Note: Descriptions are shown in the official language in which they were submitted.
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AXIAL TURBOMACHINE COMPRESSOR DRUM WITH DUAL MEANS OF BLADE
FIXING
Field of the invention
[0001] The invention relates to a rotor of an axial turbomachine. More
specifically
the invention relates to a rotor drum of an axial turbomachine compressor.
The invention relates to an axial turbomachine fitted with a low-pressure
compressor rotor drum.
Prior art
[0002] A turbomachine enables a gas to be compressed, burnt and expanded. By
this means the turbomachine provides mechanical energy. To perform these
steps, the turbomachine comprises a compressor and a turbine which are
fitted with a rotor and a housing.
[0003] The inner surface of the housing and the outer surface of the rotor
define the
contours of the primary flow path. It has variations in its annular section.
Its
inner and outer contours can increase and decrease in diameter along the
axis of the engine. In a compressor, especially a low-pressure one, the outer
housing typically has a reduced diameter downstream. Moving from
upstream to downstream, the diameter of the rotor may increase and then
decrease. This combination of surfaces enables a wide inlet area and a high
compression ratio at the output.
[0004] To transmit mechanical work to the fluid, the housing and the
compressor
rotor each comprise a plurality of annular rows of blades. The rotor blade
rows and the stator blade rows alternate axially.
[0005] The housing may include a plurality of annular stators each comprising
an
annular blade row. The stators form rings which abut each other axially for
the purpose of assembling them. In this case, each blade in the rotor row is
attached to the rotor via a root inserted in an annular groove formed on the
rotor.
[0006] During assembly of a compressor with a drum-shaped rotor, a first blade
row
is mounted on the rotor and then a stator is assembled axially facing this
first
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row. Only then can a second blade row be mounted on the rotor after the
stator relative to the first row. Assembly thus continues onwards, assembling
a rotor blade row and a stator, one after the other. This mode of assembly is
required by the fact that the stators being made in one piece and their inner
diameters do not allow the rotor with its blades to be inserted.
[0007] Patent FR 2845436 B1 discloses an axial turbomachine compressor. The
compressor comprises an outer housing formed of several stators
assembled axially. It also comprises annular rows of blades which are each
located between the stators. The rotor blades are fixed by means of roots
that are inserted into annular grooves formed in the rotor. This embodiment
makes it possible to produce a compressor that is simple to assemble.
However, the rotor is subject to vibrations. It develops complex vibrational
modes that are difficult to analyse and damp. Moreover, its implementation
requires complex and expensive machining. In addition, its structure is
massive and heavy.
Summary of the invention
[0008] The invention aims to solve at least one of the problems present in the
prior
art. More particularly, the invention aims to reduce the vibrations in an
axial
turbomachine rotor. The invention also aims to lighten the rotor of an axial
turbomachine.
[0009] The invention relates to a rotor drum of an axial turbomachine, in
particular
of a low-pressure compressor, the drum comprising a wall generally
symmetrical in revolution about its axis and having a generally curved
profile,
the said wall being designed to support multiple rows of blades; wherein a
first blade row is formed by an annular platform formed integrally with the
wall at the peak of its profile with respect to the axis; and at least one,
preferably every, second blade row directly downstream of the first and a
third blade row immediately upstream of the first, is formed by one or more
blade-retaining grooves formed on the wall.
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[0010] According to an embodiment of the invention, the outer surface of the
retaining groove(s) is an average distance from the axis which is less than
the average distance of the platform from the first row to the said axis.
[0011] According to an embodiment of the invention, the wall comprises on its
outer
surface a set of annular ribs designed to mate with an annular layer of
abradable material so as to provide a seal, the set of annular ribs being
located axially between the first and second blade rows and/or between the
first and third blade rows.
[0012] According to an embodiment of the invention, the minimum distance of
the
peaks of one set of ribs with respect to the axis is greater than the maximum
distance from the said axis to the outer surface of the adjacent retaining
grooves. It is the groove(s) of the second and/or third row blade row(s).
[0013] According to an embodiment of the invention, the blades of the first
row are
welded to the platform of the said row.
[0014] According to an embodiment of the invention, the platform of the first
blade
row comprises blade stubs on which are welded blade extensions; preferably
the height of the blade stubs is more than 10% of the radial height of the
blades in the first row, more preferably more than 25%.
[0015] According to an embodiment of the invention, the blades of the first
row are
at least partially cut into the body of the unmachined drum.
[0016] According to an embodiment of the invention, the general curved profile
of
the wall extends over most of the length of the drum and/or has a main
concavity directed towards the main axis and extending over the major part
of the length of the drum, the said profile having a radius relative to the
axis
which is at a maximum at the first blade row.
[0017] According to an embodiment of the invention, the platform of the first
blade
row is raised relative to the wall directly upstream and downstream of the
said row.
[0018] According to an embodiment of the invention, the wall comprises two
parts
extending generally radially under the platform of the first row, so that the
longitudinal section of the wall at the said platform has a n-shaped profile.
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[0019] According to an embodiment of the invention, the wall comprises at
least one
annular stiffener extending radially inwardly at the first blade row,
preferably
in the extension of at least one of the radial parts.
[0020] According to an embodiment of the invention, the wall directly upstream
and
downstream of the first row comprises a part with substantially constant
thickness which defines an annular space for housing a stator inner shell.
[0021] According to an embodiment of the invention, the rotor drum comprises
blades of the second and/or third blade row, each of the said blades
comprising a root housed in the, or a, retaining groove.
[00221 According to an embodiment of the invention, the retaining groove(s)
is/are
annular along the perimeter of the drum.
[0023] According to an embodiment of the invention, the blades in the first
row and
the annular platform form an integral unit.
[0024] According to an embodiment of the invention, the drum is made of a
metallic
material, preferably titanium.
[0025] According to an embodiment of the invention, the wall is forged and
machined from solid.
[0026] According to yet another embodiment of the invention, the annular
platform
and the retaining grooves are integral.
[0027] According to an embodiment of the invention, the drum shows material
continuity between the first row blades and the wall.
[0028] According to an embodiment of the invention, a set of annular ribs is
distributed axially over the annular junction.
[0029] According to an embodiment of the invention, all the drum blade rows,
except the first, comprise a blade-retaining groove for the purpose of
assembling them on the drum.
[0030] The invention also relates to an axial turbomachine comprising a rotor
drum,
wherein the drum is in accordance with the invention; preferably the rotor is
a low-pressure compressor rotor comprising essentially three annular rotor
blade rows.
[0031] The invention also aims to reduce the vibrations of an axial
turbomachine
rotor. To achieve this, it removes any freedom of movement between the
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annular wall and the blades in the first row. The invention can also improve
the overall rigidity of the drum. The proposed architecture can also enable
the rotor to be lightened, affecting both the drum and the blades.
[0032] Machining the surfaces of the drum and the blades can be simplified.
All of
these improvements to the drum are possible while maintaining the
compatibility of the rotor with a housing formed of annular stators.
[0033] The invention is applied to a drum provided with annular ribs used as a
means of sealing between the compression stages. This aspect is not
limiting since the invention may also be applied to a drum mating with axial
brush seals. Such seals are well known to those skilled in the art and may,
for example, correspond to those disclosed in Patent DE102005042272 Al.
Short description of the diagrams
[0034] Figure 1 shows an axial turbomachine in accordance with the invention.
[0035] Figure 2 shows a diagram of a turbomachine compressor according to the
invention.
[0036] Figure 3 illustrates a section of the rotor drum according to the
invention.
Description of the embodiments
[0037] In the following description, the terms inner or internal and outer or
external
refer to a position relative to the axis of rotation of the axial
turbomachine.
[0038] Figure 1 shows a schematic view of an axial turbomachine. In this case
it is
a double-flow turbojet. The turbojet 2 comprises a first compression stage, a
so-called low-pressure compressor 4, a second compression stage, a so-
called high-pressure compressor 6, a combustion chamber 8 and one or
more turbine stages 10. In operation, the mechanical power of the turbine 10
is transmitted through the central shaft to the rotor 12 and drives the two
compressors 4 and 6. Reduction mechanisms may increase the speed of
rotation transmitted to the compressors. Alternatively, the different turbine
stages can each be in communication with the compressor stages through
concentric shafts. These latter comprise several rotor blade rows associated
with stator blade rows. The rotation of the rotor around its axis of rotation
14
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generates a flow of air and gradually compresses it up to the inlet of the
combustion chamber 10.
[0039] An inlet fan, commonly designated a fan 16, is coupled to the rotor 12
and
generates an airflow which is divided into a primary flow 18 passing through
the various above-mentioned levels of the turbomachine, and a secondary
flow 20 passing through an annular conduit (shown in part) along the length
of the machine which then rejoins the main flow at the turbine outlet. The
primary flow 18 and secondary flow 20 are annular flows and are channelled
through the turbomachine's housing. To this end, the housing has cylindrical
walls or shells that can be internal or external.
[0040] Figure 2 is a sectional view of a compressor of an axial turbomachine 2
such
as that shown in Figure 1. The compressor may be a low-pressure
compressor 4. The teaching of the present invention may also be applied to
the rotor drum of a turbine 10.
[0041] A splitter nose 22 of the primary 18 and secondary 20 airflows can be
seen
on the compressor 4. The rotor 12 comprises a plurality of annular rotor
blade rows; in the case of Figure 2 there are three. Further blade rows can
be provided for. These three rows are axially consecutive. There is a first
row of rotor blades 24, a second row of rotor blades 26 downstream of the
first row 24 and a third row of rotor blades 28 upstream of the first row 24.
[0042] The rotor blades (24, 26, 28) spread out substantially radially from
the rotor
12. The blades in one row are regularly spaced from each other, and have
the same angular orientation to the airflow. Optionally, the spacing between
the blades can vary locally as can their angular orientation. Some blades in a
row may be different from the rest.
[0043] The compressor 4 comprises an external housing. The outer housing
comprises several stators, for example four, which each comprise an outer
shell 30, a stator blade row 32 and, optionally, an inner shell 34. An annular
layer of abradable material 36 may be applied to the inside of the outer shell
and the inner shell of a stator. The stator blades 32 of the same stator
extend radially from their outer shell 30 towards their inner shell 34. The
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stators form closed circular rings. They are assembled axially against each
other and fixed to each other by means of radial flanges 38.
[0044] The stators are associated with the fan or a row of rotor blades (24,
26, 28)
for straightening the airflow so as to convert the speed of the flow into
pressure.
[0045] The rotor 12 comprises a drum 40. The drum 40 has a wall 42 generally
symmetrical in revolution about its axis of rotation 14, which axis is common
with that of the turbomachine. The wall 42 may have an overall profile of
revolution or the average profile of revolution about the axis of rotation 14.
The general profile can be included in the thickness of the parts of the wall
42 that are axially at right angles to the stator blade rows.
[0046] The general profile is basically curved and may have a continuous
curvature
and/or continuously varying curvature. Radially it matches the variation in
the
inner surface of the primary flow 18. The exterior of the general profile is
convex. Going from upstream to downstream the radius of the inner surface
increases and then decreases, so that the profile of the wall has a maximum.
The wall 42 is basically thin. Its thickness is generally constant. Its
thickness
is less than 10.00 mm, preferably less than 5.00 mm, more preferably less
than 2.00 mm. The wall 42 forms a hollow body which defines a cavity
having a shape of an ogive or keg. The drum 40 and/or the rotor blades (24,
26, 28) are made of a metallic material, preferably titanium.
[0047] The drum 40 comprises annular ribs 44 or lip seals. They form narrow
annular strips which extend radially. They are designed to mate abrasively
with annular layers of abradable material 36 on a stator so as to provide a
seal. Generally, one abradable layer 36 mates with two annular ribs 44.
[0048] Figure 3 is a detailed sectional view of the drum 40 of Figure 2. The
drum
can also be a rotor drum of a high-pressure compressor. It can possibly also
be a turbine rotor drum.
[0049] The first blade row 24 is integrally formed on the wall by an annular
platform
46. The annular platform 46 is integrally formed with the wall 42. The annular
platform 46 is formed atop the profile of the wall 42. The annular platform 46
has a profile of revolution generally straight or substantially curved.
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[0050] The rotor blades 26 of the second row and the third row 28 each include
a
blade platform 48 defining the inside of the primary flow, a blade 50
extending radially outwardly from the blade platform 48, and a retaining root
52 extending radially inwardly from the blade platform 48. The retaining root
52 may be dovetailed. It may have a form whose axial dimension increases
as it gets closer to the inside, enabling it to lock in place.
[0051] The wall 42 of the drum 40 comprises two zones for fixing blades using
retaining grooves. The fixing zones each comprise an annular groove 54 into
which the retaining roots 52 of the second-row blades 26 and the third-row
blades 28 are inserted. The annular grooves 54 comprise annular outer
surfaces which come into contact with the blade platforms 48. The blade
platforms 48 of the second blade row 26 engage with the second outer
surface 56, and the blade platforms 48 of the third blade row 28 engage with
the third outer surface 58.
[0052] The retaining roots 52 generally have a shape matching the
corresponding
retaining groove so as to ensure radial retention. The retaining grooves 54
have a profile with a constriction at their outer face. Thus, the second row
blades 26 and the third row blades 28 are retained reversibly. Mechanical
clearance is provided between the annular wall 42 and the rotor blades of
the second and third rows, so as to allow slight movement of the blades.
However, the rotor is designed so that the centrifugal forces present during
the compressor's operation force the blades into position in their throats.
[0053] According to an alternative of the invention, the retaining grooves can
be
axial grooves. The annular wall then comprises an annular row of axial
grooves distributed over its circumference, and which each form an annular
blade row.
[0054] The outer surface (56, 58) of at least one of the annular grooves 48 is
at an
average distance from the axis 14 which is less than the mean distance
between the annular platform 46 and the first row 24 of the said axis.
Preferably, each radius at an axial end of the annular platform 48 is greater
than the maximum radius of the outer surface (56, 58) located opposite.
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[0055] The first row blades 24 are anchored to the drum in a different manner
from
those of the other rows (26, 28). The blade retention or attachment is
heterogeneous or hybrid. The first row blades 24 are fixed by welding to the
annular platform 46. They may be welded by friction, for example by a
process of orbital welding. The drum 40 thus serves as a support for fixing
both types of blades.
[0056] For this purpose, the blades corresponding to the first row 24 are
attached to
a bare drum and welded to the annular platform 46. These blades can be
directly or indirectly fitted onto the annular platform 46. The annular
platform
46 may include blade stubs 60 extending radially from its outer surface. In
this case, each blade which is welded to the second surface effectively forms
a radial portion of the final blade. The weld 62 between a stub and a blade
portion is set above the annular platform 46.
[0057] According to an alternative of the invention, the first row blades 24
can be
integrally machined into the body of the unmachined drum in which the wall
is also machined.
[0058] Thus, the wall of the drum 40 and the first row blades form an integral
unit.
They show continuity of material. Their metallic materials have crystalline
continuity at their interface. They can, at least partially, be formed
integrally.
Anchoring the blades is irreversible. The first row blades 24 are integral
with
the annular wall 42. This embodiment eliminates vibration between the first
row blades 24 and the wall 42 of the drum 40.
[0059] In addition, this method of anchoring the blades simplifies the
machining to
be carried out because the annular platform 46 and any stubs 60 are simpler
to produce than an annular groove or a plurality of axial grooves. Indeed, a
groove must be cut in a generally inaccessible space with a small tool, which
increases the manufacturing time. Alternatively, an axial groove can be
machined by broaching. However, this method for removing material
requires expensive tooling and is not suitable for all types of drum.
[0060] The wall 42 of the drum immediately upstream and downstream of the
first
blade row 24 comprises at least a part 64 of substantially constant thickness
or an axial annular join 64, with preferably two parts of substantially
constant
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thickness 64. Each constant thickness part 64 extends axially from the
annular platform 46 to the second blade row 26 or to the third blade row 28.
The annular platform 46 is radially set out from the constant thickness part
64. The constant thickness parts 64 define an annular space between the
first blade row 24 and the second blade row 26 or the third blade row 28, the
annular spaces being radially open outwards. They are designed to
accommodate the internal stator shells.
[0061] The wall 42 comprises two parts 65 which extend generally radially.
They
extend from the annular platform 46 inwardly. They may be located at each
one of the axial edges of the annular platform 46. Thus, the wall may have a
generally Tc-shaped profile. The profiles of the radial portions extend
generally perpendicular to the profile of the annular platform 46.
[0062] The annular ribs 44 are located on the constant thickness parts 64.
Each set
of ribs comprises a plurality of ribs 44. On each side of the annular platform
46 there are progressive decreases in the external radii from an edge of an
annular platform 46, ribs 44, and outer surfaces (56, 58) of the annular
grooves. The peaks of these elements form a staircase. This configuration
enables bladed stators to be fixed on both sides of the first blade row 24,
and then the second row 26 and the third row 28 to be assembled.
[0063] Figure 3 shows the blades 32 and the inner shell 36 of the two stators
upstream and downstream, respectively, of the first blade row 24. Figure 3
also illustrates with dashed lines these stators in an intermediate position
during axial assembly around the drum.
[0064] The annular wall 42 of the drum includes annular stiffeners 66. The
annular
stiffeners 66 may include annular flanges which extend radially inwardly.
These flanges are located axially at the ends of the annular platform 46,
preferably in the radial extension of the radial portions 65.
[0065] The drum is usually machined by turning starting from an unmachined
drum-
shaped blank of which the walls include the finished drum. The drum blank
must radially encompass the outer surfaces of the annular grooves 54, the
annular platform 46, the internal stiffeners 66, and any blade stubs 60.
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Depending on circumstances, it may include the first blade row 24 along the
entirety of their radial height.
