Wind tunnel test method for evaluating aerodynamic noise performance of rotorcraft

Abstract

The invention discloses a wind tunnel test method for evaluating aerodynamic noise performance of a rotorcraft, belongs to the field of wind tunnel tests, and provides a standard wind tunnel test method for aerodynamic noise of the rotorcraft by comprehensively considering the aerodynamic noise characteristics of the rotorcraft and the influence of an acoustic wind tunnel environment. The aerodynamic noise radiation characteristics of the rotorcraft can be effectively measured; a normative rotor aircraft model aerodynamic noise wind tunnel test data processing flow and method are established, and a method for extrapolating a rotor aircraft model aerodynamic noise wind tunnel test result to a real object is provided, so that the influence of background noise, a wind tunnel jet flow shear layer, atmospheric sound absorption, Doppler, a model scale and the like on test evaluation can be effectively corrected; and the accuracy of aerodynamic noise characteristic evaluation of the rotorcraft is effectively improved. The test method is standard in process, clear in data processing theory and feasible in data processing method, and can provide means and technical support for aerodynamic noise performance evaluation of the rotorcraft.

Description

Technical Field

[0001] This invention relates to the field of wind tunnel testing, and more specifically to a wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft. Background Technology

[0002] Helicopters, gyroplanes, and eVTOLs typically rely on rotors to provide lift, propulsion, and control. They possess unique capabilities such as vertical takeoff and landing, hovering, and low-altitude, low-speed flight. Their operational and speed ranges effectively fill the gaps in speed and space capabilities of modern air-to-ground transportation equipment, playing a vital role in national economic development. In recent years, with the rapid rise of the low-altitude economy worldwide, various helicopters, multi-rotor aircraft, and eVTOLs have flourished, creating an urgent demand for high-performance rotors. The rotor generates lift and propulsion through its high-speed rotation. While producing enormous power, the interaction between the high-speed rotating blades and the surrounding airflow generates strong aerodynamic noise, significantly impacting the acoustic performance of helicopters and eVTOLs. Therefore, accurately assessing the aerodynamic noise characteristics of rotors is crucial for developing high-quality gyroplanes.

[0003] Rotor aerodynamic noise is complex, encompassing thickness noise, load noise, propeller vortex interference noise, high-speed pulse noise, and broadband noise. These different types of noise have different generation mechanisms and extremely complex propagation mechanisms in space flow fields. Therefore, it is necessary to develop reliable rotor aerodynamic noise testing methods based on the complex radiation characteristics of rotor aerodynamic noise, to evaluate rotor noise radiation characteristics, and to guide the noise reduction optimization design and low-noise flight trajectory optimization of rotorcraft. Currently, several airborne acoustic wind tunnels have been built in China, providing excellent experimental platforms for rotorcraft aerodynamic noise research. To accurately and reliably measure the aerodynamic noise performance of rotorcraft, it is necessary to establish wind tunnel testing methods for evaluating rotorcraft aerodynamic noise performance, standardize and unify the data processing flow of rotorcraft aerodynamic noise wind tunnel tests, develop methods for extrapolating rotorcraft aerodynamic noise wind tunnel test data to physical objects, and form an effective rotorcraft aerodynamic noise wind tunnel testing and evaluation capability to support the evaluation and verification of advanced rotorcraft aerodynamic noise and noise reduction research. Summary of the Invention

[0004] The purpose of this invention is to accurately measure the noise of the rotor in different directions in an acoustic wind tunnel, perform systematic and standardized data processing, correct the influence of factors such as wind tunnel background noise, microphone structure, wind tunnel jet shear layer, and atmospheric sound absorption effect on the accuracy of noise measurement, accurately obtain the noise radiation characteristics of the rotor under different operating conditions, and extrapolate the wind tunnel test results of rotorcraft aerodynamic noise to the actual object, providing technical support for rotorcraft aerodynamic noise assessment and noise reduction method verification.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft disclosed in this invention comprises two parts: a wind tunnel testing method for the aerodynamic noise of a rotorcraft model and a test data processing method. The wind tunnel testing method for the aerodynamic noise of the rotorcraft model includes the following steps.

[0006] S1: Installation and commissioning of test equipment. Test equipment such as rotorcraft test bench and far-field noise measurement system are installed in sequence in the center of the acoustic wind tunnel.

[0007] The far-field noise measurement system consists of multiple quarter-circular microphone arms, free-field microphones, and synchronous data acquisition equipment. The radius of each quarter-circular microphone arm is no less than three times the characteristic dimension of the rotorcraft and is located outside the wind tunnel jet. Multiple free-field microphones are mounted on each quarter-circular microphone arm. The angle between adjacent microphones on each quarter-circular microphone arm and the center of the arm is no greater than 10°. The microphone arrangement covers an area of ​​at least 0° to 70°. During testing, the microphones must be fitted with wind caps to reduce the impact of airflow on noise measurement. Specifically, the center of each quarter-circular microphone arm is located at the center of the wind tunnel, and the azimuth angle between adjacent arms and the wind tunnel center is no greater than 60°. After the test equipment is installed, system debugging is performed to ensure that all equipment is functioning properly. A microphone calibrator is then used to calibrate each microphone to ensure the accuracy of the acoustic measurement instruments.

[0008] S2: Background noise measurement. Turn on the acoustic wind tunnel to measure the background noise of a model of an aircraft without rotors at a given wind speed.

[0009] S3: Aerodynamic noise measurement of fuselage model. Install the fuselage model (with rotor hub) of the rotorcraft on the rotor test bench, turn on the acoustic wind tunnel and rotorcraft test bench, and measure the aerodynamic noise of the fuselage model of the rotorcraft under given wind speed and rotor hub speed.

[0010] S4: Aerodynamic noise measurement of the rotorcraft model. Install the rotorcraft model and perform dynamic balancing adjustments to ensure the system's dynamic balance level reaches G2.5 or higher. The rotor speed should avoid the natural vibration frequencies of the rotor and the rotorcraft test bench to ensure the test bench does not resonate. Then, sequentially turn on the rotorcraft test bench and the acoustic wind tunnel to measure the aerodynamic noise of the rotorcraft model under given wind speed and model conditions.

[0011] Preferred, the aerodynamic noise measurement of the rotorcraft model includes the following steps: S401: Start the rotorcraft test bench and adjust the rotorcraft model to the target attitude angle and target rotor speed; S402: Turn on the acoustic wind tunnel and adjust to the target test wind speed; during the wind speed adjustment process, manipulate the rotorcraft model in real time to ensure that the rotor thrust, pitch moment, roll moment and system vibration are within the safe range; S403: Manipulate the rotorcraft model's angle of attack to the test target value, trim it, and adjust the rotor model's vertical force to the test target value, adjusting it so that the rotor model's pitch moment and roll moment values ​​are close to 0; S404: Collect noise data at the required sampling frequency and sampling time; S405: Repeat S401-S404 to complete all planned test conditions; S406: First, stop the wind tunnel and simultaneously manipulate the rotorcraft model in real time to ensure that the rotor thrust, pitch moment, roll moment, and system vibration are within a safe range. Then, gradually reduce the rotorcraft test bench speed until it stops.

[0012] The data processing method for aerodynamic noise test data of rotorcraft models includes the following steps: S5: Wind tunnel test data processing. After obtaining the aerodynamic noise wind tunnel test data of the rotorcraft model, data processing and correction are required to reduce the influence of wind tunnel background noise, wind tunnel jet shear layer, atmospheric sound absorption effect, and the microphone itself on noise measurement.

[0013] Specifically, this includes data preprocessing, spectrum analysis, background noise correction, microphone effect correction, shear layer correction, and atmospheric sound absorption correction processes. S501: Data preprocessing includes data framing and filtering. Data framing is calculated as follows: in The discrete-time acoustic signal measured by the microphone. For the first The time-domain discrete acoustic signal of the frame. For frame length, For frame shift, This is a window function, and options include Hanning window, Hamming window, etc.

[0014] Filtering includes filtering algorithms such as low-pass filtering, high-pass filtering, and band-pass filtering.

[0015] S502: Spectrum analysis mainly converts the time-domain signal measured by the microphone into a frequency-domain signal for easier subsequent processing. Specifically... in The first measurement of the microphone Frame audio domain results For frequency, The sampling interval is denoted as .

[0016] S503: Background noise correction mainly includes two parts: wind tunnel background noise subtraction and rotor aerodynamic noise extraction. When the rotor model's aerodynamic noise is more than 3dB higher than the wind tunnel background noise, a spectral subtraction method can be used to suppress the influence of wind tunnel background noise on the rotor model's aerodynamic noise measurement. The wind tunnel background noise subtraction adopts the spectral subtraction method, as detailed below. In the formula, Frequency domain data of aerodynamic noise from a rotorcraft model measured by a microphone. The background noise frequency domain data is measured by the microphone. This is the frequency domain data after background noise has been subtracted.

[0017] Rotor aerodynamic noise extraction is primarily based on the fact that rotor-related aerodynamic noise is periodically stationary, while wind tunnel background noise and support device aerodynamic noise are not. Phase averaging can be used to suppress the influence of these non-periodic noises on the rotor model aerodynamic noise measurement. First, the acoustic signal after wind tunnel background noise subtraction is segmented, and cross-correlation analysis is used for phase shifting to align the rotor-related periodic acoustic signals. Then, averaging is performed, i.e.: In the formula, The maximum average number of frames is determined by the signal-to-noise ratio requirement. For the first frame and the second frame The time corresponding to the phase shift of a frame. This is the extracted time-domain discrete signal of rotor aerodynamic noise. For the first The discrete-time signal after frame background noise is subtracted.

[0018] S504: Microphone self-influence correction. This includes corrections for the influence of the microphone housing, microphone hood, and nose cone. The specific corrections required depend on the housing, hood, and nose cone on which the microphone is installed. The correction methods are as follows: It is the angle of incidence of the sound wave from the sound source to the microphone. To correct sound pressure level, To measure sound pressure level, The correction factor for the protective shield, nose cone, or hood is specifically calibrated in the anechoic chamber.

[0019] S505: Shear Layer Influence Correction. The refraction effect caused by sound waves passing through the shear layer of an acoustic wind tunnel jet alters the direction of sound wave propagation and the magnitude of the sound pressure. The refraction effect is related to the incident angle of the sound wave in the shear layer and the Mach number within the jet. During aeroacoustic experiments, propagation path correction and amplitude correction are necessary for noise measurement data. The shear layer is typically modeled as an infinitely thin shear layer, and corrections are performed using Amiet theory; relevant literature can be consulted.

[0020] S506: Atmospheric sound absorption correction. Sound waves propagating in the air experience sound absorption, leading to sound attenuation. The amount of sound attenuation is related to atmospheric temperature, humidity, pressure, sound wave frequency, and propagation distance. The formula for atmospheric sound absorption correction is as follows: in, This is the sound pressure level after correction for air absorption. This is the sound pressure level before air absorption correction. For the distance sound travels, It is the sound intensity attenuation coefficient in air (dB / m), which is related to atmospheric temperature, humidity, pressure, and sound wave frequency.

[0021] S6: Extrapolation method from wind tunnel test data of aerodynamic noise of rotorcraft model to physical objects.

[0022] Wind tunnel tests of aerodynamic noise of rotorcraft must follow aeroacoustic similarity criteria to ensure geometric, kinematic, dynamic, structural, and fluid similarity between the model and the actual aircraft. Due to wind tunnel size limitations, scaled-down models are usually used, and the kinematic characteristics of the model and the actual aircraft relative to the measurement points are inconsistent. Therefore, Doppler effect correction and model scale correction are required for the wind tunnel test data of the rotorcraft model in order to extrapolate the aerodynamic noise wind tunnel test results of the model to the actual aircraft for evaluation of the aerodynamic noise characteristics of the rotorcraft.

[0023] S601: Doppler effect correction is mainly used to correct the influence of the physical motion of a rotorcraft on sound propagation, including propagation path correction and frequency correction, specifically... In the formula This is the distance between the model and the microphone during wind tunnel testing. The angle of incidence of the sound wave from the sound source to the microphone during wind tunnel testing; The frequency of sound radiated by the rotorcraft model during wind tunnel testing; For wind tunnel testing Mach number; This represents the distance between the rotorcraft model and the measuring point. The corrected sound frequency corresponds to the sound frequency radiated by the actual object.

[0024] S602: Model scale correction is mainly used to extrapolate the aerodynamic noise wind tunnel test results of a scaled-down rotorcraft model to a full-scale model while satisfying the aeroacoustic similarity criterion. This includes model scale correction and distance effect correction. The rotorcraft model scale correction method is as follows: In the formula For the characteristic dimensions of a physical rotorcraft, For the characteristic scale of rotorcraft models, The distance between the actual rotorcraft and the measuring point. The distance between the rotorcraft model and the measuring point. The sound pressure level of the rotorcraft model after wind tunnel testing data processing. The sound pressure level of a physical rotorcraft.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention proposes a standardized wind tunnel testing method for rotorcraft aerodynamic noise based on the aerodynamic noise radiation characteristics of rotorcraft and the acoustic wind tunnel environment. This method can effectively measure the aerodynamic noise radiation characteristics of rotorcraft. It establishes a standardized data processing flow and method for rotorcraft model aerodynamic noise wind tunnel tests and pioneers a method for extrapolating wind tunnel test results from rotorcraft model aerodynamic noise to physical models. This method effectively corrects for the influence of wind tunnel background noise, microphone structure, wind tunnel jet shear layer, atmospheric sound absorption effect, Doppler effect, and model size on rotorcraft aerodynamic noise assessment, improving the accuracy of experimental measurements and effectively evaluating rotorcraft aerodynamic noise performance. In summary, the wind tunnel testing method for rotorcraft aerodynamic noise performance assessment of this invention has a standardized experimental flow, clear data processing theory, and feasible data processing methods, providing methodological and technical support for rotorcraft aerodynamic noise assessment and noise reduction optimization verification. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 Flowchart for wind tunnel testing of aerodynamic noise of a rotorcraft model; Figure 2 Flowchart for processing aerodynamic noise test data of a rotorcraft model; Figure 3Comparison of time-domain results before and after processing aerodynamic noise data of a typical helicopter rotor model in forward flight state; Figure 4 Comparison of frequency domain results before and after processing aerodynamic noise data of a typical helicopter rotor model in forward flight state; Figure 5 This is a schematic diagram of the rotor noise directivity measurement results in forward flight mode. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0028] This embodiment includes two parts: a wind tunnel testing method for aerodynamic noise of a rotorcraft model and a method for processing test data. The wind tunnel testing method for aerodynamic noise of a rotorcraft model is as follows: Figure 1 As shown, taking a helicopter rotor model as the object, the details are as follows: S1: Installation and Debugging of Test Equipment. The rotorcraft test bench, far-field noise measurement system, and other test equipment are installed sequentially at the center of the acoustic wind tunnel. The far-field noise measurement system consists of six quarter-circular microphone arms, free-field microphones, and synchronous data acquisition equipment. The radius of each quarter-circular microphone arm is six times the radius of the rotor model and is located outside the wind tunnel jet. Nine free-field microphones are installed on each quarter-circular microphone arm, with an angle θ of 10° between adjacent microphones and the center of the arm. The microphone arrangement ranges from 0° to 80°, and the microphones are fitted with wind caps during testing. When installing the far-field noise measurement system, the center of the quarter-circular microphone arm is located at the center of the wind tunnel, with azimuth angles ψ relative to the rotor hub center of 45°, 90°, 135°, 225°, 270°, and 315°, respectively. After completing the installation of the test equipment, system debugging is performed to ensure that all equipment is functioning properly. Each microphone is calibrated using a microphone calibrator to ensure the accuracy of the acoustic measurement instruments.

[0029] S2: Background noise measurement. Turn on the acoustic wind tunnel and measure the background noise of a model of a non-rotor aircraft at a given wind speed. S3: Aerodynamic noise measurement of the fuselage model. Install the fuselage model (with rotor hub) of the rotorcraft on the rotor test bench, turn on the acoustic wind tunnel and the rotorcraft test bench, and measure the aerodynamic noise of the fuselage model of the rotorcraft under given wind speed and rotor hub speed.

[0030] S4: Aerodynamic noise measurement of the rotorcraft model. Install the rotorcraft model and perform dynamic balancing adjustments to ensure the system's dynamic balance level reaches G2.5 or higher. The rotor speed should avoid the natural vibration frequencies of the rotor and the rotorcraft test bench to ensure the test bench does not resonate. Then, sequentially turn on the rotorcraft test bench and the acoustic wind tunnel to measure the aerodynamic noise of the rotorcraft model under given wind speed and model conditions.

[0031] The specific steps for measuring the aerodynamic noise of a rotorcraft model are as follows: S401: Start the rotorcraft test bench and adjust the rotorcraft model to the target attitude angle and target rotor speed; S402: Turn on the acoustic wind tunnel and adjust it to the target test wind speed; during the wind speed adjustment process, operate the rotorcraft test bench in real time to ensure that the rotor model's thrust, pitch moment, roll moment, and system vibration are within a safe range; S403: Manipulate the rotorcraft model's angle of attack to the test target value, trim it, and adjust the rotor model's vertical force to the test target value, adjusting it so that the rotor model's pitch moment and roll moment values ​​are close to 0; S404: Collect raw noise data at the required sampling frequency and time; S405: Repeat S401-S404 to complete all planned test conditions; S406: First, stop the wind tunnel and simultaneously manipulate the rotorcraft model in real time to ensure that the rotor thrust, pitch moment, roll moment, and system vibration are within a safe range. Then, gradually reduce the rotorcraft test bench speed until it stops.

[0032] Data processing methods for aerodynamic noise tests on rotorcraft models, such as Figure 2 As shown, this includes wind tunnel test data processing and extrapolation methods from wind tunnel test data of rotorcraft model aerodynamic noise to physical objects.

[0033] S5: Wind Tunnel Test Data Processing. After obtaining the raw data of the rotorcraft model's aerodynamic noise wind tunnel test, the raw data is sequentially preprocessed, subjected to spectrum analysis, background noise correction, microphone self-influence correction, shear layer correction, and atmospheric sound absorption correction to obtain high-precision rotorcraft model aerodynamic noise wind tunnel test data. Data preprocessing includes data framing and filtering; background noise correction includes wind tunnel background noise subtraction and rotor aerodynamic noise extraction; microphone self-influence correction includes microphone shield influence correction and microphone hood influence correction; and shear layer influence correction includes propagation path correction and amplitude correction.

[0034] S6: The extrapolation method from wind tunnel test data of rotorcraft aerodynamic noise to the actual aircraft includes Doppler effect correction and model scale correction. Doppler effect correction includes propagation path correction and frequency correction, while model scale correction includes model scaling correction and distance effect correction.

[0035] Figure 3 The time-domain comparison results of the aerodynamic noise of a typical helicopter rotor model in forward flight state before and after correction are given. As can be seen from the figure, after processing the rotor noise measurement data by the rotor aircraft aerodynamic noise data processing method of the present invention, the rotor noise can be accurately extracted and separated. The extracted noise exhibits typical sawtooth wave characteristics, clearly reflecting the time variation law of rotor aerodynamic noise, which is consistent with the theoretical analysis results of rotor aerodynamic noise. Figure 4 The results of frequency domain comparison before and after aerodynamic noise correction for a typical forward-flying helicopter rotor model are presented. As can be seen from the figure, after processing the rotor noise measurement data using the rotorcraft aerodynamic noise data processing method of this embodiment, the error between the rotor blade passing frequency noise and the original data is no greater than 0.2dB. Figure 5 The results of noise directivity measurements at 90° and 270° azimuths during forward flight are presented. As shown in the figure, under these conditions, the noise on the advancing side of the rotor (right side of the figure) is significantly higher than the noise on the retreating side, and the noise on the advancing side mainly propagates towards the area approximately 30° below the rotor plane. A larger thrust system Ct corresponds to higher noise on the advancing side. In summary, this embodiment presents a wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft. This method can effectively measure the aerodynamic noise radiated by a helicopter rotor, effectively correct for the influence of the acoustic wind tunnel environment on the aerodynamic noise of the helicopter rotor, and provide a high-precision evaluation of the aerodynamic noise performance of the helicopter rotor.

[0036] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft, characterized in that... Includes the following steps: S1: Install the rotorcraft test bench and far-field noise measurement system sequentially in the center of the acoustic wind tunnel, and then debug them; S2: Measure the background noise of a model of an aircraft without rotors at a given wind speed; S3: Install a fuselage model with a rotor hub on a rotor test bench and measure the aerodynamic noise of the fuselage model under given wind speed and rotor hub speed. S4: Install the rotor model and measure the aerodynamic noise of the rotorcraft model under given wind speed and model conditions; S5: Perform data processing and correction on the aerodynamic noise data of the rotorcraft model; S6: Perform Doppler effect correction and model scaling correction on the processed data to extrapolate the experimental results to the actual object and evaluate the characteristics of the aerodynamic noise of the rotorcraft.

2. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 1, characterized in that... The far-field noise measurement system includes multiple arc-shaped microphone arms located outside the wind tunnel jet, and multiple free-field microphones are installed on the arc-shaped microphone arms.

3. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 2, characterized in that... The radius of the arc-shaped microphone arm is not less than three times the characteristic dimensions of the rotorcraft.

4. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 2, characterized in that... The angle between adjacent free-field microphones on each arc-shaped microphone arm and the center of the arm shall not exceed 10°, and the arrangement range of all free-field microphones on the arc-shaped microphone arm shall cover at least 0° to 70°.

5. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 4, characterized in that... The center of one of the arc-shaped microphone arms is located at the center of the wind tunnel, and the azimuth angle of the other adjacent arc-shaped microphone arms relative to the center of the wind tunnel is no greater than 60°.

6. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 1, characterized in that... The aerodynamic noise measurement of the rotorcraft model includes the following steps: S401: Start the rotorcraft test bench and adjust the rotorcraft model to the target attitude angle and target rotor speed; S402: Turn on the wind tunnel and adjust to the target test wind speed; S403: Manipulate the rotorcraft model's angle of attack to the test target value, trim it, and adjust the rotorcraft model's vertical force to the test target value, adjusting it so that the rotorcraft model's pitching moment and rolling moment values ​​are close to zero; S404: Collect noise data according to the set acquisition frequency and acquisition time; S405: Repeat the process from S401 to S404 to complete all test conditions; S406: Wind tunnel shutdown. The rotorcraft model is manipulated in real time to ensure that the rotor thrust, pitch moment, roll moment, and system vibration are within a safe range. The rotorcraft test bench speed is gradually reduced until it stops.

7. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 1, characterized in that... The processing of the aerodynamic noise data of the rotorcraft model includes the following steps: S501: Preprocess the data, including framing and filtering the time-domain discrete sound signal measured by the microphone; S502: Perform spectrum analysis on the preprocessed data to convert the time-domain signal measured by the microphone into a frequency-domain signal; S503: Background noise is corrected by using a spectral subtraction method to reduce wind tunnel background noise and a phase averaging method to suppress the influence of background noise and other noises on rotor noise; the phase averaging method is as follows: ， In the formula, The maximum average number of frames is determined by the signal-to-noise ratio requirement. For the first frame and the second frame The time corresponding to the phase shift of a frame. This is the extracted time-domain discrete signal of rotor aerodynamic noise. For the first The discrete-time signal after frame background noise subtraction, S504: Corrects the microphone's own effects based on the correction factors of the microphone's protective cover, hood, and nose cone; S505: Corrects the effects of the airflow shear layer, including propagation path correction and amplitude correction; S506: Correction for atmospheric sound absorption effect.

8. The wind tunnel testing method for evaluating the aerodynamic noise performance of a rotorcraft according to claim 1, characterized in that... The Doppler effect correction is used to correct the influence of the physical motion of a rotorcraft on sound propagation, including: Propagation path correction ， Frequency correction, ， The model scale correction is used to extrapolate the aerodynamic noise wind tunnel test results of a scaled-down rotorcraft model to a full-size model while satisfying the aeroacoustic similarity criterion. This includes model scale correction and distance effect correction, and the correction method is as follows: ， in: This refers to the distance between the model and the microphone during wind tunnel testing. The angle of incidence of the sound wave from the sound source to the microphone during wind tunnel testing. The frequency of sound radiated by the rotorcraft model during wind tunnel testing. To determine the Mach number for wind tunnel testing, The distance between the rotorcraft model and the measuring point. To ensure that the corrected sound frequency corresponds to the sound frequency radiated by the actual object. For the characteristic dimensions of a physical rotorcraft, For the characteristic scale of rotorcraft models, The distance between the actual rotorcraft and the measuring point. The sound pressure level of the rotorcraft model after wind tunnel testing data processing. The sound pressure level of a physical rotorcraft.

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