U.S. patent application number 12/734334 was filed with the patent office on 2010-11-18 for bluff body noise control.
Invention is credited to David Angland, Leung Choi Chow, Michael Goodyer, Matthew Spiteri, Xin Zhang.
Application Number | 20100288876 12/734334 |
Document ID | / |
Family ID | 38829950 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100288876 |
Kind Code |
A1 |
Chow; Leung Choi ; et
al. |
November 18, 2010 |
BLUFF BODY NOISE CONTROL
Abstract
An aircraft noise-reduction apparatus comprise a flow-facing
element (1) and a flow control device (2) positioned downstream of
the flow-facing element (1). The flow control device (2) is
arranged, in use, to reduce noise induced by unsteady flow
downstream of the flow-facing element (1).
Inventors: |
Chow; Leung Choi; (Bristol,
GB) ; Spiteri; Matthew; (Southampton, GB) ;
Zhang; Xin; (Southampton, GB) ; Angland; David;
(Southampton, GB) ; Goodyer; Michael;
(Southampton, GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
38829950 |
Appl. No.: |
12/734334 |
Filed: |
October 23, 2008 |
PCT Filed: |
October 23, 2008 |
PCT NO: |
PCT/GB2008/050983 |
371 Date: |
July 20, 2010 |
Current U.S.
Class: |
244/1N |
Current CPC
Class: |
B64C 21/00 20130101;
B64C 2025/003 20130101; Y02T 50/166 20130101; Y02T 50/10 20130101;
B64C 23/00 20130101; B64C 1/40 20130101; B64C 25/001 20130101; B64C
2230/14 20130101; B64C 25/16 20130101 |
Class at
Publication: |
244/1.N |
International
Class: |
B64C 23/00 20060101
B64C023/00; B64C 25/02 20060101 B64C025/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2007 |
GB |
0720973.7 |
Claims
1.-16. (canceled)
17. An aircraft noise-reduction apparatus, the apparatus comprising
an aircraft structural element and a splitter plate extending
downstream of the structural element and arranged, in use, to
reduce noise induced by unsteady flow downstream of the structural
element, wherein the splitter plate has a length which is equal to
or greater than the streamwise length of the structural
element.
18. The aircraft noise reduction apparatus of claim 17, wherein the
splitter plate is a passive flow control device.
19. The aircraft noise reduction apparatus of claim 17, wherein the
splitter plate extends in a substantially radial direction with
respect to the structural element and is substantially aligned with
the free stream airflow.
20. The aircraft noise reduction apparatus of claim 17, wherein the
splitter plate comprises a rigid plate.
21. The aircraft noise reduction apparatus of claim 17, wherein the
structural element comprises a component of an aircraft landing
gear.
22. A Landing gear for an aircraft comprising a noise reduction
apparatus according to claim 17.
23. An aircraft noise-reduction apparatus, the apparatus comprising
an aircraft structural element and a flow control device positioned
downstream of the structural element and arranged, in use, to
reduce noise induced by unsteady flow downstream of the structural
element, wherein the flow control device comprises a pneumatic
splitter plate.
24. The aircraft noise reduction apparatus of claim 23, wherein the
pneumatic splitter plate comprises an array of nozzles.
25. The aircraft noise reduction apparatus of claim 23, wherein,
the pneumatic splitter plate comprises a plurality of holes and/or
slots which are substantially aligned along the centre line of the
flow-facing element.
26. The aircraft noise reduction apparatus of claim 23, wherein the
pneumatic splitter plate is a passive flow control device.
27. The aircraft noise reduction apparatus of claim 23, wherein the
structural element comprises a component of an aircraft landing
gear.
28. A Landing gear for an aircraft comprising a noise reduction
apparatus according to claim 23.
29. An aircraft noise-reduction apparatus, the apparatus comprising
a fairing, for locating upstream of a structural element such that,
in use, airflow is at least partially diverted away from the
structural element, and a splitter plate provided in the cavity
defined between the fairing and the structural element and
arranged, in use, to reduce noise induced by unsteady flow
downstream of the fairing.
30. The aircraft noise reduction apparatus of claim 29, wherein the
splitter plate is arranged to reduce recirculating flow between the
fairing and the structural element.
31. The aircraft noise reduction apparatus of claim 29, wherein the
splitter plate is adapted to secure the fairing to the structural
member.
32. The aircraft noise reduction apparatus of claim 29, wherein
splitter plate comprises a pneumatic splitter plate.
33. The Aircraft noise reduction apparatus of claim 29, wherein the
splitter plate is a passive flow control device
34. The aircraft noise reduction apparatus of claim 29, wherein the
structural element comprises a component of an aircraft landing
gear.
35. A Landing gear for an aircraft comprising a noise reduction
apparatus according to claim 29.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to noise-reduction apparatus
for use on an aircraft. More particularly, but not exclusively, the
invention relates to a method of reducing noise generated by the
interaction of the landing gear or parts thereof and the air
flowing past it during flight, take-off and/or landing.
BACKGROUND OF THE INVENTION
[0002] Flow around bodies generates noise, which is detrimental in
particular aerodynamic applications for example where low noise
emissions are a design requirement. One such application where the
level of noise emissions is important is in the design of
commercial aircraft. Over the past decades engine noise has been
significantly reduced, for example by the introduction of
high-bypass ratio turbofan engines. However, maintaining the
minimum engine ground clearance with such high-bypass ratio turbo
fan engines results in longer landing gear. Thus, Landing gear on
commercial aircraft have been identified as major noise
contributors during approach and landing. The design of a landing
gear is primarily based on its structural and dynamic function.
This complex geometric design gives rise to unsteady flow which
leads to unwanted noise generation.
[0003] Fairings have been proposed as a means of reducing landing
gear noise. For example, a noise reduction fairing for an aircraft
landing gear is disclosed in WO 01/04003A1. Such noise reduction
fairings at least partially shield downstream components such as
struts stays and actuators from high-speed flow.
[0004] Embodiments of the present invention seek to provide
improved or alternate noise-reduction apparatus for aircraft. Some
embodiments may also reduce the noise generated by noise reduction
fairings themselves.
SUMMARY OF THE INVENTION
[0005] According to a first aspect of the invention there is
provided an aircraft noise-reduction apparatus, the apparatus
comprising a flow-facing element and a flow control device
positioned downstream of the flow-facing element, wherein the flow
control device is arranged, in use, to reduce noise induced by
unsteady flow downstream of the flow-facing element.
[0006] The applicants have found that unsteady flow, around and in
the wake of a flow-facing element can cause a significant
contribution to creation of broadband noise. In particular, it has
been noted that unsteady velocity fluctuations and/or net lift
forces generated in the flow may be a key noise generating
mechanism. As such embodiments of the invention utilise a flow
control device downstream of the flow-facing element to reduce
broadband noise.
[0007] In particular, the flow control device may be arranged to
reduce the flow fluctuations due to relatively large scale flow
structures in the wake. For example, the flow control device may be
arranged to suppress vortex shedding downstream of the flow-facing
element.
[0008] Typically, the flow control device is a passive flow control
device. A passive flow control device may be optimised to provide
the desired flow control in a particular phase of flight. For
example the flow control device may be optimised to provide the
maximum noise reduction in flow conditions that would occur during
approach and landing.
[0009] The flow control device may be a splitter plate extending
downstream of the flow-facing element. Splitter plates
(alternatively referred to as "split plates") are a known means of
aerodynamic flow control and have been primarily used to modify the
separated wake behind cylinders. Splitter plates generally extend
from centre-line of the downstream face of the cylinder.
[0010] The splitter plate according to embodiments of the invention
may be substantially aligned with the free stream airflow and may
extend in a substantially radial direction with respect to the
structural element.
[0011] In some embodiments the splitter plate may comprise a rigid
plate. The rigid plate may have a length that is equal to or
greater than the streamwise length of the structural element.
[0012] In alternate embodiments the aircraft noise reduction
apparatus may comprise a pneumatic splitter plate. In other words,
a jet of air may be blown downstream from the flow-facing element
to create an equivalent flow control effect to that of a rigid
splitter plate.
[0013] The pneumatic splitter plate may comprise an array of
nozzles, for example a series of holes and/or slots. The array may
comprise a plurality of holes and/or slots which are substantially
aligned along the centre line of the flow-facing element. The array
may comprise a plurality of holes and/or slots which are
distributed along the length of the flow-facing element.
[0014] The flow-facing element may be an aircraft structural
element. For example the flow-facing element may be a strut.
[0015] Alternatively, the flow-facing element may comprises a
fairing, for locating upstream of a structural element such that,
in use, airflow is at least partially diverted away from the
structural element, and the flow control device may be provided
between the fairing and the structural element. Such an arrangement
may help reduce self-noise which may otherwise be produced by the
fairing.
[0016] Where the flow-facing element is a fairing, the flow control
device may be arranged to reduce recirculating flow between the
fairing and the structural element.
[0017] In some embodiments a splitter plate may be arranged such
that it is also adapted to secure the fairing to the structural
member.
[0018] In alternate embodiments the flow control device may
comprises a pneumatic splitter plate arranged to provide a jet of
air between a fairing and structural member.
[0019] The structural element may comprise a component of an
aircraft landing gear.
[0020] A further aspect of the invention comprises an aircraft
landing gear comprising a noise reduction apparatus according to an
embodiment of the first aspect of the invention.
[0021] A further aspect of the invention comprises a method of
reducing noise caused by landing gear on an aircraft including the
steps of identifying a part of the landing that contributes to the
noise generated by the landing gear when in flight, and providing
an aircraft noise-reduction apparatus according to an embodiment of
the first aspect of the invention to reduce the noise generated by
said part.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Embodiments of the present invention will now be described
by way of example only with reference to the accompanying schematic
drawings in which:
[0023] FIG. 1 schematically illustrates, in plan view, a noise
reduction apparatus in accordance with an embodiment of the
invention which utilises a rigid splitter plate;
[0024] FIGS. 2A and 2B schematically illustrate, in plan view,
noise reduction apparatus in accordance with alternate embodiments
of the invention which utilise a pneumatic splitter plate;
[0025] FIGS. 3A and 3B show the pneumatic splitter plate used in
the noise reduction apparatus of FIGS. 2A and 2B; and
[0026] FIG. 4 schematically illustrates, in plan view, a noise
reduction apparatus in accordance with an embodiment of the
invention which utilises a noise reduction fairing and splitter
plate.
DETAILED DESCRIPTION OF AN EMBODIMENT
[0027] FIG. 1 shows a noise reduction apparatus in accordance with
a first embodiment of the invention. The noise reduction apparatus
comprises a structural element 1 which is exposed, in use, to an
airflow V.sub..infin.. In other words, the structural element is
flow-facing. V.sub..infin. may be assumed to be the free stream
airflow. In the case where the structural element 1 is a landing
gear component it will be appreciated that it may be deployable,
such that it is only be exposed to the airflow V.sub..infin. during
take-off, landing and approach.
[0028] The structural element 1 is a bluff body, in this case a
H-Beam. The skilled person will appreciate that a bluff body may be
generally characterised as any body where there is significant flow
separation and a generally unsteady wake.
[0029] The noise reduction apparatus further comprises a flow
control device in the form of a splitter plate 2. The splitter
plate 2 is a rigid plate attached to the downstream side of the
structural element 1. The splitter plate 2 extends perpendicularly
from the downstream surface of the structural element 1 and is
located on the centre line of the element.
[0030] The splitter plate 2 is arranged such that it is
substantially aligned with the free stream flow V.sub..infin.. When
mounted on an aircraft it may be convenient to simply align the
splitter plate 2 with the longitudinal axis of the aircraft, since
this is a reasonable approximation to the free stream airflow
during approach and landing.
[0031] Preliminary experiments were carried out to evaluate the
effectiveness of this first embodiment of the invention. A H-beam
was tested as it is considered a good example of a simple
bluff-body which produces noise over a broad range of frequency
spectrum. A splitter plate 2 having a length L, measured in the
streamwise direction, was attached to the rear of the element 1
having a length W. A selection of different splitter plate lengths
(L/W=1, L/W=2 and L/W=3), and a body without a splitter plate, were
tested.
[0032] A comparison of flow visualisations with and without the
presence of the splitter plate showed that the presence of the
splitter plate blocked interaction between shear layers in the
vicinity of the body. The shear layers continued to converge
downstream leading to a longer and wider wake.
[0033] The Coefficient of Drag for each arrangement was also
compared. The addition of the L/W=1 splitter plate resulted in a
drop in the coefficient of drag of C.sub.d=0.47. Increasing the
length of the splitter plate reduced the drag further by
C.sub.d=0.23 between L=W=1 and L=W=3.
[0034] Standard deviations of velocity plots were used to compare
the unsteady flow. The unsteadiness was concentrated around the
H-beam with the highest velocity fluctuation just aft of it. In the
L/W=1 configuration the unsteadiness moved further downstream and
away from the model.
[0035] The narrowband spectra were measured in an anechoic chamber
and plots compared for the different configurations to show how the
noise signature of the model was affected. The L/W=0 case showed a
strong tonal peak at a Stroudal Number (based upon the width of the
body) of 0.125 and broadband noise "hump" cantered about a Stroudal
Number of 0.75. In the cases of L/W=1, L/W=2 and L/W=3 the tonal
peak was suppressed and the noise was reduced over the whole
frequency range. The splitter plate configurations showed very
similar noise spectra up to a Stroudal Number of 17.5. Above that
frequency the L=W=2 configuration showed marginally lower noise
levels.
[0036] Source localization plots were used to identify where origin
of the noise reduction. The comparison between the plots showed
that the H-Beam is no longer the main noise source when the
splitter plate is used. Rather, the noise source is located towards
the trailing edge of the splitter plate.
[0037] FIG. 2A and 2B show the use of a pneumatic splitter plate
for downstream flow control. FIG. 2A illustrates a cylinder bluff
body 11a as a flow-facing element. FIG. 2B shows a H-Beam 11b
flow-facing element. In each case a pneumatic splitter plate is
provided by means of a blowing device 12a, 12b on the downstream
face of the respective element 11a, 11b. As with the rigid splitter
plate 2 of FIG. 1, the pneumatic splitter plate is located on the
centre line of the element.
[0038] As shown in FIGS. 3A and 3B, the blowing device 12a and 12b
simply comprises a pipe attached to the rear of the element 11a,
11b with a series of nozzles in form of simple holes 14 or slots
13. The holes 14 or slots 13 are distributed along length of the
pipe (and therefore, along the length of the element 11a, 11b) to
form an array. Pressurised air is provided to the pipe to provide
blowing from the nozzles in the form of a relatively small jet
downstream.
[0039] In preliminary experiments carried out to evaluate the
effectiveness of this second embodiment of the invention, the
pneumatic splitter plate was found to provide the same flow effects
as a physical split plate. For example the pneumatic splitter plate
delays the roll-up of vortices behind the element 11a, 11b and
interrupts the interaction of shear layers. The noise reduction
effect of the pneumatic splitter plate was also equivalent to that
of the rigid plate. Only a relatively small blowing rate was
required to provide the equivalent effect of the L/W=1 splitter
plate arrangement of the first embodiment.
[0040] FIG. 3 shows a further embodiment of the invention in which
the flow-facing component is a fairing 25, positioned upstream of a
structural element 21 and arranged to at least partially divert the
free stream airflow away from the element 21. Such fairings have
been proposed for noise reduction purposes. However, the applicants
have recognised that in some circumstances the noise-reduction
fairing 25 may itself contribute to the total broadband noise of
the aircraft. Thus, according to embodiments of the invention a
splitter plate 22 is provided in the cavity defined between the
fairing 25 and the element 21. The splitter plate 22 may
conveniently be arranged to support the fairing 25 from the
structural element 21.
[0041] The splitter plate 22 reduces or eliminates vortex shedding
from the fairing 25 and in turn reduces noise. As with the previous
embodiments this is due to the splitter plate 21 blocking the
interaction between opposing shear layers. The splitter plate 22
also reduced the interaction between the shear layers and the
downstream element 21.
[0042] It will be appreciated that the rigid splitter plate 22 may
alternatively be replaced by a pneumatic splitter plate (as
described above) attached to the downstream side of the fairing
25.
[0043] Preliminary experiments were carried out to evaluate the
effectiveness of this further embodiment of the invention. Three
different sizes of elements 21 were used to investigate the
possibility of reducing the size of the fairing 25 with respect to
the element 21. Aerodynamic and acoustic results were performed in
wind tunnel and anechoic facilities.
[0044] In the configurations without the splitter plate 22 a
recirculating region of flow was observed in the cavity between the
fairing 25 and the element 21 as the shear layer aft of the
fairings' trailing edge impinged on the element part, rolling up
inside the cavity. The element 21 was subjected to relatively
high-speed flow due to the shear layer interaction.
[0045] The application of the splitter plate for the two smaller
elements 21 blocked the interaction between the opposing shear
layers and inhibited the shear layer from interacting with the
element. As a result the recirculating flow inside the cavity was
reduced considerably. The larger element 21 was large enough for
the shear layer to impinge on it, nevertheless the splitter plate
22 impeded the strong recirculation flow within the cavity. Instead
a low velocity wake was observed aft of the element 21. The effect
of this change in flow structure had an impact on the noise
produced. The source strength around the apparatus was
significantly reduced as the magnitude of the velocities and the
unsteadiness around the fairing 25 and the element 21 were lower,
hence reducing the dipole strength attributed with the fluctuating
lift forces on the apparatus. The strong shedding produced a strong
tonal peak in the noise measurements, increasing the overall noise
signature. The splitter plate reduced or totally eliminated this
tone. The configurations involving the two smaller elements 21
reduced this tonal peak by about 14 dB, measured from the
1/3-octave band spectra. The larger element eliminated the tonal
peak completely although a second smaller tonal peak was observed
at a high frequency.
[0046] The skilled person will appreciate that any of the
embodiments of the invention may be applied to aircraft components
as required and may be particularly beneficial when applied to
aircraft landing gear. It may further be appreciated that different
embodiments of the invention may be preferred dependent on the
particular application and its associated design constraints. For
example, in some applications the rigid splitter plate may be
preferred due to its simplicity whereas in other applications the
pneumatic splitter since it may offer space and/or weight savings
while offering the same functionality.
[0047] Although the invention has been described above with
reference to one or more preferred embodiments, it will be
appreciated that various changes or modifications may be made
without departing from the scope of the invention as defined in the
appended claims.
[0048] For example, it will be appreciated that any of the
embodiments of the invention may be tuned for a particular
application. For example the dimensions of a rigid splitter plate
or the nozzle size, position and air-pressure of a pneumatic
splitter plate may be optimised. Such optimisation may take into
account a number of design factors, for example, the level of noise
reduction, the aerodynamic benefit (or penalty), weight and/or
space constraints may be considered.
[0049] The skilled person will appreciate that the blowing effect
of a pneumatic splitter plate could be variable in use to provide
an active flow control device. Equally a rigid plate could be
partially or fully deployable to provide an active flow control
device.
[0050] Equally, similar effects could be used to provide a noise
control system which is only activated when required (for example
during approach and landing but not during take-off, when engine
noise is dominant)
[0051] The skilled person will also appreciated that the blowing
device used in the pneumatic splitter plate embodiment is not
limited to an external pipe arrangement such as those shown in
FIGS. 2 and 3. For example the device may be formed from a pipe
embedded in the structure or may blow air from an internal plenum
chamber.
* * * * *