A method for detecting strain field of engine turbine disk based on fiber grating sensor string and high-speed optical slip ring

Abstract

This invention belongs to the field of fiber optic sensing and detection technology, and provides a method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring. The scheme includes an engine, fiber optic grating sensors, a high-speed smooth ring, a fiber optic grating signal demodulator, and a host computer. A fiber optic grating sensor with multiple reflection centers of different wavelengths is etched onto the fiber optic string. A specially made multi-point fiber optic grating is arranged at the turbine rotor blades and blade roots. The fiber optic string pigtail is connected to the rotor end pigtail of the fiber optic slip ring. The fiber optic slip ring is routed within the engine shaft. The stator end pigtail of the fiber optic slip ring is connected to the demodulator, which is connected to the host computer via a network cable for analysis. The detection method of this invention can meet the measurement requirements of blades under harsh operating conditions such as confined space, high speed, high temperature, and high pressure. It can effectively and accurately detect the strain field of the engine turbine disk and has advantages such as small size, light weight, strong resistance to electromagnetic interference, and high measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and monitoring, and specifically designs a method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring. Background Technology

[0002] Turbine blades, belonging to the hot-end components of an engine, are one of its core components, playing a crucial role in converting airflow energy into mechanical energy during engine operation. When a turbojet engine operates, air first enters through the intake port. After compression, the air pressure and temperature rise significantly. This high-temperature, high-pressure compressed air enters the combustion chamber, mixes with the injected fuel, and burns. The resulting high-temperature, high-pressure combustion gas flows at high speed towards the turbine section. The turbine stator blades guide the direction of the combustion gas flow and accelerate it. Subsequently, the combustion gas impacts the rotor blades, converting the kinetic and thermal energy of the combustion gas into the rotational mechanical energy of the blades, generating thrust and propelling the aircraft forward. It is evident that turbine blades operate in a harsh environment of high temperature, high pressure, and oil contamination with electromagnetic interference, which can lead to blade profile deformation and reduced strength. If the fatigue limit of the blade is exceeded, damage or even breakage can occur. Therefore, engine blade health monitoring is of paramount importance.

[0003] Strain value is one of the important parameters for engine blade health monitoring. Currently, strain detection methods mainly rely on traditional electrical sensors, such as resistance strain gauges. Resistance strain gauges have advantages such as high sensitivity, good frequency response characteristics, and high reliability, and are widely used in structural health monitoring, material testing, and industrial equipment monitoring. This experiment involves strain field detection of the engine turbine disk. Turbine blades are relatively small, and traditional resistance strain gauges cannot form a sensor network. The numerous signal transmission cables required cannot be laid, and they may even add mass to the engine. Under high-speed rotation, this could lead to strain gauge breakage or even detachment, affecting engine balance and the measurement of the blade's natural frequency. Furthermore, turbojet engines contain various electromagnetic interferences. For example, the ignition system generates strong high-frequency electromagnetic radiation, and the internal processing and communication circuits of the electronic control unit generate electromagnetic noise during operation, creating a complex electromagnetic environment. This electromagnetic environment interferes with traditional resistance strain gauges, resulting in large measurement errors and failing to meet the required testing accuracy.

[0004] In summary, the detection of strain field of turbojet engine turbine blades under harsh environments such as confined space, high speed rotation, high temperature and pressure, and full of electromagnetic interference has important research prospects. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for measuring the strain field of an engine turbine disk.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring, comprising the following steps:

[0008] Step 1: Drill holes at the root of the turbine rotor blades, pass the designed multi-point fiber optic grating through the holes, and use tape to initially fix the fiber optic grating sensor in the designed position.

[0009] Step 2: The high-speed smooth ring is fixed at the shaft center of the centrifugal impeller end of the engine. The optical fiber at the rotor end of the high-speed smooth ring passes through the shaft center and is fused with the fiber optic grating pigtail attached to the turbine rotor. The fused redundant optical fiber is folded on the turbine rotor disk surface near the rear nut.

[0010] Step 3: Apply the prepared high-temperature adhesive evenly to the initially attached and fixed fiber grating, so that the exposed fiber grating is covered. Seal the holes at the root of the turbine rotor blades and the holes at the rear nut of the turbine rotor with high-temperature adhesive.

[0011] Step 4: The high-speed smooth ring stator end pigtail passes through the preset hole on the rectifier cone and connects to the fiber Bragg grating signal demodulator. The fiber Bragg grating signal demodulator is then connected to the host computer.

[0012] Step 5: The assembled engine is started on the test bench. The center wavelength of the fiber optic grating reflected wave drifts. The strain field of the engine turbine disk is finally obtained through processing by the host computer.

[0013] The basic principle of the detection method provided by this invention is as follows: A fiber optic grating sensor is a diffraction grating formed by axially periodically modulating the refractive index of the core of a common silica optical fiber using a specific method. When light waves from a broadband light source propagate through the optical fiber and reach the fiber optic grating, the Bragg wavelength at the interface with different refractive indices is reflected, while light of other wavelengths continues to propagate forward in the optical path. When the phase-matching condition is met, the Bragg wavelength of the optical fiber is [value missing].

[0014] ……….(1)

[0015] in The wavelength reflected by the Bragg grating. The effective refractive index of the optical fiber core. The period is the grating period.

[0016] Differentiating both sides of equation (1), we obtain the wavelength shift at the emission center of the fiber grating. :

[0017] ……….(2)

[0018] Fiber Bragg grating (FBG) sensors are affected by multiple physical quantities, including temperature, strain, and pressure. The influence of any of these quantities will ultimately cause a shift in the center wavelength of the FBG's reflection. When the FBG is only affected by axial strain, the elasto-optic effect of the fiber material will change the effective refractive index of the fiber core. grating period The magnitude will also change. Differentiating and simplifying both sides of equation (2), we get:

[0019] ……….(3)

[0020] in, is the optical elastic coefficient of the optical fiber material.

[0021] The above describes the principle of fiber optic grating strain detection.

[0022] As a preferred embodiment of this solution, in step 1, the turbine disk blade root is provided with a wiring hole to facilitate the routing of fiber optic gratings.

[0023] As a preferred embodiment of this solution, in step 2, the high-speed smooth ring is installed at the engine intake box end, the engine body shaft is provided with a groove, and the high-speed smooth ring shift fork is embedded in the groove. The groove size is designed according to the high-speed smooth ring shift fork so that the high-speed smooth ring can rotate flexibly with the engine.

[0024] As a preferred embodiment of this scheme, the high-speed smooth ring in step 2 includes a stator end, a rotor end, and two sections of tail fiber.

[0025] As a preferred embodiment of this solution, in step 2, the outer periphery of the stator end of the high-speed smooth ring is provided with threaded holes for installation and fixing to the intake box, and the corresponding position of the intake box is also provided with threaded holes for fixed assembly. To prevent the high-speed smooth ring from being fixed by screws when the engine is rotating at high speed, an additional layer of wire is used for safety.

[0026] As a preferred embodiment of this solution, the hexagonal nut behind the turbine disk is a specially made nut, with six prisms and one of the top surfaces polished smooth and in an arc shape. The polished prisms have grooves to facilitate the routing of optical fibers.

[0027] As a preferred embodiment of this solution, the fusion splice points of the fiber optic grating sensor fiber tail and the high-speed smooth ring rotor fiber tail are protected by a thin sleeve, with adhesive injected inside the sleeve to protect the exposed fusion spliced ​​fiber.

[0028] As a preferred option in this scheme, the radius of curvature at the fiber optic splice point is relatively small, and the thin sleeve at the fiber optic splice point is kept tangent to the disk surface.

[0029] Based on the above description of the solution, the beneficial effects of the present invention are as follows:

[0030] 1. The sensor used in this invention is a fiber Bragg grating sensor with multiple points of different center wavelengths etched on a single optical fiber. This facilitates the formation of a sensing grid, enabling the testing of the strain field on the surface of a turbine disk. The spacing between adjacent fiber Bragg grating sensors is designed according to the actual object being measured. A 5mm fiber Bragg grating sensor can achieve a wider range and more accurate strain field measurement. A single optical fiber allows for multi-point detection, significantly reducing wiring and the need for fiber Bragg grating signal demodulation equipment.

[0031] 2. The inherent advantages of fiber optic grating sensors—small size and light weight—make them suitable for detection inside engines. The detection areas inside engines are often confined spaces, making wiring for traditional electrical sensors difficult. The ignition system, cables, solenoid valves, and other components in the engine inevitably generate electromagnetic interference during operation. Traditional electrical sensors are sensitive to electromagnetic interference. The fiber optic grating sensor used in this invention is resistant to electromagnetic interference, enabling non-magnetic measurements and improving measurement accuracy.

[0032] 3. The high-speed smooth ring used in this invention is used to connect the rotating components and the detection equipment, enabling optical signal transmission. The rotor fiber and stator fiber connection ensures stable signal transmission, featuring high precision and low energy consumption. The combination of a fiber optic grating sensor and the high-speed smooth ring to measure the stress field of engine blades solves the problem of difficulty in measuring high-speed rotating components. Attached Figure Description

[0033] Figure 1 This is the overall structure of the engine turbine disk strain field detection method based on fiber optic grating sensor strings and high-speed smooth rings described in this invention.

[0034] Figure 2 This is an enlarged view of the wiring diagram of the fiber grating sensor string in the engine turbine disk strain field detection method based on fiber grating sensor string and high-speed smooth ring described in this invention.

[0035] Figure 3 This is a diagram of the components used to install and fix the high-speed smooth ring in the engine turbine disk strain field detection method based on fiber optic grating sensor strings and high-speed smooth rings described in this invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] The described embodiments are some, but not all, of the embodiments of this invention. Any feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by other equivalent or similarly purposed alternative features unless specifically stated otherwise. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0038] Example:

[0039] To address the technical problem that existing technologies struggle to detect high-speed rotating components, this embodiment tests the surface temperature field of an engine turbine disk. The test material is K417G, with dimensions of 270×557mm, and the turbine rotor blade dimensions are approximately 14×34mm.

[0040] pass Figure 1 As can be seen, this solution includes an engine, a fiber Bragg grating sensor string, a high-speed smoothing ring, a fiber Bragg grating signal demodulator, and a host computer. Multiple fiber Bragg grating sensor measurement points are etched onto a single fiber optic cable. The physical spacing between adjacent measurement points and the reflection center wavelength are designed according to the actual operating conditions of the measured object. The fiber Bragg grating string is routed according to pre-set grooves. The high-speed smoothing ring is fixed to the engine intake casing shaft. The fiber Bragg grating string pigtail is connected to the high-speed smoothing ring rotor end pigtail. The high-speed smoothing ring is led out through pre-drilled holes in the engine intake casing and connected to the demodulator. The demodulator and the host computer are connected via a network cable.

[0041] This invention belongs to the field of fiber optic sensing and monitoring technology, and provides a method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring. The scheme mainly includes the following steps: Drill holes at the root of the turbine rotor blades, pass the designed multi-point fiber optic grating string through the holes, clean the area where the sensor is attached to the turbine disk with sandpaper, and then use tape to initially fix the fiber optic grating sensor in the designed position; fix the high-speed smooth ring to the end of the engine centrifugal impeller, and pass the optical fiber at the rotor end of the high-speed smooth ring through the shaft and fuse it with the fiber optic grating pigtail attached to the turbine rotor. The fused redundant optical fiber is coiled on the turbine rotor disk surface near the rear nut; apply the prepared high-temperature adhesive evenly to the initially attached and fixed fiber optic grating, ensuring that all exposed fiber optic gratings are covered; seal the holes at the root of the turbine rotor blades and the holes at the rear nut of the turbine rotor with high-temperature adhesive; pass the pigtail at the stator end of the high-speed smooth ring through a pre-set hole on the rectifier cone and connect it to the fiber optic grating signal demodulator, which is then connected to a host computer; start the assembled engine on the test bench, causing the center wavelength of the reflected wave from the fiber optic grating to drift. The strain value at any measuring point on the turbine rotor is then obtained through processing by the host computer. Currently, high-speed rotating engines face challenges such as limited testing space, harsh testing environment, and high-speed rotation. This invention overcomes these problems and enables the detection of engine strain fields.

[0042] The optical fiber used in this invention is a specially designed fiber optic grating sensor string. The number of sensors on a single fiber optic string can be adjusted according to the actual measurement point requirements and the demodulation range of the fiber optic grating signal demodulator.

[0043] The principle of strain measurement using fiber Bragg grating (FBG) sensors is as follows: When a broadband light source enters an optical fiber, the narrowband light source that satisfies the reflection center wavelength is reflected back to the FBG signal demodulator and demodulated, while the remaining optical signals continue to propagate forward in the fiber. When the external environment, such as strain, changes, the reflected wavelength of the FBG will drift. The amount of wavelength drift can be used to further calculate the strain change at the corresponding measurement point. By rationally designing the positions of multiple measurement points on the object under test, strain field information can be obtained.

[0044] In practical implementation, attention should be paid to the design of the center wavelength of the fiber optic grating sensor string. The center wavelengths between adjacent measurement points should not be the same. The spacing between adjacent center wavelengths should be designed under the premise of fully considering the maximum value of the center wavelength drift caused by various factors, so as to avoid signal loss caused by the aliasing of adjacent center wavelengths.

[0045] like Figure 2As shown, in this embodiment, the reflection center wavelengths of each fiber grating in the fiber grating sensor string are 1515nm, 1526nm, 1537nm, 1548nm, 1559nm, 1570nm, and 1571nm, respectively. The fiber grating spacing is determined based on the dynamic simulation results, and the spacing is 3.07mm, 2.03mm, 4.71mm, 18.48mm, 4.95mm, and 27.71mm.

[0046] like Figure 3 As shown, this is a component used to install and fix the high-speed smooth ring on the engine rectifier cone shaft in this embodiment. The inner ring is provided with three equally spaced threaded holes (9) for fixing the high-speed smooth ring on the component. The outer ring is provided with three equally spaced threaded holes (8) for fixing the component on the engine body. In the installation process, after the three screws of the outer ring are installed, a fuse is also required to further ensure the firmness and reliability of the high-speed smooth ring.

[0047] In this embodiment, a groove is made on the nut near the turbine shaft center of the centrifugal impeller for installing the shift fork at the end of the high-speed smooth ring rotor. The groove and the shift fork are in clearance fit, and the shift fork can rotate flexibly with the engine. The center of the turbine shaft and the center of the high-speed smooth ring are kept at the same height.

[0048] Because the motor magnet attracts the motor coil during the connection process between the engine intake casing and the main body, which can easily cause the high-speed smooth ring fiber to break, the rectifier cone is removed, and the intake casing is installed on the main body first before the high-speed smooth ring is installed.

[0049] The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring, characterized in that, Includes the following steps: Step 1: Drill holes at the root of the turbine rotor (1) blades, pass the designed multi-point fiber optic grating (2) through the holes, and use tape to initially fix the fiber optic grating (2) sensor at the designed measurement point position. Step 2, Install the high-speed smooth ring (3): The high-speed smooth ring (3) is installed and fixed on the engine intake casing shaft; the engine body shaft has a groove, and the high-speed smooth ring fork is embedded in the groove. The groove size is designed according to the high-speed smooth ring fork. The groove and the fork are in clearance fit so that the high-speed smooth ring can rotate flexibly with the engine; at the same time, the stator end of the high-speed smooth ring (3) is fixed to the engine intake casing shaft position with a special part; the bottom end of the special part, i.e. the small radius end, has an equally spaced threaded hole on the inner side shaft, which is fixed to the threaded hole on the high-speed smooth ring (3). The top end of the special part, i.e. the large radius end, has an equally spaced threaded hole, which is fixed to the threaded hole at the corresponding position of the intake casing. After the screw is fixed, a layer of iron wire is used for safety fixation; the optical fiber at the rotor end of the high-speed smooth ring (3) passes through the shaft and is fused with the fiber optic grating (2) pigtail attached to the turbine rotor (1). The fused redundant optical fiber is coiled on the turbine rotor (1) disk near the rear nut. Step 3: Apply the prepared high-temperature adhesive evenly to the initially pasted and fixed fiber optic grating (2) so that the exposed fiber optic grating (2) is evenly coated and wrapped. The holes at the root of the turbine rotor (1) blades and the holes at the rear nut of the turbine rotor (1) are sealed with high-temperature adhesive. Step 4: The stator end pigtail of the high-speed smooth ring (3) passes through the preset hole on the rectifier cone and connects to the fiber Bragg grating signal demodulator (5). The fiber Bragg grating signal demodulator (5) is connected to the host computer (6). Step 5: The assembled engine is started on the test bench. The center wavelength of the reflected wave of the fiber optic grating (2) drifts. The data is processed by the host computer (6) to finally obtain the strain field of the engine turbine disk.

2. The method according to claim 1, wherein, The fiber optic grating (2) sensor string is subjected to strain calibration measurement before being attached to the surface of the engine blade to ensure the accuracy, reliability and stability of the measurement results of the fiber optic grating (2) sensor in actual application compared with the true value.

3. The method according to claim 1, characterized in that, The center wavelength of the fiber grating (2) is designed according to the fiber grating coupling principle. Wavelength division multiplexing technology is used between the sensors. The change in the reflected center wavelength of the fiber grating (2) sensor at the highest engine speed is designed to be less than the design spacing between the center wavelengths of adjacent fiber grating (2) sensors, so that the center wavelengths of the sensors at each monitoring point will not overlap.

4. The method according to claim 1, characterized in that, The fiber optic grating (2) measuring points and spacing in the engine turbine disk strain field detection are arranged according to the dynamic simulation results.

5. The method according to claim 1, wherein, The fiber grating (2) uses a protective sleeve at the fusion splice between the pigtail and the smooth loop pigtail. The gap between the protective sleeve and the optical fiber is filled with adhesive. The protective sleeve is tangent to the disk and has a small bending radius. The remaining redundant optical fibers are coiled on the disk near the turbine shaft.

6. The method according to claim 1, wherein, The adhesive used for bonding is 7030 high thixotropic ceramic adhesive, which serves to bond and protect the fiber grating (2). The optical fibers exposed on the turbine disk are all uniformly coated and wrapped with the high-temperature adhesive.

7. The method for detecting the strain field of an engine turbine disk based on a fiber optic grating sensor string and a high-speed smooth ring according to claim 1, characterized in that, The turbine disk rear hexagonal nut is a special nut with six prisms and one of the top surfaces polished smooth and in the shape of an arc. The polished prisms have grooves to facilitate the routing of optical fibers.

8. The method according to claim 1, characterized in that, The fiber grating (2) sensor string and the high-speed smooth ring (3) are used together to solve the problem of strain field detection of high-speed rotating components. The fiber grating signal demodulator (5) is connected to the host computer (6) through a network cable. The fiber grating signal measured by the fiber grating signal demodulator (5) is transmitted to the host computer (6). The engine turbine disk strain field information is obtained by the data processing of the host computer (6).

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