Noise analysis method and system for electric aircraft with tilt rotor configuration

Abstract

The invention discloses a noise analysis method and system for an electric aircraft with a tilt rotor configuration, and belongs to the technical field of aircraft noise, and the method comprises the steps: S1, constructing a tilt rotor configuration model according to parameters of the electric aircraft, and importing the model into Ansys Fluent software; s2, grid division: firstly, performing sub-component grid division on the tilt rotor configuration model according to the grid size or the number of grids; then, the grids are optimized; s3, flow field analysis: firstly, performing steady-state flow field analysis by using an SST k-omega model; then taking an output result of the steady-state flow field analysis as an initial value, and performing transient flow field analysis by utilizing an LES large vortex model; s4, performing acoustic analogy noise analysis on the transient flow field analysis result by using an FW-H model to obtain sound source distribution; and S5, obtaining noise results of different positions around the tilt rotor configuration model by using steady-state broadband noise analysis and transient flow field pneumatic analysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft noise, and in particular relates to a noise analysis method and system for an electric aircraft with a tilt-rotor configuration. Background Art

[0002] As an innovative aircraft, the electric vertical take-off and landing aircraft with a tilt-rotor configuration combines the hovering and low-speed flight capabilities of helicopters with the long range and high-speed flight characteristics of fixed-wing aircraft. This type of aircraft shows broad application research prospects in the field of urban air traffic. At the same time, the research on noise control during its airworthiness certification is also particularly important. Through aerodynamic noise simulation and programming technology, the noise generation of the aircraft in the cruising state can be simulated. In the design stage, the noise airworthiness standards should be fully considered. The noise sources mainly include load noise and thickness noise. The rotor cuts the air during rotation to form vortices, thereby generating aerodynamic noise. Therefore, noise prediction can be carried out through a variety of methods such as theoretical analysis, numerical simulation and experimental testing. Although theoretical methods and empirical formulas can quickly provide noise results, they ignore the possible impact of shape factors, resulting in large deviations in the results. The model test method can provide more accurate flow field and noise data, but its high cost and the limitations of the scaled model make it usually used as an auxiliary means. Numerical methods are currently widely used, and there are two main ways to calculate aerodynamic noise: computational aeroacoustics and hybrid calculation methods. Computational aeroacoustics obtains results by directly solving fluid dynamics equations, but its high-precision requirements for meshes and high-precision numerical solutions result in huge computational complexity. The hybrid calculation rule is to decouple the flow equation and the wave equation, use the flow field results obtained by computational fluid dynamics as initial conditions, and then obtain the far-field noise results through the acoustic analogy method. This method can effectively reduce the computational cost and is currently widely used. By obtaining noise data through the hybrid calculation method and processing the noise audio using programming technology, the noise can be audible and subsequently visualized, which helps to design and adjust the electric vertical take-off and landing aircraft with a tilt-rotor configuration according to airworthiness regulations during research and development, thereby saving costs and improving efficiency. However, since the tilt-rotor configuration involves multiple rotors, the posture and position of each rotor are different during operation, making the noise situation more complicated. Therefore, it is of great significance to develop a noise analysis method and system for electric aircraft with a tilt-rotor configuration. Summary of the invention

[0003] The purpose of the present invention is to meet practical needs and provide a method and system for analyzing noise of an electric aircraft with a tilt-rotor configuration, which can quickly and accurately simulate the noise distribution of the tilt-rotor configuration by using computer-aided software.

[0004] To achieve the above-mentioned object of the invention, the first object of the present invention is to provide a noise analysis method for an electric aircraft with a tilt-rotor configuration, comprising the following steps:

[0005] S1. Build a tilt-rotor configuration model based on the parameters of the electric aircraft and import the model into Ansys Fluent software;

[0006] S2. Meshing: first, meshing the tilt-rotor configuration model by sub-components by setting the mesh size or the number of meshes; then optimizing the meshes;

[0007] S3. Flow field analysis, including:

[0008] Firstly, the SST k-omega model is used to analyze the steady flow field;

[0009] Then, the output results of the steady-state flow field analysis are used as the initial value to perform transient flow field analysis using the LES large eddy model;

[0010] S4. Using the FW-H model, the transient flow field analysis results are subjected to acoustic analogy noise analysis to obtain the sound source distribution;

[0011] S5. Use steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

[0012] Preferably, S1 comprises: firstly obtaining parameters of the electric aircraft, wherein the parameters include size parameters and performance parameters of each component; and then constructing a tilt-rotor configuration model by using Dassault CATIA.

[0013] Preferably, S2 includes:

[0014] S201. Lighten the tiltrotor configuration model;

[0015] S202, dividing each component into grids by setting a grid size of each component or setting the number of grids;

[0016] S203, mesh optimization, using Skewness as the mesh quality criterion to check the mesh quality of each component surface; using the surface mesh optimization tool to diagnose each component separately and using the Collapse method to merge paired nodes and edges to improve the quality, and control the skewness of each part of the mesh below 0.7;

[0017] S204, setting the default number of boundary layers, and then performing poly mesh division on the tilt-rotor aircraft fuselage and its engine.

[0018] Preferably, in S3:

[0019] The steady-state flow field analysis includes: first, each rotor of the electric aircraft is divided into a separate area, defined as an MRF area, and then the external flow field is set as a static domain; based on the MRF method, multiple rotor domains are set as rotating domains, the rotation axis is the rotor center position, and the point coordinates are obtained in Space Claim; the rotating domain and the static domain transmit data through the interface; the MRF method splits the entire calculation domain into multiple subdomains, and uses the control equations to solve them in each domain; finally, the MRF method is selected for steady-state calculations based on the SST k-omega model.

[0020] The transient flow field analysis includes: firstly, taking the steady-state flow field analysis results as the initial values ​​of the transient calculation, and then using the large eddy model to perform transient calculation.

[0021] Preferably, in S4, the result file of the sound source distribution is saved in a folder in asd format, the asd file is read in Ansys Fluent and converted into an ard file, and finally the ard file is processed by fast Fourier transform to convert the time domain into the frequency domain to obtain a spectrum diagram.

[0022] Preferably, it also includes:

[0023] S6. Perform one-third octave band analysis on the noise results at different locations around the tilt-rotor configuration model;

[0024] S7. First, the results of the one-third octave band analysis are imported into MATLAB, and then the transient flow field data are inversely Fourier transformed in MATLAB to make them visual and audible.

[0025] A second object of the present invention is to provide a noise analysis system for an electric aircraft of a tilt-rotor configuration, comprising:

[0026] The model building module builds a tilt-rotor configuration model based on the parameters of the electric aircraft and imports the model into Ansys Fluent software;

[0027] The meshing module first divides the tiltrotor configuration model into sub-components by mesh size or by setting the number of meshes; and then optimizes the meshes;

[0028] Flow field analysis module, flow field analysis specifically includes:

[0029] Firstly, the SST k-omega model is used to analyze the steady flow field;

[0030] Then, the output results of the steady-state flow field analysis are used as the initial value to perform transient flow field analysis using the LES large eddy model;

[0031] The sound source distribution calculation module uses the FW-H model to perform acoustic analogy noise analysis on the transient flow field analysis results to obtain the sound source distribution;

[0032] The noise analysis module uses steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

[0033] Preferably, the construction process of the model construction module includes: firstly obtaining the parameters of the electric aircraft, the parameters including the size parameters and performance parameters of each component; then using Dassault CATIA to construct a tilt-rotor configuration model;

[0034] The meshing process of the meshing module includes:

[0035] Lightweight the tilt-rotor configuration model;

[0036] Mesh each component by setting the mesh size of each component or setting the number of meshes;

[0037] Mesh optimization, using Skewness as the mesh quality criterion, checks the mesh quality of each component surface; diagnoses each component separately through the surface mesh optimization tool and uses the Collapse method to merge paired nodes and edges to improve the quality, and controls the mesh skewness of each part to less than 0.7;

[0038] Set the default number of boundary layers and then perform poly meshing on the tiltrotor fuselage and its engines.

[0039] A third object of the present invention is to provide a computer program product, characterized in that it comprises a computer program, which, when executed by a processor, implements the above-mentioned method for analyzing noise of an electric aircraft with a tilt-rotor configuration.

[0040] A fourth object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for analyzing noise of an electric aircraft with a tilt-rotor configuration.

[0041] The advantages and positive effects of this application are:

[0042] The present invention uses computer-aided design software (such as Dassault CATIA, Ansys Fluent and MATLAB), and the combination of these tools enables the present invention to quickly and accurately simulate the noise distribution generated by the tilt-rotor configuration. Through these advanced software, the present invention can not only obtain a detailed noise distribution map, but also further realize the audible processing of noise. This means that we can convert noise data into audible sound files through computer simulation, so as to more intuitively understand and evaluate the noise impact generated by the tilt-rotor configuration in actual operation. This process not only improves the accuracy of the simulation, but also greatly enhances our understanding and control of noise characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 A flow chart showing a preferred embodiment of the present invention is shown;

[0045] Figure 2 The broadband noise cloud diagram of the tiltrotor assembly surface in the preferred embodiment of the present invention is shown;

[0046] Figure 3 The broadband noise cloud diagram of the rotor surface in the preferred embodiment of the present invention is shown;

[0047] Figure 4 The broadband noise cloud diagram of the rotating area in the preferred embodiment of the present invention is shown;

[0048] Figure 5 The broadband noise cloud diagram of the rotor in the preferred embodiment of the present invention is shown;

[0049] Figure 6 The rotor turbulence kinetic energy diagram in the preferred embodiment of the present invention is shown;

[0050] Figure 7 A transient fuselage surface pressure cloud diagram in a preferred embodiment of the present invention is shown;

[0051] Figure 8 A transient rotor pressure cloud diagram in a preferred embodiment of the present invention is shown;

[0052] Fig. 9 A transient tiltrotor fuselage velocity vector diagram in a preferred embodiment of the present invention is shown;

[0053] Fig.10 A velocity vector diagram in a preferred embodiment of the present invention is shown;

[0054] Fig.11 It shows the fuselage cross-section trace diagram in the preferred embodiment of the present invention;

[0055] Fig.12 The noise spectrum diagram of the tiltrotor aircraft at 50m under transient conditions in the preferred embodiment of the present invention is shown;

[0056] Fig.13 The 1 / 3 octave frequency spectrum diagram of the tiltrotor aircraft at 50m under transient conditions in the preferred embodiment of the present invention is shown;

[0057] Fig.14 It shows the A-weighted 1 / 3 octave frequency spectrum at 50m from the monitoring point in the preferred embodiment of the present invention;

[0058] Fig.15 The acoustic power spectrum density diagram at 50m from the monitoring point in a preferred embodiment of the present invention is shown. DETAILED DESCRIPTION

[0059] 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.

[0060] See also Figures 1 to 15 The present invention takes a six-rotor electric aircraft as an example to explain in detail:

[0061] In the first embodiment, a noise analysis method for an electric aircraft with a tilt-rotor configuration includes the following steps:

[0062] S1. Build a tilt-rotor configuration model based on the parameters of the electric aircraft and import the model into Ansys Fluent software; specifically include:

[0063] First, the parameters of the electric aircraft are obtained, wherein the parameters include the size parameters and performance parameters of each component;

[0064] Then, Dassault CATIA was used to build the tiltrotor configuration model;

[0065] Finally, the model was imported into Ansys Fluent software;

[0066] S2. Grid division: first, the tilt-rotor configuration model is gridded by sub-components by setting the grid size or the number of grids; then the grids are optimized; specifically, the following steps are performed:

[0067] First, the model needs to be lightweight; given the complexity of the tilt-rotor model structure and the large number of analysis objects, the number of units in the calculation model is huge, and ordinary computers cannot bear the corresponding calculation tasks. For those irregular areas that have little impact on the simulation results and are difficult to mesh, the implementation of simplification can effectively reduce the amount of calculation and improve the calculation efficiency, so that ordinary computers can also complete the calculation tasks, while ensuring that the calculation results are within an acceptable error range and maintain the calculation accuracy. In addition, during the simplification process, the missing faces in the model are repaired to facilitate the subsequent meshing and quality improvement.

[0068] Lightweighting includes the removal of exterior design elements, such as fixed landing gear, and intersecting curved surfaces of the shell.

[0069] Next, meshing is performed; after the model simplification process is completed, the entire part of the model needs to be meshed. By setting the mesh size or number, the model can be meshed in subcomponents. The Curvature control method can be used to adjust the mesh density at the curved surface, initially mesh the surface, and then perform more detailed meshing in the area that needs to be encrypted to improve the surface mesh quality. Use Skewness as the mesh quality evaluation standard to check the quality of each component surface mesh. Use the surface mesh optimization tool to diagnose each component, and use the Collapse method to merge the corresponding nodes and edges to improve the quality, and control the skewness of each part of the mesh below 0.7, close to 0.5. After obtaining a surface mesh of appropriate quality, set the default number of boundary layers to 2, and then perform polyhedral meshing on the tilt-rotor fuselage and its engine.

[0070] S3. Flow field analysis, including:

[0071] First, the SST k-omega model is used to analyze the steady-state flow field. In view of the needs of simplified models and aerodynamic noise analysis, it is known that the aerodynamic noise of the tiltrotor aircraft mainly comes from the dipole sound source generated by the interaction between the high-speed rotating rotor and the air, and the sound source is located in the rotating domain where the rotor is located. Therefore, in the division of the simplified model simulation area, the six rotors are divided into six independent regions, and these regions are defined as multiple reference frame (MRF) regions in the steady-state calculation. At the same time, the external flow field is set as another stationary domain. Using the MRF method, the six rotor domains can be set as rotating domains, and their rotation axis is the center position of the rotor, and the coordinates of this position are obtained in Space Claim. The rotating domain and the fluid domain (stationary domain) transfer data through the interface. The MRF method allows the entire calculation domain to be divided into multiple subdomains, and the control equations are solved in each subdomain, so as to obtain good results while providing a high-quality initial flow field for the subsequent transient sliding grid method.

[0072] When calculating the flow field of a multi-region grid, it is necessary to establish an interface (interface) to achieve data transfer between the rotating domain and the stationary domain, so as to achieve a realistic simulation effect. The interface between the two regions is established by naming in the pre-processing stage of the rotorcraft model. Given that there are six rotors, six interfaces need to be established to transfer data to prevent simulation problems caused by missing interfaces.

[0073] After the model is lightweight, the rotation domain and the stationary domain are divided, and the mesh is divided, the MRF method is used to perform steady-state calculations based on the SSTk-omega model. The rotation speed of the MRF domain is set to 1200 rpm, and the y-direction center axis of the rotor is used as the rotation axis to rotate in the z-axis direction. The boundary conditions are set to a speed inlet of 60 m / s and the outlet condition is a pressure outlet to simulate the flow field and aerodynamic noise generated by the cruise flight of a tilt-rotor aircraft with a headwind speed of 60 m / s, in preparation for subsequent initialization and calculation. When the residual error is less than 10e-6, it is judged to be converged, and the steady-state calculation is iterated 1600 times to reach convergence. The Broadband model is imported from the steady-state calculation to obtain a broadband noise cloud map. The Broadband model is a semi-empirical correction model calculation of the turbulence parameters based on the solution of the RANS equation in Ansys Fluent to obtain the noise power of the surface unit or volume unit, which supplements the missing parts of the direct calculation method and the hybrid calculation method. The model only requires the solution of the steady-state RANS equation, so that the location of the noise source in the flow can be quickly obtained at a very low computational cost.

[0074] Then, the output results of the steady-state flow field analysis are used as the initial value, and the large eddy simulation (LES) model is used for transient flow field analysis; this model processes the Navier-Stokes (NS) equations through low-pass filtering, and divides the flow field into large-scale vortices and small-scale vortices. The motion of the large-scale vortex is simulated by directly solving the NS equations, while the small-scale vortex is approximately solved by the subgrid scale (SGS) model. In the transient flow field calculation, the calculation results of the steady-state flow field are used as the initial conditions to promote the rapid convergence of the calculation process. During the calculation, the time step is set to 10^-5 seconds, 12 iterations are performed in each time step, and the maximum number of iterations is 1600 steps. The calculation results will be saved once every 0.0008 seconds, thereby realizing the calculation of the total time of 0.016 seconds. In addition, the multiple reference frame (MRF) method is adjusted to the sliding mesh (SM) method, and the rotation domain is set to mesh motion (Mesh Motion). On this basis, the LES model is used for transient calculations, and the sub-grid model is used to solve the small-scale flow.

[0075] S4. Using the FW-H model, the transient flow field analysis results are subjected to acoustic analogy noise analysis to obtain the sound source distribution;

[0076] The LES large eddy simulation model is selected for transient state. After convergence, the FW-H model is imported to predict the noise data received at x = 50m on the back of the fuselage. The FW-H model is a model that divides the sound source into three categories, namely monopole, dipole and quadrupole. The sound source distribution can be obtained by solving the equation. The expression is:

[0077]

[0078] Where c represents the speed of sound, p ′ (x, t) is the sound pressure, v n represents the surface integral motion speed, p i ′ j represents the component of the compressive stress tensor, n j represents the integral out-of-plane normal vector component, T ij are the components of the Lighthill stress tensor, δ(f) is the Dirac delta function, and H(f) is the Heaviside function. The three terms on the right side of the equation represent the monopole, dipole, and quadrupole sound sources, respectively.

[0079] The sound source distribution can be obtained by solving the equations and generated in the Ansys Fluent software in the form of an ARD file of the noise at the observation point.

[0080] The result file is saved in the folder in asd format. The asd file is read in Ansys Fluent and converted into an ard file. Finally, the ard file is processed by fast Fourier transform to convert the time domain into the frequency domain to obtain the spectrum diagram.

[0081] S5. Use steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

[0082] Steady-state broadband noise analysis

[0083] Aerodynamic noise is mainly composed of rotating airflow noise and eddy noise. According to the analysis of pressure, speed and turbulent kinetic energy, the rotating noise of the rotor, that is, the noise radiated by the interaction between rapid rotation and air to produce continuous pressure pulsation, is the main source of aerodynamic noise. Therefore, the focus is on the distribution of dipole sound sources of tilt-rotor aircraft. As shown in the figure, the noise sources are mainly concentrated on the surface of the rotor blades, the junction between the rotor blades and the engine, and the back of the fuselage. The maximum noise value is 133.1dB, located at the blade. The reason is that the blades rotate rapidly to cut the air, which is the area with the strongest interaction with the air in the whole machine, thus generating the largest dipole noise source. And the surface noise value from the nose to the tail of the rotorcraft first rises and then decreases. At the same time, the noise value on the surface of the rotor blade gradually increases from the root to the tip of the blade, which is consistent with the description of the pressure cloud map and the turbulent kinetic energy cloud map. Combined with the analysis of the velocity cloud map, the generation of vortices at the rear of the rotor and the interaction of shedding superposition lead to pressure accumulation and radiation of eddy noise. At the same time, by analyzing the rotor surface pressure value and noise value separately, it can be obtained that the load noise generated by the surface pressure is the main source of noise of the tiltrotor aircraft.

[0084] like Figure 4 As shown in the figure, the noise level in the rotor rotation area is slightly lower than the blade surface noise, specifically 127.29 decibels. Due to the generation of rotation noise and eddy noise, the noise level in the rear area of ​​the rotor is significantly higher than other areas. The noise level in the rear area of ​​the rotor gradually decreases until the noise in the rear area of ​​the engine stabilizes between 50 and 76 decibels, which also confirms the above analysis.

[0085] via Figure 5 and Figure 6 The comparative analysis shows that there is a close relationship between the intensity of turbulent kinetic energy and the distribution of noise sources. Figure 5 shows the noise distribution cloud map, and Figure 6 The distribution cloud map of turbulent kinetic energy is presented. In the rear area of ​​rotors 1 and 3, a significant turbulent kinetic energy enhancement phenomenon was observed. At the same time, in the noise cloud map, the rear areas of the two rotors also showed higher noise values, and the range and shape of the two areas showed a high degree of consistency. This phenomenon reveals that there is a direct correspondence between areas with higher turbulent kinetic energy and areas with larger noise values.

[0086] Transient flow field aerodynamic analysis

[0087] When performing transient calculations, the large eddy simulation (LES) model was used, and the small-scale flow was solved through the sub-grid model, so that the details of the flow could be captured more accurately. At the same time, the multiple reference frame (MRF) method was optimized to the sliding grid (SM) method, and the setting of the rotation domain was adjusted to the grid motion value. By introducing the transient numerical calculation of the time term, it was observed that the maximum pressure was distributed in the nose area at the front of the fuselage, and its value was 39705.4 Pascal. Through reasonable design, the drag can be effectively reduced, thereby improving the cruise maneuverability of the aircraft.

[0088] according to Fig. 9 and Fig.10 According to the observation results, the speed of the rotorcraft tail reaches the maximum value of 86.4 meters per second. As the external flow field flows through the rotorcraft fuselage and flows downward along the fuselage, the speed gradually increases until it intersects with the maximum speed area at the tail, and then gradually returns to horizontal flow.

[0089] S6. Perform one-third octave band analysis on the noise results at different locations around the tilt-rotor configuration model;

[0090] S7, firstly, the results of the one-third octave band analysis are imported into MATLAB, and then the transient flow field data are inversely Fourier transformed in MATLAB to be visualized and audible;

[0091] After the Ansys Fluent simulation is completed, the data can be converted into a spectrogram and exported in CSV format to obtain detailed data, namely the sound pressure level corresponding to each frequency measured at the monitoring point set 50 meters from the back of the tiltrotor. First, based on the MATLAB platform, the data needs to be interpolated before being written into the audio file function audiowrite and the sound function to simulate the sound to improve the data density. Specifically, the noise frequency collected at the monitoring point is defined as the x variable, and the corresponding sound pressure level is defined as the y variable. Next, the xx variable is defined as 10,000 points with equal intervals between 1 and 10,000, and the yy variable is the amplitude of these points. At the same time, a random phase array is generated and combined with the interpolated array to add random phases to the frequency domain signal. Subsequently, the inverse fast Fourier transform is applied to convert the frequency domain data into time domain data, and the real part in the time domain is extracted by the real function, and the audiowrite function is used to output it as a WAV audio file. The audio file is stored in a 32-bit format and is read by the audioread function and played by the sound function. Finally, the audio file is imported as a plug-in in the subsequent UNITY 3D environment to achieve a combination of visual and auditory effects.

[0092] A second embodiment, a noise analysis system for an electric aircraft with a tilt-rotor configuration, is used to implement the method of the first embodiment, comprising:

[0093] The model building module builds a tilt-rotor configuration model based on the parameters of the electric aircraft and imports the model into Ansys Fluent software;

[0094] The meshing module first divides the tiltrotor configuration model into sub-components by mesh size or by setting the number of meshes; and then optimizes the meshes;

[0095] Flow field analysis module, flow field analysis specifically includes:

[0096] Firstly, the SST k-omega model is used to analyze the steady flow field;

[0097] Then, the output results of the steady-state flow field analysis are used as the initial value to perform transient flow field analysis using the LES large eddy model;

[0098] The sound source distribution calculation module uses the FW-H model to perform acoustic analogy noise analysis on the transient flow field analysis results to obtain the sound source distribution;

[0099] The noise analysis module uses steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

[0100] A third embodiment is a computer program product, characterized in that it includes a computer program, which, when executed by a processor, implements the above-mentioned noise analysis method for an electric aircraft with a tilt-rotor configuration.

[0101] A fourth embodiment is a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for analyzing noise of an electric aircraft with a tilt-rotor configuration.

[0102] The theory of the present invention is further analyzed and explained below:

[0103] The present invention mainly carries out aerodynamic noise simulation of electric vertical take-off and landing aircraft with tilt-rotor configuration and sonification processing of simulation results, and at the same time combines audio for visualization research. First, aerodynamic simulation is carried out in the cruising state of 60m / s in the external wind field of the electric vertical take-off and landing aircraft with tilt-rotor configuration. Simulation is carried out for the Joby S4 model to obtain steady-state flow field results and transient flow field results respectively. Then, based on computational fluid dynamics, the noise source is obtained and the FW-H method is used to predict the noise at the observation point. At the same time, the fast Fourier transform is used to draw the corresponding spectrum diagram, and the audio is synthesized by the inverse fast Fourier transform in the MATLAB software to achieve sonification. Finally, the tilt-rotor aircraft model and audio are imported into the UNITY 3D software, and the model cruise flight is controlled based on C# script programming. Visualization research is carried out and connected to the head-mounted device HTC VIVE to realize the extended reality function.

[0104] The main noise sources of tiltrotor aircraft come from the rotation noise and eddy noise of the rotor. Rotation noise is the pressure pulsation caused by the interaction between the high-speed rotating blades and the air, and eddy noise comes from the pressure pulsation caused by the vortex generated by the rotor and the shedding vortex. The types of sound sources can be roughly divided into three types: monopole sound source, dipole sound source and quadrupole sound source. At present, the main research method of aerodynamic noise adopts the FW-H model of Hawkings\Ffowcs-Williams and predicts the noise based on the acoustic analogy method of Lighthill by taking into account the problem of moving boundaries. The present invention adopts the SST k-omega turbulence model and the broadband model as well as the large eddy simulation model and the FW-H unsteady model to perform aerodynamic simulation numerical calculations and predict noise.

[0105] First, the tilt-rotor model needs to be simplified, that is, the model needs to be lightweight. By reducing the unnecessary simulation parts of the model, the computational cost can be reduced and the computational efficiency can be improved. Then, meshing and boundary conditions are set. The steady-state calculation based on the SST k-omega model is performed using the Markov random field method. After convergence, the broadband model is imported to obtain the broadband noise results of the rotorcraft. Then, the LES model is adjusted to use the sliding grid method for transient calculations, and the pressure isovalue changes over time are detected. The FW-H model is imported to use the acoustic analogy method to predict the noise results collected 50 meters above the back of the aircraft during the cruise state, and finally a comprehensive analysis is performed.

[0106] Numerical Calculation Theory of Aerodynamic Noise

[0107] The turbulence model selected for steady-state calculation is the shear stress transport k-omega model, namely the SST k-omega model, which combines the advantages of k-epsilon and k-omega, and is obtained by combining two standard models with a hybrid function. It has good computing performance in both the far-field area and the near-wall area. The k-epsilon model is used for calculation in the far-field area, and the k-omega model is used for near-field calculation. It is widely used because it has higher accuracy and stability and is suitable for a variety of turbulent flows. It is obtained based on the Reynolds average equation, the difference is that the eddy current coefficient is not a constant, and it is more advantageous for processing counter-gradient flows and separated flows. The present invention solves the steady-state flow field of the Reynolds average equation as the initial value of the transient calculation, which can accelerate convergence and reduce the computational cost. The broadband model calculates the noise power of the surface unit or volume unit through a semi-empirical correction model for the turbulence parameters solved based on the Reynolds average equation in Ansys Fluent. It supplements the missing parts of the direct calculation method and the hybrid calculation method, and only requires the solution of the Reynolds average equation in the steady state, so that the location of the noise source in the flow can be quickly obtained and the cause can be accurately judged under the premise of very low calculation cost. Reasonable application in industry can make corresponding noise reduction measures based on the analysis of noise sources.

[0108] The transient calculation adopts the large eddy simulation model. Its operation principle is to divide the flow field into large-scale vortices and small-scale vortices by low-pass filtering the Navier-Stokes equations. The large-scale vortices are directly solved by the Navier-Stokes equations and the small-scale vortices are approximated by the sub-grid model.

[0109] The WALE model in the large eddy model selected by the present invention makes up for the defects of the Smagorinsky model and makes the calculation simpler and more accurate.

[0110] Through design optimization, the pressure at the leading edge of the rotor is reduced, thereby reducing the generation of noise. Observation results show that the pressure field on the pressure surface of the rotor is greater than that on the suction surface, which promotes the forward cruise of the rotorcraft. At the same time, the pressure distribution on the rotor surface is uneven. For example, the leading edge pressure of rotor 5 is relatively low, while the surface pressure of rotor 6 is low and its leading edge pressure is relatively high. Aerodynamic noise is mainly composed of rotating airflow noise and vortex noise. By analyzing pressure, speed and turbulent kinetic energy, it can be seen that the rotor rotation noise, that is, the noise radiated by the continuous pressure pulsation generated by the rapid rotation of the rotor and the interaction with the air, is the main source of aerodynamic noise. Therefore, the research focuses on the distribution of dipole sound sources of tilt-rotor aircraft. The noise sources are mainly concentrated on the surface of the rotor blades, the junction between the rotor blades and the engine, and the back of the fuselage. The maximum noise value is 133.1 decibels, which is located at the blades. The reason is that the blades rotate rapidly to cut the air, which is the area in the whole machine that interacts most strongly with the air, thus generating the largest dipole noise source. The surface noise value from the nose to the tail of the rotorcraft first rises and then decreases. The noise value on the surface of the rotor blade gradually increases from the root to the tip of the blade, which is consistent with the description of the pressure cloud map and the turbulent kinetic energy cloud map. Combined with the analysis of the velocity cloud map, the generation and shedding of the vortex at the rear of the rotor interact and superimpose, resulting in pressure accumulation and radiation of vortex noise. By analyzing the rotor surface pressure value and noise value separately, it can be concluded that the load noise generated by the surface pressure is the main source of noise for the tilt-rotor aircraft.

[0111] The steady-state simulation mainly simulates the distribution of the noise source of the tiltrotor, but does not introduce the time term, so it is impossible to analyze the relationship between noise and time. In order to further study the noise characteristics of the tiltrotor in the cruise state of the external 60 m / s wind field, a monitoring point is set at x = 50 meters on the back of the fuselage with coordinates of [50000, 0, 0] (unit: mm), and a transient calculation is performed to study the noise characteristics of the monitoring point. Under transient conditions, the noise spectrum of the tiltrotor at 50 meters is as follows: Fig.12 As shown, the noise peak appears at 30307 Hz, reaching 92.02 dB. The frequency range audible to the human ear is between 20 and 20000 Hz. Through spectrum analysis, the noise value produced by the tilt-rotor aircraft audible to the human ear is between 74.58 dB and 78.27 dB. Since the noise peak is within the frequency range that is inaudible to the human ear, it can be judged that the noise of the tilt-rotor aircraft has little impact on the community, which reflects the low noise advantage of the electric vertical take-off and landing aircraft with a tilt-rotor configuration, and meets the design requirements of low-altitude economy and airworthiness.

[0112] The large eddy simulation model is used for transient flow field aerodynamic calculations, and the sub-grid model is used to solve small-scale flows, which can capture more flow details. The Markov random field method is adjusted to the SM method, and the rotation domain is set to Mesh Motion. The time term is introduced into the transient numerical calculation, and it is observed that the maximum pressure is distributed at the front nose of the fuselage, with a pressure value of 39705.4 Pascal. Reasonable design can reduce resistance and improve cruise maneuverability. Under transient conditions, the noise spectrum of the tilt-rotor aircraft is visible at 50 meters. Fig.12 .

[0113] The noise characteristics are analyzed through the 1 / 3 octave spectrum diagram under transient conditions. Since the human ear has different sensitivities to different frequencies, it is easier to distinguish low frequencies such as 100 Hz, but it is very difficult to make subtle distinctions for high frequencies such as 10,000 Hz. Therefore, the octave can roughly divide the frequencies that are inaudible to the human ear and subdivide the low frequencies to make the noise characteristics more prominent. The 1 / 3 octave represents two more frequencies between the upper and lower limit frequencies of an octave, thereby dividing it into three sections. This division method is more in line with the characteristics of the human ear and is often used to analyze the frequency distribution of noise energy. The noise of the tiltrotor reaches its maximum value in the frequency range of 30,000 to 40,000 Hz. Under transient conditions, the 1 / 3 octave spectrum of the tiltrotor at 50 meters is visible. Fig.13 .

[0114] A-weighting is a standard weighting curve for audio measurement that can well reflect the corresponding characteristics of the human ear. Its essence is to simulate the sound receiving characteristics of the human ear, which can better reflect the subjective hearing of the human ear. In the figure, the difference between the A-weighted 1 / 3 octave sound pressure level spectrum and the unweighted 1 / 3 octave sound pressure level spectrum above 30,000 Hz is large, and the representation of the low frequency area is more obvious, reflecting the response of A-weighting to the low sound level of the human ear. The A-weighted 1 / 3 octave spectrum at 50 meters from the monitoring point can be seen Fig.14 .

[0115] The power spectrum density diagram of the noise signal describes the distribution of signal power in the frequency domain, and can intuitively show the energy distribution of the signal at different frequencies. The sound power spectrum density diagram is obtained by fast Fourier transforming the sound signal at the monitoring point at 50 meters, as shown in Fig.15 As shown in Figure 1, the energy is concentrated at 30,000 Hz, which is consistent with the above image analysis results. The acoustic power spectrum density at 50 meters from the monitoring point can be seen Fig.15 .

[0116] The noise auralization processing of the electric vertical take-off and landing aircraft with a tilt-rotor configuration based on MATLAB is to convert the data obtained by measurement or simulation into noise audio audible to the human ear. The present invention performs inverse fast Fourier transform processing on the aerodynamic noise data obtained by Ansys Fluent transient numerical calculation based on MATLAB, and uses audiowrite (write audio file function) and sound function to process the data into audio playback. The audio is imported into the subsequent UNITY 3D as a plug-in to achieve the combination of visualization and auralization. After the data after Ansys Fluent simulation is drawn into a spectrum diagram, it can be exported in csv format to obtain specific data, that is, the sound pressure level corresponding to each frequency measured by the monitoring point set 50 meters away from the back of the tilt-rotor aircraft, and the data in the file is used as the object of auralization processing.

[0117] Table 1 shows the data that needs to be sonified in the document

[0118]

[0119]

[0120] Before using the audiowrite and sound functions to simulate sound, interpolation processing can be performed to increase data density. Specifically, the noise frequency collected at the monitoring point is defined as x, and the corresponding sound pressure level is defined as y. Next, set xx to 10,000 points equally spaced between 1 and 10,000, and calculate the amplitude yy of each point through the cubic spline interpolation function csapi. In addition, a random phase array is generated and combined with the interpolated array to supplement the random phase for the frequency domain signal. Subsequently, the frequency domain signal is converted into a time domain signal through an inverse fast Fourier transform, the real part in the time domain is extracted using the real function, and the audiowrite function is used to output it as a 32-bit stored wav audio file. After reading the wav file through the audioread function, use the sound function to play it, thereby realizing the audibility technology of the noise of the electric vertical take-off and landing aircraft with a tilt-rotor configuration.

[0121] In the UNITY 3D environment, convert the optimized simulation model file to FBX format and import it into the Assets of UNITY 3D. Add a skybox to enhance the light and shadow effects of the scene. Simulate gravity and inertia by adding a rigid body component in the UNITY 3D engine, which automatically performs gravity-related calculations. Next, perform animation to achieve the flight control of the tilt-rotor aircraft and the tilting function of the rotor. Arrange the scene in UNITY 3D, build a ground platform, and ensure the coordinated movement of the rotor and the engine. Control the movement of the tilt-rotor aircraft by adding a programming script to the model, and realize the rotation of the rotor through animation.

[0122] After exporting the simulated noise audio file, add an audio component in UNITY 3D and drag the processed audio file into the audio component so that you can hear the noise generated by the tiltrotor aircraft while observing the cruise flight. This implementation combined with noise visualization and sonification technology allows people to more intuitively feel the noise obtained by numerical calculation and sound analogy, thereby improving convenience in the evaluation and improvement of the design stage and the subsequent airworthiness certification process.

[0123] Immersive space extended reality technology, or XR (Extended Reality), is a general term that integrates multiple technologies such as virtual reality (VR), augmented reality (AR) and mixed reality (MR). VR provides real-time interactive experience in a computer-simulated virtual world through wearable devices such as the HTC VIVE head-mounted device. AR integrates digital media, three-dimensional models, real-time tracking, intelligent interaction and fiber optic sensing technologies on the basis of VR, making the reality and computer-simulated space more closely integrated. MR establishes a real-time interactive and realistic integrated environment between users, the real world and the virtual world. Based on extended reality technology, this paper constructs a virtual scene in UNITY 3D and imports a simplified FBX format model of the Joby S4 electric vertical take-off and landing aircraft with a real American tilt-rotor configuration. The audio signal data obtained after aeroacoustic simulation is processed and sonified through MATLAB. The frequency domain signal is restored to the time domain signal and imported into the virtual environment, and sonification and visualization are realized through the head-mounted display.

[0124] A scene of a tilt-rotor aircraft cruising flight was built on the UNITY 3D platform, and after importing the audio file, the immersive spatial extended reality interactive function was realized in combination with the HTC device. The specific operation requires the use of the plug-in on Steam to connect, connect the HTC VIVE head-mounted display device through Steam VR, and add a series of mount connections. When the indicator light turns green, it means that the HTC VIVE device has been successfully connected, thereby realizing scene interaction and achieving the purpose of immersive spatial extended reality. Before putting on the HTC VIVE head-mounted device, it is necessary to close the prompt window that pops up on the desktop so that off-site personnel can understand the spatial extended reality scene observed by the device user. Using the visual function, experience the immersive spatial extended reality technology, realize the combination of aeroacoustic simulation numerical calculation, noise auralization technology and extended reality technology, so that people can intuitively feel the noise results of numerical calculation, and at the same time contribute to the progress of airworthiness noise research.

[0125] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When the use is implemented in whole or in part in the form of a computer program product, the computer program product includes one or more computer instructions. When the computer program instructions are loaded or executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL) or wireless (e.g., infrared, wireless, microwave, etc.) mode) to another website site, computer, server or data center. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state hard disk SolidState Disk (SSD)), etc.

[0126] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for analyzing noise of an electric aircraft with a tilt-rotor configuration, characterized in that: include: S1. Build a tilt-rotor configuration model based on the parameters of the electric aircraft and import the model into Ansys Fluent software; S2. Meshing: first, meshing the tilt-rotor configuration model by sub-components by setting the mesh size or the number of meshes; then optimizing the meshes; S3. Flow field analysis, including: Firstly, the SST k-omega model is used to analyze the steady-state flow field; Then, the output results of the steady-state flow field analysis are used as initial values ​​to perform transient flow field analysis using the LES large eddy model; S4. Using the FW-H model, the transient flow field analysis results are subjected to acoustic analogy noise analysis to obtain the sound source distribution; S5. Use steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

2. The method for analyzing noise of an electric aircraft with a tilt-rotor configuration according to claim 1, characterized in that: The S1 includes: firstly obtaining parameters of the electric aircraft, wherein the parameters include size parameters and performance parameters of each component; and then constructing a tilt-rotor configuration model by using Dassault CATIA.

3. The method for analyzing noise of an electric aircraft with a tilt-rotor configuration according to claim 1, characterized in that: The S2 includes: S201. Lighten the tiltrotor configuration model; S202, dividing each component into grids by setting a grid size of each component or setting the number of grids; S203, mesh optimization, using Skewness as the mesh quality criterion to check the mesh quality of each component surface; using the surface mesh optimization tool to diagnose each component separately and using the Collapse method to merge paired nodes and edges to improve the quality, and control the skewness of each part of the mesh below 0.7; S204, setting the default number of boundary layers, and then performing poly mesh division on the tilt-rotor aircraft fuselage and its engine.

4. The method for analyzing noise of an electric aircraft with a tilt-rotor configuration according to claim 1, characterized in that: In S3: The steady-state flow field analysis includes: first, each rotor of the electric aircraft is divided into a separate area, defined as an MRF area, and then the external flow field is set as a static domain; based on the MRF method, multiple rotor domains are set as rotating domains, the rotation axis is the rotor center position, and the point coordinates are obtained in Space Claim; the rotating domain and the static domain transmit data through the interface; the MRF method splits the entire calculation domain into multiple subdomains, and uses the control equations to solve them in each domain; finally, the MRF method is selected for steady-state calculations based on the SST k-omega model. The transient flow field analysis includes: firstly, taking the steady-state flow field analysis results as the initial values ​​of the transient calculation, and then using the large eddy model to perform transient calculation.

5. The method for analyzing noise of an electric aircraft with a tilt-rotor configuration according to claim 1, characterized in that: In S4, the result file of the sound source distribution is saved in a folder in asd format. The asd file is read in Ansys Fluent and converted into an ard file. Finally, the ard file is processed by fast Fourier transform to convert the time domain into the frequency domain to obtain the spectrum diagram.

6. The method for analyzing noise of an electric aircraft with a tilt-rotor configuration according to any one of claims 1 to 5, characterized in that: Also includes: S6. Perform one-third octave band analysis on the noise results at different locations around the tilt-rotor configuration model; S7. First, the results of the one-third octave band analysis are imported into MATLAB, and then the transient flow field data are inversely Fourier transformed in MATLAB to make them visual and audible.

7. A noise analysis system for an electric aircraft with a tilt-rotor configuration, characterized in that: include: The model building module builds a tilt-rotor configuration model based on the parameters of the electric aircraft and imports the model into Ansys Fluent software; The meshing module first divides the tiltrotor configuration model into sub-components by mesh size or by setting the number of meshes; and then optimizes the meshes; Flow field analysis module, flow field analysis specifically includes: Firstly, the SST k-omega model is used to analyze the steady-state flow field; Then, the output results of the steady-state flow field analysis are used as initial values ​​to perform transient flow field analysis using the LES large eddy model; The sound source distribution calculation module uses the FW-H model to perform acoustic analogy noise analysis on the transient flow field analysis results to obtain the sound source distribution; The noise analysis module uses steady-state broadband noise analysis and transient flow field aerodynamic analysis to obtain noise results at different locations around the tilt-rotor configuration model.

8. The electric aircraft noise analysis system of the tilt-rotor configuration according to claim 7, characterized in that: The construction process of the model construction module includes: firstly obtaining the parameters of the electric aircraft, the parameters including the size parameters and performance parameters of each component; then using Dassault CATIA to build a tilt-rotor configuration model; The meshing process of the meshing module includes: Lightweight the tilt-rotor configuration model; Mesh each component by setting the mesh size of each component or setting the number of meshes; Mesh optimization, using Skewness as the mesh quality criterion, checks the mesh quality of each component surface; diagnoses each component separately through the surface mesh optimization tool and uses the Collapse method to merge paired nodes and edges to improve the quality, and controls the mesh skewness of each part to less than 0.7; Set the default number of boundary layers and then perform poly meshing on the tiltrotor fuselage and its engines.

9. A computer program product, characterized in that The invention comprises a computer program, which, when executed by a processor, implements the noise analysis method of an electric aircraft with a tilt-rotor configuration as claimed in any one of claims 1 to 6.

10. A computer-readable storage medium storing a computer program, characterized in that: When the program is executed by a processor, the noise analysis method for an electric aircraft with a tilt-rotor configuration as described in any one of claims 1 to 6 is implemented.

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