Lichtwellenleitererfassungssystem

Abstract

Optical fiber detection system comprising: a housing (14) arranged in a flow path (12); and an optical fiber sensor (16, 42) comprising: an optical fiber (28) fixed in the housing (14) and having a Bragg grating (36), the optical fiber extending substantially perpendicular to the flow path (12), the housing (14) having an opening (24) on an upstream side to allow the flow through the flow path (12) to exert pressure on the optical fiber (28) and cause deformation of the Bragg grating (36); a light source (38) for transmitting light to the optical fiber (28); and a detector (39) for detecting light filtered through the Bragg grating (36) of the optical fiber (28) and for monitoring wavelength changes of the detected light;characterized in that the housing (14) contains a substantially right-angled passage (18) with an upstream channel (20) extending in an original flow direction (D) of the flow path (12) and a downstream channel (22) extending substantially at right angles to the upstream channel (20), which has a downstream opening (26) at its downstream end.

Description

BACKGROUND The invention relates generally to detection technologies and in particular to fiber optic detection devices. Various detection devices for measuring fluid or gas flow parameters, such as flow velocity, pressure, temperature, mass flow rate, and the like, are known. For example, JP 2005-3535A discloses a fiber optic detection system having the features of the preambles of independent claims 1 and 4. A fiber optic detection system with a housing arranged in a flow path and a fiber optic sensor comprising a fiber optic cable fixed in the housing, a Bragg grating, a light source for transmitting light to the fiber optic cable, and a detector for detecting the light filtered by the Bragg grating of the fiber optic cable and for monitoring wavelength changes of the detected light is also known from EP 1179727A1 and US 2006 / 0011820A1.However, conventional measurement devices are relatively complex to implement for flow measurements through sections that are difficult to access, such as cooling flows or leakage flows through seals. It would be desirable to have an improved data collection device with a relatively small size. SHORT DESCRIPTION In accordance with an embodiment of the present invention disclosed herein, an optical fiber detection system is provided. The optical fiber detection system comprises a housing arranged in a flow path and an optical fiber sensor. The optical fiber sensor includes an optical fiber fixed in the housing, a Bragg grating, a light source for transmitting light to the optical fiber, and a detector for detecting the light filtered by the Bragg grating of the optical fiber and for monitoring wavelength changes of the detected light. The optical fiber runs substantially perpendicular to the flow path. The housing has an opening on one side upstream to allow flow through the flow path, thereby exerting pressure on the optical fiber and causing deformation of the Bragg grating.The housing has a substantially right-angled passage with an upstream channel running in an original flow direction of the flow path and a downstream channel running substantially perpendicular to the upstream channel, which has a downstream opening at its downstream end. In accordance with another embodiment of the present invention disclosed herein, an optical fiber detection system is provided. The optical fiber detection system comprises a housing arranged in a flow path and an optical fiber sensor. The housing has a polygonal cross-section and at least one pair of sides, the apex of the polygonal cross-section being mainly directly facing the flow path. The optical fiber sensor comprises an optical fiber fixed in the housing. The optical fiber runs substantially perpendicular to the flow path and has a Bragg grating. The housing has an opening on an upstream side to allow the flow through the flow path to exert pressure on the optical fiber and cause deformation of the Bragg grating.The optical fiber sensor further comprises a light source for transmitting light to the optical fiber and a detector for detecting light filtered through the Bragg gratings of the optical fiber and for monitoring wavelength changes of the detected light. The housing has a triangular cross-section, with one apex of the triangle substantially facing the flow path, and with a pair of sides, the housing having a first opening, a second opening, and a third opening at the apex and in the pair of sides. DRAWING These and other features, aspects, and advantages of the present invention will be better understood if the following detailed description is read with reference to the accompanying drawing, in which the same reference numerals in the drawing consistently represent the same parts, in which: Fig. 1 is a cross-section of an optical fiber sensing system for measuring the differential pressure of a flow according to one embodiment of the invention. Fig. 2 illustrates a wavelength change of the Bragg grating due to pressure exerted on the conductor. Fig. 3 is a cross-sectional view of an optical fiber sensing system for measuring the differential pressure and static pressure of a flow according to another embodiment of the invention. Fig. 4 is an enlarged view illustrating the reflection and transmission of light in a recess in the optical fiber sensing system according to Fig. 3.Fig. 5 is a cross-sectional view of an optical fiber sensing system for measuring the total pressure and the static pressure of the flow according to yet another embodiment of the invention. Fig. 6 is a cross-sectional view of an optical fiber sensing system for measuring the flow direction and the total pressure of the flow according to yet another embodiment of the invention. Fig. 7 is a cross-sectional view of an optical fiber sensing system along lines 7-7 according to Fig. 6. Fig. 8 is a side view of an optical fiber sensing system for measuring the total pressure, the differential pressure, and the temperature of the flow according to yet another embodiment of the invention. Fig. 9 is a cross-sectional view along line 9-9 according to Fig. 8.10 a wavelength change of three Bragg gratings due to corresponding changes in the total pressure, differential pressure and temperature of the flow is illustrated by the embodiments according to Fig. 8 and Fig. 9. DETAILED DESCRIPTION Exemplary embodiments of the invention disclose optical fiber detection systems for measuring the flow parameters of a fluid (liquid or gas). The optical fiber detection system comprises optical fiber sensors, each of which has a Bragg grating. By monitoring changes in the wavelength of the detected light, the differential pressure, static pressure, flow velocity, and / or temperature of the flow can be measured. For the sake of simplicity, the same reference numerals are used for identical elements in different embodiments. Fig. 1 illustrates an optical fiber detection system comprising a housing 14 arranged in a flow path 12 and an optical fiber sensor 16. The optical fiber sensor 16 includes an optical fiber 28 mounted in the housing 14, with a Bragg grating 36 attached to it. The optical fiber 28 runs substantially perpendicular to the flow path, and the housing 14 has an opening on its upstream side to allow flow through the flow path, thereby exerting pressure on the optical fiber 28 and causing deformation of the Bragg grating 36. The optical fiber sensor 16 further comprises a light source 38 for transmitting light through the optical fiber 28 and a detector 39 for detecting light filtered through the Bragg grating of the optical fiber and for monitoring wavelength changes of the detected light. Fig. 1 further illustrates an exemplary light source conductor detection system for measuring the differential pressure in the flow path 12. The fluid flow through the flow path 12 generally proceeds in a flow direction D, and accordingly, the two terms "downstream" and "upstream" are defined with respect to the flow direction D, as they are used below. In the embodiment according to Fig. 1, the housing 14 includes a substantially right-angled passage 18 with an upstream channel 20 extending in the flow direction D and a downstream channel 22 extending substantially perpendicular to the flow direction D. The upstream and downstream channels 20 and 22 each have an upstream opening 24 in a front face of the housing 14 and a downstream opening 26 in a bottom face of the housing 14. In the embodiment according to Fig.1 The optical fiber sensor 16 contains an optical fiber 28, which is generally arranged perpendicular to the flow direction D and whose upper and lower ends are fixed and sealed in the housing 14, so that the optical fiber ends are not in contact with the flow path 12. The optical fiber 28 contains a core 27 and an outer layer 29 that surrounds the core 27, and a central section 30 of the optical fiber 28 is arranged in the upstream channel 20 adjacent to the downstream channel 22. The fluid therefore flows through the upstream opening 24 into the passage 18 and out of the passage 18 through the downstream opening 26, with the central section 30 of the optical fiber 28 having one side 32 subjected to the total pressure Pt of the fluid flow and another side 34 subjected to the static pressure Ps of the fluid flow. The total pressure Pt and the static pressure Ps exerted on the optical fiber 28 due to the flow 12 depend on Bernoulli's equation: where "Pd" is the dynamic pressure or differential pressure, which is proportional to the square of the flow velocity according to the following equation: where p is the fluid density in kg / m³ and u is the flow velocity in m / s. Accordingly, the deformation of the optical fiber 28 is proportional to the differential pressure Pd and is in turn a measure of the flow velocity u. With further reference to Fig. 1, the optical fiber sensor 16 further comprises a Bragg grating 36 in the optical fiber 28, a light source 38 for emitting light into the optical fiber 28, and a detector 39 that receives the light reflected by the Bragg grating 36. In one embodiment, the Bragg grating 36 comprises a distributed periodic grating in the central section 30 of the optical fiber 28, while in another embodiment, the Bragg grating 36 is arranged below or above the central section 30 in the optical fiber 28. The light source 38 can, for example, be a tunable laser, an LED, a laser diode, or any other quasi-monochromatic light source capable of scanning over a wavelength range typically of 1400 to 1500 nanometers. The Bragg grating 36 can be introduced into the optical waveguide 28 by any known prior art method, and in one example, such fabrication involves the use of an interference pattern of ultraviolet light to generate a permanent modulation of the refractive index. When light from the light source 38 is transmitted through the optical waveguide 28 to the Bragg grating 36, light energy is reflected by the Bragg grating at a corresponding Bragg wavelength, which is given by the following equation: where “λB” is the Bragg wavelength, “neff” is the refractive index, and “Λ” is the grating period. Both the refractive index neff and the grating period Έ� of the grating 36 are functions of temperature and deformation. Thus, the differential pressure Pd exerted on the Bragg grating 36 causes a deformation of the grating 36, which leads to a change in the Bragg wavelength of the reflected light. In Fig. 2, the waveform shown with a solid line is the original wavelength λ at which no pressure is exerted perpendicularly on the optical fiber 28, and the waveform shown with a dashed line is the wavelength λ shifted due to a differential pressure Pd. Accordingly, the differential pressure can thus be obtained by monitoring the Bragg wavelength shift Δλ by correlating the Bragg wavelength shift Δλ with the differential pressure Pd. Optical fiber sensors are useful because they are relatively small and sensitive to deformation. Therefore, the optical fiber detection system can be used in flow regimes that are difficult to access, such as cooling flows or leakage flows through seals in gas turbine engines. Fig. 3 shows a fiber optic sensing system 40 according to another embodiment of the invention for measuring both the differential pressure Pd and the static pressure Ps, in which a fiber optic sensor 42 comprises an optical Fabry-Perot sensor including a dielectric membrane 44, which is attached to a lower end region of the housing 14 and below the fiber optic cable 28. The fiber optic cable 28 has a lower end 46. The membrane 44 has an inner surface 47 facing the fiber optic cable 28 and an outer surface 49 exposed to the flow path 12 and subjected to the static pressure Ps. A recess 48 with a distance d is formed between the lower end 46 of the fiber optic cable 28 and the inner surface 47 of the membrane 44. Referring to Fig. 4, the light from the light source 38 (Fig. 3) is transmitted through the optical fiber and partially emitted into the recess 48. The lower end of the optical fiber 28 and the membrane 44 have refractive indices n1 and n2, respectively, and in one embodiment, n1 = n2. The recess 48 has a refractive index nc, which differs from the refractive indices n1 and n2. The light emitted into the recess 48 comprises a reflected light component 50, which is reflected into the recess 48 between the lower end 46 of the optical fiber 28 and the membrane 44, and a transmitted light component 52, which is transmitted from the recess 48 through the lower end 46 of the optical fiber 28 and received by the detector 39. Assuming normal reflection conditions, the transmitted light component 52 does not interact further with the recess 48. The outer surface 49 of the membrane 44 is exposed to the static pressure Ps to be measured.An increase in static pressure Ps causes the membrane 44 to deflect towards the recess 48. As a result of the pressure increase, the inner surface of the membrane 44 is curved, thus changing the angle of reflection for the light reflected from the inner surface of the membrane 44. The intensity of the light reaching the detector 39, compared to the intensity of the light in the recess 48, is correlated with the pressure (static pressure Ps) acting on the outer surface 49 of the membrane 44. Accordingly, the static pressure Ps can be measured by measuring the intensity of the light from the recess 48. Fig. 5 illustrates an optical fiber sensing system 60 according to another embodiment of the invention for measuring both the total pressure Pt and the static pressure Ps in the flow path 12. The illustrated optical fiber sensing system 60 comprises an elongated housing 64 with a central recess 66 therein and an optical fiber sensor 62, which is mounted in the central recess 66 of the housing 64. The optical fiber sensor 62 has a comparable configuration to the optical fiber sensor 42 according to Fig. 3 and has an optical fiber 28 mounted in the central recess 66 of the housing 64, a Bragg grating 36 in the optical fiber 28, a diaphragm 44 below a lower end 46 of the optical fiber 28, and a recess 48 between the lower end 46 and the diaphragm 44. The housing 64 is arranged in a flow path 12 in one direction substantially perpendicular to the flow direction D. The housing 64 has an upstream opening 68 on an upstream side, which is connected to the central recess 66. The total pressure Pt exerted on the optical fiber 28 through the opening 68 causes a deformation of the optical fiber 28 and, in turn, causes a wavelength shift of the light through the Bragg grating 36 as described above. By monitoring the wavelength shift of the Bragg grating 36, the total pressure Pt of the flow 12 can be obtained. In certain embodiments, the optical fiber detection system 60 also includes a sealing membrane 67 to prevent the flow 12 from entering the central recess 66 through the opening 68, but to allow the total pressure Pt of the flow 12 to act on the optical fiber 28.In certain embodiments, a groove or recess 69 is provided adjacent to the downstream side of the optical fiber 28 to allow deformation of the optical fiber 28 under the overall pressure. The groove or recess 69 can be provided in the optical fiber 28 and / or in the housing 64. The membrane 44 is attached to the lower end of the housing 64 and is subjected to the static pressure Ps. As described above, a change in the distance d of the recess 48 causes a change in the intensity of the light transmitted from the recess 48, which correlates with the static pressure Ps. Accordingly, the static pressure Ps of the flow 12 can be obtained by monitoring the change in the intensity of the light from the recess 48. Figures 6 and 7 illustrate a fiber optic detection system 70 according to another embodiment of the invention for measuring the flow direction and total pressure Pt of the flow 12. Referring to Figure 6, the fiber optic detection system 70 comprises a fiber optic sensor 71 and a housing 72 for holding the fiber optic sensor 71. In one embodiment, the fiber optic sensor 71 has at least three fiber optics, comprising a first, second, and third fiber optic cable 73, 74, and 75. In one embodiment, the housing 72 has a cross-section in the form of an isosceles triangle, wherein the apex of the isosceles triangle generally points against the flow through the flow path 12, and two sides are arranged symmetrically with respect to the general flow direction.A first opening 76 is provided at the apex of the housing 72, and a second and third opening 77 and 78 are symmetrically arranged on the two sides. The first, second, and third optical fibers 73, 74, and 75 are mounted in the housing 72 and each has a section located in the first, second, and third openings 76, 77, and 78, respectively. In other embodiments, the housing can have a polygonal cross-section with an odd number of sides. The flow passes through the flow path 12 onto the sensor mounted at the apex of the polygon. At least one pair of sides is arranged symmetrically with respect to the general flow direction, and each side has an opening. In yet another embodiment, the housing 72 can have other cross-sectional shapes. The first, second, and third optical fibers 73, 74, and 75 each have a measuring surface exposed through the openings 76, 77, and 78, respectively.The orientations of the measuring surfaces each form an angle with each other. Each of the optical waveguides 73, 74, and 75 has a Bragg grating 36. In some embodiments, all Bragg gratings are identical. Referring to the preceding description in conjunction with Fig. 5, each of the optical waveguides 73, 74, and 75 deforms due to the fluid flow through the flow path 12. If the flow proceeds exactly in the flow direction D, the wavelength of light transmitted or reflected by the Bragg grating 36 in the first optical waveguide 73 is an indication of the total pressure Pt, while the pressures acting on the Bragg gratings 36 of the second and third optical waveguides 74 and 75 are lower than the total pressure and cause the same wavelength shift. If the flow direction changes, the total detected pressure acting on the Bragg grating 36 of the first optical waveguide 73 will decrease, and the pressures measured by the second and third optical waveguides 74 and 75 will change.For example, the flow direction and total pressure can be obtained by prior calibration and the establishment of a reference table. In one embodiment, the optical fiber sensor 71 further comprises a processing unit 79 (Fig. 7) for receiving signals from the detector 39 and for determining the flow direction. In another embodiment, the processing unit 79 is embedded in the detector 39, so that the detector 39 performs the determination task. In yet another embodiment, the velocity and its direction can be determined by an algorithm developed during the calibration of the optical fiber sensor 71, which can be implemented on a computer or a similar data acquisition system. Referring to Fig. 7, which illustrates a cross-sectional view along line 7-7 according to Fig. 6, in one embodiment a sealing membrane 67 is provided between the first optical waveguide 73 and the first opening 66 to prevent the flow 12 from entering the housing 72 through the first opening 76, but to allow the pressure of the flow 12 to reach the first optical waveguide 73. In certain embodiments, the opening 76 is arranged so that it is not adjacent to the Bragg grating 36 of the first optical waveguide 73 in order to protect the Bragg grating 36 from damage. In one embodiment, a groove or recess 69 is provided downstream with respect to the Bragg grating 36 to allow sufficient deformation of the first optical waveguide 73 under the pressure of the flow 12.In certain embodiments, the housing 72 has the same arrangement for holding the second and third optical waveguides 74 and 75 as for the first optical waveguide 73 according to Fig. 7. Figures 8 and 9 illustrate an optical fiber sensing system 80 according to another embodiment of the invention for measuring the total pressure Pt, the differential pressure Pd, and the temperature in the flow path 12. The optical fiber sensing system 80 comprises an optical fiber 82, a housing 84 holding the optical fiber 82, and a first, second, and third Bragg grating 86, 87, and 88 in the optical fiber 82 for measuring the differential pressure Pd, the total pressure Pt, and the temperature, respectively. In one embodiment, the Bragg gratings 86, 87, and 88 are provided in a common optical fiber 82. Referring to Figures 8 and 9, the housing 84 is provided in the flow path 12 and is arranged such that the optical fiber 82 held in the housing 84 runs substantially perpendicular to the flow direction.The optical waveguide 82 contains a first, second, and third section 90, 91, and 92, which feature the first, second, and third Bragg gratings 86, 87, and 88, respectively. The housing 84 has a lateral through-hole 94, which generally aligns with the flow direction and is located adjacent to the first section 90 of the optical waveguide 82. The flow from the flow path 12 partially passes through the through-hole 94. Accordingly, the differential pressure Pd causes a deformation of the first section 90 of the optical waveguide 82, which deforms in a downstream direction. The wavelength changes of the first Bragg grating 86 correlate with the differential pressure Pd of the flow 12. By monitoring the wavelength changes of the first Bragg grating 86, the differential pressure Pd can be determined.In certain embodiments, the Bragg grid 86 is positioned higher or lower than the through-hole 94 to protect the Bragg grid 86 from damage. In one embodiment, a recess or groove 100 is provided on the downstream side of the Bragg grid 86 to allow sufficient deformation of the first section 90 under the differential pressure of the flow. The housing 84 has a side opening 96 adjacent to the second section 91 of the optical waveguide 28. A sealing membrane 67 is provided between the optical waveguide 82 and the side opening 96 to prevent the flow from entering the housing 84 through the side opening 96, but to allow the total pressure of the flow 12 to act on the second section 91 of the optical waveguide 82. Accordingly, the second section 91 of the optical waveguide 28 is exposed to the total pressure Pt of the flow 12, and thus the wavelength change of the second Bragg grating 87 is correlated with the total pressure Pt of the flow 12. By monitoring the wavelength changes of the second Bragg grating 87, the total pressure Pt of the flow 12 can be obtained. In certain embodiments, the first and second sections 90 and 91 can each have an upper and lower end attached to the housing 84 by means of holders, and therefore the deflection of the first and second sections 90 and 91 will not be transferred to the other section. If the temperature of the third Bragg grating 88 increases by ΔT, the Bragg wavelength of the third Bragg grating 88 shifts towards a longer wavelength due to thermal expansion effects on the modulation of the refractive index and the grating period of the third Bragg grating 88. Thus, a temperature change in the flow path 12 can be monitored by monitoring the wavelength shift of the third Bragg grating 88. The housing 84 has a recess 98, and the Bragg grating 88 in the recess 98 is sensitive to temperature changes. In one embodiment, a fixed cover 102 is provided in the recess 98 to further block the influence of any pressure from the flow path 12 on the third section 92 of the optical waveguide 82. In certain embodiments, wavelength changes of the first and second Bragg gratings 86 and 87 due to temperature changes in the flow are further adjusted based on the measurement from the third Bragg grating 88. Referring to Fig. 10, in one embodiment, arrangements of first, second, and third Bragg gratings 86, 87, and 88 have different reflection spectra and reflect at different wavelengths λB1, λB2, and λB3. Therefore, the detector 39 receives all three wavelengths λB1, λB2, and λB3 of the first, second, and third gratings 86, 87, and 88 and monitors their changes. Unless otherwise specified, technical and scientific terms used herein have the same meanings as they are normally understood by a person skilled in the art in the field to which this invention belongs. The terms "first," "second," and the like, as used herein, do not denote any order, quantity, or relevance, but are used to distinguish one element from another. Similarly, the terms "a," "a," and "one" do not denote any limitation of number, but rather indicate the presence of at least one of the named items. Terms such as "front," "back," "below," and / or "above" are used merely for convenience of description and are not limited to any position or spatial arrangement unless otherwise specified. While the invention has been described with reference to exemplary embodiments, it is understood by a person skilled in the art that various modifications can be made and equivalents can replace their elements without departing from the scope of the invention. Furthermore, many modifications can be made to adapt a particular situation or material to the teachings of the invention without leaving its fundamental scope. Therefore, it is intended that the invention is not limited to the specific embodiment disclosed as a preferred embodiment for carrying out the invention, but rather that the invention encompasses all embodiments falling within the scope of the appended patent claims. It is understood that not all of the above-described objectives or advantages can necessarily be achieved with a particular embodiment. Therefore, for example, a person skilled in the art will recognize that the systems and techniques described herein can be implemented or carried out in a manner that achieves or optimizes one or more of the advantages taught herein, without necessarily achieving other objectives or advantages that may be taught or suggested herein. Furthermore, the person skilled in the art will recognize the interchangeability of various features of different embodiments. The various described features, as well as other known equivalents for each feature, can be combined and adapted by a person skilled in the art to design further systems and techniques in accordance with the principles of this disclosure. A fiber optic detection system comprises a housing 14 arranged in a flow path 12 and a fiber optic sensor 16. The fiber optic sensor 16 includes a fiber optic cable 28 mounted in the housing 14, a Bragg grating 36, a light source 38 for directing light to the fiber optic cable 28, and a detector 39 for detecting the light filtered through the Bragg grating 36 of the fiber optic cable 28 and for monitoring wavelength changes of the detected light. The fiber optic cable 28 is arranged substantially perpendicular to the flow path 12. The housing 14 has an opening 24 on an upstream side to allow the flow along the flow path 12 to exert pressure on the fiber optic cable 28 and cause deformation of the Bragg grating 36. Parts list: 12 Flow 14 Housing 16 Optical fiber sensor 18 Right-angle opening 20 Upstream channel 22 Downstream channel 24 Upstream opening 26 Downstream opening 28 Optical fiber 27 Optical fiber core 28 29 Outer layer of optical fiber 28 30 Central section of optical fiber 28 32 Side exposed to total pressure Pt 34 Side exposed to static pressure Ps 36 Bragg grating 38 Light source 39 Detector 40 Optical fiber detection system 42 Optical fiber sensor 44 Dielectric membrane 46 Lower end of optical fiber 28 48 Recess 47 Inner surface of membrane 44 49 Outer surface of membrane 44 50 Reflected light component 52 Transmitted light component 60 Optical fiber detection system 62 Optical fiber sensor 64 Housing 66 Central recess 68 Upstream opening of the housing 64 67 Sealing membrane 69 Recess,Groove 70 Fiber optic detection system 71 Fiber optic sensor 72 Housing 73 First fiber optic cable 74 Second fiber optic cable 75 Third fiber optic cable 76 First opening in housing 77 Second opening in housing 78 Third opening in housing 79 Computing unit 80 Fiber optic detection system 82 Fiber optic cable 84 Housing 86 First Bragg grating 87 Second Bragg grating 88 Third Bragg grating 90 First section of fiber optic cable 82 91 Second section of fiber optic cable 82 92 Third section of fiber optic cable 82 94 Through hole 96 Opening 98 Recess 100 Recess, groove 102 Fixed cover

Claims

Optical fiber detection system comprising: a housing (14) arranged in a flow path (12); and an optical fiber sensor (16, 42) comprising: an optical fiber (28) fixed in the housing (14) and having a Bragg grating (36), the optical fiber extending substantially perpendicular to the flow path (12), the housing (14) having an opening (24) on an upstream side to allow the flow through the flow path (12) to exert pressure on the optical fiber (28) and cause deformation of the Bragg grating (36); a light source (38) for transmitting light to the optical fiber (28); and a detector (39) for detecting light filtered through the Bragg grating (36) of the optical fiber (28) and for monitoring wavelength changes of the detected light;characterized in that the housing (14) contains a substantially right-angled passage (18) with an upstream channel (20) extending in an original flow direction (D) of the flow path (12) and a downstream channel (22) extending substantially at right angles to the upstream channel (20), which has a downstream opening (26) at its downstream end. Optical fiber detection system according to claim 1, wherein the optical fiber (28) is arranged in the upstream channel (20) with one side (32) being exposed to the total pressure (Pt) of the flow and with another side (34) being exposed to the static pressure (Ps) of the flow. Optical fiber detection system according to claim 2, wherein the optical fiber sensor (42) further comprises a membrane (44) attached to the housing (14) which faces an end (46) of the optical fiber (28), with a recess (48) formed in the housing (14) between the membrane (44) and the end (46) of the optical fiber (28), and wherein the membrane (44) is subjected to static pressure (Ps). Optical fiber detection system comprising: a housing (72) arranged in a flow path (12); and an optical fiber sensor (71) comprising: an optical fiber (73) mounted in the housing (72) and having a Bragg grating (36), the optical fiber extending substantially perpendicular to the flow path (12), the housing (72) having an opening (76) on an upstream side to allow the flow through the flow path (12) to exert pressure on the optical fiber (73) and cause deformation of the Bragg grating (36); a light source (38) for transmitting light to the optical fiber (73); and a detector (39) for detecting light filtered through the Bragg grating (36) of the optical fiber (73) and for monitoring wavelength changes of the detected light;characterized in that the housing (72) has a triangular cross-section, with one apex of the triangle mainly facing directly towards the flow path (12), and with a pair of sides, wherein the housing (72) has a first opening (76), a second opening (77) and a third opening (78) in the apex and in the pair of sides. Optical fiber detection system according to claim 4, in which a first optical fiber (73), a second optical fiber (74) and a third optical fiber (75) are provided, each having a region that faces the first opening (76) or the second opening (77) or the third opening (78). Optical fiber detection system according to claim 5, wherein the optical fiber sensor (71) further comprises a computing unit (79) for receiving signals from a detector (39) and for determining a flow direction. Optical fiber detection system according to claim 1 or 4, wherein the Bragg grating (36) is arranged downstream of the aperture (24, 76).

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