A method for quickly generating initial readings for internal strain gauge balance

Abstract

The present invention discloses a method for quickly generating initial readings suitable for an internal strain balance. The method establishes a coordinate axis conversion relationship to deduce the transformation law of each component of the internal strain balance with the model posture angle, introduces a linear transfer relationship to characterize the influence of the balance and a data acquisition device on the measurement value, and finally forms a complete mathematical equation for the initial readings. The Newton iteration method and a small amount of collected measured values ​​are used to numerically solve the unknown quantity in the mathematical equation to form a mathematical expression with the model posture angle as the independent variable and the initial reading as the dependent variable, so that the initial reading at any posture angle can be quickly generated.

Description

Technical Field

[0001] The invention relates to the field of wind tunnel tests, and in particular to a method for quickly generating initial readings of an internal strain balance, which can be used for wind tunnel steady force measurement tests of models of aircraft, vehicles and the like. Background Art

[0002] The wind tunnel steady force test requires different attitude angles (pitch angle , Sideslip Angle and roll angle ) to conduct a wind test on the model layout under the required attitude angle to obtain six aerodynamic loads (including axial force , Normal force , lateral force , rolling moment , yaw moment and pitch moment ). Among the three attitude angles, only the pitch angle and the sideslip angle are attitude description variables that determine the relative relationship between the model and the wind tunnel airflow direction. Therefore, only wind tunnel tests with different pitch angles and sideslip angles need to be carried out. The internal strain balance is a multi-component force sensor. It is usually installed inside the model and changes the attitude angle with the model. It has the characteristics of small size, fast response, simple design and processing, and easy use. It is widely used in high-speed and low-speed wind tunnel tests. The resistance value of the strain gauge in the balance changes incrementally under the action of aerodynamic loads, and the resistance increment is converted into a voltage increment signal through the measuring circuit, and finally stored in the computer for processing after analog / digital conversion by the data acquisition equipment.

[0003] The purpose of the wind tunnel test is to obtain the aerodynamic loads on the model at different attitudes. However, in the actual blowing process, the forces and moments on the strain balance include two parts: one is the aerodynamic force on the model, and the other is the gravity on the model. In order to deduct the influence of the model gravity on the measurement results, it is necessary to collect data containing only the model gravity as the initial reading before blowing, and subtract the initial reading from the blowing number to obtain the aerodynamic load. The first condition for deducting the initial reading is that the blowing number and the initial reading must be at the same attitude angle: under the same layout, the influence of the model's own weight on the balance signal will not change with the change of the sideslip angle; however, due to the different pitch angles, the forces and moments felt by the balance will change significantly, so it is necessary to collect initial readings at different pitch angles through actual measurement methods.

[0004] In the longitudinal variable pitch angle test, the traditional longitudinal initial reading collection mode is: when the model completes the layout adjustment, it is necessary to collect a complete initial reading point by point according to the pitch angle change law of the blowing number, that is, after the model is adjusted to the first attitude angle, the data collection device is started to obtain the initial reading at the current attitude angle, and then the model is adjusted to the next attitude angle and collected again, and so on, until the initial readings at all attitude angles are collected. The traditional initial reading collection mode is inefficient. For example, the pitch angle change range is , , 91 acquisitions need to be completed, each acquisition takes 3 seconds, and the angle change rate is , it takes at least 363 seconds to collect the initial readings. The time spent on collecting the longitudinal initial readings is almost the same as the time of the wind test, which seriously restricts the efficiency of the wind tunnel test. Summary of the invention

[0005] The purpose of the present invention is to derive the transformation law of each component of the internal strain balance with the model posture angle by establishing a coordinate axis conversion relationship on the basis of the existing technology, introduce a linear transfer relationship to characterize the influence of the balance and data acquisition equipment on the measured value, and finally form a complete mathematical equation for the initial reading; use Newton's iteration method and a small amount of measured values ​​collected to numerically solve the unknown quantities in the mathematical equation, form a mathematical expression with the model posture angle as the independent variable and the initial reading as the dependent variable, and quickly generate the initial reading at any posture angle.

[0006] To achieve the above object, the present invention adopts the following technical solution: Step 1: By establishing the coordinate axis transformation relationship, the transformation law of the six components of the internal strain balance with the model attitude angle is derived to form the mathematical expression of the balance components with respect to the model gravity, which is specifically: S11: Taking the airflow axis system as the reference of the model's gravity and center of gravity, a balance is given, the balance axis system moves synchronously with the airflow axis system, and the attitude angle of the model is determined to be equal to the attitude angle of the balance; Airflow shaft system As the reference of the model's gravity and center of gravity, its vertical axis Parallel to the horizontal plane, with the direction of the start of navigation as positive; its vertical axis Perpendicular to the ground plane, with upwards being positive; its horizontal axis Satisfy the right-hand rule; and remember 、 and The unit vectors of the three coordinate axes are 、 and .

[0007] For a given balance, the balance axis (including the origin position of the balance axis system and axis, Axis and The direction of the axis is determined, and the unit vectors of the three coordinate axes of the balance axis system are 、 and Because the internal balance moves with the model, the balance axis also moves with it. The magnitudes of the components of force and torque measured by the balance are relative to the balance axis. At the same time, the attitude angle of the model is also the attitude angle of the balance. According to the definition, the pitch angle The vertical axis of the balance and The angle between The vertical axis of the balance exist The projection on the ground and the vertical axis The angle between It refers to the plane of symmetry of the balance and the plane containing the vertical axis of the balance The angle between the plumb planes.

[0008] S12: Project the model gravity vector on the balance axis system, transform the airflow axis system to the balance axis system, and obtain the expressions of the three force components of the balance with respect to the model gravity: For a given model, the magnitude and direction of its gravity are fixed. No matter how the model's posture changes, the direction of the model's gravity is always vertically downward. Next, the model gravity vector It can be expressed as: (1) In the formula, is the model weight, which is a scalar; the negative sign indicates the opposite direction.

[0009] Model gravity vector In the balance shaft system In, yes axis, Axis and The projections on the axis directions are 、 and , then: (2) Combining equations (1) and (2) yields: (3) Airflow shafting To balance shaft The conversion relationship is as shown in equation (4): (4) Substituting equation (4) into equation (3), we can obtain: (5) Comparing the left and right sides of equation (5), we can get the mathematical equations of the three force components of the balance with respect to the model gravity: (6) In the formula, , and are the three force components of the balance.

[0010] S13: When the balance moves synchronously with the model, the coordinates of the center of gravity of the model are a constant under the balance axis system. The gravity torque is introduced into the balance axis system, and the expressions of the three torque components of the balance with respect to the model gravity are obtained: The moment of the model's gravity about the reference center of the balance can be expressed as: (7) in, is the radius vector from the reference center of the balance to the point of gravity (i.e., center of gravity). In the balance shaft system The coordinate value of .

[0011] Because the balance moves with the model, the coordinates of the model's center of gravity are in the balance axis system. Therefore, the gravitational moment on the balance axis is Next, it can be expressed as: (8) Substituting equation (8) into equation (6), we can obtain: (9) Finally, we can get the mathematical equations of the three torque components of the balance with respect to the model gravity: (10) In the formula, 、 and are the three torque components of the balance.

[0012] S14: Analyze the effect of model gravity on the balance components at different attitude angles. The attitude angle is usually changed in two ways in a single wind tunnel constant force test: longitudinal variable pitch angle test and lateral variable sideslip angle test. The roll angle always keeps a constant value, and under the same model layout, the analysis of equations (6) and (10) shows that the size of the balance component is independent of the sideslip angle, so: When conducting a lateral variable sideslip angle test, it is sufficient to collect balance data once at any sideslip angle. When carrying out longitudinal variable pitch angle operation, balance data is collected at different pitch angles.

[0013] Step 2: Introduce the influence of the linear transfer system on the initial readings to form a complete mathematical expression of the balance component measurement value with respect to the model gravity: The magnitude of the model gravity needs to be converted into a signal that can be processed by the computer using a balance and a data acquisition device. The balance and the data acquisition device can be regarded as a linear transmission system. After sorting out equations (6) and (10), the initial reading measurement value signal of the six components of the balance can be obtained. for: (11) in, and is the magnification and intercept of the linear transfer system with respect to the six aerodynamic components, Represents the six components of the balance (three force components 、 、 and the three torque components 、 、 ).

[0014] Step 3: Perform an identity transformation on the initial reading measurement value of the balance component to form a trigonometric function expression for the pitch angle. Specifically, perform an identity transformation on equation (11) to obtain: (12) In the formula, 、 、 are the amplitude, bias and initial phase of the trigonometric function respectively. The specific value of is shown in equation (13): , , , , , (13) Step 4: Construct equations with trigonometric expressions and use Newton's iteration method to calculate the numerical solutions of the unknown quantities in the equations. Specifically: When the model has completed the layout adjustment, no matter how the pitch angle changes, the model weight, roll angle, and balance axis system axis, Axis and The axes remain unchanged; When connected to a specific linear system, the amplification factors and intercepts of the six aerodynamic components remain unchanged before and after blowing.

[0015] Therefore, in equation (13) 、 、 do not change with the pitch angle. 、 、 ， Then for formula (12), input the required pitch angle, and the initial reading corresponding to the attitude angle can be quickly obtained: .

[0016] For those with 、 、 There are three unknown equations in total. You can select three different pitch angles to collect three initial readings. 、 、 Construct the system of equations as follows: (14) In the formula, 、 、 、 、 、 It is known that its size is the measured value. Equation (14) can be solved using the Newton iteration method. 、 、 Solve and obtain the numerical solution 、 、 .

[0017] Step 5: After all unknowns are determined, obtain the mathematical expression with the pitch angle as the independent variable. Enter the required pitch angle , then the initial reading corresponding to the attitude angle can be quickly obtained , specifically: .

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: the present invention is applicable to any model layout, and the scene of using an internal strain balance to carry out aerodynamic tests in a wind tunnel. For the longitudinal variable pitch angle test, only three data points at the pitch angle need to be collected, and the initial reading at any pitch angle can be quickly generated. The pitch angle variation range is within 99 seconds. Compared with the traditional initial reading acquisition method which takes 360 seconds, the efficiency is significantly improved; and the initial reading error generated by the present invention (compared with the traditional initial reading acquisition method) meets the advanced index requirements of low-speed wind tunnel force measurement test. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 A process for quickly generating initial readings; Figure 2a For initial reading Rapidly generated results; Figure 2b For initial reading Rapidly generated results; Figure 2c For initial reading Rapidly generated results; Figure 2d For initial reading Rapidly generated results; Figure 2e For initial reading Rapidly generated results; Figure 2f For initial reading Rapidly generated results; Figure 3a are the errors of the three force components of the initial reading; Figure 3b are the errors of the three torque components of the initial reading. DETAILED DESCRIPTION

[0020] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0021] Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0022] The specific process of this embodiment is as follows Figure 1 As shown, specifically: Step 1: Assume the required pitch angle range , the angle interval is , angle points .

[0023] Step 2: Adjust the model pitch angle in sequence. 、 、 Collect initial balance readings 3 times 、 、 .

[0024] Step 3: Construct the system of equations , in this system of equations, 、 、 、 、 、 Known. Using Newton's iteration method, we can get the numerical solution of the equation 、 、 , thus obtaining the mathematical expression with pitch angle as the independent variable .

[0025] Step 4: Enter the required pitch angle in the mathematical expression and calculate ， 。 That is, the initial readings generated at different pitch angles, a total of 46 quickly generated data points.

[0026] Figure 2a to Figure 2fThe results of the quick generation of the longitudinal initial reading are given. The vertical axis unit in the figure is word, which is the physical unit of the initial reading of the balance ( Character ). Figure 3a and Figure 3b The error of the longitudinal initial reading generated quickly is given, that is, the result of the traditional acquisition method is subtracted from the result of the quick generation, and the difference is converted into load and coefficient, and finally the aerodynamic coefficient error is obtained. It can be seen that the maximum aerodynamic coefficient error between the two meets the advanced index requirements of low-speed wind tunnel force test. , Represents the six components of the balance (three force components , , and the three torque components , , For high angle of attack or , big side slide or , currently no accuracy indicators for force measurement test data are specified.

[0027]

[0028] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for quickly generating initial readings for an internal strain balance, characterized in that: The following steps are involved: Step 1: By establishing the coordinate axis transformation relationship, the transformation law of the six components of the internal strain balance with the model attitude angle is derived to form the mathematical expression of the balance components with respect to the model gravity; Step 2: Introduce the influence of the linear transfer system on the initial readings to form a complete mathematical expression of the balance component measurement value with respect to the model gravity; Step 3: Perform identity transformation on the initial reading measurement value of the balance component to form a trigonometric function expression about the pitch angle; Step 4: Construct equations with trigonometric expressions and use Newton's iteration method to calculate the numerical solutions of the unknown quantities in the equations; Step 5: After all unknown quantities are determined, obtain a mathematical expression with the pitch angle as the independent variable. Enter the required pitch angle to quickly obtain the initial reading corresponding to the attitude angle.

2. A method for quickly generating initial readings for an internal strain balance according to claim 1, characterized in that: In the step 1, establishing the coordinate system includes the following steps: S11: Taking the airflow axis system as the reference of the model's gravity and center of gravity, a balance is given, the balance axis system moves synchronously with the airflow axis system, and the attitude angle of the model is determined to be equal to the attitude angle of the balance; S12: Project the model gravity vector on the balance axis system, transform the airflow axis system to the balance axis system, and obtain the expressions of the three force components of the balance with respect to the model gravity: ， S13: When the balance moves synchronously with the model, the coordinates of the center of gravity of the model are a constant under the balance axis system. The gravity torque is introduced into the balance axis system, and the expressions of the three torque components of the balance with respect to the model gravity are obtained as follows: ， S14: Analyze the effect of model gravity on the balance components at different attitude angles. When conducting a lateral variable sideslip angle test, it is sufficient to collect balance data once at any sideslip angle. When carrying out longitudinal variable pitch angle, balance data is collected at different pitch angles; in: , and are the three force components of the balance, , and are the three moment components of the balance, , and They are respectively the model gravity vector in the balance axis system axis, Axis and The projection on the axis direction, is the model weight, is the pitch angle, is the roll angle.

3. A method for quickly generating initial readings for an internal strain balance according to claim 1, characterized in that: In the steps 3 and 4, When the model has completed the layout adjustment, no matter how the pitch angle changes, the model weight, roll angle, and balance axis system axis, Axis and The axes remain unchanged. When connected to the linear system, the magnification and intercept of the six aerodynamic components remain unchanged before and after blowing. The system of equations is constructed using the magnitude, bias, and initial phase of the trigonometric functions of the elevation angle at three different locations: ， in: is the initial reading corresponding to the attitude angle, For three different pitch angles, is the amplitude of the trigonometric function, is the bias of the trigonometric function, is the initial phase of the trigonometric function.

4. A method for quickly generating initial readings for an internal strain balance according to any one of claims 1 to 3, characterized in that: For any pitch angle required by input, the initial number corresponding to the attitude angle is obtained as: ， in: is the initial reading quickly obtained for the attitude angle, The Newton iteration method is used to obtain 、 、 The numerical solution of represents any attitude angle, is a natural number.

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