U.S. patent application number 13/810833 was filed with the patent office on 2013-05-09 for turbine engine having two unducted propellers.
This patent application is currently assigned to SNECMA. The applicant listed for this patent is Alexandre Alfred, Gaston Vuillemin. Invention is credited to Alexandre Alfred, Gaston Vuillemin.
Application Number | 20130115083 13/810833 |
Document ID | / |
Family ID | 43707997 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130115083 |
Kind Code |
A1 |
Vuillemin; Alexandre Alfred,
Gaston |
May 9, 2013 |
TURBINE ENGINE HAVING TWO UNDUCTED PROPELLERS
Abstract
A turbine engine including two outer coaxial counter-rotating
unducted propellers, of an upstream propeller and a downstream
propeller, respectively. The blades of the downstream propeller are
retractable in the lengthwise direction thereof so as to reduce the
diameter of the propeller. The reduction in the diameter of the
downstream propeller makes it possible to reduce noise caused by
vortices generated by the upstream propeller.
Inventors: |
Vuillemin; Alexandre Alfred,
Gaston; (Fontainebleau, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vuillemin; Alexandre Alfred, Gaston |
Fontainebleau |
|
FR |
|
|
Assignee: |
SNECMA
Paris
FR
|
Family ID: |
43707997 |
Appl. No.: |
13/810833 |
Filed: |
July 13, 2011 |
PCT Filed: |
July 13, 2011 |
PCT NO: |
PCT/FR2011/051690 |
371 Date: |
January 17, 2013 |
Current U.S.
Class: |
416/1 ;
416/129 |
Current CPC
Class: |
Y02T 50/66 20130101;
F04D 19/024 20130101; Y02T 50/60 20130101; F04D 29/666 20130101;
B64C 11/003 20130101; F04D 29/324 20130101; B64C 11/306 20130101;
B64C 11/48 20130101; F04D 29/362 20130101; B64D 2027/026 20130101;
B64C 11/06 20130101; F02K 3/072 20130101 |
Class at
Publication: |
416/1 ;
416/129 |
International
Class: |
F04D 19/02 20060101
F04D019/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2010 |
FR |
1056059 |
Claims
1-9. (canceled)
10. A turbine engine comprising: two coaxial and contra-rotating
unducted external fans, respectively of an upstream and a
downstream fan, wherein a length of blades of at least one of the
two fans can be varied such that the diameter of the downstream fan
is less than the diameter of the upstream fan.
11. The turbine engine as claimed in claim 10, in which blades of
the downstream fan are retractable along their longitudinal axis,
so as to reduce the diameter of the downstream fan.
12. The turbine engine as claimed in claim 10, in which the
variable-length blades are telescopic with at least two blade
elements which nest one inside the other and can slide one relative
to the other along the axis of the blade.
13. The turbine engine as claimed in claim 12, in which the two
blade elements mounted so as to slide one relative to the other are
formed at the tip of the blades.
14. The turbine engine as claimed in claim 12, in which the two
blade elements are formed at a root end of the blades.
15. The turbine engine as claimed in claim 10, in which at least
the blades of the downstream fan are variable-pitch blades.
16. A method for reducing noise emitted by a turbine engine
including two coaxial and contra-rotating unducted external fans,
respectively of an upstream and a downstream fan, during a phase of
operation of this engine, the method comprising: modifying a length
of the blades of at least one fan so that the diameter of the
downstream fan is less than that of the upstream fan during the
phase of operation.
17. The method as claimed in claim 16, the turbine engine being
mounted on an aircraft, the phases of operation corresponding to
take-off and landing of the aircraft.
18. The method as claimed in claim 16, whereby the reduction in
blade length is compensated for by increasing loading on the blade,
by varying a blade pitch angle.
Description
[0001] The present invention relates to the field of aircraft
turbine engines having two unducted propellers or fans.
[0002] An engine of this type, known in this field as an "open
rotor" or "unducted fan" engine comprises a gas turbine engine
powering one or more free turbines with contra-rotating coaxial
rotors each associated with a fan. The two fans extend
substantially radially on the outside of the nacelle of the turbine
engine and are themselves coaxial and contra-rotating. The two fans
are driven either directly, in which case the two fans are mounted
at the periphery of the two turbine rotors, or via a mechanical
gearbox, the two fans then each being connected to one output of
the gearbox.
[0003] Unducted fan turbine engines are being researched at the
present time because they offer the advantage of performing well
while being capable of supplying significant thrust and consuming
less fuel than other equivalent ducted fan turbine engines.
[0004] However, the high noise levels generated by the mechanisms
of aerodynamic interaction between the two fans are penalizing in
this type of propulsion.
[0005] One of the sources of this noise stems from the interaction
of vortices, generated at the blade tips of the upstream fan, with
the blades of the downstream fan. The vortex generated by the
upstream fan interacts with the downstream fan very vigorously,
generating high levels of noise.
[0006] Ways of reducing fan noise seek to control the flow around
the profiles but such means have not, in the current state of the
art, yet reached maturity.
[0007] One solution for eliminating this noise is to use two fans
of different diameters, the outside diameter of the downstream fan
being smaller than that of the upstream fan so that the vortices
generated by the upstream fan pass around the outside of the
envelope of the downstream fan and do not interact with that fan.
Such a solution is unsatisfactory because it results in a reduction
in the thrust produced by the downstream fan and therefore in
reduction in engine performance. It might be possible to increase
the load on the downstream fan to compensate for the reduction in
diameter thereof, but that would also increase the aeromechanical
difficulty in designing the pair of fans which would become very
complicated and difficult to achieve.
[0008] Another solution is developed in patent application FR 2 938
502 in the name of Snecma. It proposes a turbomachine at least some
of the blades of the upstream fan of which have, on their radially
external end parts, air guidance means directed outward when
considered from upstream to downstream and intended to divert the
vortices formed at the blade tips of the upstream fan radially
around the outside of the blades of the downstream fan. These guide
means carried by the blades of the upstream fan guide outward at
least some of the vortices formed at the tips of the blades of the
upstream fan, which therefore interact a little, if at all, with
the blades of the downstream fan. That makes it possible to reduce
significantly--a reduction of up to 3dB--the acoustic disturbances
associated with the interactions between these vortices and the
downstream fan. They also allow a reduction in the intensity of the
vortices generated and therefore assist in reducing noise. This
solution therefore does not involve modifying the dimensions of the
upstream and downstream fans, which may have substantially the same
outside diameter.
[0009] However, these means do act on the flow of air through the
rotor throughout all phases of flight, even when noise reduction is
not required.
[0010] It is therefore an objective of the invention to reduce the
levels of noise generated by the fans so as, in particular, to
comply with the relatively severe acoustic certification standards
applicable to the take-off and landing phases of the aircraft
fitted with this engine.
[0011] It is another objective to provide good aerodynamic
performance during cruising flight.
[0012] These objectives are achieved according to the invention,
using a turbine engine comprising two coaxial and contra-rotating
unducted external fans, these respectively being an upstream and a
downstream fan, characterized in that the blades of the downstream
fan are retractable in their longitudinal direction, so as to
reduce the diameter of the downstream fan.
[0013] This result is achieved with a turbine engine the blades of
which are telescopic with at least two blade elements which nest
one inside the other and can slide one relative to the other along
the longitudinal axis of the blade.
[0014] By means of the invention it becomes possible to reduce the
diameter of the downstream fan enough for it not to experience the
vortices in the phases during which engine noise is to be reduced,
namely during aircraft take-off and landing. The blades of the
downstream fan are retracted preferably enough to eliminate a
significant proportion of the interactions during these phases in
the vicinity of airports.
[0015] According to one embodiment, said two elements mounted so as
to slide one relative to the other are formed at the free end of
the blades.
[0016] According to another embodiment, said two elements are
formed at the root end of the blades.
[0017] The noise emitted by the turbine engine during a phase of
operation of this engine is thus reduced by reducing the length of
the blades of the downstream fan during said phase of operation.
Said phases of operation correspond to the take-off and landing of
the aircraft.
[0018] The reduction of the blade length is advantageously
compensated for by increasing the loading on the blades, notably by
varying the blade pitch angle.
[0019] The invention is now described in greater, but nonlimiting,
detail using the attached drawings in which:
[0020] FIG. 1 is an axial section through a turbine engine with two
unducted fans;
[0021] FIG. 2 is a perspective view of an unducted fan of the prior
art, illustrating the shape of the stream lines around the fan
blades;
[0022] FIGS. 3 and 4 depict one embodiment of the invention whereby
a blade of the downstream fan has a telescopic end, viewed in two
positions, one extended and the other retracted.
[0023] Reference is made to FIG. 1 which shows a turbomachine 10 of
the "open rotor" type, this expression denoting a pair of unducted
fans which comprises, from upstream to downstream, in the direction
in which the gases flow inside the turbomachine, a compressor 12,
an annular combustion chamber 14, a high-pressure upstream turbine
16 and two lower-pressure downstream turbines 18, 20 which are
contra-rotating, which means to say which rotate in two opposite
directions about the longitudinal axis A of the turbomachine.
[0024] Each of these downstream turbines 18, 20 rotates as one with
an external fan 22, 24 extending radially on the outside of the
nacelle 26 of the turbomachine. The nacelle is a substantially
cylindrical envelope extending along the axis A around the
compressor 12, the combustion chamber 14 and the turbines 16, 18
and 20.
[0025] The flow of air 28 entering the compressor 12 is compressed
and then mixed with fuel and burnt in the combustion chamber 14.
The combustion gases are then injected into the turbines to drive
the rotation of the fans 22, 24 which supply most of the thrust
generated by the turbomachine. The combustion gases exit the
turbines and are expelled through a jet pipe 30 (arrows 32) to
increase the thrust.
[0026] The fans 22, 24 are coaxial and arranged one behind the
other. In the known way, each of these fans 22, 24 comprises a
plurality of blades 22a and 24a respectively, which are uniformly
distributed about the axis A of the turbomachine. Each blade
extends substantially radially in a plane perpendicular to the axis
of rotation and comprises an upstream edge forming the leading edge
of the blade, a downstream edge forming the trailing edge, a
radially internal end forming the root of the blade and a radially
external end forming the tip of the blade.
[0027] According to the prior art, the downstream fan 24 has
substantially the same diameter as the upstream fan 22 so that
these fans supply the same thrust during operation and so that all
of the flow of air compressed by the upstream fan is compressed
again by the downstream fan.
[0028] FIG. 2 is a partial and perspective schematic view of the
upstream fan 22 of a turbomachine of the prior art, and shows how
the stream lines evolve along a blade of this fan. The stream lines
34, 36, 38 pass between the fan blades and more or less follow the
profile of these blades, from the leading edges 40 to the trailing
edges 42 of these blades.
[0029] The stream lines 34 which pass over the radially internal
end parts of the blades are more or less parallel to one another.
By contrast, the stream lines 36, 38 that pass over the radially
external end parts have a tendency to converge toward one another,
the intensity of this phenomenon increasing with increasing
closeness to the blade tips 44. The stream lines 36 at the blade
tips 20 curl around one another and form vortices 46 which impinge
on the blades of the downstream fan 24, these impingements being
what causes very significant acoustic disturbance.
[0030] According to the invention, provision is made to allow the
blades of the downstream fan to retract longitudinally with a view
to reducing the noise emitted by the interaction of the upstream
fan on the downstream fan.
[0031] FIGS. 3 and 4 depict one embodiment of the invention. The
invariable-geometry blades 24a of the downstream fan are replaced
by variable-length blades 124a. According to the embodiment of FIG.
3, the blade 124a is telescopic with two elements 124a1 and 123a2
sliding one inside the other along the longitudinal axis XX of the
blade 124. In this instance, the element 124a1 constitutes the main
body of the blade and extends radially outward from the nacelle 26
starting from the blade root.
[0032] The blade root comprises a pivot 124b mounted such as to
rotate in a bearing of radial axis so as to allow the blade to be
rotated about its longitudinal axis XX and the pitch angle of the
blade to be altered as required. The bearings for the blades of the
fan are mounted in an annular cage 124c. The annular cage 124c is
driven by the turbine rotor set in rotation by the combustion
gases. A set up example is described in patent application FR 0 954
561 or FR 0 955 516 in the name of Snecma.
[0033] The distal end of the element 124a1 is hollow and forms a
housing for the blade tip element 124a2 in which housing this
element can slide between a deployed position shown in FIG. 3, in
which the overall length of the blade is at its maximum, and a
retracted position shown in FIG. 4.
[0034] An appropriate drive mechanism causes the end element 124a2
to move between the two positions, deployed and retracted. An
example of a drive mechanism 125 is a screw jack.
[0035] The latter comprises a threaded rod 125a rotating on itself
about the longitudinal axis of the blade element 124a1 and engaging
with a threaded housing secured to the end element 124a2. The
threaded rod is driven by a motor 125b housed inside the nacelle
26. Given that the tip element 124a2 slides inside the element
124a1 without rotating about the longitudinal axis of the blade,
rotation of the threaded rod causes this element to move
longitudinally.
[0036] The two possible configurations of the downstream fan thus
allow either optimum-output operation or noise attenuation. In the
latter position, with the blades retracted longitudinally, the
diameter of the fan is reduced. The stream lines run along the
blade tip and give rise to blade tip vortices on the upstream fan
but these vortices are prevented from impinging on the downstream
noise and from being a source of noise. Moreover, the reduction in
length of the blades is compensated for by increasing the load on
these blades, notably by varying the blade pitch angle.
[0037] In cruising flight configuration, during which there is no
need to attenuate the noise of the fans and which corresponds to
over 90% of the mission, the two fans are deployed; in particular,
the blades of the downstream fan extend in a radial direction with
respect to the axis of the engine to substantially the same length
as the blades of the upstream fan. It is on take-off or on landing
that the retracted position of the blades of the downstream fan is
activated, and that represents just 10% of the mission in
general.
[0038] Mechanisms other than screw jacks allow the blades of the
downstream fan to be retracted longitudinally. The invention is not
restricted to this mode of actuation. Moreover, other ways of
modifying the geometry of the blades are equally possible. For
example, the blades may be capable of moving radially inside a
housing in the nacelle, the telescopic elements being not at the
blade tip end but at the root end.
* * * * *