Multiple layer cooled nozzle liner

The present invention is a multiple layered nozzle liner for two-dimensional nozzles which provides both convective and film cooling, and incorporates a highly maintainable thermal barrier coating.

TECHNICAL FIELD 
The present invention relates to cooled liners, and particularly to such 
liners used in gas turbine engine exhaust nozzles. 
BACKGROUND ART 
In some applications, such as gas turbine engine exhaust nozzles, certain 
components must be protected from the high temperature exhaust to prevent 
life reduction or failure of those components. In two-dimensional exhaust 
nozzles in particular, a cooling liner is typically mounted to each wall 
of the nozzle to prevent direct contact between the exhaust and the wall. 
Cooling air fed to the "cool side" of the liner may provide impingement 
cooling, convective cooling, or film cooling to maintain the temperature 
of the liner below the maximum allowable operating temperature of the 
liner material. The "hot side", or exhaust side of such liners may 
additionally be coated with a thermal barrier material to impede heat 
transfer to the liner, thereby greatly increasing the effectiveness of the 
liner. These coatings generally wear away with time, requiring the liner 
to be recoated or replaced. 
Liner designs of the prior art include liners made of LAMILLOY.TM., a 
trademark of General Motors Corporation for a transpiration cooled liner 
material. One benefit of LAMILLOY.TM. is that it can be made of 
hard-to-form materials, such as mechanically alloyed iron based materials, 
which inherently provide high temperature durability. Liners made of 
LAMILLOY.TM. incorporate many small, straight, cooling air discharge holes 
which replenish the cooling film of the liner almost continuously. 
However, the straight cooling discharge hole configurations, to which 
LAMILLOY.TM. is limited, may not provide adequate cooling film 
effectiveness under certain nozzle operating conditions. Additionally, 
LAMILLOY.TM. cannot be coated effectively with thermal barrier material 
using current techniques, such as plasma (flame) spray coating, which tend 
to clog the discharge holes. Coating with a subsequent re-drilling of the 
holes has been tried with little success and high cost. 
Other types of liners of the prior art incorporate concave discharge holes, 
or "bathtubs", formed into the hot side surface of the liner. Such liners 
are limited by manufacturing cost to "large bathtubs" and relatively large 
spacing therebetween. Although these liners provide effective film cooling 
under some conditions, the large spacing makes such liners susceptible to 
local cooling film migration induced by the exhaust local pressure 
gradients, which, in turn, reduces the local cooling effectiveness of the 
liner. In addition, the cost effective manufacture of these liners 
requires the use of very ductile materials. 
What is needed is a nozzle cooling liner that is simple to manufacture, can 
be effectively coated with thermal barrier material, which replenishes the 
cooling film so often that it is less susceptible to local cooling film 
migration than the prior art, which gives the designer a wider choice of 
materials to use, and which allows optimization of both the hot side and 
cold side cooling. 
DISCLOSURE OF THE INVENTION 
It is therefore an object of the present invention to provide a nozzle 
cooling liner that is simple to manufacture, can be effectively coated 
with thermal barrier material, which replenishes the cooling film so often 
that it is less susceptible to local cooling film migration than the prior 
art, which gives the designer a wider choice of materials to use, and 
which allows optimization of both the hot side and cold side cooling. 
According to the present invention, a multiple layered cooled nozzle liner 
is disclosed which comprises a composite panel made of multiple sheets of 
a high temperature material. The cool side of the liner is a sheet having 
a plurality of inlet holes extending therethrough, and the hot side is a 
sheet having a plurality of substantially larger discharge holes extending 
therethrough. The total flow area of the discharge holes is substantially 
greater than the total flow area of the inlet holes, resulting in a 
relatively low discharge velocity of cooling air from the discharge holes 
which, in turn, provides highly effective film cooling. 
Sandwiched between the cool side sheet and the hot side sheet is at least 
one interior sheet. The inlet holes are offset with respect to the 
discharge holes, and internal flow channel holes in the interior sheet 
connect each inlet hole with at least one of the discharge holes. The 
internal flow channel holes provide convective heat transfer from the 
liner to the cooling air prior to the discharge thereof, allow impingement 
of the cooling air upon the back side of the hot sheet, and reduce the 
velocity of the cooling air before it is discharged. 
The hot side sheet is preferably secured to the interior and cool side 
sheets by mechanical fasteners which allow the hot side sheet to be easily 
separated from the others without damage to the individual sheets. The hot 
side sheet can thus be coated with a thermal barrier material using 
current techniques without clogging the discharge holes. As the coating 
wears away, the hot side sheet can be recoated without damaging the liner 
of the present invention, resulting in a highly maintainable nozzle liner. 
The foregoing and other features and advantages of the present invention 
will become more apparent from the following description and accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a partially cut-away view of the preferred embodiment of the 
liner (10) of the present invention. The liner preferably comprises three 
sheets (11,12,13) secured together in a manner discussed below to form a 
single composite panel (14). The first, or cold side, sheet (11), has 
first and second surfaces (15, 16), the first surface (15) being generally 
exposed to the fluid used to cool the liner (10). A plurality of inlet 
holes (17) extend between the first and second surfaces (15,16) to provide 
for the passage of the cooling fluid into the liner (10). Sandwiched 
between the first and third sheets (11,13) is the second, or interior, 
sheet (12). The interior sheet (12) has a plurality of internal flow 
channel holes (18) extending therethrough between the first and third 
sheets (11,13). The internal flow channel holes (18), which form cooling 
air passages within the liner (10), are discussed in greater detail below. 
The interior sheet (12) may be bonded to the cool side sheet (11) if 
desired, by brazing or other suitable means. The third, or hot side, sheet 
(13) includes a plurality of closely spaced discharge holes (19) arranged 
in a pattern similar to the pattern of the internal flow channel holes 
(18) in the interior sheet (12). The discharge holes (19) are 
significantly larger than the inlet holes (17), for reasons discussed 
further below. The outer surface (20) of the third sheet (13) is 
preferably coated with a thermal barrier coating to impede heat transfer 
from the exhaust gas to the liner (10). 
The hot side sheet (13) is removably secured to the cool side sheet (11) by 
a plurality of fasteners (22). Each fastener (22) preferably includes a 
plurality of pins (23) which may be brazed or otherwise attached to the 
hot side sheet (13). Each pin (23) extends from the hot side sheet (13) 
through bores (24,25) in the cool side and interior sheets (11,12). A 
groove end portion (26) of each pin (23) extends beyond the cool side 
sheet (11) where it is engaged by a locking strip (27) that prevents the 
pin (23) from retracting into the bore (24) of the cool side sheet (11). 
Although the present invention is shown and described with respect to a 
specific type of fastener (22), it is to be understood that such fastener 
(22) is exemplary only and is not intended to limit the scope of the 
claims. 
In use, coolant such as cooling air, is supplied to the first surface (15) 
of the cool side sheet (11) at a pressure significantly greater than that 
of the exhaust. The cooling air accelerates through the inlet holes (17) 
and exits into an internal flow channel hole (18) of the interior sheet 
(12) as a high velocity jet. This jet impinges the inner surface of the 
hot side sheet (13), producing turbulent heat transfer therebetween and 
significantly reducing the velocity of the cooling flow. The cooling air 
then flows toward a discharge hole (19) in the hot side sheet (13). As 
those skilled in the art will readily appreciate, the significant 
difference in flow area between the discharge holes (19) and the inlet 
holes (17) results in discharge of the cooling air into the exhaust at low 
velocity, thereby providing effective film cooling of the liner (10) 
downstream of the discharge holes (19). This effective film cooling is 
particularly useful if the coating is temperature limited. 
Since the present invention is comprised of sheet material, substantially 
any material which can be formed into sheets could conceivably be used to 
form the composite panel (14). Therefore, high temperature materials, such 
as mechanically alloyed iron based materials which, although difficult to 
form in complex shapes are relatively easy to manufacture in sheet form, 
may be used to form the composite panel (14). Known manufacturing 
processes, such as chemical or photo etching, may be used to produce the 
holes (17,18,19,24,25) in the various sheets, requiring only minimal 
machining of the sheet material. 
A second embodiment (30) of the present invention utilizes an interior 
sheet having "keyhole" shaped internal flow channel holes (32), as shown 
in FIG. 2. In this embodiment, a portion (33) of the internal flow channel 
hole (32) is elongated, increasing the heat transfer area between the 
cooling air and the liner (30), thereby enhancing convective heat 
transfer. As those skilled in the art will readily appreciate, heat 
transfer may be further enhanced in the elongated portion (33) by 
providing a tortuous cooling air flow path therein (e.g. inserting 
turbulators into the elongated portion (33), providing a zig-zag cooling 
air flow path in the elongated portion (33), etc.). 
The third embodiment (40) of the present invention, shown in FIG. 3, 
provides for transverse flow of the cooling air through internal flow 
channel holes (41) which are interconnected within the interior sheet (42) 
by the elongated portions (43). In this embodiment, cooling air flow from 
adjacent inlet holes (17) collide within the intervening internal flow 
channel holes (41), producing turbulent cooling air flow within the 
internal flow channel hole (41) and enhancing heat transfer between the 
liner (40) and the cooling air. Additionally, since each inlet hole (17) 
communicates with several discharge holes (19) within the liner (40), 
should a blockage of a single inlet hole (17) occur, a discharge hole (19) 
would not necessarily be deprived of all cooling air, as might occur in 
the embodiments of FIGS. 1 and 2. It is to be understood that the second 
and third embodiments (30,40) of the present invention include the 
fasteners and thermal barrier coating disclosed in the description of the 
preferred embodiment (10) shown in FIG. 1. For purposes of clarity, the 
fasteners and thermal barrier coating are not shown in FIGS. 2 and 3. 
Although the present invention is shown and described in terms of a three 
sheet composite panel (14), variations on the basic configurations 
described herein will be obvious to those skilled in the art. For example, 
the internal flow channel holes (12,32,41) of the interior sheet 
(12,31,42) could be etched into the inner surface of either the cool side 
sheet (11), the hot side sheet (13), or both, thereby obviating the need 
for the interior sheet (12,31,42). 
The present invention takes advantage of the inherently good convection 
cooling associated with multiple, small passages within the cooling liner 
(10,30,40) and the inherent superior film effectiveness of shaped, low 
discharge velocity holes (19). It combines the ability to manufacture 
multiple thin sheets, machined or etched (chemically or photo) with very 
close inlet and discharge hole (17,19) spacing with almost infinite 
tailoring (size, shape and spacing of inlet holes (17), discharge holes 
(19), internal flow channel holes (18,32,33,41,43) etc.) and the ability 
to use hard-to-form materials. In addition, the liner (10,30,40) of the 
present invention can be coated and recoated using the plasma (flame) 
spray process without clogging the internal flow channel holes of the 
liner (10,30,40). The result is a low cost, durable liner (10,30,40) that 
replenishes the cooling film almost continuously and is therefore less 
subject to cooling film migration than some prior art liners.