Test method and test system for droplet impingement on rotors based on acoustic probing

Abstract

The present application relates to the water-gas mixing flow field measurement technology field of cross-medium rotorcraft, and provides a kind of test method and test system for liquid drop impact rotor based on acoustic detection.The method comprises: differential working condition design, control rotor rotates at different height and speed;Data acquisition, through the sound pressure signal detection device arranged at 6R-9R from the center of the rotor disc, multi-channel time domain sound pressure signal is collected, and sound pressure level spectrum is obtained by FFT transformation;Sound source positioning, limit the analysis target in the rotor disc range, and filter out the liquid drop impact target sound source signal in the rotor disc;Feature recognition, identify the risk feature distribution band in spectrum, and mark the corresponding working condition as risk working condition.The present application uses acoustic detection to capture liquid drop impact noise, removes the interference outside the rotor disc by sound source positioning, solves the problem that traditional optical measurement is blocked by water curtain, and provides high signal-to-noise ratio data basis for drag loss evaluation and blade structure damage risk analysis of rotor near water surface operation.

Description

Technical Field

[0001] This invention belongs to the field of water-air mixing flow field measurement technology for cross-medium rotorcraft, specifically relating to a test method and test system for droplet impact on rotor based on acoustic detection. Background Technology

[0002] When a rotorcraft crosses a medium, its rotor is very close to the water surface, resulting in a large-scale, complex multiphase flow field containing droplets, waves, and rotor wakes (hereinafter referred to as the water-air mixed flow field, see reference). Figure 1 This leads to the near-water surface effect of the rotor. Existing research indicates that droplets may play a dominant role in the rotor's aerodynamic forces during the near-water surface effect; the interaction between droplets and the rotor results in significant thrust loss in the water-air mixed flow field. Furthermore, the impact of droplets on the high-speed rotor can cause structural damage to the carbon fiber blades.

[0003] Due to limitations in measurement methods, the impact of droplets on rotor aerodynamic characteristics is difficult to assess. At low speeds, when no droplets are generated, only water surface depressions affect the rotor. As the speed increases, the depressions enlarge, the water surface breaks violently, and a large number of droplets impact the rotor. However, the large number of splashed droplets forms a water curtain around the rotor disk, making it impossible to capture the interaction between droplets and the rotor using a high-speed camera. To study the impact of droplets on rotor aerodynamic characteristics, a new testing method is urgently needed to quantify the impact between droplets and the rotor. Summary of the Invention

[0004] This invention addresses the challenge of measuring droplets in rotor-induced water-air mixed flow fields using traditional optical measurement methods, proposing a test method and system for droplet impact on rotors based on acoustic detection.

[0005] Firstly, this disclosure provides a testing method for droplet impact on a rotor based on acoustic detection, including a differential operating condition design step, a data acquisition step, a sound source localization step, and a feature recognition and analysis step. In the differential operating condition design step, the rotor blades are controlled to rotate under different operating conditions, the characterization parameters of which include at least the height of the rotor blades above the water surface and the rotational speed of the rotor blades. In the data acquisition step, for each operating condition, a sound pressure signal detection device arranged at a distance of 6R to 9R from the center of the rotor disk acquires time-domain sound pressure signals from multiple channels, where R is the rotor radius, and performs a fast Fourier transform on the time-domain sound pressure signals to obtain sound pressure level spectrum diagrams for multiple channels. In the sound source localization step, the analysis target is limited to the rotor disk area of ​​the rotor blades by the sound source localization detection device, and the sound pressure level spectrum diagram corresponding to the target sound source signal generated by droplets impacting the rotor blades within the rotor disk is selected. In the feature identification and analysis step, the selected sound pressure level spectrum is divided into frequency bands, the risk characteristic distribution frequency band is identified, and the working conditions corresponding to the sound pressure level spectrum with the risk characteristic distribution frequency band are marked as risky working conditions.

[0006] Preferably, the sound pressure signal detection device is arranged at a distance from the center of the propeller disk that simultaneously satisfies three conditions: it satisfies the acoustic engineering far-field condition, i.e., the test distance r ≥ 3D, where D is the characteristic size of the sound source; it avoids the droplet splashing area, the maximum splash radius of which is 3R~3.5R; and it avoids interference from the downwash flow field, so that the aerodynamic noise induced by the downwash airflow is lower than the droplet impact noise.

[0007] In some implementations, the sound pressure signal detection device employs a four-channel microphone array, with the four microphones positioned at the four corners of the rotor test stand extending outwards at a certain distance. During the data acquisition step, the sound pressure level spectrum of the four channels is averaged to obtain an average spectrum for subsequent analysis.

[0008] Specifically, the risk characteristic distribution frequency band includes at least one of the following characteristics: Characteristic 1 is the disappearance of harmonic structure, where integer multiples of the rotor rotation frequency harmonic peaks are masked by continuously distributed broadband noise, and the spectrum curve changes from a peak shape to a flat shape; Characteristic 2 is the rise of the high-frequency broadband noise floor, where the sound pressure level is raised by more than 5dB compared to the baseline of the same frequency band far from the water surface; Characteristic 3 is the appearance of a broadband energy concentration area with a bandwidth greater than 1000Hz.

[0009] Furthermore, during the data acquisition process, force sensors are used to collect data on the tension and torque generated by the rotor rotation, and speed detectors are used to collect data on the rotor speed. The collected mechanical data, speed data, and time-domain sound pressure signals are recorded and stored synchronously on the same time reference for subsequent qualitative or quantitative analysis of risky operating conditions.

[0010] Secondly, this disclosure also provides a test system for droplet impact on a rotor based on acoustic detection, including a rotor test stand and a data acquisition system. The rotor test stand includes a rotor assembly, a height adjustment mechanism, an acoustic detection module, and a support frame. The support frame is adapted to set or install the rotor assembly and the height adjustment mechanism. The rotor assembly includes rotor blades, a rotor motor, and a force sensor. In some embodiments, the support frame is configured to include a column and a crossbar, the crossbar being connected to the column, and the rotor motor being connected to the crossbar via a force sensor. The height adjustment mechanism is connected to the rotor assembly and is used to adjust the height of the rotor blades relative to the water surface. The acoustic detection module includes a sound source localization detection device and a sound pressure signal detection device. The sound pressure signal detection device is arranged at a distance of 6R to 9R from the center of the rotor disk and is used to collect the sound pressure signal generated by the droplet impact on the rotor blades. The sound source localization detection device is used to limit the sound source localization range to within the rotor disk area. The data acquisition system is electrically connected to the force sensor, the sound source localization detection device, and the sound pressure signal detection device, respectively, and is used to perform the data processing and feature analysis steps in the test method described in the first aspect.

[0011] In some implementations, the acoustic detection module is configured as an integrated microphone array, or as a combination of a separate acoustic camera and multiple microphones. The sound source localization detection device is mounted above the crossbar, and its field of view covers the rotor disk area of ​​the rotor blades. The sound pressure signal detection device includes four microphones, each positioned at a certain distance outward from one of the four corners of the rotor test stand.

[0012] In some implementations, the data acquisition system is configured to perform the following signal processing flow: process multi-channel signals through beamforming and cross-correlation algorithms to filter out water surface breaking noise, motor electromagnetic noise and environmental steady-state noise; and cancel steady-state background noise through adaptive filtering algorithms to extract droplet impact feature signals.

[0013] In some implementations, the height adjustment mechanism is a stepper motor, which is fixed to a crossbar. The output shaft of the stepper motor is connected to the housing of the rotor motor via a rigid coupling, so as to drive the rotor assembly to move vertically.

[0014] Furthermore, the testing system also includes a speed detector, which is connected to the rotor motor to measure the real-time rotational speed of the rotor blades and transmit the speed data to the data acquisition system.

[0015] The features and advantages of this disclosure include: capturing the noise signal of the interaction between droplets and blades in a water-air mixed flow field through acoustic measurement, and using the sound source localization method to limit the analysis target to the blade disk area, eliminating the interference sound source signal outside the blade disk, thereby extracting the target sound source signal of the droplet impact with the rotor, providing a data basis for the risk analysis of blade structural damage in a water-air mixed flow field. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The image shows a real-world scene of a water-air mixing flow field induced by the rotor;

[0018] Figure 2 A schematic diagram of the system block of a test system for droplet impact on a rotor based on acoustic detection is shown.

[0019] Figure 3 A schematic diagram of the structural layout of a test system for droplet impact rotor based on acoustic detection is shown.

[0020] Figure 4 A schematic diagram of the structure of the rotor blades, rotor motor, force sensor, and speed detector is shown.

[0021] Figure 5 A schematic diagram of a test method for droplet impact on a rotor based on acoustic detection is shown;

[0022] Figures 6 to 9 The average spectrum of the multi-channel sound pressure level of the noise generated by the droplet impacting the blade based on sound source localization is shown under four different operating conditions.

[0023] Figure label: 100-Testing system, 10-Rotor test stand, 11-First column, 12-Second column, 13-First crossbar, 14-Second crossbar, 20-Support frame, 22-Rotor blade, 24-Rotor motor, 25-Height adjustment mechanism, 26-Force sensor, 28-Speed ​​detector, 32-Sound source localization detection device, 34-Sound pressure signal detection device, 40-Data acquisition system. Detailed Implementation

[0024] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0025] According to one aspect of the present invention, a test system for droplet impact on a rotor based on acoustic detection is provided, which is used to obtain the sound pressure level signal of noise generated by the interaction between droplets and blades under different operating conditions in a rotor-induced water-air mixed flow field, thereby laying the foundation for subsequent qualitative or quantitative data analysis.

[0026] refer to Figure 2 The diagram shows a system block diagram of a test system 100 for testing droplet impact on a rotor based on acoustic detection. The test system 100 includes a rotor test bench 10 and a data acquisition system 40. The rotor test bench 10 includes a support frame 20, rotor blades 22, rotor motor 24, height adjustment mechanism 25, force sensor 26, speed detector 28, sound source localization detection device 32, and sound pressure signal detection device 34.

[0027] The support frame 20 is suitable for setting or mounting the rotor blades 22, rotor motor 24, height adjustment mechanism 25, force sensor 26, and speed detector 28. The rotor motor 24, height adjustment mechanism 25, force sensor 26, and speed detector 28 are respectively coupled to the rotor blades 22. The rotor motor 24 is used to provide torque to the rotor blades 22, the height adjustment mechanism 25 is used to adjust the height of the rotor blades 22 relative to the test water surface, the force sensor 26 is used to measure the aerodynamic force generated when the rotor blades 22 rotate, and the speed detector 28 is used to measure the rotational speed of the rotor blades 22.

[0028] The sound source localization and detection device 32 (e.g., an acoustic camera) and the sound pressure signal detection device 34 (e.g., a microphone) are positioned to capture the noise signal generated by the impact of droplets on the rotor blades 22 within the rotor disk area. They should be positioned as far away from the water surface and the high-speed rotating rotor blades 22 as possible, for example, near the support frame 20 or on the support frame 20 away from the rotor blades 22. The sound source localization and detection device 32 is used to locate the sound source, thereby limiting the spatial range of the noise signal. The sound pressure signal detection device 34 is used to measure the sound pressure of the noise signal generated by the interaction between the droplets and the rotor blades 22 during rotor blade rotation. By using the sound source localization and detection device 32, the spatial range of the noise signal is localized within the rotor disk area of ​​the rotor blades 22, interfering sound source signals outside the rotor disk are eliminated, and the target acoustic signal of the droplet impacting the rotor is extracted, thus limiting the scope of subsequent data analysis.

[0029] When the distance between the rotor blade 22 and the water surface is different, the aerodynamic data measured by the force sensor 26 is different, and / or the rotational speed data measured by the speed detector 28 is different, the rotor blade 22 corresponds to different operating conditions. By using the sound source localization detection device 32 to locate the noise signal within the disk area of ​​the rotor blade 22, and the data acquisition system 40 synchronizing the mechanical signal and the target acoustic signal, experimental data under different operating conditions can be obtained.

[0030] In some implementations, reference Figure 3 The diagram shows the structural arrangement of a test system for droplet impact on a rotor based on acoustic detection. The support frame 20 is constructed including a first column 11, a second column 12, and a first crossbar 13. The two ends of the first crossbar 13 are fixed to the waist of the first column 11 and the waist of the second column 12, respectively. The space below the first column 11, the second column 12, and the first crossbar 13 is suitable for arranging the water surface required for the experiment. (See also...) Figure 3 and Figure 4 Specifically, the force sensor 26 is configured as a six-axis force sensor, and the speed detector 28 is configured as a speed encoder. The six-axis force sensor and the speed encoder are arranged above the rotor motor 24 to measure the thrust, torque, and speed generated by the rotor, respectively. The rotor blade 22, rotor motor 24, force sensor 26, and speed detector 28 are coaxially attached to the first crossbar 13, so that the rotor blade 22 is suspended below the first crossbar 13.

[0031] Preferably, the height adjustment mechanism 25 is configured as a stepper motor, which is mounted on the first crossbar 13. The output shaft of the stepper motor is coupled to the rotor blade 22 in the height direction of the support frame 20. The stepper motor is used to adjust the vertical height of the rotor blade 22, that is, to adjust the distance between the rotor blade 22 and the water surface. Specifically, the output shaft of the stepper motor is fixedly connected to the housing of the rotor motor 24 through a rigid coupling. The rotor motor 24 as a whole can move slightly in the height direction, thereby changing the height of the rotor blade 22 above the water surface. The stator of the stepper motor is fixed on the first crossbar 13. Its adjustment accuracy can be accurate to 0.1 mm.

[0032] In some embodiments, the sound source localization detection device 32 and the sound pressure signal detection device 34 are configured as an integrated detection device, for example, as a microphone array. That is, the same microphone array can provide both sound source localization and sound pressure signal detection functions. Optionally, the microphone array is a distributed array, which is mounted on top of the first column 11 and the second column 12. Optionally, the microphone array is a circular array or a spherical array, as shown in the reference. Figure 3 The support frame 20 also includes a second crossbar 14, the two ends of which are fixed to the tops of the first column 11 and the second column 12, respectively, and a circular or spherical microphone array is installed in the middle of the second crossbar 14.

[0033] In other embodiments, the sound source localization detection device 32 and the sound pressure signal detection device 34 are configured as separate detection devices. In some embodiments, the sound source localization detection device 32 is configured as a single microphone, or as an acoustic camera (acoustic imager) with a built-in microphone; the sound pressure signal detection device 34 is configured as a plurality of microphones, each microphone capable of acquiring the sound pressure signal of one channel, the number of channels being configurable to 2 to 6, for example... Figure 3 The diagram illustrates the arrangement of microphones capable of acquiring sound pressure signals from four channels. The mounting positions of the microphone array or acoustic imager are similar to those of the aforementioned integrated acoustic detection device and will not be described further.

[0034] Preferably, the acoustic camera (sound source localization and detection device 32) is installed in the middle of the second crossbar 14, at a vertical distance of approximately 5.4R (R represents the rotor radius) from the center of the rotor rotation plane, with a horizontal offset not exceeding 0.3 m. This position ensures that the field of view of the acoustic camera (approximately 60°~90°) can completely cover the 2R diameter rotor disk and the droplet impact area within a 0.3 m radius around it, while remaining away from the rotor downwash flow field and the water splash area.

[0035] Four microphones (sound pressure signal detection devices 34) are respectively arranged at the four corners of the support frame 20, extending outwards at a certain distance. The horizontal distance of the four microphones from the center of the rotor's rotation plane is 6R to 9R, preferably 6R. Preferably, this distance satisfies the acoustic far-field condition (r ≥ 3D), ensuring that the measured sound pressure signal is not contaminated by near-field hydrodynamic pressure fluctuations, while avoiding the droplet splash zone (maximum splash radius approximately 3R to 3.5R). Here, r represents the test distance, i.e., the distance from the sound pressure signal detection device 34 at the measurement point to the center of the sound source, and D represents the maximum geometric dimension of the sound source system.

[0036] This invention employs multiple microphones, such as a four-channel microphone array, offering advantages in spatially resolved sound source localization, data reliability, and anti-interference capabilities. Precise sound source localization is achieved through multi-channel synchronous acquisition combined with beamforming and cross-correlation algorithms. This strictly limits the analysis area to the target sound source of droplet impacts within the propeller disk, effectively filtering out spatially heterogeneous interference sources such as water surface breakage, motor electromagnetic noise, and environmental steady-state noise. Independent sampling across multiple channels creates signal redundancy; when a single channel experiences sudden interference, cross-validation or interpolation compensation can be performed using data from other channels, significantly improving the robustness of experimental data. The spatial differences in sound pressure levels among array units are used to invert the sound field inhomogeneity, thereby inferring the spatial distribution characteristics of droplet impact density on the propeller disk surface, providing a quantitative basis for rotor structure damage risk assessment. Adaptive filtering algorithms are used to jointly process the signals from each channel, accurately estimating and canceling the background noise floor, significantly improving the signal-to-noise ratio of droplet impact characteristic signals and ensuring the effective extraction of weak acoustic features.

[0037] The microphone is positioned 6R from the center of the rotor disk, primarily balancing measurement accuracy and environmental adaptability. This distance meets the basic requirements for the far field in acoustic engineering, helps reduce near-field acoustic measurement errors, and ensures the validity of experimental data. Simultaneously, this position effectively avoids interference from droplet splashes and high-speed downwash flow fields in a water environment, preventing microphone contamination or mechanical damage from droplets, and significantly reduces the interference of aerodynamic noise induced by the downwash airflow on the acquired signal, ensuring that the obtained acoustic signal is primarily characterized by droplet impact on the rotor. This arrangement, while ensuring measurement accuracy, also addresses the needs of equipment protection and noise measurement in complex water-air mixed environments.

[0038] According to another aspect of the present invention, a test method for droplet impact on a rotor based on acoustic detection is provided. By testing and analyzing the acoustic pressure signals of droplet impact on the rotor under different operating conditions, it is possible to determine under which operating conditions the rotor is at risk of blade structural damage.

[0039] refer to Figure 5 A test method 200 for droplet impact rotor based on acoustic detection includes: differential operating condition design 210, collecting acoustic experimental data under multiple operating conditions 220, locating the spatial range of the target sound source 230, and performing feature identification and analysis on the sound pressure level spectrum under each operating condition 240.

[0040] Specifically, step 210, the differential operating condition design, includes: rotating the rotor blades under different operating conditions, wherein the characteristic parameters of the operating conditions include the height of the rotor blades above the water surface, the rotational speed of the rotor blades, and the thrust and torque generated by the rotor rotation. Step 220, collecting acoustic experimental data under multiple operating conditions, includes: for each operating condition, acquiring time-domain sound pressure signals from multiple channels using a sound pressure signal detection device, wherein the time-domain sound pressure signals include at least the noise signal generated by droplets impacting the rotor blades, and transforming the time-domain sound pressure signals from multiple channels using a fast Fourier transform to obtain sound pressure level spectrum diagrams for multiple channels. Step 230, locating the spatial range of the target sound source, includes: using a sound source location detection device to ensure that the sound pressure level spectrum diagrams of multiple channels used for analysis and evaluation correspond to the sound pressure level spectrum diagram of the target sound source signal generated by droplets impacting the rotor blades within the rotor disk area. Step 240, which involves feature identification and analysis of the sound pressure level spectrum under each working condition, includes: dividing the sound pressure level spectrum obtained in step 230 into frequency bands, analyzing the distribution of sound pressure level (SPL) in different frequency bands, and marking the working conditions corresponding to the sound pressure level spectrum of the frequency band with risky distribution characteristics as risky working conditions.

[0041] For example, the risk characteristic distribution band refers to any of the following characteristics appearing in the high-frequency region (1000 Hz ~ 10000 Hz) in the sound pressure level spectrum:

[0042] Feature 1: Disappearance of Harmonic Structure. Under normal operating conditions, integer multiples of the rotor rotation frequency can be clearly identified in the spectrum. When a large number of droplets impact the blades, these discrete harmonic peaks are "submerged" by continuously distributed broadband noise, and the spectrum curve changes from "peaked" to "flat". Each droplet impact generates a random transient pulse, and the superposition of a large number of random pulses forms broadband noise in the continuous spectrum, masking the originally clear harmonic structure. The disappearance of the harmonic structure means that the droplet impact events are sufficiently dense and intense.

[0043] Feature 2: High-frequency broadband noise floor increase. Within the 2000–8000 Hz frequency band, the overall sound pressure level increases by more than 5 dB (compared to the baseline of the same frequency band at locations far from the water surface). The high-frequency vibrations generated by droplet impacts on the propeller surface have the highest acoustic radiation efficiency in the 2000–8000 Hz frequency band. The magnitude of the noise floor increase is directly proportional to the number and kinetic energy of the impacting droplets per unit time.

[0044] Feature 3: The emergence of new broadband energy concentration regions. For example, a broad peak (bandwidth > 1000 Hz) appears in the 3000~6000 Hz range, corresponding to the characteristic noise generated by the interaction between the water mist formed by the atomization of droplets after impacting the blades and the rotor boundary layer.

[0045] Figures 6 to 9 The sound pressure level spectrum of the noise generated by droplet impact on rotor blades (with 2 blades) is shown in Table 1 under four operating conditions. Figures 6 to 9 The average spectrum of the four-channel sound pressure level corresponds to the four operating conditions a to d in Table 1. The rotor radius R is 0.28m, and the signals from the four channels were collected from... Figure 3 The four sound pressure signal detection devices 34 (microphones) are arranged as shown. "Tension fluctuation" refers to the ratio obtained by dividing the difference between the maximum and minimum tension values ​​under the measured working condition by the average tension value.

[0046] Table 1

[0047]

[0048] from Figure 6 and Figure 7 It can be seen that when the rotor is far from the water surface, the sound pressure level is relatively high in the low-frequency region (100 Hz to 1000 Hz), indicating that the rotor produces a strong sound in this frequency range. As the frequency increases, the sound pressure level gradually decreases, meaning that the intensity of the high-frequency sound is weaker. Several peaks appearing in the high-frequency region correspond to specific rotation frequencies of the rotor or their harmonics, and the higher-order harmonic components of the dominant frequency are clearly visible. Overall, the spectrum shows a trend of gradually decreasing sound pressure level with increasing frequency.

[0049] However, as the distance between the rotor and the water surface decreases, such as Figure 8 and Figure 9 In the high-frequency region (1000Hz to 10000Hz), the sound pressure level may be affected by the air density near the water surface and by droplets, resulting in a significant difference compared to the situation further away from the water surface. Overall, the spectrum still shows a trend of gradually decreasing sound pressure level with increasing frequency. However, because the rotor is closer to the water surface, more obvious peaks or fluctuations may appear at certain frequency points. This is mainly manifested in the fact that the originally clearly visible high-frequency harmonic components are masked by broadband noise, which is caused by changes in the medium density of the space near the rotor due to droplet impact on the rotor or droplet atomization after impact on the rotor.

[0050] from Figure 8 and Figure 9 As can be seen from the example, in the sound pressure level spectrum diagram, if there are no clearly visible high-frequency harmonic components in the high-frequency region, and it is basically broadband noise, then this sound pressure level spectrum diagram can be marked as a sound pressure level spectrum diagram with risky frequency bands, and the corresponding operating condition is marked as a risky operating condition.

[0051] This invention can use acoustic detection to determine the risk of blade structural damage under which the rotor is operating. In the water-air mixed flow field of high-speed blade rotation, the acoustic detection method can obtain reliable raw measurement data, providing a solid data foundation for subsequent signal processing, feature extraction, and qualitative / quantitative determination of the degree of structural damage.

[0052] The above descriptions are merely a few embodiments of this disclosure. Those skilled in the art can make various modifications or variations to the embodiments of this disclosure based on the content disclosed in the application documents without departing from the spirit and scope of this disclosure.

Claims

1. A test method for droplet impact on a rotor based on acoustic detection, characterized in that, Including the following steps: Differential operating condition design steps: Control the rotor blades to rotate under different operating conditions, and the characteristic parameters of the operating conditions include at least the height of the rotor blades above the water surface and the rotational speed of the rotor blades; Data acquisition steps: For each operating condition, the time-domain sound pressure signal of multiple channels is acquired by a sound pressure signal detection device arranged at a distance of 6R to 9R from the center of the rotor disk, where R is the rotor radius. The time-domain sound pressure signal is then subjected to a fast Fourier transform to obtain the sound pressure level spectrum of multiple channels. Sound source localization steps: The analysis target is limited to the rotor disk area of ​​the rotor blades using a sound source localization detection device; the sound pressure level spectrum corresponding to the target sound source signal generated by the impact of droplets within the rotor disk on the rotor blades is then selected; and... Feature identification and analysis steps: Divide the selected sound pressure level spectrum into frequency bands, identify the risk characteristic distribution frequency bands, and mark the working conditions corresponding to the sound pressure level spectrum with the risk characteristic distribution frequency bands as risky working conditions; In the data acquisition step, the force and torque data generated by the rotor rotation are also collected simultaneously through the force sensor, and the rotor speed data are collected through the speed detector. The collected mechanical data, speed data and time-domain sound pressure signal are recorded and stored synchronously on the same time reference for subsequent qualitative or quantitative analysis of risky working conditions. The sound pressure signal detection device is positioned at a distance from the center of the propeller disk that simultaneously satisfies: The acoustic engineering far-field condition must be met, i.e., the test distance r ≥ 3D, where D is the characteristic size of the sound source; Avoid the droplet splash zone, where the maximum splash radius is 3R~3.5R; To avoid interference from the downwash flow field, the aerodynamic noise induced by the downwash airflow is lower than the droplet impact noise.

2. The test method according to claim 1, characterized in that, The sound pressure signal detection device adopts a four-channel microphone array, with the four microphones arranged at the four corners of the rotor test stand extending outwards at a certain distance. In the data acquisition step, the sound pressure level spectrum of the four channels is averaged to obtain an average spectrum for subsequent analysis.

3. The test method according to claim 1, characterized in that, The risk characteristic distribution frequency band includes at least one of the following characteristics: Feature 1: The harmonic structure disappears, and the integer multiple harmonic peaks of the rotor rotation frequency are masked by continuously distributed broadband noise, and the spectrum curve changes from a sharp peak to a flat one. Feature 2: High-frequency broadband noise floor rise, with the sound pressure level rising by more than 5dB compared to the baseline of the same frequency band far from the water surface; Feature 3: A wideband energy concentration region with a bandwidth greater than 1000Hz appears.

4. A test system for droplet impact on a rotor based on acoustic detection, characterized in that, Includes rotor test bench and data acquisition system; The rotor test bench includes: Rotor assembly, including rotor blades, rotor motor and force sensor; A height adjustment mechanism, connected to the rotor assembly, is used to adjust the height of the rotor blades relative to the water surface; The acoustic detection module includes a sound source localization detection device and a sound pressure signal detection device. The sound pressure signal detection device is arranged at a distance of 6R to 9R from the center of the rotor disk and is used to collect the sound pressure signal generated by the impact of droplets on the rotor blades. The sound source localization detection device is used to limit the sound source localization range to the range of the rotor disk. A rotational speed detector, connected to the rotor motor, is used to measure the real-time rotational speed of the rotor blades; and A support frame, the support frame being adapted to house or mount rotor assemblies and a height adjustment mechanism; The data acquisition system is electrically connected to the force sensor, the sound source localization and detection device, the sound pressure signal detection device, and the speed detector, respectively, and is used to perform the data processing and feature analysis steps in the test method as described in any one of claims 1 to 3; The sound source localization detection device and the sound pressure signal detection device are arranged near the support frame or on the support frame.

5. The testing system according to claim 4, characterized in that, The support frame is constructed to include columns and crossbars, with the crossbars connected to the columns; the acoustic detection module is configured as an integrated microphone array, or as a combination of a separate acoustic camera and multiple microphones. The sound source localization and detection device is installed above the crossbar; The sound pressure signal detection device includes four microphones, which are respectively arranged at the four corners of the rotor test stand, extending outward at a certain distance.

6. The testing system according to claim 5, characterized in that, The data acquisition system is configured to perform the following signal processing procedure: Beamforming and cross-correlation algorithms are used to process multi-channel signals to filter out surface breakage noise, motor electromagnetic noise and environmental steady-state noise. An adaptive filtering algorithm is used to cancel out steady-state background noise and extract droplet impact feature signals.

7. The testing system according to claim 5, characterized in that, The rotor motor is connected to the crossbar via the force sensor; the height adjustment mechanism is a stepper motor, which is fixed to the crossbar, and the output shaft of the stepper motor is connected to the housing of the rotor motor via a rigid coupling to drive the rotor assembly to move vertically.

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