Open rotor engine noise data analysis system and method

Abstract

The invention discloses an open rotor engine noise data analysis system and method, and belongs to the field of aero-engine noise analysis and mixed reality visualization. The system comprises a mixed reality interaction module used for acquiring parameters of the open type rotor engine and constructing an open type rotor engine model; the wind tunnel environment building module is used for building a simulation test environment of a low / high-speed wind tunnel test; the flight environment building module is used for simulating operation noise of the open type rotor engine at different paddle angles in a simulation test environment; the noise analysis module is used for analyzing and processing the operation noise of the low / high-speed wind tunnel and the noise of the aircraft carrying the open rotor engine, and the dynamic visualization rendering module is used for displaying the noise data in a 3D histogram according to the noise data output by the noise analysis module, and rendering and updating the histogram in real time. And the efficiency and intuition of noise characteristic analysis and airworthiness evaluation of the open rotor engine are improved.

Description

Technical Field

[0001] This application relates to the field of aircraft engine noise analysis and mixed reality visualization, and in particular to an open rotor engine noise data analysis system and method. Background Technology

[0002] With the annual growth of global air transport volume, the density of airports and the frequency of flights worldwide have increased significantly, with daily takeoffs and landings exceeding 2,000 becoming the norm, and the number of aircraft has also increased substantially. Simultaneously, urban areas are increasingly located near airports, leading to a growing problem of noise pollution around airports, directly impacting the lives of many residents. Aircraft noise has become one of the core challenges to the sustainable development of the aviation industry. During flight, the engine and landing gear are the main sources of noise, and the engine is the primary factor contributing to the differences in noise levels between different aircraft. Therefore, in aircraft noise airworthiness certification, equivalent procedures based on static noise tests of the installed engines can be used to review aircraft noise during flight. To ensure that the design and manufacture of Chinese civil aircraft meet internationally accepted noise standards, promote the healthy development of my country's civil aviation industry, and further strengthen international exchanges, researchers need to conduct corresponding noise airworthiness certification tests on aircraft in a timely manner according to updated noise certification standards.

[0003] Open rotor engines, with their ductless, counter-rotating propeller design, can theoretically achieve a 25%-30% improvement in fuel efficiency, and are considered one of the next-generation civil aviation propulsion options. Furthermore, unlike traditional turboprop engines, open rotors can operate efficiently at cruise Mach numbers similar to turbofan-powered aircraft. However, a major design challenge for open rotor engines is noise control. Because the propeller is not covered by a nacelle, the discrete noise and vibration of open rotor engines far exceed those of traditional turbofan engines, and their sound pressure level spectrum conflicts significantly with the noise attenuation curves specified in ICAO Annex 16. The open structure of open rotor engines presents unique technical challenges: their ductless layout renders traditional acoustic liner noise reduction techniques unusable, creating a technical hurdle to airworthiness certification. This engine configuration faces a dual challenge in acoustic characterization: a lack of simple and effective noise reduction technologies and the difficulty of analyzing complex sound field data. The noise and vibration generated during operation, along with the nacelle-less design, make noise problems in open rotor engines difficult to solve, posing one of the biggest challenges for this type of engine to enter the commercial market. Therefore, the study of the noise characteristics of open rotary engines has become particularly important.

[0004] The rapid iteration of extended reality (XR, including virtual reality (VR), augmented reality (AR), and mixed reality (MR)) and artificial intelligence algorithms provides a new path to solving the aforementioned challenges. XR technology enables deep integration and interaction between virtual and mixed reality, while artificial intelligence algorithms can efficiently process multi-source, non-stationary acoustic signals, automatically learn noise characteristics and patterns, and, by using artificial intelligence algorithms to analyze large amounts of aircraft noise data, reveal noise characteristics and patterns that are difficult to detect using traditional methods, providing new empirical evidence for the development of acoustic theory.

[0005] To address the noise problem of open rotor engines, this application provides an open rotor engine noise data analysis system and method. By conducting wind tunnel test simulations of open rotor engines in a virtual-real fusion environment, simulating engine operating states at various flight stages of an aircraft, and performing noise visualization analysis, this provides efficient technical support for noise reduction design and airworthiness certification of open rotor engines. Summary of the Invention

[0006] The technical problem this application aims to solve is to address the shortcomings of the existing technology by proposing a noise data analysis system and method for open rotor engines. By constructing a mixed reality environment, engine model recognition, interactive operation, and wind tunnel test scenario simulation are achieved. Data obtained from wind tunnel tests is processed to generate relevant three-dimensional noise characteristic curves and 3D bar charts, enabling simulation of engine operating states and noise visualization analysis at various flight stages. This provides efficient technical support for noise reduction design and airworthiness certification of open rotor engines.

[0007] To achieve the above objectives, this invention proposes an open rotor engine noise data analysis system, comprising: The mixed reality interaction module is configured with a camera to recognize a real engine and render an interactive virtual engine model and operating interface; it also acquires parameters of an open rotor engine and constructs an open rotor engine model. The wind tunnel environment setup module is used to configure the simulated test environment for low / high speed wind tunnel tests, simulating the operating noise of an open rotor engine in a low / high speed wind tunnel under different conditions. The flight environment construction module provides a simulation of the flight path of an aircraft equipped with an open rotor engine, simulating different flight stages and the changes in blade angle during different flight stages; The noise analysis module is used to analyze and process the operating noise of low / high speed wind tunnels and the noise of aircraft equipped with open rotor engines at different flight stages. The dynamic visualization rendering module is configured to render and update the bar chart in real time in the 3D scene based on the noise data output by the noise analysis module for the analysis, processing and simulation of low / high speed wind tunnel operating noise and noise of different flight stages of the aircraft, so that its height and color dynamically reflect the changes in noise sound pressure level. The wind tunnel environment construction module is configured with a high-speed wind tunnel test simulation environment, which is equipped with a translational aluminum plate with multiple noise measurement points integrated on the top of the model and aligned parallel to the center line of the model along the axial direction. Pressure sensors are also installed on the translational aluminum plate to synchronously sample and convert the data into a narrowband sound pressure level (SPL) spectrum at a preset frequency. The height of the translational aluminum plate is dynamically adjusted according to the test Mach number during the simulation test to obtain noise data under different flight speeds and different noise radiation directions.

[0008] Furthermore, the constructed open rotor engine model specifically includes: a front blade, a rear blade, protective fixtures, and an engine casing; the angles of the front and rear blades are adjustable, and the protective fixtures and engine casing are detachable.

[0009] Furthermore, the low-speed wind tunnel test simulation environment in the wind tunnel environment construction module is equipped with multiple noise measurement points set laterally on one side of the open rotor engine model, with each measurement point having the same lateral distance from the model's centerline.

[0010] Furthermore, the working states of the open rotor engine model in the mixed reality interaction module include at least standard takeoff, scaled-down takeoff, and approach states, with different states corresponding to different front and rear rotor blade angles; The blade angles used to simulate the operating noise of an open rotor engine in a simulated test environment are determined based on the blade angle variation data of the aircraft equipped with the open rotor engine at different flight altitudes and various operating states, as well as the variation data at different Mach numbers.

[0011] Furthermore, the changes in blade angles of an aircraft equipped with an open rotor engine at different flight altitudes and under various operating conditions include: The flight path of an aircraft equipped with an open rotor engine is simulated, including takeoff, climb, cruise, descent, approach, landing, and thrust reverse phases. Key action nodes are determined by setting the time axis, and the flight altitude and speed at different times during takeoff are set at the key action nodes to determine the flight phase and the change in propeller pitch angle.

[0012] Furthermore, the open rotor engine model in the mixed reality interaction module is a scaled-down model. The noise analysis module converts the static noise data of the scaled-down open rotor engine model in the low-speed wind tunnel simulation environment configured by the wind tunnel environment building module into noise data of the scaled-down open rotor engine in flight state, specifically including: At each measurement point, the 1-foot lossless power spectral density was... Convert to narrowband wind tunnel for sound pressure level testing , to the reference spectral density Converted to narrowband reference sound pressure level : (1) (2) in, It's a wind tunnel test for sound pressure level. It is the lossless power spectral density at 1 foot. It is the reference sound pressure level. It is the reference spectral density. f is the frequency segment width; Reference sound pressure level data Sound pressure level data from wind tunnel tests Remove from the middle to obtain corrected wind tunnel measurement sound pressure level data. : (3) in, To correct the wind tunnel sound pressure level measurements, low-frequency noise data below 700Hz were removed from the results, and the low-frequency noise data were replaced with quadratic function values ​​with a 10dB drop at 100Hz. Negative sound pressure level data remaining after removing the wind tunnel reference sound pressure level were set to zero. Then, the data was converted from indoor wind tunnel conditions to International Standard Atmospheric (ISA) conditions. (4) in It is the wind tunnel Mach number read. It is the average static pressure at all measuring points. Atm. It is the sound pressure level under the international standard atmospheric ISA. It's the speed of sound in the wind tunnel. This is the speed of sound under the international standard atmospheric ISA, the source motion index SME, the second item on the right eliminates the convective amplification effect included in the indoor wind tunnel data of the test, and the third item is the source intensity amplitude adjustment, and the emission angle at each measurement point. From geometric angle The calculation shows that: (5) Since the relative velocity between the source and the microphone is zero, there is no associated Doppler frequency shift, so the sound pressure level under the International Standard Atmospheric ISA is... for: (6) The sound pressure level under the international standard atmospheric ISA was finally obtained. .

[0013] Furthermore, the noise analysis module transforms the noise data of the open rotor engine in a scaled-down flight state in the high-speed wind tunnel simulation experimental environment configured by the wind tunnel environment construction module into the noise data of the open rotor engine in a full-scale flight state under specific flight conditions. In a high-speed wind tunnel, noise data from a scaled-down flight state of an open rotor engine is converted into full-scale flight state noise data under specific flight conditions. These specific flight conditions include the aircraft's cruise flight state. The noise data from the scaled-down flight state of the open rotor engine in the high-speed wind tunnel test includes the sound pressure level under the International Standard Atmospheric ISA. and 1 / 3 octave band frequencies, specifically including: Sound pressure level under the international standard atmospheric ISA Converted to flight state sound pressure level : (7) in, The sound pressure level during flight. For the flight Mach number, For the wind tunnel Mach number, the second term on the right adds a specific value. The third term adjusts the source intensity amplitude to correct the static conditions to the flight conditions of a standard acoustic day. The fourth term on the right is an additional correction that explains the observed source level as the free-flow Mach number increases. When data is used as input to the ANOPP acoustic data module, the Doppler frequency shift... The calculation is as follows: (8) Among them, f Static This is the frequency in the stationary state.

[0014] Based on the calculation , Specimen size scaling factor ( The parameters are obtained through calculation. and : (9) (10) in, The sound pressure level in full-scale flight configuration. This refers to the frequency for full-scale flight.

[0015] Furthermore, the dynamic visualization rendering module generates a 3D visualization to characterize changes in sound pressure level of noise, specifically including: Obtain full-scale sound pressure level and frequency data of a scaled-down model of an open rotor engine under static conditions of low-speed and high-speed wind tunnel tests; perform curve fitting on the processed data to generate 3D noise characteristic curves with frequency, angle, and sound pressure level as parameters; Based on full-scale flight sound pressure level and frequency data, a group of histograms corresponding to the noise measurement points is constructed. The real-time read full-scale sound pressure level values ​​are normalized to the [0, 1] interval, which serves as a coefficient to control the scaling ratio of the Y-axis of the histogram and the intensity of the red component in the RGB color channel, thus forming a dynamic visualization effect in which the color and altitude change in real time with the noise data.

[0016] A noise data analysis method for an open rotary engine, applied to an open rotary engine noise data analysis system, includes the following steps: Obtain the parameters of the open rotary engine and construct the open rotary engine model; A simulated test environment was set up for low / high speed wind tunnel testing; the simulated test environment included an open rotor engine model and multiple noise measurement points arranged laterally parallel to the centerline of the open rotor engine model; The operating noise of an open rotor engine at different blade angles was simulated in a simulated test environment, and noise data under different blade angles was obtained, including the sound pressure level and 1 / 3 octave band frequency at each noise measurement point. Based on noise data, a 3D visualization is generated to characterize changes in sound pressure level.

[0017] Compared with the prior art, this application achieves the following technical effects: This application addresses the core challenges in the research and development and airworthiness certification of open rotary engines by constructing an innovative virtual-real fusion solution. It effectively solves the industry pain points of traditional noise testing methods, such as high cost, lengthy cycles, and abstract data that is difficult to analyze intuitively. By integrating high- and low-speed wind tunnel test data and applying mixed reality technology, this application achieves three-dimensional spatial visualization, audibility, and interactive analysis of engine noise characteristics. This not only significantly reduces the dependence of physical testing on manpower and resources but also transforms abstract spectral data into an intuitive spatial sound field, greatly enhancing researchers' understanding of noise source characteristics and propagation patterns. Simultaneously, this application strictly adheres to CCAR36-R3 and cruise airworthiness standards, simulating the engine's operating state throughout the entire flight path, including takeoff, climb, and approach, providing efficient and reliable integrated technical support for noise reduction design and airworthiness certification of open rotary engines. Attached Figure Description

[0018] For ease of explanation, this application is described in detail below with reference to specific embodiments and accompanying drawings.

[0019] Figure 1A schematic diagram of an open rotary engine noise data analysis system; Figure 2 A flowchart of a noise data analysis method for an open rotary engine; Figure 3 Flowchart for developing physical identification of open rotary engines; Figure 4 This is a schematic diagram of the Basic interactive scenario for an open rotary engine. Figure 5 This is a schematic diagram of the front blade rotation speed control of an open rotor engine. Figure 6 This is a schematic diagram of the front rotor blade angle control for an open rotary engine. Figure 7 This is a schematic diagram of the rear rotor blade angle control for an open rotary engine. Figure 8 A schematic diagram of the low-speed wind tunnel data fitting curve when Ma is 0.2, the front rotor blade angle is 40.1, and the rear rotor blade angle is 40.8. Figure 9 A schematic diagram of the low-speed wind tunnel data fitting curve when Ma is 0.22, the front rotor blade angle is 33.5 degrees, and the rear rotor blade angle is 35.7 degrees. Figure 10 A simulation scenario of a low-speed wind tunnel test of an open rotor engine in a mixed reality environment; Figure 11 Fitting curves of high-speed wind tunnel data when Ma is 0.4, front rotor blade angle is 43.0 degrees, and rear rotor blade angle is 43.5 degrees; Figure 12 Fitting curves of high-speed wind tunnel data when Ma is 0.6, front rotor blade angle is 54.1 degrees, and rear rotor blade angle is 53.5 degrees; Figure 13 A simulation scenario of a high-speed wind tunnel test of an open rotor engine in a mixed reality environment; Figure 14 For multiple geometric angles A dynamic histogram of noise data below; Figure 15 This is a schematic diagram showing the locations of the reference noise measurement points for lateral, fly-through, and approach sections in the noise verification test procedure. Detailed Implementation

[0020] The following are specific embodiments of this application, described in conjunction with the accompanying drawings, to further illustrate the technical solutions of this application. However, this application is not limited to these embodiments. Specific details, such as particular configurations, are provided in the following description merely to aid in a comprehensive understanding of the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application.

[0021] This application provides a noise data analysis system and method for an open rotor engine, and its specific embodiments will be described in detail in conjunction with its development process, test scenario setup and other aspects.

[0022] Example 1 See Figure 1 This is a schematic diagram of an open rotor engine noise data analysis system provided in an embodiment of this application. Figure 1 As shown, the above system specifically includes: The mixed reality interaction module is configured to recognize real engines through a camera and render an interactive virtual engine model and operating interface; it also acquires open rotor engine parameters and constructs an open rotor engine model. The wind tunnel environment setup module is used to configure the simulated test environment for low / high speed wind tunnel tests, simulating the operating noise of an open rotor engine in a low / high speed wind tunnel under different conditions. The flight environment construction module provides a simulation of the flight path of an aircraft equipped with an open rotor engine, simulating different flight stages and the changes in blade angle during different flight stages; The noise analysis module is used to analyze and process the operating noise of low / high speed wind tunnels and the noise of aircraft equipped with open rotor engines at different flight stages. The dynamic visualization rendering module is configured to render and update bar charts in real time in a 3D scene based on the noise analysis module's analysis and processing of low / high-speed wind tunnel operating noise and the noise of aircraft at different flight stages, as well as the noise data output by the simulation module. The height and color of the bar charts dynamically reflect the changes in noise sound pressure level. The wind tunnel environment construction module is configured with a high-speed wind tunnel test simulation environment, which is equipped with a translational aluminum plate with multiple noise measurement points integrated on the top of the model and aligned parallel to the center line of the model along the axial direction. Pressure sensors are also installed on the translational aluminum plate to synchronously sample and convert the data into a narrowband sound pressure level (SPL) spectrum at a preset frequency. The height of the translational aluminum plate is dynamically adjusted according to the test Mach number during the simulation test to obtain noise data under different flight speeds and different noise radiation directions.

[0023] See Figure 2 The above is a flowchart of a noise data analysis method for an open rotary engine provided in an embodiment of this application. Figure 2As shown, the steps of the above method specifically include: Step 101: Obtain the parameters of the open rotor engine and construct the open rotor engine model.

[0024] The open rotor engine model specifically includes: a front blade, a rear blade, protective fixtures, and an engine casing. The angles of the front and rear blades are adjustable, and the protective fixtures and engine casing are detachable.

[0025] Step 102: Set up a simulated test environment for low / high-speed wind tunnel testing. The simulated test environment includes an open rotor engine model and multiple noise measurement points arranged laterally parallel to the centerline of the open rotor engine model.

[0026] In the simulated test environment used for low-speed wind tunnel testing, multiple noise measurement points are set laterally on one side of the open rotor engine model, with each measurement point having the same lateral distance from the model's centerline.

[0027] In the high-speed wind tunnel simulation environment, multiple noise measurement points are integrated on a translational aluminum plate directly above the model, aligned axially parallel to the model's centerline. Pressure sensors are also installed on the translational aluminum plate to synchronously sample and convert the noise into a narrowband sound pressure level (SPL) spectrum at a preset frequency. The height of the translational aluminum plate is dynamically adjusted according to the test Mach number during the simulation to obtain noise data at different flight speeds and noise radiation directions. Specifically, the aluminum plate can be lowered from the top of the wind tunnel via remote control to achieve different distances from the model's central axis. Most measurements are performed with the aluminum plate retracted and close to the top of the test section; the plate is only lowered under specific test conditions. At Mach 0.4 and with the aluminum plate retracted, the sensor only covers emission angles between 46° and 90°. When the aluminum plate is lowered to a position 0.78 rotor diameters from the model's centerline and the incoming flow velocity is Mach 0.78, the directional emission angle ranges from 12° to 97° upstream.

[0028] Step 103: Simulate the operating noise of the open rotor engine at different blade angles in the above-mentioned simulated test environment, and obtain noise data under different blade angles, including the sound pressure level and 1 / 3 octave band frequency at each noise measurement point.

[0029] The operating states of the open rotor engine include at least standard takeoff, scaled-down takeoff, and approach states, with different front and rear rotor blade angles corresponding to different states.

[0030] The blade angles used to simulate the operating noise of the open rotor engine in the above-mentioned simulated test environment are determined based on the blade angle variation data of the aircraft equipped with the open rotor engine at different flight altitudes and various operating states, as well as the variation data at different Mach numbers.

[0031] The study determined the blade angle changes of an aircraft equipped with an open rotor engine at different flight altitudes and under various operating conditions. This included simulating the flight path of the aircraft, encompassing takeoff, climb, cruise, descent, approach, landing, and thrust reverse phases. Key action nodes were identified through timeline settings, and flight altitude and speed were set at different moments during takeoff at these key action nodes to determine the relationship between flight phases and blade pitch angle changes.

[0032] Step 104: Based on the above noise data, generate a 3D visual diagram to characterize the sound pressure level changes of the noise.

[0033] Example 2 Embodiment 2 of this application is a further refinement of the technical solution of Embodiment 1, as detailed below: The entire process flow diagram for the physical identification development of open rotary engines is as follows: Figure 3 As shown, it includes the interaction and tooling assembly / disassembly of open rotor engines, the control of open rotor engine blade angle changes and rotation speed, the construction of high-speed and low-speed wind tunnel simulation tests for open rotor engines, and the flight scenario test simulation of aircraft equipped with open rotor engines.

[0034] The mixed reality environment comprises six experimental scenarios: Hub, Identify, Basic, Low Tunnel, High Tunnel, and Flight. Its main functions include: the initial interface of the mixed reality environment; virtual-real fusion and object recognition of the open rotor engine; simulation of the open rotor engine's operating state and disassembly / assembly; low-speed wind tunnel test simulation of the open rotor engine; high-speed wind tunnel test simulation of the open rotor engine; simulation of the engine's operating state during various flight phases; and simulation of airworthiness flight test simulation. The Low Tunnel and High Tunnel scenarios constitute the ORE Test scenario, which can be accessed via buttons. The ORE Test scenario, along with the Identify, Basic, and Flight scenarios, are all accessed through corresponding buttons on the initial interface (Hub) of the mixed reality environment.

[0035] The initial interface (Hub) of the mixed reality environment is accessed to perform virtual-real fusion and object identification of the open rotor engine. This application uses Unity's VuForia plugin for open rotor engine identification. The process involves selecting and constructing the model to be identified; adjusting the viewpoint and setting the model's vertical vector; selecting an appropriate size based on the actual object's dimensions; coloring and lightweighting the model; adjusting deployment settings; and exporting the initial rotor engine model.

[0036] After recognizing a real engine model, it will automatically jump to the (Basic) scene for engine interaction and disassembly / reassembly, simulating the engine's working state, such as... Figure 4 As shown.

[0037] The Basic scene mainly features an open rotor engine model and a main menu button that enables interaction with the engine. Once in the scene, users can directly move, scale, and rotate the engine.

[0038] Clicking the corresponding button in the main menu allows you to simulate the disassembly and assembly of all engine blade models and the disassembly and assembly of engine tooling.

[0039] Clicking the Control law button in the main menu allows you to simulate changing the front and rear blade angles and the rotational speed of the front propeller of an open rotor engine. Three sliders simulate the knobs on the real model: Thrust, Forward blades, and Rear blades for control.

[0040] Clicking the Thrust button brings up a slider that controls the rotational speed of the front propeller. Moving the slider dynamically changes the rotational speed, and the speed is displayed in real-time above the slider. Figure 5 As shown. Clicking the Forwardblades button brings up a slider that controls the angle of the front blades. Moving the slider dynamically changes the angle of the front blades, and the angle is displayed in real time above the slider. Figure 6 As shown. Clicking the Rear blades button will display a slider that controls the angle of the rear blades. Moving the slider dynamically changes the angle of the rear blades, and the angle is displayed in real time above the slider. Figure 7 As shown.

[0041] Clicking the "engine performance data" button in the main menu displays the relevant data panel for the open rotary engine. You can also move, zoom, and rotate the panel.

[0042] Return to the initial interface of the mixed reality environment (Hub), click to enter the ORE Test scene, and click the Low Speed ​​WindTunnel button to jump to the Low tunnel low-speed wind tunnel test scene. The noise data used in this application is received by an acoustic collection instrument, which is a single microphone with a standard bullet head, used for in-flow microphone measurements.

[0043] In this embodiment, the microphone for the low-speed wind tunnel test is mounted on a linear lateral offset 1.52 meters from the model's centerline. The edgeline measurement covers observation angles between 17.6° and 140° relative to the upstream axis of the fan. The low-speed wind tunnel provides better observation of data changes at Mach 0.2, facilitating analysis and processing. Table 1 shows the geometry of the microphone position.

[0044] Table 1. Microphone geometry in a 9×15ft LSWT at Mach 0.2

[0045] Testing activities were conducted in a 9×15-foot low-speed wind tunnel to study the noise and performance of modern open rotors under takeoff and landing conditions. Most of the available low-speed data were acquired at standard takeoff (NTO) and approach (APP) pitch angles, while a limited number of data were acquired at scaled-down takeoff (STO) pitch angles. Table 2 shows the specific front / rear rotor pitch angles for the three scenarios.

[0046] The 9×15-foot low-speed wind tunnel is 2.74 meters high, 4.67 meters wide (9×15 feet), and 8.72 meters long (28.6 feet). The test section walls have four 10.2-centimeter (4-inch) wide slits extending along the length of the test section, designed to reduce wind tunnel wall effects. The airflow is driven by three electric motors, reaching a speed of Mach 0.22, corresponding to Mach numbers under takeoff and approach conditions. During the low-speed wind tunnel tests, narrowband and 1 / 3 octave band sound pressure spectra were measured at specific observation points using an inflow-type transverse microphone array. The narrowband broadband sound pressure level was calculated by fitting a moving median curve to the narrowband data. Subsequently, based on the narrowband data, the 1 / 3 octave band sound pressure levels of the broadband noise and single-tone noise components in the spectrum were calculated separately.

[0047] Table 2 Test Parameter Comparison Table

[0048] The acquired raw test data undergoes signal separation processing to eliminate data bias caused by device gain. Subsequently, based on the microphone sensitivity parameters, a Fast Fourier Transform (FFT) is used with spectral analysis to generate frequency dimension characteristic data, converting the voltage signal into an energy distribution spectrum to obtain the power spectral density of the test data. The power spectral density is then processed. After obtaining the reference spectral density, a dual calibration is performed. First, professional calibration equipment is used to correct measurement errors caused by the microphone's inherent characteristics, yielding the microphone's corrected sound pressure level spectral density. Then, the microphone's corrected sound pressure level spectral density is processed to unify the data to an ideal state under a standard measurement distance, resulting in the 1-foot lossless power spectral density.

[0049] Static wind tunnel noise data of a scaled-down model of an open rotor engine is processed based on the baseline spectral density and the 1-foot lossless power spectral density, and converted into noise data of the open rotor engine in flight state for ANOPP noise assessment and audibility.

[0050] In low-speed wind tunnel testing, the static noise data of a scaled-down model of an open rotor engine is converted into scaled-down flight state data. The sound pressure level of the scaled-down flight state of the open rotor engine is obtained according to the following steps: At each measurement point, the 1-foot lossless power spectral density was... Convert to narrowband wind tunnel for sound pressure level testing , to the reference spectral density Converted to narrowband reference sound pressure level : (1) (2) in, It's a wind tunnel test for sound pressure level. It is the lossless power spectral density at 1 foot. It is the reference sound pressure level. It is the reference spectral density. f is a frequency segment width of 12.2Hz; Reference sound pressure level data Sound pressure level data from wind tunnel tests Remove from the middle to obtain corrected wind tunnel measurement sound pressure level data. : (3) in, To correct the wind tunnel sound pressure level measurements, low-frequency noise data below 700Hz were removed from the results, and the low-frequency noise data were replaced with quadratic function values ​​with a 10dB drop at 100Hz. Negative sound pressure level data remaining after removing the wind tunnel reference sound pressure level were set to zero. Then, the data was converted from indoor wind tunnel conditions to International Standard Atmospheric (ISA) conditions. (4) in, It is the wind tunnel Mach number read. It is the average static pressure at all measuring points. Atm. It is the sound pressure level under the international standard atmospheric ISA. It's the speed of sound in the wind tunnel. This is the speed of sound under the international standard atmospheric ISA, with the source motion index SME set to 2. The second term on the right eliminates the convective amplification effect included in the indoor wind tunnel data during the test. The third term is the source intensity amplitude adjustment, and the emission angle at each measurement point. From geometric angle The calculation shows that: (5) Since the relative velocity between the source and the microphone is zero, there is no associated Doppler frequency shift, so the sound pressure level under the International Standard Atmospheric ISA is... for: (6) The sound pressure level and frequency data of the open rotor engine in scaled-down flight state provide fundamental data support for subsequent curve fitting and visualization. Low-speed wind tunnel data was converted from static data to ISA standard atmospheric conditions by removing low-frequency noise (below 700Hz) and correcting for convective amplification effects. MATLAB was used to perform curve fitting on the noise data processed from the low-speed wind tunnel to create a 3D image, enabling noise data processing and subsequent research on noise-based airworthiness methods. The sound pressure level data of the open rotor engine in scaled-down flight state is the sound pressure level under the International Standard Atmosphere (ISA). The frequency data is for 1 / 3 octave band frequencies. For example, such as... Figure 8 The figure shows the low-speed wind tunnel data fitting curves when Ma is 0.2, the front rotor blade angle is 40.1, and the rear rotor blade angle is 40.8. Figure 9 The figure shows the low-speed wind tunnel data fitting curves when Ma is 0.22, the front rotor blade angle is 33.5 degrees, and the rear rotor blade angle is 35.7 degrees.

[0051] exist Figure 10 The scenario shown simulates a low-speed wind tunnel test of an open rotor engine in a mixed reality environment. Within the wind tunnel scenario, the angle of the open rotor engine blades and the rotational speed of the engine's front propeller can be varied to simulate wind tunnel tests of the open rotor engine under different pitch angles. The scenario includes an open rotor engine, a bracket for mounting multiple noise measurement points, microphone measurement position markings, and a low-speed wind tunnel data panel. Clicking the button on the left side of the low-speed wind tunnel data panel will display the corresponding 3D data graph.

[0052] Return to the ORE Test scene and click the High Speed ​​Wind Tunnel button to jump to the High Tunnel test scene. The high-speed wind tunnel experiment uses an unsteady pressure instrument composed of an aluminum plate with 17 flush-mounted microphone acoustic receiver sensors, axially aligned parallel to the model's centerline, for pressure measurements. Edge measurements cover the observation angles of 17 acoustic noise data measurement points between 42.3° and 137.7° relative to the upstream axis of the fan. Table 3 shows the geometry of the measurement points.

[0053] The 8×6-foot high-speed wind tunnel is 2.44 meters high, 1.83 meters wide (8 feet × 6 feet), and 7.16 meters long (23.5 feet). It has a speed range from Mach 0.27 to Mach 2.0, corresponding to cruise conditions. The test section is equipped with vents for removing the boundary layer. The vents are used when the wind tunnel is running at transonic speeds. The purpose is to measure the aerodynamic performance and near-field unsteady pressure at cruise Mach numbers and to explore the design space for reducing noise when the open rotor system achieves high propulsion efficiency.

[0054] Table 3. Geometric angles of the sensor in an 8×6 SWT at Mach number 0.78

[0055] Since the relative velocity between the source and the microphone is zero, there is no associated Doppler frequency shift. In a high-speed wind tunnel, noise data of the open rotor engine in scaled-down flight conditions are converted into sound pressure level and frequency data of the full-scale flight conditions under specific flight conditions, including aircraft cruise, takeoff, and approach.

[0056] Sound pressure level under the international standard atmospheric ISA Converted to full-scale flight state sound pressure level under specific flight conditions : (7) in, The sound pressure level during flight. For the flight Mach number, For the wind tunnel Mach number, the second term on the right adds a specific value. The third term adjusts the source intensity amplitude to correct the static conditions to the flight conditions of a standard acoustic day. The fourth term on the right is an additional correction that explains the observed source level as the free-flow Mach number increases. When data is used as input to the ANOPP acoustic data module, the Doppler frequency shift... The calculation is as follows: (8) in, fStatic This is the frequency in the stationary state.

[0057] Based on the calculation , Specimen size scaling factor ( The parameters are obtained through calculation. and : (9) (10) in, For full-scale flight sound pressure level, For full-size frequencies, The rotor diameter of a full-size open rotary engine, The rotor diameter is for the scaled-down model.

[0058] After processing high-speed wind tunnel data in the same way as low-speed wind tunnel tests, MATLAB was used to perform curve fitting on the processed high-speed wind tunnel data to draw three-dimensional images, thereby realizing the processing of noise data and subsequent research on noise-based airworthiness methods. Figure 11 The figure shows the fitting curves of high-speed wind tunnel data when Ma is 0.4, the front rotor blade angle is 43.0 degrees, and the rear rotor blade angle is 43.5 degrees. Figure 12 The figure shows the high-speed wind tunnel data fitting curves for a Mach number of 0.6, a front rotor blade angle of 54.1 degrees, and a rear rotor blade angle of 53.5 degrees. The high-speed wind tunnel tests in the 8×6-foot facility aimed to simulate cruise conditions and performance. The high-speed wind tunnel simulations primarily recorded the cruise performance of advanced open rotor blades. Most tests were conducted between Mach 0.7 and 0.85, with a small number between Mach 0.27 and 0.7. During this phase, the rotor operates at high speeds and high Mach numbers, which cannot be simulated in low-speed wind tunnels. Low-speed wind tunnel tests cannot replace noise data from high-speed flight conditions. Obtaining flight noise data directly from low-speed wind tunnels could lead to inaccurate data. Therefore, this invention designs a high-speed wind tunnel simulation test to obtain the operating conditions and performance under simulated cruise flight conditions. It simultaneously supports the construction of both low-speed and high-speed wind tunnel test environments, covering all operating conditions from takeoff / approach (low speed) to cruise (high speed). The low-speed wind tunnel scenario focuses on noise optimization during takeoff / approach, while the high-speed wind tunnel scenario focuses on noise analysis during cruise. The combination of these two approaches enables the study of the noise characteristics of open rotor engines throughout their entire lifecycle, addressing the technical gap in low-speed wind tunnels' inability to simulate high Mach number cruise noise. The high-speed wind tunnel adds Doppler frequency shift correction and free-flow Mach number compensation, accurately reproducing full-scale sound pressure level and frequency data under cruise conditions.

[0059] exist Figure 13The scenario shown simulates a high-speed wind tunnel test of an open rotor engine in a mixed reality environment. Within the wind tunnel scenario, the angle of the open rotor engine blades and the rotational speed of the engine's front propeller can be varied to simulate wind tunnel tests of the open rotor engine under different pitch angles. The scenario includes an open rotor engine, an aluminum plate with multiple microphones, microphone measurement position markings, and a high-speed wind tunnel data panel. Clicking the button on the left side of the high-speed wind tunnel data panel will display the corresponding 3D data graph.

[0060] High-speed and low-speed wind tunnel testing facilities were used to test the propellers under a wide range of conditions. The pitch angles of the fore and aft blades ranged from the minimum closure angle of 33.5° / 35.7° at Mach 0.2 in the low-speed wind tunnel to the maximum angle of 64.4° / 61.8° at Mach 0.85 in the high-speed wind tunnel. Existing low-speed wind tunnel data mainly comes from standard takeoff (NTO) and approach (APP) pitch angles, while five different pitch angles were tested in the high-speed wind tunnel. Low-speed wind tunnel experiments cannot simulate high Mach number flight conditions under cruise conditions, and the flight state noise error obtained using low-speed wind tunnel data is as high as 5%. High-speed wind tunnel experiments can simulate high Mach number conditions, and the error using both low-speed and high-speed wind tunnel experiments is less than 1%, more accurately simulating the actual flight phase.

[0061] Return to the initial interface of the mixed reality environment (Hub), click the Flight button to jump to the flight simulation scene, and simulate the flight path of an A320 aircraft equipped with an open rotor engine.

[0062] In the constructed flight path simulation scenario, based on noise data obtained from low-speed / high-speed wind tunnel simulation experiments, the simulation examines the pitch angle changes and airworthiness noise measurements of an A320 aircraft equipped with a basic open rotor engine during different flight phases. The scenario includes the open rotor engine, the A320 aircraft, and the runway. To clearly observe the changes in the forward and backward pitch angles during flight, a magnified image of the open rotor engine flies alongside the aircraft along the flight path. The simulation marks each stage of flight and key points within that stage, and animations of each flight phase and engine blade angle changes are created. The aircraft flies along a reduced-thrust flight path on a virtual runway. To prevent the flight path from becoming unobservable due to the aircraft being out of sight, the runway is included as part of the flight path markings and moves relative to the user towards the tail of the aircraft, while the aircraft itself does not undergo significant forward displacement; it only moves vertically within a fixed position.

[0063] Clicking the "Flight" button will start the aircraft to perform various flight phases according to the flight path and change the propeller pitch angle at different phases. The flight phases include takeoff, climb, cruise, descent, approach and landing phases. After landing, reverse thrust will be performed.

[0064] CCAR36-R3 stipulates that at least 6 noise flight tests must be conducted. To ensure that the 90% confidence interval of the three data values ​​does not exceed 1.5 dB, 9 flights are conducted. Clicking the "Airworthiness Test" button will cause the aircraft to fly 9 laps along the required test path, simulating the test process. The system's application scenarios span the entire process of engine development and airworthiness certification. Low-speed wind tunnel scenarios are used for noise analysis during takeoff / approach, high-speed wind tunnel scenarios are used for noise analysis during cruise, and flight environment scenarios simulate noise changes throughout the entire flight path, including takeoff, cruise, and approach.

[0065] In this embodiment, a flight scene is constructed to achieve data visualization. C# scripts `Lengh Change` and `Color Change` are used to implement the changes in the length and color of the 3D bar chart as noise data changes. A flight noise graph consisting of 18 sets of 3D bar-shaped objects is constructed to dynamically display the acoustic characteristics of noise monitoring points at different azimuths through real-time dynamic updates. The numbers marked on the Y-axis of each bar represent the frequency at the corresponding angle, and the frequencies at different angles are updated in real time. Its spatial layout uses a 3D Cartesian coordinate system, with the horizontal direction corresponding to the measured azimuth angle and the vertical direction corresponding to the mapped sound pressure level intensity. The sound pressure level can be changed over time to dynamically display the real-time frequency magnitude. Based on the full-size flight sound pressure level and frequency data, a 3D bar chart group corresponding to the noise measurement points is constructed. The real-time read full-size sound pressure level values ​​are normalized to the [0, 1] interval, serving as coefficients to control the scaling ratio of the bar chart's Y-axis and the intensity of the red component in the RGB color channel, forming a dynamic visualization effect where color and altitude change in real time with the noise data.

[0066] This application enables the visualization of dynamic noise data from open rotor engines, providing real-time updates of sound pressure levels (dB) and corresponding frequencies (Hz) at different directivity angles. Figure 14 As shown, the higher the sound pressure level (SPL) of the noise, the closer the color of the bar is to red, and vice versa. The higher the SPL of the noise, the larger the Y-axis dimension of the bar, and vice versa.

[0067] According to Annex 16 of the International Civil Aviation Organization (ICAO), "Aircraft Noise Certification," the measurement points in the noise verification test procedure include lateral, flyover, and approach reference noise measurement points. The monitoring point locations are as follows: Figure 15 As shown.

[0068] This application utilizes 3D extended reality technology to construct a scenario for noise airworthiness testing during aircraft takeoff with reduced thrust, comprehensively simulating the entire process from aircraft takeoff maneuvers to noise data visualization and analysis. A three-dimensional bar graph visually displays whether the noise distribution is appropriate compared to the limit values. A panel demonstrates the processing of converting scaled-down model wind tunnel noise data into full-scale flight state data, along with flight data surface fitting plots and data display. The entire scenario comprehensively simulates the entire process from aircraft takeoff maneuvers to noise data visualization and analysis.

[0069] The aircraft takeoff was animated, breaking down each aircraft position in the scene into independent animation segments. Key action points were defined using a timeline. Keyframes were used to define the aircraft's altitude, speed, and engine pitch angle at different flight paths; for example, the aircraft was stationary at 0 seconds and climbed to 6000 meters at 5 seconds. An animator controller was then created, defining states such as "Idle" and "Fly," with a Boolean parameter (e.g., "Flying") controlling the state transitions. When the "Takeoff" button was pressed, the "Flying" parameter was set to True, triggering the flight animation; when the "Stop" button was pressed, it was set to False, resetting the animation.

[0070] By implementing this application, users wearing relevant mixed reality devices can perform the following operations and obtain corresponding effects: Pointing the device at a real engine model instantly overlays a virtual engine onto the real environment, achieving virtual-real fusion. Users can directly grasp, rotate, and disassemble the virtual engine using gestures to intuitively understand its structure and adjust parameters via sliders for an immersive interactive experience. Entering a wind tunnel test scenario allows users to view the three-dimensional distribution surface of noise data at different Mach numbers and propeller pitch angles, providing a direct comparison of noise characteristics under different operating conditions. Entering a flight certification scenario involves starting an aircraft takeoff animation while simultaneously observing a three-dimensional noise histogram in dynamic color and altitude changes in 3D space on one side of the scenario. As the aircraft climbs, the dynamic process of noise distribution changing with distance and angle can be clearly seen, along with a direct comparison with airworthiness limits. This application, through simulating multiple flight tests required by CCAR36-R3, can intuitively demonstrate the statistical process and results of noise measurement. This application transforms complex open rotary engine noise data into intuitive, dynamic, and interactive visual information in a mixed reality space, greatly improving the efficiency, intuitiveness, and immersiveness of noise data analysis and airworthiness pre-assessment, and providing an innovative technical tool for the research, development, teaching, and airworthiness certification of open rotary engines.

[0071] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0072] Those skilled in the art to which this application pertains may make various modifications or additions to the specific embodiments described, or adopt similar methods to replace them, without departing from the concept of this application or exceeding the scope defined by the appended claims.

Claims

1. A noise data analysis system for an open rotary engine, characterized in that, include: The mixed reality interaction module is equipped with a camera to recognize the real engine and render an interactive virtual engine model and operating interface. Obtain the parameters of the open rotary engine and construct the open rotary engine model; The wind tunnel environment setup module is used to configure the simulated test environment for low / high speed wind tunnel tests, simulating the operating noise of an open rotor engine in a low / high speed wind tunnel under different conditions. The flight environment construction module provides a simulation of the flight path of an aircraft equipped with an open rotor engine, simulating different flight stages and the changes in blade angle during different flight stages; The noise analysis module is used to analyze and process the operating noise of low / high speed wind tunnels and the noise of aircraft equipped with open rotor engines at different flight stages. The dynamic visualization rendering module is configured to render and update the bar chart in real time in the 3D scene based on the noise data output by the noise analysis module for the analysis, processing and simulation of low / high speed wind tunnel operating noise and noise of different flight stages of the aircraft, so that its height and color dynamically reflect the changes in noise sound pressure level. The wind tunnel environment construction module configures a simulated test environment for the high-speed wind tunnel test, which includes a translational aluminum plate with multiple noise measurement points integrated on the top of the model, aligned axially parallel to the model's centerline. A pressure sensor is also installed on the translational aluminum plate to synchronously sample and convert the noise into a narrowband sound pressure level (SPL) spectrum at a preset frequency. The height of the translational aluminum plate is dynamically adjusted according to the test Mach number during the simulation test to obtain noise data under different flight speeds and noise radiation directions.

2. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The constructed open rotor engine model specifically includes: a front blade, a rear blade, a protective fixture, and an engine casing; the angles of the front and rear blades are adjustable, and the protective fixture and engine casing are detachable.

3. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The low-speed wind tunnel test simulation environment in the wind tunnel environment construction module is configured with multiple noise measurement points arranged laterally on one side of the open rotor engine model, and each measurement point is laterally distanced from the center line of the model.

4. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The working states of the open rotor engine model in the mixed reality interaction module include at least standard takeoff, scaled-down takeoff and approach states, with different states corresponding to different front and rear rotor blade angles. The blade angles used to simulate the operating noise of the open rotor engine in the simulated test environment are determined based on the blade angle variation data of the aircraft equipped with the open rotor engine at different flight altitudes and various operating states, as well as the variation data at different Mach numbers.

5. The noise data analysis system for an open rotor engine according to claim 4, characterized in that, The changes in blade angles of an aircraft equipped with an open rotor engine at different flight altitudes and under various operating conditions include: The flight path of an aircraft equipped with an open rotor engine is simulated, including takeoff, climb, cruise, descent, approach, landing, and thrust reverse phases. Key action nodes are determined by setting the time axis, and the flight altitude and speed at different times during takeoff are set at the key action nodes to determine the flight phase and the change in propeller pitch angle.

6. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The open rotor engine model in the mixed reality interaction module is a scaled-down model. The noise analysis module converts the static noise data of the scaled-down open rotor engine model in the low-speed wind tunnel simulation environment configured by the wind tunnel environment construction module into noise data of the scaled-down open rotor engine in flight state, specifically including: At each measurement point, the 1-foot lossless power spectral density was... Convert to narrowband wind tunnel for sound pressure level testing , to the reference spectral density Converted to narrowband reference sound pressure level : （1） （2） in, It's a wind tunnel test for sound pressure level. It is the lossless power spectral density at 1 foot. It is the reference sound pressure level. It is the reference spectral density. f is the frequency segment width; Reference sound pressure level data Sound pressure level data from wind tunnel tests Remove from the middle to obtain corrected wind tunnel measurement sound pressure level data. : （3） in, To correct the wind tunnel sound pressure level measurements, low-frequency noise data below 700Hz were removed from the results, and the low-frequency noise data were replaced with quadratic function values ​​with a 10dB drop point at 100Hz. Negative sound pressure level data remaining after removing the wind tunnel reference sound pressure level were set to zero. Then, the data was converted from indoor wind tunnel conditions to International Standard Atmospheric (ISA) conditions. （4） in It is the wind tunnel Mach number read. It is the average static pressure at all measuring points. Atm. It is the sound pressure level under the international standard atmospheric ISA. It's the speed of sound in the wind tunnel. This is the speed of sound under the international standard atmospheric ISA, the source motion index SME, the second item on the right eliminates the convective amplification effect included in the indoor wind tunnel data of the test, and the third item is the source intensity amplitude adjustment, and the emission angle at each measurement point. From geometric angle The calculation shows that: （5） Since the relative velocity between the source and the microphone is zero, there is no associated Doppler frequency shift, so the sound pressure level under the International Standard Atmospheric ISA is... for: （6） Ultimately, the sound pressure level under the international standard atmospheric ISA was obtained. .

7. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The noise analysis module converts the noise data of the open rotor engine in the scaled-down flight state in the high-speed wind tunnel simulation experimental environment configured by the wind tunnel environment construction module into the noise data of the open rotor engine in the full-scale flight state under specific flight conditions. In a high-speed wind tunnel, noise data from a scaled-down flight state of an open rotor engine is converted into full-scale flight state noise data under specific flight conditions. These specific flight conditions include the aircraft's cruise flight state, and the noise data from the scaled-down flight state of the open rotor engine in the high-speed wind tunnel test includes the sound pressure level under the International Standard Atmospheric ISA (ISA). and 1 / 3 octave band frequencies, specifically including: Sound pressure level under the international standard atmospheric ISA Converted to flight state sound pressure level : （7） in, The sound pressure level during flight. For the flight Mach number, For the wind tunnel Mach number, the second term on the right adds a specific value. The third term adjusts the source intensity amplitude to correct the static conditions to the flight conditions of a standard acoustic day. The fourth term on the right is an additional correction that explains the observed source level as the free-flow Mach number increases. When data is used as input to the ANOPP acoustic data module, the Doppler frequency shift... The calculation is as follows: （8） Among them, f Static The resting frequency; Based on the calculation , Specimen size scaling factor ( The parameters are obtained through calculation. and : （9） （10） in, The sound pressure level in full-scale flight configuration. This refers to the frequency for full-scale flight.

8. The noise data analysis system for an open rotor engine according to claim 1, characterized in that, The dynamic visualization rendering module generates a 3D visual image to characterize changes in sound pressure level of noise, specifically including: Obtain full-scale sound pressure level and frequency data of a scaled-down model of an open rotor engine under static conditions of low-speed and high-speed wind tunnel tests; perform curve fitting on the processed data to generate 3D noise characteristic curves with frequency, angle, and sound pressure level as parameters; Based on full-scale flight sound pressure level and frequency data, a group of histograms corresponding to the noise measurement points is constructed. The real-time read full-scale sound pressure level values ​​are normalized to the [0, 1] interval, which serves as a coefficient to control the scaling ratio of the Y-axis of the histogram and the intensity of the red component in the RGB color channel, thus forming a dynamic visualization effect in which the color and altitude change in real time with the noise data.

9. A method for analyzing noise data of an open rotary engine, applied to the system described in any one of claims 1-8, characterized in that, Includes the following steps: Obtain the parameters of the open rotary engine and construct the open rotary engine model; A simulated test environment is set up for low / high speed wind tunnel testing; the simulated test environment includes the open rotor engine model and multiple noise measurement points arranged laterally parallel to the centerline of the open rotor engine model; The operating noise of an open rotor engine at different blade angles was simulated in the simulated test environment, and noise data under different blade angles was obtained, including the sound pressure level and 1 / 3 octave band frequency at each noise measurement point. Based on the noise data, a 3D visualization is generated to characterize the changes in sound pressure level of the noise.

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