Aeronautics and astronautics – Aircraft structure – Details
Reexamination Certificate
1997-07-14
2001-02-27
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Details
C244S200000, C138S037000
Reexamination Certificate
active
06193191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure having a surface which reduces turbulence problems existing within the boundary layer of a fluid moving with respect to the surface.
2. Description of the Prior Art
The prior art describes various structures for controlling phenomena due to the interaction of a boundary layer of a fluid in motion with respect to a surface and notably turbulence phenomena.
These structures can be formed by surfaces provided with grooves present in the turbulence region. The axis of the grooves extends in the direction of flow of the fluid. The purpose of these grooves is to reduce the turbulence phenomena existing within the boundary layer of the fluid in motion and, by reducing friction between the surface and the fluid, to minimize pressure drops.
Experiments described in the prior art indicate pressure drop decreases up to 7% for example.
The grooves or pressure drop reduction means can have various geometries, and the number thereof can be selected as a function of the transportation conditions and/or of the nature of the fluid so as to obtain a minimum of pressure drops.
The grooves exhibit for example a slot type rectangular profile or a V-shaped profile.
The prior art also mentions the advantageous use of grooves of cylindrical shape, which can allow the obtaining of fluid anchoring effects, thus preventing development of the turbulence phenomenon in the boundary layer of the flowing fluid.
The expression “boundary layer” refers to a zone wherein a fluid is flowing in a pipe for example close to the wall or to the inner surface of this pipe, wherein the velocity gradient is the highest.
Another structure configuration considered in the prior art associates longitudinal grooves (in the direction of flow of the fluid) with a device arranged and suspended with respect to these grooves, the purpose of the latter being to “break” the swirls of great amplitude whereas the longitudinal grooves will act on the swirls of low amplitude. Such an association is however complex and bulky.
It has also been considered to use more complex geometries than a simple succession of identical grooves.
For example U.S. Pat. No. 5,386,955 describes a specific layout of similar slots or grooves. The slots of various sizes are arranged, according to a selected layout and sequence, in order to inhibit swirls of different scales within the boundary layer of the fluid.
However, such a device with an alternation of fins of different heights does not benefit locally by an addition of the effects (turbulence attenuation) resulting therefrom.
SUMMARY OF THE INVENTION
The present invention relates to a structure which inhibits the turbulence phenomena of a fluid in motion with respect to the structure. The structure exhibits a surface geometry comprising at least one series of turbulence inhibition means in a boundary layer of the fluid close to the structure, the inhibition means extending substantially longitudinally in the direction of flow of the fluid. The structure comprises at least a first series of means
0
1
of amplitude a
1
, and at least a second series of means
0
2
of amplitude a
2
, the second series of means
0
2
being arranged so as to be superposed on the first series of means
0
1
, the first series of means
0
1
inhibiting turbulences of great amplitude and the second series of means
0
2
inhibiting at least turbulences of low amplitude.
The invention notably, but not exclusively, has applications in the area of transportation of pressurized gas through a pipe. During transportation, friction occurs between the flowing pressurized gas and the wall of the inner pipe, which causes considerable pressure drop. Pressure drop must be compensated to allow optimum transportation of the fluid in the pipe.
In fact, transportation of pressurized gas represents an important economic challenge and intercontinental gas transportation pipelines involve considerable investments.
In this case, the gas transported is natural gas comprising at least 90% methane.
The invention can also be used for transportation of fluids in the form of a turbulent flow. It is also intended for transportation of industrial gases such as synthesis gases, hydrogen, ethylene, etc.
The present invention has the advantage of benefitting simultaneously and at any point from an effect of inhibition of the turbulence on at least two different scales, notably by superposing geometric profiles corresponding to different scales. In the present invention, a large-scale geometric profile forming the base line of a geometric profile of smaller scale is used.
The geometric profile defining the first series of means preferably forms the base line of the geometric profile defining the second series of means.
Advantageously, the amplitude a
1
of the first series of inhibition means
0
1
is preferably greater than the amplitude a
2
of the second series of means
0
2
, amplitude a
1
being taken with respect to the base surface of the first series of means and amplitude a
2
with respect to the base surface of the second series of means.
According to a preferred embodiment of the invention, the structure according to the invention is suited to form at least part of the inner wall of a pipe. The first series of inhibition means
0
1
exhibits for example a profile of substantially polygonal shape having n sides and r vertices. A segment of a line di delimited by two consecutive vertices forms, with respect to the previous and/or to the next segment of a line (di−1, di+1), an angle &agr;. The value of this angle &agr; is preferably always positive or at least the majority of the angles defining the segments of a line have positive values.
Preferably, the sum of all the inscribed angles for the whole or the majority of the length of the polygonal shape is substantially equal to Π (n−2) wherein n is the number of sides of the polygon.
Advantageously, the number of vertices is greater than 25.
The present invention is advantageously applied for forming the inner wall of a pipe for example with a circular geometry used for the transportation of a pressurized natural gas, under the conditions The inner wall exhibits the specific characteristics of the present invention extends over at least part of the length and the circumference of the pipe intended for transportation. It can be arranged in form of sections within the pipe, the sections being separated by predetermined intervals for example.
It can also extend over almost all or all of the length of the feeder or pipe for conveying the gas.
The pipe can comprise an inner lining exhibiting the characteristics of the aforementioned structure, whose grooves forming the first and the second inhibition means are made for example mechanically and/or chemically so as to obtain the necessary geometric characteristics for inhibiting turbulences.
The pipe intended for transportation of gas comprising at least one structure having the aforementioned characteristics is preferably made of a composite material.
The present invention also relates to a process for transporting a gas, for example a gas on turbulent flow, from a production well to a processing site for example. The process comprises at least the following stages
the gas is expanded at the well outlet to a pressure value at least equal to 5 MPa,
the gas is fed into a pipe having a section so selected that the velocity of flow of the transported gas is for example above 10 m/s, the pipe comprising, for example on at least part of its length, a structure exhibiting the aforementioned characteristics so as to inhibit turbulences in the boundary layer close to the structure.
As a result of the superposition of the turbulence reduction means on various scales, an addition of the turbulence reduction effects is observed.
Thus, by superposing two geometric profiles which, when used individually, lead each to a pressure drop decrease between 5 and 8%, a pressure drop decrease from 10 to 15% can be obtained by means of the superposed arrangement.
Falcimaigne Jean
Palermo Thierry
Rojey Alexandre
Antonelli Terry Stout & Kraus LLP
Eldred J. Woodrow
Institut Francais du Pe'trole
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