Near-field unsteady flow acoustic load separation method based on surface fancy array

Abstract

The invention discloses a near-field unsteady flow acoustic load separation method based on a surface fancy array, and the method comprises the steps: carrying out a pulsating pressure measurement test through employing a two-dimensional fancy array, and obtaining a model surface time domain signal; calculating an array signal cross spectrum matrix; taking the cross-spectrum matrix as input, and obtaining a calculation result based on a wave number domain beam forming algorithm; wave number domain beam forming results under different angular frequencies are calculated, and the sum of all the wave number domain beam forming calculation results under each angular frequency is obtained through a square summation method; and by taking the wave number boundary of the acoustic region as an integral boundary, summing the wave number domain beam forming calculation results inside and outside the integral boundary by adopting a square summing method.

Description

Technical Field

[0001] The invention relates to the fields of wind tunnel, water tunnel, flight and underwater test, and in particular to a near-field unsteady flow acoustic load separation method based on a surface pattern array. Background Art

[0002] Wall pulsating pressure is a very important issue in the field of air, space, sea and ground rapid transportation systems. Directly radiating noise outward will also cause flow-induced vibration of the wall structure, leading to structural fatigue and forming a secondary sound source. As an unsteady load, wall pulsating pressure can be divided into flow load and acoustic load. Among them, unsteady flow load is more closely related to flow-induced vibration of the structure, while acoustic load is more closely related to direct sound. Since the two have different action mechanisms, it is of great significance to identify and separate them.

[0003] Conducting wind tunnel, water tunnel, flight, underwater and other tests is the most important means to obtain the characteristics of wall pulsating pressure. The application of surface array method has effectively improved the test capabilities in this area. For example, the application of surface array and combined with wavenumber-frequency spectrum method can realize near-field flow load and acoustic load. However, the existing unsteady flow-acoustic separation method based on surface array has the following shortcomings (such as patent 202311643278.6): 1. Using one-dimensional linear array results as the test device, only flow direction results can be obtained, lacking two-dimensional features. 2. The algorithm is too old. When calculating the wavenumber-frequency spectrum, the most primitive time-space Fourier change direct algorithm is still used, and the latest cross-spectrum matrix calculation method that can be parallelized to improve the speed cannot be applied; 3. Only the energy ratio can be obtained, and the spectrum law of the unsteady flow acoustic load cannot be obtained. Summary of the invention

[0004] The purpose of the present invention is to propose a new near-field unsteady flow acoustic load separation method based on surface pattern arrays to solve the defects of the current near-field pulsating pressure flow acoustic component separation method.

[0005] To achieve the above object, the present invention adopts the following scheme: A design method for separating near-field unsteady flow acoustic loads based on a surface pattern array comprises the following steps: Step 1: Use a two-dimensional fancy array to carry out a pulsating pressure measurement test to obtain the time domain signal of the model surface.

[0006] will have M A one-dimensional line array of each channel is installed on the surface of the test model, and the lines, data acquisition equipment, and host computer are connected. After checking that everything is correct, wind tunnel / water tunnel / flight / underwater tests are carried out to collect relevant pulsating pressure signals.

[0007] Step 2: Calculate the cross-spectral matrix of array signals.

[0008] Let the cross-spectral matrix be expressed as , that is dimensional matrix whose elements are cross-spectral functions ,in m , n Representative m , n The specific definitions of the sensors are as follows: The time-space correlation function of the pulsating pressure at any two points is expressed as: (1) In the above formula p is the pulsating pressure, and are represented by the spatial coordinates of any two points, and is the coordinate difference, and represents two points in time, “<>” represents the ensemble average, and “*” represents the conjugate complex number. When the TBL pulse pressure is steady and isotropic, the formula is the same as and No relation, It can be written as , then m , n The cross-spectrum between sensors can be expressed as: (2) In the above formula, when When it is zero, it is transformed into the self-spectrum, that is, becomes ; is the experimental coefficient, which is 1 or The cross-spectrum matrix (CSM) contains the cross-spectrum between all sensors. The cross spectrum is: (3) In addition, if the positions of m and n are exchanged, the following relationship holds: (4) Right now and is complex conjugate. In order to realize computer parallel computing, equation (3) is discretized, then: (5) Where N is the data block length, represents the expectation. If necessary, a parallel computing method can be used to calculate each Improves computation efficiency.

[0009] Step 3: Using the cross-spectral matrix as input, the calculation results are obtained based on the wavenumber beamforming algorithm.

[0010] According to the requirements of the wavenumber domain beamforming algorithm, the wavenumber steering vector of the array is set for dimensional vector, each element of the pointing vector is expressed as , the specific calculation method is: (6) in, , Representative m The streamwise and spanwise coordinates of each sensor. Therefore, the array wavenumber domain beamforming result at a certain angular frequency can be expressed as: (7) here: (8) Step 4: Calculate the wave number domain beamforming results at different angular frequencies, and use the square sum method to obtain the sum of all wave number domain beamforming calculation results at each angular frequency: (9) in: is the sum of all wavenumber domain beamforming results at each angular frequency, is the flow wave number, is the spanwise wave number, is the angular frequency, for a certain , , The wavenumber domain beamforming calculation results are as follows: are the maximum and minimum values ​​of the streamwise wave number, are the maximum and minimum spanwise wavenumber values, respectively.

[0011] by Drawing, general Displayed in logarithmic coordinates, it is the total spectrum of the unsteady flow acoustic load. The unit is .

[0012] Step 5: Taking the wave number boundary of the acoustic region as the integration boundary, the wave number domain beamforming calculation results inside and outside the integration boundary are summed using the square sum method as follows: (10) (11) in: is the sum of all wavenumber domain beamforming results at each angular frequency within the boundary, corresponding to the unsteady acoustic load; is the sum of all wavenumber domain beamforming results at each angular frequency outside the boundary, corresponding to the unsteady flow load; Refers to the flow velocity, Refers to the speed of sound, the wave number boundary of the acoustic zone for: (12) Respectively , Plot the spectral function of the unsteady acoustic load and the unsteady flow load. , The unit is still .

[0013] Through the above five steps, the flow-acoustic separation is achieved. Note that if you want to obtain the frequency spectrum , rather than the angular frequency spectrum , then we need to do the following simple linear transformation: (13) In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: After obtaining the relevant near-field unsteady near-field loads using a surface fancy array in wind tunnel / water tunnel / flight / underwater tests, the highly coupled unsteady flow and acoustic loads can be identified and decoupled by using the method of the present invention, and then separated to obtain their respective spectrum rules. In addition, the algorithm can use the advantages of the cross-spectral matrix to realize parallel calculation of signal processing, thereby greatly improving the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 The invention relates to a linear array data processing method and steps for measuring the surface pulse pressure wave number-frequency spectrum; Figure 2 Schematic diagram of fancy array formation; Figure 3 for The wave number domain beamforming result when ; Figure 4 for The wave number domain beamforming result when ; Figure 5 Comparison of the total spectrum of unsteady flow acoustic loads, flow load spectrum, and acoustic load spectrum results. DETAILED DESCRIPTION

[0015] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0016] Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0017] In the following, the specific implementation of the present invention is described by taking the wind tunnel test as an example in conjunction with the accompanying drawings. The specific implementation steps are as follows: Figure 1 shown.

[0018] Step 1: Use a two-dimensional fancy array to carry out a pulsating pressure measurement test to obtain the time domain signal of the model surface.

[0019] As shown in Figure 2, this is a number of M= Schematic diagram of the fancy array formation of 76. Pulsating pressure data collection was carried out through wind tunnel tests, with a sampling frequency of 51.2kHz, a wind speed of 30.7m / s, and a sampling time of 30s.

[0020] Step 2: Calculate the cross-spectral matrix of array signals.

[0021] For 76-channel data, the cross-spectrum matrix is ​​calculated. Each element in the matrix is ​​the cross-spectrum between two sensors. During the calculation process, the block length is set to 8192, the overlap rate is 50%, and the Hanning window is used as the window function to calculate and obtain the cross-spectrum matrix Note that the parallel computing method is used here to improve the computing efficiency, that is, the different elements in the matrix are calculated in parallel, and then assigned to the matrix after completion. Pick .

[0022] Step 3: Using the cross-spectral matrix as input, the calculation results are obtained based on the wavenumber domain beamforming algorithm.

[0023] First, calculate the cross-spectral matrix of the array measurement results , and then calculate the array wave number pointing vector according to formula and formula, and then calculate different angular frequencies according to formula Figures 3 and 4 are the wavenumber domain beamforming results under the angular frequency of , The wavenumber domain beamforming result is obtained as follows: The white circle nearby is Acoustic zone boundaries are marked.

[0024] Step 4: Calculate different angular frequencies Down , and use the square sum method to obtain each Download all , Corresponding The sum of Express and calculate with the formula. Next The results are plotted and the overall spectrum of the unsteady flow acoustic load can be obtained. This is the total spectrum of the unsteady flow acoustic load displayed logarithmically.

[0025] Step 5: Based on the acoustic zone wave number boundary The integration boundary is the square sum method, and the integration boundary inside and outside the acoustic zone is calculated. Sum and get different Next and Taking Figure 5 as an example, , This is the spectral function of the unsteady acoustic load and the unsteady flow load displayed logarithmically. , , It can be seen that flow energy accounts for the vast majority of total energy, which is mainly reflected in and The acoustic energy is in the lower frequency band (less than ), higher frequency bands (greater than ) has a certain impact, which is mainly reflected in this frequency band and There are more obvious differences.

[0026] This embodiment is also applicable to flight, wind tunnel, water tunnel, self-propelled model and other tests. The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A near-field unsteady flow acoustic load separation method based on a surface pattern array, characterized in that The following steps are involved: Step 1: Use a two-dimensional fancy array to carry out a pulsating pressure measurement test to obtain the time domain signal of the model surface; Step 2: Calculate the cross-spectral matrix of array signals; Step 3: Using the cross-spectral matrix as input, the calculation results are obtained based on the wavenumber domain beamforming algorithm; Step 4: Calculate the wave number domain beamforming results at different angular frequencies, and use the square sum method to obtain the sum of all wave number domain beamforming calculation results at each angular frequency: ， Step 5: Taking the wave number boundary of the acoustic region as the integration boundary, the wave number domain beamforming calculation results inside and outside the integration boundary are summed using the square sum method as follows: ， ， in: is the sum of all wavenumber domain beamforming results at each angular frequency, is the sum of all wavenumber domain beamforming results at each angular frequency within the boundary, is the sum of all wavenumber domain beamforming results at each angular frequency outside the boundary, is the wave number boundary of the acoustic region, is the flow wave number, is the spanwise wave number, is the angular frequency, for a certain , , The wavenumber domain beamforming calculation results are as follows: are the maximum and minimum values ​​of the streamwise wave number, are the maximum and minimum spanwise wavenumber values, respectively.

2. A near-field unsteady flow acoustic load separation method based on a surface pattern array according to claim 1, characterized in that In step five, the Corresponding to the unsteady acoustic load, The corresponding unsteady flow load is the wave number boundary of the acoustic zone: ， in: Refers to the flow velocity, Refers to the speed of sound.

3. The near-field unsteady flow acoustic load separation method based on surface pattern array according to claim 1 is characterized in that In step 2, each cross-spectral function value can be calculated by a parallel computing method to improve the computing efficiency.

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