Turboprop aircraft internal and external sound field simulation method based on FW-H and acoustic-structure interaction

Abstract

The invention relates to a turboprop aircraft internal and external sound field simulation method based on FW-H and acoustic-structure interaction, and belongs to the field of aviation acoustics. The method disclosed by the invention comprises the following steps: S1, carrying out flow field initialization simulation by adopting a steady Reynolds time-averaged Navier Stokes (RANS); S2, calculating external sound pressure distribution of an aircraft cabin by adopting an unsteady Reynolds time-averaged Navier Stokes (URANS) method and a Williams Hofs (FW-H) method, and calculating the external sound pressure distribution of the aircraft cabin by adopting the Reynolds time-averaged Navier Stokes (URANS) method and the Williams Hofs (FW-H) method. S3, calculating the size of a point sound source (monopole and dipole point sources) under external excitation by adopting a novel sound source equivalent method; and S4, calculating the internal noise of the cabin by utilizing a frequency domain sound-solid coupling method. The invention provides a novel sound source space radiation equivalent method for propeller noise and a point sound source, and establishes an equation relational expression from the sound pressure p of the propeller to the monopole amplitude S and the dipole moment vector D. The fluid-structure-acoustics problem corresponding to the noise inside and outside a complex aircraft is innovatively simplified into an aeroacoustics module and a sound-structure coupling module. And the calculation consumption is greatly reduced.

Description

Technical Field

[0001] The invention relates to a method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling, and belongs to the field of aviation acoustics. Background Art

[0002] A feasible and accurate acoustic simulation of the aircraft's internal and external environment is key to the design of low-noise multi-propeller aircraft. Solving the complex challenges of aeroacoustics is essential to ensure the commercial success of aerospace vehicles, as the high noise levels they produce pose a significant barrier to wider adoption. For example, turboprop aircraft have many advantages such as low fuel consumption, good low-speed performance, and high flight efficiency, and are widely used in short-distance transportation and other fields, but noise issues are an important factor limiting their application scope.

[0003] Converting external acoustic numerical simulation data to the aircraft cabin surface and then transmitting it to the interior is a challenging numerical simulation. For fluid-structure interaction (FSI), the authorized invention patent CN 113378437B proposes a method for simulating and predicting axial fan noise under fluid-solid coupling. Through flow field simulation, the pressure information of the overall airflow excitation inside the target axial fan is extracted as the noise source, and the coupling interface between the acoustic domain air and the fan solid domain is set. The acoustic excitation is loaded, and the noise simulation calculation of the target axial fan is performed to obtain the simulation result of vibration noise. This method is not used for the noise calculation of the cabin body inside the cabin.

[0004] The authorized invention patent CN 113609590B discloses a patent for a cabin noise calculation method, system, equipment and storage medium in the field of ship design. The established cabin model is obtained, the system model parameters are input into the cabin model, and the mathematical model of the target cabin is established, and the mathematical model is solved to obtain noise data. It effectively avoids the problem of repeated modeling in the noise calculation of the ship cabin model, reduces the data transfer between the CAD model establishment and the CAE noise calculation, and improves the design efficiency of the cabin model. This method has been verified in the vehicle field. For example, Mendonca et al. (document "CAE-Based Prediction of Aero-Vibro-Acoustic Interior Noise Transmission for a Simple Test Vehicle)) demonstrated a hybrid simulation method to predict the internal and external noise of an ideal vehicle by coupling CFD, aeroacoustics and vibroacoustics methods. The total mesh size of the whole body is about 55 million cells. Nusser et al. (document "Numerical investigation of the fluid structure acoustics interaction on a simplified car model") used a 96.7 million unit grid. Their successful workflow for evaluating this FSA coupling included large eddy simulations (LES) of the turbulent flow field around the car model, as well as aeroacoustic and vibroacoustic methods to predict the sound propagation inside and outside the car. It is worth noting that the computational resource requirements are enormous, with nearly 100 million grid computing hours, and may require millions of core hours. However, computational resources and model convergence have limited the application of FSA coupling methods. .

[0005] In the invention patents CN111625905B and CN 111625904B, a high-frequency simulation method for cabin noise of a propeller aircraft and a low-frequency simulation method for cabin noise of a propeller aircraft are proposed. The simulation calculation is performed by establishing model data file management rules, simplifying the aircraft structure model, constructing structural dynamics and acoustic models, checking and debugging the model, calculating structural dynamic characteristics, and applying acoustic loads. The high-frequency simulation of this method uses the statistical energy method to calculate the cabin noise characteristics, which is suitable for high-frequency (above 1000Hz) broadband noise. The low-frequency simulation of this method uses the acoustic finite element method and the acoustic boundary element method, which is suitable for low-frequency (30Hz~1000Hz) internal noise simulation. However, the tonal noise of the propeller is higher than the broadband noise and dominates the propeller noise. Therefore, the high-frequency method has the problem of low accuracy when evaluating the internal and external noise calculation of turboprop aircraft with particularly obvious tonal noise. Although the low-frequency method can calculate broadband and tonal noise, the patent does not provide a calculation method for the propeller aerodynamic noise acoustic load.

[0006] In summary, the existing simulation calculation of the noise inside and outside the cabin of turboprop aircraft has the disadvantages of long calculation time for the fluid-structure-acoustic coupling method, and the energy method for calculating the noise inside and outside the cabin has the disadvantage of only being able to calculate broadband noise. The acoustic finite element method and the acoustic boundary element method lack the calculation method for the propeller aerodynamic acoustic load, and it is impossible to accurately and low-costly calculate the noise inside and outside the cabin. Summary of the invention

[0007] The purpose of the present invention is to provide a method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling, aiming to solve the problems that the current accurate fluid-structure-acoustic coupling method is time-consuming to calculate, and the acoustic finite element method and the acoustic boundary element method cannot be coupled with the aerodynamic noise of the propeller, so as to provide a method for simulating the internal and external sound fields of a turboprop aircraft with low calculation cost.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling comprises the following steps: S0. establishing a whole-machine mesh model of the aircraft and propeller, S1. using a steady Reynolds-averaged Navier-Stokes (RANS) method to perform an initialization simulation of the whole-machine flow field, S2. using an unsteady Reynolds-averaged Navier-Stokes (URANS) and Williams-Hawkings (FW-H) method to calculate the external sound pressure distribution of the aircraft cabin, S3. using a novel sound source equivalent method to calculate the size of a point sound source (monopole and dipole point source) under external excitation, S4. using a frequency domain acoustic-solid coupling method to calculate the internal noise of the cabin;

[0010] The computational domain of the whole machine grid model described in S0 is divided into 2 to 4 propeller rotation domains, a fuselage domain, and a far field domain;

[0011] The initialization simulation of the flow field described in S1 uses a multiple reference frame (MRF) model to perform steady-state RANS and broadband noise model simulations. The broadband noise model solves the sound power level of the entire machine, requiring 1000 to 2000 core hours of computation.

[0012] The external sound field simulation of the aircraft cabin described in S2 was performed using a sliding mesh model (SMM) for non-steady-state calculations. A time resolution of 0.1° to 1° of the propeller azimuth angle was selected as the simulation step to ensure smooth and effective convergence of each time step. At least 4 to 10 complete propeller rotations were required before sufficient convergence was achieved. In order to obtain higher frequency resolution, more rotations were selected, such as 10, and the computational effort required was 4000 to 6000 core hours.

[0013] The aircraft cabin external sound field simulation described in S2 requires the definition of cabin near sound field receiving points and propeller near sound field receiving points;

[0014] The definition of the cabin near-field acoustic receiving points is combined with the time pressure signal of the specific location of interest to define K (20 to 50) receiving points (such as M 1 , M 2 ,…,M k ,…,M K) is located in the main propeller area of ​​the fuselage. These receiving points are distributed in 6 to 12 circular cabin longitudinal sections, from 3 to 6 sections upstream of the propeller plane to 3 to 6 sections downstream. Each circular cabin longitudinal section has O (4 to 12) receiving points evenly distributed. These K receiving points will be used as monopole sound sources for the sound pressure data input at different longitudinal sections of the cabin. The position of the longitudinal section directly determines the calculation section position of the internal cabin noise.

[0015] The definition of the propeller near-field acoustic receiving points is that on the starboard side of the turboprop aircraft, the starboard propeller is equipped with a circle of J acoustic receiving points with a diameter of 4R to 6R, and the center of the circle is at the center of the starboard propeller, where R is the propeller radius. Similarly, the acoustic receiving points on the port side of the aircraft are also defined in this way. These 2×J receiving points will be used as dipole sound sources for the input sound pressure data in the cabin. The directivity curves of the dipole and propeller noise based on the circular acoustic receiving points must be consistent.

[0016] The mode conversion method of the turboprop aircraft internal and external sound field simulation method based on FW-H and acoustic-solid coupling is characterized in that the novel sound source equivalent method includes: a novel monopole equivalent method and a novel dipole equivalent method, and has the following steps:

[0017] S31. First, the amplitude and phase of each order harmonic sound pressure component of each acoustic receiving point are obtained by Fourier transform.

[0018] S32. Inputting the components of each order harmonic sound pressure into the novel monopole equivalent method and the novel dipole equivalent method to obtain the monopole amplitude S and the dipole moment vector D;

[0019] S33. Calculate the monopole amplitude S. The novel monopole equivalent method has the following expression:

[0020] Monopole sound pressure amplitude:

[0021] where f d (r k,i ) is the radiation attenuation function, p m，i is the sound pressure of the mth harmonic of the ith propeller, p {m，k} is the m-th order harmonic sound pressure obtained by Fourier transform of the calculation of URANS+FW-H, pmo,m is the acoustic sound pressure of the m-th order harmonic component of the monopole source, [α k，1 , α k，2 , …, α k，II ] represents [propeller 01, propeller 02, ..., propeller 0II] and receiving point M kThe spatial angle between the cross sections of the engine room. II in formula (2) represents II propellers, II is 2, 4. There are O acoustic receiving points numbered from k-3 to k-3+O on each longitudinal section of the engine room, O is 4 to 12, so when calculating d src II×O needs to be removed;

[0022] S34. Calculate the dipole moment vector D. Define two closely spaced monopoles as the source and sink of the monopole to describe the dipole, thereby calculating the dipole moment vector D, and using two symmetrical radiation azimuths as The propeller noise of the dipole equivalent cross section requires the directivity curves of the two to be consistent. The novel dipole equivalent method has the following expression:

[0023]

[0024]

[0025] Among them, I mo，m is the sound source intensity, d di,src is the distance between the two dipole sound sources G, d mo，src is the distance from the center of the sound source to the receiving point G, Qm is the volume flow rate of the monopole source (SI unit: m 3 / s), pdi,m is the sound pressure of the m-order harmonic component of the port dipole source, pdi,m' is the sound pressure of the m-order harmonic component of the starboard dipole source, j is the number of the acoustic receiving point between K+1 and K+J or K+J+1 and K+2×J, J is the total number of acoustic receiving points on the port or starboard side, which is 36 to 45, is the azimuth, p di,m is the mth order harmonic component of the dipole point source (SI unit: Pa), d di,src is the distance between the two dipole sound sources, I di，m is the dipole sound pressure intensity (SI unit: W / m 2 ), P di,m is the mth order radiation power harmonic component of the dipole sound source (SI unit: W), e D is the dipole radiation direction, b max It is the chord length of the propeller blade at 2 / 3 of the blade height.

[0026] The method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling is characterized in that the frequency domain acoustic-solid coupling method has the following steps:

[0027] S41. Substitute the calculated monopole amplitude S and dipole moment vector D into the Helmholtz equation,

[0028] Helmholtz equation: Where ρ is the air density, pt is the total pressure, p mo is the sound pressure of the monopole source, p di is the sound pressure of the dipole source, K is the wave number, δ(XX 0 ) is the Dirichlet function, S is the monopole amplitude (SI unit: N / m 2 ), X 0 is the source location, d src is the distance from the source center (SI unit: m), I mo，m is the monopole source intensity of the mth harmonic component (SI unit: W / m 2 ), θ is the phase of the monopole source, is the phase of the dipole source, is the speed of sound, D is the dipole moment vector (SI unit: N), e D is the radiation direction of the dipole source, ω is the angular frequency, pdi,m is the radiation power of the mth harmonic component of the dipole source (SI unit: W), γ is the adiabatic index, which is 1.4, and R is the gas constant of air, which is 287.06 J / (kg K);

[0029] S42. The elastic deformation of the cabin is calculated using a linear elastic solid model. The stress tensor σ is calculated using the two-dimensional Hooke's law for homogeneous isotropic materials.

[0030]

[0031] In the formula, ρ s is the solid density, ω is the angular frequency, u is the displacement vector, σ is the stress tensor, F v is the possible body force, φ is the direction angle of Fv, σ is the stress tensor, C is the elastic tensor (or stiffness tensor), E is Young's modulus, v is Poisson's ratio, and ε is the strain tensor;

[0032] S44. Calculation of cabin interior noise using the acoustic-solid coupling model

[0033] The conditions on the external boundaries are

[0034]

[0035] The conditions on the internal boundaries are

[0036]

[0037] where the up and down subscripts refer to the sides of the internal boundary. Thus, the acoustic load is given by the pressure drop across the thin structure, u tt is the structural acceleration, ρ c is the fluid density, n is the surface normal, p t is the total sound pressure, q drepresents the domain body force, F A is the load (force per unit area) experienced by the structure;

[0038] S45. Based on the amplitude and phase of the acoustic-solid coupling noise field under each harmonic component calculated, a synthetic sound field is calculated using a harmonic synthesis method

[0039]

[0040] Where N is the selected harmonic number, K a is the total number of selected receiving points, p k，n is the sound pressure of the nth harmonic component at position k, ζ is the phase angle, SPL k is the sound pressure level at location k and OASPL is the overall average sound pressure level for all selected locations.

[0041] Compared with the prior art, the advantages of the present invention are: a new sound source equivalence method is proposed, equations from propeller aerodynamic sound pressure to monopole amplitude and from propeller aerodynamic sound pressure to dipole moment vector are derived, and the cabin noise distribution model is simplified by equating the cross-sectional propeller noise to a monopole point sound source and the longitudinal noise to two dipole point sound sources, thereby creating a three-dimensional field. It innovatively divides the complex fluid-structure-acoustic problem into manageable parts, greatly reducing the computational cost, and solving the problem that the current precise fluid-structure-acoustic coupling method is time-consuming to calculate, and the acoustic finite element method and acoustic boundary element method cannot couple with the propeller aerodynamic noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the simulation of the sound field inside and outside the cabin of a multi-propeller aircraft of the present invention.

[0043] Figure 2 The time-varying sound pressure at the receiving point and its spectrum diagram calculated by the URANS+FW-H method of the present invention.

[0044] Figure 3 The external sound pressure distribution calculated by the URANS+FW-H method of the present invention.

[0045] Figure 4 It is a schematic diagram of propeller sound pressure propagation on the longitudinal section of the cabin of the present invention.

[0046] Figure 5 Schematic diagram of describing a dipole by a monopole source and a monopole sink of the present invention

[0047] Figure 6 Schematic diagram of the equivalent propeller noise using two symmetrical dipole acoustic point sources proposed in the present invention.

[0048] Figure 7It is a schematic diagram of the propeller noise of the cabin section and the equivalence of the dipole point source of the present invention.

[0049] Figure 8 It is a comparison diagram of propeller noise and dipole sound source directivity at each order harmonic of the present invention.

[0050] Fig. 9 It is a comparison diagram of the cabin experimental SPL under a certain phase synchronization angle of the present invention and the SPL simulated by the proposed method. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] See also Figure 1 In an embodiment of the present invention, a method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling comprises the following steps: S0. Establishing a whole-machine grid model of the aircraft and propeller, S1. Using the steady Reynolds-averaged Navier-Stokes (RANS) method to perform the whole-machine flow field initialization simulation, S2. Using the unsteady Reynolds-averaged Navier-Stokes (URANS) and Williams-Hawkings (FW-H) method to calculate the external sound pressure distribution of the aircraft cabin, S3. Using a novel sound source equivalent method to calculate the size of a point sound source (monopole and dipole point source) under external excitation, S4. Using the frequency domain acoustic-solid coupling method to calculate the internal noise of the cabin;

[0053] The computational domain of the whole machine grid model described in S0 is divided into 2 to 4 propeller rotation domains, a fuselage domain, and a far field domain;

[0054] The initialization simulation of the flow field described in S1 uses a multiple reference frame (MRF) model to perform steady-state RANS and broadband noise model simulations. The broadband noise model solves the sound power level of the entire machine, requiring 1000 to 2000 core hours of computation.

[0055] The external sound field simulation of the aircraft cabin described in S2 was performed using a sliding mesh model (SMM) for non-steady-state calculations. A time resolution of 0.1° to 1° of the propeller azimuth angle was selected as the simulation step to ensure smooth and effective convergence of each time step. At least 4 to 10 complete propeller rotations were required before sufficient convergence was achieved. In order to obtain higher frequency resolution, more rotations were selected, such as 10, and the computational effort required was 4000 to 6000 core hours.

[0056] The aircraft cabin external sound field simulation described in S2 requires the definition of cabin near sound field receiving points and propeller near sound field receiving points;

[0057] See also Figure 3 In the embodiment of the present invention, the definition of the cabin near-field acoustic receiving points is combined with the time pressure signal of the specific location of interest to define K (20 to 50) receiving points (such as M 1 , M 2 ,…,M k ,…,M K ) is located in the main propeller area of ​​the fuselage. These receiving points are distributed in 6 to 12 circular cabin longitudinal sections, from 3 to 6 sections upstream of the propeller plane to 3 to 6 sections downstream. Each circular cabin longitudinal section has O (4 to 12) receiving points evenly distributed. These K receiving points will be used as monopole sound sources for the sound pressure data input at different longitudinal sections of the cabin. The position of the longitudinal section directly determines the calculation section position of the internal cabin noise.

[0058] See also Figure 7 In the embodiment of the present invention, the definition of the propeller near-field acoustic receiving point is that on the starboard side of the turboprop aircraft, the starboard propeller is equipped with a circle of J acoustic receiving points with a diameter of 4R to 6R, and the center of the circle is at the center of the starboard propeller, where R is the propeller radius. Similarly, the acoustic receiving points on the port side of the aircraft are also defined in this way. These 2×J receiving points will be used as dipole sound sources for the input sound pressure data in the cabin. The directivity curves of the dipole and propeller noise based on the circular acoustic receiving points must be consistent.

[0059] See also Figure 2 and Figure 4 In an embodiment of the present invention, the mode conversion method of the turboprop aircraft internal and external sound field simulation method based on FW-H and acoustic-solid coupling is characterized in that the novel sound source equivalent method includes: a novel monopole equivalent method and a novel dipole equivalent method, and has the following steps:

[0060] S31. First, use Fourier transform to obtain the amplitude and phase of each harmonic sound pressure component at each acoustic receiving point. Please refer to Figure 2, which is the sound pressure at a certain acoustic receiving point and the spectrum obtained after Fourier transformation;

[0061] S32. Inputting the components of each order harmonic sound pressure into the novel monopole equivalent method and the novel dipole equivalent method to obtain the monopole amplitude S and the dipole moment vector D;

[0062] S33. Calculate the monopole amplitude S. The novel monopole equivalent method has the following expression:

[0063] Monopole sound pressure amplitude:

[0064] where f d (r k，i ) is the radiation attenuation function, p m，i is the sound pressure of the mth harmonic of the ith propeller, p {m，k} is the m-th order harmonic sound pressure obtained by Fourier transform of URANS+FW-H, pmo,m is the acoustic sound pressure of the m-th order harmonic component of the monopole source, see Figure 4 In the embodiment of the present invention, [α k,1 , α k，2 , α k,3 , α k,4 ] indicates [propeller 01, propeller 02, propeller 03, propeller 04] and receiving point M k The spatial angle between the cross sections, II in formula (2) represents II propellers, II is 4, each cabin longitudinal section has O acoustic receiving points numbered from k-3 to k-3+O, O is 4, so in calculating d src It is necessary to remove II×O=16;

[0065] S34. Calculate the dipole moment vector D, see Figure 5 In the embodiment of the present invention, two monopole sources and a monopole sink close to each other are defined to describe the dipole, so as to calculate the dipole moment vector D. Please refer to Figure 6 In the embodiment of the present invention, two symmetrical radiation azimuths are The propeller noise of the dipole equivalent cross section requires that the directivity curves of the two are consistent. Figure 8 In the embodiment of the present invention, the spatial directivity of the port propeller or the starboard propeller of the sound field reconstructed based on four dipoles should be consistent with the directivity of the aerodynamic noise of the twin propellers, and the average error under the first four harmonics is 2.8 dB, which meets the directivity accuracy. The novel dipole equivalent method has the following expression:

[0066]

[0067]

[0068] Among them, I mo，m is the sound source intensity, d di,src is the distance between the two dipole sound sources G, d mo,src is the distance from the center of the sound source to the receiving point G, Q m Volume flow rate of monopole source (SI unit: m 3 / s), p di,m is the sound pressure of the m-order harmonic component of the port dipole source, p di，m ' is the sound pressure of the m-order harmonic component of the starboard dipole source, j is the acoustic receiving point number between K+1 and K+J or K+J+1 and K+2×J, J is the total number of acoustic receiving points on the port or starboard side, which is 36 to 45, is the azimuth angle, pdi,m is the mth order harmonic component of the dipole point source (SI unit: Pa), d di,src is the distance between the two dipole sound sources, I di，m is the dipole sound pressure intensity (SI unit: W / m 2 ), P di,m is the mth order radiation power harmonic component of the dipole sound source (SI unit: W), e D is the dipole radiation direction, b max It is the chord length of the propeller blade at 2 / 3 of the blade height.

[0069] See also Fig. 9 In an embodiment of the present invention, a method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling is characterized in that the frequency domain acoustic-solid coupling method has the following steps:

[0070] S41. Substitute the calculated monopole amplitude S and dipole moment vector D into the Helmholtz equation,

[0071] Helmholtz equation: Where ρ is the air density, p t is the total pressure, p mo is the sound pressure of the monopole source, p di is the sound pressure of the dipole source, K is the wave number, δ(XX 0 ) is the Dirichlet function, S is the monopole amplitude (SI unit: N / m 2 ), X 0 is the source location, d src is the distance from the source center (SI unit: m), I mo，m is the monopole source intensity of the mth harmonic component (SI unit: W / m 2), θ is the phase of the monopole source, is the phase of the dipole source, is the speed of sound, D is the dipole moment vector (SI unit: N), e D is the radiation direction of the dipole source, ω is the angular frequency, and p dim is the radiated power of the mth harmonic component of the dipole source (SI unit: W), γ is the adiabatic index, which is 1.4, and R is the gas constant of air, which is 287.06 J / (kg K);

[0072] S42. The elastic deformation of the cabin is calculated using a linear elastic solid model. The stress tensor σ is calculated using the two-dimensional Hooke's law for homogeneous isotropic materials.

[0073]

[0074] In the formula, ρ s is the solid density, ω is the angular frequency, u is the displacement vector, σ is the stress tensor, F v is the possible body force, φ is the direction angle of Fv, σ is the stress tensor, C is the elastic tensor (or stiffness tensor), E is Young's modulus, v is Poisson's ratio, and ε is the strain tensor;

[0075] S44. Calculation of cabin interior noise using the acoustic-solid coupling model

[0076] The conditions on the external boundaries are

[0077]

[0078] The conditions on the internal boundaries are

[0079]

[0080] where the up and down subscripts refer to the sides of the internal boundary. Thus, the acoustic load is given by the pressure drop across the thin structure, u tt is the structural acceleration, ρ c is the fluid density, n is the surface normal, p t is the total sound pressure, q d represents the domain body force, F A is the load (force per unit area) experienced by the structure;

[0081] S45. Based on the amplitude and phase of the acoustic-solid coupling noise field under each harmonic component calculated, the synthetic sound field is calculated using the harmonic synthesis method, and the accuracy level achieved is an average error of 2.6 dB. The synthesis formula is as follows:

[0082]

[0083] Where N is the selected harmonic number, Ka is the total number of selected receiving points, p k，n is the sound pressure of the nth harmonic component at position k, ξ is the phase angle, SPL k is the sound pressure level at location k and OASPL is the overall average sound pressure level for all selected locations.

[0084] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some simple modifications, equivalent changes and modifications to some of the technical features therein according to the disclosed technical content without creative labor, all of which belong to the scope of the technical solution of the present invention.

Claims

1. A method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling, comprising the following steps: S0. Establishing a whole-machine mesh model of the aircraft and propeller, S1. Using the steady Reynolds-averaged Navier-Stokes (RANS) method to perform initialization simulation of the whole-machine flow field, S2. Using the unsteady Reynolds-averaged Navier-Stokes (URANS) and Williams-Hawkings (FW-H) method to simulate the external sound field of the aircraft cabin, S3. Using a novel sound source equivalent method to calculate the size of a point sound source (monopole and dipole point source) under external excitation, S4. Using the frequency domain acoustic-solid coupling method to calculate the internal noise of the cabin; The computational domain of the whole machine grid model described in S0 is divided into 2 to 4 propeller rotation domains, a fuselage domain, and a far field domain; The initialization simulation of the whole machine flow field described in S1 uses the Multiple Reference Frame (MRF) model to perform steady-state RANS and broadband noise model simulation solutions. The broadband noise model solves the sound power level of the whole machine, which requires 1000N2000 core-hours of calculation; The external sound field simulation of the aircraft cabin described in S2 was performed using a sliding mesh model (SMM) for non-steady-state calculations. A time resolution of 0.1° to 1° of the propeller azimuth angle was selected as the simulation step to ensure smooth and effective convergence of each time step. At least 4 to 10 complete propeller rotations were run before sufficient convergence was achieved. In order to obtain higher frequency resolution, more rotations were selected, such as 10, with a computational effort of 4000 to 6000 core hours. The aircraft cabin external sound field simulation described in S2 requires the definition of cabin near sound field receiving points and propeller near sound field receiving points; The definition of the cabin near-field acoustic receiving points is combined with the time pressure signal of the specific location of interest to define K (20 to 50) receiving points (such as M1, M2, ..., M k , …, M K ) is located in the main propeller area of ​​the fuselage. These receiving points are distributed in 6 to 12 circular cabin longitudinal sections, from 3 to 6 sections upstream of the propeller plane to 3 to 6 sections downstream. Each circular cabin longitudinal section has O (4 to 12) receiving points evenly distributed. These K receiving points will be used as monopole sound sources for the sound pressure data input at different longitudinal sections of the cabin. The position of the longitudinal section directly determines the calculation section position of the internal cabin noise. The definition of the propeller near-field acoustic receiving points is that on the starboard side of the turboprop aircraft, the starboard propeller is equipped with a circle of J acoustic receiving points with a diameter of 4R to 6R, and the center of the circle is at the center of the starboard propeller, where R is the propeller radius. Similarly, the acoustic receiving points on the port side of the aircraft are also defined in this way. These 2×J receiving points will be used as dipole sound sources for the input sound pressure data in the cabin. The directivity curves of the dipole and propeller noise based on the circular acoustic receiving points must be consistent.

2. The mode conversion method of the turboprop aircraft internal and external sound field simulation method based on FW-H and acoustic-solid coupling as claimed in claim 1 is characterized in that: The novel sound source equivalent method includes: a novel monopole equivalent method and a novel dipole equivalent method, and has the following steps: S31. First, the amplitude and phase of each order harmonic sound pressure component of each acoustic receiving point are obtained by Fourier transform. S32. Inputting the components of each order harmonic sound pressure into the novel monopole equivalent method and the novel dipole equivalent method to obtain the monopole amplitude S and the dipole moment vector D; S33. Calculate the monopole amplitude S. The novel monopole equivalent method has the following expression: Monopole sound pressure amplitude: where f d (r k,i ) is the radiation attenuation function, p m，i is the sound pressure of the mth harmonic of the ith propeller, p {m,k} is the mth order harmonic sound pressure obtained by Fourier transform of URANS+FW-H, p mo，m is the acoustic sound pressure of the m-order harmonic component of the monopole source, [α k,1 , α k，2 , …, α k,II ] represents [propeller 01, propeller 02, ..., propeller 0II] and receiving point M k The spatial angle between the cross sections of the engine room. II in formula (2) represents II propellers, II is 2, 4, 6, 8, and each cabin longitudinal section has O acoustic receiving points numbered from k-3 to k-3+O, O is 4 to 12, so when calculating d src II×O needs to be removed; S34. Calculate the dipole moment vector D. Define two closely spaced monopoles as the source and sink of the monopole to describe the dipole, and calculate the dipole moment vector D. Then, use two symmetrical radiation azimuths to calculate The propeller noise of the dipole equivalent cross section requires the directivity curves of the two to be consistent. The novel dipole equivalent method has the following expression: Among them, I mo，m is the sound source intensity, d di,src is the distance between the two dipole sound sources G, d mo,src is the distance from the center of the sound source to the receiving point G, Q m Volume flow rate of monopole source (SI unit: m 3 / s), p di,m is the sound pressure of the m-order harmonic component of the port dipole source, p di,m ' is the sound pressure of the m-order harmonic component of the starboard dipole source, j is the acoustic receiving point number between K+1 and K+J or K+J+1 and K+2×J, J is the total number of acoustic receiving points on the port or starboard side, which is 36 to 45, is the azimuth, p di,m is the mth order harmonic component of the dipole point source (SI unit: Pa), d di，src is the distance between the two dipole sound sources, I di，m is the dipole sound pressure intensity (SI unit: W / m 2 ), P di,m is the mth order radiation power harmonic component of the dipole sound source (SI unit: W), e D is the dipole radiation direction, b max It is the chord length of the propeller blade at 2 / 3 of the blade height.

3. The method for simulating the internal and external sound fields of a turboprop aircraft based on FW-H and acoustic-solid coupling according to claim 1, characterized in that: The frequency domain acoustic-solid coupling method comprises the following steps: S41. Substitute the calculated monopole amplitude S and dipole moment vector D into the Helmholtz equation, Helmholtz equation: Where ρ is the air density, p t is the total pressure, p mo is the sound pressure of the monopole source, p di is the sound pressure of the dipole source, K is the wave number, δ(X-X0) is the Dirichlet function, and S is the monopole amplitude (SI unit: N / m 2 ), X0 is the source location, d src is the distance from the source center (SI unit: m), I mo，m is the monopole source intensity of the mth harmonic component (SI unit: W / m 2 ), θ is the phase of the monopole source, is the phase of the dipole source, is the speed of sound, D is the dipole moment vector (SI unit: N), e D is the radiation direction of the dipole source, ω is the angular frequency, and p di，m is the radiated power of the mth harmonic component of the dipole source (SI unit: W), γ is the adiabatic index, which is 1.4, and R is the gas constant of air, which is 287.06 J / (kg K); S42. The elastic deformation of the cabin is calculated using a linear elastic solid model. The stress tensor σ is calculated using the two-dimensional Hooke's law for homogeneous isotropic materials. In the formula, ρ s is the solid density, ω is the angular frequency, u is the displacement vector, σ is the stress tensor, F v is the possible body force, φ is the direction angle of Fv, σ is the stress tensor, C is the elastic tensor (or stiffness tensor), E is Young's modulus, v is Poisson's ratio, and ε is the strain tensor; S44. Calculation of cabin interior noise using the acoustic-solid coupling model The conditions on the external boundaries are The conditions on the internal boundaries are where the up and down subscripts refer to the sides of the internal boundary. Thus, the acoustic load is given by the pressure drop across the thin structure, u tt is the structural acceleration, ρ c is the fluid density, n is the surface normal, p t is the total sound pressure, q d represents the domain body force, F A is the load experienced by the structure (force per unit area); S45. Based on the amplitude and phase of the acoustic-solid coupling noise field under each harmonic component calculated, a synthetic sound field is calculated using a harmonic synthesis method Where N is the selected harmonic number, K a is the total number of selected receiving points, p k,n is the sound pressure of the nth harmonic component at position k, ζ is the phase angle, SPL k is the sound pressure level at location k and OASPL is the overall average sound pressure level for all selected locations.

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