Sensor system, airfoil device, aircraft and related methods

Abstract

The present invention relates to a sensor system for an airfoil and related airfoil arrangement, aircraft and method. The sensor system comprises a fiber-optic sensor, a light source, an optical circulator and a signal processing device. The fiber-optic sensor is configured for attachment to the airfoil and comprises a fiber-optic core comprising a first half and a second half divided by a virtual plane extending in an axial direction of the fiber-optic core, in which first and second half a first and a second Bragg grating are respectively inscribed with different grating periods. The light source is connected to a first port of the optical circulator, an upstream side of the fiber-optic sensor is connected to a second port of the optical circulator, and the signal processing device is connected to a third port of the optical circulator. The fiber-optic sensor receives light emitted by the light source and reflects an optical signal associated with the center wavelengths of the first and second Bragg gratings to the signal processing device. The signal processing device calculates a deformation and / or a temperature of the fiber-optic sensor based on the optical signal.

Description

Technical Field

[0001] This invention relates to the field of sensors, and more particularly to sensor systems for detecting the deformation and / or temperature of airfoils, as well as associated airfoil devices, aircraft, methods for manufacturing airfoils, and measurement methods. Background Technology

[0002] The content in this section only provides background information related to this invention and may not constitute prior art.

[0003] For rotatable or movable airfoils, such as blades of aircraft engine fans or propellers, wing slats or flaps, wind turbine blades, and for any other form of fixed airfoil structure, such as for wings, it may be necessary to detect the amount of airfoil deformation, for example, for aerodynamic performance testing or for health monitoring during operation to prevent airfoil overload. The amount of airfoil deformation can be detected by converting it into an optical signal using a fiber Bragg grating (FBG) sensor. For example, at least one FBG, used as a strain sensor, can be attached to the airfoil surface, and the deformation of the grating can be considered equal to the deformation of the airfoil surface. When light passes through the FBG, light near a specific center wavelength is reflected by the grating. The center wavelength of the reflected light is related to the grating period and is shifted by grating strain and temperature. Therefore, the amount of airfoil deformation can be measured by measuring the shift in the center wavelength of the reflected light caused by grating strain. Since the center wavelength shift of the reflected light is related not only to grating strain but also to temperature, it is usually necessary to set up another fiber Bragg grating as a temperature sensor to measure the temperature and compensate for the error in the center wavelength shift of the reflected light caused by temperature. Similarly, when measuring temperature, it is also necessary to compensate for the error in the center wavelength shift of the reflected light caused by grating deformation.

[0004] In conventional designs, the number and location of temperature and strain sensors are often mismatched. For example, multiple strain sensors are typically placed at different locations to measure strain at multiple points, but only one temperature sensor is used to measure temperature. In this case, the temperature measured by the temperature sensor may differ from the temperature at the location of the strain sensor, and the deformation of the temperature sensor may also differ from that of the strain sensor, potentially leading to inaccurate measurements. In particular, for large and / or high-speed airfoils, the temperature at different locations on the airfoil may vary significantly, and some locations (e.g., the tip) may experience substantial deformation, resulting in large measurement errors. If a corresponding temperature sensor is placed at the location of each strain sensor on the airfoil, it increases the difficulty of installing, operating, and maintaining the sensor system. For example, sensor wiring, signal transmission, and signal processing become more challenging, increasing costs and making the sensor system highly complex. Furthermore, two demodulators are typically required to demodulate the signals from the fiber optic cables used as strain sensors and temperature sensors, respectively, further increasing system cost and complexity.

[0005] On the other hand, arranging fiber Bragg grating sensors on the surface of the airfoil alters the geometry of the airfoil's aerodynamic surface, which may have an adverse effect on the airfoil's aerodynamic performance. Summary of the Invention

[0006] One object of the present invention is to improve the accuracy of strain and / or temperature measurements of airfoils. Another object of the present invention is to simplify the structure of the airfoil strain and / or temperature measurement system. A further object of the present invention is to avoid damaging the aerodynamic performance of the airfoil during strain and / or temperature measurements.

[0007] A first aspect of the present invention provides a sensor system for an airfoil. The sensor system includes an optical fiber sensor, a light source, an optical circulator, and a signal processing device. The optical fiber sensor is configured for attachment to the airfoil. The optical fiber sensor includes an optical fiber core, the optical fiber core comprising a first half and a second half divided by a virtual plane extending along the axial direction of the optical fiber core, wherein a first Bragg grating and a second Bragg grating are respectively etched in the first half and the second half, the first Bragg grating and the second Bragg grating having different grating periods from each other. The optical circulator has a first port, a second port, and a third port. The light source is connected to the first port, the upstream side of the optical fiber sensor is connected to the second port, and the signal processing device is connected to the third port. The optical fiber sensor is configured to receive light emitted by the light source and reflect an optical signal associated with the center wavelengths of the first and second Bragg gratings to the signal processing device. The signal processing device is configured to calculate the deformation and / or temperature of the optical fiber sensor based on the optical signal.

[0008] In some implementations, the sensor system may include multiple fiber optic sensors connected in series, wherein all the Bragg gratings in the multiple fiber optic sensors have different grating periods and operating wavelength ranges that do not overlap with each other.

[0009] In some implementations, the fiber optic sensor can be attached to the outer surface of the airfoil.

[0010] In some implementations, the fiber optic sensor can be embedded inside the airfoil.

[0011] In some implementations, the signal processing apparatus may include a single demodulator configured to convert optical signals into electrical signals.

[0012] In some embodiments, the sensor system may further include a data receiving device and a data storage device, the data receiving device being configured to communicate with a signal processing device in a wired or wireless manner to receive data from the signal processing device, and the data storage device being configured to communicate with the data receiving device in a wired or wireless manner to store data.

[0013] In some implementations, the data storage device can be configured as cloud storage.

[0014] In some implementations, the first half and the second half can be symmetrical about the central axis of the fiber core.

[0015] In some embodiments, the fiber optic sensor may also include a fiber cladding surrounding the fiber core, and the fiber core and fiber cladding may be formed of the same material.

[0016] In some embodiments, the fiber optic sensor may also include an outer coating that surrounds the radially outer side of the fiber optic cladding.

[0017] A second aspect of the invention provides a sensor system for an airfoil. The sensor system includes an optical fiber sensor, a light source, an optical circulator, and a signal processing device. The optical fiber sensor is configured for attachment to the airfoil. A pair of Bragg gratings, arranged axially and not overlapping each other in the axial direction, are disposed in the optical fiber sensor. The pair of Bragg gratings have different grating periods. The optical circulator has a first port, a second port, and a third port. The light source is connected to the first port, the upstream side of the optical fiber sensor is connected to the second port, and the signal processing device is connected to the third port. The optical fiber sensor is configured to receive light emitted by the light source and reflect an optical signal associated with the center wavelength of each of the pair of Bragg gratings to the signal processing device. The signal processing device is configured to calculate the deformation and / or temperature of the optical fiber sensor based on the optical signal.

[0018] A third aspect of the invention provides an airfoil device. The airfoil device includes at least one airfoil element and a sensor system according to the first or second aspect described above. An optical fiber sensor of the sensor system is coupled to the airfoil element, and the sensor system is configured to detect the amount of deformation and / or temperature of the airfoil element.

[0019] In some implementations, the airfoil may include at least one of the following: a rotatable blade of a propeller mechanism, a movable wing of an aircraft, a fixed wing, a winglet, or a tail stabilizer.

[0020] In some embodiments, the airfoil device may be configured as a propeller mechanism including at least one rotatable airfoil element, and the signal processing device may be arranged at or near the axis of rotation of the propeller mechanism.

[0021] A fourth aspect of the invention provides an aircraft comprising a sensor system according to the first or second aspect described above, or an airfoil device according to the third aspect described above.

[0022] A fifth aspect of the invention provides a method for manufacturing an airfoil, the method comprising: forming an optical fiber sensor by etching a first Bragg grating and a second Bragg grating in a first half and a second half of an optical fiber, respectively, divided by a virtual plane extending in an axial direction; and sequentially stacking and bonding a plurality of composite material layers to form an airfoil, such that the optical fiber sensor is disposed between two adjacent composite material layers. Alternatively, the optical fiber sensor may be disposed in a cavity formed by the airfoil. This cavity may be machined from the airfoil after its manufacture, or it may be formed during the manufacture of the airfoil.

[0023] In some embodiments, the method may further include: forming a plurality of fiber optic sensors connected in series in the same fiber and arranging the fiber between two adjacent composite material layers.

[0024] A sixth aspect of the present invention provides a method for measuring the deformation of an airfoil, the method comprising: setting an optical fiber sensor at a test location on the airfoil, the optical fiber sensor including an optical fiber core, the optical fiber core including a first half and a second half divided by a virtual plane extending along the axial direction of the optical fiber core, a first Bragg grating and a second Bragg grating respectively etched in the first half and the second half, the first Bragg grating and the second Bragg grating having different grating periods; passing light emitted from a light source through the optical fiber sensor; receiving a first optical signal reflected by the first Bragg grating and a second optical signal reflected by the second Bragg grating; measuring the offset Δλ1 of the center wavelength of the first optical signal relative to a predetermined initial reflected light center wavelength of the first Bragg grating and the offset Δλ2 of the center wavelength of the second optical signal relative to a predetermined initial reflected light center wavelength of the second Bragg grating; calculating a common strain change Δε of the first Bragg grating and the second Bragg grating based on the offset Δλ1 of the center wavelength of the first optical signal and the offset Δλ2 of the center wavelength of the second optical signal; and calculating the deformation ΔL of the airfoil at the test location based on the strain change Δε.

[0025] In some implementations, the strain change Δε and the deformation ΔL can be calculated using the following formulas:

[0026]

[0027] ΔL=Δε*L

[0028] Among them, K ε1 K is the strain coefficient of the first Bragg grating. ε2 K is the strain coefficient of the second Bragg grating. T1 K is the temperature coefficient of the first Bragg grating. T2 Let L be the temperature coefficient of the second Bragg grating, and L be the initial length of the fiber optic sensor when it is not subjected to any external force.

[0029] A seventh aspect of the present invention provides a method for measuring the temperature of an airfoil, the method comprising: setting an optical fiber sensor at a test location on the airfoil, the optical fiber sensor including an optical fiber core, the optical fiber core including a first half and a second half divided by a virtual plane extending along the axial direction of the optical fiber core, a first Bragg grating and a second Bragg grating respectively etched in the first half and the second half, the first Bragg grating and the second Bragg grating having different grating periods; passing light emitted from a light source through the optical fiber sensor; receiving a first optical signal reflected by the first Bragg grating and a second optical signal reflected by the second Bragg grating; measuring an offset Δλ1 of the center wavelength of the first optical signal relative to a predetermined initial reflected light center wavelength of the first Bragg grating and an offset Δλ2 of the center wavelength of the second optical signal relative to a predetermined initial reflected light center wavelength of the second Bragg grating; calculating a common temperature change ΔT of the first Bragg grating and the second Bragg grating based on the offset Δλ1 of the center wavelength of the first optical signal and the offset Δλ2 of the center wavelength of the second optical signal; and calculating the temperature T of the airfoil at the test location based on the temperature change ΔT.

[0030] In some implementations, the temperature change ΔT and the temperature T are calculated using the following formulas:

[0031]

[0032] T = T0 + ΔT

[0033] Among them, K ε1 K is the strain coefficient of the first Bragg grating. ε2 K is the strain coefficient of the second Bragg grating. T1 K is the temperature coefficient of the first Bragg grating. T2 T0 is the temperature coefficient of the second Bragg grating, and T0 is the initial temperature value at the location to be measured.

[0034] This invention provides an optical fiber sensor equipped with a pair of Bragg gratings. Based on the two different reflected light wavelengths reflected by these gratings, the deformation and temperature at the measurement location can be measured simultaneously. This decouples the two correlated variables of deformation and temperature during measurement, eliminating measurement errors and improving accuracy. Furthermore, this invention significantly simplifies the structure of the strain measurement sensor system. In particular, this invention enables the embedding of the optical fiber sensor within an airfoil, allowing for the measurement of airfoil deformation and temperature without affecting the airfoil's aerodynamic performance. Attached Figure Description

[0035] Embodiments of the present invention will be described below by way of example only with reference to the accompanying drawings. In the drawings, the same features or parts are indicated by the same reference numerals, and the drawings are not necessarily drawn to scale. In the drawings:

[0036] Figure 1 A schematic diagram of a sensor system according to an embodiment of the present invention is shown;

[0037] Figure 2 It shows Figure 1 A longitudinal cross-sectional view along the central axis of the first fiber optic sensor in the sensor system.

[0038] Figure 3 A cross-sectional view of the first fiber optic sensor taken along a direction perpendicular to the central axis is shown.

[0039] Figure 4 A plan view of an aircraft equipped with a sensor system according to an embodiment of the present invention is shown;

[0040] Figure 5 It shows Figure 4 A schematic sectional perspective view of the engine of an aircraft.

[0041] Figure 6 The schematic illustration shows the manufacturing process of the fan blades of an aircraft engine according to one embodiment of the present invention;

[0042] Figure 7 It shows that Figure 6 A schematic longitudinal cross-sectional view of an engine manufactured in the manner shown, taken along its central axis.

[0043] Figure 8 A flowchart of a method for manufacturing an airfoil according to one embodiment of the present invention is shown;

[0044] Figure 9a A schematic diagram of an optical fiber sensor subjected to tensile force according to an embodiment of the present invention is shown; and

[0045] Figure 9b A schematic diagram of an optical fiber sensor under compressive force according to an embodiment of the present invention is shown. Detailed Implementation

[0046] The following description is exemplary in nature and is not intended to limit the invention, its application, or its uses. It should be understood that in all these figures, similar reference numerals indicate the same or similar parts and features. The figures are only schematic representations of the concept and principles of embodiments of the invention and do not necessarily show the specific dimensions and scale of each embodiment. Certain parts in specific figures may be exaggerated to illustrate relevant details or structures of embodiments of the invention.

[0047] In the description of embodiments of the present invention, the directional terms related to "upper" and "lower" are used to describe the upper and lower positions of the views shown in the accompanying drawings. In practical applications, the positional relationships of "upper" and "lower" used herein can be defined according to actual circumstances, and these relationships can be reversed.

[0048] Figure 1 A schematic diagram of a sensor system 1 according to an embodiment of the present invention is shown. Figure 1 As shown, the sensor system 1 generally includes at least one fiber optic sensor 10, a light source 20, an optical circulator 30, and a signal processing device 40. Each fiber optic sensor 10 is formed from an optical fiber etched with a pair of Bragg gratings arranged axially and not overlapping each other in the axial direction; its specific structure will be further described below. The sensor system 1 may include multiple fiber optic sensors 10 connected in series to perform measurements simultaneously at multiple different locations. Multiple fiber optic sensors 10 may share the same set of light source 20, optical circulator 30, and signal processing device 40 to simplify the structure of the sensor system 1 and reduce the number of components. In this embodiment, the multiple fiber optic sensors 10 include a first fiber optic sensor 11, a second fiber optic sensor 12, a third fiber optic sensor 13, and a fourth fiber optic sensor 14 connected in series from the upstream side (i.e., the side closer to the light source 20) to the downstream side (i.e., the side farther from the light source 20), each including a pair of Bragg gratings B1 to B8. A plug 50 may be connected downstream of the fourth fiber optic sensor 14 to protect the fiber end. In other embodiments, any suitable number of fiber optic sensors may be used.

[0049] The light source 20 may include a broadband laser source (BBS). In particular, the wavelength range of the light emitted by the light source 20 should cover the operating wavelength range of each Bragg grating of all fiber optic sensors 10, that is, the range in which the center wavelength of the reflected light from each Bragg grating may vary during the measurement.

[0050] An optical circulator 30 is a multi-port optical device with non-reciprocal characteristics, used to sequentially guide light from one port to the next in one direction. That is, when an optical signal is input from any port, the optical signal will be output from the next port with very little loss. In this embodiment, the optical circulator 30 has three ports. An optical signal input from the first port 301 of the optical circulator 30 can only be output from the second port 302, an optical signal input from the second port 302 can only be output from the third port 303, and so on. Figure 1As shown, the light source 20 is connected to the first port 301 of the optical circulator 30 via a first transmission fiber 61. The upstream side of the first optical fiber sensor 11 of the plurality of optical fiber sensors 10 is connected to the second port 302 of the optical circulator 30 via a second transmission fiber 62, and the downstream side of the fourth optical fiber sensor 14 is connected to the plug 50 via a third transmission fiber 63. The signal processing device 40 is connected to the third port 303 of the optical circulator 30 via a fourth transmission fiber 64. The signal processing device 40 may include, for example, a demodulator configured to convert received optical signals (e.g., reflected light wavelength signals from various Bragg gratings) into electrical signals.

[0051] like Figure 1 As shown, the sensor system 1 may further include a data receiving device 70 and a data storage device 80. The data receiving device 70 is configured to communicate with the signal processing device 40 via wired or wireless means to receive data from the signal processing device 40. The data storage device 80 is configured to communicate with the data receiving device 70 via wired or wireless means to store data. Preferably, in this embodiment, the data storage device 80 is configured as cloud storage. In other embodiments, the data storage device 80 may also be configured as any other suitable storage medium, such as volatile memory, non-volatile memory, hard disk, floppy disk, optical disk, magnetic tape, etc. In some embodiments, the data receiving device 70 and the data storage device 80 may be integrated into a single device.

[0052] Each fiber optic sensor in the fiber optic sensor 10 can have a substantially identical structure, so the following description will only take the first fiber optic sensor 11 as an example. Figure 2 It shows Figure 1 A longitudinal cross-sectional view of the first fiber optic sensor 11 along its central axis. Figure 3 A cross-sectional view of the first fiber optic sensor 11 taken along a direction perpendicular to the central axis is shown.

[0053] like Figure 2 and Figure 3As shown, the first fiber optic sensor 11 is constructed from a section of optical fiber. The first fiber optic sensor 11 may include an optical fiber core 111 and an optical fiber cladding 112 surrounding the optical fiber core 111. The optical fiber core 111 and the optical fiber cladding 112 may be formed of the same material, such as silicon dioxide. The optical fiber core 111 can be used to etch gratings and transmit optical signals, while the optical fiber cladding 112 can be used to protect the optical fiber core 111 and prevent the loss of optical signals within the optical fiber core 111. The optical fiber core 111 includes a first half 113 and a second half 114 divided by a virtual plane extending along its axial direction. Preferably, the first half 113 and the second half 114 are symmetrical about the central axis of the optical fiber core 111, so that the first half 113 and the second half 114 can have exactly the same amount of deformation when subjected to stress. In this embodiment, the optical fiber core 111 has a circular cross-section; therefore, the first half 113 and the second half 114 are constructed as two semicircles divided along the diametrical direction of the optical fiber core 111. In other embodiments, optical fibers with non-circular cross-sections, such as polygonal cross-sections, may also be used. A first Bragg grating B1 and a second Bragg grating B2 are etched in the first half 113 and the second half 114, respectively. The first Bragg grating B1 has a first grating period Λ1, and the second Bragg grating B2 has a second grating period Λ2 different from the first grating period Λ1. The axial length of the first Bragg grating B1 may be approximately the same as the axial length of the second Bragg grating B2. An outer coating 115 for improving the strength of the optical fiber sensor may also be provided radially outside the fiber cladding 112. In some embodiments, the fiber cladding 112 and the outer coating 115 may be omitted.

[0054] The remaining fiber optic sensors in the plurality of fiber optic sensors 10 may have a structure substantially the same as the first fiber optic sensor 11, and the plurality of fiber optic sensors 10 may be formed by etching multiple pairs of Bragg gratings at certain intervals on the same fiber. To distinguish the reflected light signals of different Bragg gratings, each Bragg grating may have an operating wavelength range that does not overlap with each other. Table 1 provides an example. Figure 1 The operating wavelength range of the Bragg gratings B1 to B8 and the center wavelength of the reflected light are specified. In different embodiments, a suitable operating wavelength range of the gratings can be selected based on the wavelength range of the light emitted by the light source 20 and the number of Bragg gratings in the fiber optic sensor 10.

[0055] Table 1

[0056] Prague Grating Operating wavelength range (nm) Wavelength of the reflected light center (nm) B1 1520～1526 1523 B2 1526～1532 1529 B3 1532～1538 1535 B4 1538～1544 1541 B5 1544～1550 1547 B6 1550～1556 1553 B7 1556～1562 1559 B8 1562～1568 1565

[0057] The sensor system 1 according to the present invention can be used to measure physical quantities such as deformation, temperature, and load of an airfoil. In the following description, a rotatable blade 212 and a propeller mechanism 211 including at least one blade 212 are used as examples of an airfoil and an airfoil assembly including the airfoil. Specifically, as... Figure 4 As shown, the propeller mechanism 211 in this embodiment is configured as the fan of the engine 210 of the aircraft 2. However, it should be understood that the sensor system 1 can also be applied to any other suitable rotatable or movable airfoil, such as the blades of a helicopter propeller, the blades of a wind turbine or other rotor, the movable part 221 of the wing of the aircraft 2 (e.g., flaps, slats, ailerons, etc.), the tail stabilizer 230 of the aircraft 2, etc. Furthermore, the sensor system 1 can also be applied to any type of fixed airfoil, such as the fixed wing 222, winglets 223, etc., used for the aircraft 2.

[0058] Figure 4 A plan view of the aircraft 2 equipped with sensor system 1 is shown. Figure 5 A schematic cross-sectional perspective view of the engine 210 of the aircraft 2 is shown. The fiber optic sensor 10 of the sensor system 1 can be connected to the fan blades 212 of the engine 210 to detect the deformation, temperature, load, etc., of the blades 212. Since the deformation and temperature at different locations on the blades 212 may vary significantly, multiple fiber optic sensors 10 can be arranged in series, each corresponding to a specific location for measurement. Figure 5 As shown, multiple fiber optic sensors 10 connected in series are arranged along the approximate radial direction of the fan blades 212 to be measured and can rotate with the blades 212. In this embodiment, the fiber optic sensors 10 can be attached to the outer surface of the blades 212 by adhesive or any other suitable method. These fiber optic sensors 10 share the same light source 20, optical circulator 30, signal processing device 40, data receiving device 70, and data storage device 80. The light source 20, optical circulator 30, and signal processing device 40 can, for example, be arranged at or near the fan's axis of rotation to prevent linear components such as optical fibers and wires from becoming entangled when the fan rotates. Figure 4 As shown, the data receiving device 70 and the data storage device 80 can be arranged, for example, on the fuselage of the aircraft 2, or in the cockpit. In this case, the signal processing device 40, the data receiving device 70, and the data storage device 80 can communicate wirelessly.

[0059] Figure 6 and Figure 7 An alternative arrangement of the fiber optic sensor 10 is illustrated schematically. Figure 6 The schematic diagram illustrates the manufacturing process of the fan blades 212 of the engine 210. Figure 7 It shows that Figure 6 A schematic longitudinal cross-sectional view of the engine 210 manufactured in the manner shown, taken along its central axis. Figure 6 As shown, the fan blades 212 of the engine 210 can be formed by sequentially stacking and bonding multiple composite material layers 213 in a desired shape. During the process of manufacturing the blades 212 in this way, multiple fiber optic sensors 10 can be arranged between two adjacent composite material layers 213. Thus, as Figure 7 As shown, the fiber optic sensor 10 is embedded inside the blade 212, so it does not change the geometry of the aerodynamic surface (i.e., the outer surface) of the blade 212 and does not damage the aerodynamic performance of the blade 212.

[0060] Another aspect of the present invention provides a method for manufacturing an airfoil incorporating an optical fiber sensor 10. The following description uses blade 212 as a non-limiting example of an airfoil. Figure 8 A flowchart of the method is shown. Combined with... Figures 1 to 3 and Figure 8 As shown, in step S1 of this method, an optical fiber sensor 10 is formed by etching a first Bragg grating B1 and a second Bragg grating B2 in a first half 113 and a second half 114 of an optical fiber, respectively, divided by a virtual plane extending along its axial direction. The etching of the gratings can be performed, for example, by ultraviolet light or a laser. Combined with... Figures 6 to 8 As shown, in step S2, multiple composite material layers 213 are sequentially stacked and bonded to form an airfoil (i.e., a blade 212), such that an optical fiber sensor 10 is arranged between two adjacent composite material layers 213. The method may also include forming multiple optical fiber sensors 10 connected in series in the same optical fiber and arranging the optical fiber between two adjacent composite material layers 213 used to form the airfoil.

[0061] Alternatively, the fiber optic sensor 10 can be arranged in a cavity formed by the airfoil. This cavity can be machined from the airfoil after it has been manufactured, or it can be formed during the manufacturing process of the airfoil.

[0062] The following is combined with Figure 9a and Figure 9b The specific operation process and principle of measuring the deformation and / or temperature of blade 212 using the sensor system 1 according to the present invention are explained. Figure 9a A schematic diagram is shown when the fiber optic sensor 10 is subjected to a tensile force F1. Figure 9bA schematic diagram of the fiber optic sensor 10 under compressive force F2 is shown. As described above, the fiber optic sensor 10 can be attached to the outer surface of the blade 212 or embedded inside the blade 212. Therefore, the deformation of the fiber optic sensor 10 (i.e., the elongation of the fiber optic sensor 10 under tensile force F1 or the shortening under compressive force F2) ΔL can be considered equal to the deformation of the blade 212 at the location of the fiber optic sensor 10.

[0063] Each fiber optic sensor 10 includes two Bragg gratings with different grating periods. A Bragg grating is a narrowband filter with a periodic microstructure that strongly reflects light only within a very narrow spectrum near a specific center wavelength (also known as the Bragg wavelength), allowing the remaining light waves to continue propagating through the grating. The center wavelength λ of the reflected light satisfies the Bragg equation:

[0064] λ=2nΛ

[0065] Where n is the refractive index and Λ is the grating period (i.e., the distance between two adjacent grooves in the Bragg grating).

[0066] When an optical fiber with a Bragg grating is stretched or compressed, the grating period Λ of the Bragg grating will change accordingly. Furthermore, temperature sensitivity is another characteristic of the Bragg grating. On the one hand, the thermo-optical effect will cause a change in the refractive index n; on the other hand, the thermal expansion of the grating will cause a change in the grating period Λ. Since the grating period Λ and the refractive index n are affected by grating strain and temperature, the center wavelength of the reflected light reflected by the Bragg grating will also change with strain and temperature. Therefore, the change in the corresponding physical quantity at the measurement location can be determined based on the offset of the center wavelength of the reflected light relative to the predetermined initial center wavelength of the reflected light. For example, the center wavelength of the reflected light at 0℃ and with grating strain of 0 can be used as the initial center wavelength of the reflected light. The offset Δλ of the center wavelength of the reflected light relative to the initial center wavelength of the reflected light can be expressed by formula (1):

[0067] Δλ=K ε *Δε+K T *ΔT (1)

[0068] Among them, K ε K is the strain coefficient, Δε is the strain change of the Bragg grating, and K T Let K be the temperature coefficient, and ΔT be the temperature change. ε and K T It can be determined through calibration tests.

[0069] In the actual measurement process, Δλ is calculated by the signal processing device 40 based on the reflected light signal input to it. Therefore, Δε and ΔT can be calculated in reverse according to formula (1).

[0070] Specifically, the light emitted by the light source 20 is transmitted via the first transmission fiber 61, the first port 301 and the second port 302 of the optical circulator 30, and the second transmission fiber 62 to the first fiber optic sensor 11 among the multiple fiber optic sensors 10. At the first fiber optic sensor 11, the first Bragg grating B1 and the second Bragg grating B2 reflect a first optical signal and a second optical signal near their respective center wavelengths, respectively. These two reflected optical signals are output to the signal processing device 40 via the second transmission fiber 62 and the third port 303 of the optical circulator 30. The remaining unreflected light continues to be transmitted downstream through the first fiber optic sensor 11 to the second fiber optic sensor 12, the third fiber optic sensor 13, and the fourth fiber optic sensor 14. When the light passes through each downstream fiber optic sensor, each fiber optic sensor also reflects two optical signals corresponding to the center wavelengths of the two Bragg gratings in that fiber optic sensor, and outputs the optical signals to the signal processing device 40 via the second transmission fiber 62 and the third port 303 of the optical circulator 30. That is, n fiber optic sensors 10 connected in series will output 2n different optical signals to the signal processing device 40. Since each fiber optic sensor 10 operates on the same principle, the following description will only take the first fiber optic sensor 11 as an example.

[0071] Combination Figure 2 , Figure 3 , Figure 9a and Figure 9b As shown, when the first fiber sensor 11 is stretched by tensile force F1 or shortened by compressive force F2, the fiber core 111, which is etched with the first Bragg grating B1 and the second Bragg grating B2, experiences strain. Therefore, the center wavelengths of the reflected light corresponding to the first Bragg grating B1 and the second Bragg grating B2 shift relative to their initial values. Since the first Bragg grating B1 and the second Bragg grating B2 are etched in the two halves of the same fiber segment, i.e., at the same spatial point, the first Bragg grating B1 and the second Bragg grating B2 have essentially the same ambient temperature change ΔT, and essentially the same strain change Δε when the fiber deforms. Therefore, the center wavelength shift Δλ1 of the reflected light from the first Bragg grating B1 and the center wavelength shift Δλ2 of the reflected light from the second Bragg grating B2 can be expressed by formula (2):

[0072]

[0073] Among them, K ε1 K is the strain coefficient of the first Bragg grating B1. ε2 K is the strain coefficient of the second Bragg grating B2. T1 K is the temperature coefficient of the first Bragg grating B1. T2 The temperature coefficient of the second Bragg grating B2. These coefficients can be determined, for example, through calibration tests.

[0074] The strain change Δε and temperature change ΔT can be solved from formula (2), as shown in formulas (3) and (4):

[0075]

[0076] Based on the strain change Δε calculated by formula (3) and the initial length L of the first fiber optic sensor 11 when it is not subjected to any external force, the deformation of the first fiber optic sensor 11 (i.e. the deformation of the blade 212 at the location of the first fiber optic sensor 11) ΔL can be calculated, as shown in formula (5):

[0077] ΔL=Δε*L (5)

[0078] Similarly, based on the temperature change ΔT calculated by formula (4) and the initial temperature T0 at the location to be measured, the current temperature T of the first fiber optic sensor 11 can be determined, as shown in formula (6):

[0079] T = T0 + ΔT (6)

[0080] Similar to the first fiber optic sensor 11, the deformation of the fiber optic sensor, i.e. the deformation of the blade 212 at the location of the fiber optic sensor, can be measured using the light signals reflected by the two Bragg gratings in each of the remaining fiber optic sensors, and the temperature of the fiber optic sensor can be measured simultaneously.

[0081] Furthermore, the load distribution of blade 212 can be calculated based on the strain change Δε.

[0082] As described above, the sensor system 1 according to the present invention can decouple and calculate the two variables, strain change Δε and temperature change ΔT, respectively. This allows for the simultaneous and accurate measurement of the deformation ΔL and temperature T of the fiber optic sensor 10 at the same spatial location, eliminating measurement errors caused by the coupling effect of grating deformation and temperature change leading to a shift in the center wavelength of the reflected light, thus improving measurement accuracy. Furthermore, since two Bragg gratings are integrated in a single optical fiber to simultaneously measure strain and temperature, only a single demodulator is needed to process the optical signal. This reduces the number of components required in the sensor system, simplifies wiring, reduces the size and weight of the sensor system, and optimizes its structure.

[0083] Since the deformation and temperature at different locations on the propeller blades can vary significantly, multiple fiber optic sensors 10 connected in series can be used to simultaneously measure the deformation and temperature at multiple locations. These fiber optic sensors 10 can share other components of the sensor system 1, such as the light source 20, optical circulator 30, signal processing device 40, data receiving device 70, and data storage device 80. This further simplifies the structure of the sensor system.

[0084] Preferably, the fiber optic sensor 10 of the sensor system 1 according to the invention can be disposed inside the blade of the propeller mechanism, thereby allowing the measurement of blade deformation without affecting the aerodynamic performance of the blade. Embedding the fiber optic sensor 10 inside the blade also advantageously protects the fiber optic sensor 10, enhances its durability, and extends its service life.

[0085] Exemplary embodiments of the sensor system, airfoil device, aircraft, and related methods according to the present invention have been described in detail herein. However, it should be understood that the present invention is not limited to the specific embodiments described and shown above. Various modifications and variations can be made to the present invention by those skilled in the art without departing from its spirit and scope. All such modifications and variations fall within the scope of the present invention. Moreover, all components described herein can be replaced by other technically equivalent components. For example, the sensor system according to the present invention can be applied to all types of fixed, rotatable, or movable airfoil components, including but not limited to: fixed wings of aircraft, movable wing components (e.g., flaps or slats), winglets, tail stabilizers, rotors, wind turbine blades, etc. Furthermore, the term "or" in this specification should be understood as meaning "and / or".

Claims

1. A sensor system (1) for an airfoil, comprising an optical fiber sensor (10; 11, 12, 13, 14), a light source (20), an optical circulator (30), and a signal processing device (40), wherein: The fiber optic sensor is configured for attachment to the airfoil, the fiber optic sensor including a fiber core (111), the fiber core (111) including a first half (113) and a second half (114) divided by a virtual plane extending along the axial direction of the fiber core (111), a first Bragg grating (B1) and a second Bragg grating (B2) being etched in the first half (113) and the second half (114), respectively, the first Bragg grating (B1) and the second Bragg grating (B2) having different grating periods from each other; The optical circulator (30) has a first port (301), a second port (302) and a third port (303), wherein the light source (20) is connected to the first port (301), the upstream side of the fiber optic sensor (10; 11, 12, 13, 14) is connected to the second port (302), and the signal processing device (40) is connected to the third port (303); The fiber optic sensors (10; 11, 12, 13, 14) are configured to receive light emitted from the light source (20) and reflect the optical signals associated with the center wavelengths of the first Bragg grating (B1) and the second Bragg grating (B2) to the signal processing device (40); and The signal processing device (40) is configured to calculate the deformation and / or temperature of the fiber optic sensor (10; 11, 12, 13, 14) based on the optical signal.

2. The sensor system (1) for an airfoil according to claim 1, wherein, The sensor system (1) includes a plurality of optical fiber sensors (10; 11, 12, 13, 14) connected in series with each other, wherein all the Bragg gratings in the plurality of optical fiber sensors have different grating periods and have operating wavelength ranges that do not overlap with each other.

3. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The fiber optic sensors (10; 11, 12, 13, 14) are attached to the outer surface of the airfoil.

4. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The fiber optic sensors (10; 11, 12, 13, 14) are embedded inside the airfoil.

5. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The signal processing device (40) includes a single demodulator configured to convert the optical signal into an electrical signal.

6. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The sensor system (1) further includes a data receiving device (70) and a data storage device (80), the data receiving device (70) being configured to communicate with the signal processing device (40) in a wired or wireless manner to receive data from the signal processing device (40), and the data storage device (80) being configured to communicate with the data receiving device (70) in a wired or wireless manner to store data.

7. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The first half (113) and the second half (114) are symmetrical about the central axis of the optical fiber core (111).

8. The sensor system (1) for an airfoil according to claim 1 or 2, wherein, The fiber optic sensor (10) also includes a fiber optic cladding (112) surrounding the fiber optic core (111), the fiber optic core (111) and the fiber optic cladding (112) being formed of the same material.

9. The sensor system (1) for an airfoil according to claim 8, wherein, The fiber optic sensor (10) also includes an outer coating (115) surrounding the radially outer side of the fiber optic cladding (112).

10. A sensor system (1) for an airfoil, comprising an optical fiber sensor (10; 11, 12, 13, 14), a light source (20), an optical circulator (30), and a signal processing device (40), wherein: The fiber optic sensor is configured to be attached to the airfoil, and the fiber optic sensor (10; 11, 12, 13, 14) is provided with a pair of Bragg gratings (B1, B2) arranged in the axial direction and not overlapping each other in the axial direction, the pair of Bragg gratings having different grating periods. The optical circulator (30) has a first port (301), a second port (302) and a third port (303), wherein the light source (20) is connected to the first port (301), the upstream side of the fiber optic sensor (10; 11, 12, 13, 14) is connected to the second port (302), and the signal processing device (40) is connected to the third port (303); The fiber optic sensors (10; 11, 12, 13, 14) are configured to receive light emitted from the light source (20) and reflect the optical signal associated with the center wavelength of each of the pair of Bragg gratings to the signal processing device (40); and The signal processing device (40) is configured to calculate the deformation and / or temperature of the fiber optic sensor (10; 11, 12, 13, 14) based on the optical signal.

11. An airfoil device, the airfoil device comprising at least one airfoil element and a sensor system (1) according to any one of claims 1 to 10, wherein, The fiber optic sensors (10; 11, 12, 13, 14) of the sensor system (1) are attached to the airfoil, and the sensor system (1) is configured to detect the amount of deformation and / or temperature of the airfoil.

12. The airfoil device according to claim 11, wherein, The airfoil includes at least one of the following: a rotatable blade (212) of a propeller mechanism (211), a movable wing (221) of an aircraft, a fixed wing (222), a winglet (223), and a tail stabilizer (230).

13. The airfoil device according to claim 11 or 12, wherein, The airfoil device is configured as a propeller mechanism (211) including at least one rotatable airfoil element, and the signal processing device (40) is arranged at or near the axis of rotation of the propeller mechanism (211).

14. An aircraft (2) comprising a sensor system (1) according to any one of claims 1 to 10 or an airfoil device according to any one of claims 11 to 13.

15. A method for manufacturing an airfoil, the method comprising: A fiber optic sensor (10) is formed by etching a first Bragg grating (B1) and a second Bragg grating (B2) in a first half (113) and a second half (114) of an optical fiber, which are divided by a virtual plane extending along the axial direction, respectively; and Multiple composite material layers (213) are stacked and bonded in sequence to form the airfoil, such that the fiber optic sensor (10) is arranged between two adjacent composite material layers (213).

16. The method of claim 15, further comprising: Multiple optical fiber sensors (10) are formed in series in the same optical fiber and the optical fiber is arranged between two adjacent composite material layers (213).

17. A method for measuring the deformation of an airfoil, the method comprising: An optical fiber sensor (10) is provided at the test position of the airfoil. The optical fiber sensor includes an optical fiber core (111). The optical fiber core (111) includes a first half (113) and a second half (114) divided by a virtual plane extending along the axial direction of the optical fiber core (111). A first Bragg grating (B1) and a second Bragg grating (B2) are respectively etched in the first half (113) and the second half (114). The first Bragg grating (B1) and the second Bragg grating (B2) have different grating periods from each other. The light emitted by the light source (20) passes through the fiber optic sensor (10); Receive a first optical signal reflected by the first Bragg grating (B1) and a second optical signal reflected by the second Bragg grating (B2); The offset Δλ1 of the center wavelength of the first optical signal relative to the predetermined initial reflected light center wavelength of the first Bragg grating (B1) and the offset Δλ2 of the center wavelength of the second optical signal relative to the predetermined initial reflected light center wavelength of the second Bragg grating (B2) are measured. The common strain change Δε of the first Bragg grating (B1) and the second Bragg grating (B2) is calculated based on the offset Δλ1 of the center wavelength of the first optical signal and the offset Δλ2 of the center wavelength of the second optical signal; and The deformation ΔL of the airfoil at the measured position is calculated based on the strain change Δε.

18. The method according to claim 17, wherein, The strain change Δε and the deformation ΔL are calculated by the following formulas: ΔL=Δε*L Among them, K ε1 K is the strain coefficient of the first Bragg grating (B1). ε2 K is the strain coefficient of the second Bragg grating (B2). T1 K is the temperature coefficient of the first Bragg grating (B1). T2 is the temperature coefficient of the second Bragg grating (B2), and L is the initial length of the fiber optic sensor (10) when it is not subjected to any external force.

19. A method for measuring the temperature of an airfoil, the method comprising: An optical fiber sensor (10) is provided at the test position of the airfoil. The optical fiber sensor includes an optical fiber core (111). The optical fiber core (111) includes a first half (113) and a second half (114) divided by a virtual plane extending along the axial direction of the optical fiber core (111). A first Bragg grating (B1) and a second Bragg grating (B2) are respectively etched in the first half (113) and the second half (114). The first Bragg grating (B1) and the second Bragg grating (B2) have different grating periods from each other. The light emitted by the light source (20) passes through the fiber optic sensor (10); Receive a first optical signal reflected by the first Bragg grating (B1) and a second optical signal reflected by the second Bragg grating (B2); The offset Δλ1 of the center wavelength of the first optical signal relative to the predetermined initial reflected light center wavelength of the first Bragg grating (B1) and the offset Δλ2 of the center wavelength of the second optical signal relative to the predetermined initial reflected light center wavelength of the second Bragg grating (B2) are measured. The common temperature change ΔT of the first Bragg grating (B1) and the second Bragg grating (B2) is calculated based on the offset Δλ1 of the center wavelength of the first optical signal and the offset Δλ2 of the center wavelength of the second optical signal; as well as The temperature T of the airfoil at the measured location is calculated based on the temperature change ΔT.

20. The method of claim 17, wherein, The temperature change ΔT and the temperature T are calculated using the following formula: T = T0 + ΔT Among them, K ε1 K is the strain coefficient of the first Bragg grating (B1). ε2 K is the strain coefficient of the second Bragg grating (B2). T1 K is the temperature coefficient of the first Bragg grating (B1). T2 T0 is the temperature coefficient of the second Bragg grating (B2), and T0 is the initial value of the temperature at the location to be measured.

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