JP2013036854A - Flow velocity distribution measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which is capable of measuring flow velocity distribution with a value of a flow velocity of a fluid.SOLUTION: A temperature measuring section 3 includes a pulse light source 9 to which one terminal of an optical fiber 6 is connected and which makes pulse light incident toward another terminal of the optical fiber 6, a receiver 11 which receives backward scattered light from the optical fiber 6, and a signal processor 12 which receives the backward scattered light from the receiver 11 and calculates temperature distribution of the optical fiber. Flow velocity distribution calculation means 4 receives from the signal processor 12 the temperature distribution of the optical fiber 6 during non-electrification and electrification of a heating element 7 and calculates flow velocity distribution from a temperature difference between temperatures during non-electrification and electrification at the same position of the optical fiber 6.

Description

  The present invention is intended to accurately understand the flow rate of rivers, waterways, etc., to measure the flow velocity distribution as basic information for the design of structures, and to provide groundwater in boreholes for landslide countermeasures and drainage planning. The present invention relates to a flow velocity distribution measuring apparatus using an optical fiber suitable for a flow velocity distribution measurement or the like.

  A method for investigating the groundwater level or the flow state using an optical fiber is disclosed in Patent Document 1, for example.

  In Patent Document 1, a heating / heating wire is arranged close to an optical fiber to form a fluid / flow sensor, the fluid / flow sensor is embedded in a borehole formed in the ground, and laser pulse light is incident on the optical fiber. Then, the temperature difference distribution with respect to the depth position in the borehole is obtained, and the existence and flow state of groundwater are known from the change in temperature.

  When pulsed light is incident on the optical fiber, Stokes light and anti-Stokes light are generated by Raman scattering of the backscattered light generated in the optical fiber. Since the anti-Stokes light has a strong temperature dependence with respect to the Stokes light, the time ratio of the backscattered light that is sequentially received is received by using the intensity ratio of the Stokes light and the anti-Stokes light as a function of temperature. Based on the principle of obtaining the temperature at this position from the intensity ratio while calculating the reflection position, the temperature distribution in the longitudinal direction of the optical fiber can be obtained. In Patent Document 1, when an optical fiber heated by a hot wire detects a different temperature at the depth of the ground, for example, in a certain range in the longitudinal direction of the optical fiber, the temperature is drastically lower than others. In the above range, the optical fiber is deprived of a lot of heat in the above range. Based on this, it is determined that groundwater exists or flows at a depth corresponding to the above range. It is said.

JP-A-06-214045

  According to Patent Document 1, it can be determined from the temperature drop in a specific range that groundwater exists or flows in this range. In addition, the magnitude of the flow can be relatively determined from the difference in the degree of the temperature decrease depending on the depth position. However, in patent document 1, only the judgment about the presence or absence of groundwater or its flow is made by comparing the specific range with others, and the value of the flow rate of the groundwater itself cannot be measured.

  This invention makes it a subject to provide the apparatus which can measure flow velocity distribution with the value of the flow velocity of a fluid in view of this point.

<First invention>
An apparatus for measuring a flow velocity distribution according to the present invention includes an optical fiber that extends in a direction intersecting with a fluid flow and is disposed in the fluid, and is disposed in close proximity along the optical fiber in the fluid to heat the optical fiber. A heating element, a temperature measurement unit that measures the temperature distribution of the optical fiber by transmitting and receiving pulsed light to and from the optical fiber, and switching between energization and de-energization of the power for heating the heating element A heating element power supply that can be supplied, and a flow velocity distribution calculating means for calculating a flow velocity distribution of the fluid from the temperature distribution of the optical fiber, wherein the temperature measuring unit is connected to one end of the optical fiber and connected to the other end of the optical fiber. A transmitter that receives pulsed light toward the end, a receiver that receives backscattered light from the optical fiber, and a signal processing unit that receives the backscattered light from the receiver and calculates the temperature distribution of the optical fiber. Flow velocity distribution calculation means The temperature distribution of the optical fiber when the heating element is de-energized and energized is received from the signal processing unit, and the flow velocity distribution is calculated from the temperature difference between the non-energized temperature and the energized temperature at the same position of the optical fiber. It is characterized by having.

  In such a flow velocity distribution measuring device, the heating element is disposed close to the optical fiber over the entire length of the measurement range of the optical fiber in which the temperature distribution is measured, and the signal processing unit of the temperature measuring unit measures the optical fiber. The temperature distribution of the optical fiber is calculated over the entire range when the heating element is not energized and when it is energized. Then, the flow velocity distribution calculating means calculates the temperature difference distribution from the temperature distribution, and further calculates the flow velocity distribution from the temperature difference distribution using the relationship between the known temperature difference and the flow velocity and the fluid flow velocity value.

<Second invention>
The flow velocity distribution measuring apparatus according to the present invention includes a first optical fiber portion and a second optical fiber portion that extend in a direction intersecting with a fluid flow, are arranged in the fluid, continue through the folded portion, and are located in parallel with a distance from each other. An optical fiber having an optical fiber part, a heating element that is disposed in close proximity along the first optical fiber part in fluid, and heats the first optical fiber part, and transmits and receives pulsed light to and from the optical fiber. A temperature measurement unit that measures the temperature distribution of the fiber, a power supply for the heating element that supplies power to the heating element to generate heat, and a flow velocity distribution calculation that calculates the flow velocity distribution of the fluid from the temperature distribution of the optical fiber And a temperature measuring unit comprising: a transmitter to which one end of an optical fiber is connected and incident pulsed light toward the other end of the optical fiber; a receiver to receive backscattered light from the optical fiber; After the receiver A signal processing unit that receives the scattered light and calculates the temperature distribution of the optical fiber, and the flow velocity distribution calculating unit receives the temperature distribution of the first optical fiber unit and the second optical fiber unit from the signal processing unit, The flow velocity distribution is calculated from the temperature difference at the longitudinal position of the first optical fiber portion and the second optical fiber portion of the fiber.

  In the present invention, the heating element is disposed close to the first optical fiber portion only along the first optical fiber portion of the optical fiber, and the first optical fiber portion is heated, The second optical fiber portion located at a distance from the first optical fiber is not heated. Then, the signal processing unit of the temperature measurement unit calculates the temperature distribution of the optical fiber over the entire optical fiber. Further, the flow velocity distribution calculating means calculates the temperature difference distribution at the longitudinal position of the first optical fiber portion and the second optical fiber portion, and uses the relationship between the known temperature difference and the flow velocity to calculate the fluid difference from the temperature difference distribution. The flow velocity distribution is calculated with the flow velocity value.

  In the first invention and the second invention, the optical fiber may be covered with a metal tube, and the metal tube may be a heating element. When measuring the flow velocity distribution of a fluid using an optical fiber cable that originally has an optical fiber covered with a metal tube, it is necessary to prepare other parts as the heating element by using the metal tube as a heating element. Therefore, the increase in the number of parts can be suppressed. In addition, a heating element may be disposed outside the metal tube without using the metal tube of the optical fiber as a heating element.

  In the present invention, as described above, the optical fiber is arranged so as to extend in a direction crossing the fluid flow, and a heating element for heating the optical fiber is also arranged, so that the optical fiber is not heated or By obtaining the temperature difference distribution between the temperature distribution of the optical fiber at the non-heated part and the temperature distribution at the time of heating or at the heated part, the flow velocity distribution of the fluid can be obtained from the relationship between the known temperature difference and the flow velocity. Therefore, the distribution of values of the flow velocity itself can be measured with a very simple configuration in which an optical fiber and a heating element are arranged in the fluid.

It is a conceptual diagram which shows the structure of the flow-velocity distribution measuring apparatus which concerns on 1st embodiment and 2nd embodiment, and has shown the state which measures the flow-velocity distribution of a river. It is sectional drawing in the surface orthogonal to the cable axial direction of the photoelectric composite cable in 1st embodiment. It is sectional drawing in the direction orthogonal to the cable axial direction of the photoelectric composite cable in the modification of 1st embodiment. It is sectional drawing in the direction orthogonal to the axial direction of the photoelectric composite cable in 2nd embodiment. It is a conceptual diagram which shows the structure of the flow-velocity distribution measuring apparatus which concerns on 2nd embodiment, and has shown the state which measures the flow-velocity distribution of groundwater.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<First embodiment>
This embodiment demonstrates the example which measures the flow velocity distribution of a river using a flow velocity distribution measuring apparatus. FIG. 1 is a conceptual diagram showing a configuration of a flow velocity distribution measuring apparatus 1 according to the present embodiment, and shows a state in which a flow velocity distribution of a river is measured. The portions (second optical fiber portion 6B and folding portion 6C described later) indicated by a two-dot chain line in FIG. 1 are portions according to a second embodiment described later, and the flow velocity distribution measuring apparatus 1 according to the present embodiment includes This two-dot chain line portion is not included. FIG. 2 is a cross-sectional view taken along a plane perpendicular to the cable axial direction of the photoelectric composite cable 2 in the present embodiment. In FIG. 2, for convenience of explanation, hatching indicating a cross section is attached only to the heating element 7 described later, and is omitted for the optical fiber 6 and the insulator 8.

  As seen in FIG. 1, the flow velocity distribution measuring apparatus 1 has an optical fiber 6 and a heating element 7 which will be described later, and extends in a direction intersecting the water flow in the river R (a direction orthogonal to FIG. 1). An optical / electrical composite cable 2, a temperature measuring unit 3 connected to one end of the optical fiber 6 of the optical / electrical composite cable 2 outside the river R (on the ground) for measuring the temperature distribution of the optical fiber 6, and the temperature A flow velocity distribution calculating means 4 connected to the measuring unit 3 for calculating the flow velocity distribution of the river R, and connected to one end of the heating element 7 of the photoelectric composite cable 2 outside the river R, a constant current is supplied to the heating element 7. And a constant current power source 5 as a heating element power source to be supplied.

  In FIG. 1, for convenience of explanation, the optical fiber 6 of the photoelectric composite cable 2 is shown as being located outside the heating element 7, but actually, as shown in FIG. The optical fiber 6 is covered with a heating element 7 formed as follows, and the heating element 7 is further covered with an insulator 8. That is, the heating element 7 is disposed close to the optical fiber 6 along the optical fiber 6.

  As shown in FIG. 1, the photoelectric composite cable 2 has one end (right end) located on one river bank outside the river R and the other end (left end) located in running water and grounded near the opposite bank. ing. A constant current power source 5 is connected to one end of the heating element 7 of the photoelectric composite cable 2. The constant current power source 5 supplies electric power to the heating element 7 so as to be switched between energization and non-energization. When energized, the heating element 7 is supplied with electric power from the constant current power source 5 and generates heat due to Joule heat to heat the optical fiber 6 in the metal tube as the heating element 7. Further, as seen in FIG. 1, the other end of the heating element 7 is grounded in water.

  The temperature measuring unit 3 is connected to one end of an optical fiber 6, a pulse light source 9 as a transmitter that inputs pulsed light from the one end toward the other end of the optical fiber 6, and incidence of pulsed light to the optical fiber 6. And a coupler 10 that allows the backscattered light from passing through the optical fiber 6, a receiver 11 that receives the backscattered light that has passed through the coupler 10, and a backscattered light received from the receiver 11. And a signal processing unit 12 for calculating the light reflection position and the temperature distribution of the optical fiber 6.

  The pulse light source 9 of the temperature measuring unit 3 is made of a semiconductor that outputs pulsed light having a wavelength of 1550 nm, for example. Further, the signal processing unit 12 calculates each reflection position of the backscattered light from the reception time of the backscattered light received by the receiver 11, and calculates the intensity ratio of the Stokes light and the anti-Stokes light in the backscattered light. Then, the temperature at each reflection position is calculated by averaging the intensity ratio. As a result, the temperature distribution in the longitudinal direction of the portion of the optical fiber 6 that is located in the river R and extends in the direction intersecting the flow of the river R (hereinafter referred to as “first optical fiber portion 6A”) is a signal. Calculated by the processing unit 12.

  A flow rate distribution calculating unit 4 is connected to the signal processing unit 12 of the temperature measuring unit 3. The flow velocity distribution calculating means 4 receives the temperature distribution of the first optical fiber portion 6A when the heating element 7 is not energized and energized from the signal processing unit 12, and the same position of the first optical fiber portion 6A for each reflection position. The temperature difference between the non-energized temperature and the energized temperature is calculated to obtain a temperature difference distribution in the longitudinal direction of the first optical fiber portion 6A. In addition, the flow velocity distribution calculating means 4 has, as known data, data on the correspondence relationship between the temperature difference between the non-energized temperature and the energized temperature of the first optical fiber portion 6A and the corresponding water flow velocity ( Hereinafter, “correspondence data” is stored in advance. Then, the flow velocity distribution calculating means 4 refers to the correspondence data, and calculates the flow velocity distribution corresponding to the temperature difference distribution calculated based on the temperature distribution from the signal processing unit 12 with the flow velocity value. calculate. The following well-known formula (1) is used for calculation of this flow velocity distribution.

  Hereinafter, the operation of the flow velocity distribution measuring apparatus 1 according to the present embodiment will be described. First, the photoelectric composite cable 2 is laid in the water of the river R to stabilize the position so that the photoelectric composite cable 2 extends so as to cross the water flow (orthogonal in FIG. 1). Then, in a state where the heating element 7 is not energized, that is, in a state where the heating element 7 does not generate heat and the optical fiber 6 is not heated, pulse light is transmitted from the pulse light source 9 of the temperature measuring unit 3 through the coupler 10 to the optical fiber. 6 is incident. When pulsed light is incident, backscattered light is generated in the optical fiber 6, and Stokes light and anti-Stokes light are generated by Raman scattering of the backscattered light. This backscattered light is received by the receiver 11 via the coupler 10.

  Next, the signal processing unit 12 of the temperature measurement unit 3 calculates the reflection position of the backscattered light from the reception time of the backscattered light received by the receiver 11, and the Raman scattered light of the backscattered light is calculated. The temperature distribution of the first optical fiber portion 6A is calculated by calculating the temperature at the reflection position from the intensity ratio of the Stokes light and the anti-Stokes light. At this time, since the optical fiber 6 is not heated, the calculated temperature distribution of the first optical fiber portion 6A becomes substantially equal to the temperature distribution of running water along the photoelectric composite cable 2.

  Next, the heating fiber 7 is energized, and the optical fiber 6 is heated by supplying power to the heating element 7 to generate heat. Since the amount of heat generated in the heating element 7 is taken away by the flowing water in the river R through the insulator 8, if the flow is constant speed, the temperature of the heating element 7 is stabilized with a certain temperature difference with respect to the flowing water. . Then, when the temperature of the heating element 7 is stabilized, the signal processing unit 12 of the temperature measuring unit 3 calculates the temperature distribution of the first optical fiber unit 6A as in the case of the non-energization described above.

  The flow velocity distribution calculating means 4 calculates the temperature difference by subtracting the non-energized temperature from the energized temperature at the same position of the first optical fiber unit 6A, thereby calculating the first optical fiber unit 6A in the longitudinal direction. Obtain the temperature difference distribution. Then, the flow velocity distribution calculation means 4 calculates the flow velocity distribution based on the temperature difference distribution based on the temperature difference distribution by referring to the correspondence data described above.

  In the present embodiment, the signal processing unit 12 calculates the temperature distribution of the optical fiber based on the intensity ratio of the Stokes light and the anti-Stokes light, but instead of this, for example, Raman of the backscattered light The temperature distribution may be obtained by calculating the intensity ratio between the anti-stroke light of the scattered light and the Rayleigh scattered light, and averaging the calculated ratio.

  In this embodiment, the heating element is formed by a metal tube that covers the optical fiber as shown in FIG. 2, but instead of this, for example, as shown in FIG. 3, the heating element is separately provided outside the metal tube. It may be arranged.

  FIG. 3 is a cross-sectional view in the direction perpendicular to the cable axial direction of the photoelectric composite cable in the modification of the present embodiment. In the figure, for convenience of explanation, hatching indicating a cross section is omitted. As shown in FIG. 3, in the photoelectric composite cable 2 in this modification, one optical fiber cable 21 and a plurality of metal armored wires 22 are twisted along the outer peripheral surface of a core wire 23 described later. Is formed. The optical fiber cable 21 has a configuration in which one optical fiber 6 is covered with a metal tube 24. In this modification, the metal tube 24 does not have a function as a heating element. Further, the armored wire 22 has a function as a tension member in addition to a function of protecting the core wire 23, and enhances the durability of the photoelectric composite cable 2. The core wire 23 is composed of an interposition 25 made of, for example, an insulator, a heating element 7 as a metal layer that covers the interposition 25, and an insulating layer 26 that further covers the heating element 7.

  3, the constant current power source 5 is connected to one end (right end in FIG. 1) of the heating element 7 as the metal layer of the interposition 25, and the heating element 7 has the constant current. Electric power is supplied from the power source 5 to generate heat, and the optical fiber 6 is heated through the insulating layer 26 and the metal tube 24.

<Second embodiment>
In the first embodiment, the temperature distribution at the time of energization is calculated after calculating the temperature distribution at the time of non-energization. However, in the present embodiment, the temperature distribution obtained in the non-energized state and the temperature distribution obtained in the energized state are calculated. Is different from the first embodiment in that both are calculated simultaneously.

  This embodiment will be described with reference to FIG. The flow velocity distribution measuring apparatus 1 according to the present embodiment is that the optical fiber 6 also includes a portion indicated by a two-dot chain line in FIG. The configuration is different from that of the flow velocity distribution measuring apparatus 1. Specifically, the optical fiber 6 of the present embodiment has an end portion (as shown by the two-dot chain line in the drawing) of the optical fiber 6 in the first embodiment shown by a solid line in FIG. It is folded back and extended at the left end in FIG. 1 and has first and second optical fiber portions as described below.

  In the present embodiment, the portions of the optical fiber 6 that are positioned in parallel with each other in the river R are referred to as “first optical fiber portion 6A” (shown by a solid line in FIG. 1) and “second optical fiber portion”, respectively. 6B "(illustrated by a two-dot chain line in FIG. 1), and a folded portion connecting the first optical fiber portion 6A and the second optical fiber portion 6B is defined as a" folded portion 6C "(indicated by a two-dot chain line in FIG. 1). (Illustrated). As will be described later, in the present embodiment, only the first optical fiber portion 6A is heated, and the second optical fiber portion 6B is not heated.

  FIG. 4 is a cross-sectional view in a direction perpendicular to the axial direction of the photoelectric composite cable 2 in the present embodiment. In FIG. 4, for convenience of explanation, only the heating element 7 is hatched to show a cross section, and other portions are not hatched. The photoelectric composite cable 2 extends to the left end in FIG. 1 in a state where a plurality of (six in FIG. 4) side lines 32A to 32F are twisted along the outer peripheral surface of the main interposition 31 made of, for example, an insulator.

  Among the side lines 32 </ b> A to 32 </ b> F shown in FIG. 4, the side line 32 </ b> A located on the upper side in FIG. 4 includes one optical fiber cable 33 and a plurality of metal armor wires 34 along the outer peripheral surface of the core wire 35. And twisted. The optical fiber cable 33 is formed by covering the first optical fiber portion 6 </ b> A with a metal tube 36. In the present embodiment, the metal tube 36 covering the first optical fiber portion 6A does not have a function as a heating element. The core wire 35 is composed of a heating element 7 formed of a metal wire and an insulating layer 37 that covers the heating element 7.

  Among the side lines 32A to 32F shown in FIG. 4, the side line 32D located on the lower side in FIG. 4 is configured such that the core wire is a sub-intervening 38 made of an insulator, and includes one optical fiber cable 33 and a metal. A plurality of armored wires 34 made of wire are twisted along the outer peripheral surface of the sub-interposition 38. In the side line 32D, the optical fiber cable 33 has a second optical fiber portion 6B covered with a metal tube 36.

  Side lines 32B, 32C, 32E, and 32F other than the side lines 32A and 32D are formed by twisting a plurality of armor wires 34 along the outer peripheral surface of the sub-interposition 38 as a core wire.

  In the optical / electrical composite cable 2 having the configuration shown in FIG. 4, the heating element 7 is arranged at a position close to the first optical fiber portion 6A and away from the second optical fiber portion 6B, as shown in FIG. ing. Therefore, when the heating element 7 is energized, when power is supplied from the constant current power source 5 to the heating element 7 and the heating element 7 generates heat, the first optical fiber portion 6A is heated, but the second light The fiber part 6B is not heated.

  In this embodiment, after the signal processing unit 12 of the temperature measurement unit 3 calculates the temperature distribution over the entire longitudinal direction of the optical fiber 6 during the energization, the flow velocity distribution calculation unit 4 is within the range of the first optical fiber unit 6A. The temperature difference distribution is calculated by subtracting the temperature distribution in the range of the second optical fiber portion 6B from the temperature distribution. Furthermore, the flow velocity distribution calculating means 4 calculates the flow velocity distribution based on the temperature difference distribution based on the temperature difference distribution by referring to the correspondence data as the known data.

  That is, in the first embodiment described above, after calculating the temperature distribution when not energized, that is, when the optical fiber 6 is not heated, the temperature distribution is calculated when energized, that is, when the optical fiber 6 is heated. According to this embodiment, with the heating element 7 energized, the temperature distribution during heating can be calculated simultaneously with the first optical fiber portion 6A, and the temperature distribution of the non-heated portion can be calculated simultaneously with the second optical fiber portion 6B. Therefore, there is no difference between the calculation time of the temperature distribution during heating and the calculation time of the temperature distribution of the non-heated part. By calculating the flow velocity distribution based on these temperature distributions, a more accurate flow velocity distribution can be obtained. Can do.

  The photoelectric composite cable is not limited to the configuration shown in FIG. In the optical / electrical composite cable, the first optical fiber portion and the second optical fiber portion extend in parallel with each other, the heating element is located close to one optical fiber portion, and is separated from the other optical fiber portion. It is sufficient that one optical fiber portion is heated by the heating element and the other optical fiber portion is not heated.

  As mentioned above, although the example which measures the flow velocity distribution in a river using the flow velocity distribution measuring apparatus 1 which concerns on this embodiment was demonstrated, the environment which can apply this flow velocity distribution measuring apparatus 1 is not restricted to this, For example, other than a river The flow velocity distribution in the water channel may be measured, or the flow velocity distribution of groundwater can be measured.

  FIG. 5 is a conceptual diagram showing the configuration of the flow velocity distribution measuring apparatus 1 according to this embodiment, and shows a state in which the flow velocity distribution of groundwater is measured. As shown in FIG. 5, the flow velocity distribution measuring apparatus 1 is embedded in a borehole H formed in the ground in a state where the photoelectric composite cable 2 extends in the vertical direction. In the manner described above, the flow velocity distribution of groundwater flowing in the direction intersecting the vertical direction is calculated.

  In the embodiment of FIG. 5, an optical / electrical composite cable having a configuration in which the first optical fiber portion 6A and the second optical fiber portion 6B of the optical / electrical composite cable 2 shown in FIG. 4 are replaced is used. Accordingly, as shown in FIG. 5, the heating element 7 is positioned in the vicinity of the second optical fiber portion 6B and heats only the second optical fiber portion 6B. Further, unlike the configuration of FIG. 1, the heating element 7 is not grounded in water, and as shown in FIG. 5, both ends are connected to the constant current power source 5 and supplied to the heating element 7. The current is fed back to the constant current power source 5.

DESCRIPTION OF SYMBOLS 1 Flow velocity distribution measuring device 3 Temperature measurement part 4 Flow velocity distribution calculation means 5 Constant current power supply (power supply for heating elements)
6 Optical fiber 6A 1st optical fiber part 6B 2nd optical fiber part 6C Folding part 7 Heating element 9 Pulse light source (transmitter)
11 Receiver 12 Signal Processing Unit 24 Metal Tube 36 Metal Tube

Claims (4)

  An optical fiber extending in a direction intersecting the flow of the fluid and disposed in the fluid; a heating element disposed in close proximity along the optical fiber in the fluid to heat the optical fiber; and the optical fiber A temperature measuring unit that transmits and receives pulsed light to measure the temperature distribution of the optical fiber, and a heating element power supply that supplies power for heating the heating element so that the heating element can be switched between energized and de-energized, A flow velocity distribution calculating means for calculating a flow velocity distribution of the fluid from the temperature distribution of the optical fiber, wherein the temperature measuring unit is connected to one end of the optical fiber and transmits the pulsed light toward the other end of the optical fiber. A receiver that receives backscattered light from the optical fiber, and a signal processing unit that receives the backscattered light from the receiver and calculates the temperature distribution of the optical fiber. When not energized and when energized The flow velocity distribution measurement is characterized in that the flow velocity distribution is calculated from the temperature difference between the non-energized temperature and the energized temperature at the same position of the optical fiber. apparatus.   An optical fiber including a first optical fiber portion and a second optical fiber portion that extend in a direction intersecting with the flow of the fluid, are arranged in the fluid, continue through the folded portion, and are positioned parallel to each other at a distance; A heating element that is disposed in close proximity along the first optical fiber section and that heats the first optical fiber section, and a temperature measurement section that measures the temperature distribution of the optical fiber by transmitting and receiving pulsed light to and from the optical fiber. A heating element power supply for supplying power to the heating element to generate heat, and a flow velocity distribution calculating means for calculating a flow velocity distribution of the fluid from the temperature distribution of the optical fiber, and the temperature measuring unit A transmitter to which one end of an optical fiber is connected and incident pulsed light toward the other end of the optical fiber, a receiver that receives backscattered light from the optical fiber, and backscattered light received from the receiver Optical fiber temperature A signal processing unit for calculating a cloth, and the flow velocity distribution calculating means receives the temperature distribution of the first optical fiber unit and the second optical fiber unit from the signal processing unit, and the first optical fiber unit and the first optical fiber unit of the optical fiber. A flow velocity distribution measuring apparatus characterized in that a flow velocity distribution is calculated from a temperature difference at a longitudinal position of two optical fiber portions.   3. The flow velocity distribution measuring apparatus according to claim 1, wherein the optical fiber is covered with a metal tube, and the metal tube serves as a heating element.   The flow velocity distribution measuring apparatus according to claim 1 or 2, wherein the optical fiber is covered with a metal tube, and a heating element is arranged outside the metal tube.

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