Turbine blade squealer tip peripheral end wall with cooling passage arrangement

A turbine blade squealer tip has a cooling passage arrangement which includes a peripheral end wall surrounding a central portion of an end cap of the squealer tip, an outer peripheral groove defined in an outer surface of the peripheral end wall being spaced outwardly from the central portion of the end cap, and a multiplicity of holes extending through the end wall from the outer groove to an internal source of cooling air flow within the turbine blade, bypassing the central portion of the end cap of the squealer tip. The outer groove which receives the flow of cooling air from outlets of the holes tends to trap the air therein so as to form an annular air seal about the outer surface of the squealer tip end wall which impedes leakage of hot gas flow past the squealer tip.

CROSS REFERENCE TO RELATED APPLICATIONS 
Reference is hereby made to the following U.S. patent applications dealing 
with related subject matter and assigned to the assignee of the present 
invention: 
(1) "Turbine Blade Squealer Tip Having Air Cooling Holes Contiguous With 
Tip Interior Wall Surface" by Ching P. Lee et al, assigned U.S. Ser. No. 
615,520 and filed Nov. 19, 1990 (13DV-9683), now abandoned. 
(2) "Cooling Hole Arrangements In Jet Engine Components Exposed To Hot Gas 
Flow" by Ching P. Lee et al, assigned U.S. Ser. No. 801,136 and filed Dec. 
2, 1991 (13DV-10789), now U.S. Pat. No. 5,326,224. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to gas turbine engine blades and, 
more particularly, to a turbine blade squealer tip peripheral end wall 
with a cooling passage arrangement. 
2. Description of the Prior Art 
It is well known that a reduction in gas turbine engine efficiency results 
from leaking of hot expanding combustion gases in the turbine across a gap 
between rotating turbine blades and stationary seals or shrouds which 
surround them. The problem of sealing between such relatively rotating 
members to avoid loss in efficiency is very difficult in the turbine 
section of the engine because of high temperatures and centrifugal loads. 
One method of improving the sealing between the turbine blade and shroud is 
the provision of squealer type tips on turbine blades. A squealer tip 
includes a continuous peripheral end wall of relatively small height 
surrounding and projecting outwardly from an end cap on the outer end of a 
turbine blade which closes a cooling air plenum in the interior of the 
blade. 
During operation of the engine, temperature changes create differential 
rates of thermal expansion and contraction on the blade rotor and shroud 
which may result in rubbing between the blade tips and shrouds. 
Centrifugal forces acting on the blades and structural forces acting on 
the shrouds create distortions thereon which may also result in rubbing 
interference. 
Such rubbing interference between the rotating blade tips and surrounding 
stationary shrouds causes heating of the blade tips resulting in excessive 
wear or damage to the blade tips and shrouds. It is, therefore, desirable 
to cool the blade tips. However, in the case of squealer type blade tips, 
heating produced by such rubbing interference is actually augmented by the 
presence of a cavity defined by the end cap and peripheral end wall of the 
squealer tip. Therefore, squealer type blade tips, though fostering 
improved sealing, actually require additional cooling. 
Because of the complexity and relative high cost of replacing or repairing 
turbine blades, it is desirable to prolong as much as possible the life of 
blade tips and respective blades. Blade tip cooling is a conventional 
practice employed for achieving that objective. The provision of holes for 
directing air flow to cool blade tips is known in the prior art, for 
instance as disclosed in U.S. Pat. No. 4,247,254 to Zelahy, and have been 
applied to squealer type blade tips as disclosed in U.S. Pat. No. 
4,540,339 to Horvath. 
Turbine engine blade designers and engineers are constantly striving to 
develop more efficient ways of cooling the tips of the turbine blades to 
prolong turbine blade life and reduce engine operating cost. However, 
cooling air used to accomplish this is expensive in terms of overall fuel 
consumption. Thus, more effective and efficient use of available cooling 
air in carrying out cooling of turbine blade tips is desirable not only to 
prolong turbine blade life but also to improve the efficiency of the 
engine as well, thereby again lowering engine operating cost. 
Consequently, there is a continuing need for a cooling hole design that 
will make more effective and efficient use of available cooling air. 
SUMMARY OF THE INVENTION 
The present invention provides a turbine blade squealer tip peripheral end 
wall having a cooling passage arrangement designed to satisfy the 
aforementioned need. In accordance with the present invention, the cooling 
passage arrangement provides an outer peripheral groove in an outer 
surface of the squealer end wall and a multiplicity of intersecting holes 
extending through the end wall from the outer groove to an internal source 
of cooling air flow within the turbine blade. The intersecting holes 
provide a larger cooling surface area and thereby more effective 
convective cooling than do conventional separate single holes. Also, the 
flow intersections formed by the intersecting holes more effectively 
restrict the flow of cooling air from the internal cooling passage and 
thereby cause a more highly turbulent flow within the holes. Further, the 
intersecting holes are individually straight holes that can be drilled by 
a cost-effective laser process. The outer groove tends to trap the cooling 
air therein so as to form an annular air seal about the outer surface of 
the squealer tip end wall which impedes leakage of hot gas flow. 
Accordingly, the present invention is directed to a cooling passage 
arrangement in a turbine blade having an interior source of cooling air 
flow and an outer end cap with a continuous peripheral portion. The 
cooling passage arrangement comprises: (a) a peripheral end wall connected 
to, extending around, and projecting outwardly from the peripheral portion 
of the end cap of the blade so as to surround a central portion of the end 
cap, the end wall having an outer surface spaced outwardly from the 
central portion of the end cap; (b) an outer groove defined in the outer 
surface of the peripheral end wall, the outer groove extending about at 
least a portion of the extent of the outer surface of the peripheral end 
wall; and (c) a multiplicity of holes extending through the peripheral end 
wall from the internal source of cooling air flow to the outer groove, the 
holes being arranged to intersect with one another and to bypass the 
central portion of the end cap of the blade. 
More particularly, preferably, the outer cooling groove is continuous about 
the outer Surface of the peripheral end wall. Also, the multiplicity of 
holes includes a first plurality of generally parallel extending holes and 
a second plurality of generally parallel extending holes intersecting the 
holes of the first plurality such that each of the holes intersect with 
more than one other hole. 
These and other features and advantages and attainments of the present 
invention will become apparent to those skilled in the art upon a reading 
of the following detailed description when taken in conjunction with the 
drawings wherein there is shown and described an illustrative embodiment 
of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description, like reference characters designate like or 
corresponding parts throughout the several views. Also in the following 
description, it is to be understood that such terms as "forward", 
"rearward", "left", "right", "upwardly", "downwardly", and the like, are 
words of convenience and are not to be construed as limiting terms. 
Prior Art Gas Turbine Engine Blade 
Referring now to the drawings, and particularly to FIG. 1, there is 
illustrated a prior art gas turbine engine hollow rotor blade, being 
generally designated by the numeral 10. The blade 10 includes an airfoil 
12 having a pressure side 14 and a suction side 16, and a base 18 mounting 
the airfoil 12 to a rotor (not shown) of the engine (not shown). The base 
18 has a platform 20 rigidly mounting the airfoil 12 and a dovetail root 
22 for attaching the blade 10 to the rotor. 
At an outer end portion 24, the airfoil 12 of the blade 10 has a squealer 
tip 26. The squealer tip 26 includes an end cap 28 which closes the outer 
end portion 24 of the hollow blade 10, and an end wall 30 attached to, and 
extending along the periphery 12A of, and projecting outwardly from, the 
end cap 28 so as to define a cavity therewith. The end cap 28 of the 
squealer tip 26 is provided with an arrangement of tip cooling holes 32 
formed therethrough for permitting passage of cooling air flow from the 
interior of the blade 10 through the end cap 28 to the cavity defined by 
the end wall 30 and end cap 28 for purposes of cooling the blade squealer 
tip 26. 
The tip of a turbine blade is designed to serve three purposes. One purpose 
is to maintain the blade integrity in the event of rubbing between the 
blade tip and a stationary shroud (not shown). The second purpose is to 
minimize the leakage flow across the blade tip from the pressure side to 
the suction side in the direction of the arrows depicted in FIG. 3. The 
third purpose is to cool the blade tip within the material limit. The 
squealer tip 26 described above is provided in an attempt to meet these 
three purposes. The squealer tip 26 provides the rubbing capability and 
also serves as a two-tooth seal to discourage the leakage flow. Tip 
cooling is provided through the pressure side film cooling and the 
convective cooling on the squealer tip surface inside of the tip cavity. 
Unfortunately, the film cooling near the tip surface is not efficient due 
to the strong secondary flow in the gas flowpath. The cooling inside the 
tip cavity is also diluted by the circulation of hot leakage flow inside 
the tip cavity. Therefore, it is important to have an improved design to 
achieve all three purposes of the blade tip. 
Cooling Passage Arrangement of Present Invention 
Turning now to FIGS. 2-4, there is illustrated a cooling passage 
arrangement, generally indicated by the numeral 34, which provides a means 
to achieve all three purposes of the blade tip. The arrangement 34 is 
provided in a turbine blade 36 being constructed substantially the same as 
the turbine blade 10 described above with reference to FIG. 1, except for 
the differences noted below. Thus, the turbine blade 36 has an airfoil 38 
defining an interior source 40 of cooling air flow and having an outer end 
portion 38A. The outer end portion 38A of the airfoil 38 has a squealer 
tip 39 which includes an outer end cap 42 attached thereon having a 
continuous peripheral portion 42A. 
The cooling passage arrangement 34 of the present invention includes a 
peripheral end wall 44 connected to, extending around, and projecting 
outwardly from the peripheral portion 42A of the end cap 42 of the 
squealer tip 39. The peripheral end wall 44 surrounds a central portion 
42B of the end cap 42. The peripheral end wall 44 has an inclined interior 
surface 46 and a substantially horizontal outer surface 48 spaced 
outwardly from the central portion 42B of the end cap 42. The peripheral 
end wall 44 of the blade 36 is somewhat thicker than the peripheral end 
wall 30 of the squealer tip 26 of FIG. 1. 
The cooling passage arrangement 34 also includes an outer groove 50 defined 
in the outer surface 48 of the peripheral end wall 44 and extending about 
at least a portion of the extent of the outer surface 48 of the peripheral 
end wall 44 preferably, the outer groove 50 is continuous and extends 
completely about the outer surface 48 on the peripheral end wall 44. As 
seen in FIG. 3, the outer groove 50 can be semi-circular in cross-section. 
Alternatively, the outer groove 50 can be rectangular in cross-section as 
shown in FIG. 5. Other cross-sectional shapes are also possible. 
The cooling passage arrangement 34 further includes a multiplicity of 
elongated holes 52 which extend in criss-cross fashion through the 
peripheral end wall 44 from the internal source 40 of cooling air flow to 
the bottom 50A of the outer groove 50. The elongated holes 52 are arranged 
in the criss-cross fashion to intersect with one another and also to 
bypass the central portion 42B of the end cap 42 of the blade squealer tip 
39. Each hole 52 intersects with more than one other hole 52. More 
particularly, the multiplicity of criss-crossed holes 52 includes a first 
plurality of generally parallel extending holes and a second plurality of 
generally parallel extending holes intersecting the holes of the first 
plurality. 
Preferably, the elongated holes 52 are substantially straight and of 
uniform cross-sectional size. Each hole 52 has a flow inlet 52A 
communicating with the interior source 40 of cooling air flow of the 
airfoil 38, and a flow outlet 52B opening at the bottom 50A of, and 
communicating with, the outer groove 50 defined in the outer surface 48 of 
the peripheral end wall 44 of the squealer tip 39. Pairs of the holes 52 
intersect at the inlets 52A thereof and are located side-by-side at the 
outlets 52B thereof such that the area at the outlets is larger than that 
at the intersections 52C. The holes 52 are disposed in an inclined 
relation to a radial line R through the airfoil 38 and so extend in a 
convergent relation with respect to one another through the peripheral end 
wall 44 from the outer groove 50 to the internal source 40 of cooling air 
flow within the turbine blade 36, bypassing the central portion 42B of the 
end cap 42. 
The intersecting holes 52 provide a larger cooling surface area and thereby 
more effective convective cooling than do conventional single holes. Also, 
the flow intersections formed by the intersecting holes 52 more 
effectively restrict the flow of cooling air from the internal source 40 
and thereby cause a more highly turbulent flow within the holes 52. Also, 
the intersecting holes 52 being individually straight holes can be drilled 
by a cost-effective laser process. The outer groove 50 which receives the 
flow of cooling air from the outlets 52B of the holes 52 tends to trap the 
air therein so as to form an annular air seal about the outer surface 48 
of the squealer tip end wall 44 which discourages leakage of hot gas flow. 
In summary, from a mechanical perspective, the above-described outer 
cooling groove 50 provides a four-tooth seal feature on the outer end of 
the peripheral end wall 44, as opposed to the two-tooth seal feature 
provided heretofore by the peripheral end wall alone. From an aerodynamics 
perspective, the outer cooling groove 50 provides an annular air seal 
feature. These two features when combined together reduce the tip leakage 
flow. The criss-crossed or meshed hole feature will allow for drilling 
larger holes to prevent dust plugging and still restrict the flow. The 
meshed hole feature also has a much larger cooling area than the 
conventional single holes and provides an effective convective cooling. 
The cooling groove and the large meshed hole features will also prevent 
the hole plugging in the event of tip rub. The groove can be either cast 
or EDM and the meshed holes can be drilled by a laser or cast. Depending 
upon the engine design condition, the cooling groove and meshed holes can 
be designed for a local region without covering the entire squealer tip 
39. 
It is thought that the present invention and many of its attendant 
advantages will be understood from the foregoing description and it will 
be apparent that various changes may be made in the form, construction and 
arrangement of the parts thereof without departing from the spirit and 
scope of the invention or sacrificing all of its material advantages, the 
forms hereinbefore described being merely preferred or exemplary 
embodiments thereof.