Aerofoil structure feature-oriented fiber grating load measurement method

Abstract

The present application belongs to the technical field of fiber grating sensing, and particularly relates to a fiber grating load measurement method for airfoil structure characteristics. The fiber grating measurement point is determined on the airfoil profile, the flap load sensitivity, the edgewise load sensitivity, and the torsional load sensitivity of all the fiber grating measurement points on the airfoil profile are measured, the edgewise grating combination point position, the torsional grating combination point position, and the temperature compensation grating combination point position are determined, the fiber grating measurement point positions of m load monitoring profiles are determined, and then the fiber grating string is used to complete the pasting of all the monitoring profile measurement points. The static calibration of the flap, edgewise, and torsional load is completed through hierarchical loading, the load calibration coefficient matrix K of the edgewise, flap, and torsional grating measurement point combination is obtained, in the actual test flight, the measured edgewise, flap, and torsional grating measurement point combination wavelength is first deducted from the static initial value, then the wavelength offset value of the upper and lower temperature compensation gratings is deducted, and then the calibration coefficient matrix K is multiplied to obtain the high-precision flap, edgewise, and torsional load measurement result.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic grating sensing technology, and particularly relates to a fiber optic grating load measurement method for airfoil structure characteristics. Background Technology

[0002] To achieve better aerodynamic characteristics, rotor or wing airfoil structures are typically designed in a teardrop shape. As a key lift mechanism for aircraft, the design and testing of rotor or wing aerodynamic performance, strength, fatigue life, and dynamic characteristics all require load measurements. However, the teardrop airfoil structure leads to cross-coupling of flapping, flaring, and torsional loads on the rotor or wing. Considering the complex motion attitudes of the rotor or wing during actual flight, this coupling is further amplified. Therefore, the biggest challenge in the testing applications of fiber Bragg grating sensors for rotors or wings is the high-precision decoupling of flapping, flaring, and torsional loads tailored to the characteristics of the airfoil structure. The existing patent "A Method for Decoupling and Calibrating Blade Bending Moment Based on Fiber Optic Strain Combined Bridge Circuit" (CN202110158338.X) describes a fiber Bragg grating bridging method for flapping and flaring loads, as well as a method for calibrating the coupling coefficient and load / wavelength coefficient of flapping and flaring loads. The existing patent, "Method for Decoupling Bending Moment in Rotor Load Identification Based on Fiber Bragg Grating Sensor" (CN115165175A), describes a method for combining fiber Bragg gratings with flapping, oscillation, and torsion of helicopter rotor blades, as well as a decoupling calibration method.

[0003] However, the invention "A Method for Decoupling and Calibrating Blade Bending Moment Based on Fiber Optic Strain Combined Bridge" (CN202110158338.X) only briefly describes the calculation method for the coupling coefficient of flapping and flaring strain combinations, without describing the layout of the torsional combination. Furthermore, the decoupling coefficient calculation method in this invention cannot reflect the ratio of the response of the fiber optic grating flaring combination in the flapping direction to the response in the flaring direction under the same unit load. In the invention "A Method for Decoupling Bending Moment in Rotor Load Identification Based on Fiber Optic Grating Sensors" (CN115165175A), the torsional layout is not on the same airfoil section and has a single layout angle; the flaring layout is also single. This will lead to significant differences in the coupling coefficient under different airfoil structural characteristics. In addition, the decoupling coefficient calculation method in this invention only considers the coupling effect between single loads, without considering the multiple coupling effects of flapping, flaring, and torsional loads. Therefore, the final decoupling accuracy of this method is limited. Summary of the Invention

[0004] The technical problem solved by this invention: In order to solve the problems existing in the above-mentioned invention, this invention proposes a flapping, oscillation and torsional load measurement method with low coupling characteristics for the airfoil cross-sectional structural features of rotors or wings, thereby realizing high-precision measurement of blade loads.

[0005] The technical solution of the present invention:

[0006] A method for measuring fiber optic grating loads oriented towards airfoil structural characteristics, the method comprising:

[0007] S1, Determine the bonding layout of the fiber Bragg grating measurement points on the airfoil profile;

[0008] S2, measure the flapping load sensitivity, oscillation load sensitivity, and torsional load sensitivity of all fiber optic grating measurement points on the airfoil profile;

[0009] S3, determine the placement of the oscillating grating assembly points;

[0010] S4, Determine the placement of the twisted grating assembly points;

[0011] S5, Determine the placement of the temperature compensation grating assembly;

[0012] S6. Repeat S1 to S5 to determine the positions of the fiber optic grating measurement points for the m load monitoring profiles, and then use a customized fiber optic grating string to complete the pasting of all monitoring profile measurement points.

[0013] S7, complete the static calibration of swinging, oscillating, and torsional loads by graded loading, and obtain the load calibration coefficient matrix K of the combination of oscillating, swinging, and torsional grating measurement points;

[0014] In actual test flights, the combined wavelength of the waving, swaying, and torsional grating measurement points is first deducted from the static initial value, then the wavelength offset values ​​of the upper and lower temperature compensation gratings are deducted, and then multiplied by the calibration coefficient matrix K to obtain high-precision waving, swaying, and torsional load measurement results.

[0015] Furthermore, S1 specifically refers to:

[0016] Fiber Bragg grating strain sensors with multi-angle floral and parallel layouts are attached to the target airfoil profile, specifically:

[0017] Four fiber Bragg grating strings with a total of N grating measurement points are pasted on the upper and lower surfaces of the target airfoil profile. The layout of the fiber Bragg grating measurement points on the upper and lower surfaces is the same. Channel 1 on the upper surface and channel 3 on the lower surface are multi-angle flower-shaped channels, with the flower center located at 1 / 4 chord length on the upper and lower surfaces. The pasting direction of the grating measurement points ranges from -90° to 75°. The pasting direction of the grating is parallel to the blade spanwise at 0°. The far end of the grating pointing to the leading edge of the airfoil indicates that the pasting angle is positive. The gratings are evenly distributed at intervals of no more than 15°. Channel 2 on the upper surface and channel 4 on the lower surface are parallel layout channels, with the grating pasting direction at 0°.

[0018] Furthermore, full-load static calibration was performed in the swinging, flaring, and torsional directions to obtain the sensitivity coefficients of each measuring point, specifically:

[0019] Based on the structural characteristics of the airfoil profile, the flapping load can be represented by the combined difference of the 0° grating measurement points in the multi-angle pattern at 1 / 4 chord length of the upper and lower surfaces. By adjusting the installation angle at the blade root, the angle at which the wavelength change of the flapping grating combination under the full-load calibration state is less than ±5pm compared to the no-load state is found. That is, the airfoil profile is in a pure flapping calibration attitude, and the leading edge is under tension as a positive flapping load.

[0020] After rotating the blade root mounting angle by 90°, the airfoil profile is in a pure flapping calibration attitude, and the lower surface is subjected to a positive flapping load.

[0021] The load that causes the airfoil profile to produce a pitching moment is a positive torque load;

[0022] Full-load calibrations for single-positive oscillation, single-positive flapping, and single-positive torsion were performed using the methods described above, with each grating measurement point C... h The wavelength change of iN0j divided by the applied bending moment yields the C value at each grating measurement point. h The sensitivity coefficient K of iN0j for oscillation, flapping, and torsional loads ij =[K ij-b K ij-h K ij-n ];C h iN0j represents the j-th grating measurement point of the i-th channel.

[0023] Furthermore, S3 specifically refers to:

[0024] Select 2 to 4 grating measurement points from N gratings to form a oscillating grating combination; the optimal oscillating grating combination logic is to select the grating measurement point combination with the highest oscillation sensitivity from all combinations that satisfy both the waving-oscillation coupling coefficient and the torsional-oscillation coupling coefficient being less than 5%, specifically:

[0025] When two grating measurement points are selected to form a oscillating grating combination, and N grating measurement points are combined using addition and subtraction respectively, the total number of combinations is... There are several combinations, and the xth combination is C. h i′N o j′+C h i″N o j″, the combined oscillation load sensitivity is k x-b =k i′j′-b +k i″j″-b The waving load sensitivity is k x-h =k i′j′-h +k i″j″-h The torsional load sensitivity is k x-n =k i′j′-n +k i″j″-n The wave-sway coupling coefficient c x-h / b =kx-h / k x-b Torsional-sway coupling coefficient c x-n / b =k x-n / k x-b ;

[0026] exist Find all combinations where both the waving-swing coupling coefficient and the torsional-swing coupling coefficient are less than 5%, and then select the combination with the highest swing load sensitivity as the swing grating combination placement location.

[0027] Furthermore, if no combination can be found where both the waving-swaying coupling coefficient and the torsional-swaying coupling coefficient are <5%, the following two schemes shall be adopted:

[0028] Option 1: Increase the grating dot density on the airfoil profile to increase the number of N in the combination;

[0029] Option 2: Select a combination of 3 or 4 grating measurement points to increase the number of available samples.

[0030] Furthermore, S5 specifically refers to:

[0031] Temperature-compensated grating measurement points are added to the upper and lower surfaces of the airfoil profile, specifically as follows:

[0032] Find the minimum sum of the absolute values ​​of flapping, oscillation, and torsional sensitivity at N / 2 grating measurement points on each of the upper and lower surfaces of the airfoil profile. Find the |K| values ​​on the upper and lower surfaces. 上ij-b |+|K 上ij-h |+|K 上ij-n | and | K 下ij-b |+|K 下ij-h |+|K 下ij-n The smallest grating measurement point is used as the attachment position for temperature compensation measurement points;

[0033] The fiber gratings placed at the temperature compensation measurement points need to have an additional capillary layer added to isolate the wavelength changes caused by blade strain.

[0034] Furthermore, S7 completes the static calibration of swinging, oscillation, and torsional loads through graded loading, specifically as follows:

[0035] First, the oscillation load calibration was completed. The blade root mounting angle was rotated to bring the blade into a oscillation attitude with the leading edge under tension. Standard weights were then applied to the 0.7R~0.8R section of the blade to achieve positive oscillation load application. The 5-level oscillation load was recorded as M. b = [100%M] b 80% M b 60% M b 40% M b 20% M b[0], and simultaneously record the wavelength values ​​of the combination of oscillating, waving, and torsional grating measurement points, where the wavelength values ​​measured by the combination of oscillating grating measurement points under different oscillating loads are λ b1 , λ b2 , λ b3 , λ b4 , λ b5 , λ b0 After deducting the set of combined wavelengths of the oscillation under no-load conditions, it can be represented by a 6×1 matrix as Λ b-b =(λ b1 -λ b0 , λ b2 -λ b0 , λ b3 -λ b0 , λ b4 -λ b0 , λ b5 -λ b0 ,0); The set of combined wavelengths Δ for waving measurement points is obtained using the same data processing method. h-b The combined wavelength set Δ of the torsion measuring points n-b This completes the wavelength value matrix Λ of the three measuring points (wagging, swinging, and torsion) under the calibration of a 5-level wagging load. b =(Λ) b-b Λ h-b Λ n-b ), Λ b It is a 6×3 matrix;

[0036] Next, the flapping load calibration was completed. The blade root mounting angle was rotated to bring the blade into a flapping posture with tension on its lower surface. Standard weights were then applied to the same cross-section as the oscillation calibration to achieve positive flapping load. The 5-level flapping load was recorded as M. h = [100%M] h 80% M h 60% M h 40% M h 20% M h [0] Simultaneously, the wavelength values ​​of the combination of oscillation, waving, and torsion grating measurement points are recorded. The wavelength data processing method of the grating measurement point combination is the same as that used in the oscillation calibration steps to obtain the wavelength value matrix Λ of the combination of the three measurement points for oscillation, waving, and torsion under the 5-level waving load calibration. h =(Λ) b-h Λ h-h Λ n-h ), Λ h It is a 6×3 matrix;

[0037] Finally, the torsional load calibration was completed. Weights were applied to the blade airfoil fixture using a pulley mechanism to achieve positive torsional load. The five levels of torsional load were recorded as M. n = [100%M] n80% M n 60% M n 40% M n 20% M n [0], simultaneously record the wavelength values ​​of the combination of oscillation, waving, and torsion grating measurement points; use the same grating measurement point combination wavelength data processing method as the oscillation calibration step to obtain the wavelength value matrix Λ of the combination of the three measurement points for oscillation, waving, and torsion under 5-level torsional load calibration. n =(Λ) b-n Λ h-n Λ n-n ), Λ n It is a 6×3 matrix.

[0038] Furthermore, in S7, the load calibration coefficient matrix K for the combination of oscillation, flapping, and torsional grating measurement points is obtained, specifically as follows:

[0039] The three wavelength matrices under combined oscillation, flapping, and torsional calibrations As the input matrix, the loads of oscillation, flapping, and torsional calibration loading are combined. As the output matrix, where Λ and M are both 18×3 matrices, the load calibration coefficient matrix K of the combination of pendulum, flapping, and torsion grating measurement points is obtained by matrix solving. The Δ×K=M matrix is ​​solved to obtain the load calibration coefficient matrix K of the combination of pendulum, flapping, and torsion grating measurement points, where K is a 3×3 matrix.

[0040] Furthermore, S8 specifically refers to:

[0041] In actual test flights, the combined wavelength of the waving, oscillating, and torsional grating measurement points should first be subtracted from the static initial value, then the wavelength offset of the upper and lower temperature compensation gratings should be subtracted, and then multiplied by the calibration coefficient matrix K to obtain high-precision waving, oscillating, and torsional load measurement results, specifically:

[0042] First, record the initial wavelength values ​​λ of the static swinging, waving, and torsional grating measurement point combinations and the upper and lower surface temperature compensation gratings. t0 =(λ tb0 , λ th0 , λ tn0 , λ tu0 , λ tl0 );

[0043] The airfoil profile was measured during flight tests for yaw, flapping, and torsion. The measurement points included combinations of gratings, and the wavelength variation λ of the upper and lower surface temperature compensation gratings. t =(λ tb , λ th , λ tn , λ tu , λ tl );

[0044] Δλ is obtained by subtracting the static initial wavelength. t =(λ tb -λ tb0 , λ th -λ th0 , λ tn -λ tn0 );

[0045] Subtracting the wavelength drift caused by temperature changes yields the true wavelength change Δλ of the airfoil profile due to aerodynamic loads. If the combination of the oscillating gratings is the sum of the wavelengths measured at the upper and lower surfaces, then the temperature wavelength shift that needs to be subtracted is (λ... tu -λ tu0 )+(λ tl -λ tl0 If the combination of the oscillating gratings is the wavelength of the upper surface measuring point minus the wavelength of the lower surface measuring point, then the temperature wavelength offset that needs to be deducted is (λ). tu -λ tu0 )-(λ tl -λ tl0 If the combination of the oscillating gratings is the sum of the wavelengths at the upper surface measurement points and the wavelengths at the upper surface measurement points, then the temperature wavelength offset that needs to be deducted is 2 × (λ). tu -λ tu0 If the combination of the oscillating gratings is the wavelength of the upper surface measuring point minus the wavelength of the upper surface measuring point, then the temperature wavelength offset that needs to be deducted is 0.

[0046] The load measurement results M of the airfoil profile are obtained using Δλ×K. t =[M bt M ht M nt ].

[0047] This method measures the sensitivity distribution of airfoil profile features using various angled floral and parallel layout schemes. It then finds the optimal combination of flapping, oscillation, and torsion grating measurement points through a full combination method involving addition and subtraction, demonstrating good physical decoupling. Furthermore, this method is highly versatile and applicable to load decoupling and measurement of various airfoil profiles. Using the full wavelength matrix calibrated under oscillation, flapping, and torsion as input and the loaded load matrix as output, the sensitivity coefficient matrix obtained through matrix solving exhibits better quadratic numerical decoupling effectiveness compared to one-to-one mapping of sensitivity coefficient changes, further improving load measurement accuracy. The temperature-compensated grating designed in this method enhances its adaptability to outdoor open-field testing and flight trials. Attached Figure Description

[0048] Figure 1 A schematic diagram of a pulley mechanism loading weights onto an airfoil clamp for a blade.

[0049] Figure 2 This diagram illustrates the combined responses of oscillation and torsion under swing loading. Detailed Implementation

[0050] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] This invention addresses the problem of significant coupling of flapping, flaring, and torsional loads caused by the airfoil structural characteristics of rotors or wings in the prior art. It provides a fiber optic grating load measurement method specific to airfoil structural characteristics. This method obtains the load sensitivity distribution map of the airfoil profile through analysis of the strain response laws of multi-angle flower-shaped patterns and parallel layouts. Furthermore, through full combination decoupling calculations of the fiber optic grating measurement points, a fiber optic grating combination layout scheme with all mutual coupling coefficients below 2% under individual flapping, flaring, and torsional loading conditions is found, thereby achieving high-precision flapping, flaring, and torsional load measurements.

[0052] Specifically,

[0053] Step 1, Layout of fiber optic grating measuring points on the airfoil profile: Fiber optic strain sensors with multi-angle floral and parallel layouts are attached to the target airfoil profile, specifically as follows:

[0054] Four fiber Bragg grating strings, totaling N grating measurement points, are pasted on the upper and lower surfaces of the target airfoil profile. The layout of the fiber Bragg grating measurement points is identical on both the upper and lower surfaces. Channel 1 on the upper surface and channel 3 on the lower surface are multi-angle flower-shaped channels, with the flower center located at 1 / 4 chord length on both the upper and lower surfaces. The pasting direction of the grating measurement points ranges from -90° to 75° (0° is defined as the grating pasting direction parallel to the blade spanwise, and a positive pasting angle is defined as the grating's far end pointing towards the airfoil's leading edge). They are evenly distributed at intervals not exceeding 15°. Channel 2 on the upper surface and channel 4 on the lower surface are parallel layout channels (0° grating pasting direction). 2-4 parallel measurement points are evenly arranged at the airfoil's leading edge, and 4-8 measurement points are evenly arranged at the trailing edge, respectively. The *a* grating measurement points in the series of channels 1 on the upper surface and 3 on the lower surface are defined as C... h 1N01~C h 1N0a and C h 3N01~C h 3N0a, the b grating measurement points connected in series on the upper surface (2 channels) and the lower surface (4 channels) are defined as C respectively. h 2N01~C h 2N0b and C h 4N01~C h 4N0b, where a+b=N / 2.

[0055] Step 2: Sensitivity measurement of all fiber optic grating measurement points under flapping, oscillation, and torsional loads: Full-load static calibration is performed in the oscillation, flapping, and torsional directions respectively to obtain the sensitivity coefficients of each measurement point, specifically:

[0056] Based on the structural characteristics of the airfoil profile, the flapping load can typically be represented by the combined difference of the 0° grating measurement points in the multi-angle pattern at 1 / 4 chord length of the upper and lower surfaces. By adjusting the installation angle at the blade root, the angle at which the wavelength change of the flapping grating combination under full-load oscillation calibration is less than ±5 pm compared to the no-load state can be found. This indicates that the airfoil profile is in a pure oscillation calibration attitude, with the leading edge under tension as a positive oscillation load. Rotating the blade root installation angle by 90° results in the airfoil profile being in a pure flapping calibration attitude, with the lower surface under tension as a positive flapping load. The load that causes the airfoil profile to generate a pitching moment is the positive torque load. Full-load calibrations for single positive oscillation, single positive flapping, and single positive torsion are performed using the above method, using the measurement points C of each grating. h The wavelength change (pm) of iN0j divided by the applied bending moment (N*m) yields the C value at each grating measurement point. h The sensitivity coefficient K of iN0j for oscillation, flapping, and torsional loads ij =[K ij-b K ij-h K ij-n (Unit: pm / N*m)

[0057] Step 3, Selection of grating combination point locations: Select 2-4 points from the N grating measurement points to form a grating combination. The grating measurement point combination method can be sum or difference. The optimal grating combination logic is to select the grating measurement point combination with the highest grating sensitivity from all combinations that satisfy both the waving-swing coupling coefficient and the torsional-swing coupling coefficient being less than 5%. Specifically:

[0058] Taking a combination of two grating measurement points forming a oscillating grating as an example (in practice, it may not be limited to two grating measurement points), the total number of combinations of N grating measurement points using addition and subtraction is... There are several combinations, with the xth combination being C. h i′N o j′+C h i″N o Taking j″ as an example, the combined oscillation load sensitivity is k x-b =ki ′j′-b +k i″j″-b The waving load sensitivity is k x-h =k i′j′-h +k i″j″-h The torsional load sensitivity is k x-n =k i′j′-n +k i″j″-n The wave-sway coupling coefficient c x-h / b=k x-h / k x-b Torsional-sway coupling coefficient c x-n / b =k x-n / k x-b .exist Among the various combinations, we find all combinations where both the waving-swing coupling coefficient and the torsion-swing coupling coefficient are less than 5%. Then, we select the combination with the highest swing load sensitivity among these combinations. The selected swing grating combination has both good low coupling characteristics of waving / swing / torsion and high sensitivity coefficient to meet the load measurement accuracy.

[0059] Furthermore, if no combination can be found where both the waving-swaying coupling coefficient and the torsional-swaying coupling coefficient are less than 5%, the following two solutions can be considered:

[0060] Option 1: Increase the grating dot density on the airfoil profile, i.e., increase... The number of N in the first combination; Option 2, select a combination of 3 or 4 grating measurement points, and the combination method can also be a mixture of addition and subtraction, which will significantly increase the number of samples to choose from.

[0061] Step 4, Selection of Torsional Grating Combination Points: Select 2-4 points from the N grating measurement points to form a torsion grating combination. The grating measurement point combination method can be either summation or difference. The optimal torsion grating combination logic is to select the grating measurement point combination with the highest torsional sensitivity from all combinations that satisfy both the waving-torsional coupling coefficient and the oscillation-torsional coupling coefficient being less than 5%. Specifically:

[0062] Similar to step three, taking a torque grating combination composed of two grating measurement points as an example (in practice, it may not be limited to two grating measurement points), the N grating measurement points are combined using addition and subtraction respectively, resulting in a total of There are several combinations, with the xth combination being C. h i′N o j′+C h i″N o Taking j″ as an example, the combined oscillation load sensitivity is k x-b =k i′j′-b +k i″j″-b The waving load sensitivity is k x-h =k i′j′-h +k i″j″-h The torsional load sensitivity is k x-n =k i′j′-n +k i″j″-n , wave-torsion coupling coefficient c x-h / n =k x-h / k x-n The oscillation-torsional coupling coefficient c x-b / n =k x-b / kx-n .exist Among the various combinations, we search for all combinations where both the waving-torsion coupling coefficient and the oscillation-torsion coupling coefficient are less than 5%. Then, we select the combination with the highest torsional load sensitivity among these combinations. The selected torsional grating combination has both good waving / oscillation / torsion low coupling characteristics and a high torsional sensitivity coefficient to meet the load measurement accuracy.

[0063] Furthermore, if no combination can be found where both the swing-torsion coupling coefficient and the oscillation-torsion coupling coefficient are <5%, the two alternative solutions supplemented in step four can also be referenced:

[0064] Step 5, Selection of Temperature Compensation Grating Assembly Locations: Due to the influence of sunlight exposure on the rotor or wing in the open-air environment, the temperature difference between the upper and lower surfaces of the blades is significant. Therefore, temperature compensation grating measurement points must be added to both the upper and lower surfaces of the airfoil profile. Specifically:

[0065] Find the minimum sum of the absolute values ​​of flapping, oscillation, and torsional sensitivity at N / 2 grating measurement points on each of the upper and lower surfaces of the airfoil profile, i.e., find the minimum value of |K| on the upper and lower surfaces. 上ij-b |+|K 上ij-h |+|K 上ij-n | and | K 下ij-b |+|K 下ij-h |+|K 下ij-n The smallest grating measurement point is used as the location for attaching the temperature compensation measurement point.

[0066] Furthermore, the fiber gratings arranged at the temperature compensation measurement points need to have an additional capillary layer added to isolate the wavelength changes caused by blade strain. It is recommended that the capillary material be metal with an outer diameter not exceeding 0.25 mm.

[0067] Step Six: Repeat steps one through five to select the locations of the fiber Bragg grating measurement points for the m load monitoring profiles of the propeller blades. Then, use a customized fiber Bragg grating string to complete the layout and pasting of all monitoring profile measurement points.

[0068] Step 7: Complete the static calibration of swinging, oscillation, and torsional loads by applying loads in stages, with no fewer than 5 loading stages (excluding no-load). Specifically:

[0069] Taking the Level 5 calibration as an example, the oscillation load calibration is first completed. The blade root installation angle is rotated to place the blade in a oscillation posture with the leading edge under tension. Standard weights are then applied to the blade profile at 0.7R–0.8R to achieve positive oscillation load application. The Level 5 oscillation load is recorded as M. b = [100%M] b 80% M b 60% M b 40% M b20% M b [0], and simultaneously record the wavelength values ​​of the combination of oscillating, waving, and torsional grating measurement points, where the wavelength values ​​measured by the combination of oscillating grating measurement points under different oscillating loads are λ b1 , λ b2 , λ b3 , λ b4 , λ b5 , λ b0 After deducting the set of combined wavelengths of the oscillation under no-load conditions, it can be represented by a 6×1 matrix Λ b-b =(λ b1 -λ b0 , λ b2 -λ b0 , λ b3 -λ b0 , λ b4 -λ b0 , λ b5 -λ b0 The same data processing method can be used to obtain the combined wavelength set Λ of the waving measurement points. k-b Wavelength set Λ of combined torsion measuring points n-b This led to the completion of the wavelength value matrix Λ for the combination of three measuring points—wagging, swinging, and torsion—under a 5-level wagging load calibration. b =(Λ) b-b Λ h-b Λ n-b ), Λ b It is a 6×3 matrix;

[0070] Next, the flapping load calibration was completed. The blade root installation angle was rotated to place the blade in a flapping posture with tension on its lower surface. Standard weights were then applied to the same cross-section as in the oscillation calibration to achieve a positive flapping load. The 5-level flapping load was recorded as M. h = [100%M] h 80% M h 60% M h 40% M h 20% M h [0], simultaneously record the wavelength values ​​of the combination of grating measurement points for oscillation, waving, and torsion. Using the same grating measurement point combination wavelength data processing method as the oscillation calibration procedure, obtain the wavelength value matrix Λ of the three measurement point combinations for oscillation, waving, and torsion under 5-level waving load calibration. h =(Λ) b-h Λ h-h Λ n-h ), Λ h It is a 6×3 matrix;

[0071] Finally, the torsional load calibration was completed. (The process is as follows...) Figure 1The pulley mechanism shown loads weights onto the airfoil clamp to achieve positive torsional load application. The 5th level torsional load is recorded as M. n = [100%M] n 80% M n 60% M n 40% M n 20% M n [0], simultaneously record the wavelength values ​​of the combination of oscillation, waving, and torsion grating measurement points. Using the same grating measurement point combination wavelength data processing method as the oscillation calibration procedure, obtain the wavelength value matrix Λ of the three measurement point combinations for oscillation, waving, and torsion under five levels of torsional load calibration. n =(Λ) b-n Λ h-n Λ n-n ), Λ n It is a 6×3 matrix.

[0072] Step 8: The final calibration result is given by solving a matrix, as follows:

[0073] The three wavelength matrices under combined oscillation, flapping, and torsional calibrations As the input matrix, combine the loads from oscillation, flapping, and torsional calibration loading. The output matrix is ​​Λ and M, both of which are 18×3 matrices. The load calibration coefficient matrix K of the combination of oscillating, flapping, and torsional grating measurement points is obtained by solving the matrix, that is, solving the matrix Δ×K=M. The solved K is a 3×3 matrix.

[0074] Step Nine: In actual test flights, the combined measurement points of the flapping, oscillation, and torsional gratings should first subtract the static initial value, then subtract the wavelength offset of the upper and lower temperature compensation gratings, and multiply by the calibration coefficient matrix K to obtain high-precision measurement results of flapping, oscillation, and torsional loads. Specifically:

[0075] First, record the initial wavelength values ​​λ of the static swinging, waving, and torsional grating measurement point combinations and the upper and lower surface temperature compensation gratings. t0 =(λ tb0 , λ th0 , λ tn0 , λ tu0 , λ tl0 );

[0076] Further measurements were taken of the airfoil profile during flight tests, including yaw, flapping, and torsion. The measurements also included the wavelength variation λ of the upper and lower surface temperature compensation gratings. t =(λ tb , λ th , λ tn , λ tu , λ tl );

[0077] Further subtraction of the static initial wavelength yields Δλ t =(λ tb -λ tb0 , λ tb0 , λ th -λ th0 , λ tn -λ tn0 );

[0078] Further subtracting the wavelength drift caused by temperature changes yields the true wavelength change Δλ of the airfoil profile due to aerodynamic loads. Temperature compensation requires careful consideration of the position and combination of the grating measurement points in the flaring, flapping, and torsional combinations. If the flaring grating combination is (wavelength of the upper surface measurement point + wavelength of the lower surface measurement point), then the temperature wavelength shift to be subtracted is (λ...). tu -λ tu0 )+(λ tl -λ tl0 If the combination of the oscillating gratings is (wavelength of the upper surface measuring point - wavelength of the lower surface measuring point), then the temperature wavelength offset that needs to be deducted is (λ). tu -λ tu0 )-(λ tl -λ tl0 If the combination of the oscillating gratings is (wavelength at the upper surface measurement point + wavelength at the upper surface measurement point), then the temperature wavelength offset that needs to be deducted is 2 × (λ). tu =λ tu0 If the combination of the oscillating gratings is (wavelength of the upper surface measuring point - wavelength of the upper surface measuring point), then the temperature wavelength offset that needs to be deducted is 0.

[0079] Furthermore, the load measurement result M of the airfoil profile can be obtained by using Δλ×K. t =[M bt M ht M nt ].

[0080] like Figure 2 The diagram shows the combined responses of oscillation and torsion under swing loading.

[0081] This method measures the sensitivity distribution of airfoil profile features using various angled floral and parallel layout schemes. It then finds the optimal combination of flapping, oscillation, and torsion grating measurement points through a full combination method involving addition and subtraction, demonstrating good physical decoupling. Furthermore, this method is highly versatile and applicable to load decoupling and measurement of various airfoil profiles. Using the full wavelength matrix calibrated under oscillation, flapping, and torsion as input and the loaded load matrix as output, the sensitivity coefficient matrix obtained through matrix solving exhibits better quadratic numerical decoupling effectiveness compared to one-to-one mapping of sensitivity coefficient changes, further improving load measurement accuracy. The temperature-compensated grating designed in this method enhances its adaptability to outdoor open-field testing and flight trials.

Claims

1. A fiber optic grating load measurement method for airfoil structure characteristics, characterized in that, The method includes: S1, Determine the bonding layout of the fiber Bragg grating measurement points on the airfoil profile; S2, measure the flapping load sensitivity, oscillation load sensitivity, and torsional load sensitivity of all fiber optic grating measurement points on the airfoil profile; S3, determine the placement of the oscillating grating assembly points; S4, Determine the placement of the twisted grating assembly points; S5, Determine the placement of the temperature compensation grating assembly; S6. Repeat S1 to S5 to determine the positions of the fiber optic grating measurement points for the m load monitoring profiles, and then use a customized fiber optic grating string to complete the pasting of all monitoring profile measurement points. S7, complete the static calibration of swinging, oscillating, and torsional loads by graded loading, and obtain the load calibration coefficient matrix K of the combination of oscillating, swinging, and torsional grating measurement points; In actual test flights, the combined wavelength of the waving, swaying, and torsional grating measurement points is first deducted from the static initial value, then the wavelength offset values ​​of the upper and lower temperature compensation gratings are deducted, and then multiplied by the calibration coefficient matrix K to obtain high-precision waving, swaying, and torsional load measurement results.

2. The fiber optic grating load measurement method for airfoil structure features according to claim 1, characterized in that, S1 specifically refers to: Fiber Bragg grating strain sensors with multi-angle floral and parallel layouts are attached to the target airfoil profile, specifically: Four fiber Bragg grating strings with a total of N grating measurement points are pasted on the upper and lower surfaces of the target airfoil profile. The layout of the fiber Bragg grating measurement points on the upper and lower surfaces is the same. Channel 1 on the upper surface and channel 3 on the lower surface are multi-angle flower-shaped channels, with the flower center located at 1 / 4 chord length on the upper and lower surfaces. The pasting direction of the grating measurement points ranges from -90° to 75°. The pasting direction of the grating is parallel to the blade spanwise at 0°. The far end of the grating pointing to the leading edge of the airfoil indicates that the pasting angle is positive. The gratings are evenly distributed at intervals of no more than 15°. Channel 2 on the upper surface and channel 4 on the lower surface are parallel layout channels, with the grating pasting direction at 0°.

3. The fiber optic grating load measurement method for airfoil structure features according to claim 1, characterized in that, Full-load static calibration was performed in the swinging, flaring, and torsional directions to obtain the sensitivity coefficients at each measuring point, as follows: Based on the structural characteristics of the airfoil profile, the flapping load can be represented by the combined difference of the 0° grating measurement points in the multi-angle pattern at 1 / 4 chord length of the upper and lower surfaces. By adjusting the installation angle at the blade root, the angle at which the wavelength change of the flapping grating combination under the full-load calibration state is less than ±5pm compared to the no-load state is found. That is, the airfoil profile is in a pure flapping calibration attitude, and the leading edge is under tension as a positive flapping load. After rotating the blade root mounting angle by 90°, the airfoil profile is in a pure flapping calibration attitude, and the lower surface is subjected to a positive flapping load. The load that causes the airfoil profile to produce a pitching moment is a positive torque load; Full-load calibrations for single-positive oscillation, single-positive flapping, and single-positive torsion were performed using the methods described above, with each grating measurement point C... h The wavelength change of iN0j divided by the applied bending moment yields the C value at each grating measurement point. h Sensitivity coefficients of iN0j for oscillation, flapping, and torsional loads C h iN0j represents the j-th grating measurement point of the i-th channel.

4. The fiber optic grating load measurement method for airfoil structure features according to claim 1, characterized in that, S3 specifically refers to: Select 2 from N grating measurement points Four oscillating gratings are combined; among all combinations that satisfy both the waving-oscillating coupling coefficient and the torsional-oscillating coupling coefficient being less than 5%, the grating measurement point combination with the highest oscillating sensitivity is selected, specifically: When two grating measurement points are selected to form a oscillating grating combination, and N grating measurement points are combined using addition and subtraction respectively, the total number of combinations is... There are several combinations, and the xth combination is... The combined oscillation load sensitivity is The swing load sensitivity is Torsional load sensitivity is , wave-swing coupling coefficient Torsional-sway coupling coefficient ; exist Find all combinations where both the waving-swing coupling coefficient and the torsion-swing coupling coefficient are less than 5%, and then select the combination with the highest swing load sensitivity as the swing grating combination placement position.

5. The fiber optic grating load measurement method for airfoil structure features according to claim 4, characterized in that, If a combination of both the swing-sway coupling coefficient and the torsional-sway coupling coefficient being less than 5% cannot be found, the following two schemes shall be adopted: Option 1: Increase the grating dot density on the airfoil profile to increase the number of N in the combination; Option 2: Select a combination of 3 or 4 grating measurement points to increase the number of available samples.

6. The fiber optic grating load measurement method for airfoil structure features according to claim 4, characterized in that, S5 specifically refers to: Temperature-compensated grating measurement points are added to the upper and lower surfaces of the airfoil profile, specifically as follows: Find the minimum sum of the absolute values ​​of flapping, oscillation, and torsional sensitivity at N / 2 grating measurement points on each of the upper and lower surfaces of the airfoil profile. and The smallest grating measurement point is used as the bonding position for the temperature compensation measurement point; The fiber gratings placed at the temperature compensation measurement points need to have an additional capillary layer added to isolate the wavelength changes caused by blade strain.

7. The fiber optic grating load measurement method for airfoil structure features according to claim 4, characterized in that, S7, the static calibration of swinging, oscillation, and torsional loads is completed by graded loading, specifically as follows: First, the oscillation load calibration was completed. The blade root mounting angle was rotated to bring the blade into an oscillation posture with the leading edge under tension. At a blade angle of 0.7R... A standard weight with a profile of 0.8R was used to apply a positive pendulum load, and the 5th level pendulum load was recorded as follows: Simultaneously, the wavelength values ​​of the combination of oscillating, waving, and torsional grating measurement points were recorded. The wavelength values ​​measured by the oscillating grating measurement point combination under different oscillating loads were as follows: After deducting the set of combined wavelengths of the oscillation under no-load conditions, it can be represented by a 6×1 matrix as follows: The same data processing method was used to obtain the combined wavelength set of the waving measurement points. Wavelength set of combined torsion measurement points This completes the wavelength value matrix of the three measurement points (wagging, swinging, and torsion) under a 5-level wagging load calibration. , It is a 6×3 matrix; Next, the flapping load calibration was completed. The blade root mounting angle was rotated to bring the blade into a flapping posture with tension on its lower surface. Standard weights were then applied to the same cross-section as in the oscillation calibration to achieve a positive flapping load. The five levels of flapping load were recorded as follows: Simultaneously, the wavelength values ​​of the combination of grating measurement points for oscillation, waving, and torsion are recorded. Using the same grating measurement point combination wavelength data processing method as the oscillation calibration procedure, a wavelength value matrix of the three measurement point combinations for oscillation, waving, and torsion under five-level waving load calibration is obtained. , It is a 6×3 matrix; Finally, the torsional load calibration was completed. Weights were added to the blade airfoil fixture via a pulley mechanism to achieve positive torsional load application. The five levels of torsional load were recorded as follows: Simultaneously, the wavelength values ​​of the combined grating measurement points for oscillation, flapping, and torsion are recorded; using the same grating measurement point combination wavelength data processing method as the oscillation calibration procedure, a wavelength value matrix of the three measurement point combinations for oscillation, flapping, and torsion under five levels of torsional load calibration is obtained. , It is a 6×3 matrix.

8. The fiber optic grating load measurement method for airfoil structure features according to claim 4, characterized in that, In S7, the load calibration coefficient matrix K of the combination of oscillation, flapping, and torsion grating measurement points is obtained, specifically as follows: The three wavelength matrices under combined oscillation, flapping, and torsional calibrations As the input matrix, the loads of oscillation, flapping, and torsional calibration loading are combined. As the output matrix, where Both M and K are 18×3 matrices. The load calibration coefficient matrix K for the combination of oscillation, flapping, and torsion grating measurement points is obtained by matrix solving. The matrix is ​​used to obtain the load calibration coefficient matrix K of the combination of pendulum, waving, and torsion grating measurement points. K is a 3×3 matrix.

9. The fiber optic grating load measurement method for airfoil structure features according to claim 4, characterized in that, S8 specifically refers to: In actual test flights, the combined wavelength of the waving, oscillating, and torsional grating measurement points should first be subtracted from the static initial value, then the wavelength offset of the upper and lower temperature compensation gratings should be subtracted, and then multiplied by the calibration coefficient matrix K to obtain high-precision waving, oscillating, and torsional load measurement results, specifically: First, record the initial wavelength values ​​of the static swinging, waving, and torsional grating measurement point combinations, as well as the upper and lower surface temperature compensation gratings. ; The airfoil profile was measured during test flights for yaw, flapping, and torsion. The measurement points included combinations of gratings, and the wavelength variations of the upper and lower surface temperature compensation gratings. ; Subtracting the static initial wavelength yields ; Subtracting the wavelength drift caused by temperature changes yields the true wavelength change of the airfoil profile due to aerodynamic loads. If the combination of the oscillating gratings is the sum of the wavelengths measured at the upper and lower surfaces, then the temperature wavelength shift that needs to be subtracted is... If the combination of the oscillating gratings is the wavelength of the upper surface measurement point minus the wavelength of the lower surface measurement point, then the temperature wavelength offset that needs to be deducted is: If the combination of the oscillating gratings is the sum of the wavelengths at the upper surface measurement points and the wavelengths at the upper surface measurement points, then the temperature wavelength offset that needs to be deducted is: If the combination of the oscillating gratings is the wavelength of the upper surface measuring point minus the wavelength of the upper surface measuring point, then the temperature wavelength offset that needs to be deducted is 0. use Obtain load measurement results for airfoil profiles .

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