Method for accurately acquiring dominant mode in jet flow wind tunnel flow field

Abstract

According to the method for accurately obtaining the dominant mode in the jet flow wind tunnel flow field, a single-frequency mode decomposition method is used for carrying out mode decomposition on pulsating pressure in the jet flow wind tunnel flow field, and the overall dynamic characteristics of the jet flow wind tunnel flow field can be obtained; the modals obtained through modal decomposition are sorted according to the energy ratio, the frequency corresponding to the modal with the large energy ratio is the dominant jet flow wind tunnel flow field pressure pulsation frequency, the disturbance source of the frequency can be judged according to the spatial distribution result of the single frequency modal, and the growth rate information of the frequency can also be accurately obtained. The method is convenient and rapid, can accurately obtain the pulsating pressure frequency and growth rate information of the flow field of the complex jet flow wind tunnel, obtains the global modal structure of the flow field, and rapidly judges the frequency source which has the greatest influence on the pulsating pressure of the flow field of the wind tunnel. A new method is provided for construction and safe operation of a large-scale high-speed jet wind tunnel, improvement of flow field quality and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of unsteady fluctuation mechanism of flow field of jet wind tunnel, and particularly relates to a method for accurately obtaining a dominant mode in the flow field of jet wind tunnel based on single-frequency proper orthogonal decomposition. BACKGROUND

[0002] A wind tunnel is an indispensable experimental equipment for aerodynamics research, and has played an important role in aerodynamic research and aerodynamic design of aircraft. Many modern large wind tunnels are based on the principle of accelerating variable-area nozzle to generate jet. Therefore, the vibration, noise and flow field quality of the wind tunnel are closely related to the unsteady characteristics of the jet. The jet problem in wind tunnel engineering mainly originates from the unsteady characteristics of the jet itself and the interaction with complex flow structure, and a deep understanding of the physical mechanism of unsteady flow field of the jet is a fundamental prerequisite for solving engineering technical problems.

[0003] The traditional steady numerical simulation method cannot explain the unsteady characteristics of the jet, such as the development and movement of shear layer and vortex structure. With the progress of computer hardware and numerical methods, the full three-dimensional unsteady flow field distribution of the jet can be obtained through large-scale unsteady numerical calculation, so as to explore the flow details of the jet flow field and deeply explore the mechanism of unsteady flow. Large-scale unsteady numerical simulation will generate a large amount of unsteady data information, and how to quickly and scientifically analyze the data is a new challenge.

[0004] In order to reveal the dynamic characteristics of the unsteady flow field of the jet, it is necessary to explore a more efficient flow field feature extraction method, extract the dynamic characteristics of the jet flow field, explore the evolution law of the flow structure, reveal the jet flow mechanism and improve the quality of the jet flow field. SUMMARY

[0005] The technical purpose of the present application is to provide a method for accurately obtaining a dominant mode in the flow field of jet wind tunnel, which uses single-frequency mode decomposition method to perform mode decomposition on the fluctuating pressure in the flow field of jet wind tunnel, can accurately obtain the global dynamic characteristics of the flow field of jet wind tunnel, obtain the frequency of the dominant pressure fluctuation of the flow field of jet wind tunnel, and further judge the disturbance source of the frequency according to the spatial distribution result of the single frequency mode.

[0006] To achieve the above technical purpose, the present application adopts the following technical scheme:

[0007] A method for accurately obtaining a dominant mode in the flow field of jet wind tunnel, comprising the following steps:

[0008] obtaining the fluctuating pressure field information in the test cabin of the jet wind tunnel changing with time by numerical simulation method;

[0009] arranging the fluctuating pressure field information in the test cabin of the jet wind tunnel into a two-dimensional space-time data matrix;

[0010] mode decomposition is performed on the two-dimensional data matrix of the fluctuating pressure field in the test cabin of the jet wind tunnel to obtain the global dynamic characteristics of the jet wind tunnel flow field, the dynamic characteristics being three-dimensional spatial distribution information, corresponding frequency information, growth rate information and energy proportion of different modes;

[0011] The different modes obtained by mode decomposition are sorted according to the energy proportion, and the first q modes are selected as the dominant modes in the jet wind tunnel flow field, the frequency corresponding to the dominant modes being the frequency of the dominant fluctuating pressure of the jet wind tunnel flow field, and the energy sum of the first q modes being 90% of the total energy sum of all modes.

[0012] Preferably, the fluctuating pressure field information in the test cabin of the jet wind tunnel is calculated by a numerical simulation method, and the method is as follows:

[0013] A mathematical model is established according to the actual wind tunnel, and redundant interference is removed to simplify the model of the test cabin of the wind tunnel;

[0014] A plurality of structured grids are drawn, and grid and time step independence verification is performed;

[0015] The detached eddy simulation method is used for unsteady calculation to obtain the three-dimensional spatial distribution information of the fluctuating pressure of the test cabin of the jet wind tunnel, i.e. the fluctuating pressure field information.

[0016] Preferably, the fluctuating pressure field information in the test cabin of the jet wind tunnel is arranged into a two-dimensional data matrix, and the method is as follows:

[0017] The unsteady flow field fluctuating pressure information of the test cabin of the jet wind tunnel at N time points is intercepted, and the three-dimensional spatial distribution information of the fluctuating pressure in the test cabin of the jet wind tunnel at each time point is arranged into a single column vector according to a certain rule, and is defined as representing the pressure field [p1, p2, …, p M ] at the i-th time point, wherein M represents the number of grid points of the test cabin of the jet wind tunnel;

[0018] The radial basis interpolation method is used to reduce the data amount, and then the fluctuating pressure fields at N time points are selected to form an M×N two-dimensional data matrix.

[0019] Preferably, mode decomposition is performed on the two-dimensional data matrix of the fluctuating pressure field in the test cabin of the jet wind tunnel to obtain the global dynamic characteristics of the jet wind tunnel flow field, and the method is as follows:

[0020] The left singular matrix U, the diagonal matrix S and the right singular matrix V are obtained by performing the eigen-orthogonal decomposition on the two-dimensional time-space data matrix of the fluctuating pressure field in the test cabin of the jet wind tunnel, wherein the time variable U×S is obtained by multiplying the left singular matrix U by the time variable S, and the column vector of the right singular matrix V is the mode of the eigen-orthogonal decomposition;

[0021] The characteristic value of each eigen-orthogonal decomposition mode is obtained by taking the square of the diagonal element of the matrix S and dividing the square by N, that is, the energy corresponding to each mode;

[0022] Then, the frequency information of the time variable corresponding to each mode is obtained by performing the fast Fourier transform on the time variable U×S corresponding to each mode;

[0023] The time variable information containing only the dominant frequency is obtained by performing the inverse Fourier transform on the dominant frequency and the frequency in the field of each mode; the frequency in the field refers to the frequency between two dominant frequencies;

[0024] The pressure field under the action of a single frequency is obtained by linearly superimposing the time variables containing the same dominant frequency in different modes and the corresponding modes, and the pressure field has accurate growth rate information.

[0025] Preferably, the disturbance source and the growth rate information of the frequency can be judged according to the spatial distribution result of the single frequency mode.

[0026] A system for accurately obtaining the dominant mode of the jet wind tunnel flow field, comprising a fluctuating pressure field information acquisition module, a two-dimensional data matrix generation module, a jet wind tunnel flow field global dynamic characteristic acquisition module, and a jet wind tunnel flow field dominant mode acquisition module;

[0027] The fluctuating pressure field information acquisition module: the fluctuating pressure field information in the test cabin of the jet wind tunnel is calculated by a numerical simulation method;

[0028] The two-dimensional data matrix generation module: the fluctuating pressure field information in the test cabin of the jet wind tunnel is arranged into a two-dimensional data matrix;

[0029] The jet wind tunnel flow field global dynamic characteristic acquisition module: the two-dimensional time-space data matrix of the fluctuating pressure field in the test cabin of the jet wind tunnel is subjected to mode decomposition to obtain the global dynamic characteristics of the jet wind tunnel flow field;

[0030] The jet wind tunnel flow field dominant mode acquisition module: different modes obtained by mode decomposition are sorted in descending order according to the energy proportion, and the first q modes are selected as the dominant modes of the jet wind tunnel flow field, the frequency corresponding to the dominant mode is the frequency of the dominant fluctuating pressure of the jet wind tunnel flow field, and the energy sum of the first q modes is 90% of the total energy sum of all modes.

[0031] Preferably, the fluctuating pressure field information acquisition module is implemented as follows:

[0032] Establish a mathematical model based on the actual wind tunnel, remove unnecessary interference, and simplify the wind tunnel test chamber model;

[0033] Draw multiple structured grids and verify grid and time step independence;

[0034] The detached eddy simulation method is used to perform unsteady calculations to obtain the three-dimensional spatial distribution information of the pulsating pressure of the jet wind tunnel test chamber that changes with time, that is, the pulsating pressure field information.

[0035] Preferably, the two-dimensional data matrix generation module is implemented as follows:

[0036] The unsteady flow field pulsating pressure information of the jet wind tunnel test chamber at N moments is intercepted, and the pulsating pressure three-dimensional spatial distribution information of the jet wind tunnel test chamber at each moment is arranged into a single column vector according to a certain rule. The definition is Represents the pressure field at the i-th moment [p1,p2,…,p M ], where M represents the number of grid points in the jet wind tunnel test chamber;

[0037] The radial basis interpolation method is used to reduce the amount of data, and then the pulsating pressure field at N moments is selected Construct an M×N two-dimensional data matrix.

[0038] Preferably, the jet wind tunnel flow field global dynamic characteristics acquisition module is implemented as follows:

[0039] The two-dimensional space-time data matrix of the pulsating pressure field in the jet wind tunnel test chamber is subjected to intrinsic orthogonal decomposition to obtain the left singular matrix U, the diagonal matrix S, and the right singular matrix V, where U×S is the time variable and the column vector of V is the mode of the intrinsic orthogonal decomposition.

[0040] The eigenvalue of each intrinsic orthogonal decomposition mode is obtained by squaring the diagonal elements of the matrix S and dividing by N, that is, the energy corresponding to each mode;

[0041] Then, the time variable U×S corresponding to each mode is subjected to fast Fourier transform to obtain the frequency information of the time variable corresponding to each mode;

[0042] Performing an inverse Fourier transform on the dominant frequency in each mode and the frequencies within its domain to obtain time variable information containing only the dominant frequency; the frequencies within the domain refer to frequencies between the two dominant frequencies;

[0043] The time variables containing the same dominant frequency in different modes are multiplied by the corresponding modes and then linearly superimposed to obtain the pressure field under the action of a single frequency, which has accurate growth rate information.

[0044] The advantages of the present invention compared with the prior art are:

[0045] This method uses a single-frequency modal decomposition method to perform modal decomposition on the fluctuating pressure in a jet wind tunnel flow field. This method accurately captures the global dynamic characteristics of the jet wind tunnel flow field, determines the dominant frequency of the pressure fluctuations, and identifies the cause of each individual frequency. Compared to traditional modal decomposition methods, this method can more accurately capture the dominant frequency and growth rate information in a jet wind tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of the process of the method for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to the present invention;

[0047] Figure 2 This is a simplified schematic diagram of the free jet wind tunnel model;

[0048] Figure 3 This is the unsteady vortex structure diagram of the free jet wind tunnel flow field;

[0049] Figure 4 is the energy proportion of single-frequency mode in the free jet wind tunnel flow field;

[0050] Figure 5 is the modal distribution of frequency A. DETAILED DESCRIPTION

[0051] Example:

[0052] like Figure 1 As shown in the figure, taking the large-scale free jet wind tunnel pulsating pressure calculation example as an example, the method of accurately obtaining the dominant mode in the jet wind tunnel flow field using the method of the present invention is given as follows:

[0053] 1. First, establish a digital model based on the actual wind tunnel, remove unnecessary interference, and simplify the wind tunnel test chamber model (such as Figure 2 ); perform high-precision structured grid drawing and grid and time step independence verification; use detached eddy simulation method to perform unsteady calculations to obtain the unsteady flow field pulsating pressure field information of the jet wind tunnel test chamber (such as Figure 3 shown).

[0054] 2. Intercept the unsteady flow field pulsating pressure information of the jet wind tunnel test chamber within a period of time (N moments), and arrange the pulsating pressure three-dimensional spatial distribution information of the jet wind tunnel test chamber at each moment into a single column vector according to a certain rule (definition Represents the pressure field at the i-th moment [p1,p2,…,p M ], where M represents the number of grid points in the jet wind tunnel test chamber). Considering that the number of column vectors and rows at a single moment is too large due to the large number of grid points in the wind tunnel test chamber, the RBF (Radial Basis Interpolation) method can be used to reduce the amount of data. Then the pulsating pressure field at N moments is selected. Construct an M×N two-dimensional data matrix.

[0055] 3. The global dynamic characteristics of the jet wind tunnel flow field are obtained by single-frequency modal decomposition. Compared with other modal decomposition methods, the single-frequency modal decomposition method can more accurately capture the dynamic characteristics of the pulsating pressure in the jet wind tunnel test chamber. The two-dimensional spatiotemporal data matrix of the pulsating pressure field in the jet wind tunnel test chamber is subjected to intrinsic orthogonal decomposition (POD) to obtain U, S, and V. U is a left singular matrix, S is a diagonal matrix, and V is a right singular matrix. U×S is the time variable, corresponding to the change of the amplitude of the mode with time, which can be used for time series analysis. The column vector of V is the mode of POD; the eigenvalue of each POD mode is obtained by squaring the diagonal elements of the matrix S and dividing it by N, that is, the energy corresponding to each mode. The main POD modes can be extracted by sorting by energy proportion; then the time variable (U×S) corresponding to each mode is subjected to fast Fourier transform (FFT) ) can obtain the frequency information of the time variable corresponding to each mode (Note: Different from the dynamic mode decomposition (DMD) method, the time information corresponding to the mode obtained by POD decomposition has multiple coupling frequencies); because there are multiple dominant frequencies in the pulsating pressure field in the jet wind tunnel test chamber, the dominant frequency in the mode and the frequency within its domain (the frequency within the domain refers to the frequency between the two main frequencies) are subjected to inverse Fourier transform to obtain the time variable information containing only the dominant frequency; the time variables containing the same dominant frequency in different modes are multiplied by the corresponding mode and then linearly superimposed to obtain the pressure field under the action of a single frequency, and it has accurate growth rate information.

[0056] 4. Sort the different modes obtained by modal decomposition according to their energy proportions, and select the first q modes as the dominant modes in the jet wind tunnel flow field. The frequency corresponding to the dominant mode is the frequency of the pulsating pressure of the dominant jet wind tunnel flow field. The energy sum of the first q modes is close to 90% of the total energy of all modes. (e.g. Figure 4 shown).

[0057] 5. Based on the spatial distribution results of a single frequency mode, the source of the disturbance at that frequency can be determined, and the frequency growth rate information can also be accurately obtained. Figure 5 The figure shows the spatial distribution of the mode of frequency A. The larger amplitudes are mainly distributed near the jet shear layer, indicating that the source of the disturbance at this frequency is the vortex structure developed by the shear layer motion of the jet flow field.

[0058] Further, if the spatial distribution result of the mode of a certain frequency B shows that the larger amplitude is mainly distributed near the core region of the jet and the shear layer, it indicates that the disturbance source of the frequency is the interference between the jet wave structure and the jet shear layer; the spatial distribution result of the mode of frequency C shows that the larger amplitude is mainly distributed near the jet tunnel collector, indicating that the disturbance source of the frequency is the pressure fluctuation generated by the interaction of the jet shear layer vortex shedding and the collector; the spatial distribution result of the mode of frequency D shows that the larger amplitude is mainly distributed near the corner of the jet tunnel test cabin, indicating that the disturbance source of the frequency is the acoustic vibration of the closed space of the test cabin.

[0059] The present application uses a single frequency modal decomposition method to perform modal decomposition on the fluctuating pressure in the jet tunnel flow field, and can obtain the global dynamic characteristics of the jet tunnel flow field; the modes obtained by modal decomposition are sorted according to the energy proportion, and the frequency corresponding to the mode with a larger energy proportion is the frequency of the dominant jet tunnel flow field pressure fluctuation; the disturbance source of the frequency can be judged according to the spatial distribution result of the single frequency mode, and the growth rate information of the frequency can also be accurately obtained. The method proposed in the present application is convenient and fast, and can accurately obtain the pressure fluctuation frequency and growth rate information of the complex jet tunnel flow field, obtain the global mode structure of the flow field, quickly judge the frequency source that has the greatest influence on the pressure fluctuation of the flow field of the wind tunnel, and provide a new method for the construction, safe operation and flow field quality improvement of a large high-speed jet tunnel.

[0060] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

[0061] The contents not described in detail in the specification of the present application are the known technology of those skilled in the art.

Claims

1. A method for accurately obtaining the dominant mode in a jet wind tunnel flow field, characterized in that: The steps are as follows: The time-varying pulsating pressure field information in the jet wind tunnel test chamber is obtained by numerical simulation. Arrange the pulsating pressure field information in the jet wind tunnel test chamber into a two-dimensional space-time data matrix; Perform modal decomposition on the two-dimensional data matrix of the pulsating pressure field in the jet wind tunnel test chamber to obtain the global dynamic characteristics of the jet wind tunnel flow field. The dynamic characteristics are the three-dimensional spatial distribution information of different modes, corresponding frequency information, growth rate information and energy proportion; The different modes obtained by modal decomposition are sorted according to their energy proportions, and the first q modes are selected as the dominant modes in the jet wind tunnel flow field. The frequency corresponding to the dominant mode is the frequency of the pulsating pressure of the dominant jet wind tunnel flow field, and the energy sum of the first q modes is 90% of the total energy of all modes.

2. The method for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 1, characterized in that: The time-varying pulsating pressure field information in the jet wind tunnel test chamber is calculated using numerical simulation methods as follows: Establish a mathematical model based on the actual wind tunnel, remove unnecessary interference, and simplify the wind tunnel test chamber model; Draw multiple structured grids and verify grid and time step independence; The detached eddy simulation method is used to perform unsteady calculations to obtain the three-dimensional spatial distribution information of the pulsating pressure of the jet wind tunnel test chamber that changes with time, that is, the pulsating pressure field information.

3. The method for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 1, characterized in that: The pulsating pressure field information in the jet wind tunnel test chamber is arranged into a two-dimensional data matrix as follows: The unsteady flow field pulsating pressure information of the jet wind tunnel test chamber at N moments is intercepted, and the pulsating pressure three-dimensional spatial distribution information of the jet wind tunnel test chamber at each moment is arranged into a single column vector according to a certain rule. The definition is Represents the pressure field at the i-th moment [p1,p2,…,p M ], where M represents the number of grid points in the jet wind tunnel test chamber; The radial basis interpolation method is used to reduce the amount of data, and then the pulsating pressure field at N moments is selected Construct an M×N two-dimensional data matrix.

4. The method for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 1, characterized in that: The modal decomposition of the two-dimensional data matrix of the pulsating pressure field in the jet wind tunnel test chamber is performed to obtain the global dynamic characteristics of the jet wind tunnel flow field. The method is as follows: The two-dimensional space-time data matrix of the pulsating pressure field in the jet wind tunnel test chamber is subjected to intrinsic orthogonal decomposition to obtain the left singular matrix U, the diagonal matrix S, and the right singular matrix V, where U×S is the time variable and the column vector of V is the mode of the intrinsic orthogonal decomposition. The eigenvalue of each intrinsic orthogonal decomposition mode is obtained by squaring the diagonal elements of the matrix S and dividing by N, that is, the energy corresponding to each mode; Then, the time variable U×S corresponding to each mode is subjected to fast Fourier transform to obtain the frequency information of the time variable corresponding to each mode; Performing an inverse Fourier transform on the dominant frequency in each mode and the frequencies within its domain to obtain time variable information containing only the dominant frequency; the frequencies within the domain refer to frequencies between the two dominant frequencies; The time variables containing the same dominant frequency in different modes are multiplied by the corresponding modes and then linearly superimposed to obtain the pressure field under the action of a single frequency, which has accurate growth rate information.

5. The method for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 1, characterized in that: According to the spatial distribution results of a single frequency mode, the disturbance source and frequency growth rate information of the frequency can be determined.

6. A system for accurately obtaining the dominant modes in a jet wind tunnel flow field, characterized in that: It includes a pulsating pressure field information acquisition module, a two-dimensional data matrix generation module, a jet wind tunnel flow field global dynamic characteristics acquisition module, and a jet wind tunnel flow field dominant mode acquisition module; Pulsating pressure field information acquisition module: obtains the time-varying pulsating pressure field information in the jet wind tunnel test chamber through numerical simulation methods; Two-dimensional data matrix generation module: arranges the pulsating pressure field information in the jet wind tunnel test chamber into a two-dimensional data matrix; Jet wind tunnel flow field global dynamic characteristics acquisition module: Perform modal decomposition on the two-dimensional spatiotemporal data matrix of the pulsating pressure field in the jet wind tunnel test chamber to obtain the global dynamic characteristics of the jet wind tunnel flow field; Jet wind tunnel flow field dominant mode acquisition module: The different modes obtained by modal decomposition are sorted from large to small according to the energy proportion, and the first q modes are selected as the dominant modes in the jet wind tunnel flow field. The frequency corresponding to the dominant mode is the frequency of the pulsating pressure of the dominant jet wind tunnel flow field. The energy sum of the first q modes is 90% of the total energy of all modes.

7. The system for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 6, characterized in that: The implementation method of the pulsating pressure field information acquisition module is as follows: Establish a mathematical model based on the actual wind tunnel, remove unnecessary interference, and simplify the wind tunnel test chamber model; Draw multiple structured grids and verify grid and time step independence; The detached eddy simulation method is used to perform unsteady calculations to obtain the three-dimensional spatial distribution information of the pulsating pressure of the jet wind tunnel test chamber that changes with time, that is, the pulsating pressure field information.

8. The system for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 6, characterized in that: The implementation method of the two-dimensional data matrix generation module is as follows: The unsteady flow field pulsating pressure information of the jet wind tunnel test chamber at N moments is intercepted, and the pulsating pressure three-dimensional spatial distribution information of the jet wind tunnel test chamber at each moment is arranged into a single column vector according to a certain rule. The definition is Represents the pressure field at the i-th moment [p1,p2,…,p M ], where M represents the number of grid points in the jet wind tunnel test chamber; The radial basis interpolation method is used to reduce the amount of data, and then the pulsating pressure field at N moments is selected Construct an M×N two-dimensional data matrix.

9. The system for accurately obtaining the dominant mode in the flow field of a jet wind tunnel according to claim 6, characterized in that: The implementation method of the global dynamic characteristics acquisition module of the jet wind tunnel flow field is as follows: The two-dimensional space-time data matrix of the pulsating pressure field in the jet wind tunnel test chamber is subjected to intrinsic orthogonal decomposition to obtain the left singular matrix U, the diagonal matrix S, and the right singular matrix V, where U×S is the time variable and the column vector of V is the mode of the intrinsic orthogonal decomposition. The eigenvalue of each intrinsic orthogonal decomposition mode is obtained by squaring the diagonal elements of the matrix S and dividing by N, that is, the energy corresponding to each mode; Then, the time variable U×S corresponding to each mode is subjected to fast Fourier transform to obtain the frequency information of the time variable corresponding to each mode; Performing an inverse Fourier transform on the dominant frequency in each mode and the frequencies within its domain to obtain time variable information containing only the dominant frequency; the frequencies within the domain refer to frequencies between the two dominant frequencies; The time variables containing the same dominant frequency in different modes are multiplied by the corresponding modes and then linearly superimposed to obtain the pressure field under the action of a single frequency, which has accurate growth rate information.

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