Dynamic derivative data processing method based on discrete Fourier transform

Abstract

The invention discloses a dynamic derivative data processing method based on discrete Fourier transform, and belongs to the technical field of aviation aerodynamic wind tunnel special test data processing. The problem that in the prior art, a traditional dynamic derivative data processing method is low in result precision due to the non-frequency multiplication phenomenon is solved. The method comprises the following steps: acquiring a pitching moment signal and an angle element signal of an aircraft model in a vibration process through a balance; according to a set sampling rate and a set sample number, calculating to obtain a resolution frequency; obtaining a discrete Fourier transform formula under the main vibration frequency according to the correlation function calculation formula and the resolution frequency; according to the first phase difference and the second phase difference, calculating to obtain a phase difference between the collected pitching moment signal and the angle element signal; according to a dynamic derivative calculation formula in the pitching direction and the phase difference, a final dynamic derivative value is obtained through calculation. The method effectively improves the accuracy of the aircraft model dynamic derivative processing result, and can be applied to processing the aircraft model dynamic derivative test data.

Description

Technical Field

[0001] The invention relates to a dynamic derivative data processing method, in particular to a dynamic derivative data processing method based on discrete Fourier transform, and belongs to the technical field of special test data processing of aviation aerodynamic wind tunnel. Background Art

[0002] The high-speed wind tunnel dynamic derivative test is a special wind tunnel test for obtaining the unsteady aerodynamic forces of an aircraft. The commonly used test process is to use a vibration system to force the aircraft model to perform simple harmonic vibrations in the wind tunnel test flow field, and then use a balance to measure the aerodynamic coefficients and angular vibration displacements of the aircraft model during the movement, and then obtain the final dynamic derivative test value of the aircraft model through data processing.

[0003] When the aircraft model is subjected to forced vibration in the wind tunnel, the torque signal reflected by the balance includes not only the basic vibration torque signal (fundamental pitch torque signal), high-order harmonic signal, static torque signal and random noise signal, etc. The torque signal formula collected in forced vibration is expressed as: ; in, To collect signals, is the static torque signal, is the fundamental pitch moment signal, i.e. the signal generated by the main vibration frequency, is a high-order harmonic signal, is a random noise signal; In the dynamic derivative test data processing, the fundamental pitch moment signal is a useful signal. The moment signal formula collected in the forced vibration is multiplied by the sine function on both sides. and cosine function Then perform integration to obtain the integrated signal formula; The integrated signal formula is expressed as: ; ; According to the properties of trigonometric functions, we can deduce , ,in, is the amplitude of the fundamental pitch moment signal, is the phase difference between the angle element signal and the moment fundamental signal. According to the dynamic derivative calculation formula in the pitch direction, To find the necessary value of the dynamic derivative of the model, to obtain Common data processing methods include signal cross-correlation method and ellipse area method. Signal cross-correlation method is to multiply the collected angle element signal with the collected vibration torque signal, which can remove the influence of static torque signal, high-order harmonic signal and random noise signal. The data acquisition equipment can filter out some useless signals by setting the low-pass filter frequency, and then extract the necessary values ​​through digital operation. and the amplitude of the angle element signal, and finally the dynamic derivative value of the aircraft model is obtained; the ellipse area method is that the collected dynamic torque and angle curve is a hysteresis loop, which can be regarded as an ellipse. The size of the dynamic derivative is estimated according to the size of the ellipse area, but the ellipse area method is only used for verification and cannot be applied in engineering.

[0004] Therefore, the most mainstream method for solving dynamic derivative data is the signal cross-correlation method. However, the application premise is that the sinusoidal vibration of the model is stable, and during the vibration of the model, the collected signal does not contain the non-harmonic situation of the fundamental frequency. However, often, during the test, due to the aerodynamic unsteadiness of the aircraft model itself, the vibration of the strut, the clearance of the motion mechanism, etc., it is impossible to ensure that the collected signal is completely a high-order simple harmonic signal, and there is often a non-harmonic signal phenomenon, that is, the signal formula after integration When the value is not an integer, the non-frequency doubling phenomenon cannot be eliminated by the orthogonality of trigonometric functions. In this case, the formula derived from the properties of trigonometric functions will not hold, and the above two methods will no longer be applicable. At the same time, in the process of data processing, it is often necessary to The torque waveforms are extracted together without calculating the individual phase angles and analyzing the torque amplitude of each cycle. When the torque waveform does not meet the test requirements, the accuracy of the results will be seriously affected.

[0005] In summary, when the vibration model acquisition signal has non-frequency doubling phenomenon, the conventional test processing method has obvious shortcomings, and a dynamic derivative data processing method based on discrete Fourier transform is needed to accurately obtain the model dynamic derivative. Summary of the invention

[0006] A brief overview of the present invention is provided below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0007] In view of this, in order to solve the problem of low result accuracy caused by non-frequency doubling phenomenon in the traditional dynamic derivative data processing method in the prior art, the present invention provides a dynamic derivative data processing method based on discrete Fourier transform.

[0008] The technical solution is as follows: A method for processing dynamic derivative data based on discrete Fourier transform, comprising the following steps: S1. Perform a dynamic derivative test to collect the pitch moment signal and angle element signal of the aircraft model during vibration through a balance; S2. Calculate the resolution frequency according to the set sampling rate and number of samples; S3. Based on the correlation function calculation formula and the resolution frequency, the discrete Fourier transform formula at the main vibration frequency is obtained; S4. According to the discrete Fourier transform formula, the amplitude and the first phase difference of the pitch moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency are calculated; S5. Calculate the phase difference between the pitch moment signal and the angle element signal collected according to the first phase difference and the second phase difference; S6. Calculate the final dynamic derivative value according to the dynamic derivative calculation formula in the pitch direction and the phase difference.

[0009] Furthermore, in S1, the pitch moment signal is expressed as ,in, is the amplitude of the fundamental pitch moment signal, is the static torque signal, is the sum of the noise signals of all simple harmonic oscillation signals, is the main vibration frequency, is the first phase difference, For time; The angle signal is expressed as ,in, is the amplitude of the angle element signal, is the interference signal, is the second phase difference.

[0010] Furthermore, in S2, the frequency resolution It is expressed as: ; in, is the sampling rate, is the number of samples.

[0011] Furthermore, in S3, the correlation function calculation formula is expressed as: ; in, is the sampling value, is the serial number, For the k The relevant function value under the sequence number; The discrete Fourier transform formula is expressed as: ; in, .

[0012] Furthermore, in S5, the phase difference between the pitch moment signal and the angle element signal is It is expressed as: .

[0013] Furthermore, in S6, for the pitching vibration process in the high-speed dynamic derivative wind tunnel test, the amplitude of the fundamental pitching moment signal obtained in step S4 and step S5 is and phase difference Substitute the dynamic derivative calculation formula in the pitch direction to obtain the final dynamic derivative value; The calculation formula of the dynamic derivative in the pitch direction is expressed as: ; in, is the angular velocity of the aircraft model vibration, , is the dynamic derivative value in the pitch direction caused by the change of angular velocity, is the dynamic derivative value in the pitch direction caused by the change of the angle of attack, and The sum is the final dynamic derivative value in the pitch direction in the forced vibration dynamic derivative test.

[0014] The beneficial effects of the present invention are as follows: the present invention proposes a dynamic derivative processing method based on discrete Fourier transform, by setting the minimum frequency, so that the vibration waveforms contained in the collected signal are all integer multiples of the minimum frequency, based on the discrete Fourier transform solution method, the phase difference between the pitch moment signal and the angle element signal is obtained, and finally the model dynamic derivative value is obtained; the present invention can solve the problems of unstable sinusoidal vibration of the aircraft model and inaccurate conventional test data processing methods when the collected signal has non-doubled frequencies, and can accurately obtain the torque, angular displacement and phase angle of the aircraft model at the vibration frequency, and accurately obtain the dynamic derivative of the aircraft model; the present invention can process collected signals with poor sinusoidal properties such as doubled frequencies, non-doubled frequencies and other signals containing multiple frequencies; the present invention only needs to process the original signal, the signal processing process is simple, and the results obtained are accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It is a flowchart of a method for processing dynamic derivative data based on discrete Fourier transform; Figure 2The present invention is a schematic diagram of an implementation example of a method for processing dynamic derivative data based on discrete Fourier transform, wherein (a) is a schematic diagram of an implementation example in which the original signal value is used without signal extraction, (b) is a schematic diagram of an implementation example in which a 1 Hz resolution frequency is used for signal extraction, and (c) is a schematic diagram of an implementation example in which a 0.5 Hz resolution frequency is used for signal extraction. DETAILED DESCRIPTION

[0016] In order to make the technical solutions and advantages of the embodiments of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0017] refer to Figure 1 and Figure 2 The present embodiment is described in detail, a method for processing dynamic derivative data based on discrete Fourier transform, specifically comprising the following steps: S1. Perform a dynamic derivative test to collect the pitch moment signal and angle element signal of the aircraft model during vibration through a balance; S2. Calculate the resolution frequency according to the set sampling rate and number of samples; S3. Based on the correlation function calculation formula and the resolution frequency, the discrete Fourier transform formula at the main vibration frequency is obtained; S4. According to the discrete Fourier transform formula, the amplitude and the first phase difference of the pitch moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency are calculated; Specifically: Substitute all the above values ​​into the discrete Fourier transform formula to find the k The correlation function value under the sequence number The real and imaginary parts of the fundamental pitch moment signal are obtained by , the first phase difference , the amplitude of the angle element signal and the second phase difference ; S5. Calculate the phase difference between the pitch moment signal and the angle element signal collected according to the first phase difference and the second phase difference; S6. According to the dynamic derivative calculation formula in the pitch direction, the final dynamic derivative value is obtained.

[0018] Furthermore, in S1, the pitch moment signal is expressed as ,in, is the amplitude of the fundamental pitch moment signal, is the static torque signal, is the sum of the noise signals of all simple harmonic oscillation signals, is the main vibration frequency, is the first phase difference, For time; The angle signal is expressed as ,in, is the amplitude of the angle element signal, which depends on the dynamic derivative vibration mechanism, is the interference signal, is the second phase difference; Furthermore, in S2, the frequency resolution It is expressed as: ; in, is the sampling rate, is the number of samples.

[0019] Specifically, to resolve the frequency As small as possible, increasing the sampling time during data acquisition as much as possible.

[0020] Furthermore, in S3, the correlation function calculation formula is expressed as: ; in, is the sampling value, is the serial number, For the k The relevant function value under the sequence number; The discrete Fourier transform formula is expressed as: ; in, .

[0021] Furthermore, in S5, the phase difference It is expressed as: .

[0022] Furthermore, in S6, for the pitching vibration process in the high-speed dynamic derivative wind tunnel test, the amplitude of the fundamental pitching moment signal obtained in step S4 and step S5 is and phase difference Substitute the dynamic derivative calculation formula in the pitch direction to obtain the final dynamic derivative value; The calculation formula of the dynamic derivative in the pitch direction is expressed as: ; in, is the angular velocity of the aircraft model vibration, , is the dynamic derivative value in the pitch direction caused by the change of angular velocity, is the dynamic derivative value in the pitch direction caused by the change of the angle of attack, and The sum is the final dynamic derivative value in the pitch direction in the forced vibration dynamic derivative test; Specifically, by collecting the yaw moment signal and angle signal, the rolling moment signal and angle signal of the aircraft model during the vibration process through a balance, the calculation formula of the yaw direction dynamic derivative and the calculation formula of the rolling direction dynamic derivative can be obtained; The calculation formula of the yaw direction dynamic derivative is expressed as: ; in, is the dynamic derivative value in the yaw direction caused by the change of angular velocity, is the dynamic derivative value in the yaw direction caused by the change of sideslip angle, is the angle of attack, is the yaw moment signal amplitude, is the yaw vibration angle amplitude; The calculation formula of the dynamic derivative in the rolling direction is expressed as: ; in, is the dynamic derivative value of the rolling direction caused by the change of angular velocity, is the dynamic derivative value of the rolling direction caused by the change of the sideslip angle, is the rolling moment signal amplitude, is the rolling vibration angle amplitude; The principle of the present invention is that, for the dynamic derivative test, assuming that the collected signal is identified with a particularly small resolution, the information of all signals of the resolution frequency and its integer multiple frequencies can be obtained, that is, the main vibration frequency of the aircraft model concerned is obtained by using the discrete Fourier formula. , the pitch moment signal and angle element signal can be considered to be By comparison, the first phase difference between the pitch moment signal and the standard signal can be obtained. and the amplitude of the pitch moment signal , the second phase difference between the angle signal and the standard signal and the amplitude of the angle element signal , at this time, the phase difference between the pitch moment signal and the angle element signal is obtained , and thus the value of the model dynamic derivative is obtained according to Formula 5.

[0023] Usually in the dynamic derivative test, Solved as a whole, but the present invention does not solve at the same time , but solve the amplitude and phase difference separately. When the resolution frequency is as small as possible during the calculation process, the non-frequency doubling effect can be eliminated. refer to Figure 2 , different frequency resolutions have an impact on signal extraction. For a signal, As shown in Figure (a), it contains vibration signals of 6 Hz, 8.5 Hz and 11 Hz. As shown in Figure (b), when the resolution frequency is 1 Hz, the waveform of the 8.5 Hz signal cannot be resolved, and the amplitude of the resolved 11 Hz signal also has an error, which is significantly less than 3.5. However, according to the implementation of the present invention, when the resolution frequency is 0.5 Hz, all signals can be resolved without error.

[0024] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

Claims

1. A method for processing dynamic derivative data based on discrete Fourier transform, characterized in that: The following steps are involved: S1. Perform a dynamic derivative test to collect the pitch moment signal and angle element signal of the aircraft model during vibration through a balance; S2. Calculate the resolution frequency according to the set sampling rate and number of samples; S3. Based on the correlation function calculation formula and the resolution frequency, the discrete Fourier transform formula at the main vibration frequency is obtained; S4. According to the discrete Fourier transform formula, the amplitude and the first phase difference of the pitch moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency are calculated; S5. Calculate the phase difference between the pitch moment signal and the angle element signal collected according to the first phase difference and the second phase difference; S6. Calculate the final dynamic derivative value according to the dynamic derivative calculation formula in the pitch direction and the phase difference.

2. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 1, characterized in that: In S1, the pitch moment signal is expressed as ,in, is the amplitude of the fundamental pitch moment signal, is the static torque signal, is the sum of the noise signals of all simple harmonic oscillation signals, is the main vibration frequency, is the first phase difference, For time; The angle signal is expressed as ,in, is the amplitude of the angle element signal, is the interference signal, is the second phase difference.

3. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 2, characterized in that: In S2, the resolution frequency It is expressed as: ； in, is the sampling rate, is the number of samples.

4. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 3, characterized in that: In S3, the calculation formula of the correlation function is expressed as: ； in, is the sampling value, is the serial number, For the k The relevant function value under the sequence number; The discrete Fourier transform formula is expressed as: ； in, .

5. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 4, characterized in that: In S5, the phase difference between the pitch moment signal and the angle element signal It is expressed as: 。 6. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 5, characterized in that: In S6, for the pitch vibration process in the high-speed dynamic derivative wind tunnel test, the amplitude of the fundamental pitch moment signal obtained in step S4 and step S5 is and phase difference Substitute the dynamic derivative calculation formula in the pitch direction to obtain the final dynamic derivative value; The calculation formula of the dynamic derivative in the pitch direction is expressed as: ； in, is the angular velocity of the aircraft model vibration, , is the dynamic derivative value in the pitch direction caused by the change of angular velocity, is the dynamic derivative value in the pitch direction caused by the change of the angle of attack, and The sum is the final dynamic derivative value in the pitch direction in the forced vibration dynamic derivative test.

Images