Rotor aircraft cabin noise prediction method based on sound ray tracking

Abstract

The embodiment of the invention discloses a method for predicting noise in a cabin of a rotorcraft based on sound ray tracking, relates to the technical field of aerodynamic noise of rotors, and can realize efficient prediction of noise in the cabin of the rotorcraft in a full-frequency range. According to the scheme, theoretical modeling is carried out based on rotorcraft cabin noise prediction of a sound ray tracking method. A theoretical model for predicting the noise in the cabin of the rotorcraft based on the sound ray method is established by combining a theoretical formula of indoor geometric acoustics, and the model reflects a parameter influence rule of the sound ray method and is the key of subsequent noise prediction. The sound ray tracking method is applied to a three-dimensional model on a rotorcraft. The model is an important basis and basis for subsequent in-cabin noise prediction. And carrying out in-cabin noise prediction based on the sound ray method model and the rotor craft three-dimensional model.

Description

Technical Field

[0001] The present invention relates to the technical field of rotor aerodynamic noise, and particularly to a method for predicting in-cabin noise of a rotorcraft based on ray tracing. Background Art

[0002] Rotorcraft generally refer to aircraft that generate lift using rotors, mainly including helicopters, tiltrotors, and other new configuration rotorcraft. Their vertical takeoff and landing characteristics greatly enhance their operational flexibility in limited spaces, but they generate significant noise and vibration during flight. The in-cabin noise of rotorcraft mainly comes from three aspects: aerodynamic noise generated by the rotor, structural noise caused by the power / transmission system, and atmospheric turbulence noise. Prolonged exposure to high-level noise can cause great harm to the physical and mental health of the passengers and crew in the cabin. Therefore, vibration reduction and noise reduction of the aircraft are the main means to improve the riding comfort. Since the core of vibration reduction and noise reduction in the cabin is to predict the in-cabin noise, an efficient and high-precision method for predicting in-cabin noise is crucial.

[0003] Existing in-cabin prediction methods include two types: the analytical method and the numerical analysis method.

[0004] The analytical method is mainly used in laboratory environments. Although it can provide a clear physical mechanism image, the solution process is cumbersome and not suitable for practical engineering problems.

[0005] The numerical analysis method includes technical means such as statistical energy analysis, finite element / boundary element analysis, etc. Statistical energy analysis divides a complex structure into multiple weakly coupled subsystems with modal parameters distributed according to statistics. Although it can effectively calculate the response of the structure and the sound field distribution under high-frequency excitation, the calculation accuracy for low-frequency noise is relatively low; finite element / boundary element analysis divides the solution domain into multiple small and simple subdomains, i.e., elements, and uses simple shape functions such as linear or high-order polynomials to approximate the solution in each element. The boundary element method is based on boundary integral equations, which transforms the problem-solving from the entire domain to the boundary. However, as the calculation frequency increases, the computational workload of these two methods will increase rapidly, and the calculation efficiency and solution accuracy will be greatly reduced. Therefore, they are mainly applicable to the low-frequency range.

[0006] Generally speaking, the existing numerical analysis methods have certain limitations in practical engineering applications. It is difficult to achieve a comprehensive full-frequency range for predicting the in-cabin noise of rotorcraft, and the computational workload is large, making it difficult to achieve high prediction efficiency. Summary of the Invention

[0007] An embodiment of the present invention provides a method for predicting in-cabin noise of a rotorcraft based on ray tracing, which can achieve efficient prediction of the in-cabin noise of a rotorcraft in the full-frequency range.

[0008] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0009] S1. Preprocess the three-dimensional model of the rotary-wing aircraft. The preprocessing includes: dividing the outer surface of the skin into plates;

[0010] S2. Collect the time-domain signals on the outer surface of the skin and convert them into frequency-domain signals through Fast Fourier Transform (FFT);

[0011] S3. Perform ray tracing using the obtained frequency-domain signals and the sound pressure corresponding to the plate division to obtain point source data;

[0012] S4. Generate the cabin sound pressure level cloud map of the rotary-wing aircraft according to the point source data.

[0013] For the method for predicting the cabin noise of a rotary-wing aircraft based on ray tracing provided by the embodiments of the present invention, compared with the limitation of the existing numerical analysis method that can only predict high frequencies or low frequencies, the method for predicting the cabin noise of a rotary-wing aircraft based on ray tracing in this embodiment can achieve full-band prediction. Compared with the existing boundary element method / finite element method, the solution in this embodiment is simpler and faster. Through the propagation analysis of indoor geometric acoustics, when the wavelength of the sound wave is much smaller than the size of the objects in the sound field, this solution calculates the attenuation of the sound wave energy and has high prediction efficiency with shorter calculation time. Description of the Drawings

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a schematic diagram of the technical route for predicting the cabin noise of a rotary-wing aircraft based on ray tracing provided by the embodiments of the present invention;

[0016] Figure 2 It is a schematic diagram of the simulation calculation process of the ray tracing method;

[0017] Figure 3 It is a schematic diagram of the simplified modeling of the overall structure of a tiltrotor aircraft;

[0018] Figures 4a to 4c It is the pressure cloud map on the outer surface of the fuselage of a tiltrotor aircraft under three flight conditions;

[0019] Figure 5 It is a schematic diagram of the regional division of the outer surface of the cockpit of a tiltrotor aircraft;

[0020] Figure 6 It is a schematic diagram of the layout of the field points and point sound sources on the cockpit surface of a tilt-rotor aircraft. Specific implementation manners

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners. The implementation manners of the present invention will be described in detail below. Examples of the implementation manners are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The implementation manners described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and cannot be construed as a limitation to the present invention. Those skilled in the art of the present technology can understand that unless specifically stated, the singular forms "a", "an", "the" and "said" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present invention means the presence of the described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. It should be understood that when we say that an element is "connected" or "coupled" to another element, it can be directly connected or coupled to other elements, or there may also be intermediate elements. In addition, the "connection" or "coupling" used here may include wireless connection or coupling. The phrase "and / or" used here includes any unit and all combinations of one or more related listed items. Those skilled in the art of the present technology can understand that unless otherwise defined, all terms (including technical terms and scientific terms) used here have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art and will not be interpreted with an idealized or overly formal meaning unless defined as here.

[0022] An embodiment of the present invention provides a method for predicting the in-cabin noise of a rotorcraft based on ray tracing, as Figure 1 、 2 shown. The design idea of this embodiment is as follows: For the time-domain signals of the outer skin of the cockpit of the rotorcraft under different flight conditions, which are affected by aerodynamic loads or atmospheric turbulence excitation, calculate the sound insulation amount to obtain the sound pressure inside the aircraft cabin. Simplify the radiated noise in the cabin into point sound sources, and obtain the internal noise level of the cabin by calculating the sound power of the point sound sources. The specific method includes:

[0023] S1. Preprocess the three-dimensional model of the rotorcraft, and the preprocessing includes: dividing the outer surface of the skin into plates;

[0024] S2. Collect the time-domain signals on the outer surface of the skin and convert them into frequency-domain signals through FFT; where, Fast Fourier Transform (FFT). The Fast Fourier Transform (FFT) is an algorithm for efficiently calculating the Discrete Fourier Transform (DFT) and its inverse transform, which converts time-domain signals into their frequency-domain representations and is fast and efficient when processing large-scale data.

[0025] S3. Use the obtained frequency-domain signals and the sound pressure corresponding to the block division for sound ray tracing to obtain point source data;

[0026] Among them, as Figure 2 shown, the Ray Tracing Method is based on geometric acoustics. In this embodiment, it is applied to the noise prediction of the rotorcraft. Geometric acoustics is suitable for the sound simulation in an enclosed space and is based on the concepts of sound particles or sound rays. When the wavelength of the sound wave is much smaller than the size of the objects in the sound field, the sound wave can be approximately regarded as a sound ray, similar to geometric optics. Ignoring the wave nature of sound, that is, ignoring the diffraction phenomenon, it imagines a part of the spherical wave emitted by the sound source as a sound ray bundle. Each sound ray carries equal energy and shoots out in a straight line at the speed of sound and propagates following geometric laws. The energy of the sound ray decreases as it propagates through the medium and contacts the structure. Considering the diffusion effect, the calculation speed is fast. Assuming that the sound source emits rays carrying the same energy in all directions, when the sound ray hits the wall, specular reflection and scattering occur. The reflection direction follows the law of reflection, and scattering occurs randomly with a certain probability. Each time the sound ray collides with the wall, the energy of the sound ray decreases by a factor of a, where a is the sound absorption coefficient of the wall. When the ratio of the sound ray energy to the initial carried energy is less than the set energy threshold, the sound ray stops propagating. The smaller the threshold, the more accurate the sound intensity calculated by superimposing the energies of all sound rays. Usually, 0.001 is taken.

[0027] S4. Generate the in-cabin sound pressure level cloud map of the rotorcraft according to the point source data. For example: Set the sound power of the point source in the LMS software, and the sound pressure level cloud map of the surface field points can be calculated through the software.

[0028] In this embodiment, as Figures 3 - 6 shown, the block division of the outer surface of the skin includes: generating a pressure distribution cloud map of the outer surface of the skin corresponding to the three-dimensional model of the rotorcraft, and dividing the cockpit part into n regions with approximately equal areas according to the pressure distribution, where the difference in the pressure values within each region is within a preset range.

[0029] Among them, dividing the plate specifically refers to dividing the cockpit part into n regions with approximately equal areas according to the pressure distribution cloud map of the outer surface of the airframe (specifically, it can be called the pressure distribution cloud map of the outer surface of the skin). The pressure values in each region are basically the same. The pressure value at the center point of each region is selected as the representative of the pressure value of this region, so that the pressure value inside the cabin can be obtained, and the external sound source is simplified into an internal point sound source. The pressure on the outer surface of the skin refers to the pressure on the outer surface of the skin, that is, when the aerodynamic force calculation reaches the convergence state, the pulsating pressure load on the outer surface of the rotorcraft. This can be a unified statement; through CFD calculation, a time-domain signal can be obtained, which is specifically expressed in the form of a change curve related to pressure and time. The Fourier transform is used to convert the time-domain signal into a frequency-domain signal; the time-domain signal is obtained by setting monitoring points during the CFD simulation calculation, and the time-domain signal at the monitoring points can be directly extracted.

[0030] In this embodiment, S2 includes: obtaining the pressure on the outer surface of the skin of the rotorcraft under different flight conditions based on CFD aerodynamic alternating load calculation. Based on the basic parameters such as the rotor speed, radius, and oncoming flow velocity of the rotorcraft, the rotor passing frequency of the noise is determined, and the CFD software Fluent is used to calculate the rotor aerodynamic load to obtain the pressure on the outer surface of the skin of the rotorcraft under different flight conditions. Furthermore, the FFT is used to convert the time-domain signal of the aerodynamic load into a frequency-domain signal to obtain the sound pressure level on the skin surface. Computational Fluid Dynamics (CFD) calculates by solving the Reynolds-averaged N-S equations. The k-ω turbulence model is selected, and the sliding mesh technology is adopted. Specifically, the pressure on the outer surface of the skin of the rotorcraft under the corresponding flight conditions is obtained through the CFD model. The CFD model includes: the N-S equation model and the k-ω turbulence model in the Cartesian coordinate system. The form of the N-S equation in the Cartesian coordinate system is: U is the conserved variable, F1, F V are the non-viscous flux and the viscous flux, Q is the source term, and t represents the time parameter.

[0031] The k-ω turbulence model includes

[0032] Turbulent kinetic energy model:

[0033]

[0034] ω model:

[0035]

[0036] ρ is the fluid density, k is the turbulent kinetic energy, t is the time, U i 、U j are the velocity components, τ ij is the sub-grid scale stress, xj is the characteristic length, μ is the hydrodynamic viscosity, μ T is the turbulent viscosity, ω is the turbulent dissipation rate, σ * = 1.0, β * = 1.92, σ ε = 1.3.

[0037] S3 includes: According to the division of the panel on the outer surface of the skin, taking the pressure value at the central part of each divided area as the external sound pressure of this area, and then converting it into the internal sound pressure according to the sound insulation amount. Among them, the calculation method of the external sound pressure is obtained by converting the time-domain signal into the frequency-domain signal. Obtain the point sound source of the radiated noise in the cabin according to the internal sound pressure.

[0038] Specifically, as Figures 4a to 4c shown, the conversion of the internal sound pressure according to the sound insulation amount includes: performing sound insulation amount calculation, for example, combining with the VTL module in the VAone acoustic simulation software. The VTL (Vertical Transmission Loss) sound insulation amount refers to the degree of reduction of the sound energy transmitted through vertical structures such as walls and floors. Its calculation involves various factors such as acoustic characteristics, material properties, and geometric shapes. The calculation formula is generally: P 内 = P 外 -R, R = L1 - L2, where, P 内 is the internal sound pressure, P 外 is the external sound pressure, R is the sound insulation amount, L1 is the incident sound level, that is, the sound energy before passing through the material, and L2 is the transmitted sound level. That is, the sound energy after passing through the material. The propagation losses of sound waves with different frequencies in the material are different. Generally, the sound insulation performance of low-frequency sound waves is poor, while that of high-frequency sound waves is good. Divide the cabin wall panel of the rotary-wing aircraft into areas, take the pressure value at the central part of each area as the representative of this area, and then obtain the internal sound pressure radiated into the cabin after calculating the sound insulation of the skin outer surface sound pressure.

[0039] Before S4, convert the data form in the point sound source data from the sound pressure level to the sound power level. The conversion method includes: L w = L p + 10log 10 A, L w is the sound power level, L p is the sound pressure level, and A is the sound pressure acting area.

[0040] Furthermore, the obtaining of the point sound source of the radiated noise in the cabin according to the internal sound pressure includes:

[0041] Based on the ray tracing method, simplify the radiated noise in the cabin to a point sound source, calculate the sound power of the point sound source, and obtain the internal noise level of the cockpit. If the sound source power is I, the initial sound ray I nIt can be expressed as: n is the number of sound rays, and s(x, y, z) is the initial propagation path when it is emitted from the sound source.

[0042] Sound pressure level of the point sound source at space i: Among them, I n represents the initial sound ray, n is the number of sound rays, x i 、y i 、z i represent the coordinates at space i, ∑I n (x, y, z) is the incoherent superposition summation of the sound ray energy passing through space i, ρ0 is the air density, and c0 is the sound propagation speed in the air.

[0043] Specifically, this solution is based on the theoretical modeling of the in-cabin noise prediction of a rotorcraft using the sound ray tracing method. Combining the theoretical formula basis of indoor geometric acoustics, a theoretical model for predicting the in-cabin noise of a rotorcraft based on the sound ray method is established. This model reflects the parameter influence law of the sound ray method and is the key to subsequent noise prediction. The sound ray tracing method is applied to the three-dimensional model of the rotorcraft. This model is an important basis and basis for subsequent in-cabin noise prediction. Based on the model based on the sound ray method and the three-dimensional model of the rotorcraft, in-cabin noise prediction is carried out. The calculation result of the sound ray method is related to the number of sound rays emitted and the number of reflections. The more the number of sound rays emitted from each sound source point and the more the number of reflections, the better the traversability of the sound rays, the closer to the actual situation, the more uniform the cloud map distribution, and the more accurate the result. Considering the calculation efficiency, after comparing the influence of different parameter settings of the ray number and the reflection number on the cloud map and the numerical value, 10,000 rays are emitted from each sound source point and reflected 15 times, and the obtained result is relatively accurate and the calculation efficiency is relatively high.

[0044] The simulation results of the in-cabin noise prediction of the rotorcraft based on the sound ray tracing method of the present invention show that for an enclosed cabin where the sound wave wavelength is much smaller than the size of the objects in the sound field, its prediction frequency band covers low frequency, medium frequency, and high frequency, reflecting a wide application range and being applicable to the noise prediction of the entire frequency band. Compared with the boundary element method, its calculation efficiency can reach 100 times that of the boundary element method, and the simulation efficiency is significantly improved. And for the low-frequency simulation results compared with the boundary element method and the medium-high frequency simulation results compared with the statistical energy method, their prediction accuracies are both relatively high. Therefore, the proposed prediction method of the sound ray tracing method has the advantages of full frequency, high prediction accuracy, and low calculation cost, and has important application potential in the field of in-cabin noise prediction and noise control of rotorcraft.

[0045] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the device embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, reference can be made to the corresponding descriptions in the method embodiments. As mentioned above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for predicting the in-cabin noise of a rotary-wing aircraft based on ray tracing, characterized in that Including: S1. Preprocess the three-dimensional model of the rotary-wing aircraft. The preprocessing includes: dividing the outer surface of the skin into plates; S2. Collect the time-domain signal of the outer surface of the skin and convert it into a frequency-domain signal through FFT; S3. Perform acoustic ray tracing using the obtained frequency-domain signal and the sound pressure corresponding to the plate division to obtain point source data; S4. Generate a cabin sound pressure level cloud map of the rotary-wing aircraft according to the point source data.

2. The method according to claim 1, wherein The dividing the outer surface of the skin into plates includes: Generate a pressure distribution cloud map of the outer surface of the skin corresponding to the three-dimensional model of the rotary-wing aircraft, and divide the cockpit part into n regions with approximately equal areas according to the pressure distribution. n is a positive integer, and the difference in pressure values within each region is within a preset range.

3. The method according to claim 1, characterized in that, n≥10。 4. The method according to claim 1, wherein S2 includes: Obtain the skin outer surface pressure of the rotary-wing aircraft under the corresponding flight conditions through a CFD model. The CFD model includes: an N-S equation model and a k-ω turbulence model in a Cartesian coordinate system. The N-S equation model includes: U is a conserved variable, F1, F V are non-viscous fluxes and viscous fluxes, Q is a source term, and t represents a time parameter.

5. The method according to claim 4, characterized in that, The k-ω turbulence model includes Turbulent kinetic energy model: ω model: ρ is the fluid density, k is the turbulent kinetic energy, t is the time, U i , U j are the velocity components, τ ij is the sub-grid scale stress, x j is the characteristic length, μ is the dynamic viscosity of the fluid, μ T is the turbulent viscosity, ω is the turbulent dissipation rate, σ * = 1.0, β * = 1.92, σ ε = 1.

3.

6. The method according to claim 1, characterized in that, S3 includes: According to the plate division of the outer surface of the skin, take the pressure value at the center of each divided region as the sound pressure outside this region, and then convert it into the internal sound pressure according to the sound insulation quantity; Obtain the point source of the radiation noise in the cabin according to the internal sound pressure.

7. The method according to claim 6, wherein The conversion of the sound insulation quantity into the internal sound pressure includes: P 内 = P 外 - R, where R = L1 - L2, and where P 内 is the internal sound pressure, P 外 is the external sound pressure, R is the sound insulation quantity, L1 is the incident sound level, i.e., the sound energy before passing through the material, and L2 is the transmitted sound level.

8. The method according to claim 6, characterized in that, The obtaining the point source of the radiation noise in the cabin according to the internal sound pressure includes: Sound pressure level of a point sound source at location i in space: where I n represents the initial sound ray, n is the number of sound rays, and x i and y i and z i represent the coordinates at location i in space, ΣI n (x, y, z) is the incoherent superposition summation of the sound ray energy passing through location i in space, ρ0 is the air density, and c0 is the sound propagation speed in air.

9. The method according to claim 8, wherein Also including: Before S4, convert the data form in the point source data from sound pressure level to sound power level. The conversion method includes: L w = L p + 10 log 10 A, L w is the sound power level, L p is the sound pressure level, and A is the sound pressure acting area.

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