Distributed optical fiber anemograph and wind speed measuring system

Abstract

The invention discloses a distributed optical fiber anemograph and a wind speed measuring system, and relates to the technical field of optical fiber sensors. The anemograph comprises a sensing optical fiber, the outer side of the sensor optical fiber is sleeved with a heat conduction pipe, the two ends of the sensing optical fiber extend out of the two ends of the heat conduction pipe respectively, the outer side of the heat conduction pipe is sleeved with a metal pipe, the positive electrode of a constant current source is connected with one end of the metal pipe, and the negative electrode of the constant current source is connected with the other end of the metal pipe; the constant current source directly applies current to the metal tube, the metal tube emits heat, and the heat is conducted to the heat conduction tube through the metal tube and is finally transmitted to the sensing optical fiber through the heat conduction tube. The method can accurately measure the wind speed, and is reliable in data and good in continuity.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensors, and in particular to a distributed optical fiber anemometer and a wind speed measurement system. Background Art

[0002] Wind speed measurement is an important task in many fields such as meteorology, aviation, navigation, environmental protection, agriculture, etc. Accurate wind speed measurement is crucial for weather forecasting, flight safety, ocean navigation, disaster warning, etc.

[0003] Existing wind speed measurement technologies mainly include mechanical anemometers, ultrasonic anemometers, lidar, microwave radar, and fiber optic sensing technology that has emerged in recent years. Traditional mechanical anemometers, such as cup anemometers, measure wind speed by rotating blades driven by wind. Although simple in structure and low in cost, they have problems such as slow response and susceptibility to mechanical wear, especially unstable performance under extreme weather conditions. Ultrasonic anemometers use the time difference of sound waves in the air to measure wind speed. This technology does not require moving parts and has high measurement accuracy and stability. However, the performance of ultrasonic anemometers may be affected in strong winds and bad weather conditions, and the cost is relatively high. Lidar technology measures wind speed by emitting laser pulses and receiving echo signals. It can achieve remote non-contact measurement and is suitable for atmospheric science research. However, the complexity and high cost of lidar systems limit their widespread application.

[0004] In recent years, fiber optic sensing technology has gained more and more attention in wind speed measurement due to its unique advantages. Fiber optic sensors not only have the ability to resist electromagnetic interference, but also can realize multi-point distributed measurement. Wind speed measurement based on optical fiber has made certain progress. Some experts and scholars have developed a Fabry-Perot interferometer fiber optic point sensor for wind speed measurement, which has a temperature self-calibration function, but cannot provide the same type of high-resolution velocity curve data as distributed sensing technology. There are also fiber Bragg grating sensing technology that uses multiplexing technology to generate multiple flow measurement values ​​in a single optical fiber, and generates its own heating through lasers. A cross-grid sensor with two mutually perpendicular fiber grating sensors is used to sense the velocity and yaw angle of the flow. Fiber grating sensors are usually limited by the number of sensor points per optical fiber, which is in the order of tens, making it inconvenient to use. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to provide a distributed optical fiber anemometer and a wind speed measurement system that can accurately measure wind speed.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a distributed fiber optic anemometer, including a sensing fiber, the outer side of the sensor fiber is sheathed with a heat conduction tube, and the two ends of the sensing fiber extend from the two ends of the heat conduction tube respectively, the outer side of the heat conduction tube is sheathed with a metal tube, the positive pole of the constant current source is connected to one end of the metal tube, and the negative pole of the constant current source is connected to the other end of the metal tube; the constant current source directly applies current to the metal tube to heat the metal tube, and the heat is then conducted from the metal tube to the heat conduction tube, and finally transferred from the heat conduction tube to the sensing fiber.

[0007] The present invention also discloses a distributed optical fiber wind speed measurement system, comprising the optical fiber anemometer and a tunable laser. The light source output end of the tunable laser is divided into two paths after passing through a first optical fiber coupler, the first path is connected to an input end of a second optical fiber coupler, the second path is connected to an input end of a third optical fiber coupler after passing through a bias controller, an output end of the second optical fiber coupler is connected to one end of a sensing optical fiber in the optical fiber anemometer, the other output end of the second optical fiber coupler is connected to an input end of the third optical fiber coupler, the output end of the bias controller is connected to the other input end of the third optical fiber coupler, an output end of the third optical fiber coupler is connected to the input end of a polarization beam splitter, the two output ends of the polarization beam splitter are respectively connected to a detector, and the signal output end of the detector is connected to a host computer.

[0008] A further technical solution is that the continuous light output by the tunable light source is divided into two paths by the first optical fiber coupler, one of which is injected into the sensing optical fiber through the second optical fiber coupler. When the laser propagates in the sensing optical fiber, it continuously generates backward Rayleigh scattered light, part of which is transmitted forward and coupled to the third optical fiber coupler through the second optical fiber coupler; the other light beam passes through the polarization controller and enters the third optical fiber coupler as reference light. The two optical signals interfere with each other and are divided into two polarization signals by the polarization beam splitter. They enter the detector respectively and are converted into electrical signals. Then, the spectrum is calculated on the host computer, and the wind speed is calculated by the host computer.

[0009] The beneficial effect of adopting the above technical solution is that the anemometer uses optical fiber as a signal transmission medium, which can realize long-distance data collection, reduce the demand for traditional sensor networks, and reduce maintenance costs. Optical fiber itself is not affected by electromagnetic fields, so the distributed optical fiber anemometer can work normally in an environment with severe electromagnetic interference, ensuring the accuracy of the data. Compared with traditional wind speed measurement devices, distributed optical fiber anemometers are small in size, light in weight, and more convenient and quick to install. Distributed systems allow wind speed measurements at multiple locations at the same time, which is very useful for understanding the wind speed distribution in a large area. Optical fiber materials usually have good corrosion resistance and durability, and can work stably for a long time under harsh climatic conditions. Due to its distributed characteristics, even if a part fails, it will not affect the operation of the entire system, ensuring the reliability and continuity of the data. Distributed optical fiber anemometers can also be used in aviation, navigation, wind farm management and other fields, and can provide accurate wind speed measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0011] Figure 1 is a principle block diagram of the distributed optical fiber anemometer according to an embodiment of the present invention;

[0012] Figure 2 is a principle block diagram of the wind speed measurement system according to an embodiment of the present invention (without connecting the optical fiber anemometer);

[0013] Among them: 1. tunable laser; 2. first fiber coupler; 3. bias controller; 4. polarization beam splitter; 5. detector; 6. host computer; 7. sensing fiber; 8. metal tube; 9. heat pipe; 10. wire; 11. constant current source; 12. second fiber coupler; 13. third fiber coupler. DETAILED DESCRIPTION

[0014] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0016] like Figure 1 As shown, the embodiment of the present invention discloses a distributed optical fiber anemometer, including a sensing optical fiber 7, the outer side of the sensing optical fiber 7 is sheathed with a heat pipe 9, and the two ends of the sensing optical fiber 7 extend from the two ends of the heat pipe 9 respectively. Preferably, the heat pipe 9 uses a silica capillary. The outer side of the heat pipe 9 is sheathed with a metal pipe 8, the positive electrode of the constant current source 11 is connected to one end of the metal pipe 8 through a wire 10, and the negative electrode of the constant current source 11 is connected to the other end of the metal pipe 8 through the wire 10; the constant current source 11 directly applies current to the metal pipe 8 to make the metal pipe 8 heat up, and the heat is then transferred from the metal pipe 8 to the heat pipe 9, and finally transferred from the heat pipe 9 to the sensing optical fiber 7.

[0017] Adjust the constant current source 11 and directly apply current to the metal tube 8. Since the metal tube 8 has resistance, it will generate heat when current is generated. The heat is then transferred to the silica capillary and finally to the sensing optical fiber 7. When the current is constant and the surrounding environment is constant, the sensing optical fiber 7 can eventually reach a steady state under the action of time. The metal tube is not limited to the stainless steel tube. The silica capillary can also be replaced by other good thermal conductors. A two-layer structure can also be used to place the sensing optical fiber directly in the metal tube. The core feature is to heat the metal tube, perform temperature testing on the sensing optical fiber, and finally reach a steady state. Metal-coated optical fiber can also be directly used to optimize the structure. The key element is that the metal tube / metal-coated optical fiber must be cylindrical, and its state is best in a straight line.

[0018] Further, such as Figure 2 As shown, an embodiment of the present invention further discloses a distributed optical fiber wind speed measurement system, including the optical fiber anemometer, and also including a tunable laser 1, the light source output end of the tunable laser 1 is divided into two paths after passing through a first optical fiber coupler 2, the first path is connected to an input end of a second optical fiber coupler 12, the second path is connected to an input end of a third optical fiber coupler 13 after passing through a bias controller 3, an output end of the second optical fiber coupler 12 is connected to one end of a sensing optical fiber 7 in the optical fiber anemometer, the other output end of the second optical fiber coupler 12 is connected to an input end of the third optical fiber coupler 13, the output end of the bias controller 3 is connected to another input end of the third optical fiber coupler 13, an output end of the third optical fiber coupler 13 is connected to the input end of a polarization beam splitter 4, the two output ends of the polarization beam splitter 4 are respectively connected to a detector 5, and the signal output end of the detector 5 is connected to a host computer 6.

[0019] The continuous light output by the tunable light source 1 is divided into two paths by the optical first fiber coupler 2. One path of light waves is injected into the sensing optical fiber 7. When the laser propagates in the sensing optical fiber 7, it continuously generates backward Rayleigh scattered light. These backward Rayleigh scattered lights become signal lights and are coupled to the third optical fiber coupler 13 through the second optical fiber coupler 12. The other path of light beam passes through the polarization controller 3 and enters the third coupler 13 as reference light. The two optical signals generate interference at the output end of the third coupler. The interference signal enters the polarization beam splitter 4 and is divided into two polarization signals. They enter the detector 5 respectively and are converted into electrical signals. After that, the spectrum is calculated in the host computer 6. Since the laser light source is a linear tunable light source, the optical frequencies of the backward Rayleigh scattered lights at different positions on the sensing optical fiber 7 are different. Therefore, by detecting the optical frequency on the detector, the position information on the optical fiber can be obtained; on the other hand, when the sensing optical fiber 7 is affected by temperature, the Rayleigh scattering spectrum drifts, and the cross-correlation operation of the Rayleigh scattering spectrum to be measured (external temperature) and the local reference spectrum (initial state) is performed to obtain the temperature result by multiplying the movement of the Rayleigh scattering spectrum by the temperature coefficient. The core of this method is to achieve continuous distributed optical signal detection and demodulation.

[0020] The distributed fiber optic method can sense the effects outside the fiber optic cable. The thermal conductivity of the metal tube must be analyzed to account for the heat factor along the metal tube, thereby accurately linking the temperature sensed at a certain axial position on the metal tube to the flow velocity at that position.

[0021] Create a calculation method for heat conduction along a metal tube. Its one-dimensional conduction equation is as follows, including convection and radiation heat transfer:

[0022]

[0023] in, represents axial heat conduction, h(x)P(x)[T(x)-T f ] represents convective heat transfer, represents radiation heat transfer; for a metal circular tube with a constant diameter, the above equation simplifies to:

[0024]

[0025] The boundary conditions are set to x = 0 and x = L; in the metal tube structure, Tx = 0 is given as the set temperature, and the temperature gradient when x = L is represented by T(L):

[0026]

[0027] The electric current heats the metal tube, generating Joule heat in the system Combining the parameters of heat conduction, material, geometric dimensions, etc. in the above equations, the following equation is obtained:

[0028]

[0029] According to the energy conservation theory of moving fluid, there is the following relationship between convection heat transfer and Joule heat:

[0030]

[0031] The Nusselt number Nu d Reynolds number d There is the following corresponding relationship:

[0032] Nu d =C*Re d m *P r n (6)

[0033] Reynolds number d The relationship between it and wind speed U is as follows:

[0034]

[0035] Finally, the wind speed U is obtained;

[0036] Where A represents the metal area in the cross section of the metal pipe; c represents the metal area in the cross section of the metal pipe; p is the specific heat capacity of the sensing optical fiber; d is the diameter of the metal tube; h is the convection heat transfer coefficient; I is the output current of the constant current source; k is the thermal conductivity coefficient, k flow is the fluid thermal conductivity, k air is the air thermal conductivity; L is the length of the metal tube; Nu d is the Nusselt number based on the diameter of the metal tube; P is the surface area of ​​the metal tube; Pr is the Prandtl number; q j Re is the joule heat per unit length of the metal tube after electricity is passed through it; d is the Reynolds number based on the diameter of the metal tube; T represents the temperature, T f is the fluid temperature, T wire is the metal tube temperature, T surr is the ambient temperature, Tx represents the temperature test result at a certain position of the metal tube; V is the applied voltage; x is the distance along the metal tube; ε is the thermal emissivity of the material; ρ is the resistivity of the material; σ is the Stefan-Boltzmann constant; τ is the heating / cooling time constant; α is the thermal diffusion coefficient of the material; ν is the kinematic viscosity of the material; C, m, n are constants.

[0037] The Nusselt number is calculated based on the results of formula (4) and formula (5), the Reynolds number is calculated based on formula (6), and the wind speed result is finally obtained based on formula (7). The constant coefficient in formula (6) is the result obtained after multiple test calibrations.

Claims

1. A distributed optical fiber anemometer, characterized in that: The invention comprises a sensing optical fiber (7), wherein a heat conducting tube (9) is sheathed on the outer side of the sensing optical fiber (7), and two ends of the sensing optical fiber (7) extend out from two ends of the heat conducting tube (9), and a metal tube (8) is sheathed on the outer side of the heat conducting tube (9). The positive electrode of a constant current source (11) is connected to one end of the metal tube (8) through a wire (10), and the negative electrode of the constant current source (11) is connected to the other end of the metal tube (8) through a wire (10). The constant current source (11) directly applies current to the metal tube (8), so that the metal tube (8) generates heat, and the heat is then transferred from the metal tube (8) to the heat conducting tube (9), and finally transferred from the heat conducting tube (9) to the sensing optical fiber (7).

2. The distributed optical fiber anemometer according to claim 1, characterized in that: The heat conducting tube (9) is a silicon dioxide capillary tube.

3. The distributed optical fiber anemometer according to claim 1, characterized in that: The metal tube (8) is cylindrical.

4. A distributed optical fiber wind speed measurement system, characterized in that The optical fiber anemometer comprises the optical fiber anemometer as claimed in any one of claims 1 to 3, and further comprises a tunable laser (1), wherein the light source output end of the tunable laser (1) is divided into two paths after passing through a first optical fiber coupler (2), the first path is connected to an input end of a second optical fiber coupler (12), and the second path is connected to an input end of a third optical fiber coupler (13) after passing through a bias controller (3), an output end of the second optical fiber coupler (12) is connected to one end of a sensing optical fiber (7) in the optical fiber anemometer, the other output end of the second optical fiber coupler (12) is connected to an input end of the third optical fiber coupler (13), the output end of the bias controller (3) is connected to the other input end of the third optical fiber coupler (13), an output end of the third optical fiber coupler (13) is connected to the input end of a polarization beam splitter (4), the two output ends of the polarization beam splitter (4) are respectively connected to a detector (5), and the signal output end of the detector (5) is connected to a host computer (6).

5. The distributed optical fiber wind speed measurement system according to claim 4, characterized in that: The continuous light output by the tunable light source (1) is divided into two paths by the first optical fiber coupler (2), wherein one path of light waves is injected into the sensing optical fiber (7) through the second optical fiber coupler (12), and the laser light continuously generates backward Rayleigh scattered light when propagating in the sensing optical fiber (7), and the backward Rayleigh scattered light part is transmitted forward and coupled into the third optical fiber coupler (13) through the second optical fiber coupler (12); the other path of light beam passes through the polarization controller (3) and enters the third optical fiber coupler (13) as reference light, and the two paths of light signals generate interference and are divided into two polarization signals through the polarization beam splitter (4), respectively entering the detector (5), and converted into electrical signals, and then spectrum calculation is performed on the host computer, and the wind speed is calculated by the host computer.

6. The distributed optical fiber wind speed measurement system according to claim 5, characterized in that: The host computer obtains the wind speed by the following method: in, represents axial heat conduction, h(x)P(x)[T(x)-T f ] represents convective heat transfer, represents radiation heat transfer; for a metal circular tube with a constant diameter, the above equation simplifies to: The boundary conditions are set to x = 0 and x = L; in the metal tube structure, T(x = 0) is given as the set temperature, and the temperature gradient when x = L is represented by T(L): The electric current heats the metal tube, generating Joule heat in the system Combining the parameters of heat conduction, material, geometric dimensions, etc. in the above equations, the following equation is obtained: According to the energy conservation theory of moving fluid, there is the following relationship between convection heat transfer and Joule heat: The Nusselt number Nu d Reynolds number d There is the following corresponding relationship: Not d =C*Re d m *P r n (6) Reynolds number d The relationship between it and wind speed U is as follows: Finally, the wind speed U is obtained; in, A represents the metal area in the cross section of the metal pipe; c p is the specific heat capacity of the sensing optical fiber; d is the diameter of the metal tube; h is the convection heat transfer coefficient; I is the output current of the constant current source; k is the thermal conductivity coefficient, k flow is the fluid thermal conductivity, k air is the air thermal conductivity; L is the length of the metal tube; Nu d is the Nusselt number based on the diameter of the metal tube; P is the surface area of ​​the metal tube; Pr is the Prandtl number; q j Re is the joule heat per unit length of the metal tube after electricity is passed through it; d is the Reynolds number based on the diameter of the metal tube; T represents the temperature, T f is the fluid temperature, T wire is the metal tube temperature, T surr is the ambient temperature, Tx represents the temperature test result at a certain position of the metal tube; V is the applied voltage; x is the distance along the metal tube; ε is the thermal emissivity of the material; ρ is the resistivity of the material; σ is the Stefan-Boltzmann constant; τ is the heating / cooling time constant; α is the thermal diffusion coefficient of the material; v is the kinematic viscosity of the material; C, m, n are constants.

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