Note: Descriptions are shown in the official language in which they were submitted.
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
TURBINE AIRFOIL TRAILING EDGE BIFURCATED COOLING HOLES
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001]The present invention relates generally to gas turbine engine turbine
airfoil
cooling and, more specifically, to turbine airfoil trailing edge cooling
slots.
DESCRIPTION OF RELATED ART
[0002] In a gas turbine engine, air is pressurized in a compressor and mixed
with
fuel in a combustor for generating hot combustion gases. The hot gases are
channeled through various stages of a turbine which extract energy therefrom
for
powering the compressor and producing work, such as powering an upstream
fan in a typical aircraft turbofan engine application.
[0003] The turbine stages include stationary turbine nozzles having a row of
hollow vanes which channel the combustion gases into a corresponding row of
rotor blades extending radially outwardly from a supporting rotor disk. The
vanes
and blades have corresponding hollow airfoils with corresponding cooling
circuits
therein.
[0004] The cooling air is typically compressor discharge air which is diverted
from
the combustion process and, therefore, decreases overall efficiency of the
engine. The amount of cooling air must be minimized for maximizing the
efficiency of the engine, but sufficient cooling air must nevertheless be used
for
adequately cooling the turbine airfoils for maximizing their useful life
during
operation. Each airfoil includes a generally concave pressure sidewall and, an
opposite, generally convex suction sidewall extending longitudinally or
radially
outwardly along a span from an airfoil base to an airfoil tip and axially in
chordwise direction between leading and trailing edges. For a turbine blade,
the
airfoil span extends from a root at the radially inner platform to a radially
outer tip
spaced from a surrounding turbine shroud. For a turbine vane, the airfoil
extends
from a root integral with a radially inner band to a radially outer tip
integral with
1
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
an outer band.
[0005]Each turbine airfoil also initially increases in thickness aft of the
leading
edge and then decreases in thickness to a relatively thin or sharp trailing
edge
where the pressure and suction sidewalls join together. The wider portion of
the
airfoil has sufficient internal space for accommodating various forms of
internal
cooling circuits and turbulators for enhancing heat transfer cooling inside
the
airfoil, whereas, the relatively thin trailing edge has correspondingly
limited
internal cooling space.
[0006]Each airfoil typically includes various rows of film cooling holes
extending
through the sidewalls thereof which discharge the spent cooling air from the
internal circuits. The film cooling holes are typically inclined in the aft
direction
toward the trailing edge and create a thin film of cooling air over the
external
surface of the airfoil that provides a thermally insulating air blanket for
additional
protection against the hot combustion gases which flow over the airfoil
surfaces
during operation.
[0007]The thin trailing edge is typically protected by a row of trailing edge
cooling
slots which breach the pressure sidewall at a breakout immediately upstream of
the trailing edge for discharging film cooling air thereover. Each trailing
edge
cooling slot has an outlet aperture in the pressure side which begins at a
breakout and may or may not be bounded in the radial direction by exposed
lands at aft ends of axially extending partitions which define the cooling
slots.
[0008]The axial partitions may be integrally formed with the pressure and
suction
sides of the airfoil and themselves must be cooled by the air discharged
through
the cooling slots defined thereby. The partitions typically converge in the
aft
direction toward the trailing edge so that the cooling slots diverge toward
the
trailing edge with a shallow divergence angle that promotes diffusion of the
discharged cooling air with little if any flow separation along the sides of
the
partitions.
[0009]Aerodynamic and cooling performance of the trailing edge cooling slots
is
directly related to the specific configuration of the cooling slots and the
intervening partitions. The flow area of the cooling slots regulates the flow
of
2
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
cooling air discharged through the cooling slots, and the geometry of the
cooling
slots affects cooling performance thereof.
[0010]The divergence or diffusion angle of the cooling slots can effect
undesirable flow separation of the discharged cooling air which would degrade
performance and cooling effectiveness of the discharged air. This also
increases
losses that impact turbine efficiency. Portions of the thin trailing edge
directly
under the individual cooling slots are effectively cooled by the discharged
cooling
air, with the discharged air also being distributed over the intervening
exposed
lands at the aft end of the partitions. The lands are solid portions of the
pressure
sidewall integrally formed with the suction sidewall and must rely for cooling
on
the air discharged from the adjacent trailing edge cooling slots.
[0011]Notwithstanding, the small size of the these outlet lands and the
substantial cooling performance of the trailing edge cooling slots, the thin
trailing
edges of turbine airfoils nevertheless typically limit the life of those
airfoils due to
the high operating temperature thereof in the hostile environment of a gas
turbine
engine.
[0012]Accordingly, it is desired to provide a turbine airfoil having improved
trailing edge cooling and cooling slots for improving airfoil durability and
engine
performance. It is also desired to minimize the amount of cooling flow used
for
trailing edge cooling in order to maximize fuel efficiency of the turbine and
the
engine.
SUMMARY OF THE INVENTION
[0013] A gas turbine engine turbine airfoil includes widthwise spaced apart
pressure and suction sidewalls extending outwardly along a span from an
airfoil
base to an airfoil tip and extend chordwise between opposite leading and
trailing
edges. A spanwise row of spanwise spaced apart bifurcated trailing edge
cooling
holes are encased in the pressure sidewall and end at corresponding spanwise
spaced apart trailing edge cooling slots extending chordally substantially to
the
trailing edge. The cooling holes are separated from each other by axially
extending inter-hole partitions. Each of the cooling holes include a
convergent
3
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
divergent inlet between adjacent pairs of the inter-hole partitions. The
convergent divergent inlet includes in downstream serial cooling flow
relationship
a convergent inlet section, a throat, and a divergent inlet section. An axial
intra-
hole partition extending downstream towards the trailing edge bifurcates the
cooling hole into spanwise spaced apart and spanwise diverging upper and lower
diverging sections downstream and aft of the divergent inlet section. A
forward
end of the intra-hole partition divides or splits an aft or downstream end of
the
divergent inlet section into spanwise spaced apart upper and lower inlet
flowpaths leading to the upper and lower diverging sections respectively. The
upper and lower diverging sections lead into the trailing edge cooling slot.
[0014] The inlet may be a constant area inlet upstream of the divergent inlet
section. The constant area inlet has a downstream extending first length and
includes a metering section having a constant area flow cross section, a
constant
width, and a constant height through the entire first length.
[0015] The pressure and suction sidewalls include pressure and suction
sidewall
surfaces respectively in the hole and the pressure sidewall surface may be
planar through the entire upper and lower diverging sections. The width may be
constant through the upper and lower diverging sections of the hole.
[0016] Lands may be disposed between spanwise adjacent ones of the trailing
edge cooling slots and slot floors may be disposed in the trailing edge
cooling
slots between the lands. The lands may be coplanar or flush with an external
surface of the pressure sidewall around each of the cooling slots.
Alternatively,
the lands angled away from the external surface by a land angle in a range
between 0-5 degrees.
[0017] The diverging sections may have a race track shaped flow cross section.
The race track shaped flow cross section includes a rectangular section
between
spanwise spaced apart rounded or semi-circular inner and outer end sections
having corner radii. Fillets having fillet radii are in slot corners between
the lands
and the slot floors and the fillet radii are substantially the same size as
the corner
radii of the flow cross section.
[0018] At least one of the upper and lower diverging sections may include
raised
4
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
floors extending downstream and at least partially through the cooling slots.
Each of the raised floors includes, in downstream serial relationship, a flat
or
curved up ramp in the upper and lower diverging sections, a flat or curved
down
ramp in the trailing edge cooling slot, and a transition section between the
up and
down ramps. The up ramp ramps up from the suction sidewall surface in the
upper and lower diverging sections. The down ramp ramps down and extends
downstream from the transition section to the trailing edge.
[0019] The lands may be angled towards the slot floor and away from the
external surface of the pressure sidewall and the lands and intercept the slot
floor
upstream of the trailing edge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing aspects and other features of the invention are explained
in
the following description, taken in connection with the accompanying drawings
where:
[0021] FIG. 1 is a longitudinal, sectional view illustration of an exemplary
embodiment of turbine vane and rotor blade airfoils having bifurcated cooling
holes culminating at spanwise spaced apart trailing edge cooling slots.
[0022] FIG. 2 is an enlarged view illustration of a blade illustrated in FIG.
1.
[0023] FIG. 3 is a pressure side sectional view illustration of cooling holes
with a
bifurcated inlet followed by bifurcated diffusing sections leading into two of
the
trailing edge cooling slots illustrated in FIG. 2.
[0024] FIG. 4 is a cross sectional schematical view illustration of one of the
two
diffusing sections and its corresponding trailing edge cooling slot taken
through
4-4 in FIG. 3.
[0025] FIG. 5 is an upstream looking perspective view illustration of the
trailing
edge cooling slots illustrated in FIG. 3.
[0026] FIG. 6 is a cross sectional schematical view illustration of an
elongated
flow cross section in the constant width metering section taken through 6-6 in
FIG. 3.
[0027] FIG. 7 is a cross sectional schematical view illustration of an
elongated
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
flow cross section in the diffusing section taken through 7-7 in FIG. 3.
[0028] FIG. 8 is a cross sectional schematical view illustration of a race
track
shaped flow cross section having four equal corner radii.
[0029] FIG. 9 is a cross sectional schematical view illustration of an
alternative
race track shaped flow cross section with a larger width to height ratio than
the
race track shaped flow cross section illustrated in FIG. 8.
[0030] FIG. 10 is a cross sectional schematical view illustration of an
alternative
flow cross section with unequal top and bottom corner radii.
[0031] FIG. 11 is a cross sectional schematical view illustration of another
alternative flow cross section with in elongated and fully curved and includes
curved quarter sides.
[0032] FIG. 12 is a cross sectional schematical view illustration of curved up
and
down ramps of a raised floor in the cooling holes and the trailing edge
cooling
slots.
[0033] FIG. 13 is a pressure side sectional view illustration of an
alternative inlet
with a constant width and constant height metering section.
[0034] FIG. 14 is a perspective view illustration of one of the metering
section in
FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Illustrated in FIG. 1 is an exemplary gas turbine engine high pressure
turbine stage 10 circumscribed about an engine centerline axis 8 and
positioned
between a combustor 20 and a low pressure turbine (LPT) 24. The combustor
20 mixes fuel with pressurized air for generating hot combustion gases 19
which
flows downstream through the turbines.
[0036] The high pressure turbine stage 10 includes a turbine nozzle 28
upstream
of a high pressure turbine (HPT) 22 through which the hot combustion gases 19
are discharged into from the combustor 20. The exemplary embodiment of the
high pressure turbine 22 illustrated herein includes at least one row of
circumferentially spaced apart high pressure turbine blades 32. Each of the
turbine blades 32 includes a turbine airfoil 12 integrally formed with a
platform 14
6
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
and an axial entry dovetail 16 used to mount the turbine blade on a perimeter
of
a supporting rotor disk 17.
[0037] Referring to FIG. 2, the airfoil 12 extends radially outwardly along a
span
S from an airfoil base 34 on the blade platform 14 to an airfoil tip 36.
During
operation, the hot combustion gases 19 are generated in the engine and flow
downstream over the turbine airfoil 12 which extracts energy therefrom for
rotating the disk supporting the blade for powering the compressor (not
shown).
A portion of pressurized air 18 is suitably cooled and flowed to the blade for
cooling thereof during operation.
[0038] The airfoil 12 includes widthwise spaced apart generally concave
pressure
and convex suction sidewalls 42 and 44. The pressure and suction sidewalls 42,
44 extend longitudinally or radially outwardly along the span S from the
airfoil
base 34 to the airfoil tip 36. The sidewalls also extend axially in a
chordwise
direction C between opposite leading and trailing edges LE, TE. The airfoil 12
is
hollow with the pressure and suction sidewalls 42, 44 being spaced widthwise
or
laterally apart between the leading and trailing edges LE, TE to define an
internal
cooling cavity or circuit 54 therein for circulating pressurized cooling air
or coolant
flow 52 during operation. The pressurized cooling air or coolant flow 52 is
from
the portion of pressurized air 18 diverted from the compressor.
[0039] The turbine airfoil 12 increases in width W or widthwise from the
leading
edge LE to a maximum width aft therefrom and then converges to a relatively
thin
or sharp trailing edge TE. The size of the internal cooling circuit 54
therefore
varies with the width W of the airfoil, and is relatively thin immediately
forward of
the trailing edge where the two sidewalls integrally join together and form a
thin
trailing edge portion 56 of the airfoil 12. Spanwise spaced apart trailing
edge
cooling slots 66 are provided at or near this thin trailing edge portion 56 of
the
airfoil 12 to cool it.
[0040] Referring to FIG. 3, a row 38 of spanwise spaced apart bifurcated
trailing
edge cooling holes 30 encased or buried and formed in the pressure sidewall 42
leading to corresponding ones of the spanwise spaced apart trailing edge
cooling
slots 66. The cooling holes 30 are separated radially along the span S from
each
7
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
other by downstream extending axial inter-hole partitions 80. The trailing
edge
cooling slots 66 extend chordally substantially to the trailing edge TE. The
trailing edge cooling holes 30 are disposed along the span S of the trailing
edge
TE in flow communication with the internal cooling circuit 54 for discharging
the
coolant flow 52 therefrom during operation.
[0041] The trailing edge cooling holes 30 are illustrated in more
particularity in
FIG. 3. Each of the cooling holes 30 includes a convergent divergent inlet 70
located between adjacent pairs of the inter-hole partitions 80. The inlet 70
includes in downstream serial flow relationship a convergent inlet section
106, a
throat 104, and a divergent inlet section 108. An axial intra-hole partition
68
extending downstream towards the trailing edge TE bifurcates the cooling hole
30 into spanwise spaced apart and spanwise diverging upper and lower diverging
sections 102, 103 downstream and aft of the divergent inlet section 108. A
forward end 72 of the intra-hole partition 68 divides or splits an aft or
downstream
end 110 of the divergent inlet section 108 into spanwise spaced apart upper
and
lower inlet flowpaths 112, 114 leading to the upper and lower diverging
sections
102, 103 respectively. The forward end 72 of the partitions 68 is semi-
circular
having a base diameter 73 that defines the beginning of the upper and lower
diverging sections 102, 103.
[0042] Each of the upper and lower diverging sections 102, 103 leads into one
of
the trailing edge cooling slots 66 and supplies the slot with cooling air or
coolant
flow 52 for film cooling. The trailing edge cooling slot 66 begins at a
breakout 58
at a downstream end 69 of each of the upper and lower diverging sections 102,
103. The trailing edge cooling slot 66 embodiment illustrated herein diverges
in a
spanwise direction defined by the span S. The intra-hole partition 68 extends
downstream from the upper and lower flowpaths 112, 114 of the downstream end
110 of the divergent inlet section 108 towards the trailing edge TE and
separate
the upper and lower diverging sections 102, 103 from each other.
[0043] Referring to FIGS. 3-5, a spanwise height H of each of the upper and
lower diverging sections 102, 103 is defined between the upper and lower hole
surfaces 46, 48 of the intra-hole and the inter-hole partitions 68, 80
respectively
8
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
(as illustrated in FIG. 3). A hole width W of each of the upper and lower
diverging sections 102, 103 is defined between pressure and suction sidewall
surfaces 39, 40 of the pressure and suction sidewalls 42, 44 respectively in
each
of the upper and lower diverging sections 102, 103 as illustrated in FIG. 4.
The
trailing edge cooling slots 66 include a slot floor 51 open and exposed to the
hot
combustion gases 19 that pass through the high pressure turbine 22. The slot
floor 51 extends for the entire third length L3 along the suction sidewall 44.
[0044] Referring to FIGS. 6 and 7, each of the upper and lower diverging
sections
102, 103 has a generally spanwise elongated flow cross section 74 and the
spanwise height H is substantially greater than the hole width W. Each of the
upper and lower diverging sections 102, 103 has a height to width ratio H/W in
a
range of about 2:1 to 10:1 (see FIGS. 4-10). The pressure and suction sidewall
surfaces 39, 40 of the pressure and suction sidewalls 42, 44 respectively
widthwise bound the hole 30. The upper and lower diverging sections 102, 103
and the trailing edge cooling slots 66 have downstream extending second and
third lengths L2 and L3 respectively as illustrated in FIG. 3.
[0045] The embodiment of the upper and lower diverging sections 102, 103
illustrated in FIG. 4 has a fixed or constant width W through the upper and
lower
diverging sections 102, 103 and the pressure and suction sidewall surfaces 39,
40 are parallel through the entire second length L2 of the upper and lower
diverging sections 102, 103. The pressure sidewall surface 39 is flat or
planar
through the entire second length L2 of the diverging sections. In this
embodiment of the cooling hole 30 the suction sidewall surface 40 is flat or
planar through the entire upper and lower diverging sections 102, 103 and
their
corresponding second lengths L2. The slot floor 51 is coplanar with suction
sidewall surface 40 in the hole 30. The upper and lower diverging sections
102,
103 or are of constant width W, in the embodiment of the trailing edge cooling
holes 30 illustrated in FIG. 3 and schematically illustrated in solid line in
FIG. 4.
The upper and lower diverging sections 102, 103 diverge in the spanwise
direction.
[0046] The upper and lower diverging sections 102, 103 of the cooling holes 30
9
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
lead into the trailing edge cooling slots 66 which breach the external surface
43
of the pressure sidewall 42 at a breakout lip 49 spaced forward or upstream
from
the trailing edge TE. Each trailing edge cooling slot 66 is radially or
spanwise
bounded by exposed lands 50 at aft ends 116 of the intra-hole and the inter-
hole
partitions 68, 80. As illustrated in solid line in FIG. 4, the lands 50 are
coplanar
or flush with the external surface 43 of the pressure sidewall 42 around each
of
the exposed cooling slot 66, including the common breakout lip 49 extending
radially therebetween. This maximizes flow continuity of the pressure side of
the
airfoil.
[0047] Referring to FIGS. 4 and 5, slot surfaces 60 extend widthwise between
the
lands 50 along the slot floors 51. Fillets 62 in slot corners 64 between the
lands
50 and the slot floors 51 have fillet radii RF that may be substantially the
same
size as bottom corner radii RT of the flow cross section 74 of the diverging
sections 102 adjacent the bottom corner radii RT. The fillet radii RF helps
with
castability of the trailing edge cooling slots 66. The fillet radii RF helps
improve
cooling of the lands 50 by redistributing coolant flow 52 in the trailing edge
cooling slots from the slot floor 51 to the lands 50 in order to make coolant
flow
52 film coverage on the slot floors 51 and the lands 50 more uniformly.
[0048]Another embodiment of the lands 50 is illustrated in dashed line in FIG.
4
and provides for the lands 50 not being coplanar or flush with the external
surface 43 of the pressure sidewall 42 around each of the exposed cooling slot
66. The lands 50 may be more angled towards the slot floor 51 and away from
the external surface 43 of the pressure sidewall 42. The lands 50 may be
angled
away from the external surface 43 by a land angle A3 in a range between 0-5
degrees and the lands 50 may intercept the slot floor 51 upstream of the
trailing
edge TE.
[0049] The embodiment of the flow cross section 74 illustrated in FIGS. 3-6
has a
race track shaped flow cross section 74 with the rectangular section 75
between
spanwise or radially spaced apart rounded or semi-circular inner and outer end
sections 82, 84. Four exemplary shapes suitable for the flow cross section 74
are illustrated in FIGS. 8-11. The race track shaped flow cross section 74
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
illustrated in FIG. 8 is spanwise elongated, has four equal corner radii R,
and has
a width to height ratio W/H in a range of 0.25-0.50. The race track shaped
flow
cross section 74 illustrated in FIG. 9 is spanwise elongated, has four equal
corner radii R, and has a width to height ratio W/H in a range of 0.15-0.50.
The
race track shaped flow cross section 74 illustrated in FIG. 10 is similar to
the one
illustrated in FIG. 8 but has unequal top and bottom corner radii RB, RT. An
exemplary range of a corner ratio RB/RT is 1-3. The race track shaped flow
cross section 74 illustrated in FIG. 11 is spanwise elongated and fully curved
and
includes curved quarter sides 78 that may be elliptical, parabolic, or
polynomial
blends.
[0050]The cooling holes 30, trailing edge cooling slots 66, and lands 50 are
cast
in cooling features. Casting these features provides good strength, low
manufacturing costs, and durability for the airfoil and blades and vanes. The
race track shaped flow cross section 74 with the rectangular section 75
between
spanwise or radially spaced apart rounded or semi-circular inner and outer end
sections 82, 84 provides good cooling flow characteristics which reduces the
amount of the coolant flow 52 needed to cool the airfoils. The corner radii R
contribute to good cooling, castability, and strength of these cooling
features and,
in particular, help cool the lands 50 thus reducing the amount of the coolant
flow
52 used.
[0051]The embodiments of the cooling hole 30 and the trailing edge cooling
slot
66 illustrated in FIGS. 3 and 5 includes a diverging trailing edge cooling
slot 66.
The diverging upper and lower diverging sections 102, 103 and the
corresponding trailing edge cooling slots 66 may diverge at different first
and
second diverging angles Al, A2 respectively as illustrated in FIG. 3. The
spanwise height H of the diverging sections of the cooling hole 30 and the
trailing
edge cooling slots 66 increases in the downstream direction D. A more
favorable
flow angle relative to the lands for getting coolant flow 52 onto the lands at
the
breakout is set up by the expansion angle Al of the diverging sections of the
cooling hole 30 and the difference between the diverging angles of the cooling
slots and the diverging sections, i.e., A2 Al.
11
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
[0052] The diverging upper and lower diverging sections 102, 103 expands the
flow coverage at the breakout 58, redistributes coolant flow 52 in the
trailing edge
cooling slots from the slot floor 51 to the lands 50 in order to make coolant
flow
52 film coverage on the slot floors 51 and the lands 50 more uniform. The
constant width W of the diverging upper and lower diverging sections 102, 103
helps keep the coolant flow 52 fully attached in the diverging sections.
[0053] This in turn allows an increase surface area of the slot floor 51 and
decrease in surface area of the lands 50. The constant width W upper and lower
diverging sections 102, 103 helps set up a more favorable flow angle at the
breakout relative to the lands 50 to get more coolant flow 52 onto the lands.
The
planar pressure sidewall surface 39 through the entire second length L2 of the
upper and lower diverging sections 102, 103 also helps set up a more favorable
flow angle at the breakout relative to the lands 50 to get more coolant flow
52
onto the lands. The constant width and separately the planar pressure sidewall
surface 39 of the cooling hole 30 help keep the coolant flow 52 flow attached
in
the expansion section of the slot.
[0054] Another embodiment of the cooling hole 30 is illustrated in dashed line
in
FIG. 4 and provides for a variable width WV instead of a constant width W
inside
the upper and lower diverging sections 102, 103 of the hole 30 between the
pressure and suction sidewall surfaces 39, 40 of the pressure and suction
sidewalls 42, 44 respectively. The variable width WV is provided by a raised
floor
88 that extends downstream through at least a part of the upper and lower
diverging sections 102, 103 and into and at least partially through the
cooling slot
66. The raised floor 88 includes in downstream serial relationship a flat or
curved
up ramp 90 in the upper and lower diverging sections 102, 103, a flat or
curved
down ramp 94 in the trailing edge cooling slot 66, and a transition section 92
between the up and down ramps 90, 94.
[0055] The flat up and down ramps 90, 94 are illustrated in FIG. 4 and the
curved
up and down ramps 90, 94 and curved transition section 92 are illustrated in
FIG.
12. The up ramp 90 ramps up from the suction sidewall surface 40 in each of
the
upper and lower diverging sections 102, 103 and extends downstream. The
12
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
down ramp 94 ramps down and extends downstream from the transition section
92 to the trailing edge TE. The transition section 92 may be flat or curved.
The
curved up and down ramps 90, 94 and the curved transition section 92 may be
designed and constructed using Bezier splines.
[0056]This variable width WV upper and lower diverging sections 102, 103 of
the
hole 30 helps keep the exit velocity of the coolant flow 52 and the gas
velocity of
the hot combustion gases along the external surface 43 of the pressure
sidewall
42 at the breakout about equal to minimize aero losses and resultant negative
effect on turbine efficiency.
[0057]An alternative constant area inlet 70 is illustrated in FIGS. 13 and 14.
The
alternative inlet 70 includes a constant width W and constant height H
metering
section 100. The metering section 100 has a constant area flow cross section
74. The metering section 100 has a downstream extending first length L1,
Downstream of the metering section 100 is the divergent inlet section 108 as
illustrated in FIG. 3. The forward end 72 of the intra-hole partition 68
divides or
splits the aft or downstream end 110 of the divergent inlet section 108 into
the
spanwise spaced apart upper and lower inlet flowpaths 112, 114 leading to the
upper and lower diverging sections 102, 103 respectively as illustrated in
FIG. 3.
[0058]The downstream extending first length L1 of the metering section 100 has
a hydraulic diameter Dh = (4*A)/P, wherein A = flow area and P = "wetted"
perimeter of the flow area of the metering section 100 as illustrated in FIG.
3.
The metering section 100 illustrated herein has a preferred first length L1
equal
up to one and one half times the hydraulic diameter (1.5*Dh).
[0059] The present invention has been described in an illustrative manner. It
is to
be understood that the terminology which has been used is intended to be in
the
nature of words of description rather than of limitation. While there have
been
described herein, what are considered to be preferred and exemplary
embodiments of the present invention, other modifications of the invention
shall
be apparent to those skilled in the art from the teachings herein and, it is,
therefore, desired to be secured in the appended claims all such modifications
as
fall within the true spirit and scope of the invention.
13
CA 02872247 2014-10-30
WO 2014/011276 PCT/US2013/036056
[0060] Accordingly, what is desired to be secured by Letters Patent of the
United
States is the invention as defined and differentiated in the following claims:
14
