JP7484367B2 - Flow direction measurement system and flow direction measurement method using optical fiber - Google Patents

Description

The disclosed technology relates to a flow direction measurement system and flow direction measurement method using optical fiber, which is suitable for measuring wind direction, etc.

In recent years, advances in computer technology have led to widespread use of fluid dynamics (CFD). CFD makes it possible to simulate the dynamic changes in fluids.

Furthermore, optical fibers are widely used in optical communications and the like. Optical fibers are also used as sensors to measure temperature, strain, and the like. Known sensing techniques using optical fibers include a method in which measurements are made using scattered light generated by injecting pulsed light into an optical fiber, and a method in which a specific diffraction grating (FBG: Fiber Bragg Grating) is formed in an optical fiber and a specific reflected light from the FBG is used for measurements.

Patent Document 1 discloses a device that uses optical fibers to measure the flow velocity distribution of fluids, specifically, flowing water such as rivers and groundwater. The device uses a special cable (optical-electrical composite cable) that uses optical fibers.

The optical-electrical composite cable has a core wire with a heating element. A long, thin metal tube with an optical fiber inserted and multiple armor wires are spirally wound around the outer surface of the core wire. The optical fiber is heated by passing electricity through the heating element.

The optical-electrical composite cable is laid underwater in the river so as to cross the river. The device measures the temperature distribution along the optical-electrical composite cable both when the optical fiber is heated by a heating element and when it is not heated. The temperature difference distribution is then obtained from the difference between these measured values.

The device uses scattered light to measure temperature. That is, a pulse of light is input into one end of the optical fiber. The pulse of light generates scattered light and propagates through the optical fiber while attenuating.

Part of the scattered light returns to the incident end. The scattered light contains a component that is temperature dependent. From that component, the temperature at the location where the scattering occurred can be determined. Then, from the time that has elapsed from when the light enters until it returns, the location where the scattering occurred can be determined. This allows the temperature at multiple locations along the length of the optical fiber, in other words, the temperature distribution, to be measured.

The temperature distribution is measured both in a heated and unheated state, and the temperature difference distribution is obtained from the difference between these measured values. The device is also pre-loaded with data for calculating flow velocity from temperature difference. By referring to this data, the flow velocity distribution in the width direction of the river is calculated from the obtained temperature difference distribution.

The optical-electrical composite cable is folded back at the edge of the river to place two optical-electrical composite cables side by side underwater. Patent document 1 also discloses a method for simultaneously measuring the temperature distribution in both heated and unheated states.

JP 2013-36854 A

CFD is also used in automotive research and development. For example, outside air flows into the engine room to cool the engine. The outside air flows in various directions within the engine room. For this reason, CFD is used to analyze the air flow within the engine room.

However, the information obtained by CFD is a predicted value. To verify the accuracy of the predicted value, it is necessary to compare it with an actual measured value. For this reason, a measuring device that can measure wind direction (anemometer) is installed in the engine room, and the wind direction is actually measured.

However, various types of equipment are densely packed inside the engine room. In order to actually measure wind direction inside the engine room, the wind vane must be installed in a small, complex space, avoiding these devices. Furthermore, to measure wind direction with high accuracy, it is necessary to avoid the wind direction being changed by the wind vane itself.

The main objective of the technology disclosed here is to provide a measurement system that can measure flow direction with high accuracy even in small, complex spaces.

One of the techniques disclosed relates to a flow direction measurement system. The measurement system includes a heatable heating element arranged to extend into the fluid, three or more optical fibers arranged to extend parallel to the longitudinal direction of the heating element around the heating element, a cover that covers the outer periphery of the heating element and a part of the group of optical fibers, and a measurement device that controls the heating state of the heating element and measures the temperature with each of the optical fibers by irradiating light into the optical fibers.

When the cross section of the heating element is defined as a cross section taken perpendicular to the longitudinal direction of the heating element, the three or more optical fibers are arranged such that, at the position where the heating element cross section is obtained, the central angle defined by the center of the cross section of the heating element and the positions of two of the three or more optical fibers that are in a one-end to other-end relationship in the circumferential direction of the heating element cross section is greater than 90 degrees.

Each of the optical fibers has a pair of adjacent measurement sites at the same location in the longitudinal direction, where temperature is measured. One of the measurement sites is a covered measurement site that is covered by the cover body, and the other measurement site is an exposed measurement site that is not covered by the cover body. A flow direction determination unit capable of measuring the flow direction is configured by the group of covered measurement sites and exposed measurement sites of the optical fiber.

The measurement device then performs a heating process to heat the heating element, a temperature measurement process to measure the temperature of each of the covered measurement parts and the exposed measurement parts in a heated state, a heat transfer coefficient calculation process to calculate the heat transfer coefficient of each of the optical fibers in the flow direction identification part based on the measured temperatures, and a flow direction identification process to identify the flow direction of the fluid in the flow direction identification part based on the circumferential distribution of the heat transfer coefficient in the flow direction identification part.

In other words, according to this measurement system, a heatable heating element is arranged to extend into a fluid, such as an air passage. Around the heating element, multiple optical fibers that measure temperature are arranged to extend in parallel with a predetermined distribution. Each of these optical fibers has a pair of adjacent measurement sites (an exposed measurement site and a covered measurement site covered with a cover body) at the same location in the longitudinal direction, and the covered measurement site and exposed measurement site form a flow direction identification unit.

The measuring device then measures the temperature of each of the coated and exposed measurement parts while the heating element is in a heated state. Adjacent coated and exposed measurement parts are heated under approximately the same conditions, but a temperature difference occurs depending on whether or not they are coated. Based on this temperature difference, the measuring device calculates the heat transfer coefficient of each optical fiber in the flow direction identification section.

As will be described in more detail later, a unique distribution of heat transfer coefficients is formed around the heating element in accordance with the flow direction. The flow direction can then be identified from this unique distribution of heat transfer coefficients. The control device then identifies the flow direction of the fluid based on the circumferential distribution of heat transfer coefficients.

In this measurement system, the part that measures the flow direction is composed of multiple optical fibers and a heating element. Since it contains optical fibers, there is a bending limit, but it is flexible. Therefore, it can be installed while avoiding contact with various equipment and piping. Moreover, it can be made sufficiently thin compared to conventional wind vanes, etc.

Therefore, this measurement system can be installed even in small and complex spaces. It also suppresses adverse effects caused by the part that measures the flow direction itself. In other words, this measurement system can measure the flow direction, such as wind direction, with high accuracy.

Specifically, the measurement portion may be composed of an FBG that reflects reflected light whose wavelength changes according to the distortion of the measurement portion, the measurement device may have flow direction identification information that defines the relationship between the flow direction of the fluid in the flow direction identification portion and the circumferential distribution of the heat transfer coefficient, the measurement device may acquire the reflected light reflected from each of the covered measurement portions and each of the exposed measurement portions in the temperature measurement process, and calculate the temperature of each of the covered measurement portions and each of the exposed measurement portions based on the change in the wavelength of the acquired reflected light, the heat transfer coefficient calculation process may calculate the heat transfer coefficient of each of the optical fibers in the flow direction identification portion based on the heating state of the heating element and the difference in temperature measured at each of the adjacent covered measurement portions and exposed measurement portions of each of the optical fibers, and the flow direction identification process may identify the flow direction of the fluid in the flow direction identification portion by collating the circumferential distribution of the heat transfer coefficient in the flow direction identification portion with the flow direction identification information.

In other words, this measurement system uses light reflected by an FBG formed in an optical fiber to measure temperature. Since the temperature is measured at the location where the FBG is formed, the position of the measurement location is clear. Therefore, the temperature of the targeted location can be accurately measured. In addition, since the measurement location can be identified by changing the wavelength of the reflected light, high-precision temperature measurements can be performed even when multiple measurement locations are placed closely together. Therefore, this measurement system is suitable for measuring temperature at adjacent covered measurement locations and exposed measurement locations.

The measurement device has flow direction identification information that specifies the relationship between the flow direction of the fluid in the flow direction identification part and the circumferential distribution of the heat transfer coefficient. That is, a specific distribution of the heat transfer coefficient corresponding to the flow direction formed around the flow direction identification part is set in advance in the measurement device. Therefore, the measurement device can actually measure the heat transfer coefficient in the flow direction identification part, obtain the distribution of the heat transfer coefficient from the actual measurement value, and then identify the flow direction of the fluid by comparing the distribution with the flow direction identification information. Therefore, with this measurement system, a series of processes for measuring the flow direction can be automatically executed. That is, the flow direction can be measured with a single button operation.

The measurement system may also include a plurality of thin tubes having an inner diameter slightly larger than the outer diameter of the optical fiber and having thermal conductivity, the thin tubes being arranged to extend parallel to the circumference of the heating element, and each of the optical fibers being inserted into the thin tubes.

Since the optical fiber does not come into direct contact with the fluid, stable temperature measurements can be performed. The optical fiber is surrounded by a thin tube with excellent thermal conductivity, with only a small gap separating them, so the temperature of the optical fiber can be quickly and stably matched to the surrounding atmospheric temperature.

When the optical fiber comes into direct contact with the thin tube, the distortion of the thin tube affects the distortion of the optical fiber. Therefore, when measuring temperature from the amount of distortion, there is a risk that the accuracy of the temperature measurement will deteriorate. However, if there is a gap between the thin tube and the optical fiber, such problems can be avoided.

The measurement system may also be such that the multiple thin tubes are arranged around the entire circumference of the heating element, either in contact with each other or separated by a small gap.

This allows the temperature to be measured precisely all around the heating element. It also allows the circumferential distribution of heat transfer coefficient to be obtained thoroughly all around the circumference. This allows the flow direction to be measured with high precision.

The measurement system may also include a thermally conductive cylinder surrounding the heating element, and a plurality of fine holes having an inner diameter slightly larger than the outer diameter of the optical fiber and extending parallel to the heating element are provided at the outer periphery of the cylinder with slits interposed therebetween, and each of the optical fibers is inserted into the fine holes.

In other words, in this measurement system, the multiple capillaries described above are replaced by multiple pores formed in a cylinder. Therefore, these pores can achieve the same effect as the capillaries described above. They are also advantageous in that they are easier to process and arrange than arranging multiple capillaries.

The measurement system may also be configured such that the flow direction determining units are provided at intervals along the longitudinal direction of the group of optical fibers, and flow direction measurements are performed simultaneously at multiple locations.

In other words, this measurement system can measure the flow direction at multiple locations simultaneously. Therefore, highly accurate flow direction measurements can be performed efficiently. Moreover, because it is done simultaneously, the distribution of wind direction can be measured with high accuracy.

In particular, the fluid is air, making it suitable for measuring wind direction.

For example, if it is used to measure wind direction in an engine room, it can be measured with high accuracy, which can be effectively used to verify the results of CFD analysis.

Another technology we disclose relates to a method for measuring flow direction using a specified measuring device.

The measuring device includes three or more optical fibers arranged around a heatable heating element so as to extend parallel to the longitudinal direction of the heating element, a cover body that covers the outer periphery of a portion of the group of optical fibers together with the heating element, and a measurement control unit that controls the incident light entering the optical fibers to measure the temperature of each of the optical fibers.

As with the previous technology, the three or more optical fibers are arranged so that the central angle defined by the center of the cross section of the heating element and the positions of two of the three or more optical fibers that are in a one-end to other-end relationship in the circumferential direction of the cross section of the heating element is greater than 90 degrees.

Each of the optical fibers has a pair of adjacent measurement sites at the same location in the longitudinal direction where temperature is measured, one of the measurement sites being a covered measurement site covered by the cover body, and the other of the measurement sites being an exposed measurement site not covered by the cover body, and these covered measurement site and exposed measurement site form a flow direction identification unit capable of measuring the flow direction.

The measurement method includes a preparation step of placing the heating element and the group of optical fibers in the fluid so that the flow direction identification portion is located at a measurement location, a heating step of heating the heating element, a temperature measurement step of operating the measurement device to measure the temperature of each of the coated measurement portions and the exposed measurement portions, a heat transfer coefficient calculation step of calculating the heat transfer coefficient of each of the optical fibers in the flow direction identification portion based on the difference in temperature measured at each of the adjacent coated measurement portions and exposed measurement portions of each of the optical fibers, and a flow direction identification step of identifying the flow direction of the fluid in the flow direction identification portion based on the circumferential distribution of the heat transfer coefficient in the flow direction identification portion.

In experiments, it may be necessary to measure the flow direction by combining existing devices and equipment. In particular, devices that use optical fibers to measure temperature are in practical use and can be easily used. With this measurement method, it is possible to measure the flow direction using such devices, albeit semi-automatically.

In other words, this measurement method uses a specific measurement device that can perform measurements using multiple optical fibers. As in the measurement system described above, a group of these optical fibers is placed around the heating element. These are then placed in the fluid so that the flow direction identifying part is located at the measurement point. The heating element is then heated, and the measurement device is operated to measure the temperature.

By using a personal computer or the like, the difference in temperature measured at each of the adjacent coated measurement parts and exposed measurement parts of each optical fiber is calculated from the measured temperature. Then, based on the calculation results, the heat transfer coefficient of each optical fiber in the flow direction identification part is calculated. Based on the circumferential distribution of the heat transfer coefficient in the flow direction identification part thus obtained, the flow direction of the fluid in the flow direction identification part is identified.

Therefore, this measurement method allows highly accurate measurement of the flow direction using existing equipment. In other words, this measurement method is versatile and convenient.

The disclosed technology makes it possible to measure flow direction with high accuracy even in small, complex spaces. This makes it possible to measure wind direction with high accuracy even in places such as engine compartments.

1 is a schematic diagram showing a state in which the measurement system is used to measure the wind direction in an engine compartment, as viewed from the right side of the engine compartment. 1 is a schematic diagram showing a state in which the wind direction in an engine room is measured using a measurement system, the engine room being viewed from above. 1 is a schematic diagram of a measurement system, showing an enlarged tip portion of a measurement sensor. 3 is a schematic cross-sectional view taken along the arrow line Y1-Y1 in FIG. 2. 3 is a schematic cross-sectional view taken along the arrow line Y2-Y2 in FIG. 2. 1 is a schematic diagram illustrating a structure of a main part of an optical fiber. FIG. 2 is a block diagram showing a functional configuration of the measurement device. FIG. 11 is a schematic diagram showing flow direction identification information in the form of a graph. 1 is a diagram for explaining the flow of wind around a measurement sensor; FIG. 2 is a simplified diagram of a measurement sensor in accordance with the explanation. FIG. 6C is a diagram showing an example of flow direction identification information corresponding to FIG. 6B. 1 is a flowchart showing a flow of main processes performed by the measurement system. FIG. 13 is a diagram for explaining a case where wind direction is measured using three optical fibers. FIG. 11 is a schematic cross-sectional view showing a modified example of the measurement sensor. FIG. 1 is a schematic diagram showing a measurement system of an application example.

The following describes in detail the embodiments of the disclosed technology with reference to the drawings. However, the following description is essentially merely an example and does not limit the present invention, its applications, or its uses.

For example, in this embodiment, a flow direction measurement system 1 (hereinafter, simply referred to as measurement system 1) to which the disclosed technology is applied is used to measure wind direction. That is, the fluid that is the object of measurement by the measurement system 1 of this embodiment is air.

Figures 1A and 1B show an engine room 100 provided at the front of the vehicle body. Inside the engine room 100, an engine 101, a radiator 102, a radiator fan 103, etc. are installed. Although not shown in the figure, in addition to these, various other devices, pipes, etc. are densely arranged inside the engine room 100.

A front grille 104 is provided in front of the front part of the vehicle body. The radiator 102 is disposed close to the rear of the front grille 104. When the vehicle is running, outside air is taken into the engine compartment 100 through the front grille 104. When the vehicle is stopped, outside air is taken into the engine compartment 100 by driving the radiator fan 103. The cooling water flowing through the radiator 102 is cooled by heat exchange with the outside air.

After passing through the radiator 102 and the radiator fan 103, the outside air passes through a small and complex space in the engine room 100, and then branches off in various directions before flowing toward the rear of the engine room 100. The measurement system 1 is used to measure (actually measure) the wind direction of the outside air.

The measurement system 1 is roughly composed of a measurement sensor 10 and a measurement device 30. As will be described in detail later, the measurement sensor 10 is formed long and thin from multiple linear or rod-shaped members including multiple optical fibers 13. The measurement device 30 is formed small and lightweight by housing various parts such as electrical components and a light source in a box-shaped case. The base end portion of the measurement sensor 10 is connected to the measurement device 30.

In the measurement system 1 of this embodiment, the tip of the measurement sensor 10 measures the wind direction. In this embodiment, the measurement location is the space between the radiator fan 103 and the engine 101 located behind it. Therefore, the tip of the measurement sensor 10 is positioned in that space so that it extends across the air flow path.

The measuring device 30 is installed in the empty space to the side of the radiator 102 and the radiator fan 103. Therefore, the measuring sensor 10 extends from that empty space.

The measurement sensor 10 is flexible, although it has a bending limit because it contains an optical fiber 13. Therefore, the measurement sensor 10 can be installed at a location far away from the measurement device 30 while avoiding contact with various equipment and piping. Moreover, the measurement sensor 10 is thin.

Therefore, this measurement system 1 can be installed even in a small and complex space. Even if the measurement sensor 10 is placed so as to cross the measurement location, the change in wind direction caused by the measurement sensor 10 itself can be suppressed. In other words, this measurement system 1 can measure wind direction with high accuracy.

<Measurement sensor 10>
Fig. 2 shows an enlarged view of the tip portion of the measurement sensor 10. Fig. 3A shows a schematic cross-sectional view taken along the direction indicated by the arrow line Y1-Y1 in Fig. 2. Fig. 3B shows a schematic cross-sectional view taken along the direction indicated by the arrow line Y2-Y2 in Fig. 2.

The tip of the measurement sensor 10 is composed of a heater 11 (an example of a heating element), multiple thin tubes 12, multiple optical fibers 13, and a covering 14 (an example of a covering body). The tip of the measurement sensor 10 is formed into a roughly cylindrical shape by these components.

The heater 11 is made of a thin rod-shaped member. The heater 11 has a cylindrical shape and its cross section is circular. The heater 11 is electrically connected to the measuring device 30 via an electric wire. The heater 11 generates heat when electricity is passed through it. The temperature of the heater 11 is controlled by adjusting the amount of electricity passed through it. The heater 11 radiates heat evenly around the entire circumference.

The capillaries 12 are long, thin tubes made of a metal with excellent thermal conductivity, such as an aluminum alloy. The capillaries 12 are much thinner than the heater 11. In this embodiment, twelve capillaries 12 are arranged so as to extend in parallel around the heater 11. These capillaries 12 are arranged around the entire circumference of the heater 11, with adjacent two capillaries 12 in contact with each other or separated by a small gap.

A group of the thin tubes 12 is arranged in a circular ring shape around the heater 11. Each thin tube 12 is in contact with the heater 11. Note that the number and arrangement of the thin tubes 12 are merely an example. As will be described later, there should be at least three thin tubes 12 for one heater 11. Also, each thin tube 12 may be somewhat distant from the heater 11 as long as it can be heated evenly.

An optical fiber 13 is inserted into each capillary 12. That is, in this embodiment, twelve optical fibers 13 are used. The twelve optical fibers 13 are arranged so as to extend in parallel around the heater 11. As will be described later, at least three optical fibers 13 are required for one heater 11. Also, it is not necessary for the optical fibers 13 to be inserted into all capillaries 12.

Each capillary 12 has an inner diameter slightly larger than the outer diameter of the optical fiber 13. As a result, a gap exists between the inner surface of the capillary 12 and the outer surface of the optical fiber 13.

As described below, the optical fiber 13 measures temperature by utilizing the distortion caused by thermal deformation of the optical fiber 13. In contrast, in this measurement sensor 10, the optical fiber 13 is surrounded by a thin tube 12 with excellent thermal conductivity, with a small gap between them. This allows the temperature of the optical fiber 13 to quickly and stably match the ambient temperature around it.

Furthermore, if the optical fiber 13 comes into direct contact with the thin tube 12, the distortion of the optical fiber 13 will be affected by the distortion of the thin tube 12, which may result in a deterioration in the accuracy of the temperature measurement. If there is a gap between the thin tube 12 and the optical fiber 13, it is possible to prevent the optical fiber 13 from coming into direct contact with the thin tube 12. Therefore, such a problem can also be avoided.

Each optical fiber 13 is provided with a pair of adjacent measurement sites 21, 22 at the same location in its longitudinal direction (extension direction) where temperature measurements are performed. That is, a pair of measurement sites (first measurement site 21 and second measurement site 22) is provided at the tip portion of each optical fiber 13. These first measurement site 21 and second measurement site 22 are adjacent (close to each other) in the extension direction of the optical fiber 13.

The first measurement sites 21 and the second measurement sites 22 are each provided at the same location in the extension direction of each optical fiber 13. As a result, a group of first measurement sites 21 and a group of second measurement sites 22 are each connected in a ring shape and surround the heater 11.

The covering ring 14 is made of a cylindrical member made of a material with excellent heat insulating properties, such as synthetic resin. The covering ring 14 has a length (length in the extension direction) slightly greater than the measurement site. The covering ring 14 covers a part of the outer periphery of the measurement sensor 10, specifically, one of the measurement sites (in this embodiment, the second measurement site 22) as shown in Figures 2 and 3B. The covering ring 14 can be, for example, a rubber band.

As a result, one of the measurement sites (first measurement site 21) is an exposed measurement site that is exposed to the outside. The other measurement site (second measurement site 22) is a covered measurement site that is covered with a covering 14 and insulated from the outside. The group of covered measurement sites and exposed measurement sites of these optical fibers 13 constitute a "flow direction determination unit 20" that can measure the wind direction, i.e., the flow direction (the flow direction determination unit 20 will be described later).

<Optical Fiber 13>
4 shows a main part of the optical fiber 13. An FBG 13c (Fiber Bragg Grating) is formed in the optical fiber 13 used in this embodiment. The measurement system 1 measures temperature by utilizing the FBG 13c in order to measure wind direction.

The optical fiber 13 has a linear core 13a and a cladding 13b that surrounds the core 13a. The light that enters the optical fiber 13 (incident light) is configured to propagate through the core 13a.

FBG 13c is a diffraction grating in which the refractive index of its core 13a is changed at a predetermined length period (grating period) along the extension direction of the optical fiber 13. FBG 13c reflects only light of a specific wavelength (Bragg wavelength) according to the grating period of the incident light, and transmits light of other wavelengths.

Each measurement site is composed of an FBG 13c. The FBG 13c of the first measurement site 21 and the FBG 13c of the second measurement site 22 have different grating periods. As a result, the wavelengths of the light reflected (reflected light) are different between the first measurement site 21 and the second measurement site 22 (λ1, λ2). The difference in wavelength allows the reflected light L1 of the first measurement site 21 and the reflected light L2 of the second measurement site 22 to be distinguished.

When the temperature at the measurement site changes, a distortion occurs at the measurement site in response to the temperature change, causing the FBG 13c to expand and contract. When the FBG 13c expands and contracts, the grating period changes accordingly. As a result, the reflected light of the FBG 13c shifts to the shorter or longer wavelength side depending on the change in the Bragg wavelength.

For example, as shown in the lower diagram of Figure 4, when the temperature of the first measurement site 21 changes, the wavelength λ1 of the reflected light L1 shifts to wavelength λ1'. Similarly, when the temperature of the second measurement site 22 changes, the wavelength λ2 of the reflected light L2 shifts to wavelength λ2'.

The change in the wavelength of this reflected light has a linear correlation with the change in temperature of the measurement site. Therefore, the temperature of the measurement site can be determined from the degree of change in the wavelength of the reflected light, in other words, the amount of distortion of the measurement site. The measuring device 30 directs a laser beam into each of the optical fibers 13 and measures the temperature of each measurement site from the reflected light.

<Measuring device 30>
5A shows a block diagram illustrating the functional configuration of the measurement device 30. The measurement device 30 of this embodiment includes a control unit 31, a light emitting unit 32, a light receiving unit 33, a power supply unit 34, and a processing unit 35. Although not shown, the measurement device 30 is electrically connected to an external power source to receive a supply of power.

The control unit 31 controls the operation of the light-emitting unit 32, the light-receiving unit 33, the current-carrying unit 34, and the processing unit 35 in accordance with the operation of the measuring device 30. The light-emitting unit 32 has a light source. The light-emitting unit 32 emits a laser beam of a predetermined wavelength into each of the optical fibers 13 in accordance with the control of the control unit 31. The light-receiving unit 33 receives the light reflected from each of the optical fibers 13 and outputs the information to the processing unit 35.

The power supply unit 34, under the control of the control unit 31, applies electricity to the heater 11 to perform a process of heating the heater 11 (heating process). The control unit 31 controls the amount of electricity to be applied, thereby controlling the heating state of the heater 11. This adjusts the temperature of the heater 11. Information regarding the amount of electricity applied is output to the processing unit 35.

The processing unit 35 executes various processes in cooperation with the control unit 31. For example, the processing unit 35 executes a process (temperature measurement process) of measuring the temperature of each of the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 in a heated state. The processing unit 35 also executes a process (heat transfer coefficient calculation process) of calculating the heat transfer coefficient of each optical fiber 13 in the flow direction identification unit 20 based on the difference in temperature measured at each of the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13.

Furthermore, the processing unit 35 executes a process (flow direction determination process) for determining the wind direction in the flow direction determination unit 20 based on the circumferential distribution of the heat transfer coefficient in the flow direction determination unit 20. The processing unit 35 has flow direction determination information 35a in order to execute this flow direction determination process. The flow direction determination information 35a is made up of information such as a map, and is obtained in advance by experiments or the like. The flow direction determination information 35a specifies the relationship between the wind direction in the flow direction determination unit 20 and the circumferential distribution of the heat transfer coefficient.

Figure 5B shows an example of a graph of flow direction identification information 35a. The horizontal axis is the central angle of the measurement sensor 10 placed in the fluid, i.e., in the flowing air. This angle corresponds to the wind direction. In this graph, a central angle of 0 degrees is set to "upwind." The vertical axis represents the heat transfer coefficient around the measurement sensor 10 that corresponds to the central angle. In the flow direction identification information 35a, multiple graphs (information) are defined according to the strength of the wind speed (specifically, according to the Reynolds number).

<Flow direction identification unit 20>
As described above, the flow direction identification unit 20, which identifies the wind direction, is composed of an exposed measurement portion (first measurement portion 21) and a covered measurement portion (second measurement portion 22) of a group of optical fibers 13 arranged in a ring shape around the heater 11.

By carrying out the heating process, the heater 11 is heated to a predetermined temperature. This indirectly heats the portion of each optical fiber 13 around the heater 11, i.e., the flow direction identification portion 20. If there is no wind around the flow direction identification portion 20, the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 are also heated to approximately the same temperature as the heater 11. Therefore, in this state, no temperature difference occurs between the first measurement portion 21 and the second measurement portion 22.

In contrast, when there is wind around the flow direction identification unit 20, the exposed first measurement portion 21 is cooled by heat exchange with the air. The temperature of the covered second measurement portion 22 is maintained. Therefore, in this state, a temperature difference occurs between the first measurement portion 21 and the second measurement portion 22. If the wind speed is strong, the temperature difference becomes larger.

By executing the temperature measurement process, the temperatures of the first measurement location 21 and the second measurement location 22 of each optical fiber 13 are measured. Because the first measurement location 21 and the second measurement location 22 of each optical fiber 13 are adjacent to each other, it can be assumed that the wind direction and wind speed for both of them are approximately the same. Therefore, the processing unit 35 calculates the heat transfer coefficient of each optical fiber 13 from the temperature difference. The second measurement location 22 functions as a reference that serves as the standard for the temperature.

Specifically, the processing unit 35 calculates the heat transfer coefficient of each optical fiber 13 using the following predetermined relational equation:

Heat input = heat transfer area x heat transfer coefficient x temperature change ("・" indicates multiplication)
The amount of heat input corresponds to the amount of heat given to each optical fiber 13, and is determined by the amount of electricity supplied to the heater 11. The heat transfer area is a specific value determined by the structure of the measurement sensor 10, such as the inner circumferential surface of the capillary 12. The temperature change is determined by the temperature difference between the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 being measured.

That is, the heat transfer coefficient of each optical fiber 13 in the flow direction identification unit 20 can be calculated from the amount of electricity supplied to the heater 11 and the temperature difference between the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13. The processing unit 35 calculates the heat transfer coefficient of each optical fiber 13 in the flow direction identification unit 20 by executing a heat transfer coefficient calculation process. Then, the processing unit 35 uses the calculated heat transfer coefficient to identify the wind direction in the flow direction identification unit 20, as described next.

<Determining wind direction>
6A illustrates a simplified model M (cylinder) corresponding to the measurement sensor 10. Wind flows from the direction indicated by the arrow A1. The wind that strikes the windward portion (indicated by P1) of the simplified model M is divided into two and flows along the outer circumferential surface.

Most of the split wind separates from the simplified model M at the furthest points on either side of the windward area P1, and flows downwind. These separation points are indicated by P2 and P4.

Due to turbulence generated at separation points P2 and P4, some of the diverted wind does not separate from the simplified model M, but flows along the outer periphery on the downwind side. These winds collide at the downwind point (indicated as P3) located furthest downwind of the simplified model M, and flow downwind, away from the simplified model M.

As a result, differences in the heat transfer coefficient occur on the outer periphery of the simple model M. At the windward portion P1, the heat transfer coefficient is high due to the collision of the wind. At the separation portions P2 and P4 (specifically, slightly downwind of the separation portions P2 and P4), the heat transfer coefficient is high due to the turbulence generated by the separation. At the leeward portion P3, the heat transfer coefficient is high due to the turbulence generated by the collision. As a result, the heat transfer coefficient changes significantly in the vicinity of these portions P1 to P4, and peaks occur.

The heat transfer coefficient increases symmetrically near the two separation sites P2 and P4. The heat transfer coefficient increases between the windward site P1 and the leeward site P3. The heat transfer coefficient near the windward site P1 and the leeward site P3 has a different value and changes from the heat transfer coefficient near the two separation sites P2 and P4. These changes in heat transfer coefficient occur at a specified central angle with respect to the wind flow.

Figure 6B shows a schematic diagram of the measurement sensor 10. Figure 6C shows an example of flow direction identification information 35a corresponding to Figure 6B. In Figure 6B, the direction indicated by arrow A2 is the upwind direction. This direction is also set as the central angle of the measurement sensor 10 at 0 degrees, with the central angle increasing clockwise. The optical fiber 13 located at the central angle of 0 degrees is set as the first optical fiber 13, and the optical fibers 13 in the clockwise direction are set sequentially as the second to twelfth optical fibers 13. The position of each optical fiber 13 is indicated by its number.

When the measurement sensor 10 in FIG. 6B is compared with the simplified model M in FIG. 6A, the heat transfer coefficients of the fourth and fifth optical fibers 13 located near the peeling sites P2 and P4 and the heat transfer coefficients of the ninth and tenth optical fibers 13 are high. In addition, the heat transfer coefficients of the first optical fiber 13 located near the windward site P1 and the seventh optical fiber 13 located near the leeward site P3 are also high. These heat transfer coefficients have a specific distribution in the circumferential direction, as shown in FIG. 6C.

The circumferential distribution of the heat transfer coefficient has the four peaks (first to fourth peaks Pk1 to Pk4) mentioned above. The first and second peaks Pk2 and Pk4 correspond to the heat transfer coefficients of the fourth and fifth optical fibers 13 and the ninth and tenth optical fibers 13. The third peak Pk3 corresponds to the heat transfer coefficient of the seventh optical fiber 13. And the first peak Pk1 corresponds to the heat transfer coefficient of the first optical fiber 13.

In this way, a unique distribution of heat transfer coefficient corresponding to the wind direction is formed around the measurement sensor 10. The measurement system 1 measures the wind direction based on this circumferential distribution of heat transfer coefficient.

<Wind direction measurement using measurement system 1>
Fig. 7 illustrates main processes performed by the measurement system 1 to measure the wind direction in the engine room 100. The measurement sensor 10 and the measurement device 30 are disposed in predetermined positions shown in Fig. 1 and Fig. 2, respectively. When the measurement device 30 is activated to start measuring the wind direction, the control unit 31 energizes the heater 11 to heat it (step S1).

The control unit 31 is preset with a target heating temperature. The control unit 31 heats the heater 11 until the temperature of the heater 11 reaches the heating temperature. Then, when the temperature of the heater 11 reaches the heating temperature (Yes in step S2), the light emitting unit 32 outputs a laser beam to each of the optical fibers 13 at that timing (step S3).

When the laser beam incident on each optical fiber 13 reaches the first measurement site 21 and the second measurement site 22, a specific wavelength of reflected light is reflected at each of them. At this time, distortion occurs at each of these measurement sites 21, 22 according to its temperature. The wavelength of the reflected light also changes in response to the amount of distortion.

The light receiving unit 33 receives the light reflected from each of the optical fibers 13 and obtains information regarding the change in wavelength (step S4). The light receiving unit 33 then outputs the information to the processing unit 35. The processing unit 35 calculates the amount of distortion of each of the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 based on the information input from the light receiving unit 33 (step S5).

The processing unit 35 further calculates the temperature of each of the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 from the amount of strain (step S6). The processing unit 35 then calculates the difference in temperature measured at each of the adjacent first measurement portion 21 and second measurement portion 22 of each optical fiber 13 from the calculated temperatures (step S7).

The processing unit 35 substitutes the temperature difference between the first measurement portion 21 and the second measurement portion 22 of each optical fiber 13 and the amount of electricity supplied to the heater 11 into the above-mentioned predetermined relational expression. This calculates the heat transfer coefficient of each optical fiber 13 in the flow direction identification unit 20 (step S8). As a result, the processing unit 35 obtains the circumferential distribution of the heat transfer coefficient in the flow direction identification unit 20.

The processing unit 35 compares the acquired circumferential distribution of the heat transfer coefficient in the flow direction identification unit 20 with the flow direction identification information 35a. The acquired circumferential distribution of the heat transfer coefficient in the flow direction identification unit 20 has a unique distribution corresponding to the wind direction in the flow direction identification unit 20. The processing unit 35 identifies the wind direction in the flow direction identification unit 20 based on the unique distribution (step S9).

In other words, by comparing the circumferential distribution of heat transfer coefficients obtained by the flow direction identification unit 20 with the flow direction identification information 35a, a waveform graph (information) that matches the distribution can be found. Since the wind direction and central angle are associated in each graph, the wind direction (upwind position) can be identified from the graph with the matching distribution.

<Number of Optical Fibers 13>
In the above-described embodiment, an example was shown in which the wind direction was determined by the measurement sensor 10 in which twelve optical fibers 13 were arranged all around the heater 11. However, taking into consideration the unique distribution of the heat transfer coefficient, the wind direction can be determined by three or more optical fibers 13 if they are arranged so as to be distributed at least in a range exceeding 90 degrees in central angle.

Here, "three or more optical fibers 13 are arranged so that they are distributed over a range that exceeds at least 90 degrees in terms of the central angle" specifically means the following. That is, in the heater 11, a cross section taken perpendicular to its longitudinal direction is defined as the heating element cross section. At the acquisition position of the heating element cross section, the group of optical fibers 13 is arranged so that the central angle defined by the center of the heating element cross section and the positions of two optical fibers 12, 12 (the two optical fibers 12, 12 located at both ends in the circumferential direction) that are one end and the other end of the heating element cross section in the group of three or more optical fibers 13 is greater than 90 degrees.

As shown in FIG. 8(a), a measurement sensor 10 is used as an example in which optical fibers 13 are arranged at three points (points A, B, and C) around a heater 11, the points being arranged at a predetermined central angle. Points A and C are separated by a central angle of 90 degrees or more (α>90 degrees). Measurements are performed using this measurement sensor 10 in the same manner as the measurement system 1 described above.

The obtained values of the heat transfer coefficient of each optical fiber 13 are then provisionally plotted on the flow direction identification information 35a according to the central angle of each point, as shown in FIG. 8(b). In this example, the heat transfer coefficient of point A is plotted at a central angle of 0 degrees (a position corresponding to the windward direction) on the flow direction identification information 35a, and the heat transfer coefficients of points B and C are also plotted at positions according to their respective central angles. In this example, the plots of each point do not match any of the graphs at the provisional positions.

The plots of each point at the provisional position are then slid in the circumferential direction as shown by the arrows in Figure 8(b) to search for a matching graph. Then, as shown in Figure 8(c), a graph is found where the plots of each point match (overlap), and the central angle β moved from the provisional position is identified.

In this flow direction identification information 35a, the provisional position with a central angle of 0 degrees corresponds to upwind. Therefore, as shown in FIG. 8(d), the flow direction identification information 35a can identify the position at the central angle β back from the provisional position as upwind.

Even if there are a large number of optical fibers 13, if they are arranged within a central angle of 90 degrees, the unique distribution of heat transfer coefficient in the circumferential direction caused by the four peaks cannot be utilized. Therefore, the wind direction cannot be identified. On the other hand, if they are arranged within a central angle of more than 90 degrees, as described above, the wind direction can be identified even with three optical fibers 13.

However, it is preferable to have a large number of optical fibers 13. This allows the circumferential distribution of heat transfer coefficient to be obtained with high accuracy. This makes it easier to compare with flow direction identification information, allowing the wind direction to be measured with high accuracy.

<Modification>
9A shows a modified example of the measurement sensor 10. In the above-described embodiment, a plurality of thin tubes 12 are arranged around the heater 11, and the optical fiber 13 is inserted therein. In contrast, in this modified example, a thick cylindrical body 40 surrounds the heater 11. The body 40 is made of a material with excellent thermal conductivity, such as an aluminum alloy. The inner surface of the body 40 is in close contact with the outer surface of the heater 11. Therefore, when the heater 11 generates heat, the heat is directly transferred to the body 40.

A number of pores 41 extending parallel to the heater 11 are provided in the outer periphery of the cylindrical body 40, aligned in the circumferential direction. The inner diameter of these pores 41 is slightly larger than the outer diameter of the optical fiber 13. A slit 42 is provided between two adjacent pores 41, cutting toward the center of the cylindrical body 40.

That is, the outer peripheral portion of the tube 40 divided into multiple pieces by the slits 42 corresponds to the thin tube 12 in the above-mentioned embodiment. Each optical fiber 13 is inserted through these fine holes 41. Therefore, these fine holes 41 also provide the same effect as the thin tube 12. Each optical fiber 13 can be heated more evenly and effectively than the thin tube 12. This modified example is also advantageous in that it is easier to process than arranging multiple thin tubes 12.

<Application Examples>
9B shows an application example of the measurement system 1. In the above-described embodiment, the measurement system 1 is exemplified as measuring the wind speed at one point at the tip of the measurement sensor 10. In contrast, the measurement system 1' is configured so that the measurement sensor 10 can measure the wind speed at multiple points. In other words, the measurement system 1' can simultaneously measure the wind direction at multiple points.

To achieve this, the heater 11 and the thin tube 12 that constitute the measurement site are extended from the tip portion of the measurement sensor 10 toward the base portion. An optical fiber 13 is inserted into each thin tube 12. Furthermore, flow direction determination units 20 are provided at multiple locations spaced apart in the extension direction (four locations in the illustrated example).

Each of the group of optical fibers 13 constituting each of these flow direction determination units 20 is provided with a pair of measurement sites (first measurement site 21 and second measurement site 22) as described above. However, the FBG 13c of each of these multiple measurement sites is formed with a different grating period so that reflected light can be identified. This allows the processing unit 35 to identify the measurement sites and measure the temperature, even if there are many of them.

The measurement system 1' of this application example can measure wind speeds at multiple locations simultaneously, allowing for efficient and highly accurate wind direction measurement. In addition, this measurement system 1' can measure not only the wind direction at multiple locations, but also the strength of the wind at multiple locations.

That is, as shown in FIG. 5B, the flow direction identification information 35a specifies multiple pieces of information according to the strength of the wind speed. When specifying the wind direction, the actually measured heat transfer coefficients at multiple locations are compared with the heat transfer coefficients specified according to the strength of the wind speed. Therefore, the strength of the wind speed can be identified. In this case, since the actually measured heat transfer coefficients are obtained under the same wind force conditions, it is possible to measure the difference in wind direction at each location as well as the relative difference in wind force. Therefore, more advanced measurements can be performed.

<Another embodiment>
In the above-described embodiment, modified example, and application example, a case has been exemplified in which all processing is performed by one completed measurement system 1. However, in an experiment or the like, there may be cases in which wind direction is measured by combining existing devices, equipment, etc. In particular, devices that measure temperature using optical fiber 13 have been put to practical use. Therefore, in this embodiment, a method of measuring wind direction using such a device is exemplified.

In this measurement method, the wind direction is measured using a temperature measuring device 30 that can measure with multiple optical fibers 13. The heater 11, optical fibers 13, thin tube 12, and covering 14 constitute the measurement sensor 10 as in the above-mentioned embodiment.

Each optical fiber 13 has a pair of adjacent measurement sites (first measurement site 21 and second measurement site 22) at the same location in the longitudinal direction. The number of optical fibers 13 may be three or more.

Each of the optical fibers 13 is inserted into the thin tube 12 and arranged so that it extends parallel to the periphery of the heater 11 that can be heated. They are arranged so that they are distributed over a range that exceeds at least a central angle of 90 degrees. Then, one of the measurement sites is covered with a covering ring 14. This forms the flow direction identification unit 20. The measurement sensor 1 may be configured as a modified example or application example.

Then, the measurement sensor 10 is placed in the air flow so that the flow direction identification unit 20 is located at the measurement point (preparation step). The heater 11 is then heated while measuring the amount of current passing through it (heating step). The temperature measuring device 30 is operated at a predetermined timing to measure the temperature of each of the first measurement location 21 and the second measurement location 22 (temperature measurement step).

By using a personal computer or the like, the difference in temperature measured at the adjacent first measurement portion 21 and second measurement portion 22 of each optical fiber 13 is calculated from the measured temperature. Furthermore, the heat transfer coefficient of each optical fiber 13 in the flow direction identification unit 20 is calculated based on the calculated temperature difference and the information on the amount of current flow (heat transfer coefficient calculation step).

Then, the calculated circumferential distribution of the heat transfer coefficient of each optical fiber 13 is compared with the flow direction identification information 35a. In this way, the wind direction in the flow direction identification unit 20 is identified (flow direction identification step).

This measurement method allows for immediate and highly accurate measurement of wind direction using only existing equipment. Measurements can be made even in small, complex spaces, making it ideal for measuring wind direction inside the engine room 100.

The measurement system etc. relating to the disclosed technology is not limited to the above-mentioned embodiment, but also includes various other configurations.

For example, in the embodiment, "air" is exemplified as the fluid to be measured. However, the fluid to be measured may be a gas other than air, or a liquid such as water.

In the previous embodiment, a case was exemplified in which the heating process using a heating element and the measurement process of temperature and wind direction using optical fiber were performed by a single measurement device. However, these heating processes and measurement processes may each be performed by separate devices.

Methods for measuring temperature using optical fibers are not limited to those that use reflected light from an FBG. Temperature may also be measured using scattered light, as in the device of Patent Document 1.

1 Measurement system 10 Measurement sensor 11 Heater (heating element)
12 Thin tube 13 Optical fiber 13a Core 13b Clad 13c FBG
14 Covering (cover body)
20 Flow direction identification unit 21 First measurement portion (exposure measurement portion)
22 Second measurement site (covered measurement site)
30. Measuring Equipment

Claims (8)

1. A flow direction measurement system comprising:
a heatable heating element disposed to extend into the fluid;
Three or more optical fibers are arranged around the heating element so as to be able to heat the heating element evenly and are arranged so as to extend parallel to the longitudinal direction of the heating element;
a cover body that covers an outer peripheral side of the heating element and a part of the group of optical fibers;
a measuring device that controls a heating state of the heating element and measures a temperature with each of the optical fibers by irradiating light to the optical fibers;
Equipped with
In the heat generating element, when a cross section taken perpendicular to the longitudinal direction of the heat generating element is defined as a heat generating element cross section,
At the acquisition position of the cross section of the heating element, the three or more optical fibers are arranged so that a central angle defined by a cross-sectional center of the cross section of the heating element and positions of two optical fibers among the three or more optical fibers that are in a one-end and other-end relationship in the circumferential direction of the cross section of the heating element is greater than 90 degrees;
each of the optical fibers has a pair of adjacent measurement sites at the same position in the longitudinal direction thereof, where temperature measurements are performed;
one of the measurement sites is a covered measurement site that is covered with the cover body, and the other of the measurement sites is an exposed measurement site that is not covered with the cover body;
a flow direction determining unit capable of measuring a flow direction is configured by the coated measurement portion and the exposed measurement portion of the group of optical fibers,
The measuring device comprises:
A heat treatment for heating the heating element;
a temperature measurement process for measuring the temperatures of the covered measurement portion and the exposed measurement portion in a heated state;
a heat transfer coefficient calculation process for calculating a heat transfer coefficient of each of the optical fibers in the flow direction specifying unit with respect to the fluid based on a heating state of the heating element and a difference in temperature measured at each of the adjacent covered measurement portions and exposed measurement portions of each of the optical fibers;
a flow direction identification process for identifying a flow direction of the fluid in the flow direction identification unit based on a circumferential distribution of a heat transfer coefficient in the flow direction identification unit;
A flow directional measurement system that performs 2. The flow direction measurement system according to claim 1,
the measurement site is made of an FBG that reflects reflected light whose wavelength changes in response to distortion of the measurement site,
the measurement device has flow direction identification information that defines a relationship between a flow direction of the fluid in the flow direction identification unit and a circumferential distribution of a heat transfer coefficient,
The measuring device includes:
In the temperature measurement process, the reflected light reflected from each of the covered measurement sites and each of the exposed measurement sites is acquired, and a temperature of each of the covered measurement sites and each of the exposed measurement sites is calculated based on a change in wavelength of the acquired reflected light ;
a flow direction measurement system for identifying a flow direction of the fluid in the flow direction identifying unit by comparing a circumferential distribution of heat transfer coefficient in the flow direction identifying unit with the flow direction identifying information in the flow direction identifying process. 3. The flow direction measuring system according to claim 1,
A flow direction measurement system comprising a plurality of thin tubes having an inner diameter slightly larger than the outer diameter of the optical fiber and having thermal conductivity, the thin tubes being arranged to extend parallel to the periphery of the heating element, and each of the optical fibers being inserted into the thin tubes. 4. The flow direction measurement system according to claim 3,
A flow direction measurement system, in which the multiple thin tubes are arranged around the entire circumference of the heating element, either in contact with each other or separated by a small gap. 3. The flow direction measuring system according to claim 1,
The heating element further includes a thermally conductive cylinder surrounding the heating element,
a plurality of pores having an inner diameter slightly larger than an outer diameter of the optical fiber and extending parallel to the heating element are provided in an outer peripheral portion of the cylindrical body with slits interposed therebetween;
A flow directional measurement system, wherein each of said optical fibers is threaded through said aperture. In the flow direction measurement system according to any one of claims 1 to 5,
A flow direction measurement system, wherein the flow direction specifying portion is provided at intervals in a longitudinal direction of the group of optical fibers, and flow direction measurement is performed simultaneously at a plurality of locations. In the flow direction measurement system according to any one of claims 1 to 6,
A flow direction measurement system, the fluid being air, for measuring wind direction. A method for measuring a flow direction using a predetermined measuring device, comprising:
The measuring device includes:
Three or more optical fibers are arranged around a heatable heating element so as to be able to heat the heating element evenly and are arranged so as to extend parallel to the longitudinal direction of the heating element;
a cover body that covers the heating element and an outer peripheral side of a part of the group of optical fibers;
a measurement control unit that controls incident light into the optical fibers to measure a temperature at each of the optical fibers;
Equipped with
In the heat generating element, when a cross section taken perpendicular to the longitudinal direction of the heat generating element is defined as a heat generating element cross section,
At the acquisition position of the cross section of the heating element, the three or more optical fibers are arranged so that a central angle defined by a cross-sectional center of the cross section of the heating element and positions of two optical fibers among the three or more optical fibers that are in a one-end and other-end relationship in the circumferential direction of the cross section of the heating element is greater than 90 degrees;
each of the optical fibers has a pair of adjacent measurement sites at the same position in the longitudinal direction thereof, where temperature measurements are performed;
one of the measurement sites is a covered measurement site that is covered by the cover body, and the other of the measurement sites is an exposed measurement site that is not covered by the cover body, and the covered measurement site and the exposed measurement site constitute a flow direction specifying unit that is capable of measuring the flow direction,
A preparation step of placing the heating element and the group of optical fibers in the fluid so that the flow direction specifying portion is located at a measurement point;
A heating step of heating the heating element;
a temperature measuring step of measuring temperatures of the covered measurement portion and the exposed measurement portion by operating the measurement device;
a heat transfer coefficient calculation step of calculating a heat transfer coefficient of each of the optical fibers in the flow direction specifying unit with respect to a fluid based on a heating state of the heating element and a difference in temperature measured at each of the adjacent covered measurement portions and exposed measurement portions of each of the optical fibers;
a flow direction identifying step of identifying a flow direction of the fluid in the flow direction identifying portion based on a circumferential distribution of a heat transfer coefficient in the flow direction identifying portion;
A method for measuring flow direction, including:

Images