Parachute aerodynamic force test method based on photoelectric data fusion

Abstract

The invention discloses a parachute aerodynamic force testing method based on photoelectric data fusion, and relates to the field of parachute testing. According to the photoelectric data fused parachute aerodynamic force test method, environmental data of a wind tunnel stable section are obtained, a dynamic pressure real-time correction mathematical model of the environmental data is established, a test space coordinate system is established, and the attack angle of a tested parachute is calculated in real time in a coordinate system of the tested parachute; the method comprises the following steps: establishing an input condition optimization proportionality coefficient and integration time of a PI control model according to different blockage ratios and the wind speed of a central point of a test section to achieve an optimal state, and analyzing and converting actual transverse aerodynamic force and longitudinal aerodynamic force of the tested umbrella according to an attack angle of the tested umbrella and stress analysis of aerodynamic force torque sensed by a force measurement balance, the aerodynamic force torque coefficient of the tested parachute is converted according to the nominal geometric characteristics of the tested parachute and real-time dynamic pressure correction data, the aerodynamic force test research is carried out through photoelectric data and environmental parameter fusion by the photoelectric data fusion parachute aerodynamic force test method, and the accuracy of the test data of the aerodynamic characteristics of the parachute can be optimized.

Description

Technical Field

[0001] The present application relates to the field of parachute testing, and in particular to a parachute aerodynamic testing method using optoelectronic data fusion. Background Art

[0002] A parachute is a highly efficient aerodynamic deceleration device that provides resistance, lift and stability, and is widely used in the aerospace field. A parachute is a flexible fabric that is gas-permeable. It undergoes a sharp structural deformation during the opening process. Therefore, the physical phenomena such as the canopy flow characteristics, the mutual interference between the cargo-parachute system and the pressure distribution of the parachute dynamic load are very complex. Only by deeply studying the parachute wake flow field can we master its working mechanism in order to explain many aerodynamic phenomena such as the canopy inflation "breathing" and bottom shaking. Practice has proved that theoretical research cannot accurately calculate the working mechanism of the parachute. Only in wind tunnel tests can instruments or measuring devices be used to measure the parachute's aerodynamic force and flow field data, such as six-component aerodynamic force, pressure distribution, and flow velocity around the canopy. From a theoretical analysis, the aerodynamic drag of a parachute is one of its core technical indicators. The aerodynamic drag is mainly composed of four parts: friction drag, pressure difference drag, wave drag and induced drag. For a general axisymmetric parachute, there is no induced drag. However, since the parachute shape of the wing is similar to that of the wing, it also generates induced drag during the descent of the wing like the wing. The amount of drag generated by a parachute when moving in the air is related to factors such as movement speed, air density, object shape and geometric dimensions. Its aerodynamic parameters are mainly expressed by drag characteristics.

[0003] At present, when various wind tunnel scientific research and experimental units or other universities in China carry out conventional aerodynamic tests on parachutes, they usually connect force sensors or various professional force balances to a single-pole device or a tensioning connection device, and then connect the parachute's connecting rope ring to the force balance or the force sensor's loading connector. The wind tunnel is used to establish dynamic pressure on the parachute canopy, and then the force sensor or professional force balance feels the parachute's aerodynamic force. The air density parameter required for the dynamic pressure test and control process usually uses a quantitative value of 1.225kg / m 3, the dynamic pressure control mode generally adopts an open-loop motor steady speed control mode. In terms of data processing, the main work is to carry out tunnel wall interference correction, establish a rigid aerodynamic data conversion method, bracket interference correction and blockage factor correction, so that the parachute can obtain a purer aerodynamic force as much as possible. In fact, through the theoretical aerodynamic analysis of parachutes, it is found that due to the soft texture of parachutes and the large differences in umbrella structures, the canopy flow field mostly presents a nonlinear aerodynamic coupling body, which will cause the wind tunnel airflow disturbance to change unsteadily, and the Reynolds number will also fluctuate with the fullness characteristics. Therefore, the conventional open-loop steady speed control method of wind tunnel dynamic pressure cannot eliminate the problem of large canopy flow velocity fluctuations due to the lack of real-time correction of dynamic pressure feedback, resulting in a larger difference between the actual canopy dynamic pressure and the dynamic pressure felt by the pitot tube. In terms of data processing, in addition to the conventional data correction processing method mentioned above, since the parafoil type parachute is a fully flexible structure, it is only fixed by the parachute rope connection in the wind tunnel. Therefore, the spatial position relationship of the parafoil cannot be predetermined before the test, and during the wind test, the position of the parafoil will change with the change of attitude or speed pressure. Accordingly, the position of the parafoil moment reference point (the center of gravity of the parafoil system and the 1 / 4 chord of the longitudinal symmetry plane of the parafoil, respectively) relative to the balance cannot be fixed like the rigid support of the rigid model. Affected by the flexible characteristics of the parafoil, the parachute rope has a certain amount of rise and length after the wing surface is stressed, and the geometric relationship between the parafoil connection state and the balance is non-steady. In addition, the angle sensor and the parachute rope have poor tracking performance. Under the influence of both, the data is inaccurate.

[0004] Therefore, a parachute aerodynamic test method is needed to improve the accuracy of aerodynamic tests and the repeatability of test data. Summary of the invention

[0005] The purpose of this application is to provide a parachute aerodynamic test method with optoelectronic data fusion, which can optimize the accuracy of parachute aerodynamic characteristics test data to support parachute development and research.

[0006] This application is implemented as follows:

[0007] The present application provides a parachute aerodynamic test method using optoelectronic data fusion, comprising the following steps:

[0008] S1. Obtain atmospheric pressure, temperature and humidity data in the stable section of the wind tunnel;

[0009] S2. According to the distribution of water vapor pressure at saturation temperature in the stable section of the wind tunnel, a dynamic pressure real-time correction mathematical model using multi-environmental parameter sensor data fusion technology is established;

[0010] S3, establishing a number of characteristic marking points representing the canopy shape on the canopy surface of the tested umbrella and calculating the spatial coordinates of the characteristic marking points;

[0011] S4. Establish the test space coordinate system: take the center of the bracket of the fixed parafoil in the wind tunnel test section as the origin of the coordinate system O, the direction along the flow field as the positive direction of the X axis, and the vertically upward direction as the positive direction of the Y axis to establish the right-hand coordinate system O-XYZ, and take the moment reference point of the parafoil as the origin of the wind axis system to determine different coordinates converted by aerodynamic force: balance coordinate system, airflow coordinate axis system, test parachute body axis system and transition coordinate system, and calculate the test parachute's angle of attack in real time in the test parachute's coordinate system;

[0012] S5. According to the actual windward area of ​​the wind tunnel test parachute model and historical test data, the modal relationship between the rotation speed and wind speed under different blockage ratio conditions is formulated, and the input conditions of the PI control model are established according to different blockage ratios and the wind speed at the center of the test section. According to the transfer function principle of the PI controller, the proportional coefficient and the integral time are optimized to achieve the best state;

[0013] S7. According to step S2 and step S5, the dynamic pressure condition of the flow through the canopy of the test parachute is established, and then the actual lateral aerodynamic force and longitudinal aerodynamic force of the test parachute are converted according to the optical interpretation of the angle of attack of the test parachute and the force analysis of the aerodynamic torque felt by the force measuring balance, and the aerodynamic torque coefficient of the test parachute is calculated according to the nominal geometric characteristics of the test parachute and the real-time dynamic pressure correction data.

[0014] In some optional embodiments, pressure sensors, temperature sensors and humidity sensors are installed on the wall of the stable section of the wind tunnel to obtain atmospheric pressure, temperature and humidity data of the stable section of the wind tunnel.

[0015] In some optional implementation schemes, when calculating the spatial coordinates of the feature marker points, the image point coordinates of the images synchronously taken by the cameras that meet the intersection conditions are respectively interpreted by the photogrammetric forward intersection method, and the spatial coordinates of the feature marker points are calculated according to the image point coordinates and the camera point coordinates according to the photogrammetric forward intersection method.

[0016] In some optional implementation schemes, when calculating the angle of attack of the test parachute in the coordinate system of the test parachute, the angle between the parachute ropes on the symmetry plane of the test parachute and the plane of the parachute rope fixing frame is calculated through the trigonometric function relationship through the spatial coordinate system data of the characteristic points according to the structural dimensions of the wing-shaped parachute, the balance and the parachute rope frame, and the geometric relationship between the parachute ropes and the chord length is used to calculate the angle of attack of the test parachute in real time.

[0017] In some optional implementation schemes, when establishing a dynamic pressure real-time correction mathematical model of multi-environmental parameter sensor data fusion technology, the dynamic pressure value of the wind tunnel test section is corrected in real time according to the following formula: Where: 实 is the real-time density of airflow in the wind test section, kg / m 3 ; V A V is the wind speed on the left inner wall of the nozzle, m / s; B is the wind speed on the right inner wall of the nozzle, m / s; ΔP is the correction value of the dynamic pressure value of the test section.

[0018] In some optional embodiments, the real-time air density of the wind tunnel test section is 实 Calculated using the following formula:

[0019]

[0020] Where: 实 is the real-time density of airflow in the wind tunnel test section, kg / m 3 ; P is the atmospheric pressure of the test section, kpa; T is the thermodynamic temperature of the test section, K; ψ is the relative humidity of the test section, %; P t is the partial pressure of water vapor in saturated air at the test section temperature t, Pa.

[0021] In some optional implementation schemes, the proportional coefficient and the integral time are optimized to achieve the best state using the following formula according to the PI controller transfer function principle:

[0022]

[0023] Where: u(t) is the output signal of the PI controller; K p is the proportional coefficient; e(t) is the PI controller input signal; T i is the integration time.

[0024] The beneficial effects of the present application are as follows: the parachute aerodynamic test method with optoelectronic data fusion provided in the present application establishes synchronous collection of optical data, velocity pressure and balance signals, and conducts refined aerodynamic test research based on data fusion technology through the two fusion technologies of optoelectronic data and environmental parameters, which can optimize the accuracy of parachute aerodynamic characteristics test data to support parachute development and research. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A schematic diagram of the process of the parachute aerodynamic test method using optoelectronic data fusion provided in an embodiment of the present application;

[0027] Figure 2A schematic diagram of a coordinate system for measuring the angle of the parachute symmetry plane of the airfoil parachute and the plane of the parachute rope fixing frame in real time using an optical intersection measurement method in the parachute aerodynamic test method of the optoelectronic data fusion provided in an embodiment of the present application, and calculating the angle of attack of the airfoil parachute in real time using the geometric relationship between the parachute rope and the airfoil chord length;

[0028] Figure 3 The PI control parameter is adjusted to K for the parachute aerodynamic test method of photoelectric data fusion provided in the embodiment of the present application. p = 0.6 and T i =1.5 when adjusting the tracking curve of the output effect;

[0029] Figure 4 It is a schematic diagram of optical coordinate marking points used for longitudinal aerodynamic data conversion of the parafoil;

[0030] Figure 5 It is a schematic diagram of optical coordinate marking points used for lateral aerodynamic data conversion of the parafoil;

[0031] Figure 6 The parachute aerodynamic test method using optoelectronic data fusion provided in the embodiment of the present application obtains aerodynamic parameters of an axis system of a parafoil;

[0032] Figure 7 This is a schematic diagram of the trend of the lift and drag characteristics of the parafoil changing with the angle of attack in existing wind tunnel tests at home and abroad. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0034] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0035] The features and performance of the parachute aerodynamic test method with optoelectronic data fusion of the present application are further described in detail below in conjunction with the embodiments.

[0036] like Figure 1 As shown, the embodiment of the present application provides a parachute aerodynamic test method with optoelectronic data fusion, comprising the following steps:

[0037] S1. Install pressure sensors, temperature sensors, and humidity sensors on the walls of the stable section of the wind tunnel, install a high-definition high-speed camera to capture images of the canopy of the test parachute in the wind tunnel test section, install a pitot tube and a corresponding differential pressure sensor on the walls of both sides of the wind tunnel test section, connect the trigger end of the time system equipment to the aerodynamic collector and the trigger signal end of the high-definition high-speed camera, and connect the differential pressure sensor to the speed pressure controller; obtain the environmental parameter data such as atmospheric pressure, temperature, and humidity of the stable section of the wind tunnel collected in real time by the pressure sensor, temperature sensor, and humidity sensor, and fix the canopy of the test parachute in the test section of the wind tunnel with a bracket;

[0038] S2. According to the distribution of water vapor pressure at saturation temperature in the stable section of the wind tunnel, a dynamic pressure real-time correction mathematical model using multi-environmental parameter sensor data fusion technology is established;

[0039] During the wind tunnel test, with the long-term friction between the airflow and the tunnel wall, the temperature rise in the tunnel will reach 3°C / h. According to the calculation based on 100 train trips, it will take 6 hours of working time to make the temperature rise reach 18°C. According to the distribution of water vapor pressure at saturated temperature, the air density and humidity in the test section will change greatly. According to statistics, the humidity change reaches 20%. The corresponding dynamic pressure values ​​caused by these environmental parameter changes have a maximum difference of 15% (relative to standard air conditions). Therefore, in order to obtain a more accurate study of the correction ideas of dynamic pressure under variable air density conditions, it is necessary to carry out technical research through theoretical calculations of specific environmental parameters.

[0040] The dynamic pressure value of the wind tunnel test section is corrected in real time according to the following formula: Where: 实 is the real-time density of the airflow in the test section, kg / m 3 ; V A V is the wind speed on the left inner wall of the nozzle, m / s; B is the wind speed on the right inner wall of the nozzle, m / s; ΔP is the correction value of the dynamic pressure value of the test section.

[0041] The atmospheric pressure, temperature and relative humidity of the test section are measured by the corresponding sensors installed on the wind tunnel. The partial pressure of water vapor in the saturated air at the test section temperature t is obtained by difference calculation between the temperature measured in the stable section and the data in Table 1. The real-time air density ρ of the test section is calculated using the following formula 实 :

[0042]

[0043] Where: 实 is the real-time density of the airflow in the test section, kg / m 3 ; P is the atmospheric pressure of the test section, kpa; T is the thermodynamic temperature of the test section, K; ψ is the relative humidity of the test section, %; P tis the partial pressure of water vapor in saturated air at the test section temperature t, Pa.

[0044] Table 1 Water vapor pressure data at saturation temperature (typical)

[0045]

[0046] The inner walls of sections A and B on both sides of the wind tunnel test section are airflow boundaries. Considering that the energy loss is mainly caused by the friction between the airflow and the wind tunnel wall, the Bernoulli equation is applied to sections A and B to obtain the formula:

[0047]

[0048] Where: P B , P A are the static pressure values ​​of sections B and A on both sides of the wind tunnel test section, Pa; V B , V A are the wind speeds of sections B and A on both sides of the wind tunnel test section, m / s; ρ 实 is the real-time air density of the wind tunnel airflow, kg / m 3 ; K BA is the energy loss coefficient between section B and section A.

[0049] When conducting a wind blowing test, the static pressure drop method is used to measure the static pressure drop of the inner walls of section A and section B on both sides of the wind tunnel test section and the real-time air density of the test section, and the wind speed corresponding to the corrected dynamic pressure at the center of the wind tunnel test section can be calculated in real time.

[0050] S3, such as Figure 4 and Figure 5 As shown, a number of characteristic marking points representing the canopy shape are established on the canopy surface of the test parachute, and the spatial coordinates of the characteristic marking points are calculated; optionally, when calculating the spatial coordinates of the characteristic marking points, the image point coordinates of the images synchronously taken by the cameras that meet the intersection conditions are respectively interpreted by the photogrammetric forward intersection method, and the spatial coordinates of the characteristic marking points are calculated according to the image point coordinates and the camera station coordinates according to the photogrammetric forward intersection method.

[0051] S4, the atmospheric pressure, temperature and humidity data signals of the wind tunnel stable section collected by the pressure sensor, temperature sensor and humidity sensor are divided into two paths, one path is connected and input into the speed pressure controller, and the other path is connected and input into the aerodynamic force collector, and the time reference signal is unified, and the signal sent by the time system equipment is used as the test time zero point;

[0052] S5. Establish the test space coordinate system: take the center of the bracket of the fixed parafoil in the wind tunnel test section as the origin of the coordinate system O, the direction along the flow field as the positive direction of the X axis, and the vertically upward direction as the positive direction of the Y axis to establish a right-handed coordinate system O-XYZ, and take the moment reference point of the parafoil as the origin of the wind axis system to determine different coordinates converted by aerodynamic force: balance coordinate system, airflow coordinate axis system (wind axis system), test parafoil axis system and transition coordinate system. Use two cameras to synchronously shoot two digital images of the same scene from different angles. Based on the calibrated internal and external parameters and positional relationship of the two high-speed cameras, a stereoscopic image is constructed. For the spatial geometric model of beam delivery, the three-dimensional coordinates of the parachute marking points in the scene are calculated, and then the angle of attack of the test parachute is further derived in the coordinate system of the test parachute in real time; wherein, the wing parachute moment reference point is the center of gravity of the parachute system, which changes with the change of the wing angle of attack; optionally, when calculating the angle of attack of the test parachute in the coordinate system of the test parachute, the angle between the parachute rope of the symmetry plane of the test parachute and the plane of the parachute rope fixing frame is calculated through the trigonometric function relationship through the spatial coordinate system data of the feature points, and the geometric relationship between the parachute rope and the chord length is used to calculate the angle of attack of the test parachute in real time.

[0053] The force balance is connected to the parachute rope fixing frame through the upper cover, and connected to the lower angle adjustment mechanism of the bottom wall of the wind tunnel test section through the lower cover. During installation, ensure that the center of the balance coincides with the projection point of the parafoil theoretical torque reference point on the parachute rope fixing frame as much as possible. Figure 2 In the process, the optical "intersection measurement method" is used to measure the angle between the parachute rope on the symmetry plane of the airfoil parachute and the plane of the parachute rope fixing frame in real time, and the geometric relationship between the parachute rope and the airfoil chord length is used to calculate the airfoil parachute angle of attack in real time.

[0054] The coordinates of the wing parachute moment reference point, i.e. the origin of the wind axis system, are determined as follows: p X p Y p Z p is the balance coordinate system, OX q Y q Z q is the airflow coordinate axis system (wind axis system), O p X q Y q Z q is the body axis system, OX b Y b Z b is the transition coordinate system.

[0055] Balance change a c When A becomes θ A ', but θ A '-θ A ≠a c In O p X bY b Z b In the coordinate system, according to the structural dimensions of the wing parachute, the balance and the parachute rope frame, the formula for the actual angle of attack of the wing parachute can be obtained:

[0056] According to the distance from the real-time torque reference point of the optical test coordinate system to points C and D and the structural geometric relationship, the coordinates (x, y, z) of point O can be obtained.

[0057] From the cosine theorem we get:

[0058]

[0059] From the law of sine we get:

[0060]

[0061] Therefore, we can get:

[0062]

[0063] O P x b y b z b The coordinate system rotates to O P x q y q z q Coordinate system, the coordinates of point O are:

[0064]

[0065] Subtract the calculated balance load from the bracket test result to get the result of only removing the interference of the single bracket. P x p y p z p Rotate to O P x q y q z q Axis system. The rotation transformation formula is as follows:

[0066] Y=Y P cosα C -X P sinα C ;

[0067] X=(X P cosα C +Y P sinα C )cosβ c -Z p sinβ c ;

[0068] M Z =M ZP cosβ c +(M yp sinα C -M xp cosβ c )sinβ c ;

[0069] Z=Z P cosβ c +(X P cosα C +Y P sinα C )sinβ c ;

[0070] M y =M yP cosα C +M xp sinα C ;

[0071] M x =(M xp cosα C -M yp sinα C )cosβ z +M zp sinβ c ;

[0072] Translate the load to the wind axis system with O(x0, y0, z0) as the moment reference point.

[0073] Y q1 =Y;

[0074] X q1 =X;

[0075] Z q1 =Z;

[0076] M zq1 =M Z -Y·x0-X·y0;

[0077] M yq1 =M y +Z·x0+X·z0;

[0078] M xq1 =M x +Y·z0-Z·y0;

[0079] According to the requirements of the parafoil test, the test results are given in the form of aerodynamic coefficients, and the calculation formula is as follows:

[0080]

[0081] In the above formula: α is the real-time attack angle of the parafoil; α c is the balance tilt angle; q is the real-time correction dynamic pressure of the data; s is the nominal area of ​​the tested parachute, b is the extension length, and c is the chord length; C Lw ,C Dw ,C mw ,C yw ,C nw ,C lw They are the parachute lift coefficient, parachute drag coefficient, parachute pitch moment coefficient, parachute lateral force coefficient, parachute yaw moment coefficient, and parachute rolling torque coefficient after data fusion processing; X p , Y p , Z p , M xp , M yp , M zp They are the drag, lift, lateral force, rolling torque, yaw moment, and pitch moment directly measured by the balance; X q1 , Y q1 , Z q1 , M xq1 , M yq1 , M zq1 They are respectively the resistance, lift, lateral force, rolling torque, yaw moment, and pitch moment of the wind axis system after the load is translated; X, Y, Z, M x , M y , M z The resistance, lift, lateral force, rolling torque, yaw moment and pitch moment of the wind axis after the original data of the balance is rotated and converted; β c Turn the balance; ∠O p AB; ∠O p BA;θ A θ is the angle between the leading edge parachute rope and the plane of the balance before the balance is adjusted; A ' is the angle between the leading edge parachute rope and the balance plane after the balance is adjusted; θ B X is the angle between the trailing edge parachute line and the balance plane; C , Y C , X D , Y D are the horizontal and vertical coordinates of points C and D in the parafoil axis system; AB, CD, AD, BC, OD, O p A, O P B etc. are the corresponding known geometric lengths in plane ABCD.

[0082] S6. According to the actual windward area of ​​the wind tunnel test parachute model and historical test data, the modal relationship between the rotation speed and wind speed under different blockage ratio conditions is formulated, and the input conditions of the PI control model are established according to different blockage ratios and the wind speed at the center of the test section. According to the transfer function principle of the PI controller, the proportional coefficient and the integral time are optimized to achieve the best state;

[0083] During the wind tunnel test, whether it is a static force measurement test or a dynamic parachute opening dynamic load test, there are different blockage ratios due to the limitation of the wind tunnel nozzle size. The blockage ratio is calculated as shown in the following formula.

[0084]

[0085] Where: S 模型 is the windward area during the test, m 2 ; S 喷口 is the cross-sectional area of ​​the nozzle, m 2 .

[0086] According to the actual windward area of ​​the wind tunnel test parachute or model and historical test data, the blockage ratio of the test parachute or model currently borne by the wind tunnel is distributed in 3%, 5%, 10%, and 12%. When studying the analysis and resolution of the modal relationship between the rotation speed and wind speed under different blockage ratios, the input conditions of the PI control model are established with these commonly used blockage ratios and the wind speed VC at the center of the test section. According to the transfer function principle of the PI controller, the proportional coefficient and integral time are optimized to achieve the best state.

[0087] The control indicators of wind tunnel airflow at low speed are: 1) fan motor speed; 2) wind speed (speed pressure). The fan speed control system is composed of motor, power supply, speed measuring equipment, frequency converter and other equipment. The main circuit control scheme of the AC asynchronous motor driving the fan blades is controlled by the variable frequency speed regulation system. The rotary encoder installed at the output shaft end of the motor and the high-precision speed and pressure sensor installed in the wind tunnel test section are used as the feedback signals of the motor speed and speed and pressure measurement respectively. The host computer in the central control room realizes the full digital dual closed-loop control of the steady speed and pressure through the programmable controller.

[0088] The speed pressure regulator uses the classic PI controller. PI control refers to the control deviation formed by the given value and the actual output value. The proportion and integral of the deviation are linearly combined to form the control quantity to control the controlled object. The control formula for optimizing the proportional coefficient and integral time to achieve the best state according to the transfer function principle of the PI controller is as follows:

[0089]

[0090] Where: u(t) is the output signal of the PI controller; K p is the proportional coefficient; e(t) is the PI controller input signal; T iis the integration time; t is the time.

[0091] Among them, K p and T i It can be adjusted as needed to achieve the ideal control effect.

[0092] S7. According to step S2 and step S6, the dynamic pressure condition of the flow through the canopy of the test parachute is established, and then the actual lateral aerodynamic force and longitudinal aerodynamic force of the test parachute are converted according to the optical interpretation of the angle of attack of the test parachute and the force analysis of the aerodynamic torque felt by the force measuring balance, and the aerodynamic torque coefficient of the test parachute is calculated according to the nominal geometric characteristics of the test parachute and the real-time dynamic pressure correction data.

[0093] The parachute aerodynamic test method with optoelectronic data fusion provided in the embodiment of the present application innovatively establishes a synchronous acquisition and control system for optical data, velocity pressure and balance signals, and proposes a new aerodynamic conversion data processing method and a double closed-loop stable dynamic pressure control method through the two fusion technologies of optoelectronic data and environmental parameters, and further carries out the research on aerodynamic refinement test based on data fusion technology. The results obtained are intended to further optimize the accuracy of parachute aerodynamic characteristics test data to support model development and related research topics.

[0094] The wing parachute described in this application is a wing-shaped parachute, that is, the tested parachute.

[0095] Example 1

[0096] Using the parachute aerodynamic test method with optoelectronic data fusion provided in the above embodiment of the present application, a steady dynamic pressure control system based on PI control technology and a real-time dynamic pressure correction technology based on multi-environmental parameter sensor data fusion technology were established successively. The wind speed and drag characteristic data of the stable parachute under the conditions of unsteady dynamic pressure and steady dynamic pressure were obtained. The test data were summarized and analyzed, and the fluctuation of the drag characteristic was reduced.

[0097] According to actual records, the corresponding data of wind speed and rotation speed under different wind tunnel blockage ratios are shown in Table 2.

[0098] Table 2 Corresponding data of wind speed and rotation speed under different blocking ratio conditions

[0099]

[0100] From the table above, we can see that in the low wind speed range (0m / s~30m / s), the wind speed ratio varies greatly, and the average is approximately 6; in the common speed range (30m / s~70m / s), the wind speed ratio is approximately 5.8 on average; in the high wind speed range (70m / s~100m / s), the wind speed ratio is approximately 5.7 on average. Input the above data into the PLC steady wind speed control module.

[0101] Adjusting PI control parameters (proportional coefficient, integral time) can effectively adjust the output effect of PI controller, thus achieving the purpose of stable control. According to the transfer function principle of PI controller, increasing the proportional coefficient K p It can improve the system tracking speed, but if the proportional coefficient is too large, it will cause system oscillation; increase the integral time T i It can reduce the hysteresis of the integral and the overshoot, but when the integral time is too long, the system will eliminate the error more slowly. Therefore, first set the PI parameter to (K p =0.6, T i =1.5) to obtain the tracking curve as Figure 3 As shown:

[0102] Depend on Figure 3 The middle curve shows that the overall performance of the tested parachute system has been greatly improved, without obvious overshoot and oscillation, and basically meets the requirements. Through subsequent continuous optimization, the control parameters of the PI controller are finally determined to be (K p =0.1, T i =2.9), write this parameter into the corresponding control module of PLC.

[0103] After setting the PI control parameters, adjust the steady wind speed control function of the wind tunnel control system, set multiple different wind speeds for a stable parachute test, check the tracking effect, and judge whether the parameters and accuracy meet the index requirements. Finally, the tracking results under various wind speed conditions are obtained as shown in Table 3.

[0104] Table 3 Wind speed control accuracy debugging results

[0105] Serial number Set wind speed (m / s) Actual wind speed with unsteady dynamic pressure (m / s) Actual wind speed at steady dynamic pressure (m / s) 1 20 19.88～20.05 19.98～20.05 2 30 29.86～30.03 29.96～30.03 3 40 39.85～40.03 39.95～40.03 4 45 44.87～45.04 44.97～45.04 5 50 49.78～50.04 49.98～50.04 6 60 59.65～60.02 59.95～60.02 7 65 64.86～65.04 64.96～65.04 8 70 69.84～70.06 69.94～70.06 9 80 79.73～80.03 79.93～80.03

[0106] The optical "intersection measurement method" is used to measure the angle between the parachute rope on the symmetric surface of the airfoil and the plane of the parachute rope fixing frame in real time. Figure 2 The geometric relationship coordinate points of the marked parachute rope and airfoil chord length are used to calculate the parafoil angle of attack in real time. In this process, it is assumed that the airfoil is kept in good condition, the chord length is unchanged, the parachute rope is stiff, and small deformation is not considered. Then, the photoelectric data processing formula is used to process the aerodynamic parameters of the body axis system at two typical mass centers of the parafoil. Figure 6 The typical characteristic coordinate point data are shown in Table 4.

[0107] Table 4 Coordinates of typical aerodynamic transformation feature points of single-layer parafoil

[0108]

[0109] Analysis of the above Figure 6 and Figure 7 From the pictures and test data in Table 4, it can be seen that the change trend of the lift characteristic curve of the parafoil with the angle of attack in wind tunnel tests at home and abroad is consistent. As the angle of attack increases, it first increases approximately linearly and then decreases slowly. At the same angle of attack, the lift coefficient of the single-layer parafoil is larger and the lift characteristics are better. The pitch moment coefficients of the two basically fluctuate around 0. The change trend of the parafoil drag characteristic curve obtained in the wind tunnel test of this application is consistent, and the optimization research effect is basically achieved.

[0110] In view of the problem that the non-fixed moment reference point during the parafoil wind tunnel test causes the inability to accurately convert the aerodynamic data of the balance, key technical research ideas such as photoelectric time system acquisition and real-time fusion processing of photoelectric data are proposed. With a single-layer parafoil as the test object, by building a high-precision six-component balance test system, a high-definition camera system, a time system and a real-time dynamic pressure correction system, the data obtained conforms to the aerodynamic laws, providing data support for the optimization design of the aerodynamic characteristics of the single-layer parafoil, and also providing an important reference for the research of parafoil wind tunnel test technology.

[0111] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

Claims

1. A parachute aerodynamic test method using optoelectronic data fusion, characterized in that: The following steps are involved: S1. Obtain atmospheric pressure, temperature and humidity data in the stable section of the wind tunnel; S2. According to the distribution of water vapor pressure at saturation temperature in the stable section of the wind tunnel, a dynamic pressure real-time correction mathematical model using multi-environmental parameter sensor data fusion technology is established; S3, establishing a number of characteristic marking points representing the canopy shape on the canopy surface of the tested umbrella and calculating the spatial coordinates of the characteristic marking points; S4. Establish the test space coordinate system: take the center of the bracket of the fixed parafoil in the wind tunnel test section as the origin of the coordinate system O, the direction along the flow field as the positive direction of the X axis, and the vertically upward direction as the positive direction of the Y axis to establish the right-handed coordinate system O-XYZ, and take the moment reference point of the parafoil as the origin of the wind axis system to determine different coordinates converted by aerodynamic force: balance coordinate system, airflow coordinate axis system, test parachute body axis system and transition coordinate system, and calculate the test parachute's angle of attack in real time in the test parachute's coordinate system; S5. According to the actual windward area of ​​the wind tunnel test parachute model and historical test data, the modal relationship between the rotation speed and wind speed under different blockage ratio conditions is formulated, and the input conditions of the PI control model are established according to different blockage ratios and the wind speed at the center of the test section. According to the transfer function principle of the PI controller, the proportional coefficient and the integral time are optimized to achieve the best state; S6. According to step S2 and step S5, the dynamic pressure condition of the flow through the canopy of the test parachute is established, and then the actual lateral aerodynamic force and longitudinal aerodynamic force of the test parachute are converted according to the optical interpretation of the angle of attack of the test parachute and the force analysis of the aerodynamic torque felt by the force measuring balance, and the aerodynamic torque coefficient of the test parachute is calculated according to the nominal geometric characteristics of the test parachute and the real-time dynamic pressure correction data.

2. The method for testing parachute aerodynamics by photoelectric data fusion according to claim 1, characterized in that: Pressure sensors, temperature sensors and humidity sensors are installed on the wall of the stable section of the wind tunnel to obtain the atmospheric pressure, temperature and humidity data of the stable section of the wind tunnel.

3. The parachute aerodynamic test method of photoelectric data fusion according to claim 1, characterized in that: When calculating the spatial coordinates of the feature marking points, the image point coordinates of the images synchronously taken by the cameras that meet the intersection conditions are interpreted respectively by the photogrammetric forward intersection method, and the spatial coordinates of the feature marking points are calculated according to the image point coordinates and the camera point coordinates according to the photogrammetric forward intersection method.

4. The method for testing parachute aerodynamics by photoelectric data fusion according to claim 1, characterized in that: When calculating the angle of attack of the test parachute in the coordinate system of the test parachute, the angle between the parachute rope on the symmetry plane of the test parachute and the plane of the parachute rope fixing frame is calculated through the trigonometric function relationship through the spatial coordinate system data of the characteristic points according to the structural dimensions of the wing-shaped parachute, the balance and the parachute rope frame, and the geometric relationship between the parachute rope and the chord length is used to calculate the angle of attack of the test parachute in real time.

5. The method for testing parachute aerodynamics by photoelectric data fusion according to claim 1, characterized in that: When establishing the dynamic pressure real-time correction mathematical model of multi-environmental parameter sensor data fusion technology, the dynamic pressure value of the wind tunnel test section is corrected in real time according to the following formula: Where: 实 is the real-time density of airflow in the wind test section, kg / m 3 ; V A V is the wind speed on the left inner wall of the nozzle, m / s; B is the wind speed on the right inner wall of the nozzle, m / s; ΔP is the correction value of the dynamic pressure value of the test section.

6. The method for testing parachute aerodynamics by photoelectric data fusion according to claim 5, characterized in that: The real-time air density ρ of the wind tunnel test section 实 Calculated using the following formula: Where: 实 is the real-time density of airflow in the wind tunnel test section, kg / m 3 ; P is the atmospheric pressure of the test section, kpa; T is the thermodynamic temperature of the test section, K; ψ is the relative humidity of the test section, %; P t is the partial pressure of water vapor in saturated air at the test section temperature t, Pa.

7. The method for testing parachute aerodynamics by photoelectric data fusion according to claim 1, characterized in that: According to the PI controller transfer function principle, the following formula is used to optimize the proportional coefficient and integral time to achieve the best state: Where: u(t) is the output signal of the PI controller; K p is the proportional coefficient; e(t) is the PI controller input signal; T i is the integration time.

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