A bionic noise reduction method based on the performance of air duct aerodynamic noise of an automobile air conditioning system

Abstract

The application discloses a kind of based on automobile system air duct aerodynamic noise bionic noise reduction method, belong to automobile air conditioning technical field.The method is through the abnormal frequency point aerodynamic noise problem of automobile air conditioning air duct defrosting condition, in-depth study its aerodynamic noise characteristics, bionic structure design and noise suppression law, and proposes reasonable noise reduction solution.First, theoretically analyzes the source of automobile air conditioning air duct aerodynamic noise, and analyzes the noise characteristics by test measurement.Secondly, with automobile air conditioning defrosting air duct as research object, using RNG model and LES model to defrosting air duct steady and transient fluid simulation calculation, and through sound analogy method calculates defrosting air duct outlet noise, establishes air conditioning air duct aerodynamic noise calculation model.Thirdly, it is proposed to use the microscopic scale structure of shark skin as bionic object design bionic guide cell, and better cell cross-sectional shape is determined by comparing simulation analysis to reduce noise effect;Afterwards, bionic guide cell is applied to defrosting air duct inner wall, with the minimum outlet noise as target, carries out its arrangement optimization design.The experimental results show that, compared with original air duct, defrosting air duct using bionic structure design has achieved good noise reduction effect.The application designs bionic guide cell structure by imitating the microscopic structure of shark skin scale groove and applies it to the inner wall of automobile defrosting air duct, realizes the purpose of suppressing wideband aerodynamic noise from the source, has the advantages of significant noise reduction effect, flow field performance collaborative optimization, space utilization rate, etc., can effectively improve in-vehicle sound quality and ride comfort.

Description

Technical Field

[0001] This invention relates to a biomimetic noise reduction method based on the aerodynamic noise performance of automotive air conditioning system ducts, belonging to the field of automotive air conditioning technology. Background Technology

[0002] As a key component ensuring thermal comfort and air quality within the vehicle, the noise level of the automotive air conditioning system directly impacts the passenger experience. Especially with the rapid popularization of new energy vehicles, the noise of traditional powertrain systems has been significantly reduced, making the aerodynamic noise of the air conditioning system more prominent and a crucial factor affecting the acoustic comfort of the in-vehicle environment. Therefore, reducing the aerodynamic noise of automotive air conditioning systems is of great significance.

[0003] Traditional methods for reducing aerodynamic noise in automotive air conditioning system ducts typically fall into three categories: First, leveraging engineering experience to optimize duct geometry by reducing the number of bends, increasing turning radii, and adding guide vanes to improve airflow distribution. However, such structural optimization schemes are often limited by the interior space layout of the vehicle, making it difficult to achieve an ideal duct design. Second, attaching sound-absorbing cotton or porous materials to the inner wall of the duct to absorb sound energy and reduce noise. For example, existing technology discloses a duct assembly that uses wavy noise-reducing sponges on the inner wall of the duct body to reduce wind speed and sound frequencies. However, the addition of sound-absorbing materials increases airflow resistance, increases blower load, and is prone to failure in high humidity environments. Third, integrating sound-absorbing structures such as expansion cavities and Helmholtz resonators into the duct to suppress noise at specific frequencies. Existing technology discloses a noise-reducing duct that achieves broadband noise reduction by designing a noise-reducing unit with a Helmholtz resonator. However, such structures occupy a large space and have limited effectiveness in suppressing broadband noise.

[0004] In summary, current research on aerodynamic noise control in automotive air conditioning systems mostly focuses on optimizing the duct structure at the noise source. However, the duct structures of air conditioning systems vary significantly across different vehicle models, leading to substantial differences in optimization and improvement methods. Therefore, there is an urgent need to explore a low-cost method that effectively controls low- and mid-frequency aerodynamic noise to achieve efficient control of automotive air conditioning aerodynamic noise. Summary of the Invention

[0005] The purpose of this invention is to provide a biomimetic noise reduction method based on the aerodynamic noise performance of automotive air conditioning system ducts. This method analyzes the aerodynamic noise sources in the ducts and their noise characteristics through experiments. Taking the automotive defrosting duct as the target object, steady-state flow field and sound field calculations are performed using CFD and CAA (acoustic analogy method). Based on the analysis results and biomimetic noise reduction theory, a biomimetic flow-guiding cell is designed using the microscopic shield scale structure of shark skin as the biomimetic object. The structure is designed, and finally, simulation and experiments verify that this structure has a good noise reduction effect when applied to the defrosting duct.

[0006] The technical solution of this invention provides a biomimetic noise reduction method based on the aerodynamic noise performance of an automotive air conditioning system duct, mainly including the following steps:

[0007] Step 1: Theoretical Study of Aerodynamic Noise and Flow Field in Ducts

[0008] First, we analyzed three common types of aerodynamic noise sources—monopoles, dipoles, and quadrupoles—and explored their respective generation mechanisms, providing theoretical support for accurate and rigorous numerical simulation of the internal flow field of automotive air conditioning ducts. Second, we established aerodynamic noise control equations for the duct to provide a theoretical basis for the numerical simulation calculation of the duct sound field.

[0009] The equation for calculating aerodynamic noise is expressed as follows: ; ; ; In the formula, For wall functions; and They represent the fluid in The velocity components in the direction of the solid boundary normal; The velocity of the solid boundary; Let be the stress tensor. The first, second, and third terms on the right-hand side of the FW-H equation correspond to monopole, dipole, and quadrupole sound sources, respectively. When the solid boundary is stationary, i.e., the velocity... When the flow conditions are low, the FW-H equations can be simplified to the Cole equations. In this case, the right-hand side of the equations only contains dipole and quadrupole sound sources, and under low Mach number flow conditions, dipole sound sources dominate.

[0010] Step 2: Coupled simulation analysis of airflow field and acoustic field in the duct and experimental verification of aerodynamic noise in the duct. A three-dimensional geometric model of the automotive air conditioning duct was established, meshed, and computational fluid dynamics was used to numerically simulate the flow field within the duct, obtaining the velocity field, pressure field, and turbulent kinetic energy distribution. Based on the flow field calculation results, a broadband noise source model was used to identify the location and type of the main aerodynamic noise sources. The broadband noise source model includes the Curle noise source model and the Proudman noise source model. The Curle noise source model is used to calculate dipole noise in the boundary layer of low Mach number flows, calculating the sound intensity per unit area based on the turbulent time scale, characteristic length, and wall shear force. The Proudman noise source model, based on the isotropic turbulent flow field prediction assumption, is used to calculate spatial quadrupole noise sources, calculating the sound intensity per unit volume through the turbulent characteristic length and characteristic time.

[0011] Meanwhile, aerodynamic noise tests were conducted on the air conditioning ducts, and the simulation results were compared with the measured data to verify the accuracy and reliability of the calculation model.

[0012] Step 3: Bionic Structural Design Based on numerical simulation results of the airflow and sound field in automotive air conditioning ducts and biomimetic noise reduction theory, a biomimetic flow guide cell is designed using the microscopic shield scale structure of shark skin as the biomimetic object. The cross-section and arrangement of this cell are then designed. Furthermore, to explore the optimal arrangement, multi-objective parameter optimization is performed on the biomimetic flow guide cell structure.

[0013] Step 4: Verification of the noise reduction effect of the biomimetic flow-guiding cell structure By applying the optimal biomimetic flow-guiding cell structure calculated in the previous step to the defrosting duct of an automotive air conditioning system, flow and sound field calculations were performed on the structure containing the biomimetic flow-guiding cell structure. The results were compared with the original defrosting duct, and the noise spectrum, streamline turbulent kinetic energy, and sound power before and after optimization were compared to verify the biomimetic noise reduction effect. Simultaneously, based on the optimized biomimetic structural parameters, a biomimetic noise reduction duct prototype was fabricated using 3D printing, and aerodynamic noise tests were conducted in a semi-anechoic chamber to verify the effectiveness of the biomimetic noise reduction method.

[0014] The beneficial effects of this invention are: 1. This invention demonstrates significant broadband noise reduction for air conditioning aerodynamics: By mimicking the drag-reducing and noise-reducing structure of shark skin's scales, a biomimetic flow-guiding cell structure is established and applied to the inner wall of the defrosting duct, achieving effective noise reduction over a wide frequency range. Research shows that the biomimetic structure can suppress the formation of turbulent eddies in the duct, thereby improving the noise level at the duct outlet and enhancing the overall vehicle NVH performance.

[0015] 2. This invention suppresses noise at its source: Based on the Curle noise source model and the Proudman noise source model, the type and location of noise sources are accurately identified, and corresponding biomimetic structures are matched for the characteristics of noise sources in different locations to suppress the generation of aerodynamic noise at its source.

[0016] 3. This invention has strong design capabilities: It establishes a systematic biomimetic noise reduction design method. Through parametric modeling and multi-objective optimization, it can flexibly adjust the biomimetic structural parameters according to different air duct structures and operating conditions to achieve customized noise reduction design. Attached Figure Description

[0017] Figure 1 Flowchart of the steps in implementing this invention; Figure 2 (a) Schematic diagram of the air conditioning system and its interfaces Figure 2 (b) CFD model of automotive air conditioning Figure 3 (a) Diagram of air conditioning aerodynamic noise testing equipment Figure 3 (b) Test diagram of air conditioning aerodynamic noise bench Figure 4 Comparison of simulation and experimental results of noise spectrum Figure 5 (a) Surface acoustic power diagram of Curle defrosting duct Figure 5 (b) Proundman defrosting duct internal bulk acoustic power diagram Figure 5 (c) Internal flow diagram of defrosting duct Figure 6 (a) Shark skin groove structure Figure 6 (b) Microstructure of shark skin dermal scales Figure 7 (a) Conical cross section Figure 7 (b) Trapezoidal section Figure 7 (c) Rectangular section Figure 8 (a) Sound power diagram of the tapered cross-section structure Figure 8 (b) Sound power diagram of trapezoidal cross-section structure Figure 8 (c) Sound power of rectangular cross-section structures Figure 9 (a) Turbulent kinetic energy diagram of the conical cross-section structure Figure 9 (b) Turbulent kinetic energy diagram of trapezoidal cross-section structure Figure 9(c) Turbulent kinetic energy diagram of rectangular cross-section structure Figure 10 Sound pressure level diagrams of different cross-section shapes Figure 11 Schematic diagram of biomimetic flow guiding structure parameters Figure 12 Biomimetic flow-guiding cell array defrosting air duct turbulent kinetic energy cloud map Figure 13 Defrosting air duct with biomimetic flow guiding cell structure Figure 14 Optimized defrosting duct sound power diagram Figure 15 Actual image of a car defrosting air duct with a biomimetic airflow guiding structure Figure 16 (a) Original duct noise test bench Figure 16 (b) Optimized duct noise test bench Figure 17 Comparison of noise spectrum before and after optimization Detailed Implementation

[0018] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention: The biomimetic noise reduction method based on the aerodynamic performance of the air duct of the automotive air conditioning system described in this invention is achieved through simulation methods based on the software STARCCM+ and ISIGHT numerical simulation and by building an aerodynamic noise test in a semi-anechoic chamber.

[0019] (1) STARCCM+ software was used as the CFD simulation platform for automotive air conditioning. Automotive air conditioning duct systems typically consist of an HVAC assembly (including a blower, evaporator, heater core, mixing damper, etc.), connecting ducts, and various air outlets. Typically, the air conditioning simulation model is appropriately simplified while controlling the error range of the simulation results. Simultaneously, when establishing the automotive air conditioning system model, the system needs to be divided into multiple regions. The air filter, evaporator, heater core, and PTC heater are simplified to porous media, and the pressure drop characteristics and heat transfer performance are derived from test data provided by the supplier. The HVAC housing and duct inlet, as well as the contact surface of the porous media, are also established using interface operation commands. The external circulation inlet is defined as a mass flow inlet, and the duct outlet is set as a pressure outlet. The fluid is set as an ideal constant-density compressible gas, with the pressure and velocity coupling using the SIMPLE method. Steady-state calculations employ the standard k-ε model and multiple coordinate reference frame technique. The converged steady-state results are used as the initial values ​​for transient calculations. Transient calculations utilize the LES model and sliding mesh technique, with a time step of 2.5 × 10⁻⁶. －4The total calculation time is 2 seconds. Since the flow field goes through a process from oscillation to stability, the sampling time starts from 0.5 seconds to obtain the noise characteristics at different locations.

[0020] To verify the rationality of the numerical calculation method and model, and to quantify the simulation results of aerodynamic noise, a test bench for the target air conditioning system was built in an anechoic chamber. The test equipment mainly included a HEAD data acquisition system and microphone units (1 / 2 inch). Before the test, the microphones were calibrated using a standard acoustic calibrator (generating a specified level of 114 dB sound pressure at a frequency of 1000 Hz), with a sampling bandwidth ≥12800 Hz, a resolution of 1 Hz, and an output format of linear auto-power spectrum. To more realistically simulate the aerodynamic noise in the duct at the driver's ear, the microphone was positioned on the side closest to the driver, with the centerline of the defrost vent as the reference and the center of the vent as the origin, at coordinates (1050mm, -337mm, 510mm). All noises during driving were simulated, such as... Figure 7 As shown. During the test, the blower voltage was set to 12V, the current to 17.5A, the speed to approximately 3848 rpm, and the air volume to 6m³. 3 / min. Finally, the experimental results are compared with the simulation results. (2) Based on the numerical simulation results of the flow field and sound field of automotive air conditioning ducts and the theory of biomimetic noise reduction, a biomimetic flow guiding cell structure was designed using the microscopic shield scale structure of shark skin as the biomimetic object. Three biomimetic flow guiding cell structures with different cross-sectional shapes were designed based on the shark skin shield scale structure. After analyzing the flow field and sound field of the ducts using the three different cross-sectional flow guiding cell structures, it can be seen from the comparison of Curle sound power and turbulent kinetic energy values ​​that the conical flow guiding biomimetic structure has the best effect on reducing the aerodynamic noise of the defrosting duct. At the same time, comparing the sound pressure level curves of the three different cross-sectional flow guiding cell structures also shows that the peak noise of the conical cross-section is lower than that of the other two cross-sectional shapes in the 0-2000Hz frequency band. Based on the above analysis, the conical flow guiding cell structure has the best effect on reducing the aerodynamic noise of the defrosting duct.

[0021] (3) Through numerical simulation of biomimetic flow guiding cell structures with different cross-sectional shapes, it was concluded that the conical biomimetic flow guiding cell structure has the best effect in reducing the aerodynamic noise of the defrosting duct. Therefore, only the array mode of the conical biomimetic flow guiding unit structure was investigated. First, the structural parameters of the conical flow guiding biomimetic cell were determined by imitating the microstructure of shark skin scales. Then, the optimal Latin hypercube was used for sample sampling. After determining the design variables and value range, CATIA software was used to perform geometric modeling on 40 sample points extracted from the Latin hypercube experiment. The arrangement of the biomimetic flow guiding cells was precisely adjusted without changing the overall size of the defrosting duct. Using the duct flow field calculation scheme and the mesh scheme, steady-state simulation calculations were performed on the 40 duct flow fields constructed based on the biomimetic flow guiding cell sample models. In order to accurately calculate the noise value of the duct outlet, the transient simulation calculation was performed after the steady-state simulation stabilized. After Fourier transform of the transient results, the total sound pressure level corresponding to each monitoring point was obtained. Sample data was imported into ISIGHT and fitted using an RBF (neural network model). The optimization algorithm NSGA-II (non-dominated sorting genetic algorithm) was then employed. After 2000 iterations, the optimal biomimetic flow-guiding cell structure was obtained.

[0022] (4) To verify the noise reduction effect of the biomimetic flow-guiding cell structure, the optimal biomimetic flow-guiding cell structure was applied to the automotive defrosting duct. Flow field and sound field calculations were performed on the defrosting duct containing the biomimetic flow-guiding cell structure, and compared with the original defrosting duct. The results show that the flow field inside the duct was improved, with reduced turbulence and eddies at the outlet corner. Simultaneously, while ensuring airflow, the turbulent kinetic energy value at the duct outlet decreased from the original 19.7 m... 2 / s 2 Reduced to 16.7m 2 / s 2 Secondly, regarding the sound field, comparing the sound pressure level curve at the original air outlet of the duct, it was found that in the 0-500Hz frequency band, the noise peak at 136Hz in the optimized duct was 64.2dB, a decrease of 5.3dB compared to the original 69.5dB noise peak at 168Hz. Simultaneously, the sound pressure level was significantly reduced in the 500-2000Hz frequency band.

[0023] To further verify the impact of the biomimetic flow-guiding structure on the aerodynamic noise of the duct, a physical prototype of the optimized defrosting duct was fabricated, and an aerodynamic noise test bench was built. The sound pressure spectrum before and after optimization was compared. After adopting the shark-scale biomimetic flow-guiding cell array, the noise peak at 410Hz in the 0-500Hz frequency band decreased from 42.3dB to 39.5dB, a reduction of 2.8dB. In the 500-1000Hz frequency band, the noise peak at 620Hz in the optimized duct was 1.2dB lower than the original duct's 47.3dB noise peak at 640Hz. In the 1500-2000Hz frequency band, the noise peak at 1770Hz decreased from 44.4dB to 39.9dB, a reduction of 4.5dB. The total sound pressure level decreased by 2.6dB compared to the original duct.

Claims

1. The purpose of this invention is to provide a biomimetic noise reduction method based on the aerodynamic noise performance of automotive air conditioning system ducts. By analyzing the aerodynamic noise sources of the ducts and analyzing the noise characteristics of the ducts through experimental means, the steady-state flow field and sound field calculations are performed using CFD and CAA (acoustic analogy method) with the automotive defrosting duct as the target object. Based on the analysis results and biomimetic noise reduction theory, a biomimetic flow guiding cell is designed using the microscopic shield scale structure of shark skin as the biomimetic object, and its structure is designed. Finally, simulation and experiments verify that the structure has a good noise reduction effect when applied to the defrosting duct.

2. The technical solution of the present invention provides a biomimetic noise reduction method based on the aerodynamic noise performance of an automotive air conditioning system duct, mainly including the following steps: Step 1: Theoretical Study of Aerodynamic Noise and Flow Field in Ducts First, we analyzed three common types of aerodynamic noise sources—monopoles, dipoles, and quadrupoles—and explored their respective generation mechanisms, providing theoretical support for accurate and rigorous numerical simulation of the internal flow field of automotive air conditioning ducts. Second, we established aerodynamic noise control equations for the duct to provide a theoretical basis for the numerical simulation calculation of the duct sound field.

3. The equation for calculating aerodynamic noise is as follows: In the formula, For wall functions; and They represent the fluid in The velocity components in the direction of the solid boundary normal; The velocity of the solid boundary; Let be the stress tensor. The first, second, and third terms on the right-hand side of the FW-H equation correspond to monopole, dipole, and quadrupole sound sources, respectively. When the solid boundary is stationary, i.e., the velocity... At this point, the FW-H equation can be simplified to the Cole equation. In this case, the right-hand side of the equation contains only dipole and quadrupole sound sources, and under low Mach number flow conditions, the dipole sound source dominates.

4. Step Two: Coupled Simulation Analysis of Airflow Field and Acoustic Field in Duct and Experimental Verification of Airflow Noise A three-dimensional geometric model of the automotive air conditioning duct was established, meshed, and computational fluid dynamics (CFD) was used to numerically simulate the flow field within the duct, obtaining the velocity field, pressure field, and turbulent kinetic energy distribution. Based on the flow field calculation results, a broadband noise source model was used to identify the locations and types of major aerodynamic noise sources. The broadband noise source model includes the Curle noise source model and the Proudman noise source model, wherein: The Curle noise source model is used to calculate dipole noise in the boundary layer of low Mach number flows, calculating the sound intensity per unit area based on the turbulent timescale, characteristic length, and wall shear force. The Proudman noise source model is based on the isotropic turbulent flow field prediction assumption and is used to calculate spatial quadrupole noise sources, calculating the sound intensity per unit volume through the turbulent characteristic length and characteristic time.

5. At the same time, conduct aerodynamic noise tests on the air conditioning ducts, and compare the simulation results with the measured data to verify the accuracy and reliability of the calculation model.

6. Step Three: Bionic Structural Design Based on numerical simulation results of the airflow and sound field in automotive air conditioning ducts and biomimetic noise reduction theory, a biomimetic flow guide cell is designed using the microscopic shield scale structure of shark skin as the biomimetic object. The cross-section and arrangement of this cell are then designed. Furthermore, to explore the optimal arrangement, multi-objective parameter optimization is performed on the biomimetic flow guide cell structure.

7. Step Four: Verification of Noise Reduction Effect of Bionic Flow Guiding Cell Structure By applying the optimal biomimetic flow-guiding cell structure calculated in the previous step to the defrosting duct of an automotive air conditioning system, flow and sound field calculations were performed on the structure containing the biomimetic flow-guiding cell structure. The results were compared with the original defrosting duct, and the noise spectrum, streamline turbulent kinetic energy, and sound power before and after optimization were compared to verify the biomimetic noise reduction effect. Simultaneously, based on the optimized biomimetic structural parameters, a biomimetic noise reduction duct prototype was fabricated using 3D printing, and aerodynamic noise tests were conducted in a semi-anechoic chamber to verify the effectiveness of the biomimetic noise reduction method.

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