A method for calculating continuous moving derivatives based on the principle of periodic cross-correlation

Abstract

A method for calculating continuous dynamic derivatives based on the principle of periodic cross-correlation belongs to the field of dynamic derivative measurement technology. In order to obtain dynamic derivative data that continuously changes with the attitude angle, the present invention includes performing dynamic derivative tests under windless and windy conditions, and after reaching the target frequency and stabilizing, continuously changing the attitude angle, obtaining the balance load and vibration angle, and deducting the trend item of the balance load changing with the attitude angle, and then performing periodic and discrete cross-correlation processing on the balance load and vibration angle displacement after deducting the trend item to obtain the damping derivative under a single vibration cycle under windless and windy conditions. The average attitude angle under each vibration cycle is obtained, and the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle are established respectively; the damping derivatives under windy conditions and those under windless conditions are subtracted one by one to obtain the dimensional aerodynamic damping derivative, and then dimensionless processing is performed to obtain the continuous dynamic derivative.

Description

Technical Field

[0001] The invention belongs to the technical field of dynamic derivative measurement, and in particular relates to a continuous dynamic derivative calculation method based on the principle of periodic cross-correlation. Background Art

[0002] The dynamic derivative measurement test uses a model to perform small-amplitude simple harmonic motion in a wind tunnel to measure the time rate of change of the aerodynamic force and torque acting on the aircraft model with respect to the motion parameters, thereby extracting the dynamic derivative.

[0003] At present, the common method for testing dynamic derivatives in wind tunnel tests is to obtain dynamic derivative data at a single angle of attack by step-changing the angle of attack. However, at certain angles of attack, the aerodynamic hysteresis loop of the dynamic derivative will show a kink phenomenon. At this time, the dynamic derivative near the equilibrium angle of attack will change dramatically with a small change in the angle of attack. The traditional dynamic derivative processing method can only give a fixed value at a certain angle of attack, which cannot fully reflect the trend of changes with the angle of attack.

[0004] To solve this problem, some domestic units have developed a low-speed wind tunnel continuous measurement test method for longitudinal dynamic derivatives suitable for low-speed wind tunnels. The principle of this method is based on the traditional longitudinal aerodynamic derivative aerodynamic model modeling idea, and the dynamic derivatives at different angles of attack are identified by parameter identification methods. However, due to the existence of shock waves on the model surface in high-speed wind tunnels, this aerodynamic model is not suitable for high-speed wind tunnel test environments. In addition, since this aerodynamic model is a longitudinal derivative model and there is no mature aerodynamic model that describes the coupling characteristics of longitudinal and lateral aerodynamic forces, this method is currently only applicable to the identification of dynamic derivatives in the pitch direction, and is not yet applicable to the acquisition of dynamic derivatives in the roll and yaw directions. Summary of the invention

[0005] The problem to be solved by the present invention is to obtain dynamic derivative data that continuously changes with the attitude angle, and a continuous dynamic derivative calculation method based on the principle of periodic cross-correlation is proposed.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for calculating continuous moving derivatives based on the principle of periodic cross-correlation includes the following steps:

[0008] S1. Perform a dynamic derivative test under windless conditions. After reaching the target frequency and stabilizing, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then perform periodic and discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration period under windless conditions.

[0009] S2, conduct a dynamic derivative test under windy conditions. After reaching the target frequency and stabilizing, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then, perform periodic and discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration period under windy conditions;

[0010] S3. Obtaining the average attitude angle in each vibration cycle, and establishing the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle;

[0011] S4. Then, the damping derivatives under windy conditions and those under no wind conditions are subtracted one by one to obtain the dimensional aerodynamic damping derivatives, which are then dimensionally processed to obtain the continuous dynamic derivatives.

[0012] Furthermore, the specific implementation method of step S1 includes the following steps:

[0013] S1.1. Perform a dynamic derivative test under windless conditions, collect the dynamic voltage signal of the balance, and perform low-pass filtering;

[0014] S1.2. Using the calibration coefficients of the balance certificate, iterate the dynamic balance signal to obtain the balance force, torque, and angular displacement ;

[0015] S1.3. Angular displacement As a benchmark, the zero point is used as the judgment criterion to perform periodic processing to obtain the pitch moment in each vibration cycle. and ;

[0016] S1.4. The pitching moment in each vibration cycle , angular displacement Subtract the corresponding average value and deduct the trend item of the single cycle. The expression is:

[0017] ;

[0018] ;

[0019] in, is the average value of the pitching moment, is the deducted pitching moment, is the average value of the angular displacement, is the angular displacement of the deduction;

[0020] S1.5. Based on the torque signal reflected by the balance, including the vibration torque signal at the set frequency, the gap of the test mechanism, the influence of electromagnetic interference factors, the existence of various harmonic signals, static torque signals and random noise interference signals, the torque of the model is obtained. The expression is:

[0021] ;

[0022] in, is the static torque signal, is the torque fundamental signal, are the harmonic signals of the torque, is a random noise signal, is the model vibration angular velocity, is the phase difference between the vibration angle signal and the torque signal, t is the time, is the harmonic order;

[0023] In order to eliminate the interference signal, based on the principle of digital cross-correlation, the torque on both sides of the obtained model is multiplied by After integration, the expression is:

[0024] ；

[0025] in, is the angular displacement amplitude for each vibration period;

[0026] S1.6. According to the properties of trigonometric functions, the expression is:

[0027] ;

[0028] Converted into discrete form, we can get , the expression is:

[0029] ;

[0030] in, The total number of acquisition points for each vibration cycle;

[0031] Angular displacement amplitude per vibration cycle By identifying the maximum angular displacement amplitude under a single cycle and minimum angular displacement amplitude The formula is as follows:

[0032] ;

[0033] Vibration angular velocity The formula is as follows:

[0034] ;

[0035] in, is the nominal vibration frequency;

[0036] S1.7. Based on the obtained , as well as Multiply and solve for the pitch damping derivative at each vibration cycle , the expression is:

[0037] ;

[0038] in, is the mechanical damping coefficient;

[0039] The dynamic derivative test was carried out under windless conditions, and the damping derivative under windless conditions for a single vibration cycle was obtained as follows: .

[0040] Furthermore, in step S2, a dynamic derivative test is performed under windy conditions, and the damping derivative under a single vibration cycle under windy conditions is obtained as follows: .

[0041] Furthermore, the specific implementation method of step S3 includes the following steps:

[0042] S3.1. Get the average attitude angle corresponding to each vibration cycle time , the formula is as follows;

[0043] ;

[0044] in, For the i The attitude angle corresponding to the collection point is i for n Any one of;

[0045] S3.2. Establish the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle as follows: , .

[0046] Furthermore, the specific implementation method of step S4 includes the following steps:

[0047] S4.1. Subtract the damping derivatives under windy conditions from those under no wind conditions one by one to obtain the dimensioned aerodynamic damping derivatives;

[0048] S4.2. Then, dimensionless processing is performed to obtain the continuous dynamic derivative, which is expressed as:

[0049] ;

[0050] in, is the dimensionless pitch damping derivative, For speed pressure, is the reference area, For local factors, is the reference length.

[0051] Beneficial effects of the present invention:

[0052] The continuous dynamic derivative calculation method based on the principle of periodic cross-correlation described in the present invention does not need to establish a complex aerodynamic model, and can measure the dynamic derivative without relying on the theoretical aerodynamic model. It is not only applicable to low-speed wind tunnels, but also to high-speed wind tunnels and situations with large angles of attack where it is difficult to establish an accurate aerodynamic model.

[0053] The continuous dynamic derivative calculation method based on the periodic cross-correlation principle described in the present invention is suitable for continuous measurement tests of dynamic derivatives in high-speed wind tunnels, is convenient and fast, and has high engineering application value; the method is not limited by changes in attitude angles, and can achieve continuous measurement of dynamic derivatives under conditions of continuously changing angles of attack, sideslip angles, and roll angles; the method is suitable for dynamic derivative tests of three vibration types, namely, pitch, yaw, and roll, and can obtain pitch, roll, and yaw dynamic derivatives; the method can be expanded and applied to continuous measurement tests of dynamic derivatives in low-speed wind tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flow chart of a method for calculating continuous moving derivatives based on the principle of periodic cross-correlation according to the present invention;

[0055] Figure 2 The target torque and angular displacement time history and trend curves, where (a) is the target torque curve and (b) is the angular displacement curve;

[0056] Figure 3 It is the comparison curve between the continuous dynamic derivative measurement and the step-variable angle of attack dynamic derivative result;

[0057] Figure 4 Flowchart for the implementation of continuous dynamic derivative measurement tests. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0059] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0060] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 -Attached Figure 4 The detailed instructions are as follows:

[0061] Embodiment 1:

[0062] A method for calculating continuous moving derivatives based on the principle of periodic cross-correlation includes the following steps:

[0063] S1. Perform a dynamic derivative test under windless conditions. After reaching the target frequency and stabilizing, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then perform periodic and discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration period under windless conditions.

[0064] Furthermore, the specific implementation method of step S1 includes the following steps:

[0065] S1.1. Perform a dynamic derivative test under windless conditions, collect the dynamic voltage signal of the balance, and perform low-pass filtering;

[0066] Furthermore, the dynamic voltage signal of the balance is , , , , , ;

[0067] in, , , , , , They are the voltage signals of six elements, namely, balance lift, pitch moment, roll moment, lateral force, yaw moment, and angular displacement;

[0068] S1.2. Using the calibration coefficients of the balance certificate, iterate the dynamic balance signal to obtain the balance force, torque, and angular displacement ;

[0069] S1.3. Angular displacement As a benchmark, the zero point is used as the judgment criterion to perform periodic processing to obtain the pitch moment in each vibration cycle. and ;

[0070] S1.4. The pitching moment in each vibration cycle , angular displacement Subtract the corresponding average value and deduct the trend item of the single cycle. The expression is:

[0071] ;

[0072] ;

[0073] in, is the average value of the pitching moment, is the deducted pitching moment, is the average value of the angular displacement, is the angular displacement of the deduction;

[0074] S1.5. Based on the torque signal reflected by the balance, including the vibration torque signal at the set frequency, the gap of the test mechanism, the influence of electromagnetic interference factors, the existence of various harmonic signals, static torque signals and random noise interference signals, the torque of the model is obtained. The expression is:

[0075] ;

[0076] in, is the static torque signal, is the torque fundamental signal, are the harmonic signals of the torque, is a random noise signal, is the model vibration angular velocity, is the phase difference between the vibration angle signal and the torque signal, t is the time, is the harmonic order;

[0077] In order to eliminate the interference signal, based on the principle of digital cross-correlation, the torque on both sides of the obtained model is multiplied by After integration, the expression is:

[0078] ;

[0079] in, is the angular displacement amplitude for each vibration period;

[0080] S1.6. According to the properties of trigonometric functions, the expression is:

[0081] ;

[0082] Converted into discrete form, we can get , the expression is:

[0083] ;

[0084] in, The total number of acquisition points for each vibration cycle;

[0085] Angular displacement amplitude per vibration cycle By identifying the maximum angular displacement amplitude under a single cycle and minimum angular displacement amplitude The formula is as follows:

[0086] ;

[0087] Vibration angular velocity The formula is as follows:

[0088] ;

[0089] in, is the nominal vibration frequency;

[0090] S1.7. Based on , as well as Multiply and solve for the pitch damping derivative at each vibration cycle , the expression is:

[0091] ;

[0092] in, is the mechanical damping coefficient;

[0093] The dynamic derivative test was carried out under windless conditions, and the damping derivative under windless conditions for a single vibration cycle was obtained as follows: .

[0094] Furthermore, according to the D'Alembert principle, at any moment, the various torques acting on the entire elastic system (i.e., mechanical damping torque, elastic restoring torque, aerodynamic static torque, aerodynamic damping torque, inertia torque, and external forced torque, etc.) should be balanced, and the model vibration equilibrium equation can be expressed as:

[0095] ;

[0096] in, is the moment of inertia of the model around the pitch axis, is the vibration angle, is the mechanical damping coefficient, is the forcing torque amplitude, is the phase difference between the vibration angle signal and the torque signal;

[0097] Ideally, the model vibration curve is a standard sine curve, and the model motion equation is:

[0098] ;

[0099] S2, conduct a dynamic derivative test under windy conditions. After reaching the target frequency and stabilizing, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then, perform periodic and discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration period under windy conditions;

[0100] Furthermore, in step S2, a dynamic derivative test is performed under windy conditions, and the damping derivative under a single vibration cycle under windy conditions is obtained as follows: .

[0101] S3. Obtaining the average attitude angle in each vibration cycle, and establishing the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle;

[0102] Furthermore, the specific implementation method of step S3 includes the following steps:

[0103] S3.1. Get the average attitude angle corresponding to each vibration cycle time , the formula is as follows;

[0104] ;

[0105] in, For the i The attitude angle corresponding to the collection point is i for n Any one of;

[0106] S3.2. Establish the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle as follows: , .

[0107] S4. Then, the damping derivatives under windy conditions and those under no wind conditions are subtracted one by one to obtain the dimensional aerodynamic damping derivatives, which are then dimensionally processed to obtain the continuous dynamic derivatives.

[0108] Furthermore, the specific implementation method of step S4 includes the following steps:

[0109] S4.1. Subtract the damping derivatives under windy conditions from those under no wind conditions one by one to obtain the dimensioned aerodynamic damping derivatives;

[0110] S4.2. Then, dimensionless processing is performed to obtain the continuous dynamic derivative, which is expressed as:

[0111] ;

[0112] in, is the dimensionless pitch damping derivative, For speed pressure, is the reference area, For local factors, is the reference length.

[0113] Furthermore, a dynamic derivative test device is installed in the wind tunnel, and a method for conducting a dynamic derivative test is as follows: Figure 4 As shown:

[0114] a) Test system trial operation to verify whether the movement indicators of the mechanism can meet the test requirements;

[0115] b) Adjust the balance to the equilibrium position and install the model. Adjust the balance to the vibration equilibrium position, enable / lock the motor; install the model, level the model attitude angle, and control the error within 3';

[0116] c) During the air-vibration test under windless conditions, the angle of attack mechanism reaches the starting angle of attack and the model begins to vibrate. When the model vibration reaches the target frequency, the wind tunnel main control system simultaneously sends two trigger signals to the angle of attack mechanism control system and the data acquisition system respectively. After receiving the trigger signal, the angle of attack mechanism starts to continuously change the angle of attack at a given speed. At the same time, the data acquisition system starts to collect signals such as the force balance and vibration angle. When the angle of attack mechanism reaches the target angle of attack, the acquisition system stops collecting, and then obtains the air-vibration damping derivative under the condition of continuously changing angle of attack under windless conditions.

[0117] d) During the wind test, the model is first kept fixed at the 0° angle of attack position. After the flow field starts and stabilizes, the driving source is started and the model begins to vibrate. The angle of attack is moved to the starting angle of attack. When the angle of attack mechanism reaches the target angle of attack and the flow field is judged to be stable for the second time, the wind tunnel main control system simultaneously sends two trigger signals to the angle of attack mechanism control system and the data acquisition system respectively. After receiving the trigger signal, the angle of attack mechanism starts to move the angle of attack continuously at a given speed, and the data acquisition system starts to collect data at the same time. When the angle of attack mechanism reaches the target angle of attack, the data acquisition system stops collecting data and the wind tunnel stops, thereby obtaining the air vibration damping derivative under the condition of continuously changing angle of attack under windless conditions.

[0118] e) obtaining the required dynamic derivatives through data processing;

[0119] f) After the first vehicle test is completed, at least one repetitive test is required to verify the reliability of the test system;

[0120] g) According to the requirements of the test project, change the model state or motion parameters and repeat the process of d), e), and f);

[0121] h) After confirming that all test tasks have been completed and the data are qualified, the model and test equipment are dismantled and the test is completed.

[0122] The invention discloses a continuous variable angle of attack dynamic derivative measurement test technology and a data processing method, which is convenient and fast, can realize continuous measurement of dynamic derivatives, has high engineering application value, and is suitable for dynamic derivative tests in three vibration directions of pitch, yaw and roll in high / low speed wind tunnels.

[0123] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0124] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for calculating continuous moving derivatives based on the principle of periodic cross-correlation, characterized in that: The steps include: S1. Perform a dynamic derivative test under windless conditions. After the model vibration reaches the target frequency and stabilizes, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then perform periodic discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration cycle under windless conditions. The specific implementation method of step S1 includes the following steps: S1.

1. Carry out a dynamic derivative test under windless conditions, collect the dynamic voltage signal of the balance, and perform low-pass filtering; S1.

2. Using the calibration coefficients of the balance certificate, iterate the dynamic balance signal to obtain the balance force, torque, and angular displacement; S1.

3. Taking the angular displacement as the reference and the zero crossing point as the judgment criterion, perform periodic processing to obtain the pitch moment M in each vibration cycle. z (i) and angular displacement θ(i); S1.

4. The pitching moment M under each vibration cycle z (i), subtract the angular displacement θ(i) from its corresponding average value, and deduct the trend term of the single cycle. The expression is: M z扣 (i)=M z (i)-M z (i) mean i 扣 (i)=θ(i)-θ(i) mean Among them, M z (i) mean is the average value of the pitching moment, M z扣 (i) is the deducted pitching moment, θ(i) mean is the average value of the angular displacement, θ 扣 (i) is the subtracted angular displacement; S1.

5. Based on the torque signal reflected by the balance, including the vibration torque signal at the set frequency, the gap of the test mechanism, the influence of electromagnetic interference factors, the existence of various harmonic signals, static torque signals and random noise interference signals, the torque M' exerted on the model is obtained z扣 The expression is: Among them, M zj is the static torque signal, M z0 sin(ωt+λ) is the fundamental signal of torque, is the harmonic signal of torque, M c (t) is the random noise signal, ω is the model vibration angular velocity, λ is the phase difference between the vibration angle signal and the torque signal, t is time, and N is the harmonic order; In order to eliminate the interference signal, based on the principle of digital cross-correlation, the torque on both sides of the obtained model is multiplied by θ0cos(ωt) and then integrated to obtain the expression: Where θ0 is the angular displacement amplitude per vibration period; S1.

6. Based on the properties of trigonometric functions, the expression is: Convert to discrete form and get M' for each vibration cycle z扣 sinλ, the expression is: Where n is the total number of acquisition points for each vibration cycle; The angular displacement amplitude θ0 of each vibration cycle is determined by identifying the maximum angular displacement amplitude θ(i) under a single cycle. max and the minimum angular displacement amplitude θ(i) min The formula is as follows: The formula for the vibration angular velocity ω is as follows: ω=2πf Where, f is the nominal vibration frequency; S1.

7. Based on the obtained θ0, ω and M' z扣 Sinλ product, solve the pitch damping derivative at each vibration cycle The expression is: Where, c is the mechanical damping coefficient; The dynamic derivative test was carried out under windless conditions, and the damping derivative under windless conditions for a single vibration cycle was obtained as follows: S2, conduct a dynamic derivative test under windy conditions. After reaching the target frequency and stabilizing, continuously change the attitude angle to obtain the balance load and vibration angle, and deduct the trend term of the balance load changing with the attitude angle. Then perform periodic discrete cross-correlation processing on the balance load and vibration angular displacement after deducting the trend term to obtain the damping derivative under a single vibration period under windy conditions; In step S2, a dynamic derivative test is performed under windy conditions, and the damping derivative under a single vibration cycle under windy conditions is obtained as follows: S3. Obtain the average attitude angle in each vibration cycle, and establish the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle; S4. Then, the damping derivatives under windy conditions and those under no wind conditions are subtracted one by one to obtain the dimensional aerodynamic damping derivatives, which are then processed dimensionlessly to obtain the continuous dynamic derivatives.

2. The method for calculating continuous moving derivatives based on the principle of periodic cross-correlation according to claim 1, characterized in that: The specific implementation method of step S3 includes the following steps: S3.

1. Obtain the average attitude angle α corresponding to each vibration cycle time mean , the formula is as follows; Among them, α(i) is the attitude angle corresponding to the i-th acquisition point, and i is any one of n; S3.

2. Establish the corresponding relationship between the damping derivative under windless conditions and the average attitude angle and the corresponding relationship between the damping derivative under windy conditions and the average attitude angle:

3. The method for calculating continuous moving derivatives based on the principle of periodic cross-correlation according to claim 2, characterized in that: The specific implementation method of step S4 includes the following steps: S4.

1. Subtract the damping derivatives under windy conditions from those under no wind conditions one by one to obtain the dimensioned aerodynamic damping derivatives; S4.

2. Then, dimensionless processing is performed to obtain the continuous dynamic derivative, which is expressed as: in, is the dimensionless pitch damping derivative, Q is the velocity pressure, S is the reference area, V is the local factor, C A is the reference length.

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