U.S. patent application number 11/878878 was filed with the patent office on 2008-01-31 for mounting disc.
Invention is credited to Nicholas Bayley, Philip Scope.
Application Number | 20080025843 11/878878 |
Document ID | / |
Family ID | 37006299 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080025843 |
Kind Code |
A1 |
Scope; Philip ; et
al. |
January 31, 2008 |
Mounting disc
Abstract
Mounting discs (20, 30, 40, 50) are used in gas turbine engines
to present turbine or compressor blades. These discs (20, 30, 40,
50) incorporate a bore or cob end 31, 41, 51 which in turn
previously had a flat end face surface. Such flat end face surfaces
are weight efficient but can lead to reduced component life and a
limitation with regard to rotational speed due to Von-Mises
stresses. By providing a deviation (39, 49, 59, 69) in the end face
from a flat aspect, a reduction in axial stress is achieved with a
marginal increase in hoop stress but with a net result that there
is a reduction in the general operational Von-Mises stresses and
therefore improvement in disc life or potential rotation speed
capacity or both.
Inventors: |
Scope; Philip; (Derby,
GB) ; Bayley; Nicholas; (Derby, GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Family ID: |
37006299 |
Appl. No.: |
11/878878 |
Filed: |
July 27, 2007 |
Current U.S.
Class: |
416/204A |
Current CPC
Class: |
F01D 5/30 20130101; F01D
5/02 20130101; F05D 2250/711 20130101 |
Class at
Publication: |
416/204.A |
International
Class: |
F01D 5/02 20060101
F01D005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2006 |
GB |
0614972.8 |
Claims
1. A disc for mounting rotating components, the disc characterised
in that the bore end has an end face with deviation from a flat
perpendicular aspect relative to radial plane.
2. A disc as claimed in claim 1 wherein the deviation is a convex
curve.
3. A disc as claimed in claim 2 wherein the convex curve has a
consistent convex radius.
4. A disc as claimed in claim 2 wherein the convex radius has a
maximum radius equivalent to half of the axial width of the disc
across the radial plane.
5. A disc as claimed in claim 2 wherein the convex curve is a
smooth curve.
6. A disc as claimed in claim 2 wherein the convex curve is
conic.
7. A disc as claimed in claim 2 wherein the convex curve is semi
circular.
8. A disc as claimed in claim 1 wherein the deviation comprises a
trapezoidal shape for the bore end.
9. A disc as claimed in claim 8 wherein the trapezoidal shape has a
side projection relative to the radial plane having an angle in the
range 5-45.degree..
10. A disc as claimed in claim 1 wherein the deviation is
triangular.
11. A disc as claimed in claim 10 wherein an apex for the
triangular deviation is rounded.
12. A disc as claimed in claim 1 wherein the cob end has a stepped
portion to achieve a desired weight distribution in the disc.
13. A disc as claimed in claim 1 wherein a ratio of the depth of
the deviation divided by width of the mounting disc across from the
flat perpendicular to the radial plane is in the range 0.03 to
0.5.
14. A disc as claimed in claim 1 wherein the shape and extent of
deviation provided is subject to material and rotational speed
determined to substantially provide zero compression axial stress
differential across the mounting end.
15. A disc as claimed in claim 1 wherein the deviation is outward.
Description
[0001] The present invention relates to mounting discs and more
particularly to a mounting disc utilised to secure rotating blades
in compressor or turbine stages of a gas turbine engine.
[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] In view of the above, it will be understood that a gas
turbine engine incorporates a number of compressor and turbine
stages. The blades for those compressor and turbine stages are
secured upon mounting discs such that the blades can rotate as
appropriate. The mounting discs are secured to the rotating shaft
through a disc cob. It will be appreciated relatively high
temperatures are generated within a gas turbine engine such that
the engine thermo dynamic cycle dictates to a significant extent
the disc cob size. The weight efficient solution to meet an over
speed requirement is to provide a flat cob end for the mounting
disc. Rotational speed and mass dictate size whilst thermal
gradients worsen stressing for large disc sizes.
[0006] In order to increase efficiency, it is generally desirable
to provide smaller and faster engine cores. Such smaller and faster
engine cores result in relatively large mounting disc cob sizes to
meet expected over speed requirements. It will be appreciated as
the cob disc size increases, the potential for large thermal
gradients across the disc cob end also increases. It will be
understood that a disc cob end essentially comprises a relatively
thick section and therefore high thermal gradients between surface
portions of the mounting disc and the centre of that disc cob can
be created. It is not unusual for there to be a differential of
several hundred degrees centigrade with a result that there is high
biaxial stress across the cob end of the mounting disc. This high
biaxial stress becomes a fatigue life limiting feature of a
mounting disc. In any event, provision of a plain flat cob end,
that is to say a flat end perpendicular to the radial plane,
results in relatively low disc operational life at a desired
rotational speed or a shaft speed limit or both. It will be
understood that biaxial stress relates to both centrifugal stress
(hoop) and axial stress within the cob end. Furthermore,
accumulation of significant axial compressive stress in conjunction
with high hoop stress results in a considerable fatigue life
reduction when compared to a uniaxial stress field of the same
magnitude. Such a combination of hoop and axial stress is generally
combined into a single stress measure called Von-Mises stress and
it is accepted that the higher the Von-Mises stress, the sooner a
fatigue crack will be initiated resulting in a lower fatigue
life.
[0007] In accordance with aspects of the present invention there is
provided a disc for mounting rotating components, the disc
characterised in that the bore end has an outward deviation from a
flat perpendicular aspect relative to the radial plane.
[0008] Typically, the deviation is outward.
[0009] Typically, the deviation is a convex curve. Generally, the
convex curve has a consistent convex radius. Potentially, the
convex radius has a maximum radius equivalent to half of the axial
width of the disc across the radial plane. Generally, the convex
curve is a smooth curve. Potentially, the convex curve is conic.
Potentially, the convex curve is semi circular.
[0010] Alternatively, the deviation comprises a trapezoidal shape
for the cob or bore end. Potentially, the trapezoidal shape has a
side projection relative to the radial plane having an angle in the
range 5-45.degree..
[0011] Possibly, the deviation is triangular. Advantageously, an
apex for the triangular deviation is rounded.
[0012] Further alternatively, the cob or bore end has a stepped
portion to achieve a desired weight distribution in the disc.
[0013] Possibly, a ratio of the depth of the deviation divided by
width of the mounting disc across from the flat perpendicular to
the radial plane is in the range 0.03 to 0.5.
[0014] Possibly, the shape and extent of deviation provided is
subject to material and rotational speed determined to
substantially provide zero compression axial stress differential
across the mounting end.
[0015] Embodiments of the present invention will now be described
by way of example and with reference to the accompanying drawings
in which:
[0016] FIG. 1 illustrates a sectional side view of the upper half
of a gas turbine engine;
[0017] FIG. 2 is a schematic illustration of a prior flat end
mounting disc;
[0018] FIG. 3 is a schematic cross section of a first embodiment of
a mounting disc in accordance with aspects of the present
invention;
[0019] FIG. 4 is a schematic illustration of a second embodiment of
a mounting disc in accordance with aspects of the present
invention;
[0020] FIG. 5 is a schematic illustration of a third embodiment of
a mounting disc in accordance with aspects of the present
invention; and,
[0021] FIG. 6 is a schematic illustration of a fourth embodiment of
a mounting disc in accordance with aspects of the present
invention.
[0022] As indicated above, as desired engine core speeds increase
whilst the size of the cores becomes smaller, potential problems
with respect to fatigue failure as a result of stress and in
particular Von-Mises stress, become problematic. Traditionally,
weight, particularly with regard to aeronautical applications of
gas turbine engines, has been a significant factor and therefore
provision of a flat end surface for a bore end of a mounting disc
has been considered the most efficient solution.
[0023] FIG. 2 illustrates a typical flat or plain end mounting disc
configuration. It will be appreciated that only one side of the
mounting discs is illustrated with an annular disc secured upon a
rotating shaft. The mounting disc 120 has three major portions
namely, a bore or cob end 121, a diaphragm portion 122 and a rim
portion 123. The bore end 121 essentially allow the mounting disc
120 to be secured to a shaft. In use it will be appreciated that
mounting discs 120 are utilised with respect to turbine blades and
compressor blades in a gas turbine engine. Particularly with
respect to high pressure turbine blades it will be understood that
increasing thrust increases the level of hot gasses adjacent to the
mounting disc and therefore heating of the cob area 121. As this
cob area 121 has a relatively thick cross section thermal inertia
ensures that peripheral surface portions of the cob end 121 heat up
much quicker than central parts of the cob end 121 resulting in a
temperature differential of a few hundred degrees centigrade across
the cob end 21.
[0024] The stresses on the cob or bore end are a combination of
axial stress due to rotation of the mounting discs and associated
blades as well as circumferential. These stresses are combined as
Von-Mises stresses.
[0025] Broken line 124 schematically illustrates a typical axial
stress band in a flat or plane face mounting end 121. As indicated,
these stresses can result in premature failure or a design
limitation on shaft speed or both. Ideally, an objective is to
optimise in terms of shape the mounting end 121 to minimise or
control Von-Mises stress. However, it should be understood that it
is the net effect in reducing Von-Mises stress that is desirable in
order to achieve an increased life at the bore surface. Thus,
selecting a profile which significantly reduces the level of
compressive axial stresses although slightly increasing the
circumferential stress would be acceptable in terms of achieving a
net reduction in Von-Mises stresses or vice versa. A further
advantage is with regard to separating the location of peak hoop
stress and peak axial stress within the disk 120. As indicated, by
achieving a net reduction in Von-Mises stress, a greater disc
fatigue life and potentially higher shaft speeds will be
possible.
[0026] Aspects of the present invention relate to providing a
deviation from a flat surface as depicted in FIG. 2. In such
circumstances, by providing a convexed or other outward deviation
from a flat perpendicular aspect relative to a radial plane will
allow material to expand more readily reducing barriers to
expansion and therefore stresses.
[0027] FIG. 3 illustrates a trapezoidal cob or bore end 31 in a
disc 30. It has been found by re-distributing the material in the
cob end 31, as indicated above, there is an overall increase in
allowability with respect to expansion such that stress
distribution shown by broken line 34 results in a peak hoop stress
at an area 35 and peak axial stress at an area 36. It has been
found that the axial compression stress is lowered whilst there is
an increase in the hoop stress but overall the net result is a
Von-Mises stress level which is lower and therefore a net
improvement in operational performance. By creating the deviation
from a flat perpendicular aspect shown by the plane X rearwardly
the benefits with respect to reduction of Von-Mises stresses is
achieved. It will be understood that the disc 31 has a general
radial plane 37 through its centre line and the cob or mounting end
31 extends either side of this radial plane 37. In such
circumstances, it is the deviation in a face 39 of the cob or
mounting end 31 along the radial plane 37 which is determinant as
to the stress variation. It can be seen that this deviation has a
depth depicted between arrowheads 38 along the radial plane 37 and,
as indicated, generally takes a trapezoidal shape in the first
embodiment depicted in FIG. 3. The angle 33 at the sides may be in
the range of 5-45.degree. dependent upon requirements.
[0028] FIG. 4 illustrates a typical convex end face 49 to a cob or
bore 41 of a disc 40. Again, as can be seen, the disc 40 has a
radial plane 47. The face 49 deviates by a depth 48 with a smooth
convex curve. In such circumstances, again by shaping of the face
expansion is more readily allowed so reducing Von-Mises stress and
therefore operational effectiveness of the disc 40.
[0029] FIG. 5 illustrates a third embodiment of a disc in
accordance with aspects of the present invention. As previously,
the disc 50 has a cob or mounting end 51 with an end face 59 which
deviates to the depth 58 for a continual flat perpendicular aspect
X-X relative to a radial plane 57 for the disc 50. In the third
embodiment depicted in FIG. 5 a face 59 substantially reflects a
triangle which again through shaping allows easier expansion and
therefore reduction in Von-Mises stresses within the end 51
resulting in a longer operational life and/or potentially higher
rotational speeds for the disc 50. It will be noted the triangular
nature of the end 51 is exaggerated for illustration purposes.
[0030] It will be understood in order to provide a minimum hoop
stress, generally a maximum amount of material in the cob end
should be towards the radial plane of the disc. In such
circumstances as depicted in FIG. 6 with regard to a fourth
embodiment of aspects of the present invention, it will be
appreciated that a fully semi circular end face 69 would be ideal
in a disc 60 in order to provide the desired material distribution.
Thus, within a cob or mounting end 61 the end face 69 would be
ideal in a disc 60 in order to provide the desired material
distribution. Within the cob or mounting end 61 the end face 69
extends away from notional flat perpendicular plane to a radial
plane 67 of the disc 60.
[0031] In view of the above, it will be appreciated that aspects of
the present invention provide through the deviation to the face for
the bore or cob end potential for adjusting the Von-Mises stress
effects. By creating a cob end which deviates from a flat surface,
as indicated, generally there will be a reduction in the axial
stress but an increase in hoop stress. However, by judicious choice
of the deviation a net reduction cross over point can be provided
where the benefits of a reduction in axial stress outweigh the
potential increases in hoop stresses.
[0032] As indicated above, the particular degree and shape of
deviation in the cob or mounting end will depend upon operational
requirements in terms of material available, acceptability of
weight penalties and desired or expected rotational speeds.
However, where the deviation is a convexed face (FIG. 4) it is
expected that the maximum radius of the curvature will be half the
axial width of the bore, that is to say the width of the disc
extending either side of the radial plane of that disc. Where the
deviation is a trapezium it is expected the side angles will be in
the range 5-45.degree. leading to a flat bottom surface of narrower
width. It will be understood, as indicated, that the cob end may
incorporate a triangular end face with an apex end of that triangle
rounded. It will also be understood that the cob end may
incorporate, as indicated, a smooth convex surface and that this
smooth surface may be conic in section.
[0033] The depth of deviation (38 in FIG. 3, 48 in FIG. 4, 58 in
FIG. 5) will be in the ratio whereby the deviation depth divided by
the width of the cob or mounting end relative to the radial plane
will be in the range 0.03 to 0.5.
[0034] It will be appreciated that generally the deviation depth
relative to width will be chosen to reduce maximum compressive
axial stress differential across the disc bore in comparison with a
disc bore with no deviation depth, that is to say flat or
plain.
[0035] Generally, as indicated above, by altering the face surface
of the cob or mounting end, adjustments in axial and hoop stresses
can be made which on balance and net lead to an improvement in
component life and/or a potential for higher rotational speeds.
[0036] Modifications and alterations to aspects of the invention
described above will be appreciated by those skilled in the art.
Thus, as indicated, in order to achieve minimum hoop stress the
maximum amount of metal should be presented towards the centre line
or radial plane of the disc.
[0037] 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.
* * * * *