function. e Let μ be the internal energy term and μ be the dynamic viscosity coefficient. Based on the distribution of various variables in the flow field, calculate the second invariant Q of the standardized velocity gradient tensor. n Identify the location of the main vortex structures in the flow field, Q n Defined as:

[0059]

[0060] in, For vortex tensor, Let x be the deformation rate tensor. i With x j The coordinates in the Cartesian coordinate system are: U i For velocity U at x i Components in direction.

[0061] In a preferred embodiment of the noise propagation model design method based on the simulated whale fin wave leading edge fan blade, in the fourth step (S4), the equivalent monopole, dipole, and quadrupole noise sources on the control surface are solved based on the FW-Williams-Hawkings acoustic analogy equation, wherein the FW-Hawkings acoustic analogy equation is:

[0062]

[0063] Where ρ′ represents far-field noise and c0 represents the speed of sound. For the Laplace operator, T ij For Lighthill stress tensor, T ij =ρU′ i U j ′,U′ i For velocity fluctuations U′ in x i The components in the direction, f is the wall function, and H(f) is the Herveyd function:

[0064]

[0065] δ(f) is the Dirac function, F i =ρU i (U n -v n )+ρn i -τ ij n j For an equivalent dipole noise source, where U nFor the fluid velocity perpendicular to the control surface, v n To control the surface velocity, n i n j x represents the vertical normal vector of the blade surface, respectively. i x j Directional component, τ ij For fluid stress tensor; Q = ρU n -(ρ-ρ0)v n For an equivalent monopole sound source, ρ0 is the initial density of the fluid.

[0066] In a preferred embodiment of the noise propagation model design method based on a whale fin wave-leading edge fan blade, in the fifth step (S5), based on the surface of the whale fin wave-leading edge fan blade, boundary element meshes of varying densities are divided, and boundary element mesh independence is verified. The noise generated by equivalent monopole, dipole, and quadrupole noise sources on the surface is used as incident noise. The sound pressure within the entire computational domain is calculated based on the boundary element method integral formula, thus establishing a noise propagation model for the whale fin wave-leading edge fan rotor. The boundary element method integral formula is:

[0067]

[0068] Where C is the surface shape function and G is the free-space Green's function. The sound pressure level at frequency ω and These are the frequency domain representations of the Lighthill stress tensor, the dipole equivalent sound source, and the monopole equivalent sound source, respectively. i is the imaginary unit, Ω is the control surface, and V is the computational domain.

[0069] In a preferred embodiment of the noise propagation model design method based on the simulated whale fin wave leading edge fan blade, the boundary element mesh independence verification includes the following steps:

[0070] S501. Based on the surface shape of the leading edge of a whale fin wave, divide the surface into 3 to 5 sets of structural meshes with different densities using predetermined mesh parameters.

[0071] S502. Calculate the Lighthill stress tensor, dipole equivalent sound source, and monopole equivalent sound source on the FW-H control surface using the FW-H formula. and The expression,

[0072] S503. Using the aforementioned 3 to 5 sets of structural meshes with different densities, calculate the sound pressure distribution throughout the entire computational domain based on the boundary element method integral formula. Specify a point within the computational domain and calculate the noise sound pressure level at that point.

[0073] S504. Compare the far-field noise sound pressure level calculation results based on grids of different densities. If the error does not exceed 5%, retain a grid with a suitable density. Otherwise, repeat steps S501, S502 and S503 until the calculation error does not exceed 5%.

[0074] In a preferred embodiment of the noise propagation model design method based on the wave-leading edge fan blades of a whale fin, the predetermined grid parameters are: each grid must contain at least 6 sound wave wavelengths at the frequencies of interest.

[0075] In one embodiment, the noise propagation model design method based on a whale fin-inspired wave-leading fan rotor includes the following steps:

[0076] In the first step: Based on the wave leading edge shape control equation, a three-dimensional model of a whale fin wave leading edge fan blade is established;

[0077] In the second step: Based on the three-dimensional model of the whale fin wave-leading blade, a computational domain model of the interference between the incoming turbulence and the whale fin wave-leading fan rotor is established. The computational domain model is meshed with preset mesh quality parameters, the fluid flow velocity is calculated with a predetermined Reynolds number, and the boundary conditions of the computational domain are set.

[0078] In the third step: Based on the large eddy simulation turbulence model, solve the full three-dimensional compressible Naiver-Stoke flow field control equations, calculate the vorticity distribution in the flow field, and identify the location of vortex structures.

[0079] In the fourth step: based on the location of the vortex structure in the flow field, a control surface containing the main vortex structure in the flow field is established, and based on the Ffowcs Williams-Hawkings (FW-H) acoustic analogy equation, the equivalent sound source on the control surface is solved;

[0080] In the fifth step: Based on the surface of the leading edge fan blades of the whale fin wave, boundary element meshes with different densities are divided to control the equivalent sound source on the surface as incident noise. Mesh independence verification is performed. Under the premise that the density of the boundary element mesh has little impact on the calculation results, a noise propagation model of the rotor of the leading edge fan of the whale fin wave is established.

[0081] In the method, in the first step,

[0082] In the first step (S1), based on the wave leading edge shape governing equation:

[0083]

[0084] Establish as Figure 2 The image shows a three-dimensional model of a leading-edge fan blade inspired by a whale fin wave pattern, where c(z) is the distribution function of the chord length along the span of the leading-edge fan blade inspired by a whale fin wave pattern. The average chord length of the leading edge blades, which mimic the wave pattern of a whale fin, is given by h = 10.01 mm, representing the amplitude from the crest to the trough of the wave-shaped leading edge, λ = 9.04 mm, and x. s x represents the abscissa of the cross-sectional control curve at different z positions of the wavy leading-edge blade. w The position of the wavy leading edge blade curve along the mid-arc line, y s The thickness of the reference blade along the mid-arc line, y w The thickness of the wavy leading edge blade along the mid-arc line.

[0085] In the method, in the second step,

[0086] In the second step (S2), a cuboid computational domain is established to represent the interference between the incoming turbulence and the rotor of the simulated whale fin wave-shaped leading edge fan. The origin of the computational domain coincides with the origin of the control curves for different cross-sectional shapes of the wave-shaped leading edge. The width of the computational domain is equal to the span of the simulated whale fin wave-shaped leading edge blade. s =36.04mm is the same, the distance from the entrance of the computational domain to the origin of the computational domain is the same. Distance of the computation domain exit from the computation domain origin The upper and lower boundaries of the computational domain are both at a distance from the origin of the computational domain. The dimensionless distance y of the boundary layer mesh wall of the wave-leading blade of the whale fin + Satisfy y + <1. The mesh height growth rate perpendicular to the blade wall does not exceed 1.2, and the mesh skewness is less than 0.5 are the preset mesh quality parameters. The mesh type is structured mesh. The computational domain model is meshed according to the predetermined Reynolds number. Calculate the average flow velocity of the fluid Where v is the kinematic viscosity coefficient; and the boundary conditions at the entrance of the computational domain are set as velocity inlet, the boundary conditions at the exit of the computational domain are set as pressure outlet, the left and right sides are set as cyclic boundary conditions, and the top and bottom sides are set as symmetrical boundary conditions.

[0087] In the method, in the third step,

[0088] Based on the large eddy simulation turbulence model, the fully three-dimensional compressible Naiver-Stokes equations are solved to calculate the velocity U and pressure p distributions in the computational domain. The fully three-dimensional compressible Naiver-Stokes equations are defined as follows:

[0089]

[0090] Where T is the fluid temperature, p is the fluid pressure, and ρ is the fluid density. For differential operators, The matter derivative is defined as follows: U is the fluid velocity vector, s MLet e ​​be the momentum source term, k be the internal energy per unit fluid, Φ be the thermal conductivity, and S be the dissipation function. e Let μ be the internal energy term and μ be the dynamic viscosity coefficient. Based on the distribution of various variables in the flow field, calculate the second invariant Q of the standardized velocity gradient tensor. n Identify the location of the main vortex structures in the flow field, Q n Defined as:

[0091]

[0092] in, For vortex tensor, Let x be the deformation rate tensor. i With x j U is the coordinate in the Cartesian coordinate system. i For velocity U at x i Component in direction, when Q n When the value is 5, the positions of the main vortices in the flow field are as follows: Figure 3 As shown.

[0093] In the method, in the fourth step,

[0094] Based on such Figure 3 The locations of vortex structures within the flow field are shown. An FW-H control surface containing the main vortex structures in the flow field is established. Based on the FW-H acoustic analogy equation, the equivalent monopole, dipole, and quadrupole noise sources on the control surface are solved. The FW-H acoustic analogy equation is defined as follows:

[0095]

[0096] Where ρ′ represents far-field noise and c0 represents the speed of sound. For the Laplace operator, T ij For the Lighthill stress tensor, when the Reynolds number is low and thermal conduction is negligible, it simplifies to T. ij =ρU′ i U j ′,U′ i For velocity fluctuations U′ in x i The components in the direction, f is the wall function, and H(f) is the Herveyd function:

[0097]

[0098] δ(f) is the Dirac function, F i =ρU i (U n -v n )+ρn i -τ ij nj For an equivalent dipole noise source, where U n For the fluid velocity perpendicular to the control surface, v n To control the surface velocity, n i n j x represents the vertical normal vector of the blade surface, respectively. i x j Directional component, τ ij For fluid stress tensor; Q = ρU n -(ρ-ρ0)v n For an equivalent monopole sound source, ρ0 is the initial density of the fluid.

[0099] In the method, in the fifth step,

[0100] Based on the surface of a whale-fin wave-leading edge fan blade, boundary element meshes of varying densities were created, and their independence was verified. Noise generated by equivalent monopole, dipole, and quadrupole noise sources on the surface was used as incident noise. Sound pressure throughout the computational domain was calculated using the boundary element method integral formula, thus establishing a noise propagation model for the whale-fin wave-leading edge fan rotor. The boundary element method integral formula is as follows:

[0101]

[0102] Where C is the surface shape function and G is the free-space Green's function. The sound pressure level at frequency ω and These are the frequency domain representations of the Lighthill stress tensor, the dipole equivalent sound source, and the monopole equivalent sound source, respectively. i is the imaginary unit, Ω is the control surface, and V is the computational domain.

[0103] Figure 4 This is a flowchart of the independence verification process for boundary element meshes; such as... Figure 1 As shown, the independence verification of the boundary element mesh includes the following steps:

[0104] 1) Based on the surface shape of the leading edge of a whale fin wave, 3 to 5 sets of structural meshes with different densities are divided using predetermined mesh parameters.

[0105] 2) Calculate the Lighthill stress tensor, dipole equivalent sound source, and monopole equivalent sound source on the FW-H control surface using the FW-H formula. and The expression,

[0106] 3) Using the 3-5 sets of structural meshes with different densities, calculate the sound pressure distribution throughout the entire computational domain based on the boundary element method integral formula. Specify a point within the computational domain and calculate the noise sound pressure level at that point.

[0107] 4) Compare the far-field noise sound pressure level calculation results based on different grid densities. If the error does not exceed 5%, retain a grid with a moderate density. Otherwise, repeat steps 1), 2), and 3) until the calculation error does not exceed 5%.

[0108] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A noise propagation model design method based on a whale fin-inspired wave-leading edge fan blade, characterized in that, It includes the following steps, In the first step (S1): a three-dimensional model of a whale fin-shaped wave-leading fan blade is established based on the wave-leading shape control equation. The wave-leading shape control equation is: ， in, The distribution function of the chord length along the span of the leading edge blades, mimicking the wave pattern of a whale fin. The average chord length of the leading edge blades is designed to mimic the wave-like shape of a whale fin. This represents the amplitude from the crest to the trough of the wavy leading edge. The wavelength of the wavy leading edge. Different positions of the wavy leading edge blade The x-coordinate of the cross-sectional control curve at that location This refers to the position of the wavy leading-edge blade curve along the mid-arc line. The thickness of the reference blade along the mid-arc line, The thickness of the wavy leading-edge blade along the mid-arc line; In the second step (S2): Based on the three-dimensional model of the imitation whale fin wave leading edge fan blade, a computational domain model of the interference between the incoming turbulence and the imitation whale fin wave leading edge fan rotor is established. The computational domain model is meshed with preset mesh quality parameters, the fluid flow velocity is calculated with a predetermined Reynolds number, and the boundary conditions of the computational domain are set. In the third step (S3): Based on the large eddy simulation turbulence model, solve the full three-dimensional compressible Naiver-Stoke flow field control equations, calculate the vorticity distribution in the flow field, and identify the location of vortex structures; In the fourth step (S4): Based on the location of the vortex structure, a control surface containing the vortex structure is established, and based on the FfowcsWilliams-Hawkings acoustic analogy equation, the equivalent monopole, dipole and quadrupole noise sources on the control surface are solved. In the fifth step (S5): Based on the surface of the imitation whale fin wave leading edge fan blade, boundary element meshes with different densities are divided to control the equivalent monopole, dipole and quadrupole noise sources on the surface as incident noise, mesh independence verification is performed, and a noise propagation model of the imitation whale fin wave leading edge fan rotor is established.

2. The noise propagation model design method based on the wave-leading edge fan blades inspired by whale fins as described in claim 1, wherein, In the second step (S2), a cuboid computational domain is established to represent the interference between the incoming turbulence and the rotor of the simulated whale fin wave-shaped leading edge fan. The origin of the computational domain coincides with the origin of the control curves for different cross-sectional shapes of the wave-shaped leading edge. The width of the computational domain is equal to the span of the simulated whale fin wave-shaped leading edge blades. The same applies to the distance from the origin of the computational domain at the entrance of the computational domain. The distance from the computation domain exit to the computation domain origin The upper and lower boundaries of the computational domain are both far from the origin of the computational domain. ; Dimensionless distance of the boundary layer mesh wall of the wave-like leading edge blades of a whale fin satisfy The preset mesh quality parameters are: a mesh height growth rate perpendicular to the blade wall not exceeding 1.2, and a mesh skewness less than 0.

5. The mesh type is a structured mesh. The computational domain model is then meshed according to a predetermined Reynolds number. Calculate the average flow velocity of the fluid. ,in, The value is the kinematic viscosity coefficient; and the boundary conditions at the entrance of the computational domain are set as velocity inlet, the boundary conditions at the exit of the computational domain are set as pressure outlet, the left and right sides are set as cyclic boundary conditions, and the top and bottom sides are set as symmetrical boundary conditions.

3. The noise propagation model design method based on the leading edge fan blades of a whale fin as described in claim 2, wherein, In the third step (S3), the fully three-dimensional compressible Naiver-Stoke equations are: ， in, For fluid temperature, This refers to fluid pressure. For fluid density, For differential operators, The matter derivative is defined as follows: , For fluid flow velocity vector, For momentum source term, The internal energy contained in a unit fluid. Thermal conductivity, Let be the dissipation function. For internal energy items, The dynamic viscosity coefficient is used; based on the distribution of various variables in the flow field, the second invariant of the standardized velocity gradient tensor is calculated. Identify the locations of the main vortex structures in the flow field. Defined as: ， in, For vortex tensor, For the deformation rate tensor, and The coordinates are in the Cartesian coordinate system. For fluid flow velocity vector exist Components in direction, The time-averaged fluid flow velocity vector. For fluid flow velocity vector exist The velocity component in the direction.

4. The noise propagation model design method based on the wave-leading edge fan blades inspired by whale fins as described in claim 1, wherein, In the fourth step (S4), based on the FWW-Williams-Hawkings acoustic analogy equation, the equivalent monopole, dipole, and quadrupole noise sources on the control surface are solved, where the FW-H acoustic analogy equation is: ， in, For far-field noise, For the speed of sound, For the Laplace operator, For the Lighthill stress tensor, , For speed pulsation exist Components in direction, For wall functions, For Herveside functions: ， For the Dirac function, As an equivalent dipole noise source, where, For the fluid velocity perpendicular to the control surface, To control the surface speed, , These represent the vertical normal vectors of the blade surface, respectively. , Directional components, For fluid stress tensor; As an equivalent monopole sound source, where, The initial density of the fluid, The coordinates are in the Cartesian coordinate system. For fluid density, For speed pulsation exist Components in direction, For fluid flow velocity vector exist The velocity component in the direction.

5. The noise propagation model design method based on the wave-leading edge fan blades inspired by whale fins as described in claim 4, wherein, In the fifth step (S5), based on the surface of the simulated whale fin wave-leading edge fan blades, boundary element meshes of varying densities are divided, and the independence of the boundary element mesh is verified. Noise generated by equivalent monopole, dipole, and quadrupole noise sources on the control surface is used as incident noise. The sound pressure within the entire computational domain is calculated based on the boundary element method integral formula, establishing a noise propagation model for the simulated whale fin wave-leading edge fan rotor. The boundary element method integral formula is: ， in, For surface shape function, For free space Green's function, For frequency The sound pressure level is lower. , and These are the frequency domain representations of the Lighthill stress tensor, the dipole equivalent sound source, and the monopole equivalent sound source, respectively. The imaginary unit, To control the surface, For the computational domain.

6. The noise propagation model design method based on the leading edge fan blades of a whale fin as described in claim 5, wherein, The independence verification of the boundary element mesh includes the following steps: S501. Based on the surface shape of the leading edge of a whale fin wave, 3-5 sets of structural meshes with different densities are divided using predetermined mesh parameters. S502. Calculate the Lighthill stress tensor, dipole equivalent sound source, and monopole equivalent sound source on the FW-H control surface using the FW-H formula. , and The expression, S503. Using the aforementioned 3-5 sets of structural meshes with different densities, calculate the sound pressure distribution throughout the entire computational domain based on the boundary element method integral formula. Specify a point within the computational domain and calculate the noise sound pressure level at that point. S504. Compare the far-field noise sound pressure level calculation results based on different density grids. If the error does not exceed 5%, retain one set of grids. Otherwise, repeat steps S501, S502 and S503 until the calculation error does not exceed 5%.

7. The noise propagation model design method based on the wave-leading edge fan blades inspired by whale fins as described in claim 6, wherein, The predetermined grid parameters are: each grid must contain at least 6 acoustic wavelengths at the frequencies of interest.

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