GB2223316A

GB2223316A - Fluid velocity sensor

Info

Publication number: GB2223316A
Application number: GB8816328A
Authority: GB
Inventors: Patrick Lawrence Corley-Byrne; Peter John Barkway
Original assignee: LEIGH INSTR; Plessey Co Ltd
Current assignee: LEIGH INSTR; Plessey Co Ltd
Priority date: 1988-07-08
Filing date: 1988-07-08
Publication date: 1990-04-04
Anticipated expiration: 2008-07-08
Also published as: GB8816328D0; GB2223316B

Abstract

A fluid velocity sensor which is useful in hovering aircraft and helicopters where air speeds of less than 60 knots need to be measured accurately comprises an air box (10) having a circular venturi (12) in its upper surface which serves to produce a cone of air (A) from high pressure air fed to the box (10) through an air inlet (14). The air stream to be measured impinges upon the air cone (A) and causes it to be deflected or distorted, such deflection or distortion being detected by pressure ports (16, 18, 20) which are connected through respective pipes (24) to pressure transducers where the air speed and direction is calculated with the aid of a micro-processor. <IMAGE>

Description

Fluid Velocity Sensor This invention relates to a fluid velocity sensor which measures both the speed and direction of a fluid.

Its primary application is in air where low velocities (less than 60 knots) need to be measured accurately. For this reason the invention will be described with particular reference to the air application, but it is to be understood that the device will also function in other fluids.

In GB-B-1,089,180 there is described a fluid flow measuring device which comprises a power nozzle, means for connecting the nozzle to a pressure fluid source to cause a jet of fluid to issue from the nozzle, receiver means including a pair of receiver mouths, means mounting the receiver means to space the receiver mouths from the nozzle substantially in the direction of flow of the jet, with each mouth oriented to receive fluid from the jet, means for locating the nozzle and the receiver mouths in the fluid stream with the jet extending directly across the stream direction and with the receiver mouths spaced apart in the stream direction, and means connected to the receiver means for . measuring the differential fluid pressure between the receiver mouths.

The aim of the present invention is to devise a fluid velocity sensor which is an improvement over this earlier device both as regards its construction and operation, and according to the invention, a fluid velocity sensor comprises a circular venturi which, for applications in air, receives high pressure air and forms it into a cone of air, and means for detecting deflection or distortion of the cone of air as the air stream to be measured impinges upon it.

The sensor of the invention finds particular application in hovering aircraft and helicopters, but it can also be used for higher speeds, especially where a flush-mounted unit is required. It is omni-directional in a given plane and will indicate wind speed and direction over 3600. Moreover, it has no moving parts in the air stream and is very reliable with low weight and drag.

An example of a fluid velocity sensor in accordance with the invention is shown in the accompanying drawings, in which Figure 1 is a vertical section through the sensor; Figure 2 is a top plan view of the sensor shown in Figure 1; and Figures 3 and 4 are sections similar to Figure 1 to illustrate the cones of air produced by the sensor.

The illustrated fluid velocity sensor comprises an air box 10 of circular section having a top opening 12 in the form of a circular venturi opening. An air inlet 14 is connected to an air compressor (not shown) or other source of air under pressure so that high pressure air is fed to the narrow circular venturi 12 and forms a cone of air A above the centre of the sensor as shown in Figure 3.

Three equi-distant pressure ports 16, 18 and 20 are sited in the upper central area 22 of the air box 10 as shown in Figure 2, and these ports are connected by pipes or tubes 24 to pressure transducers (not shown).

Under zero air speed conditions, the high pressure cone A will be centered symmetrically above the three pressure ports as in Figure 3 so that their respective pressure transducers will record equal pressures. However, for any air speeds other than zero, the cone will be deflected or distorted by the external air flow F as shown at A' in Figure 4 so that differential air pressures will be produced at the three ports 16, 18 and 20 and at their respective transducers. The magnitude and relative position of these differential pressures will then be translated into a reading of air speed and direction over the skin 26 of the aircraft.

The high pressure air supply to the air inlet 14 does not present any special problem. Thus, in the case of gas turbine powered aircraft or helicopters, the simplest source of air would be a bleed supply from the H.P.

compressor. The amount of air required is very low and will therefore have negligible performance implications.

The use of warm air from the compressor will also have the advantage of keeping the sensor de-iced.

The pressure transducers connected to the pressure ports 16, 18 and 20 by the pipes 24 can be standard aircraft quality pressure transducers used preferably in the differential mode as the critical measurement will be the variation in pressure between the three ports. The differential pressure readings will then be fed to a small micro-processor which will carry out the necessary calculations to determine air speed and direction.

It is to be noted that the circular venturi 12 as defined by the opposing surfaces 28 and 30 tapers upwardly and inwardly so as to produce the air cone A. In the particular construction shown in the drawings, the frustoconical surface -28 is at an angle of about 450 to the horizontal, while the frusto-conical surface 30 is at an angle of about 570 to the horizontal. It is to be understood, however, that these figures are given by way of illustration only and that the invention is not restricted to a circular venturi of these specific dimensions.

Claims

1. A fluid velocity sensor comprising a circular venturi which, for applications in air, receives high pressure air and forms it into a cone of air, and means for detecting deflection or distortion of the cone of air as the air stream to be measured impinges upon it.

2. A sensor according to claim 1, in which the circular venturi is formed as a top opening in an air box which is preferably of circular section, there being an air inlet in the air box for the supply of compressed air thereto.

3. A sensor according to claim 1 or claim 2, in which the means for detecting deflection or distortion of the cone of air comprise pressure ports located inwardly of the circular venturi, the said pressure ports being connected by pipes or other passages to pressure transducers.

4. A sensor according to claim 3, in which the pressure transducers serve to detect differential pressures at the pressure ports for further translation into a reading of air speed and direction with the use preferably of a micro-processor.

5. A sensor according to claim 3 or claim 4, in which three equidistant pressure ports are located inwardly of the circular venturi.

6. A fluid velocity sensor substantially as described herein with reference to the accompanying drawings.

7. A hovering aircraft or helicopter incorporating a fluid velocity sensor as claimed in any preceding claim.

8. A hovering aircraft or helicopter according to claim 7, in which the sensor is flush-mounted on the aircraft skin.

9. A hovering aircraft or helicopter according to claim 7 or claim 8, in which the compressed air fed to the sensor is a bleed supply from the high pressure compressor of a gas turbine powering the aircraft or helicopter.