U.S. patent application number 13/190990 was filed with the patent office on 2011-11-17 for engine, particularly cror engine, for an aircraft.
This patent application is currently assigned to Deutsches Zentrum fur Luft- und Raumfahrt e.V.. Invention is credited to Arne Sturmer.
Application Number | 20110277447 13/190990 |
Document ID | / |
Family ID | 42317343 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110277447 |
Kind Code |
A1 |
Sturmer; Arne |
November 17, 2011 |
Engine, Particularly CROR Engine, for an Aircraft
Abstract
An engine for an aircraft flying in a cruise flight direction
comprises at least one rotor having a plurality of rotor blades.
The at least one rotor is driven about a rotor axis at a rotational
frequency. The rotor axis is oriented in the cruise flight
direction of the aircraft, and at least one geometric parameter of
the rotor blades that influences the propulsion characteristics of
the rotor is variable. The engine further comprises a controller
which periodically varies the geometric parameter of the rotor
blades at at least one frequency that is at least as high as the
rotational frequency of the rotor.
Inventors: |
Sturmer; Arne;
(Braunschweig, DE) |
Assignee: |
Deutsches Zentrum fur Luft- und
Raumfahrt e.V.
Cologne
DE
|
Family ID: |
42317343 |
Appl. No.: |
13/190990 |
Filed: |
July 26, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2010/050950 |
Jan 27, 2010 |
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13190990 |
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Current U.S.
Class: |
60/224 |
Current CPC
Class: |
Y02T 50/60 20130101;
F02K 3/072 20130101; B64C 11/48 20130101; Y02T 50/66 20130101; B64D
2027/005 20130101; B64C 11/308 20130101 |
Class at
Publication: |
60/224 |
International
Class: |
F01D 7/00 20060101
F01D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2009 |
DE |
10 2009 007 013.3 |
Claims
1. An engine for an aircraft flying in a cruise flight direction,
the engine comprising at least one rotor having a plurality of
rotor blades, the at least one rotor being driven about a rotor
axis at a rotational frequency, the rotor axis being oriented in
the cruise flight direction of the aircraft, at least one geometric
parameter of the rotor blades that influences the propulsion
characteristics of the rotor being variable, and a controller which
periodically varies the geometric parameter of the rotor blades at
at least one frequency, the at least one frequency being at least
as high as the rotational frequency of the rotor.
2. The engine of claim 1, wherein the at least one frequency is a
multiple of the rotational frequency of the rotor.
3. The engine of claim 1, wherein the controller varies the
geometric parameter of the individual rotor blades depending on an
angle position of the individual rotor blades relative to an engine
mount of the engine.
4. The engine of claim 1, wherein the controller varies the
geometric parameter in such a way that unsteady forces to which the
rotor blades are subjected are minimized.
5. The engine of claim 1, wherein the controller varies the
geometric parameter in such a way that excitations of air-borne
noise or solid-borne noise by the rotor are minimized.
6. The engine of claim 1, wherein the at least one rotor is an open
rotor.
7. The engine of claim 1, and comprising a further rotor having a
plurality of rotor blades, which is arranged downstream of the at
least one rotor with regard to the cruise flight direction, and
which is driven in an opposite direction to the at least one rotor
about the rotor axis.
8. The engine of claim 7, wherein a numbers of the blades of the
further rotor and a number of the blades of the at least one rotor
are equal.
9. The engine of claim 8, wherein the controller varies the
geometric parameter of all blades of the at least one rotor
simultaneously.
10. The engine of claim 8, wherein the controller varies the
geometric parameter of all blades of the at least one rotor
depending on a relative angle position of the further rotor and the
at least one rotor.
11. The engine of claim 7, wherein a rotational frequency of the
further rotor is equal to the rotational frequency of the at least
one rotor.
12. The engine of claim 11, wherein the frequency at which the
controller varies the geometric parameter of all blades of the at
least one rotor is at least 2n times as high as the rotational
frequency of the at least one rotor, n being the number of blades
of the front rotor.
13. The engine of claim 12, wherein the frequency at which the
controller varies the geometric parameter of all blades of the at
least one rotor is in a range from 10 to 250 Hz.
14. The engine of claim 7, wherein both the further rotor and the
at least one rotor are open rotors.
15. The engine of claim 7, wherein the geometric parameter is
selected from a group of geometric parameters including a pitch
angle of the rotor blades, a torsion of the rotor blades, and a
airfoil shape distribution of the rotor blades.
16. A Contra Rotating Open Rotor (CROR) engine for an aircraft
flying in a cruise flight direction, the CROR engine comprising a
first open rotor having a first number of rotor blades, a second
open rotor having a second number of rotor blades, the first number
and the second number of rotor blades being equal, the first and
the second rotors being driven about a common rotor axis in
opposite rotational directions at same rotational frequencies, the
rotor axis being oriented in the cruise flight direction of the
aircraft, the first rotor being arranged in front of the second
rotor with regard to the cruise flight direction, at least one
geometric parameter of the rotor blades of the second rotor that
influences the blade loading of the second rotor being variable,
and a controller which periodically varies the geometric parameter
of all blades of the second rotor at the same time and at at least
one frequency depending on a relative angle position of the first
rotor and the second rotor, the at least one frequency being at
least 2n times as high as the rotational frequencies of the first
and second rotors, n being the equal number of blades of the first
and the second rotors.
17. The engine of claim 16, wherein the geometric parameter is
selected from a group of geometric parameters including a pitch
angle of the rotor blades, a torsion of the rotor blades, and a
airfoil shape distribution of the rotor blades.
18. The engine of claim 16, mounted in a pusher configuration.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application No. PCT/EP2010/050950, filed Jan. 27,
2010, that claims priority to German Patent Application No. 10 2009
007 013.3, filed Jan. 31,2009.
FIELD
[0002] The invention relates to an engine for an aircraft flying in
a cruise flight direction. Particularly, the invention relates to
an engine for an aircraft flying in a cruise flight direction,
which comprises at least one rotor driven about a rotor axis
oriented in the cruise flight direction and having a plurality of
rotor blades, wherein at least one geometric parameter of the rotor
blades that influences the propulsion characteristics of the rotor
is variable. Even more particularly, the invention relates to such
an engine for an aircraft which is designated as a CROR (Contra
Rotating Open Rotor) drive or engine, and in which two open rotors
are driven in opposite directions about a common rotor axis
oriented in the cruise flight direction of the aircraft.
[0003] The formulation "rotor axis oriented in the cruise flight
direction" used here is not intended to mean that the rotor axis
has to be exactly parallel to the cruise flight direction of the
aircraft. Instead there may be a pitch angle or pitch between the
rotor axis and the cruise flight direction. Further, there will
typically be a variation of the pitch of the rotor axis over
different flight configurations of the aircraft. In the present
invention, however, the pitch of the rotor axis remains
comparatively small and is always smaller than 45.degree. . As a
rule, it remains below 15.degree. . In the present invention, it is
also possible, but by no means mandatory, to track the cruise
flight direction with the rotor axis of the engine. Usually, the
rotor axis will be fixed with regard to the structure of the
aircraft to which the engine is mounted.
BACKGROUND
[0004] Aircraft with engines comprising at least one rotor driven
about a rotor axis oriented in the cruise flight direction of the
aircraft, which are generally designated as propeller-driven
aircraft, display basic advantages in short-haul flight operation
as compared to jet-driven aircraft. This particularly applies to
aircraft with CROR engines. Propeller-driven aircraft, however, are
also connected with general disadvantages. The excitation of
vibrations in the structure of a propeller-driven aircraft, i.e. of
structure-borne noise, and of air-borne noise at a frequency which
is a product of the number of blades of the rotors and their
rotational frequency as well as higher harmonics thereof belongs to
these disadvantages.
[0005] In CROR engines so-called interaction tones provide a
further source of noise. Interaction tones are generated by the
interaction of different flows of both rotors, like for example of
blade tip vortices and blade wakes. The frequencies of the
interaction tones results from arbitrary sums of the products of
the blade numbers and the rotational frequency of the rotors and of
higher harmonics thereof.
[0006] Further, blades of propellers and open rotors are directly
subject to any variations of the incident flow resulting from pitch
or stall effects, which may result in azimuthally variable blade
loads and thus also in generation of noise.
[0007] In a known engine for an aircraft, which comprises a rotor
driven about a rotor axis oriented in the cruise flight direction
of the aircraft, a variability of a geometric parameter which
influences the propulsion of the rotor serves for having a further
variable for adjusting the thrust of the engine besides the
rotational frequency of the rotor. Here, the geometric parameter
influencing the propulsion of the rotor is simultaneously adjusted
for all rotor blades of the rotor, and this is done at a very low
frequency as compared to the rotational frequency of the rotor. As
a rule, the geometric parameter influencing the propulsion of the
rotor is the pitch angle of the profile of the rotor blades with
regard to their plane of rotation about the rotor axis.
[0008] In CROR engines it is known that some design parameters have
a beneficial effect on the interaction noise generated in that the
interaction of the back rotor with the blade tip vortices and the
blade wakes of the front rotor is reduced. The distance between the
two rotors, the load, particularly on the front rotor, a reduced
diameter of the back rotor, and the rotational frequencies of the
rotors or the resulting blade tip velocities belong to these design
parameters. These measures for noise reduction, however, often
result in a reduction of the performance and/or the efficiency of
the engine. Thus, up to now, always a compromise between
performance and noise emission had to be found.
[0009] A periodic variation of the pitch angle of the individual
rotor blades of a rotor is known from helicopters and is a
precondition for a lateral movement of helicopters having a rotor
axis which is oriented essentially vertically.
[0010] US 2006/0097103 A1 discloses an integrated propulsion and
guiding system for an aircraft in which the blade pitch variation
principle of a helicopter is used for an engine having a rotor axis
which is not oriented vertically but which is strongly inclined
with regard to the cruise flight direction of the aircraft.
[0011] A dynamic pitch control for wind power plants is known from
DE 202 20 134 U1. By using the signal of sensors integrated into
the rotor blades of a wind power plant the energy take-up of the
individual rotor blades is determined. On the basis of these data,
the pitch angle, i.e. the angle of incidence, of the individual
rotor blades is adjusted for homogenizing the energy take-up of all
rotor blades. In this way, the torque transmitted to the drive
train of the wind power plant is more uniformly distributed over
the entire flow area covered by the rotor blades.
[0012] There still is a need for a engine for an aircraft, which
comprises at least one rotor driven about a rotor axis oriented in
the cruise flight direction of the aircraft, and in which a
generation of noise which increases with the performance or
efficiency of the engine or which is due to stall effects is
reduced or even avoided.
SUMMARY
[0013] The following presents a simplified summary in order to
provide a basic understanding of one or more aspects of the
invention. This summary is not an extensive overview of the
invention, and is neither intended to identify key or critical
elements of the invention, nor to delineate the scope thereof.
Rather, the primary purpose of the summary is to present some
concepts of the invention in a simplified form as a prelude to the
more detailed description that is presented later
[0014] The present invention relates to a engine for an aircraft
flying in a cruise flight direction. The engine comprises at least
one rotor having a plurality of rotor blades. The at least one
rotor is driven about a rotor axis at a rotational frequency; the
rotor axis is oriented in the cruise flight direction of the
aircraft; and at least one geometric parameter of the rotor blades
that influences the propulsion characteristics of the rotor is
variable. Further, the engine of the present invention comprises a
controller which periodically varies the geometric parameter of the
rotor blades at at least one frequency. This frequency is at least
as high as the rotational frequency of the rotor.
[0015] Further, the present invention relates to a Contra Rotating
Open Rotor (CROR) engine for an aircraft flying in a cruise flight
direction. The CROR engine comprises a first open rotor having a
first number of rotor blades, and a second open rotor having a
second number of rotor blades. The first number and the second
number of rotor blades are equal; the first and the second rotors
are driven about a common rotor axis in opposite rotational
directions at same rotational frequencies; the rotor axis is
oriented in the cruise flight direction of the aircraft; the first
rotor is arranged in front of the second rotor with regard to the
cruise flight direction; and at least one geometric parameter of
the rotor blades of the second rotor that influences the blade
loading of the second rotor is variable. The CROR engine of the
present invention further comprises a controller which periodically
varies the geometric parameter of all blades of the second rotor at
the same time and at at least one frequency depending on a relative
angle position of the first rotor and the second rotor. This
frequency is at least 2n times as high as the rotational
frequencies of the first and second rotors, n being the equal
number of blades of the first and the second rotors.
[0016] Other features and advantages of the present invention will
become apparent to one with skill in the art upon examination of
the following drawings and the detailed description. It is intended
that all such additional features and advantages be included herein
within the scope of the present invention, as defined by the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention can be better understood with reference to the
following drawings. The components in the drawings are not
necessarily to scale, emphasis instead being placed upon clearly
illustrating the principles of the present invention. In the
drawings, like reference numerals designate corresponding parts
throughout the several views.
[0018] FIG. 1 is a perspective view on a CROR engine with two
rotors each having eight rotor blades.
[0019] FIG. 2 is a side view on the CROR engine according to FIG.
1; and
[0020] FIG. 3 shows a front view on a CROR according to FIGS. 1 and
2, and a plot of the unsteady blade loads over the rotation angle
of the two rotors of the CROR engine.
DETAILED DESCRIPTION
[0021] In the engine of the present invention the geometric
parameter of the rotor blades, which is variable, and which
influences the propulsive force of the rotor is periodically varied
by a controller at at least one frequency which is at least as high
as the rotational frequency of the rotor. This means that, in the
engine of the present invention, the variation of the geometric
parameter of the rotor blades takes place much quicker as it would
be necessary and useful for adjusting the rotor to different
operation conditions of the engine, like for example to optimize
the engine for providing different thrusts in different flight
conditions of the aircraft. In the engine of the present invention,
the geometric parameter of each rotor blade, which influences the
propulsion characteristics of the rotor, is at least once changed
and returned to its starting value over each rotation of the rotor
blade about the rotor axis. The general intention of the present
invention is to avoid unsteady loads on the rotor blades by which
vibrations, particularly noise, may be excited. In principle, this
is achieved in that different incident flows on each individual
rotor blade over its various rotational positions about the rotor
axis are compensated for by varying its geometric parameter in such
a way that the load on the rotor blade is kept constant to an as
far extent as possible.
[0022] The frequency at which the controller has to vary the
geometric parameter for keeping the load constant depends on the
particularities of the engine. As a rule, it is as high as the
rotational frequency of the rotor or it is a plurality thereof.
[0023] Particularly, the controller may vary the geometric
parameter of the individual rotor blades depending on their angle
position with regard to an engine mount of the engine. The location
of the engine mount by which the engine is mounted to the structure
of its aircraft influences the flow incident on the rotor and
particularly the distribution of different incident flows over the
flow area covered by the rotor. These influences are due to the
engine mount itself or due to a resulting location of the engine
with regard to, for example, a wing of the aircraft. A known
phenomenon in this regard is the wing box humming in
propeller-driven aircraft, which is caused by the individual rotor
blades passing through the flow areas in front of the high pressure
side and in front of the low pressure side of the wing. By means of
the present invention, this wing box humming may be reduced if not
avoided completely.
[0024] It has already been mentioned that the controller preferably
varies the geometric parameter in such a way that any unsteady
forces to which the rotor blades are subjected are minimized. For
this purpose, force sensors may be provided at the rotor blades
whose signals are supplied to the controller as a value to be kept
constant. In this case, the controller is a closed loop controller
for keeping the force signals constant.
[0025] The controller may also be designed in such a way that it
minimizes a secondary effect of the instationary incident flow on
the rotor blades in that it varies the geometric parameter in such
a way that excitations of air-borne or solid-borne noise by the
rotor are minimized. In this case, corresponding vibration sensors
for monitoring the respective noise are to be provided whose
signals are supplied to the controller. Here, the controller is a
closed loop controller which minimizes the supplied vibration
signals.
[0026] The present invention is particularly intended for use with
engines comprising open rotors. Even more particularly, the engine
according to the present invention is a CROR engine having two open
rotors driven in opposite directions about a common rotor axis. In
this case, the controller at least varies the geometric parameter
of the rotor blades of the back rotor, i.e. of the rotor located in
a more downstream position with regard to the incident flow.
Additionally, the controller may also vary the same or another
geometric parameter of the blades of the front rotor.
[0027] Particularly advantageous conditions for applying the
present invention in a CROR engine are present, if the blade
numbers of both rotors are the same. In this case, the controller
may vary the geometric parameter with all rotor blades of the back
rotor always at the same time to compensate for a varying incident
flow on the rotor blades of the back rotor.
[0028] In a CROR engine, the controller may generally vary the
geometric parameter of the rotor blades of the back rotor depending
on the relative angle position of both rotors, as this relative
angle position determines the variation of the flow incident on the
rotor blades of the back rotor by the rotor blades of the front
rotor. The frequency at which the controller varies the geometric
parameter influencing the propulsion characteristics in a CROR
engine is preferably at least 2n times as high as the rotational
frequency of its two rotors. Here, n is the blade number of the
front rotor. The absolute frequency at which the controller varies
the geometric parameter of the Blades is in a typical range from 10
to 250 Hz.
[0029] The geometric parameter influencing the propulsion
characteristics of the rotor may particularly be the angle of
incidence of the respective rotor blade which is also designated as
the pitch of the rotor blade. It may, however, also be a torsion of
the respective rotor blade or the airfoil shape distribution of the
respective rotor blade should this deometry of the rotor blades be
dynamically variable.
[0030] In a particular embodiment of the present invention, the
CROR engine is designed to be mounted in a pusher configuration to
the aircraft. Here, variations of the flow incident on the rotor
blades of both rotors due to, for example, a pylon to which the
engine is attached may also be compensated for by the variation of
the geometric parameter influencing the propulsion characteristics
of the rotor blades according to the present invention to such an
extent that no vibration, particularly no noise is induced by
them.
[0031] Referring now in greater detail to the drawings, FIGS. 1 and
2 depict an engine 1 which is a so-called CROR engine 2. A CROR
engine has two rotors 3 and 4 one arranged behind the other which
are rotating in opposite directions about a common rotor axis 5.
Both rotors 3 and 4 are open rotors in which the incident flow is
not limited in radial direction with regard to the rotor axis 5.
Here, both rotors 3 and 4 comprise a same number of eight rotor
blades 6 and 7, respectively. The pitch 12 of the individual rotor
blades 6 and 7 with regard to the rotational planes of the rotors 3
and 4 is variable by means of a controller 13 as indicated with
rotor blade 7'. Particularly, the pitch of each rotor blade 6 and 7
may be varied for a plurality of times over each rotation of the
rotors 3 and 4 about the rotor axis 5 depending on their absolute
rotation angle about the rotor axis 5 and on the relative rotation
angle of the two rotors 3 and 4. In this way, unsteady loads on the
rotor blades 6 and 7 and resulting excitations of air-borne and
solid-borne noise are reduced or even completely removed.
[0032] The CROR engine 2 depicted in FIGS. 1 and 2 is intended to
be mounted to an aircraft in a pusher configuration, and is
attached to the structure of the aircraft via an upstream located
pylon not depicted here. By this pylon or by wakes starting from
the pylon, unsteady loads on the rotor blades 6 and 7 occur at a
frequency which is a product of the rotational frequency and the
number of blades 6 and 7 of the rotors 3 and 4. Such unsteady loads
are also known from engines having one rotor only. Due to the
interaction of the flow variations generated by the two rotors 3
and 4 there are additional unsteady loads at a frequency which is
2n-times the rotational speed of the rotors 3 and 4. These
additional unsteady loads particularly occur at the rotor blades 7
of the back rotor 4 but also at the rotor blades 6 of the front
rotor 3.
[0033] In FIG. 3 these unsteady loads are plotted for one rotor
blade of each rotor over the rotation angle 4) about the rotation
axis 5. The curve 8 indicates the load on one rotor blade 6 of the
front rotor 3, whereas the curve 9 indicates the load on one rotor
blade 7 of the back rotor 4. The curves 10 and 11 show the
development of the average values of the curves 8 and 9. The
variation of the curves 8 and 9 indicate that the unsteady loads on
the blades of the back rotor 4 are higher but generally of the same
frequency as the unsteady loads on the blades of the front rotor 3
which is attributable to the same number of blades of the rotors 3
and 4 here. Superimposed on the unsteady loads of this higher
frequency is a variation of the loads on the blades 6 and 7 which
is shown by the curves 10 and 11, and which, for example, results
from a pylon to which the engine 1 is mounted or from an incident
angle of the rotation axis with regard to the cruise flight
direction of the entire aircraft. All unsteady parts of the loads
on the blades 6 and 7 may be minimized in that a parameter
influencing the propulsion characteristics of the individual rotor
blades 6 and 7, respectively, such as the pitch 12 of the rotor
blades according to FIG. 1, is varied by the controller 13
according to FIGS. 1 and 2 at a frequency of the unsteady
components of the loads such that in case of a higher than average
load on the respective blade the parameter is varied towards a
smaller thrust production. This, for example means, that the pitch
of the respective blade is reduced. Vice versa, in case of a lower
than average load on the respective blade the parameter is varied
towards a higher thrust production. This, for example means, that
the pitch of the respective blade is increased.
[0034] The realization of the present invention may be based on an
adjustment of the incident angle (pitch) of the rotor blades which
is anyway provided with most engines. For the realization of the
present invention it is, however, at least necessary that the
adjustment of the pitch may be varied at a higher frequency than
usual. It may also be necessary that the adjustment is possible for
the individual rotor blades at different points in time. Particular
in case of a CROR engine, however, there are also embodiments of
the present invention in which the geometric parameter of all rotor
blades of a rotor may be synchronously changed (see above). Then,
the individual rotor blades do not have to be controllable with
regard to their parameter varying the thrust individually.
[0035] Many variations and modifications may be made to the
preferred embodiments of the invention without departing
substantially from the spirit and principles of the invention. All
such modifications and variations are intended to be included
herein within the scope of the present invention, as defined by the
following claims.
* * * * *