Note: Descriptions are shown in the official language in which they were submitted.
CA 02900399 2015-08-13
ROTOR FOR GAS TURBINE ENGINE
TECHNICAL FIELD
[0001] The application relates generally to gas turbine engines and, more
particularly, to rotors thereof.
BACKGROUND
[0002] Rotors of gas turbine engines, which may include or form part of
an
impeller, fan, compressor, turbine, etc., are often subjected to significant
centrifugal
forces stemming from the relatively high rotational speeds at which gas
turbine
engines are operated. The rotors are engineered to withstand these
structurally
harsh operating conditions and while static effects are relatively
straightforward to
deal with, dynamic effects can pose particular engineering challenges.
[0003] Minimizing weight is a permanent concern in the aeronautics
industry in
general, and is a particularly significant concern in the case of rotors since
the
weight of rotors can influence the extent of the rotor dynamic effects which
may
need to be dealt with by further additional weight at the shaft. While
attempts to limit
the amount of material used in the rotor, and thus limit its associated
weight, have
been made, there remain practical limitations to the designing of the rotor
shape
however, such as limitations imposed by the context of commercial-scale
production
for instance.
[0004] Although known rotors and associated methods are satisfactory to a
certain degree, there always remains room for improvement. Particularly, any
weight
savings which can be achieved is desirable in aero gas turbine applications.
SUMMARY
[0005] There is provided a gas turbine engine rotor comprising a body
having a
solid-of-revolution-shaped portion centered around a rotation axis, the body
defining
an annular cavity centered around the rotation axis, the annular cavity
penetrating
into the body from an annular opening, the annular cavity extending between
two
opposite annular wall portions each leading to a corresponding edge of the
opening;
and at least one structural plate mounted to and extending between the two
opposite annular wall portions and forming an interference fit therewith.
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[0006] There is also provided a gas turbine engine comprising a shaft
adapted to
rotate about an axis of rotation and a rotor fixed to the shaft, the rotor
including a
body having a solid-of-revolution-shaped portion centered around a rotation
axis
and having an annular cavity centered around the rotation axis, the annular
cavity
penetrating into the body from an annular opening, the annular cavity
extending
between two opposite annular wall portions each leading to a corresponding
edge of
the opening; and at least one structural plate mounted to and extending
between
the two opposite annular wall portions and forming an interference fit
therewith.
[0007] There is further provided a method of manufacturing a rotor of a
gas
turbine engine comprising: providing a rotor body, the rotor body being solid
and
having a solid-of-revolution-shaped portion centered around a rotation axis of
the
rotor; forming an annular cavity in the rotor body, the annular cavity
extending
between two wall portions of the rotor body; and mounting at least one
structural
plate between the two wall portions with an interference fit.
[0008] Further details of these and other aspects of the present invention
will be
apparent from the detailed description and figures included below.
DESCRIPTION OF THE DRAWINGS
[0009] Reference is now made to the accompanying figures, in which:
[0010] Fig. 1 is a schematic cross-sectional view of a gas turbine
engine;
[0011] Fig. 2A is a fragmented longitudinal cross-sectional view of a rotor
of the
gas turbine engine of Fig. 1, with Fig. 2B being an alternate embodiment to
the rotor
of Fig. 2A;
[0012] Fig. 3 is a cross-sectional view taken along lines 3-3 of Fig. 2A;
[0013] Fig. 4 is a perspective, axially sectioned, view of a gas turbine
engine rotor
and shaft assembly;
[0014] Fig. 5 is an exploded view of the rotor/shaft assembly of Fig. 4.
DETAILED DESCRIPTION
[0015] Fig.1 illustrates a turbofan gas turbine engine 10 of a type
preferably
provided for use in subsonic flight, generally comprising in serial flow
communication a fan 12 through which ambient air is propelled, a multistage
compressor 14 for pressurizing the air, a combustor 16 in which the compressed
air
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is mixed with fuel and ignited for generating an annular stream of hot
combustion
gases, and a turbine section 18 for extracting energy from the combustion
gases.
[0016] Turning now to Fig. 2A, a first example embodiment of a rotor 20
which
can be adapted to the gas turbine engine 10 is shown. The rotor 20 can be any
one
of a plurality of rotary gas turbine engine components such as an impeller, a
fan, a
compressor component or a turbine component, to name a few examples.
[0017] The rotor 20 has a body 22 which generally has a solid of
revolution shape
(except for the rotor blades) centered around a rotation axis 24 thereof. In
this
embodiment, the rotor 20 has an optional axial bore 26 to receive a shaft
therein.
Although only partially shown in Fig. 2A, a plurality of rotor blades 21
extend radially
outwardly from the body 22 of the rotor 20. The radially-inner (i.e. near the
axis 24)
portion of the rotor 20 can thus be referred to as the hub 28. In this
embodiment, the
weight of the rotor 20 is addressed (i.e. limited) in part by the presence of
an
annular cavity 30 which is generally surrounded by a hollow toroidal-shaped
structure of the body 22 of the rotor 20. This annular cavity 30 may be
enclosed by
the body 22 of the rotor 20 on all sides except for the circumferential,
radially
inwardly opening, gap defined between axially spaced apart flanges 32 and 34
of
the hub 28, as will be seen.
[0018] The annular cavity 30 can be said to penetrate into the body 22
from the
axial bore 26 in the radially-outward direction. The annular cavity 30 can be
formed
as part of the body 22 of the rotor 20 and since it forms a partially open
void shape
in the body 22, the body 22 can still be formed by casting, forging,
machining, by
additive material manufacturing, and/or by welding two or more body portions
together, for instance.
[0019] In the illustrated 'impeller-type' embodiment, the wall portions 33,
35
forming the axially-opposite walls of the annular cavity 30 correspond to a
forward
annular flange 32 and a rearward annular flange 34 of the rotor 20. A first
seat 36 is
formed in the radially-inner portion of the forward annular flange 32, and a
second
seat 38 is formed in the radially-inner portion of the rearward annular flange
34, and
the annular opening 31 extends axially between the first seat 36 and the
second
seat 38. One or more structural components, which will be referred to herein
as
structural plates 40 for the sake of convenience, is/are interference-fitted
between
the two seats 36, 38 and used in compression therebetween to impart a force
acting
to maintain the radially-inner ends of the two annular flanges 32, 34 away
from one
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another. This feature is significant as during rotation of the rotor 20 at
operating
speeds, the centrifugal effect can be such that it tends to 'stretch' the
rotor in the
radial orientation (i.e. normal to the axis 24), thereby bringing the radially
inner ends,
and seats 36, 38, toward one another. The structural plate(s) 40 acts in
compression between the seats 36, 38 against this axially collapsing force in
order,
at least to a certain extent, to substantially maintain the structural shape
of the rotor
body 22 notwithstanding the forces due to the centrifugal effect. The shaped
portions referred to above as 'seats' 36, 38, are optional, as in alternate
embodiments, the structural plate(s) can be positioned in the annular cavity,
directly
against the wall portions 33, 35, for instance. In alternate embodiments, such
as a
fan embodiment for instance, the annular cavity can penetrate axially into the
rotor
body and the structural plate(s) can be in the radial orientation, for
example.
[0020] This
'extending' force exerted by the structural plate(s) 40 onto the seats
36, 38 can be made to increase from the original interference-fitted state
when the
rotor is in operation to ensure that the structural plate(s) 40 remain(s) well
fixed in
place and/or oppose the growing, opposite, 'compressive' force stemming from
the
centrifugal effect.
[0021] In a
first example, in an embodiment where the rotor 20 is subjected to a
significant increase in temperature during operation, the material of the
structural
plate(s) 40 can be selected with a thermal expansion coefficient which leads
to a
greater thermal growth of the plate 40 than that of the rotor body 22 itself.
For
instance, if the rotor body 22 is made of a single, uniform, material, the
structural
plates(s) 40 can be made of a material having a thermal expansion coefficient
which
is greater than the thermal expansion coefficient of the uniform material of
the rotor
body 22.
[0022] In a
second example, the structural plate(s) can have a shape which
dynamically reacts to the centrifugal effect by extending substantially
axially. For
instance, the embodiment shown in Fig. 2B shows a structural plate(s) 140
which
has a radially-inwardly-curved axial-cross-section shape. In other words, it
has a
center portion 142 which is closer to the axis 124 than the two axial ends, or
legs
146, 148, which rest in the seats 136, 138. When subjected to centrifugal
force, the
central portion 142 is driven radially-outwardly and the centrifugal force is
partially
transformed by this shape at the two axial ends into an axially directed
extension
force which pushes the seats 136, 138, and thus the flanges, away from one
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another, as shown by the arrows 150. Such a functional shape will be referred
to
herein as a splayed shape, for convenience. This centrifugal-extending
function can
further be increased or attenuated by increasing or decreasing, respectively,
the
weight of the central portion 142. To this end, in the embodiment of Fig. 2B,
the
central portion 142 has a greater thickness than the axial ends or legs 146,
148.
[0023] The interference-fit of the structural plate(s) 40, 140 into and
between the
seats 36, 38, 136, 138 can be achieved by any suitable process known to
persons
of ordinary skill in this art, such as cold-fitting or press-fitting for
instance. Cold-
fitting is particularly suitable in embodiments where the thermal expansion
coefficient of the structural plate(s) 40, 140 is greater than the thermal
expansion
coefficient of the body 22.
[0024] An interesting feature of the use of one or more structural
plate(s) 40 in
this manner is the possibility of leaving an aperture extending across the
general
location of the structural plate(s) 40. This can allow the cavity 30 to
breathe (heat,
water, oil), or even allow boroscopy inspection of the cavity 30 across the
barrage of
structural plate(s). The one or more structural plates themselves can be
provided
with apertures across their radial thickness, or apertures can be provided by
leaving
spacings between the circumferential edges of the one or more structural
plates.
[0025] Referring to Fig. 3, which shows a transversal cross-section by
opposition
to the axial or longitudinal cross sections views of Figs. 1 and 2, an
embodiment is
shown where six independent structural plates 40 are used in a
circumferentially-
interspaced manner, leaving six corresponding spacings 50 therebetween. The
plates 40 may be circumferentially equally spaced apart, such that the
circumferential spacings 50 are also equally spaced apart. In this example,
the
spacings 50 are specifically sized in a manner to allow inspection of the
annular
cavity 30 from the axial bore 26 using a given piece of boroscopy equipment,
without removing the structural plates 40.
[0026] Figs. 4 and 5 show more exemplary details of a possible
embodiment,
where the rotor 20 of Fig. 2A is shown mounted to a shaft 19 of the gas
turbine
engine 10 (Fig. 4), and exploded therefrom (Fig. 5), respectively, for
additional
clarity and completeness with respect to an embodiment.
[0027] The above description is meant to be exemplary only, and one
skilled in
the art will recognize that changes may be made to the embodiments described
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without departing from the scope of the invention disclosed. For example, the
one or
more structural plates and the body can be provided in various shapes or
sizes, and
can be manufactured using various processes. The longitudinal cross-section of
the
structural plate(s) can also be inclined relative to the axis rather than
being relatively
parallel thereto as shown in Figs 2A and 2B. In cases where more than one
circumferentially spaced-apart structural plates are used, the forward annular
flange
seat and/or the rearward annular flange seat can include a plurality of
circumferentially interspaced seat portions each being associated to a
corresponding one of the structural plates. The rotor can be used as any
suitable
rotary component of a turbofan gas turbine engine or of any other gas turbine
engine type which can have an axial bore or not. In alternate embodiments, the
annular cavity can extend into the body from the rear or the front, in a
partially or
completely axial orientation, rather than extending into the body in the
radially-outer
direction from a hub, axial bore, or other radially-inwardly located annular
opening;
accordingly, in such other embodiments, the plate or plates can extend fully
or
partially in the radial orientation, or in any suitable orientation between
the axial
orientation and the radial orientation. The use of distinctly shaped seats is
optional,
as in some alternate embodiments, the plate or plates can be positioned
directly at
a suitable depth in the cavity. Still other modifications which fall within
the scope of
the present invention will be apparent to those skilled in the art, in light
of a review
of this disclosure, and such modifications are intended to fall within the
scope of the
appended claims.
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