Method for identifying shock wave motion frequency and growth rate

Abstract

The invention relates to a method for identifying shock wave motion frequency and growth rate, which comprises the following steps of: performing modal decomposition on airfoil profile surrounding flow field pressure data of transonic airfoil profile forced oscillation by using a single-frequency modal decomposition method to obtain frequency and modal characteristics of a surrounding flow field during transonic airfoil profile forced oscillation; the single-frequency modes are sequenced according to the energy ratio from large to small, the first-order mode is shock waves formed on the two sides of the airfoil profile under forced oscillation, and the frequency of the first-order mode is consistent with the motion frequency of the shock waves; the second-order mode reflects frequency doubling structures formed on the two sides of the airfoil profile in the swing process of shock waves on the two sides of the airfoil profile; the third-order mode reflects a slow evolution structure of the flow field from the initial state to the periodic pulsation state, and the frequency of the third-order mode is the frequency corresponding to the total physical duration of all the flow fields participating in mode decomposition; and identifying the shock wave growth rate according to the time coefficient amplitude of each order modal. The frequency and growth rate of the shock wave can be accurately captured, and the form of the shock wave is given.

Description

Technical Field

[0001] The invention belongs to the technical field of unsteady flow field information extraction and relates to a method for identifying shock wave motion frequency and growth rate. Background Art

[0002] Advances in science and technology are driving the continuous development of aircraft towards higher maneuverability and agility. When performing high-speed maneuvers, aircraft are subject to unsteady aerodynamic forces and significant aerodynamic hysteresis, which not only affects flight performance but can also lead to unpredictable or uncontrollable motion states, or even loss of control. To effectively control an aircraft during rapid maneuvers, it is essential to quickly and accurately identify the unsteady characteristics of the flow field around the aircraft, particularly the motion pattern and frequency of shock waves.

[0003] Traditional methods for identifying shock wave frequencies rely on Fourier transforms to extract the pressure pulsation frequency of the flow field near the shock wave, which can be used to determine the shock wave's frequency. However, these methods are limited in that they can only approximate the shock wave's frequency based on pressure changes at a few individual monitoring points. They are unable to capture the shock wave's motion morphology within the flow field or accurately determine its growth rate. Summary of the Invention

[0004] The technical problem solved by the present invention is to overcome the deficiencies of the prior art and propose a method for identifying the frequency and growth rate of shock wave motion, thereby solving the problem that the motion mode and frequency of shock waves are difficult to accurately identify.

[0005] The solution to the technical problem of the present invention is: using the single-frequency modal decomposition method to perform modal decomposition on the pulsating pressure in the jet wind tunnel flow field, it can accurately obtain the global dynamic characteristics of the jet wind tunnel flow field, and obtain the frequency of the dominant jet wind tunnel flow field pressure pulsation. According to the spatial distribution results of the single frequency mode, the source of the disturbance of the frequency can be determined.

[0006] Specifically, a method for identifying the frequency and growth rate of shock wave motion is proposed, comprising the following steps:

[0007] The flow field pressure data around the airfoil of the transonic airfoil forced oscillation is obtained through CFD calculation, and the flow field pressure data is converted into a time-space matrix;

[0008] The single-frequency modal decomposition method is used to perform modal decomposition on the pressure data of the flow field around the transonic airfoil during forced oscillation, and the frequency, modal characteristics and time coefficient corresponding to the mode of the surrounding flow field during forced oscillation of the transonic airfoil are obtained.

[0009] The single-frequency modes obtained by modal decomposition are sorted in descending order of energy proportion, and the N-order modes with an energy proportion of not less than 90% are selected. The first-order mode is the shock wave formed on both sides of the airfoil due to forced oscillation. The frequency of the first-order mode is consistent with the frequency of the shock wave motion; the second-order mode reflects the frequency-doubled structure formed on both sides of the airfoil due to the swing of the shock wave on both sides of the airfoil; the third-order mode reflects the slow evolution structure of the flow field from the initial state to the periodic pulsation state. The frequency of the third-order mode is the frequency corresponding to the total physical duration of all flow fields participating in the modal decomposition;

[0010] The amplitude of the time coefficient corresponding to each single-frequency mode changes with time, reflecting the growth rate information of each single-frequency mode over time. The growth rate of the time coefficient corresponding to the first-order mode is the growth rate of the shock waves formed on both sides of the airfoil due to forced oscillation.

[0011] Furthermore, the pressure data of the flow field around the airfoil of the transonic airfoil forced oscillation is obtained through CFD calculation, specifically:

[0012] A mathematical model was established based on the existing airfoil database, and structured mesh rendering and mesh independence verification of the transonic airfoil flow field were performed. The RANS simulation method was used for unsteady calculations to obtain transient pressure field data of the transonic airfoil forced oscillation. The airfoil pressure data at each moment were arranged into a single column vector by numbering, and the airfoil pressure data column vectors at m moments were obtained to construct a space-time matrix; m is greater than twice the period of the transonic airfoil shock wave motion.

[0013] Furthermore, the CFD calculation condition is set to inviscid flow.

[0014] Furthermore, the control equation of the CFD calculation is set to the three-dimensional Euler equation.

[0015] Furthermore, the spatial discretization method of the CFD calculation is set to adopt the AUSM+-up format.

[0016] Furthermore, the single-frequency modal decomposition method is used to perform modal decomposition on the flow field pressure data around the airfoil of the transonic airfoil forced oscillation, specifically as follows:

[0017] Perform intrinsic orthogonal decomposition on the pressure data matrix of the flow field around the airfoil of the transonic airfoil forced oscillation 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;

[0018] The eigenvalue of each intrinsic orthogonal decomposition mode, that is, the energy corresponding to each mode, is obtained by squaring the diagonal elements of the matrix S and dividing by N. Then, the time variable U×S corresponding to each mode is fast Fourier transformed to obtain the frequency information of the time variable corresponding to each mode.

[0019] 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;

[0020] 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.

[0021] The beneficial effects of the present invention compared with the prior art are:

[0022] (1) The method of identifying the frequency and growth rate of shock wave motion in the present invention can obtain the global dynamic characteristics of the flow field of the transonic airfoil forced oscillation; the method is convenient and fast, and can accurately extract the main modal distribution and corresponding single frequency information in the flow field near the airfoil during the transonic airfoil forced oscillation, and obtain the shock wave motion frequency and morphology, providing a new method for obtaining the shock wave motion frequency during the transonic airfoil forced oscillation.

[0023] (2) The method of the present invention for identifying the frequency and growth rate of shock wave motion can accurately capture the frequency and growth rate of shock wave and can give the shape of shock wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a method for identifying the frequency and growth rate of shock wave motion;

[0025] Figure 2 This is a schematic diagram of a C-type grid according to an embodiment of the present invention;

[0026] Figure 3 This is a partial enlarged view of the head of the airfoil calculation grid according to an embodiment of the present invention;

[0027] Figure 4 This is a partial enlarged view of the tail of the airfoil calculation grid according to an embodiment of the present invention;

[0028] Figure 5 The lift coefficient changes over time in an embodiment of the present invention;

[0029] Figure 6 The pitching moment coefficient changes over time in the embodiment of the present invention;

[0030] Figure 7 is the energy proportion of the first 20 single-frequency modes of the F-POD according to the embodiment of the present invention;

[0031] Figure 8 The first three-order modal space distribution (F-POD) of the embodiment of the present invention;

[0032] in: Figure 8 (1) is the first-order mode (6.5Hz), Figure 8 (2) is the second-order mode (13.5Hz), Figure 8 (3) is the third-order mode (0.5Hz);

[0033] Figure 9 are the time coefficients corresponding to the first three modes in the embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings and examples.

[0035] like Figure 1 As shown, the present invention proposes a method for identifying the frequency and growth rate of shock wave motion, comprising the following steps:

[0036] S1. Obtain the flow field pressure data around the airfoil of the transonic airfoil forced oscillation through CFD calculation, and convert the flow field pressure data into a time-space matrix;

[0037] S2. Use the single-frequency modal decomposition method (F-POD) to perform modal decomposition on the pressure data of the flow field around the airfoil during the forced oscillation of the transonic airfoil to obtain the dynamic characteristics of the flow field around the airfoil during the forced oscillation of the transonic airfoil, including the frequency, modal characteristics and time coefficient corresponding to the mode of the flow field;

[0038] S3. Sort the single-frequency modes obtained by modal decomposition in descending order of energy proportion, and select the N-order modes with an energy proportion of not less than 90%. The first-order mode is the shock wave formed on both sides of the airfoil by forced oscillation. The frequency of the first-order mode is consistent with the frequency of the forced oscillation of the transonic airfoil, that is, the frequency of the first-order mode corresponds to the shock wave motion frequency; the second-order mode reflects the frequency-harmonic structure formed on both sides of the airfoil due to the swing of the shock wave on both sides of the airfoil; the third-order mode reflects the slowly evolving structure of the flow field from the initial state to the periodic pulsation state. The frequency of the third-order mode is the frequency corresponding to the total physical duration of all flow fields participating in the modal decomposition;

[0039] S4. The amplitude of the time coefficient corresponding to each single-frequency mode changes over time, reflecting the growth rate of each single-frequency mode over time. The growth rate information obtained through the single-frequency modal decomposition method is accurate. The growth rate of the time coefficient corresponding to the first-order mode is the growth rate of the shock waves formed on both sides of the airfoil due to forced oscillation.

[0040] Among them, the flow field pressure data around the airfoil of the transonic airfoil forced oscillation is obtained by CFD calculation, specifically:

[0041] Firstly, a mathematical model is established based on the existing airfoil database, and the structured grid drawing and grid independence verification of the transonic airfoil flow field are performed. Then, the RANS simulation method is used for unsteady calculations to obtain the transient pressure field data of the transonic airfoil forced oscillation. The airfoil pressure data at each moment are arranged into a single column vector by numbering, and the airfoil pressure data column vectors at m moments are obtained to obtain a space-time matrix; m is greater than twice the period of the transonic airfoil shock wave motion.

[0042] Set the CFD calculation condition to inviscid flow.

[0043] Set the governing equation for CFD calculation to the three-dimensional Euler equation.

[0044] The spatial discretization method for CFD calculations is set to AUSM+-up format.

[0045] The specific implementation method of step S2 is:

[0046] Perform intrinsic orthogonal decomposition on the pressure data matrix of the flow field around the airfoil of the transonic airfoil forced oscillation 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;

[0047] The eigenvalue of each intrinsic orthogonal decomposition mode, that is, the energy corresponding to each mode, is obtained by squaring the diagonal elements of the matrix S and dividing by N. Then, the time variable U×S corresponding to each mode is fast Fourier transformed to obtain the frequency information of the time variable corresponding to each mode.

[0048] 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;

[0049] 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.

[0050] Example 1

[0051] Taking CT5 (NACA0012 steady-state airfoil with Ma=0.755) as an example, the flow around the steady-state airfoil is calculated. The calculation grid of the airfoil is as follows: Figures 2 to 4 As shown, the airfoil pitches about 0.25 times the chord length. The forced pitching oscillation of the flow around a typical airfoil is defined as a sinusoidal function of the angle of attack with time as follows:

[0052] α(t)=A0+A m sin(ω·t)

[0053] Among them, A0 is the initial angle of attack, A0=0.016°, A m is the amplitude angle of the airfoil motion, A m =2.51°, ω is the angular frequency of motion, ω=2kV ∞ / l, k is the reduction frequency. In this embodiment, under the Mach number, k=0.0814, l is the chord length of the airfoil, V ∞ is the incoming flow velocity at infinity.

[0054] This embodiment adds a linear growth rate to the above formula to construct a piecewise function. When t<3s, the amplitude of the airfoil rotation angle has a linear growth rate. When t≥3s, the airfoil rotation angle changes with a constant amplitude.

[0055]

[0056] The transient flow field data of 2s (2s-4s) during the transition to stability of the forced oscillation of the transonic airfoil were selected (e.g. Figure 5 and Figure 6 The F-POD method can identify a maximum frequency of 100 Hz and a minimum frequency of 0.5 Hz.

[0057] The energy ratio of each single frequency mode in the modal decomposition result is obtained by F-POD modal decomposition, such as Figure 7 As shown in the figure, the strong pitching flow field of the transonic airfoil has three main single-frequency information, namely 6.5Hz, 13.5Hz, and 0.5Hz. Among them, the frequency of the first-order mode is consistent with the frequency of the fully developed transonic airfoil forced oscillation (6.5Hz), the second-order mode is its double frequency (13.5Hz), and the frequency of the third-order mode is the frequency corresponding to the total physical duration of all the flow fields involved in the modal decomposition (0.5Hz).

[0058] Figure 8 (1) to (3) show the first three modal structures of the F-POD, where the cloud diagrams are normalized by the maximum value of each mode. From the comparison of the cloud diagrams, it can be found that the first-order mode describes the shock waves generated on both sides of the airfoil due to strong oscillation. The second-order mode mainly reflects the frequency-harmonic structure formed on both sides of the airfoil due to the swing of the shock wave on both sides of the airfoil, while the third-order mode mainly reflects the slowly evolving structure of the flow field, from the initial state to the periodic pulsation state.

[0059] like Figure 9 As shown in Figure 3, the time coefficient amplitude obtained by the F-POD method, corresponding to the first and second order states, shows the irregular evolution process of the actual flow field from the initial state to periodic pulsation over time, which first grows slowly and then becomes uniform and unchanged.

[0060] The present application provides a computer-readable storage medium storing computer instructions. When the computer instructions are executed on a computer, the computer executes Figure 1 The method described.

[0061] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage and optical storage, etc.) that contain computer-usable program code.

[0062] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0063] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0064] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0065] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

[0066] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for identifying shock wave motion frequency and growth rate, characterized in that: The following steps are involved: The flow field pressure data around the airfoil of the transonic airfoil forced oscillation is obtained through CFD calculation, and the flow field pressure data is converted into a time-space matrix; The single-frequency modal decomposition method is used to perform modal decomposition on the pressure data of the flow field around the transonic airfoil during forced oscillation, and the frequency, modal characteristics and time coefficient corresponding to the mode of the surrounding flow field during forced oscillation of the transonic airfoil are obtained. The single-frequency modes obtained by modal decomposition are sorted in descending order of energy proportion, and the N-order modes with an energy proportion of not less than 90% are selected. The first-order mode is the shock wave formed on both sides of the airfoil due to forced oscillation. The frequency of the first-order mode is consistent with the frequency of the shock wave motion; the second-order mode reflects the frequency-doubled structure formed on both sides of the airfoil due to the swing of the shock wave on both sides of the airfoil; the third-order mode reflects the slow evolution structure of the flow field from the initial state to the periodic pulsation state. The frequency of the third-order mode is the frequency corresponding to the total physical duration of all flow fields participating in the modal decomposition; The amplitude of the time coefficient corresponding to each single-frequency mode changes with time, reflecting the growth rate information of each single-frequency mode over time. The growth rate of the time coefficient corresponding to the first-order mode is the growth rate of the shock waves formed on both sides of the airfoil due to forced oscillation.

2. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: The pressure data of the flow field around the airfoil of the transonic airfoil forced oscillation are obtained by CFD calculation, specifically: A mathematical model was established based on the existing airfoil database, and structured mesh rendering and mesh independence verification of the transonic airfoil flow field were performed. The RANS simulation method was used for unsteady calculations to obtain transient pressure field data of the transonic airfoil forced oscillation. The airfoil pressure data at each moment were arranged into a single column vector by numbering, and the airfoil pressure data column vectors at m moments were obtained to construct a space-time matrix; m is greater than twice the period of the transonic airfoil shock wave motion.

3. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: Set the CFD calculation condition to inviscid flow.

4. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: Set the governing equation for CFD calculation to the three-dimensional Euler equation.

5. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: The spatial discretization method for CFD calculations is set to AUSM+-up format.

6. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: The single-frequency modal decomposition method is used to perform modal decomposition on the flow field pressure data around the airfoil of the transonic airfoil forced oscillation, specifically as follows: Perform intrinsic orthogonal decomposition on the pressure data matrix of the flow field around the airfoil of the transonic airfoil forced oscillation 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, that is, the energy corresponding to each mode, is obtained by squaring the diagonal elements of the matrix S and dividing by N. Then, the time variable U×S corresponding to each mode is fast Fourier transformed 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.

7. The method for identifying shock wave motion frequency and growth rate according to claim 1, characterized in that: The transonic airfoil is a NACA0012 steady-state airfoil.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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