Model making method for wind tunnel zero-stiffness support aerodynamic measurement

Abstract

The present invention relates to the technical field of wind tunnel testing, and in particular to a method for making a model for measuring aerodynamic forces with zero stiffness support in a wind tunnel. The method comprises the following steps: obtaining wind tunnel flow field parameters and the geometric shape and size of a model to be made; estimating the magnitude of aerodynamic forces acting on the model in the wind tunnel flow field and the area where the pressure center is located; determining a design range for the combination of the model's mass, moment of inertia, and the distance from the pressure center to the center of mass; selecting data values ​​for the model's mass, moment of inertia, and the distance from the pressure center to the center of mass; determining the mass distribution of the model; making a model shell; arranging corresponding counterweights within the made model shell to obtain a model entity; determining an accelerometer combination based on final measurement parameters, actual parameters of the model entity, and wind tunnel flow field parameters; and embedding the accelerometer combination and an offline data acquisition device in the model entity based on the determined accelerometer combination, thereby ultimately obtaining a model for testing. The present invention can produce a model for measuring aerodynamic forces with zero stiffness support.

Description

Technical Field

[0001] The present invention relates to the technical field of wind tunnel testing, and in particular to a model making method for wind tunnel zero-rigidity support aerodynamic measurement and a zero-rigidity support measurement system design method. Background Art

[0002] Pulse wind tunnels are essential equipment for conducting ground tests of hypersonic aircraft in flight environments. Hypersonic aircraft aerodynamic measurements typically involve installing an aircraft model in a pulse wind tunnel, generating a flow field that meets simulation conditions and acting on the model to measure the aerodynamic loads.

[0003] The current aerodynamic measurement technology primarily relies on tail-supported internal balance aerodynamic measurement. The tail-supported internal balance aerodynamic measurement test device is a cantilever beam, resulting in a low frequency response, making it difficult to accurately measure millisecond-scale aerodynamic signals. Zero-stiffness support measurement can improve the aerodynamic measurement frequency response from the approximately 20 Hz of tail-supported internal balance aerodynamic measurement technology to over 1000 Hz. Furthermore, the measurement system is more compact and rigid, reducing the interference of difficult-to-handle low-frequency interference on the model's aerodynamic measurement signal and improving data reliability. However, due to the lack of a support structure, the model's attitude is susceptible to changes in the wind tunnel flow field, and the aerodynamic loads it experiences also change, affecting the aerodynamic load measurement results. Therefore, it is necessary to design and manufacture a model suitable for wind tunnel zero-stiffness support aerodynamic testing, taking into account the characteristics of zero-stiffness support measurement. Summary of the Invention

[0004] The object of the present invention is to address at least some of the above-mentioned deficiencies and to provide a model fabrication method for wind tunnel zero-stiffness support aerodynamic measurement and a zero-stiffness support measurement system design method, so as to obtain a model and system that can be used for zero-stiffness support measurement tests.

[0005] To achieve the above-mentioned object, the present invention provides a model making method for wind tunnel zero-stiffness support aerodynamic measurement, comprising:

[0006] Obtain wind tunnel flow field parameters and the geometric shape and size of the model to be made;

[0007] Based on the wind tunnel flow parameters and the geometry and size of the model, finite element simulation is used to estimate the magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field and the location of the center of pressure.

[0008] Based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass is determined. The combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass includes multiple combinations of moment of inertia and distance from the center of pressure to the center of mass data in which the attitude change does not exceed the angle change threshold within the effective test time.

[0009] Based on the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass, the combined design range of the model's mass, moment of inertia, and the distance from the center of pressure to the center of mass are determined through the relationship between moment of inertia and mass. The combined design range of the model's mass, moment of inertia, and the distance from the center of pressure to the center of mass includes multiple combinations of mass, moment of inertia, and distance from the center of pressure to the center of mass data in which the posture change does not exceed the angle change threshold within the effective test time.

[0010] The model's mass, moment of inertia and distance from the center of pressure to the center of mass are selected within their combined design ranges using a multi-objective optimization method.

[0011] Determine the mass distribution of the model based on the estimated area where the model's center of pressure is located and the selected model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values;

[0012] Based on the geometric shape and size, a model shell is produced;

[0013] According to the determined mass distribution of the model, corresponding counterweights are set in the manufactured model shell to obtain a model entity;

[0014] Determining an accelerometer combination based on the final measurement parameters, actual parameters of the model entity, and the wind tunnel flow field parameters; determining the accelerometer combination includes determining the number of accelerometers, the final measurement parameters corresponding to each accelerometer, the expected installation position, the measurement range, and the measurement accuracy; the final measurement parameters include one or more of axial force, normal force, lateral force, pitch moment, yaw moment, and roll moment;

[0015] According to the determined accelerometer combination, the accelerometer combination and the offline data acquisition device are embedded in the model entity, and finally a model for the test is obtained; the offline data acquisition device is connected to each of the accelerometers and is used to collect and store the measurement results of the accelerometers.

[0016] Optionally, after determining the combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass based on the combined design range of the model's moment of inertia and distance from the center of pressure to the center of mass by using the relationship between the moment of inertia and the mass, and before selecting the model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values ​​within the combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass by using the multi-objective optimization method, the method further includes:

[0017] According to the geometric shape and size of the model and the actual production conditions of the model, the combined design range of the model's mass, moment of inertia and distance from the center of pressure to the center of mass is reduced to eliminate data combinations that cannot be achieved under actual production conditions.

[0018] Optionally, determining the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass based on the estimated magnitude of the aerodynamic force acting on the model in the wind tunnel flow field, a preset angle change threshold, and an effective test time includes:

[0019] Based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, the control lines for the model's pitch, yaw, and roll are calculated, and the design domain is defined. The control lines represent the relationship between the model's moment of inertia and the distance from the center of pressure to the center of mass. On these control lines, the model's attitude change during the effective test time is equal to the corresponding angle change threshold.

[0020] Delineate the design domain based on the control lines of the model's pitch, yaw, and roll;

[0021] Based on the design domains corresponding to the model's pitch, yaw, and roll, determine the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass.

[0022] Optionally, the method of selecting the data values ​​of the mass, moment of inertia and distance from the center of pressure to the center of mass of the model by a multi-objective optimization method within a combined design range of the mass, moment of inertia and distance from the center of pressure to the center of mass of the model comprises:

[0023] Obtaining preset optimization objectives and constraints; the optimization objectives include maximizing the signal-to-noise ratio of the final measurement parameters;

[0024] According to the preset optimization objectives and constraints, the model's mass, moment of inertia and distance from the center of pressure to the center of mass data values ​​are selected through a multi-objective optimization method.

[0025] Optionally, determining the accelerometer combination based on the final measurement parameters, the actual parameters of the model entity, and the wind tunnel flow field parameters includes:

[0026] If the final measurement parameter includes the pitch moment, two identical uniaxial accelerometers are respectively arranged on the front and rear sides or the upper and lower sides of the center of mass of the model. The two uniaxial accelerometers arranged on the front and rear sides of the center of mass both measure the upward or downward acceleration, and the two uniaxial accelerometers arranged on the upper and lower sides of the center of mass respectively measure the acceleration of the model along the axial direction and in the opposite direction of the axial direction;

[0027] If the final measurement parameter includes the yaw moment, two identical uniaxial accelerometers are respectively arranged on the left and right sides or the front and rear sides of the center of mass of the model. The two uniaxial accelerometers arranged on the left and right sides of the center of mass both measure the acceleration of the model along the axial direction, and the two uniaxial accelerometers arranged on the front and rear sides of the center of mass both measure the acceleration of the model to the left or right;

[0028] If the final measurement parameter includes the rolling moment, two identical uniaxial accelerometers are respectively arranged on the left and right sides or the upper and lower sides of the center of mass of the model. The two uniaxial accelerometers arranged on the left and right sides of the center of mass both measure the upward or downward acceleration of the model, and the two uniaxial accelerometers arranged on the upper and lower sides of the center of mass respectively measure the left and right acceleration of the model;

[0029] If the final measurement parameter includes axial force, the axial acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the left and right sides or the upper and lower sides of the center of mass of the model;

[0030] If the final measurement parameter includes the normal force, the normal acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the front and back sides of the model's center of mass;

[0031] If the final measurement parameter includes lateral force, the lateral acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the upper and lower sides or the front and rear sides of the center of mass of the model.

[0032] Optionally, the determining of the accelerometer combination based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters further includes:

[0033] Determining the expected installation position of each accelerometer based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters;

[0034] According to the expected installation position of each accelerometer and the estimated magnitude of the aerodynamic force on the model in the wind tunnel flow field, the numerical range of the measurement results of each accelerometer is determined respectively;

[0035] Based on the numerical range of the accelerometer measurement results, the measurement range and measurement accuracy of the accelerometer are determined.

[0036] Optionally, embedding the accelerometer combination in the model entity includes:

[0037] providing an accelerometer mounting seat at each expected installation position of the accelerometer in the model entity;

[0038] The accelerometer is correspondingly mounted in the accelerometer mounting seat, and the accelerometer mounting seat is provided with a pressing force by a wave spring.

[0039] Optionally, the model making method further comprises:

[0040] The accelerometers in the model used for the test are calibrated to determine the actual installation position of each accelerometer.

[0041] Optionally, calibrating the accelerometer in the model used for the test includes:

[0042] Fix the model on the turntable;

[0043] Record the distance between the center of the rotating shaft of the turntable and the center of the bottom of the model;

[0044] Taking the center of the bottom of the model as the origin, calibrate the center of mass of the model and record it;

[0045] running the turntable and recording angular acceleration information of the turntable;

[0046] Obtaining output data of each accelerometer inside the model when the turntable is running;

[0047] Calculating the distance of each accelerometer relative to the center of mass of the model based on the output data of each accelerometer to determine the actual installation position of each accelerometer; calculating the distance of the accelerometer relative to the center of mass of the model includes:

[0048] Calculating the distance between the accelerometer and the center of the rotation axis of the turntable based on the output data of the accelerometer and the angular acceleration information of the turntable;

[0049] Calculating a distance value of the accelerometer relative to the center of mass of the model based on the center of mass of the model, the distance between the center of the rotation axis and the center of the bottom of the model, and the distance of the accelerometer relative to the center of the rotation axis of the turntable;

[0050] Determine whether the calculated distance value of the accelerometer relative to the model center of mass converges. If so, use the converged data value as the distance of the corresponding accelerometer relative to the model center of mass. Otherwise, repeat the above steps to continue to obtain the distance value of the accelerometer relative to the center of mass.

[0051] The present invention also provides a zero-rigidity support measurement system design method, comprising:

[0052] Determine the geometry of the object to be measured;

[0053] Determine the geometry of the model to be made based on the geometry of the object to be measured, and determine the size of the model to be made in combination with the cross-sectional area of ​​the uniform zone of the wind tunnel;

[0054] Using any of the above-mentioned model making methods, a model for testing is made;

[0055] Placing the model in a wind tunnel flow field in the form of a zero-stiffness support, and obtaining measurement results of all accelerometers within an effective test time;

[0056] Based on the measurement results obtained from all the accelerometers, the actual aerodynamic force acting on the model in the wind tunnel flow field is calculated.

[0057] The above technical solution of the present invention has the following advantages: the present invention provides a model production method for wind tunnel zero-stiffness support aerodynamic measurement. The present invention estimates the force conditions of the model in the wind tunnel flow field, combines the preset angle change threshold and the effective test time, and defines the model parameter combination that ensures that the posture remains almost unchanged during the test. Then, through multi-objective optimization, the model parameters are screened and determined, and then a model entity is obtained based on the corresponding model parameters, and an accelerometer combination and an offline data acquisition device are embedded in the model entity, finally obtaining a model that can be used for wind tunnel zero-stiffness support aerodynamic measurement.

[0058] The present invention also provides a zero-stiffness support measurement system design method. This method combines wind tunnel conditions and the conditions of the object to be measured to determine the relevant data of the model to be made. Then, through the above-mentioned model making method, a model that is suitable for the wind tunnel conditions and can reflect the characteristics of the object to be measured is made to realize the wind tunnel zero-stiffness support aerodynamic measurement test. Compared with the existing technology, it can effectively improve the measurement frequency response of the aerodynamic signal and the data credibility, and realize accurate measurement in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a schematic diagram of the steps of a method for making a model for wind tunnel zero-stiffness support aerodynamic measurement in an embodiment of the present invention;

[0060] Figure 2 Schematic diagram of the positional relationship and sensitive direction of each accelerometer in an accelerometer combination relative to the model mass center in an embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of the principle of two accelerometers calculating linear acceleration and rotational acceleration;

[0062] Figure 4 It is a schematic diagram of the steps of a zero-rigidity support measurement system design method in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0064] The primary aerodynamic measurement technology currently used is the tail-support internal balance aerodynamic measurement technique. During measurement, a strain gauge is built into the model, and the tail of the model is positioned in the wind tunnel via a support structure. The strain gauge measures the aerodynamic forces exerted on the model. This is essentially a static force measurement technique. Due to the limitations of its operating principle, the effective test time in a pulsed wind tunnel is typically only a few hundred microseconds to tens of milliseconds, making the entire test process dynamic and subject to significant vibration interference. Because the tail-support internal balance aerodynamic measurement device is a cantilever beam, the axial force has a high natural vibration frequency, resulting in a high frequency response, reaching over 1kHz, capable of accurately reproducing aerodynamic signals with a duration of less than 1ms. However, due to the model mass and the aspect ratio of the supporting struts, the natural frequencies of the model's normal force and pitching moment rarely exceed 100Hz, resulting in a frequency response often limited to a few dozen hertz. This allows for only reproducing aerodynamic signals with a duration of more than 100ms, and exhibits strong vibration interference for shorter aerodynamic signals. Zero-stiffness support aerodynamic measurement technology can effectively reduce the impact of vibration interference on model aerodynamic measurement results. However, due to the lack of a support structure, the model has a higher degree of freedom, and the model's attitude is prone to change in the wind tunnel flow field. If the model's attitude changes during the effective test time, the aerodynamic loads it experiences will also change with the model's attitude, potentially affecting the aerodynamic load measurement results. In view of this, the present invention provides a model fabrication method for wind tunnel zero-stiffness support aerodynamic measurement, thereby producing a test model with minimal attitude changes during the effective test time, which does not affect the measurement results.

[0065] The specific implementation of the above concept is described below.

[0066] like Figure 1 As shown, an embodiment of the present invention provides a model making method for wind tunnel zero-stiffness support aerodynamic measurement, comprising:

[0067] Step 100, obtaining wind tunnel flow field parameters and the geometric shape and size of the model to be manufactured;

[0068] Step 102 , estimating the magnitude of the aerodynamic force acting on the model in the wind tunnel flow field and the area where the center of pressure is located by finite element simulation based on the wind tunnel flow field parameters and the geometric shape and size of the model;

[0069] This step 102 does not require an exact solution, but can be estimated, which can save time and reduce the amount of calculation;

[0070] Step 104 , determining a combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass based on the estimated magnitude of the aerodynamic force acting on the model in the wind tunnel flow field, a preset angle change threshold, and an effective test time;

[0071] The combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass includes multiple combinations of moment of inertia and distance from the center of pressure to the center of mass data whose posture changes do not exceed the angle change threshold within the effective test time;

[0072] In this step 104, in order to achieve accurate measurement, the preset angle change threshold is preferably that the pitch, yaw and roll are no more than 3′;

[0073] Step 106 , based on the combined design range of the moment of inertia and the distance from the center of pressure to the center of mass of the model and by using the relationship between the moment of inertia and the mass, determine the combined design range of the mass, moment of inertia, and the distance from the center of pressure to the center of mass of the model;

[0074] The combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass includes multiple combinations of mass, moment of inertia, and distance from the center of pressure to the center of mass data whose posture changes do not exceed the angle change threshold within the effective test time;

[0075] Step 108, selecting the model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values ​​within the combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass using a multi-objective optimization method;

[0076] Step 110 , determining the mass distribution of the model based on the estimated area where the model's center of pressure is located and the selected model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values;

[0077] In this step 110, based on the estimated area where the model's center of pressure is located and the distance data value from the center of pressure to the center of mass, the center of mass can be determined. Combined with the model's mass and moment of inertia, the model's mass distribution can be determined.

[0078] Step 112, making a model shell based on the geometric shape and size;

[0079] In this step 112 , the model shell is preferably made of hard material to obtain a model shell with high rigidity;

[0080] Step 114: according to the determined mass distribution of the model, corresponding counterweights are set in the manufactured model shell to obtain a model entity;

[0081] Step 116: Determine an accelerometer combination based on the final measurement parameters, actual parameters of the model entity, and the wind tunnel flow field parameters; determining the accelerometer combination includes determining the number of accelerometers, the final measurement parameters corresponding to each accelerometer, the expected installation position, the measurement range, and the measurement accuracy; the final measurement parameters include one or more of axial force, normal force, lateral force, pitch moment, yaw moment, and roll moment;

[0082] Step 118: Based on the determined accelerometer combination, the accelerometer combination and the offline data acquisition device are embedded in the model entity, and finally a model for testing is obtained; the offline data acquisition device is connected to each of the accelerometers to collect and store the measurement results of the accelerometers.

[0083] The above-mentioned embodiment of the present invention provides a model production method for wind tunnel zero-stiffness support aerodynamic measurement. Based on the wind tunnel flow field parameters and the geometric shape and size of the model, the force conditions of the model in the wind tunnel flow field are estimated. Combined with the preset angle change threshold and the effective test time, a model parameter combination that can ensure that the posture remains almost unchanged during the test is determined. Then, through multi-objective optimization, the model parameters are screened and determined, and then a model entity is produced according to the corresponding model parameters. An accelerometer combination and an offline data acquisition device are embedded in the model entity, and finally a model that can be used for wind tunnel zero-stiffness support aerodynamic measurement is obtained.

[0084] In the process of selecting model parameters, the present invention limits the attitude change of the model within the effective test time to no more than the angle change threshold. When the zero-rigidity support form is used to replace the tail support internal balance aerodynamic measurement technology for testing, for example, the model is placed in the wind tunnel flow field in the form of zero-rigidity support in a free-fall manner within the effective test time. Due to the short effective test time, the model's attitude change, speed, and axial displacement are small. Compared with the wind tunnel flow field with a flow rate of several thousand meters per second, the model can be equivalent to a static state. The aerodynamic load in the uniform area of ​​the wind tunnel flow field can be considered to be constant, and accurate measurement of millisecond-level aerodynamic signals can be achieved, thereby improving the frequency response and data credibility of the aerodynamic load measurement.

[0085] Optionally, step 104 of determining the combined design range of the moment of inertia of the model and the distance from the center of pressure to the center of mass further includes:

[0086] Based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, the control lines for the model's pitch, yaw, and roll are calculated, and the design domain is defined. The control lines represent the relationship between the model's moment of inertia and the distance from the center of pressure to the center of mass. On these control lines, the model's attitude change during the effective test time is equal to the corresponding angle change threshold.

[0087] Delineate the design domain based on the control lines of the model's pitch, yaw, and roll;

[0088] Based on the design domains corresponding to the model's pitch, yaw, and roll, determine the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass.

[0089] Taking the preset angle change threshold including the pitch angle change of 3′ as an example, the relationship between the pitch moment Mz, the pitch change angle a, the angular acceleration α, and the moment of inertia about the Z axis Iz can be expressed as follows:

[0090] Mz=α·Iz

[0091] a=αt 2 / 2

[0092] Then we have:

[0093]

[0094] It can be seen that, given a constant effective test time t, the magnitude of the model's moment of inertia about the Z axis, Iz, and the magnitude of the pitching moment, Mz, jointly determine the magnitude of the model's pitch angle change, a, in the flow field. The magnitude of the model's moment of inertia about the Z axis, Iz, is primarily affected by the distribution of the model's mass relative to the Z axis. The Z axis passes through the model's center of mass. The pitching moment, Mz, = l × F, where F represents the aerodynamic force in the pitch direction. Zero-stiffness supports can be considered to be the center of mass for rotation, and l represents the distance from the center of mass to the center of pressure. The aerodynamic force in the pitch direction is determined based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field. Substituting this into the equation, we obtain a control line with a pitch angle of 3'. The region surrounding this control line represents the design domain that satisfies the requirement for pitch angle change within the effective test time. Within this design domain, combinations of the moment of inertia and the distance from the center of mass to the center of pressure can meet the requirement for minimal pitch angle change. It has been verified that the relative distance between the center of mass and the center of pressure is the primary factor determining the model's pitch angle change within the effective test time, followed by the model's moment of inertia. By integrating the design domains corresponding to the model's pitch, yaw, and roll, the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass can be determined.

[0095] Optionally, after step 106 and before step 108, the model making method further includes:

[0096] According to the geometric shape and size of the model and the actual production conditions of the model, the combined design range of the model's mass, moment of inertia and distance from the center of pressure to the center of mass is reduced to eliminate data combinations that cannot be achieved under actual production conditions.

[0097] The above embodiments take into account the constraints imposed by actual manufacturing conditions on model parameter selection. For example, based on the acquired geometry and dimensions, the moment of inertia of the model's shell (i.e., minimum moment of inertia) and the moment of inertia of the solid core (i.e., maximum moment of inertia) are estimated through finite element simulation to determine the achievable range of the model's moment of inertia. Based on the acquired geometry and dimensions, combined with the actual available counterweight density, the achievable range of the model's mass can be determined. Data combinations outside the achievable range are unachievable under actual manufacturing conditions and therefore need to be eliminated.

[0098] Optionally, step 108 of selecting the model's mass, moment of inertia, and distance from the center of pressure to the center of mass data may further include:

[0099] Obtaining preset optimization objectives and constraints; the optimization objectives include maximizing the signal-to-noise ratio of the final measurement parameters;

[0100] According to the preset optimization objectives and constraints, the model's mass, moment of inertia and distance from the center of pressure to the center of mass data values ​​are selected through a multi-objective optimization method.

[0101] This step 108 can use existing technologies such as ant colony algorithms and genetic algorithms to perform multi-objective optimization to screen out the best model parameter data combination. The preset constraints may include model stiffness requirements and / or mass, moment of inertia, distance from the center of pressure to the center of mass, and other parameter requirements.

[0102] Optionally, in step 116, determining the accelerometer combination further includes:

[0103] If the final measurement parameter includes the pitch moment, two identical uniaxial accelerometers are placed on the front and rear sides or the upper and lower sides of the center of mass of the model respectively; the two uniaxial accelerometers placed on the front and rear sides of the center of mass of the model both measure the upward acceleration or the downward acceleration (that is, the two uniaxial accelerometers placed on the front and rear sides of the center of mass both measure the upward acceleration of the model or both measure the downward acceleration of the model), such as Figure 2 The accelerometer s1 and accelerometer s2 are shown in FIG. Figure 2 The volume of the accelerometer is not shown, and only the measurement direction of the accelerometer is indicated by an arrow. The position of the arrow shows the relative position relationship between the accelerometer and the center of mass O. Usually, the direction of the model axis from head to tail is set as the positive direction of the x-axis (that is, the axial direction), and a right-handed Cartesian coordinate system is established. In this case, the normal force is the force in the y-axis direction, and the lateral force is the force in the z-axis direction). The two uniaxial accelerometers arranged on the upper and lower sides of the center of mass of the model respectively measure the acceleration of the model along the axial direction and in the opposite direction of the axial direction (that is, the two uniaxial accelerometers arranged on the upper and lower sides of the center of mass, one measures the acceleration of the model along the axial direction, and the other measures the acceleration of the model in the opposite direction of the axial direction), as shown in FIG. Figure 2 The accelerometer s10 and the accelerometer s11 shown in FIG;

[0104] If the final measurement parameter includes the yaw moment, two identical uniaxial accelerometers are placed on the left and right sides or the front and back sides of the center of mass of the model. The two uniaxial accelerometers placed on the left and right sides of the center of mass of the model both measure the acceleration of the model along the axial direction, such as Figure 2 The accelerometers s3 and s4 shown in FIG are two single-axis accelerometers arranged on both sides of the center of mass of the model to measure the left or right acceleration of the model. Figure 2 accelerometer s8 and accelerometer s9 shown in;

[0105] If the final measurement parameter includes the rolling moment, two identical uniaxial accelerometers are placed on the left and right sides or the upper and lower sides of the center of mass of the model. The two uniaxial accelerometers placed on the left and right sides of the center of mass of the model both measure the upward or downward acceleration of the model, such as Figure 2 The accelerometers s5 and s6 shown in FIG are two single-axis accelerometers arranged on the upper and lower sides of the center of mass of the model to measure the left and right accelerations of the model respectively. Figure 2 The accelerometers s12 and s13 are shown.

[0106] It should be noted that the directional words such as "up", "down", "left", "right", "front" and "back" in the above embodiments are all directions relative to the center of mass. The upper side is the side relatively far away from the ground, and the front side is the side relatively close to the flow field.

[0107] Each accelerometer is preferably arranged on a coordinate axis with the center of mass as the origin O. If it is not on the coordinate axis, it needs to be projected onto the corresponding coordinate axis for solution.

[0108] The above embodiment shows how to determine the required number of accelerometers and the positional relationship of each accelerometer relative to the center of mass of the model based on the final measurement parameters. The distance of each accelerometer relative to the center of mass, that is, the specific expected installation position of the accelerometer, can be selected according to actual needs. The model produced by the present invention calculates the corresponding angular acceleration based on the linear acceleration measured by the accelerometer, and then solves the torque. Compared with the method of measuring displacement, measuring acceleration can better reflect the aerodynamic load characteristics in a short period of time, and has lower cost, objective and simple data processing process, and more reliable test data.

[0109] Furthermore, in step 116, if the final measurement parameter includes axial force, the axial acceleration of the model is measured and solved by two identical uniaxial accelerometers arranged on the left and right sides or the upper and lower sides of the center of mass of the model;

[0110] If the final measurement parameter includes the normal force, the normal acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the front and back sides of the model's center of mass;

[0111] If the final measurement parameter includes lateral force, the lateral acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the upper and lower sides or the front and rear sides of the center of mass of the model.

[0112] The above embodiment uses two accelerometers to form a combined measurement and resolve motion acceleration. The force can continue to be measured using the accelerometer used to measure torque. In other words, the force and torque can be simultaneously resolved by two uniaxial accelerometers. For example, two uniaxial accelerometers arranged on both sides of the center of mass measure upward acceleration. If the two uniaxial accelerometers are symmetrical with respect to the center of mass, then the measurement results of the two uniaxial accelerometers are added together to obtain twice the normal linear acceleration. The measurement results of the two uniaxial accelerometers are subtracted to obtain twice the pitch rotation acceleration. Combined with the accelerometer positions, the angular acceleration in the pitch direction can be determined. If the two uniaxial accelerations are not symmetrical with respect to the center of mass, they can also be resolved by combining the center of mass position and the accelerometer setting position. Through the corresponding accelerometer combination, combined with the accelerometer setting position and the center of mass position, the corresponding linear acceleration or rotation acceleration can be solved, and then the corresponding force or torque can be solved.

[0113] like Figure 3 As shown, it is assumed that two uniaxial accelerometers are respectively provided at points A and B on a certain axis, the measuring direction (i.e., sensitive direction) is perpendicular to line segment AB, point C is the center of mass, and point D is the center of pressure. The accelerometer at point A measures acceleration a A =a F +a mA , the accelerometer at point B measures acceleration a B =a F +a mB , a F is the linear acceleration of the vertical line segment AB, a mA is the linear acceleration (i.e. rotational acceleration) caused by rotation at point A, a mB is the linear acceleration caused by rotation at point B. Let AC distance be l1, BC distance be l2, DC distance be L. Aerodynamic force F acts on the pressure center. With the center of mass as the center of rotation, angular acceleration α is generated. mA =αl1,a mB =-αl2, with a A -a B =a mA -a mB ,(a A -a B ) / (l1+l2)=α=M / J, M represents torque, J represents moment of inertia, and we can solve M=(a A -a B )J / (l1+l2); similarly, l1amB / (l1+l2)+l2a mA / (l1+l2)=l1(-αl2) / (l1+l2)+l2(αl1) / (l1+l2)=0, then l1a A / (l1+l2)+l2a B / (l1+l2)=a F =F / m, where m represents mass, and we can solve F=[l1a A / (l1+l2)+l2a B / (l1+l2)]m.

[0114] Furthermore, a three-axis accelerometer can be set at the center of mass of the model, such as Figure 2 Accelerometer s7, shown at the center of mass O, measures three-dimensional linear acceleration in the X, Y, and Z axes, thereby verifying and correcting the results obtained by the uniaxial accelerometer. In the free state, the center of rotation of the model system is the center of mass. Accelerometer s7 has no linear acceleration due to rotation, so decoupling is not required. The measured result is the model's translational acceleration.

[0115] Optionally, the determining of the accelerometer combination based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters further includes:

[0116] Determining the expected installation position of each accelerometer based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters;

[0117] According to the expected installation position of each accelerometer and the estimated magnitude of the aerodynamic force on the model in the wind tunnel flow field, the numerical range of the measurement results of each accelerometer is determined respectively;

[0118] Based on the numerical range of the accelerometer measurement results, the measurement range and measurement accuracy of the accelerometer are determined.

[0119] Preferably, the step of determining the expected installation position of each accelerometer based on the final measurement parameters, the actual parameters of the model entity, and the wind tunnel flow field parameters further comprises:

[0120] Based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters, the accelerometer is adjusted to a position with lower vibration interference through modal analysis, and the expected installation position of the accelerometer is determined.

[0121] In the above embodiment, after determining the required accelerometer combination and the positional relationship of each accelerometer relative to the center of mass based on the specific final measurement parameters, modal analysis is used to adjust the corresponding accelerometer to a position with low vibration interference. For example, the accelerometer is located at a vibration node, or two accelerometers corresponding to the same measurement are arranged symmetrically at the vibration node to reduce the impact of vibration interference on the accelerometer measurement results. For wind tunnel zero-stiffness support aerodynamic measurements, the frequency of the vibration interference signal differs from the effective signal (quasi-zero frequency) by more than one order of magnitude. At the same time, the modal vibration frequency bands are far apart, and there is no vibration coupling. The vibration interference signal can be separated and filtered out using low-pass filtering or methods such as wavelet and EMD, providing favorable conditions for effective signal processing.

[0122] Preferably, the measurement range and measurement accuracy of the accelerometer are determined based on the numerical range of the accelerometer measurement results, including making the numerical range of the accelerometer measurement results within 50% to 80% of the corresponding accelerometer range, and the measurement accuracy is as high as possible to obtain more accurate measurement results.

[0123] By adopting the above embodiment, a model capable of accurately measuring aerodynamic force signals can be produced.

[0124] Optionally, step 118 of embedding the accelerometer combination in the model entity further includes:

[0125] providing an accelerometer mounting seat at each expected installation position of the accelerometer in the model entity;

[0126] The accelerometer is correspondingly mounted in the accelerometer mounting seat, and the accelerometer mounting seat is provided with a pressing force by a wave spring.

[0127] The use of a wave spring to provide the accelerometer mounting base with compression force can prevent the accelerometer from being loose, thereby reducing the interference of vibration on the measurement results.

[0128] Optionally, the model making method further includes:

[0129] Step 120 : calibrate the accelerometers in the model used for the test to determine the actual installation position of each accelerometer.

[0130] Furthermore, the accelerometers in the model used for the test were calibrated, including:

[0131] Fix the model on the turntable;

[0132] Record the distance between the center of the rotating shaft of the turntable and the center of the bottom of the model;

[0133] Taking the center of the bottom of the model as the origin, calibrate the center of mass of the model and record it;

[0134] running the turntable and recording angular acceleration information of the turntable;

[0135] Obtaining output data of each accelerometer inside the model when the turntable is running;

[0136] Calculating the distance of each accelerometer relative to the center of mass of the model based on the output data of each accelerometer to determine the actual installation position of each accelerometer; calculating the distance of the accelerometer relative to the center of mass of the model includes:

[0137] Calculating the distance between the accelerometer and the center of the rotation axis of the turntable based on the output data of the accelerometer and the angular acceleration information of the turntable;

[0138] Calculating a distance value of the accelerometer relative to the center of mass of the model based on the center of mass of the model, the distance between the center of the rotation axis and the center of the bottom of the model, and the distance of the accelerometer relative to the center of the rotation axis of the turntable;

[0139] Determine whether the calculated distance value of the accelerometer relative to the model center of mass converges. If so, use the converged data value as the distance of the corresponding accelerometer relative to the model center of mass. Otherwise, repeat the above steps to continue to obtain the distance value of the accelerometer relative to the center of mass.

[0140] When using static principles to measure aerodynamic forces directly from the model's mass, moment of inertia, and the average of the accelerometer's raw output, it's necessary to accurately know the accelerometer's spatial distance from the center of mass. To avoid deviations between the actual position and the expected installation location, accurate calibration is required. The above-described embodiment calibrates the accelerometer using a turntable, calculating its actual position using accelerometer output data. A cyclic calibration approach, introducing statistical methods, eliminates random errors during the calibration process and improves calibration accuracy.

[0141] like Figure 4 As shown, the present invention also provides a zero-stiffness support measurement system design method, comprising:

[0142] Step 400, determining the geometric shape of the object to be measured;

[0143] Step 402: determining the geometric shape of the model to be manufactured based on the geometric shape of the object to be measured, and determining the size of the model to be manufactured in combination with the cross-sectional area of ​​the uniform zone of the wind tunnel;

[0144] Step 404: Using the model making method described in any of the above embodiments, make a model for testing;

[0145] Step 406: placing the manufactured model in a wind tunnel flow field in the form of a zero-stiffness support, and obtaining measurement results of all accelerometers within the effective test time;

[0146] Placing the model in the wind tunnel flow field in the form of zero-stiffness support includes: placing the model in a preset posture above a uniform area of ​​the wind tunnel flow field, and releasing the model to enter the uniform area of ​​the wind tunnel flow field in the form of free fall, thereby being in the wind tunnel flow field in the form of zero-stiffness support within the effective test time; or placing the model in the uniform area of ​​the wind tunnel flow field in a preset posture by suspending or lifting, releasing the suspension or lifting structure, and allowing the model to be in the wind tunnel flow field in the form of zero-stiffness support within the effective test time, etc.

[0147] Step 408 : Calculate the actual aerodynamic force on the model in the wind tunnel flow field based on the measurement results obtained from all the accelerometers.

[0148] Optionally, step 402 of determining the size of the model to be produced further includes:

[0149] According to the cross-sectional area of ​​the uniform zone at the wind tunnel nozzle outlet, the maximum cross-sectional area of ​​the model to be manufactured is determined by the following formula:

[0150] (1+1 / cosα)(A m0 / A T )≤0.4

[0151] Among them, α is the model attack angle, A m0 is the maximum cross-sectional area of ​​the model, A T is the cross-sectional area of ​​the uniform zone at the wind tunnel nozzle outlet;

[0152] The size of the model to be produced is determined based on the maximum cross-sectional area of ​​the model to be produced and the geometric shape of the model to be produced.

[0153] The above process can be considered as determining the model scale. Optionally, the uniform zone diameter can be conservatively estimated as 0.6 times the nozzle exit diameter, and the maximum angle of attack can be calculated as 15°. By defining the maximum cross-sectional area of ​​the model to be fabricated and the maximum cross-sectional area of ​​the object to be measured, the model scale is determined, ensuring that the resulting model is suitable for the corresponding wind tunnel flow field.

[0154] In summary, the present invention provides a model fabrication method and a zero-stiffness support measurement system design method for wind tunnel zero-stiffness support aerodynamic measurement, so as to obtain a model and system that can be used for zero-stiffness support measurement tests. Large-scale and large-mass model aerodynamic tests can be realized, and when the model has a large inertia (mass, moment of inertia), the disadvantage of the short effective test time of the shock wind tunnel becomes an advantage in terms of model attitude control. Within a very short effective test time, the position and attitude of the model remain almost unchanged under the action of aerodynamic force, and there is no flow field interference caused by struts or support devices. The flow field structure of the model is consistent with the real object, the simulation is more realistic, and the frequency response and data credibility of the aerodynamic load measurement can be improved.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A model making method for wind tunnel zero-stiffness support aerodynamic measurement, characterized in that: include: Obtain wind tunnel flow field parameters and the geometric shape and size of the model to be made; Based on the wind tunnel flow parameters and the geometry and size of the model, finite element simulation is used to estimate the magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field and the location of the center of pressure. Based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass is determined. The combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass includes multiple combinations of moment of inertia and distance from the center of pressure to the center of mass data in which the attitude change does not exceed the angle change threshold within the effective test time. Based on the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass, the combined design range of the model's mass, moment of inertia, and the distance from the center of pressure to the center of mass are determined through the relationship between moment of inertia and mass. The combined design range of the model's mass, moment of inertia, and the distance from the center of pressure to the center of mass includes multiple combinations of mass, moment of inertia, and distance from the center of pressure to the center of mass data in which the posture change does not exceed the angle change threshold within the effective test time. The model's mass, moment of inertia and distance from the center of pressure to the center of mass are selected within their combined design ranges using a multi-objective optimization method. Determine the mass distribution of the model based on the estimated area where the model's center of pressure is located and the selected model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values; Based on the geometric shape and size, a model shell is produced; According to the determined mass distribution of the model, corresponding counterweights are set in the manufactured model shell to obtain a model entity; Determining an accelerometer combination based on the final measurement parameters, actual parameters of the model entity, and the wind tunnel flow field parameters; determining the accelerometer combination includes determining the number of accelerometers, the final measurement parameters corresponding to each accelerometer, the expected installation position, the measurement range, and the measurement accuracy; the final measurement parameters include one or more of axial force, normal force, lateral force, pitch moment, yaw moment, and roll moment; According to the determined accelerometer combination, the accelerometer combination and the offline data acquisition device are embedded in the model entity, and finally a model for the test is obtained; the offline data acquisition device is connected to each of the accelerometers and is used to collect and store the measurement results of the accelerometers.

2. The model making method according to claim 1, characterized in that: After determining the combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass based on the combined design range of the model's moment of inertia and distance from the center of pressure to the center of mass by using the relationship between the moment of inertia and the mass, and before selecting the model's mass, moment of inertia, and distance from the center of pressure to the center of mass data values ​​within the combined design range of the model's mass, moment of inertia, and distance from the center of pressure to the center of mass by using the multi-objective optimization method, the method further includes: According to the geometric shape and size of the model and the actual production conditions of the model, the combined design range of the model's mass, moment of inertia and distance from the center of pressure to the center of mass is reduced to eliminate data combinations that cannot be achieved under actual production conditions.

3. The model making method according to claim 1, wherein: The combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass is determined based on the estimated magnitude of the aerodynamic force acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, including: Based on the estimated magnitude of the aerodynamic forces acting on the model in the wind tunnel flow field, the preset angle change threshold, and the effective test time, the control lines for the model's pitch, yaw, and roll are calculated, and the design domain is defined. The control lines represent the relationship between the model's moment of inertia and the distance from the center of pressure to the center of mass. On these control lines, the model's attitude change during the effective test time is equal to the corresponding angle change threshold. Delineate the design domain based on the control lines of the model's pitch, yaw, and roll; Based on the design domains corresponding to the model's pitch, yaw, and roll, determine the combined design range of the model's moment of inertia and the distance from the center of pressure to the center of mass.

4. The model making method according to claim 3, characterized in that: The multi-objective optimization method is used to select the data values ​​of the mass, moment of inertia and distance from the center of pressure to the center of mass of the model within the combined design range of the mass, moment of inertia and distance from the center of pressure to the center of mass of the model, including: Obtaining preset optimization objectives and constraints; the optimization objectives include maximizing the signal-to-noise ratio of the final measurement parameter; According to the preset optimization objectives and constraints, the model's mass, moment of inertia and distance from the center of pressure to the center of mass data values ​​are selected through a multi-objective optimization method.

5. The model making method according to claim 1, characterized in that: The step of determining the accelerometer combination based on the final measurement parameters, the actual parameters of the model entity, and the wind tunnel flow field parameters includes: If the final measurement parameter includes the pitch moment, two identical uniaxial accelerometers are respectively arranged on the front and rear sides or the upper and lower sides of the center of mass of the model. The two uniaxial accelerometers arranged on the front and rear sides of the center of mass both measure the upward or downward acceleration, and the two uniaxial accelerometers arranged on the upper and lower sides of the center of mass respectively measure the acceleration of the model along the axial direction and in the opposite direction of the axial direction; If the final measurement parameter includes the yaw moment, two identical uniaxial accelerometers are respectively arranged on the left and right sides or the front and rear sides of the center of mass of the model. The two uniaxial accelerometers arranged on the left and right sides of the center of mass both measure the acceleration of the model along the axial direction, and the two uniaxial accelerometers arranged on the front and rear sides of the center of mass both measure the acceleration of the model to the left or right; If the final measurement parameter includes the rolling moment, two identical uniaxial accelerometers are respectively arranged on the left and right sides or the upper and lower sides of the center of mass of the model. The two uniaxial accelerometers arranged on the left and right sides of the center of mass both measure the upward or downward acceleration of the model, and the two uniaxial accelerometers arranged on the upper and lower sides of the center of mass respectively measure the left and right acceleration of the model; If the final measurement parameter includes axial force, the axial acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the left and right sides or the upper and lower sides of the center of mass of the model; If the final measurement parameter includes the normal force, the normal acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the front and back sides of the model's center of mass; If the final measurement parameter includes lateral force, the lateral acceleration of the model is measured and solved by placing two identical uniaxial accelerometers on the upper and lower sides or the front and rear sides of the center of mass of the model.

6. The model making method according to claim 5, characterized in that: The determining of the accelerometer combination based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters further includes: Determining the expected installation position of each accelerometer based on the final measurement parameters, the actual parameters of the model entity and the wind tunnel flow field parameters; According to the expected installation position of each accelerometer and the estimated magnitude of the aerodynamic force on the model in the wind tunnel flow field, the numerical range of the measurement results of each accelerometer is determined respectively; Based on the numerical range of the accelerometer measurement results, the measurement range and measurement accuracy of the accelerometer are determined.

7. The model making method according to claim 1, characterized in that: Embedding the accelerometer combination in the model entity includes: providing an accelerometer mounting seat at each expected installation position of the accelerometer in the model entity; The accelerometer is correspondingly mounted in the accelerometer mounting seat, and the accelerometer mounting seat is provided with a pressing force by a wave spring.

8. The model making method according to claim 1, wherein: Also includes: The accelerometers in the model used for the test are calibrated to determine the actual installation position of each accelerometer.

9. The model making method according to claim 8, characterized in that: The calibrating of the accelerometer in the model used for the test includes: Fix the model on the turntable; Record the distance between the center of the rotating shaft of the turntable and the center of the bottom of the model; Taking the center of the bottom of the model as the origin, calibrate the center of mass of the model and record it; running the turntable and recording angular acceleration information of the turntable; Obtaining output data of each accelerometer inside the model when the turntable is running; Calculating the distance of each accelerometer relative to the center of mass of the model based on the output data of each accelerometer to determine the actual installation position of each accelerometer; calculating the distance of the accelerometer relative to the center of mass of the model includes: Calculating the distance between the accelerometer and the center of the rotation axis of the turntable based on the output data of the accelerometer and the angular acceleration information of the turntable; Calculating a distance value of the accelerometer relative to the center of mass of the model based on the center of mass of the model, the distance between the center of the rotation axis and the center of the bottom of the model, and the distance of the accelerometer relative to the center of the rotation axis of the turntable; Determine whether the calculated distance value of the accelerometer relative to the model center of mass converges. If so, use the converged data value as the distance of the corresponding accelerometer relative to the model center of mass. Otherwise, repeat the above steps to continue to obtain the distance value of the accelerometer relative to the center of mass.

10. A zero-stiffness support measurement system design method, characterized in that: include: Determine the geometry of the object to be measured; Determine the geometry of the model to be made based on the geometry of the object to be measured, and determine the size of the model to be made in combination with the cross-sectional area of ​​the uniform zone of the wind tunnel; Using the model making method according to any one of claims 1 to 9 to make a model for testing; Placing the model in a wind tunnel flow field in the form of a zero-stiffness support, and obtaining measurement results of all accelerometers within an effective test time; Based on the measurement results obtained from all the accelerometers, the actual aerodynamic force acting on the model in the wind tunnel flow field is calculated.

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