Method for correcting blade dynamic load estimation precision

Abstract

The invention provides a blade dynamic load estimation precision correction method. The method comprises the steps of obtaining actually measured rigidity of a blade in the spanwise direction; interpolation is carried out on the actually-measured rigidity, and blade rotation dynamic characteristics are calculated; comparing the rotation dynamic characteristic of the blade with a test result of a real rotation dynamic characteristic test, and correcting the actually measured rigidity to obtain the corrected rigidity; calculating the rigidity of the propeller hub; superposing the propeller hub rigidity and the corrected rigidity to obtain a rigidity parameter of the rotor wing; performing a shimmy damping test to obtain shimmy damping, and obtaining equivalent damping according to the shimmy damping; adding the equivalent damping to a calculation model, and calculating the dynamic load of the blade by using the rigidity parameter of the rotor wing; the calculation input of the calculation model is corrected, and the prediction precision of the blade dynamic load can be effectively improved.

Description

Technical Field

[0001] The present application belongs to the technical field of rotor blade dynamics design, and in particular relates to a method for correcting the accuracy of blade dynamic load estimation. Background Art

[0002] The load calculation of rotor blades is an important input for blade dynamics design. Improving the calculation accuracy of blade dynamic loads can effectively improve the design level of rotor dynamics.

[0003] However, in the current calculation of helicopter rotor blade dynamic loads, the calculation error of blade dynamic loads is large due to the limitation of calculation model accuracy. Summary of the Invention

[0004] Purpose of the invention: This application addresses the problem of large errors in blade structural parameters during load calculation and proposes a method for correcting the accuracy of blade dynamic load estimation.

[0005] The present application provides a method for correcting the blade dynamic load estimation accuracy, the method comprising:

[0006] Obtain the measured stiffness of the blade along the span direction;

[0007] interpolating the measured stiffness to calculate the blade rotational dynamic characteristics;

[0008] Comparing the blade rotational dynamic characteristics with test results of a real rotational dynamic characteristics test, and correcting the measured stiffness to obtain a corrected stiffness;

[0009] Calculate hub stiffness;

[0010] Superimposing the hub stiffness and the corrected stiffness to obtain a stiffness parameter of the rotor;

[0011] Performing a shimmy damping test to obtain shimmy damping, and obtaining equivalent damping based on the shimmy damping;

[0012] The equivalent damping is added to the calculation model, and the dynamic load of the blade is calculated using the stiffness parameters of the rotor.

[0013] Preferably, the measured stiffness includes flapping bending stiffness, shimmy bending stiffness, and torsional stiffness.

[0014] Preferably, interpolating the measured stiffness to calculate the blade rotational dynamic characteristics includes:

[0015] Select some vibration frequency sensitive points as interpolation positions, and use the Lagrange interpolation formula for the specific interpolation;

[0016]

[0017] Where: a1, a2, ... a n ,a n+1 are the blade positions, b1, b2, ... b n ,b n+1 is the interpolated stiffness term;

[0018] After obtaining the measured stiffness of the blade at multiple sections, the rotation frequency of the blade at different speeds can be calculated.

[0019] Preferably, comparing the blade rotational dynamic characteristics with test results of a real rotational dynamic characteristics test, and correcting the measured stiffness to obtain the corrected stiffness, comprises:

[0020] The dynamic similarity criterion is used to compare the calculated values ​​of the blade's rotational dynamic characteristics with the experimental values. By comparing the differences in the modal frequencies of each order, the flapping stiffness, shimmy stiffness, and torsional stiffness of the interval points in the measured section are further corrected to fit more accurate blade structural parameters.

[0021] The blade stiffness of the blade that changes with the spanwise position is obtained by interpolation, and the blade stiffness matrix K is obtained.

[0022]

[0023] Where K1 is the blade stiffness matrix, and K2 is the hub stiffness matrix.

[0024] By solving The natural frequencies of each order of the rotor system are obtained, and then the calculated values ​​of the rotational dynamic characteristics of the blades are compared with the test values ​​of the rotational dynamic characteristics of the blades, and the K1 matrix is ​​fine-tuned to obtain the corrected blade stiffness.

[0025] Preferably, the calculating the hub stiffness includes:

[0026] Finite element software ANSYS is used to calculate the propeller hub parameters. By applying loads to various positions of the hub and obtaining strain, the hub stiffness is calculated. The calculation formula is as follows:

[0027]

[0028] Where dM is the applied bending moment, dθ is the change in rotation angle, and l is the distance from the loading point to the fixed support end.

[0029] Preferably, the superimposing the hub stiffness and the corrected stiffness to obtain the stiffness parameter of the rotor includes:

[0030] The overlapping positions of the hub and blades are superimposed according to the force transmission path of the rotor to obtain the stiffness parameters of the entire rotor.

[0031] Preferably, the step of performing a shimmy damping test to obtain shimmy damping, and obtaining equivalent damping according to the shimmy damping, comprises:

[0032] When installing the test piece for the helicopter rotor hydraulic damper performance test, the test piece length meets the installation length requirements. It is installed on the material testing machine and loaded along the hydraulic damper axis through the fork ear to simulate the boundary conditions of the rotor hydraulic damper.

[0033] For the blade dynamic load calculation towards larger shimmy damping, the shimmy damper correction method is used to carry out the correction work. The damper is mainly used to increase the shimmy damping, especially the first-order shimmy. Therefore, the first-order shimmy is used as the working frequency of the damper. The curve of the hydraulic shimmy damper work changing with displacement and frequency is obtained from the experiment, and the equivalent damping is calculated using energy equivalence.

[0034] Preferably, the adding of the equivalent damping to the calculation model and calculating the dynamic load of the blade using the stiffness parameter of the rotor comprises:

[0035] The rotor stiffness parameters and equivalent damping are used to calculate the blade dynamic load using CAMRAD.

[0036] Beneficial technical effects of this application:

[0037] The influence of various calculation inputs on the dynamic load of the blade is fully considered, and a vibration damping correction method suitable for the rotor load calculation is further designed. The calculation input of the calculation model is corrected, which can effectively improve the prediction accuracy of the blade dynamic load. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the hydraulic damper performance test device provided in an embodiment of the present application;

[0039] Figure 2 This is a comparison diagram before and after correction of dynamic load estimation provided by an embodiment of the present application;

[0040] Figure 3 This is another comparison diagram before and after the dynamic load estimation correction provided by an embodiment of the present application;

[0041] Among them: 1-fork ear; 2-hydraulic damper; 3-material testing machine. DETAILED DESCRIPTION

[0042] See also Figure 1-Figure 3 , a calculation correction method for improving load prediction accuracy proposed in this application includes:

[0043] First, based on the dynamic similarity criterion, the calculated and actual values ​​of the blade's structural parameters were corrected. The blade's stiffness was measured to obtain the measured stiffness of the fixed section. Further corrections to the blade's structural parameters were then made based on the dynamic similarity criterion. To address the large errors in the calculated blade shimmy loads, the measured values ​​of the shimmy damper were used to correct the loads at the main shimmy frequencies, ultimately resulting in a more ideal load calculation result.

[0044] In an embodiment of the present application, a method for calculating and correcting a blade dynamic load is provided, comprising the following steps:

[0045] Step 1: Obtain the measured stiffness of the blade along the span direction;

[0046] Among them, the measured blade stiffness of each section is measured by bonding strain gauges to the blades. The sum of the tensile and compressive strains on the strain gauges is obtained by applying loads in a specific direction, and the measured stiffness of the blade is further calculated. Multiple tests are carried out to obtain the average value, and finally the measured stiffness of the blade is obtained.

[0047] The flapping bending stiffness test data is calculated according to formula (1) at each level of load and the average value of the flapping bending stiffness is finally calculated.

[0048]

[0049] Where: M is the bending moment, M = PL; P is the applied load; L is the distance between the measured section and the loaded section; C is the distance between the strain gauges on the upper and lower surfaces of the same measured section; ε is the sum of the tensile and compressive strains.

[0050] The shimmy bending stiffness test data is calculated according to formula (2) under various load levels, and finally the average shimmy bending stiffness is calculated.

[0051]

[0052] Where: M is the bending moment, M = PL; P is the applied load; L is the distance between the measured section and the loaded section; h is the average distance between the strain gauges at the leading and trailing edges of the same measured section; ε is the sum of the tensile and compressive strains.

[0053] The relative torsion angle between different sections is calculated by averaging Calculate the relative torsional deformation per unit length of the blade Then, the average torsional stiffness between each section is calculated using formula (3).

[0054]

[0055] Where: P is the couple value; L is the distance between the two loads; Δγ is the distance between the measured sections; is the torsion angle between the measured sections.

[0056] Step 2: interpolate the measured stiffness to calculate the blade rotation dynamic characteristics.

[0057] Among them, the number of sections with measured stiffness is often small, so some vibration frequency sensitive points are selected as interpolation positions, and the specific interpolation adopts the Lagrange interpolation formula.

[0058]

[0059] Where: a1, a2, ... a n ,a n+1 are the blade positions, b1, b2, ... b n ,b n+1 is the interpolated stiffness term.

[0060] After obtaining the measured stiffness of the blade at multiple sections, the rotation frequency of the blade at different speeds can be calculated.

[0061] Step 3: Compare the blade rotational dynamic characteristics with the test results of the actual rotational dynamic characteristics test, correct the measured stiffness, and obtain a corrected stiffness.

[0062] Among them, since damping does not affect the rotational dynamic characteristics of the blade, the dynamic similarity criterion can be used to compare the calculated values ​​of the rotational dynamic characteristics of the blade with the experimental values ​​of the rotational dynamic characteristics of the blade. By comparing the differences in the modal frequencies of each order, the flapping stiffness, swing stiffness and torsional stiffness of the interval points in the measured section can be further corrected to fit more accurate blade structural parameters.

[0063] The blade stiffness of the blade that changes with the spanwise position is obtained by interpolation, and the blade stiffness matrix K is obtained.

[0064]

[0065] Where K1 is the blade stiffness matrix, and K2 is the hub stiffness matrix.

[0066] By solving The natural frequencies of each order of the rotor system are obtained, and then the calculated values ​​of the rotational dynamic characteristics of the blades are compared with the test values ​​of the rotational dynamic characteristics of the blades, the K1 matrix is ​​fine-tuned, and the corrected blade stiffness parameters are obtained.

[0067] Step 4: Calculate the hub stiffness, and superimpose the hub stiffness with the corrected stiffness to obtain the stiffness parameters of the rotor.

[0068] Among them, in the second step of stiffness correction, the blade parameters used need to be superimposed with the hub parameters to further reflect the influence of the hub stiffness on the rotor natural frequency. The superposition method is determined according to the force transmission path and connection method between the hub and the blade, and the hub parameters are calculated using the finite element software ANSYS. By applying loads to various positions of the hub and obtaining strain, the hub stiffness is calculated. The calculation formula is as follows.

[0069]

[0070] Where dM is the applied bending moment, dθ is the change in rotation angle, and l is the distance from the loading point to the fixed support end.

[0071] Finally, the overlapping position of the hub and the blade should be superimposed according to the force transmission path of the rotor to obtain the stiffness parameters of the entire rotor.

[0072] Step 5: Perform a shimmy damping test to obtain shimmy damping, and obtain equivalent damping based on the shimmy damping.

[0073] Among them, the length of the helicopter rotor hydraulic damper performance test specimen when installed meets the Figure 1 The medium installation length requirement is met. It is installed on a material testing machine and loaded along the axis of the hydraulic damper through the fork ear to simulate the boundary conditions of the rotor hydraulic damper.

[0074] Current blade dynamic load calculations should be oriented toward greater shimmy damping. This correction is performed using a shimmy damper. The damper primarily increases shimmy damping, particularly first-order shimmy, so the first-order shimmy is used as the damper's operating frequency. The curve of hydraulic shimmy damper power versus displacement and frequency can be obtained experimentally (the area enclosed by the closed loop of the force-displacement curve represents the energy lost per cycle). Energy equivalence is used to calculate the equivalent damping coefficient, ensuring that the energy lost by the damper is equal over one cycle.

[0075] Select a load cycle curve and calculate the work according to the following formula:

[0076]

[0077] Among them, n1 is the starting point of a cycle, n2 is the end point of the cycle, F i is the load at point i, S i is the displacement of point i.

[0078] Using equivalent damping, the power loss in one cycle can be obtained as follows:

[0079]

[0080] Where W is the work, f d is the equivalent damping, ce is the equivalent damping coefficient, is the speed of the damper, a is the dynamic response of the shimmy damper, and ω is the excitation frequency.

[0081] Comparing the two descriptions, the equivalent damping coefficient is

[0082]

[0083] The equivalent oscillation angle damping coefficient Dlag and the equivalent damping coefficient c used in the calculation process e The relationship is as follows, where l is the hydraulic damper arm.

[0084] Dlag=c e ×l 2 ………(10)

[0085] After obtaining the equivalent shimmy angle damping coefficient, further verification is required to determine the correspondence between the shimmy damping dynamic response, the damping coefficient, and the experimental value. The shimmy damping calculation value corresponding to the current calculation state is selected. As the number of dynamic response iterations increases, the response change gradually decreases. When the shimmy damper's dynamic response remains virtually unchanged, the selected equivalent shimmy damping is considered to be consistent with the test.

[0086] Step 6: Add the equivalent shimmy damping to the calculation model and calculate the dynamic load of the blade using the stiffness parameters of the rotor.

[0087] Then, using the corrected rotor stiffness parameters and equivalent shimmy damping, CAMRAD is used to calculate the blade load. That is, the corrected blade stiffness parameters are input into CAMRAD, usually 20 sections are suitable, and the equivalent shimmy damping is input into DlAG to complete the blade load calculation. This will yield more accurate blade load calculation results. The specific calculation results are as follows: Figure 2 and Figure 3 shown.

[0088] In other embodiments of this application, the specific implementation plans are as follows:

[0089] (1) First, the blade stiffness test is carried out to measure the strain of the blade under the corresponding bending moment. Multiple tests are carried out to calculate the average value. The flapping bending stiffness test data is calculated according to formula (1) under various load levels. Finally, the average value of the flapping bending stiffness is calculated.

[0090]

[0091] Where: M is the bending moment, M = PL; P is the applied load; L is the distance between the measured section and the loaded section; C is the distance between the strain gauges on the upper and lower surfaces of the same measured section; ε is the sum of the tensile and compressive strains.

[0092] The shimmy bending stiffness test data is calculated according to formula (2) under various load levels, and finally the average shimmy bending stiffness is calculated.

[0093]

[0094] Where: M is the bending moment, M = PL; P is the applied load; L is the distance between the measured section and the loaded section; h is the average distance between the strain gauges at the leading and trailing edges of the same measured section; ε is the sum of the tensile and compressive strains.

[0095] The relative torsion angle between different sections is calculated by averaging Calculate the relative torsional deformation per unit length of the blade Then, the average torsional stiffness between each section is calculated using formula (3).

[0096]

[0097] Where: P is the couple value; L is the distance between the two loads; Δγ is the distance between the measured sections; is the torsion angle between the measured sections.

[0098] (2) The calculation is then compared with the rotational dynamic characteristics test of the blade using the dynamic similarity criterion, and the differences in the modal frequencies of each order are compared. The flapping stiffness and shimmy stiffness of the interval points in the measured section are further corrected to fit more accurate blade structural parameters. For the flapping and shimmy frequencies, the positions that are more sensitive to the modal frequencies are mainly considered. The interpolation adopts the Lagrange interpolation formula:

[0099]

[0100] Where: a1, a2, ... a n ,a n+1 are the blade positions, b1, b2, ... b n ,b n+1 is the interpolated stiffness term.

[0101] Due to the fact that the number of sections with measured stiffness is often small, some vibration frequency sensitive points are selected as interpolation positions in the first round of interpolation. The natural frequency of the rotor blade is then calculated, and the frequencies of these sensitive points are further modified so that the frequencies and vibration modes gradually approach the experimental values, thereby completing the correction of the blade structural parameters.

[0102] (3) In the second step of stiffness correction, the blade parameters used need to be superimposed with the hub parameters to further reflect the influence of hub stiffness on the rotor natural frequency. The superposition method is determined according to the force transmission path and connection method between the hub and the blade, and the hub parameters are calculated using finite element software.

[0103] (4) The calculation of the current blade dynamic load should be directed towards a larger shimmy damping. The shimmy damper correction method should be used to carry out the correction work. The damper is mainly used to increase the shimmy damping, especially the first-order shimmy. Therefore, the first-order shimmy is used as the operating frequency of the damper. The curve of the hydraulic shimmy damper power versus displacement and frequency can be obtained from the test (the area enclosed by the closed loop of the force-displacement curve is the energy lost in one cycle). The equivalent damping coefficient is calculated using energy equivalence to ensure that the energy lost in one damper cycle is equal.

[0104] Select a load cycle curve and calculate the work according to the following formula:

[0105]

[0106] Among them, n1 is the starting point of a cycle, n2 is the end point of the cycle, F i is the load at point i, S i is the displacement of point i.

[0107] Using equivalent damping, described as The power loss in one cycle can be obtained as follows:

[0108]

[0109] Comparing the two descriptions, the equivalent damping coefficient is

[0110]

[0111] The equivalent oscillation angle damping coefficient Dlag and the equivalent damping coefficient c used in the calculation process e The relationship is as follows, where l is the hydraulic damper arm.

[0112] Dlag=c e ×l 2 ………(8)

[0113] After obtaining the equivalent shimmy angle damping coefficient, further verification is needed to determine the correspondence between the shimmy damping dynamic response, the damping coefficient, and the experimental value. The shimmy damping calculation value corresponding to the current calculation state is selected. As the number of dynamic response iterations increases, the response change gradually decreases. When the shimmy damper's dynamic response remains virtually unchanged, the selected shimmy damping is considered to be consistent with the test.

Claims

1. A method for correcting blade dynamic load estimation accuracy, characterized in that: The method comprises: Obtain the measured stiffness of the blade along the span direction; interpolating the measured stiffness to calculate the blade rotational dynamic characteristics; Comparing the blade rotational dynamic characteristics with test results of a real rotational dynamic characteristics test, and correcting the measured stiffness to obtain a corrected stiffness; Calculate hub stiffness; Superimposing the hub stiffness and the corrected stiffness to obtain a stiffness parameter of the rotor; Performing a shimmy damping test to obtain shimmy damping, and obtaining equivalent damping based on the shimmy damping; The equivalent damping is added to the calculation model, and the dynamic load of the blade is calculated using the stiffness parameters of the rotor.

2. The method according to claim 1, characterized in that The measured stiffness includes flapping bending stiffness, shimmying bending stiffness, and torsional stiffness.

3. The method according to claim 1, characterized in that The interpolating the measured stiffness to calculate the blade rotational dynamic characteristics includes: Select some vibration frequency sensitive points as interpolation positions, and use the Lagrange interpolation formula for the specific interpolation; Where: a1, a2, ... a n ,a n+1 are the blade positions, b1, b2, ... b n ,b n+1 is the interpolated stiffness term; After obtaining the measured stiffness of the blade at multiple sections, the rotation frequency of the blade at different speeds can be calculated.

4. The method according to claim 1, wherein The comparing the blade rotational dynamic characteristics with the test results of the actual rotational dynamic characteristics test, and correcting the measured stiffness to obtain the corrected stiffness, includes: The dynamic similarity criterion is used to compare the calculated values ​​of the blade's rotational dynamic characteristics with the experimental values. By comparing the differences in the modal frequencies of each order, the flapping stiffness, shimmy stiffness, and torsional stiffness of the interval points in the measured section are further corrected to fit more accurate blade structural parameters. The blade stiffness of the blade that changes with the spanwise position is obtained by interpolation, and the blade stiffness matrix K is obtained. Where K1 is the blade stiffness matrix, and K2 is the hub stiffness matrix. By solving The natural frequencies of each order of the rotor system are obtained, and then the calculated values ​​of the rotational dynamic characteristics of the blades are compared with the test values ​​of the rotational dynamic characteristics of the blades, and the K1 matrix is ​​fine-tuned to obtain the corrected blade stiffness.

5. The method according to claim 1, wherein The calculation of the hub stiffness includes: Finite element software ANSYS is used to calculate the propeller hub parameters. By applying loads to various positions of the hub and obtaining strain, the hub stiffness is calculated. The calculation formula is as follows: Where dM is the applied bending moment, dθ is the change in rotation angle, and l is the distance from the loading point to the fixed support end.

6. The method according to claim 5, characterized in that The step of superimposing the hub stiffness and the corrected stiffness to obtain the stiffness parameter of the rotor includes: The overlapping positions of the hub and blades are superimposed according to the force transmission path of the rotor to obtain the stiffness parameters of the entire rotor.

7. The method according to claim 1, characterized in that The shimmy damping test is performed to obtain shimmy damping, and equivalent damping is obtained based on the shimmy damping, including: When installing the test piece for the helicopter rotor hydraulic damper performance test, the test piece length meets the installation length requirements. It is installed on the material testing machine and loaded along the hydraulic damper axis through the fork ear to simulate the boundary conditions of the rotor hydraulic damper. For the blade dynamic load calculation towards larger shimmy damping, the shimmy damper correction method is used to carry out the correction work. The damper is mainly used to increase the shimmy damping, especially the first-order shimmy. Therefore, the first-order shimmy is used as the working frequency of the damper. The curve of the hydraulic shimmy damper work changing with displacement and frequency is obtained from the experiment, and the equivalent damping is calculated using energy equivalence.

8. The method according to claim 1, characterized in that Adding the equivalent damping to the calculation model and calculating the dynamic load of the blade using the stiffness parameter of the rotor includes: The rotor stiffness parameters and equivalent damping are used to calculate the blade dynamic load using CAMRAD.

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