Fluid handling – Flow affected by fluid contact – energy field or coanda effect – Structure of body of device
Reexamination Certificate
2000-06-07
2001-11-27
Lee, Kevin (Department: 3753)
Fluid handling
Flow affected by fluid contact, energy field or coanda effect
Structure of body of device
C137S826000
Reexamination Certificate
active
06321790
ABSTRACT:
The invention relates to a fluidic oscillator that is symmetrical about a longitudinal plane of symmetry P, the oscillator comprising an opening enabling a fluid to enter into an “oscillation” chamber in the form of a two-dimensional fluid jet oscillating transversely relative to said plane of symmetry P, an obstacle occupying the major portion of said oscillation chamber and possessing a front wall provided with a cavity situated facing said opening and swept over by the fluid jet in oscillation.
BACKGROUND OF THE INVENTION
Fluidic oscillators are well known and document WO 93/22627 gives an example which is shown in plan view in FIG.
1
.
That oscillator
1
which is symmetrical about a longitudinal plane of symmetry P comprises an oscillation chamber
3
and an obstacle
5
housed inside the chamber.
The obstacle
5
has a front wall
7
in which a “front” cavity
9
is formed facing an opening
11
.
The opening
11
defines a fluid inlet into the oscillation chamber
3
and it is suitable for forming a two-dimensional fluid jet that oscillates transversely about the longitudinal plane of symmetry P of the oscillator.
During operation of the fluidic oscillator, when the fluid jet encounters the front cavity
9
and sweeps over it during oscillation, main vortexes T
1
, T
2
form on either side of the jet (
FIG. 1
) and alternate between being strong and weak, in phase opposition, and in relationship with the oscillation of the jet.
In
FIG. 1
, the vortex T
1
occupies space that is much greater than the space occupied by the front cavity of the obstacle, and the pressure of this vortex is such that the jet is deflected into an extreme position in spite of the presence of the other vortex T
2
located between the front wall
7
of the obstacle
5
adjacent to the cavity and the wall
13
facing the oscillation chamber and connected to the opening
11
.
When the fluid jet is in this position, a portion of the flow from the jet is directed downstream from the obstacle, and another portion feeds the vortex T
2
which grows larger and larger and whose pressure increases up to the moment when the pressure is sufficient to cause the jet to change over to the other side, into the opposite extreme position.
The jet thus oscillates from one extreme position to the other, and by detecting the frequency of oscillation of the jet, it is possible to determine the flow rate of the fluid, with the frequency being considered as being proportional to the flow rate.
To reduce errors in determining the fluid flow rate, the ratio of frequency of oscillation to flow rate must not vary too much as a function of flow conditions.
Unfortunately, under so-called “transition” conditions, i.e. when the Reynolds' numbers calculated for the flow at the opening
11
are situated at around
300
, the Applicant has observed that a high pressure zone (vortex T
3
) appears in the vicinity of the base of the fluid jet on the side where the vortex T
1
is to be found, together with other localized vortexes facing the front wall beneath the vortexes T
1
and T
3
in FIG.
1
.
These vortexes reinforce the action of the vortex T
1
, and as a result, more time is required by the vortex T
2
to acquire enough force to counterbalance the pressures exerted by T
1
and T
3
, thereby reducing the frequency of oscillation and thus giving rise to errors in fluid flow rate determination.
Also, document U.S. Pat. No. 4,244,230 discloses a fluidic oscillator having a nozzle which extends towards a U-shaped obstacle defining an oscillation chamber. The longitudinal size of the side walls of the nozzle is equal to or greater than the distance between the ends of the walls of the obstacle and the apex of the downstream surfaces of two elements of semi-oval section disposed perpendicularly relative to the duct and whose main axes are parallel to the flow direction of the fluid. During operation of the fluidic oscillator, that type of nozzle affects the oscillation of the jet by considerably impeding the development of the vortex T
1
.
BRIEF SUMMARY OF THE INVENTION
The present invention seeks to remedy those problems by providing a fluidic oscillator that is symmetrical about a longitudinal plane of symmetry P, the oscillator comprising an opening enabling a fluid to enter into an “oscillation” chamber in the form of a two-dimensional fluid jet oscillating transversely relative to said plane of symmetry P, an obstacle occupying the major portion of said oscillation chamber and possessing a front wall provided with a cavity situated facing said opening and swept over by the fluid jet in oscillation, wherein the two side walls extend towards the obstacle on either side of the opening, prolonging it in such a manner as to form a nozzle inside the oscillation chamber and having longitudinal size that is strictly less than the distance between the opening and the front wall of the obstacle so that the ends of said walls are not too close to the cavity.
The nozzle forms a screen protecting the fluid jet against the vortexes situated in the high pressure zone close to the base of said jet and contributing to deflecting the jet excessively.
The fluid jet is therefore less subject to the influence of those disturbing vortexes than in the prior art.
The fluidic oscillator of the invention thus presents a frequency of oscillation under transition conditions that is higher than that of the prior art fluidic oscillator.
According to a characteristic, the side walls are substantially parallel to each other. Preferably, the longitudinal size Le of the side walls lies in the range 0.75b and
b
, where
b
designates the transverse size or width of the opening.
For example, the longitudinal size Le of the side walls is substantially equal to
b
.
Advantageously, the front wall of the obstacle has two essentially plane front surfaces on either side of the cavity of said obstacle, the planes of each of said surfaces being substantially perpendicular to the longitudinal plane of symmetry P.
Advantageously, the oscillation chamber possesses two wall portions situated on either side of the opening and comprising two surfaces disposed facing respective front surfaces of the obstacle and being substantially parallel thereto.
According to a characteristic of the invention, the cavity is defined by a surface which possesses, in the plane of oscillation of the fluid jet, firstly two straight portions that are substantially parallel to the longitudinal plane of symmetry P at locations where said surface meets each of said front surfaces, and secondly a portion of semicircular shape connected to said straight portions.
Preferably, the portion of the cavity farthest from the opening is situated at a distance Lo from the front wall of the obstacle lying in the range 2.2b to 2.5b, where
b
is the transverse size or width of the opening.
According to another characteristic of the invention, the distance L between the opening and the front wall of the obstacle lies in the range 2.8b to 3.2b, where
b
designates the transverse size or width of the opening.
According to a characteristic of the invention, the fluidic oscillator has at least two sensors for detecting speed or pressure variations in the fluid flow.
Advantageously, sensors for detecting speed variations of the fluid flow are disposed in the vicinity of the end of the nozzle.
REFERENCES:
patent: 5396808 (1995-03-01), Huang et al.
patent: 5983943 (1999-11-01), Parry et al.
Carver Andrew John
Soreefan Ibné
Lee Kevin
Pojunas Leonard W.
Schlumberger Industries S.A.
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