FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION:
TURBOMACHINE CENTRE BLADE COMPRISING A CURVED PORTION
2. APPLICANT:
Name: SNECMA
Nationality: France
Address: 2, boulevard du Général Martial Valin, F-
75015 Paris, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the
invention and the manner in which it is to be
performed:
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Technical field
The invention relates to a turbomachine blade
which is implemented in such a way as to limit the
coincidences of vibrational frequencies of the blade in
relation to the frequencies of solicitation of the
blade during the operation of the turbomachine, which
would risk resulting in a deterioration of the blade or
even breakage of it.
Prior art
During the operation of a turbomachine, the flow
of gas along stator blades causes the blades to vibrate.
Each blade has one or several natural frequencies
for which the amplitude of the vibration can become
excessive and cause the deterioration or breakage of
the blade.
US 3.745.629 describes a turbomachine blade which
is curved according to a profile which is similar to
the profile of a blade in vibration in one of its
natural frequencies.
This curvature makes it possible to limit the
vibrations of the blade in a range of frequencies that
correspond to the operating conditions of the
turbomachine, and as such limit the risks of breakage
of the blade.
However, such a curvature also reduces the
effectiveness and the aerodynamic performance of the
blade.
The invention has for purpose to propose a
turbomachine blade which is carried out in such a way
that the natural frequency or frequencies are different
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from the frequencies of solicitation of the blade
during the operation of the turbomachine.
Description of the invention
The invention proposes a turbomachine compressor
blade of radial main orientation with respect to the
main axis of the turbomachine, with the blade
comprising a radially internal root portion, a radially
external tip portion and a radially intermediate
portion,
characterised in that the blade comprises a curved
portion in tangentially direction and at least one
straight portion on the root portion and/or on the tip
portion.
Such a tangentially curved portion modifies the
vibrational response of the blade to the vibrational
solicitations, and removes the frequencies at risk
outside of the operating range of the blade.
More preferably, the radial length L1 of the
curved portion is between 30% and 60% of the radial
length L of the blade.
More preferably, the tangential amplitude A of the
curved portion is between 1% and 5% of the radial
length L of the blade.
More preferably, said straight portion is inclined
by an angle less than or equal to 30° with respect to
the main radial direction of the blade.
More preferably, the curved portion is positioned
radially on the root portion.
More preferably, the curved portion is positioned
radially on the tip portion.
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More preferably, the curved portion is positioned
radially on the median portion.
More preferably, the curved portion is
tangentially curved in the direction of the intrados of
the blade.
The invention also proposes a turbomachine
compressor stator comprising radial blades distributed
around the main axis of the turbomachine, characterised
in that each blade is carried out such as defined
hereinabove.
The invention also proposes a turbomachine
comprising a stator that comprises blades such as
defined hereinabove.
Brief description of the drawings
Other characteristics and advantages of the
invention shall appear when reading the following
detailed description for the understanding of which
reference will be made to the annexed figures along
which:
- figure 1 is a diagrammatical drawing in
perspective of a blade comprising a curved portion
according to the invention;
- figure 2 shows the tangential stacking law of
the centre of gravity of the sections of a blade
according to the invention.
Detailed description of particular embodiments
In the following description, identical, similar
or analogous elements shall be designated by the same
reference numbers.
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For the description of the invention, in a nonlimiting
manner the radial, tangential and axial
orientations shall be adopted according to the marking
R, T, A shown in figure 1, wherein the radial
orientation is the main orientation of the blade and
the tangential orientation is the orientation
perpendicular to a main axial plane of the blade.
Figure 1 shows a blade 10 that is part of a stator
(not shown) of the compressor of a turbomachine.
The compressor comprises a plurality of blades 10
which are evenly distributed around the main axis of
the turbomachine, in order to form an annular set,
called a rectifier grid, through which a flow of gas,
here air, passes.
The blade 10 extends globally radially according
to the orientation R with respect to the main axis of
the turbomachine.
The blade 10 comprises a radially internal portion
12, called the root of the blade, on which the blade 10
is fixed to an inner ferrule of the compressor (not
shown).
The blade 10 comprises a radially external portion
14 called the tip of the blade, on which the blade 10
is fixed to an outer ferrule of the compressor (not
shown).
The blade 10 comprises an intermediate portion 16
that connects the root 12 to the tip 14 of the blade 10.
The inner ferrule and the outer ferrule of the
compressor delimit an annular duct called a stream,
wherein the flow of air flows and interacts with the
blade 10.
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The blade 10 further comprises a leading edge 18,
which is located axially upstream according to the
direction of the gas flow with respect to the blade 10,
and a trailing edge 20 that is located axially
downstream according to the direction of the gas with
respect to the blade 10.
The blade 10 is furthermore cambered and comprises
a face 22 called intrados, that is located on the side
opposite the camber and a face 24 called extrados that
is located on the side of the camber.
Figure 2 shows a curve 26 showing the tangential
stacking law of the centre of gravity of the sections
of the blade 10.
This tangential stacking law corresponds to the
position of the centre of gravity of each section of
the blade according to a plane perpendicular to the
main radial direction of the blade, with respect to the
main radial axis of the blade 10.
This curve 26 comprises a root portion 28
corresponding to the root 12 of the blade 10, a tip
portion 30 corresponding to the tip 14 of the blade 10
and an intermediate portion 32 corresponding to the
intermediate portion of the blade 10.
According to the invention, the blade 10 is
carried out in such a way that it comprises a portion
34 that is curved tangentially and at least one
straight portion.
As such, as can be seen in more detail in figure 2,
the curve 26 comprises a tangentially curved portion 36
corresponding to the curbed portion 34. The curve 26
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further comprises at least one curved portion
corresponding to the straight portion of the blade 10.
According to the invention, the straight portion
of the blade 10 is located on the root 12 and/or on the
tip 14 of the blade 10, according to the position of
the curved portion 34.
As such, the straight portion of the curve 26 is
located on the root portion 28 and/or on the tip
portion 30, according to the radial position of the
curved portion 36.
According to a first aspect of the invention, the
curved portion 34 is located radially on the root 12 of
the blade 10. The straight portion is then located on
the tip 14 of the blade 10. Consequently, the curved
portion 36 is located radially on the root portion 28
and tip portion 30 of the curve 26 is straight.
According to a second aspect of the invention, the
curved portion 34 is located radially on the tip 14 of
the blade 10. The straight portion is then located on
the root 12 of the blade 10. The curved portion 36 of
the curve 26 is consequently located radially on the
tip portion 30 and the root portion 28 of the curve 26
is straight.
According to a third aspect of the invention, the
curved portion 34 is located radially on the
intermediate portion 16 of the blade 10. The root 12
and the tip 14 of the blade 10 each form a straight
portion of the blade 10.
Consequently, the curved portion 36 is located
radially on the intermediate portion 32 and the root
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portion 28 and the tip portion 30 of the curve 26 are
both straight.
Furthermore, according to a preferred embodiment,
the blade 10 is curved in such a way that the curved
portion 34 is tangentially curved in the direction of
the intrados 22, as shown in figure 1.
According to an alternative embodiment not shown,
the curved portion 34 is curved in the direction of the
extrados 24.
The dimensions of the curved portion 36 are
defined with respect to the radial length "L" of the
blade 10.
As such, the radial dimension "L1" of the curved
portion 36 is between 30% and 60% of the radial
dimension "L" of the blade 10.
As such, the tangential dimension "A" of the
curved portion 36 is between 1% and 5% of the radial
dimension "L" of the blade 10.
As was mentioned hereinabove, according to the
radial position of the curved portion, the root portion
28 and/or the tip portion 30 is straight.
In this case, each tip portion 28 and/or root
portion 30 that is straight, is inclined with respect
to the main radial direction of the blade by an angle
of which the value is less than or equal to 30°.
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We claim:
1. Turbomachine compressor blade (10) of main
radial orientation with respect to the main axis of the
turbomachine,
the blade (10) comprising a radially internal root
portion (12), a radially external tip portion (14) and
a radially intermediate portion (16),
characterised in that the blade (10), comprises a
curved portion (34) perpendicularly to a main axial
plane of the blade in a direction and at least one
straight portion on the root portion (12) and/or on the
tip portion (14).
2. Blade (10) as claimed in the preceding claim,
characterised in that the radial length L1 of the
curved portion (34) is between 30% and 60% of the
radial length L of the blade (10).
3. Blade (10) as claimed in any preceding claim,
characterised in that the tangential amplitude A of the
curved portion (34) is between 1% and 5% of the radial
length L of the blade (10).
4. Blade (10) as claimed in any preceding claim,
characterised in that said straight portion is inclined
by an angle less than or equal to 30° with respect to
the main radial direction of the blade (10).
5. Blade (10) as claimed in any preceding claim
characterised in that the curved portion (34) is
positioned radially on the root portion (12).
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6. Blade (10) according to any of claims 1 to 4,
characterised in that the curved portion (34) is
positioned radially on the tip portion (14).
7. Blade (10) according to any of claims 1 to 4,
characterised in that the curved portion (34) is
positioned radially on the median portion (16).
8. Blade (10) as claimed in any preceding claim,
characterised in that the curved portion (34) is
tangentially curved in the direction of the intrados of
the blade (10).
9. Turbomachine compressor stator comprising
radial blades (10) distributed around the main axis of
the turbomachine,
characterised in that each blade (10) is carried
out as claimed in any preceding claim.
10. Turbomachine comprising a stator that
comprises blades (10) as claimed in the preceding claim.