Engine turbine disc strain field detection method based on fiber grating sensor string and high-speed smooth ring

Abstract

The invention belongs to the technical field of optical fiber sensing detection, and provides an engine turbine disc strain field detection method based on a fiber grating sensor string and a high-speed smooth ring. The scheme comprises an engine, a fiber bragg grating sensor, a high-speed smooth ring, a fiber bragg grating signal demodulator and an upper computer. A plurality of fiber grating sensors with different reflection center wavelengths are etched on the fiber string, a specially-made multi-point fiber grating is arranged at a turbine rotor blade and a blade root, a tail fiber of the fiber string is connected with a tail fiber at the rotor end of the fiber slip ring, the fiber of the fiber slip ring is wired in the axis of an engine, and a tail fiber at the stator end of the fiber slip ring is connected to a demodulator. The demodulator is connected with an upper computer through a network cable, and the upper computer carries out analysis. According to the detection method, the measurement requirements of the blade under harsh working conditions such as narrow space, high rotating speed, high temperature and high pressure can be met, the engine turbine disc strain field can be effectively and accurately detected, and the method has the advantages of being small in size, light in weight, high in electromagnetic interference resistance, high in measurement precision and the like.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber sensing monitoring, and specifically designs an engine turbine disk strain field detection method based on an optical fiber grating sensor string and a high-speed smooth ring. Background Art

[0002] Turbine blades belong to the hot end components of the engine and are one of the core components of the engine. They play a key role in converting airflow energy into mechanical energy during the operation of the engine. When the turbojet engine is working, air first enters through the air inlet. After being compressed, the air pressure and temperature rise sharply. The compressed high-temperature and high-pressure air enters the combustion chamber and mixes with the injected fuel and burns. The generated higher-temperature and high-pressure gas flows to the turbine part at a high speed. The turbine stator blades guide the direction of the gas flow and accelerate the flow of gas. After that, the gas impacts the rotor blades, converting the kinetic energy and thermal energy of the gas into mechanical energy for blade rotation, generating thrust and pushing the aircraft forward. It can be seen that the turbine blades work in a harsh working environment of high temperature, high pressure, full of oil and electromagnetic interference, which may cause the blade surface deformation, reduced tolerance strength and other performance. If the fatigue limit of the blade is exceeded, the blade will be damaged or even broken. Therefore, engine blade health detection is of great significance.

[0003] Strain value is one of the important parameters for engine blade health detection. At present, the strain detection method is mainly based on traditional electrical sensors represented by resistance strain gauges. Resistance strain gauges have the advantages of high sensitivity, good frequency response characteristics, and high reliability. They are widely used in structural health monitoring, material testing, industrial equipment monitoring and other fields. The engine turbine disk detection in this experiment is a strain field detection. The turbine blades are small in size. Traditional resistance strain gauges cannot build a sensor network, and the large number of signal transmission cables configured cannot be wired or even give the engine additional mass. Under high-speed rotation conditions, the strain gauges may be damaged or even fall off, affecting the engine balance and blade natural frequency measurement. In addition, there are various electromagnetic interferences inside the turbojet engine. 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. Such a complex electromagnetic environment interferes with the traditional resistance strain gauges, resulting in large measurement errors and not meeting the test accuracy requirements.

[0004] In summary, how to realize the strain field detection of turbojet engine turbine blades in harsh environments such as narrow space, high-speed rotation, high temperature and high pressure, and full of electromagnetic interference has important research prospects. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies in the prior art and provide a method for measuring the strain field of an engine turbine disk.

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

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

[0008] Step 1: Drill a hole at the root of the turbine rotor blade, pass the designed multi-point fiber grating string through the hole, and use tape to preliminarily fix the fiber grating sensor at the designed position;

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

[0010] Step 3, evenly apply the prepared high temperature glue on the initially pasted and fixed optical fiber Bragg grating, so that the exposed optical fiber Bragg grating is coated and wrapped, and the holes at the root of the turbine rotor blades and the holes at the rear nut of the turbine rotor are sealed with high temperature glue;

[0011] Step 4, the pigtail at the stator end of the high-speed smooth ring passes through the preset hole on the rectifier cone and is connected to the fiber grating signal demodulator, and the fiber grating signal demodulator is connected to the host computer;

[0012] Step 5: The assembled engine is started on the test bench, and the central wavelength of the fiber grating reflection 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 the present invention is that the fiber Bragg grating sensor is a diffraction grating formed by axially periodically modulating the core refractive index of ordinary quartz optical fiber by a certain method. When the light wave of the broadband light source propagates through the optical fiber and reaches the fiber Bragg grating, the fiber Bragg wavelength at the interface with different refractive indices is reflected, while the 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:

[0014] λ B =2n eff Λ (1)

[0015] where λ B is the Bragg grating reflection wavelength, n eff is the effective refractive index of the optical fiber core, and Λ is the grating period.

[0016] Differentiate both sides of equation (1) to obtain the fiber Bragg grating emission center wavelength drift Δλ B :

[0017] Δλ=2n eff ΔΛ+2Δn effΛ (2)

[0018] Fiber Bragg grating sensors are affected by multiple physical quantities such as temperature, strain and pressure. The influence of any physical quantity will eventually cause the fiber Bragg grating reflection center wavelength to drift. When the fiber Bragg grating is only affected by the axial strain factor, the elastic-optical effect of the fiber material will change the effective refractive index n of the fiber core. eff , the size of the grating period Λ will also change. Taking the derivative of both sides of equation (2) and simplifying it, we get:

[0019]

[0020] Among them, P e is the elastic-optical coefficient of the optical fiber material.

[0021] The above is the principle of fiber Bragg grating strain detection.

[0022] As a preferred embodiment of this solution, in step 1, a wiring hole is provided at the root of the turbine disk blade to facilitate the fiber grating to pass through and route the wires.

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

[0024] As a preferred embodiment of this solution, the smooth ring in step 2 is a high-speed smooth ring.

[0025] As a preferred embodiment of this solution, the high-speed smooth ring in step 2 includes a stator end, a rotor end and two sections of pigtails.

[0026] As a preferred embodiment of this scheme, in the step 2, the outer periphery of the stator end of the high-speed smooth ring is provided with a threaded hole for installation and fixation on the air intake box, and the corresponding position of the air intake box is also provided with a threaded hole for fixed assembly to prevent the high-speed smooth ring from being screwed and then a layer of insurance is provided with iron wire when the engine rotates at high speed.

[0027] As a preferred embodiment of this solution, the hexagonal nut behind the turbine disk is a special nut, and the six prisms and one of the top surfaces are polished smooth and arc-shaped. The polished prisms are provided with grooves to facilitate the extraction of optical fiber embedding and routing.

[0028] As a preferred embodiment of this solution, the fusion joint between the tail end of the fiber grating sensor fiber and the tail end of the high-speed smooth ring rotor fiber is protected by a thin sleeve, and adhesive is injected into the sleeve to protect the exposed fusion joint of the fiber.

[0029] As a preferred embodiment of this solution, the radius of curvature at the optical fiber fusion point is small, so that the thin sleeve at the optical fiber fusion point is kept tangent to the disk surface.

[0030] According to the description of the above scheme, the beneficial effects of the present invention are as follows:

[0031] 1 The sensor used in the present invention is a fiber Bragg grating sensor that can etch multiple points with different central wavelengths on one optical fiber. It is easy to form a sensing grid and can test the strain field on the surface of the turbine disk. The interval between adjacent fiber Bragg grating sensors is designed according to the actual object to be measured. The fiber Bragg grating sensor with a size of 5mm can achieve more accurate strain field measurement in a larger range. One optical fiber and multi-point detection greatly reduce the wiring and fiber Bragg grating signal demodulation equipment.

[0032] 2 The inherent advantages of fiber Bragg grating sensors, such as small size and light weight, make them suitable for detection inside the engine. The detection parts inside the engine are mostly narrow spaces, which are not easy to wire with traditional electrical sensors. The ignition system, cables, solenoid valves, etc. in the engine will inevitably generate electromagnetic interference during operation, and traditional electrical sensors are sensitive to electromagnetic interference. The fiber Bragg grating sensor used in the present invention is resistant to electromagnetic interference, can achieve non-magnetic measurement, and improve measurement accuracy.

[0033] 3 The high-speed lubricating ring used in the present invention is used to realize the connection between the rotating parts and the detection equipment, realize the optical signal transmission, and the rotor optical fiber and the stator optical fiber docking signal transmission is stable, with the characteristics of high precision and low energy consumption. The combination of fiber grating sensor and high-speed lubricating ring is used to measure the stress field of the engine blade, which solves the problem that high-speed rotating parts are difficult to measure. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the overall composition of the engine turbine disk strain field detection method based on fiber grating sensor string and high-speed smooth ring described in the present invention.

[0035] Figure 2 It is an enlarged view of the fiber grating sensor string wiring of a single turbine rotor blade in the engine turbine disk strain field detection method based on the fiber grating sensor string and the high-speed smooth ring described in the present invention.

[0036] Figure 3 This is a diagram of parts used to install and fix a high-speed smooth ring in the engine turbine disk strain field detection method based on a fiber grating sensor string and a high-speed smooth ring described in the present invention. DETAILED DESCRIPTION

[0037] The technical solution in the example of the present invention will be described in detail below with reference to the accompanying drawings in the example of the present invention.

[0038] The described embodiments are part of the embodiments of the present invention, but not all of them. Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments of the present invention are within the scope of protection of the present invention.

[0039] Example:

[0040] In order to solve the technical problem that the prior art is difficult to detect on high-speed rotating parts, this embodiment tests the surface temperature field of the engine turbine disk. The test material is K417G, the size is 270×557mm, and the turbine rotor blade size is about 14×34mm.

[0041] pass Figure 1 It can be seen that this scheme includes an engine, a fiber grating sensor string, a high-speed smooth ring, a fiber grating signal demodulator and a host computer. Multiple fiber grating sensor measuring points are etched on a string of optical fibers. The physical spacing and reflection center wavelength between adjacent measuring points are designed according to the actual working conditions of the object being measured. The fiber grating string is routed according to the grooves preset in advance. The high-speed smooth ring is fixed at the axis of the engine air intake box. The fiber grating string pigtail is connected to the pigtail at the rotor end of the high-speed smooth ring. The high-speed smooth ring is led out according to the hole reserved at the engine air intake box and connected to the demodulator. The demodulator and the host computer are connected via a network cable.

[0042] The invention belongs to the technical field of optical fiber sensing monitoring, and provides an engine turbine disk strain field detection method based on an optical fiber grating sensor string and a high-speed smooth ring. The scheme mainly includes the following steps: drilling a hole at the root of the turbine rotor blade, passing the designed multi-point fiber grating string through the hole, polishing the turbine disk where the sensor is pasted with sandpaper, and then using tape to preliminarily fix the fiber grating sensor at the designed position; the high-speed smooth ring is fixed to the end of the engine centrifugal impeller, the optical fiber at the rotor end of the high-speed smooth ring passes through the axis, and is fused with the fiber grating pigtail pasted on the turbine rotor, and the fused redundant optical fiber is coiled on the turbine rotor disk near the rear nut; the prepared high-temperature glue is evenly applied to the preliminarily pasted and fixed fiber grating, so that the exposed fiber grating is coated and wrapped, and the hole at the root of the turbine rotor blade and the hole at the rear nut of the turbine rotor are sealed with high-temperature glue; the pigtail at the stator end of the high-speed smooth ring passes through the preset hole on the rectifier cone and is connected to the fiber grating signal demodulator, and the fiber grating signal demodulator is connected to the host computer; the assembled engine is started on the test bench, and the central wavelength of the fiber grating reflection wave drifts, and the strain value of any measuring point on the turbine rotor is finally obtained through the host computer processing. Currently, the detection space of high-speed rotating engines is small, the detection environment is harsh, and the engines rotate at high speeds. The present invention can overcome the existing problems and realize engine strain field detection.

[0043] The optical fiber used in the present invention is a specially made fiber Bragg grating sensor string, and the number of sensors on a string of optical fibers can be adjusted and designed according to the actual measurement point requirements and the demodulation range of the fiber Bragg grating signal demodulator.

[0044] The principle of strain measurement by fiber Bragg grating sensor is that when a broadband light source enters the optical fiber, a narrowband light source that meets the reflection center wavelength is reflected back to the fiber Bragg grating signal demodulator and demodulated, and the remaining light signal continues to propagate forward in the optical fiber. When the external environment such as strain changes, the fiber Bragg grating reflection wavelength will drift. The wavelength drift can be further used to calculate the strain change at the corresponding measuring point. The position of multiple measuring points of the measured object can be reasonably designed to measure the strain field information.

[0045] During specific implementation, attention should be paid to the design of the center wavelength of the fiber grating sensor string. The center wavelengths of adjacent measuring points should not be the same. The adjacent center wavelength interval should be designed under the premise of fully considering the maximum value of the center wavelength drift change caused by various factors to avoid signal loss caused by aliasing of adjacent center wavelengths.

[0046] like Figure 2As shown, the reflection center wavelengths of each fiber Bragg grating of the fiber Bragg grating sensor string of this embodiment are 1515nm, 1526nm, 1537nm, 1548nm, 1559nm, 1570nm, and 1571nm respectively. The fiber Bragg grating spacing is arranged according to the dynamic simulation results, and the arrangement spacing is 3.07mm, 2.03mm, 4.71mm, 18.48mm, 4.95mm, and 27.71mm.

[0045] like Figure 3 As shown in the figure, it is a component used to install and fix the high-speed smooth ring at the axis of the engine fairing cone 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, and 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 installing the three screws of the outer ring, it is necessary to install a fuse to further ensure the firmness and reliability of the high-speed smooth ring.

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

[0048] Since the motor magnet attracts the motor coil during the connection between the engine air intake case and the body, which can easily cause the high-speed smooth ring optical fiber to break, the rectifier cone is removed, and the air intake case is first installed on the body and then the high-speed smooth ring is installed.

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

Claims

1. A method for detecting strain field of engine turbine disk based on fiber grating sensor string and high-speed smooth ring, characterized in that: The following steps are involved: Step 1, drilling a hole at the root of a turbine rotor (1) blade, passing the designed multi-point fiber Bragg grating (2) string through the hole, and using tape to preliminarily fix the fiber Bragg grating (2) sensor at the designed measuring point position; Step 2, the high-speed smooth ring (3) is fixed at the axis of the end of the engine centrifugal impeller (4), the optical fiber at the rotor end of the high-speed smooth ring (3) passes through the axis and is fused with the fiber optic grating (2) pigtail attached to the turbine rotor (1), and the redundant optical fiber is fused and coiled on the disk surface of the turbine rotor (1) near the rear nut; Step 3, evenly apply the prepared high temperature glue on the initially pasted and fixed optical fiber Bragg grating (2), so that the exposed optical fiber Bragg grating (2) is evenly coated and wrapped, and the holes at the root of the blades of the turbine rotor (1) and the holes at the rear nut of the turbine rotor (1) are sealed with the high temperature glue; Step 4, the pigtail at the stator end of the high-speed smooth ring (3) passes through the preset hole on the rectifying cone and is connected to the fiber grating signal demodulator (5), and the fiber grating signal demodulator (5) is connected to the host computer (6); Step 5, the assembled engine is started on the test bench, the central wavelength of the reflected wave of the fiber grating (2) drifts, and the engine turbine disk strain field is finally obtained by processing the data through the host computer (6).

2. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The fiber optic Bragg grating (2) sensor string is subjected to strain calibration measurement before being attached to the engine blade surface, thereby ensuring the accuracy, reliability and stability between the measurement result of the fiber optic Bragg grating (2) sensor in actual application and the true value.

3. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The central wavelength of the fiber Bragg grating (2) is designed according to the fiber Bragg grating coupling principle, and wavelength division multiplexing technology is used between the sensors. The change in the central wavelength of the fiber Bragg grating (2) sensor reflection at the highest engine speed is designed to be smaller than the central wavelength spacing of adjacent fiber Bragg grating (2) sensors, so that the central wavelengths of the sensors at each monitored point will not overlap.

4. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The measuring points and spacing of the fiber grating (2) in the engine turbine disk strain field detection are arranged according to the dynamics simulation results.

5. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: A protective sleeve is used at the fusion joint between the fiber grating (2) string tail fiber and the fiber slip ring tail fiber, and 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 close to the turbine shaft.

6. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The high temperature adhesive is a 7030 high thixotropic ceramic adhesive, which can play a good role in bonding under conditions such as fire resistance and heat shock resistance, and plays a role in bonding and protecting the optical fiber grating (2). The optical fibers exposed on the turbine disk are evenly coated with high temperature adhesive.

7. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The hexagonal nut behind the turbine disk is a special nut, and the six prisms and one of the top surfaces are polished smooth and arc-shaped. The polished prism is provided with a groove to facilitate the extraction of the optical fiber and embedding and routing.

8. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The optical fiber slip ring (3) is a high-speed optical fiber slip ring, which is installed and fixed on the axis of the engine air intake box. The axis of the engine body is provided with a groove, and the high-speed optical fiber slip ring fork is embedded in the groove. The size of the groove is designed according to the high-speed optical fiber slip ring fork. The groove and the fork are in clearance fit, so that the high-speed optical fiber slip ring can rotate flexibly with the engine.

9. The method for detecting strain field of an engine turbine disk based on a fiber grating sensor string and a high-speed smooth ring according to claim 1, characterized in that: The high-speed smooth ring (3) is fixed to the axis center of the engine air intake casing by using a special part. The bottom end of the special part, i.e., the inner side shaft of the small radius end, is provided with equidistant threaded holes that cooperate with the threaded holes provided on the high-speed smooth ring (3) for fixing. The top end of the special part, i.e., the large radius end, is provided with equidistant threaded holes that are fixed with the threaded holes provided at the corresponding position of the air intake casing. In order to prevent the high-speed smooth ring and other parts from accidentally detaching and being thrown out when the engine rotates at high speed, the screws are fixed and then a layer of iron wire is used to fix them.

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

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