Undershot gate flow control system with flow diverter

An undershot gate system controls flow of liquid through an open channel or pipe. The system includes a gate leaf adapted to be raised and lowered by a control to allow flow of liquid along the open channel or pipe. The gate leaf has a flow diverter at an end of the gate leaf to guide liquid under the gate leaf and through an opening when the gate leaf is in an open position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application pursuant to 35 U.S.C. §371 of International Application No. PCT/AU2013/001185, filed Oct. 11, 2013, which claims priority to Australian Patent Application No. 2012904449, filed Oct. 11, 2012, the disclosures of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to flow measurement through a submerged orifice and relates particularly, but not exclusively, to flow measurement through an undershot irrigation gate.

SUMMARY OF THE INVENTION

According to one aspect, the present invention provides an undershot gate system to control flow of liquid through an open channel or pipe, said system including a gate leaf adapted to be raised and lowered by a control means to allow flow of liquid along said open channel or pipe, said gate including a flow diverter at an end of said gate leaf to guide liquid under said gate leaf and through an opening when said gate leaf is in an open position.

In one embodiment, said flow diverter includes a substantially horizontally disposed projection from one side of said end of said gate leaf, either upstream or downstream of said gate leaf. Preferably an arcuate section is provided along the free end of said substantially horizontally disposed projection.

In a further embodiment, said flow diverter includes an arcuate section along one side of said end of said gate leaf. Preferably said flow diverter further includes a substantially horizontally disposed projection from the other side of said end of said gate leaf.

Preferably said undershot gate system further includes a pair of acoustic transducers on the bottom of said open channel or pipe, adapted to provide an acoustic path to and from underneath said substantially horizontally disposed projection to allow measurement of the opening of said gate leaf.

Preferably said undershot gate system further includes a plurality of pairs of acoustic transducers forming an acoustic array on opposing sides of said open channel or pipe to provide, in use, a plurality of multiple planes of crossed acoustic paths for measurement of flow velocity through said gate opening.

In one embodiment, said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are downstream and adjacent said gate leaf.

In a further embodiment, said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are upstream and adjacent said gate leaf.

In yet a further embodiment, one set of respective acoustic transducers of said plurality of pairs of acoustic transducers on opposing sides of said open channel or. pipe are downstream and adjacent said gate leaf, and the other set of respective acoustic transducers of said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are upstream and adjacent said gate leaf, with said plurality of multiple planes of crossed acoustic paths crossing through said gate opening.

Preferably said plurality of pairs of acoustic transducers have a small beam angle to the direction of flow, to allow each acoustic array to have a shorter width.

According to a further aspect, the present invention provides an undershot gate system to control flow of liquid through an open channel or pipe, said system including a gate leaf adapted to be raised and lowered by a control means to allow flow of liquid along said open channel or pipe, a plurality of pairs of acoustic transducers forming an acoustic array on opposing sides of said open channel or pipe to provide, in use, a plurality of multiple planes of crossed acoustic paths for measurement of flow velocity through said gate opening, and a means to measure the height of the opening of said gate leaf.

Preferably said undershot gate system further includes a pair of acoustic transducers on the bottom of said open channel or pipe, adapted to provide an acoustic path to and from underneath said gate leaf to allow measurement of the opening of said gate leaf.

In one embodiment, said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are downstream and adjacent said gate leaf.

In a further embodiment, one set of respective acoustic transducers of said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are downstream and adjacent said gate leaf, and the other set of respective acoustic transducers of said plurality of pairs of acoustic transducers on opposing sides of said open channel or pipe are upstream and adjacent said gate leaf, with said plurality of multiple planes of crossed acoustic paths crossing through said gate opening.

Preferably said plurality of pairs of acoustic transducers have a small beam angle to the direction of flow, to allow each acoustic array to have a shorter width.

Preferably said undershot gate system further includes a flow diverter at an end of said gate leaf to guide liquid under said gate leaf, and through the gate opening, when said gate leaf is in an open position.

In one embodiment, said flow diverter includes an arcuate section along one side of said end of said gate leaf. Preferably said flow diverter further includes a substantially horizontally disposed projection from the other side of said end of said gate leaf.

In a further embodiment, said flow diverter includes a substantially horizontally disposed projection from one side of said end of said gate leaf, either upstream or downstream of said gate leaf. Preferably an arcuate section is provided along the free end of said substantially horizontally disposed projection.

According to yet a further aspect, the present invention provides a method of measuring flow rate of a liquid passing through an open gate of an undershot gate system installed in an open channel or pipe, said method including the steps of: providing a plurality of pairs of acoustic transducers forming an acoustic array on opposing sides of said open channel or pipe, said acoustic arrays producing a plurality of multiple planes of crossed acoustic paths; providing means to measure the height of said open gate relative to a base of said open channel or pipe; determining a vertical velocity profile of said liquid passing through said open gate utilising said acoustic arrays; determining the height of said open gate utilising said means to measure the height of said open gate relative to said base of said open channel or pipe; calculating a velocity integral of said vertical velocity profile utilising said determined height of said open gate; and, calculating said flow rate of said liquid passing through said open gate by multiplying said velocity integral by a predetermined internal width of said acoustic arrays.

These and other essential or preferred features of the present invention will be apparent from the description that now follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to avoid duplication of description, identical reference numerals will be shown, where applicable, throughout the illustrated embodiments to indicate similar integers.

The flow passing through a submerged rectangular orifice is commonly computed by the following energy equation:
Q=Ccw·h√{square root over (2g(u−d))}
Where:

Q=flow rate in m3/s

w=width of rectangular orifice opening in m

h=height of rectangular orifice opening in m

g=acceleration due to gravity in (m/s2)

u=water level upstream of orifice in m

d=water level downstream of orifice in m
Cc=contraction coefficient=depth of water jet behind orifice/orifice opening height

This equation is derived from Bernoulli's equation, which simply states that the sum of kinetic and potential energy is always a constant at constant pressure.
p+½ρV2+pgh=constant

p is the pressure

ρ is the density

V is the velocity

h is the elevation

g is the gravitational acceleration

The velocity is computed from Bernoulli's equation as the value:
V=√{square root over (2g(u−d))}

The flow rate is determined by multiplying this velocity by the apparent area of the jetting velocity field passing through the orifice.

This invention will allow the measurement of flow rate by measuring the jetting velocity field passing through a rectangular submerged orifice, and then multiplying this velocity field by the measured area of the rectangular submerged orifice.

InFIG. 1there is shown a submerged rectangular orifice or opening10between the end face12—of a vertically movable gate16and the floor14of an irrigation open channel. The jetting velocities of the flow through gate16need to be measured to provide an accurate flow rate of water flowing through gate16. The streamlines A to G show a typical profile upstream, through and downstream of gate16. It can be seen that the streamlines A to G passing through the orifice10are parallel to the floor14of orifice10. If there is a sufficient straight approach length upstream of the orifice10then the streamlines A to G are also parallel to the walls (not shown) enclosing each side of the orifice10.

It can be seen inFIG. 1that there is generally known to be a contraction of the streamlines A to G downstream of the orifice10such that the depth of the velocity field hi is less than the opening height of the orifice x; The ratio h1/x is commonly referred to as a contraction coefficient (Cc).FIG. 1shows that adjacent to the jetting streamlines A to G passing beneath the orifice10there is a stagnant region of water with a zero net velocity. The entire flow velocity passes through a depth h1. Hence the flow rate passing through the orifice can be determined by integrating the vertical velocity profile passing through orifice10through a vertical range bounded by the floor14of the orifice10and by the height h1of the velocity field and then multiplying this velocity integral by the known width of the orifice10. The height of the velocity field h1may be determined through knowledge of the vertical velocity distribution as measured by an acoustic array.

FIGS. 2 and 8show the inclusion of a pair of opposing acoustic arrays18,20downstream of gate16. Each pair of acoustic arrays includes a pair of acoustic transducers22,24which operate in a crossed path arrangement i.e. acoustic transducer22of array18interacts with the opposing acoustic transducer24of array20to provide multiple planes of crossed path acoustic transit time velocity measurements. Each acoustic array18,20consist of eight (or any number as is reasonably practicable) horizontal velocity measurement planes. The velocity field passing through the rectangular submerged orifice10is measured based on the transit time velocity measurement principle as previously described in International Patent Application No. PCT/AU2010/001052 (the contents of which are herein incorporated) and in the ISO Standard 16:2004(E) Hydrometry—Measurement of discharge by the ultrasonic (acoustic) method. Acoustic arrays18,20have a small beam path angle relative to the direction of flow of 11.25°, however any angle may be used as is practicable. The choice of a small beam angle allows the acoustic arrays18,20to have a short overall assembly width such that the measured field of view lies immediately in the vicinity of the submerged rectangular orifice10. The acoustic arrays18,20are arranged adjacent gate16to ensure that there is a sufficient straight approach length upstream of orifice, such that each of the streamlines A to G pass through the length of the acoustic arrays18,20at a constant angle relative to the parallel walls28,30, enclosing each side of the orifice10, and do not experience a change in direction as they pass through the length of the acoustic arrays18,20.

The multitude of measurement planes are combined in a vertical array to provide a high-resolution sample of the vertical velocity profile of the flow passing though the acoustic arrays18,20.FIG. 2illustrates that three velocity samples are available for computing the integral of the velocity field encompassed by the jetting flow streamlines. An abrupt transition is known to occur at the boundary of the jetting streamlines to a stationary water region behind the gate16with zero net velocity. The velocity field passing through the acoustic arrays18,20is vertically integrated from the floor14of the array to the ceiling of the array. It is known that the velocity field transitions abruptly from a high velocity to a zero velocity at the measured top boundary of the jetting velocity field. The location of the boundary of the velocity field can be determined by several means including by measurement of the gate opening height, and by analysis of the velocity profile observed by the acoustic planes located within the jetting velocity field. As the opening of the gate16changes, so does the boundary between the jetting flow and the stationary water along with the number of acoustic measurement planes incorporated into the velocity integration. Flow is computed by integrating this vertical velocity profile from the floor14of the acoustic arrays18,20to the ceiling of the acoustic arrays18,20, and multiplying this integral by the known internal width of the rectangular acoustic arrays18,20. If the gate16is opened above the water surface, such that there is a free water surface below the end face12of gate16, then the gate opening height is not used in the measurement of flow. In this instance the vertical velocity profile is integrated from the floor14of the acoustic arrays18,20, to the water level as measured by a water level sensor (not shown). This velocity integral is then multiplied by the known internal width of the rectangular acoustic arrays18,20to compute the flow rate passing through the acoustic arrays18,20. The orifice opening x may be measured by any suitable means including linear encoder, drawstring, or by an acoustic transducer (not shown) which measures the distance between the floor14of the orifice10and the end face12of gate16.

Seals or a sealing compound46will prevent leakage between sidewalls28,30and acoustic arrays18,20. Similarly, seals or a sealing compound48will prevent leakage between sidewalls28,30, and gate frame50in which gate16is slidably received.

FIG. 3illustrates the difference between the operations of the system disclosed in International Patent Application No. PCT/AU2010/001052, and the present embodiment. The distinction is that the invention defined in PCT/AU2010/001052 measures accurately upstream of a submerged orifice10where the vertical velocity distribution is a smooth function without any discontinuities. The present embodiment measures accurately downstream of the submerged orifice10where there is a ‘step function’ discontinuity in the vertical velocity distribution at the location of the gate end face12. The present embodiment uses the measured elevation of the gate16to locate the elevation of this velocity discontinuity, and hence, to determine the elevation at which the flow velocity transitions rapidly to zero. This allows accurate velocity integration by integrating the velocity step function vertically from the floor14to the elevation of the velocity discontinuity as determined from the elevation of the gate end face12. Without knowledge of the velocity discontinuity elevation, a trapezoidal integration would result in a significant over-read or under-read of the velocity integral by attempting to interpolate using a straight line connecting each velocity sample.FIG. 3shows the velocity profile upstream of the submerged orifice10on the left hand side velocity-elevation trend, and the velocity profile downstream of the submerged orifice10on the right hand side velocity-elevation trend.

FIG. 3illustrates that trapezoidal integration would result in a large over-estimate of flow passing beneath the gate. The over-read would be proportional to the triangular area34above the velocity discontinuity as shown in the right-hand side diagram.

FIG. 4is a similar embodiment to that ofFIG. 2, with an arcuate section36along the end of gate16upstream of gate16. It has been determined through computational fluid dynamics analysis, and through velocity field observations in a flow laboratory, that the inclusion of curved surface38on gate16reduces the contraction of the velocity field downstream of the orifice10, such that the height h1is closely approximated by the measurable orifice opening height x, i.e. h1is approximately equal to x. A comparison withFIG. 2illustrates this difference.

FIG. 5is a further alternative embodiment toFIG. 2, where gate16is located between the columns of acoustic transducers22,24of acoustic arrays18,20. Such an arrangement allows the acoustic transducers22,24to be very close to gate16.

FIG. 6is a variation of the embodiment ofFIG. 5, including an acoustic transducer40located on floor14that is used to determine the height from floor14to the end face or underside12of gate16. A standard acoustic distance measurement is undertaken in which an acoustic pulse is transmitted from the transducer40, reflects off the underside12of gate16, and returns to the transducer40or to a secondary receiving transducer (not shown). The flight time of an acoustic pulse is measured by timing electronics (not shown). Given knowledge of the speed of sound in water, the distance between the floor and underside12of gate16is computed. Two transducers are preferably used with one transducer acting as a transmitter and the other acting as a receiver. This configuration overcomes the blanking distance commonly associated with single transducer configurations, limiting the minimum distance that can be measured. Any embodiment of this specification can utilise transducer40, and therefore its use is not limited toFIG. 6.

FIG. 7is a variation of the embodiment ofFIG. 4, where gate16in the open channel closes a pipe42with a headwall44.FIG. 7has acoustic arrays18,20located downstream of gate16, and inserted into pipe42downstream of headwall44.

FIG. 9is a perspective view of a variation of the embodiment ofFIG. 7, with the addition of transducer40fromFIG. 6. This embodiment uses circular acoustic arrays52,54, instead of rectangular acoustic arrays18,20of the prior embodiments.

FIG. 10shows the same configuration as the embodiment ofFIG. 2, but with the inclusion of a flow diverter56rigidly connected to the downstream end of gate16that forms a ceiling58of closed rectangular acoustic arrays18,20, completely containing the jetting velocity profile. The flow passing through orifice10is computed by integrating the sampled velocity field from the floor14to the ceiling58of the acoustic arrays18,20. The height of the ceiling58of the acoustic arrays18,20is determined by any commonly employed linear measurement technique, with a preferred solution being an acoustic sensor, which is used to measure the height of the ceiling58above the floor14of the acoustic arrays18,20. The flow diverter56will assist in parallel alignment of flow streamlines relative to the floor14and flow diverter ceiling58. This will assist in more accurate measurement of flow velocities.

FIG. 11is a variation of the embodiment ofFIG. 10, with an arcuate section60along the end of gate16, upstream of gate16. It has been determined through computational fluid dynamics analysis, and through velocity field observations in a flow laboratory, that the inclusion of curved surface62reduces the contraction of the velocity field downstream of the orifice10, in a similar manner to the embodiment ofFIG. 4.

FIG. 12is a variation of the embodiment ofFIG. 11, including an acoustic transducers)40located on floor14that is used to determine the height from floor14to the ceiling58of flow diverter56, as described with reference toFIG. 6. The configuration of the upward ranging transducer(s)40defined in this embodiment of the invention avoids any impact from silt on floor14. When gate16is closed, the ceiling58covers the upwardly ranging transducer(s)40such that no silt can settle upon them. Instead, the silt will settle on top of flow diverter56. When the gate16is opened, jetting velocities passing through the meter will flush any debris or sediment off the face of the upward shooting acoustic transducers40. Hence these upward ranging acoustic transducers40are in a self-cleaning configuration and are not subject to attenuation and malfunction caused by deposited silt and sediment as is known to occur with other technologies which employ upward ranging water level sensors in an irrigation canal and natural waterway environment.

FIG. 13is a variation of the embodiment shown inFIG. 11, where the arcuate section60is affixed at the free end64of flow diverter56facing the upstream end of gate16, rather than the downstream end shown inFIG. 11. In addition, acoustic arrays18,20are also positioned at the upstream end of gate16to create an adjustable geometry rectangular conduit which encompasses the acoustic arrays18,20, and which causes the streamlines passing through the acoustic arrays18,20to be parallel with the four walls of the rectangular conduit. This embodiment is well suited to installations where the acoustic arrays18,20cannot be located on the downstream side of gate16.

FIG. 14is a similar embodiment to that ofFIG. 13, which includes acoustic transducer(s)40to determine the height of ceiling58, of flow diverter56, as previously discussed with reference toFIG. 6.

FIG. 15is a similar embodiment to that ofFIG. 14, where the acoustic arrays18,20are located upstream of the gate16, on a pipe entry headwall44of pipe42.

FIG. 16is a similar embodiment to that ofFIG. 15, only the direction of flow of water through the pipe42is reversed. Hence, this time the acoustic arrays18,20are located downstream of gate16, on the downstream exit headwall44of pipe42.

FIG. 17is a view that depicts a motor66controlling movement of an undershot gate16in some embodiments. In this embodiment, movement of gate16is controlled by a motor66driven or hydraulic arm coupled to the top68of gate16. By pulling or pushing the top68of gate16the gate16will be raised or lowered to act as an undershot gate.

The invention will be understood to embrace many further modifications as will be readily apparent to persons skilled in the art and which will be deemed to reside within the broad scope and ambit of the invention, there having been set forth herein only the broad nature of the invention and certain specific embodiments by way of example.