EP-4469809-B1 - FLUID FLOW SENSORS

Inventors

• JIMENEZ-GARCIA, Antonio
• DEMERLE, Nils

Dates

Publication Date

20260513

Application Date

20230120

Claims (10)

1. An acoustic resonance fluid flow sensor (400, 500, 600) comprising: a first reflector surface (410, 510, 610); a second reflector surface (420, 520. 620) spaced apart from the first reflector surface; a generally cylindrical cavity (430. 530. 630) between the first and second reflector surfaces, the cavity comprising a central longitudinal axis; and a plurality of transducers (140, 141, 142) located in the first reflector surface, at least one transducer of the plurality of transducers occupying a space from a first radial distance from the longitudinal axis to a second radial distance from the longitudinal axis; wherein the cavity further comprises a narrowest part where a separation between the first and second reflector surfaces is a minimum distance, the minimum distance being less than a separation between the first and second reflector surfaces along the longitudinal axis, and wherein the narrowest part at least partially surrounds the longitudinal axis, characterized in that the narrowest part is at least partially located between the first radial distance and the second radial distance from the longitudinal axis.
2. A fluid flow sensor according to claim 1, wherein one of the first and second reflector surfaces comprises a ridge (440, 650) surrounding a centre of that reflector surface and wherein the narrowest part of the cavity is defined between the ridge and the other of the first and second reflector surfaces.
3. A fluid flow sensor according to claim 2 wherein the ridge is a continuous annular ridge that surrounds the centre of the reflector surface on which it is formed.
4. A fluid flow sensor according to claim 2 or claim 3 wherein the ridge has an arc-shaped cross-section.
5. A fluid flow sensor according to any preceding claim, wherein at least one of the first and second reflector surfaces comprises an indentation (540, 640) at least partially surrounded by the narrowest part of the cavity.
6. A fluid flow sensor according to claim 5 wherein the indentation is concave.
7. A fluid flow sensor according to any preceding claim further comprising a lip (860) surrounding at least one of the first and second reflector surfaces.
8. A fluid flow sensor according to any preceding claim, wherein the at least one transducer has a centre at a third radial distance from the longitudinal axis, and wherein the narrowest part is at least partially located at a radial location between the second radial distance and half of the third radial distance.
9. A fluid flow sensor according to any preceding claim wherein the at least one transducer comprises a centre at a third radial distance from the longitudinal axis, and wherein the narrowest part of the cavity is entirely located at a distance of at least half the third radial distance from the longitudinal axis.
10. A fluid flow sensor according to any preceding claim wherein the narrowest part of the cavity is entirely located at least a distance equal to 30% of a radius of a smaller of the first and second reflector surfaces from the longitudinal axis.

Description

FIELD OF THE INVENTION The present invention relates to fluid flow sensors. BACKGROUND TO THE INVENTION Acoustic resonance fluid flow sensors measure the speed and direction of fluid flow by measuring excited acoustic waves in a cavity at a resonant frequency thereof. The cavities of such sensors are typically defined between a pair of reflector surfaces and acoustic waves are typically excited and measured within the cavity by electro-acoustic transducers in one of the reflector surfaces. US 5,877,416 A discloses an anemometer comprising an acoustic resonant cavity between two plates and open in the direction of flow of a fluid, the cavity having at least one pair of electro acoustic transducers which are energised at an Eigenfrequency to produce a standing wave perpendicular to the direction of flow of the fluid and a travelling wave perpendicular to the standing wave. SUMMARY OF THE INVENTION According to an embodiment of the invention, there is provided an acoustic resonance fluid flow sensor comprising: a first reflector surface; a second reflector surface spaced apart from the first reflector surface; a generally cylindrical cavity between the first and second reflector surfaces, the cavity comprising a central longitudinal axis; and a plurality of transducers located in the first reflector surface, at least one transducer of the plurality of transducers occupying a space from a first radial distance from the longitudinal axis to a second radial distance from the longitudinal axis. The cavity further comprises a narrowest part where a separation between the first and second reflector surfaces is a minimum distance, the minimum distance being less than a separation between the first and second reflector surfaces along the longitudinal axis. The narrowest part at least partially surrounds the longitudinal axis and is at least partially located between the first radial distance and the second radial distance from the longitudinal axis. In some embodiments, one of the first and second reflector surfaces comprises a ridge surrounding a centre of that reflector surface. The narrowest part of the cavity may be defined between the ridge and the other of the first and second reflector surfaces. The ridge may be continuous annular ridge that surrounds the centre of the reflector surface on which it is formed and/or may have an arc-shaped cross section. The ridge may be comprised by the second reflector surfaces, may be radially symmetric (and/or axisymmetric) about the longitudinal axis. The ridge may be at least partially surround the centre of the reflector surface by which it is comprised. The ridge may comprise an inclined inner face facing towards the longitudinal axis, which may be arranged to surround the centre of the reflector surface by which it is comprised. The reflector surface comprising the ridge may comprise an area more distant from the longitudinal axis than the ridge that is substantially flat and which surrounds the ridge. The ridge may be located entirely further from the longitudinal axis than 30% of a radius of a smaller of the first and second reflector surfaces. The ridge may comprise a crest located entirely between a radius from the longitudinal axis equal to 55% of a radius of a smaller of the first and second reflector surfaces and a radius equal to 80% of the radius of the smaller of the first and second reflector surfaces. In some embodiments, at least one of the first and second reflector surfaces comprises an indentation at least partially surrounded by the narrowest part of the cavity. The indentation may be concave. The reflector surface comprising the indentation may comprise an area more distant from the longitudinal axis than the indentation and which surrounds the indentation, wherein the surrounding area is substantially flat. The narrowest part of the cavity may be defined between this area and the other of the first and second reflector surfaces. The reflector surface comprising the indentation may further comprise a ridge as described above. An edge of the ridge may be flush with a lip of the indentation. The indentation may be radially symmetric or axisymmetric about the longitudinal axis. In some embodiments, the sensor further comprises a lip surrounding at least one of the first and second reflector surfaces. The lip may be entirely located at a greater distance from the longitudinal axis than the second radial distance. The lip may surround the first reflector surface, and/or may surround a reflector surface opposite a reflector surface comprising an annular ridge and/or central indentation. In some embodiments, the lip may not overlap the narrowest part in a view/projection along the longitudinal axis. In some embodiments, the at least one transducer has a centre at a third radial distance from the longitudinal axis, and wherein the narrowest part is at least partially located at a radial location between the second radial distance and half of the third radial di