GB2111680A - Vortex flowmeter - Google Patents

Abstract

A vortex flowmeter has a bluff body 11 mounted as a cantilever across a fluid passageway 10 and means for detecting the frequency of the oscillations induced in the body as a result of the alternating vortex pressure created by the shedding of vortices in response to fluid flow through the passageway. The body 11 may comprise, or be constituted solely by, an optical fibre. <IMAGE>

Description

SPECIFICATION Vortex flowmeter This invention relates to a vortex flowmeter, particularly a miniature vortex flowmeter which may be used, for example, to monitor the fuel and air flow in an internal combustion engine.

In a vortex flowmeter, the relative speed of fluid flowing through a passageway is determined from measurements of the frequency at which vortices are shed from a bluff (nonstreamlined) body disposed in the fluid stream. The term fluid employed herein is understood to include both liquids and gases.

Prior art meters have included various forms of sensor for sensing the pressure variations in the fluid produced by the shed vortices.

In our co-pending application 8114743, we disclose a particular form of sensor in which an optic fibre is contained within the bluff body, the fibre oscillating in response to the vortices shed by the body. An optical signal is transmitted to the fibre along a single fibre optic cable, the oscillating fibre then modulating the reflected signal which is fed back along the cable. A frequency measurement and output unit finally converts the received modulation frequency to a fluid velocity or volume flow measure.

In accordance with the present invention, a vortex flowmeter comprises a hollow body defining a fluid passageway, a bluff elastic body mounted across the passageway in such a manner that vortices shed by the body in response to fluid flow through the passageway induce oscillations of the body at a frequency dependent on the frequency of shedding, and a frequency sensor for sensing the frequency of the oscillations.

The bluff body is preferably mounted as a cantilever, and the sensor preferably includes an optic fibre forming at least part of the cantilevered body construction. The sensor may alternatively be in the form of strain gauges, PZT/PVF2, magnetic, or capacitative.

By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic side view of a vortex meter embodying the invention, Figure 2 is an end view of the meter, and, Figure 3 is a perspective view of one possible configuration for the bluff body.

Referring to these drawings, the flowmeter includes a pipe 10 forming a fluid passageway. A bluff body 11 is cantilevered off the wall of the pipe and extends substantially across the pipe diameter.

The bluff body 11 may have the shape shown in Fig. 3, consisting of an optic fibre 14 and an integral plate 15. Other bluff body shapes would of course be possible. An optical signal is transmitted to the optic fibre 1 4 through a single-optic-fibre cable 12, the signal being reflected by a mirror 1 3 disposed in the wall of the pipe 10 opposite the free end of the fibre 14. The reflected signal is transmitted back to a receiver along the optic cable 12, the transmitter and the receiver being coupled to the optic cable by a Ycoupler as more fully described in our copending application 8114743.

When fluid flows through the pipe 10, vortices are shed from the bluff body 11, and the alternating vortex pressure displaces the bluff body at right angles to the flow causing the fibre to oscillate at the vortex frequency.

The oscillations are illustrated on an exaggerated scale by the dashed outlines in Fig. 2.

The resulting oscillations of the fibre 1 4 with respect to the fixed mirror 1 3 modulates the intensity of the returned optical signal, and this modulating frequency is detected in the receiver to derive a frequency output proportional to the rate of fluid flow.

Other fibre flexure modulation techniques, such as microbending loss or speckle pattern effects, may be used in place of the fixed mirror system.

If the whole of the bluff body 11 is formed as an optic fibre, motion of the body in the direction of flow is preferably constrained by a rigid constraining member 1 6 downstream of the body.

While the invention has been described with respect to a flowmeter in which fluid flows through a hollow body, it is equally applicable to flowmeters in which the body is moved through the fluid as in a ship's log.

1. A vortex flowmeter comprising a hollow body defining a fluid passageway, a bluff body mounted across the passageway in such a manner that vortices shed by the body in response to fluid flow through the passageway induce oscillations of the body at a frequency dependent the frequency of shedding, and a frequency sensor for sensing the frequency of the oscillations.

2. A flowmeter according to claim 1 in which the body is an elongate body mounted as a cantilever.

3. A flowmeter according to claim 2 in which the sensor includes an optic fibre movable with the cantilevered body.

4. A flowmeter according to claim 3 in which the fibre forms the, or is contained within, the cantilevered body.

5. A flowmeter according to claim 3 or claim 4, in which the optic fibre extends the length of the elongate body to the free end thereof, and in which light reflecting means are positioned in the passageway opposite the said free end.

6. A flowmeter according to claim 1 and substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Vortex flowmeter This invention relates to a vortex flowmeter, particularly a miniature vortex flowmeter which may be used, for example, to monitor the fuel and air flow in an internal combustion engine. In a vortex flowmeter, the relative speed of fluid flowing through a passageway is determined from measurements of the frequency at which vortices are shed from a bluff (nonstreamlined) body disposed in the fluid stream. The term fluid employed herein is understood to include both liquids and gases. Prior art meters have included various forms of sensor for sensing the pressure variations in the fluid produced by the shed vortices. In our co-pending application 8114743, we disclose a particular form of sensor in which an optic fibre is contained within the bluff body, the fibre oscillating in response to the vortices shed by the body. An optical signal is transmitted to the fibre along a single fibre optic cable, the oscillating fibre then modulating the reflected signal which is fed back along the cable. A frequency measurement and output unit finally converts the received modulation frequency to a fluid velocity or volume flow measure. In accordance with the present invention, a vortex flowmeter comprises a hollow body defining a fluid passageway, a bluff elastic body mounted across the passageway in such a manner that vortices shed by the body in response to fluid flow through the passageway induce oscillations of the body at a frequency dependent on the frequency of shedding, and a frequency sensor for sensing the frequency of the oscillations. The bluff body is preferably mounted as a cantilever, and the sensor preferably includes an optic fibre forming at least part of the cantilevered body construction. The sensor may alternatively be in the form of strain gauges, PZT/PVF2, magnetic, or capacitative. By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic side view of a vortex meter embodying the invention, Figure 2 is an end view of the meter, and, Figure 3 is a perspective view of one possible configuration for the bluff body. Referring to these drawings, the flowmeter includes a pipe 10 forming a fluid passageway. A bluff body 11 is cantilevered off the wall of the pipe and extends substantially across the pipe diameter. The bluff body 11 may have the shape shown in Fig. 3, consisting of an optic fibre 14 and an integral plate 15. Other bluff body shapes would of course be possible. An optical signal is transmitted to the optic fibre 1 4 through a single-optic-fibre cable 12, the signal being reflected by a mirror 1 3 disposed in the wall of the pipe 10 opposite the free end of the fibre 14. The reflected signal is transmitted back to a receiver along the optic cable 12, the transmitter and the receiver being coupled to the optic cable by a Ycoupler as more fully described in our copending application 8114743. When fluid flows through the pipe 10, vortices are shed from the bluff body 11, and the alternating vortex pressure displaces the bluff body at right angles to the flow causing the fibre to oscillate at the vortex frequency. The oscillations are illustrated on an exaggerated scale by the dashed outlines in Fig. 2. The resulting oscillations of the fibre 1 4 with respect to the fixed mirror 1 3 modulates the intensity of the returned optical signal, and this modulating frequency is detected in the receiver to derive a frequency output proportional to the rate of fluid flow. Other fibre flexure modulation techniques, such as microbending loss or speckle pattern effects, may be used in place of the fixed mirror system. If the whole of the bluff body 11 is formed as an optic fibre, motion of the body in the direction of flow is preferably constrained by a rigid constraining member 1 6 downstream of the body. While the invention has been described with respect to a flowmeter in which fluid flows through a hollow body, it is equally applicable to flowmeters in which the body is moved through the fluid as in a ship's log. CLAIMS

1. A vortex flowmeter comprising a hollow body defining a fluid passageway, a bluff body mounted across the passageway in such a manner that vortices shed by the body in response to fluid flow through the passageway induce oscillations of the body at a frequency dependent the frequency of shedding, and a frequency sensor for sensing the frequency of the oscillations.

2. A flowmeter according to claim 1 in which the body is an elongate body mounted as a cantilever.

3. A flowmeter according to claim 2 in which the sensor includes an optic fibre movable with the cantilevered body.

4. A flowmeter according to claim 3 in which the fibre forms the, or is contained within, the cantilevered body.

5. A flowmeter according to claim 3 or claim 4, in which the optic fibre extends the length of the elongate body to the free end thereof, and in which light reflecting means are positioned in the passageway opposite the said free end.

6. A flowmeter according to claim 1 and substantially as herein described with reference to the accompanying drawings.