U.S. patent application number 11/074676 was filed with the patent office on 2005-10-13 for flow control arrangement.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Xu, Liping.
Application Number | 20050226717 11/074676 |
Document ID | / |
Family ID | 32320674 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050226717 |
Kind Code |
A1 |
Xu, Liping |
October 13, 2005 |
Flow control arrangement
Abstract
A flow control arrangement (30; 50; 70) is described in which an
inlet slot 35, 55, 85 is positioned prior to a stationary structure
(33; 43; 53; 73; 83) such as a stator or pylon in order that air
flow is bled or removed from a main flow 31, 51, 81. The removed
air passes through a passage duct 36, 56 and is re-injected through
an outlet nozzle 37, 57, 87 with an askew angle consistent with
rotor blades 32, 52, 72, 82 of a turbine. In such circumstances,
distortion in the flow due to the stationary structure 33, 43, 53,
83 is relieved such that there is less instability downstream from
that structure 33, 43, 53, 83.
Inventors: |
Xu, Liping; (Cambridge,
GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
ROLLS-ROYCE PLC
London
GB
|
Family ID: |
32320674 |
Appl. No.: |
11/074676 |
Filed: |
March 9, 2005 |
Current U.S.
Class: |
415/58.5 |
Current CPC
Class: |
F04D 29/681 20130101;
F04D 29/526 20130101; F05D 2240/121 20130101; Y10S 415/914
20130101; F04D 29/682 20130101; F04D 29/685 20130101; F05D 2240/307
20130101; F04D 27/023 20130101; F04D 29/684 20130101; F01D 11/10
20130101; F04D 27/0238 20130101; F04D 27/0207 20130101 |
Class at
Publication: |
415/058.5 |
International
Class: |
F03B 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2004 |
GB |
0408126.1 |
Claims
I claim:
1. A flow control arrangement for turbine engines, the arrangement
comprising a turbine to force fluid flow directed towards a
stationary structure through a conduit whereby that fluid flow is
susceptible to distortion instability downstream from the
stationary structure, the arrangement characterised in that a slot
in the conduit prior to the stationary structure is provided in
order to remove in use fluid from that fluid flow and an outlet
provided prior to the turbine through which the removed fluid is
released.
2. An arrangement as claimed in claim 1 wherein the slot is
substantially aligned with the stationary structure.
3. An arrangement as claimed in claim 1 wherein the fluid is
air.
4. An arrangement as claimed in claim 1 wherein the outlet is
aligned with the stationary structure with a pre-determined angular
offset.
5. An arrangement as claimed in claim 1 wherein the stationary
structure is a pylon or guide vane or drooped inlet or
non-axisymmetric intake.
6. An arrangement as claimed in claim 1 wherein the outlet has a
trenched end.
7. An arrangement as claimed in claim 1 wherein the slot presented
width to the stationary structure is determined for flow removal in
order to provide flow stability downstream of that stationary
structure.
8. An arrangement as claimed in claim 1 wherein the position of the
slot relative to the structure is chosen to provide flow
stabilisation.
9. An arrangement as claimed in claim 1 wherein removed fluid
passes along a passage from the slot to the outlet.
10. An arrangement as claimed in claim 9 wherein the removed fluid
utilises the pressure of the rotor outlet in order to drive removed
fluid movement along the passage.
11. An arrangement as claimed in claim 1 wherein the slot includes
diffuser vanes.
12. An arrangement as claimed in claim 11 wherein the diffuser
vanes de-swirl the removed fluid flow to facilitate movement
through the passage.
13. An arrangement as claimed in claim 1 wherein the outlet
includes guide vanes to guide removed fluid release toward the
turbine.
14. An arrangement as claimed in claim 13 wherein the guide vanes
direct released flow for consistency with blades of the rotor and
in particular the angle of those blades.
15. An arrangement as claimed in claim 9 wherein the passage is
shaped to facilitate at least one of: removal of fluid flow by the
slot; and presentation of the removed fluid to the outlet for
appropriate release prior to the turbine.
16. An arrangement as claimed in claim 15 wherein the passage
narrows or constricts from the slot to the outlet.
17. A turbine engine incorporating an arrangement as claimed in
claim 1.
Description
[0001] The present invention relates to flow control arrangements
and more particularly to such arrangements utilised within turbine
engines.
[0002] Referring to FIG. 1, a gas turbine engine is generally
indicated at 10 and comprises, in axial flow series, an air intake
11, a propulsive fan 12, an intermediate pressure compressor 13, a
high pressure compressor 14, a combustor 15, a turbine arrangement
comprising a high pressure turbine 16, an intermediate pressure
turbine 17 and a low pressure turbine 18, and an exhaust nozzle
19.
[0003] The gas turbine engine 10 operates in a conventional manner
so that air entering the intake 11 is accelerated by the fan 12
which produce two air flows: a first air flow into the intermediate
pressure compressor 13 and a second air flow which provides
propulsive thrust. The intermediate pressure compressor compresses
the air flow directed into it before delivering that air to the
high pressure compressor 14 where further compression takes
place.
[0004] The compressed air exhausted from the high pressure
compressor 14 is directed into the combustor 15 where it is mixed
with fuel and the mixture combusted. The resultant hot combustion
products then expand through, and thereby drive, the high,
intermediate and low pressure turbines 16, 17 and 18 before being
exhausted through the nozzle 19 to provide additional propulsive
thrust. The high, intermediate and low pressure turbines 16, 17 and
18 respectively drive the high and intermediate pressure
compressors 14 and 13 and the fan 12 by suitable interconnecting
shafts.
[0005] As can be seen there are a number of fixed structures such
as pylons and stator vanes utilised in order to control air flow
and also to support casing structures, etc. These structural
features create flow distortions further downstream and/or
upstream, and these distortions can reduce the stability margin of
downstream components. Furthermore, it is known that the onset of
instability in terms of rotating stall/surge is triggered by such
distortions but is not random but always occurs in a particular
location relative to the structure induced distortion.
[0006] Conventional approaches to addressing instability in the
flow relate to so-called casing treatment in terms of creating
casing distortions, that is to say bumps and hollows to adjust and
stabilise fan exit flow distortion, etc as well as asymmetrical
flow path cross-sections. Such approaches can significantly add to
engine complexity and more importantly may reduce engine
efficiency.
[0007] Stationary distortions usually occur in an otherwise
axisymmetric designed device due to structural requirements, such
as fan exit flow distortion caused by a pylon. The situation is
graphically illustrated in FIG. 2 below. The view is that looking
down from the fan 101 tips and the air flows into the engine from
the left side. The presence of a pylon 100 causes high pressure in
front of it (p+) and further away in the two sides the pressure is
relatively low (marked as p-). The pressure field of the pylon 100
may also transmit into the core compressor to induce an inlet flow
distortion in that core. A fan and compressor subject to such
distortions in general show a reduced stability margin which may
endanger the engine during operation. Guide vanes 102 may also be
provided and these vanes will add to potential complexity.
[0008] In addition to use of passive casing treatments it will also
be understood that active control techniques with regard to
compressor stabilities can be used whereby specific control
elements are adjusted to achieve stability during operation. These
control elements may include altering through flap movements the
available flow cross-section and also injecting additional control
air feeds. These techniques as indicated add significantly to
complexity and cost.
[0009] In accordance with the present invention there is provided a
flow control arrangement for turbine engines, the arrangement
comprising a turbine to force fluid flow directed towards a
stationary structure through a conduit whereby that fluid flow is
susceptible to distortion instability downstream from the
stationary structure, the arrangement characterised in that a slot
in the conduit prior to the stationary structure is provided in
order to remove in use fluid from that fluid flow and an outlet
provided prior to the turbine through which the removed fluid is
released.
[0010] Generally, the slot is substantially aligned with the
stationary structure.
[0011] Normally, the fluid is air.
[0012] Normally, the outlet is also aligned with the stationary
structure with a predetermined angular offset.
[0013] Typically, the stationary structure is a pylon or guide
vaneor a non axisymmetric intake.
[0014] Generally, the outlet has a trenched end.
[0015] Normally, the slot presented width to the stationary
structure is determined for flow removal in order to provide flow
stability downstream of that stationary structure. Similarly, the
position of the slot relative to the structure is chosen to provide
flow stabilisation.
[0016] Generally, removed fluid passes along a passage from the
slot to the outlet. Normally, the removed fluid utilises the
pressure of the fluid flow in order to drive removed fluid movement
along the passage.
[0017] Preferably, the passage incorporates diffuser vanes at the
slot. Normally, the outlet incorporates presentation vanes for
release of the removed fluid.
[0018] Also, in accordance with the present invention there is
provided an engine incorporating an arrangement as described
above.
[0019] Embodiments of the present invention will now be described
by way of example and with reference to the accompanying drawings
in which:
[0020] FIG. 3 is a schematic cross-section of an arrangement in
accordance with a first embodiment of the present invention;
[0021] FIG. 4 is a schematic cross-section of an arrangement in
accordance with a second embodiment of the present invention;
[0022] FIG. 5 is a schematic front view of an outlet in accordance
with the present invention as viewed upstream from a stationary
structure; and,
[0023] FIG. 6 is a schematic plan cross-section illustrating the
arrangement depicted in FIG. 4.
[0024] The present invention combines active control of turbine
compressor stabilities and passive casement treatment to limit
dynamic losses due to mixing downstream of a stable structure.
Essentially, there is a fluid bleed from high pressure air at a
location where flow pressure is high and that removed fluid is
re-injected back into the flow close to a rotor turbine leading
edge at the tip and with flow location at the correct flow angle
relative to the rotor blade of the turbine. As the removed fluid
bleeding and re-injection are specifically localised it will be
understood that the fluid mass flow involved is typically only a
fraction of a percentage of the total fluid mass flow through the
engine casing conduit incorporating the turbine. Additionally, as
the removed fluid is taken at an overpressurised flow location, the
tendency of the fluid flow to form a high pressure blockage will be
relieved and some efficiency benefit is normally achieved as well
as improved flow stability margin downstream of the stationary
structure.
[0025] As indicated above, air flows through an engine such as that
schematically illustrated in FIG. 3 may be axisymmetrically or non
axisymmetrically presented. For example, for accommodation purposes
it is not unusual to provide for inlet droop with regard to an
engine used in an aircraft and this inherently creates non
axisymmetrically flows through that engine. With such non
axisymmetric flows in particular, it is possible for distortions
downstream of static structures such as stator vanes or pylons to
cause distortions which in turn result in the onset of instability
in the flow with detrimental consequences with regard to engine
efficiency.
[0026] FIGS. 3 and 4 illustrate two potential embodiments of the
present invention. FIG. 3 illustrates a flow control arrangement 30
in which an air flow 31 is forced by rotor blades 32 of a turbine
in the direction depicted. Downstream of the turbine formed by
blades 32 is a fixed stator structure 33. The distortion presented
at inlet 31 will cause premature instability. It has been found
that the positions of such instability are predictable and so in
accordance with the present invention air is bled from positions
prior to the stator 33 in order to rectify flow distortions due to
angular presentation of flow to the turbine rotor blades 32 and/or
stator 33.
[0027] In accordance with the present invention, a slot 35 is
provided intermediate to the rear of the blades 32 and the front
edge of the stator 33. This slot 35 collects or removes air flow.
The removed air flows along a duct 36 and is re-injected through an
outlet nozzle 37. The slot 35 is associated near its entrance with
diffuser vanes 38 which act to de-swirl the bled or removed air
flow in order to reduce flow losses within the duct 36. Generally,
the duct 36 progressively narrows from the inlet slot 35 end to the
outlet nozzle 37 end. It is necessary to provide a wider
cross-section towards the slot 35 end of the duct 36 in order not
to cause any resistance to bleed removal of air flow. However, the
narrower cross-section towards the outlet nozzle 37 end allows
vanes 39 to present the re-injected air flow at the correct angle
dependent upon rotor blade 32 angle within its turbine.
[0028] Normally, as described later the outlet nozzle 37 has a
trenched end configuration whereby a bottom edge extends down below
the notional casing conduit inner surface in order to present a
re-injected air flow 40 towards the tips of the blades 32. As
described previously, the angle of the re-injected flow 40 will be
facilitated by the vanes 37 and chosen dependent upon the angle of
the blades 32 in the turbine driving flow 31 towards the stator
33.
[0029] The size and position of the inlet slot 35 will be chosen
dependent upon operational requirements in terms of the rate of
airflow 31, blades 32 and stator 33 as well as necessary action to
prevent distortion and subsequently instability at positions
downstream of the stator 33. Generally, the inlet slot 35 will be
oval and have a ratio in the order of 4. The major dimension of
that oval will be presented across the stator 33 or other
structure. Typically, the width of the slot 35 will be greater than
several pitches of the stator 33.
[0030] The inlet slot 35 is typically flush with the surface of a
casing conduit 41 within which the flow 31 is directed. It will be
understood that such flush presentation of the inlet slot 35 avoids
possible turbulence created by a raised or a sunken position.
[0031] It will be appreciated that the distortion and therefore
instability created by the static may vary with flow 31 rate. In
such circumstances it may be possible within the duct 36 to provide
for reduced or enhanced re-injected flow 40. Reduction in the
re-injected flow 40 may be achieved by bleeding from the duct 36 to
reduce the returned air volume whilst increasing that volume may be
achieved through pressurised air addition to the flow through the
duct 36 removed from flow 31 via the inlet slot 35. Nevertheless,
as indicated above, these approaches add significantly to
complexity and will normally be avoided in accordance with the
present invention.
[0032] FIG. 4 illustrates a second embodiment of the present
invention as a schematic part cross-section. Thus, a flow control
arrangement 50 comprises a rotor blade 52 as part of a turbine to
drive an air flow 51 in the direction of the arrowhead towards a
guide vane 53 and a pylon 43. As previously, the guide vane 53 and
pylon 43 are stationary and may cause distortions and therefore
instability in the rotor 52. The rotor blades 52 form part of a
turbine within a casing conduit 61 generally supported by the pylon
43 and within which guide vanes 53 are presented for appropriate
airflow 51 angular presentation.
[0033] In accordance with the present invention an inlet slot 55
bleeds or removes air from the flow 51 into a passage 56 which is
then re-injected through an outlet nozzle 57 at the tip periphery
of the rotor blades 52 of the turbine. In such circumstances
removed air passes in the direction of arrowheads 63 through the
duct passage 56. As described previously generally the passage 56
has a wider cross-section towards the inlet slot 55 end in
comparison with the outlet nozzle 57 end. Diffuser vanes 58 are
provided near the entrance of the inlet slot 55 in order to reduce
swirl and so flow losses through the duct 56. Vanes 59 are provided
near the trenched outlet nozzle 57 in order that the re-injected
air flow 60 is appropriately angularly presented to the tips of the
blades 52.
[0034] It will be understood that the embodiments depicted in FIGS.
3 and 4 generally operate in accordance with the present invention
in a similar fashion. Thus the re-injection outlet nozzle 37, 57 is
located just upstream from the rotor blade 52 turbine bank beneath
the casing conduit 61. The outlet nozzle 37, 57 has a width of
approximately the width of a rotor pitch. As described above the
outlet nozzle 37, 57 will have a trench step in order to minimise
mis-alignment of the re-injected flow 40, 60 with the main flow 31,
51 respectively. Importantly, each outlet nozzle 37, 57
incorporates vanes 39, 59 to provide angular presentation to the
re-injected flow 37, 57 removed from the main flow via the inlet
slots 35, 55. Thus, the re-injected flows 37, 57 are directed
towards the rotor blades 32, 52 staggered directional angle.
[0035] It will be understood that bled or removed flow and
re-injection in accordance with the present invention in order to
avoid distortion and subsequent instability is only needed for the
distorted part of the flow circumference, that is to say about
stationary structures such as stator, guide vanes or pylons. The
relatively high pressure behind rotors 32, 52 is utilised in order
to drive removed or bled flow through the duct passages 36, 56 and
this bleeding of the air fluid flow relieves the high pressure
distortion. The use of vanes 39, 59 as indicated creates askewed
angular high speed re-injection of air flows 40, 60 towards the
blades 32, 52 which is concentrated at the tips of those blades 32,
52. In such circumstances the present invention provides improved
resistance to instability caused by distortion. In effect
distortion is suppressed by bleeding air flow from the high
pressure part of the circumference. Clearly, with respect to
removal of instability there is a significant improvement in
efficiency and overall pressure rise.
[0036] As indicated above, generally flow is removed or bled
through an inlet slot due to the localised high pressure at
differing positions on the circumference. It will be appreciated
that these localised high pressures are due to axi-symmetric flow
so that the inlet slot may be substantially aligned with the
stationary structure such as a pylon or stator or positioned to one
side or the other depending upon presented flow from the rotor
blade turbine assembly. Such localised collection of bled or
removed fluid air flow may possibly relieve flow blockage towards
the rear of the turbine. The removed high pressure fluid flow is
de-swirled using diffuser vanes and subsequently vented through a
duct passage to an outlet slot or nozzle appropriately positioned
in front of the rotor blades. The exit of the outlet nozzle or slot
has small vanes in order to guide and direct the injected flow
towards rotor blade tips. This injected flow at the rotor tips
suppresses any instability. As indicated above, a local trenched
step in the outlet nozzles helps to keep the injected flow adjacent
to and in the vicinity of the casing conduit at the rotor blade
tips.
[0037] FIG. 5 provides a part schematic cross-section illustrating
an arrangement in accordance with the present invention. Thus, a
flow control arrangement 70 includes a turbine with rotating rotor
blades 72 which drive an air flow in the direction perpendicularly
out of the plane of the drawing. In accordance with the present
invention a duct passage 76 is provided through which the bled or
removed air passes in order that that air can be re-injected prior
to the blades 72. An outlet nozzle 77 includes vanes 79 which act
to direct the injected air flow towards tip portions 71 of the
blades 72 as they rotate past the outlet nozzle 77. Generally, the
injected flow remains close to the inner surface 73 of a casing
conduit 74 within which the duct passage 76 is formed.
[0038] FIG. 6 is a schematic part plan view of an arrangement in
accordance with the present invention. A pylon 83 is positioned
relative to a rotor turbine bank 82 with guide vanes 83 positioned
to straighten air flow 81 as it progresses in the direction of
arrowhead A. It will be appreciated that the turbine 82 forces flow
81 through a conduit (not shown). In accordance with the present
invention an inlet slot 85 is positioned relative to the pylon 83
in order to relieve high pressure. As indicated previously, the
removed or bled fluid air flow passes through a duct passage (not
shown) to an outlet nozzle 87 upstream of the turbine 82. A
re-injected flow 90 is presented through the outlet 87 utilising
vanes within that outlet 87 in order that the flow 90 is
appropriately skewed and angled relative to the blades of the
turbine 82. Broken line arrow 86 shows the direction of removed air
flow from the inlet slot 85 to the outlet nozzle 87. It will also
be noted that the notional passage shown by broken lines 88
indicates the constriction from that inlet slot 85 to the outlet
slot 87. In such circumstances the inherent nature of such
presentation of the removed or bled air forces projection of the
flow 90 through the vanes of the outlet 87 in order to avoid
creation of distortion in the overall flow 81 and so instability,
particularly subsequent to pylon 83.
[0039] As described above, the actual presented aspect width of the
inlet slot utilised in accordance with the present invention will
depend upon a number of factors including the width of the
structure which may cause distortion and therefore downstream
instability as well as the flow rate and turbine blade structure.
The inlet slot will generally be oval or a rectangular slit in
order to ensure that appropriate fluid flow removal or bleed is
achieved. Generally the presented cross-section will be greater
than the width of the structure downstream.
[0040] The position of the outlet nozzle will be chosen in order to
provide best relief of distortions and therefore instability in the
main fluid airflow. Thus, as depicted in FIGS. 6, the outlet nozzle
87 is slightly askew and not aligned with the pylon 83. In such
circumstances it will be appreciated that the dimensions, position
and relative alignments of the principal elements, that is to say
inlet slot, outlet nozzle and stationary structure may be varied by
operational and performance criteria and requirements.
Nevertheless, only a fraction of a percentage of the overall main
fluid air flow will be bled through the inlet slot for re-injection
such that there will be little significant effect upon the overall
mass flow through an engine incorporating an arrangement in
accordance with the present invention.
[0041] Whilst endeavouring in the foregoing specification to draw
attention to those features of the invention believed to be of
particular importance it should be understood that the Applicant
claims protection in respect of any patentable feature or
combination of features hereinbefore referred to and/or shown in
the drawings whether or not particular emphasis has been placed
thereon.
* * * * *