Integrated fluidic CD nozzle for gas turbine engine

An exhaust nozzle for a gas turbine engine includes converging and diverging nozzles joined together at a throat and attached to a frame. An injection slot is disposed at the throat in flow communication with a transition duct for channeling injection air therethrough as controlled by an injection valve for fluidically varying throat area for exhaust gases discharged through the exhaust nozzle.

BACKGROUND OF THE INVENTION 
The present invention relates generally to gas turbine engines, and, more 
specifically, to variable area exhaust nozzles therefor. 
One type of turbofan gas turbine engine for powering an aircraft in flight 
includes an afterburner or augmenter for providing additional thrust when 
desired, with a variable area exhaust nozzle disposed at the aft end 
thereof. Since the engine operates at varying power levels including idle, 
cruise, and maximum afterburner, the exhaust nozzle is suitably adjustable 
for optimizing performance with maximum efficiency. 
A typical variable area exhaust nozzle is an assembly including a 
converging duct or nozzle defined by a plurality of circumferentially 
adjoining primary exhaust flaps pivoted at their leading edges to an outer 
casing. A diverging duct or nozzle is defined by a plurality of 
circumferentially adjoining secondary exhaust flaps pivoted at their 
leading edges to the trailing edges of the primary flaps. The trailing 
edges of the secondary flaps are pivotally joined to a plurality of 
circumferentially adjoining outer flaps which in turn are joined to the 
outer casing. The converging-diverging (CD) nozzle includes an inlet at 
the entrance to the converging nozzle, a throat of minimum flow area, 
designated A.sub.8, at the juncture between the converging and diverging 
nozzles, and an outlet having a larger flow area, designated A.sub.9. 
During operation, suitable actuators pivot radially inwardly and outwardly 
the primary flaps to adjust the angle of convergence and the throat area, 
and in turn adjust the angle of divergence of the secondary flaps and the 
outlet area. In this way, the exhaust gases from the engine may be 
accelerated in the converging nozzle to a choked velocity of Mach 1 at the 
throat, and then expanded in the diverging duct at supersonic velocities 
for enhanced performance. 
The resulting variable area exhaust nozzle is relatively complex in 
construction and requires many individual components pivotally joined 
together, and adjusted in position using suitable actuators and linkages. 
The individual primary and secondary flaps must be suitably cooled and 
sealed at their junctions to control undesirable leakage of the exhaust 
gases therebetween. 
Fixed area exhaust nozzles are also known but are used in less demanding 
applications. For example, a simple converging nozzle may be used without 
a cooperating diverging nozzle, with fixed inlet and throat flow areas. 
Or, a fixed diverging nozzle may be used in conjunction with the fixed 
converging nozzle with the flow areas at the inlet, throat, and outlet 
also being fixed and therefore optimized for only a single region of 
engine performance. Fixed area CD nozzles are therefore not practical or 
desirable for an aircraft engine operating over a wide range of power in 
its flight envelope. 
Accordingly, it is desired to have a relatively simple fixed CD exhaust 
nozzle with variable flow area capability for enhancing engine performance 
without complex area control mechanisms and attendant weight. 
SUMMARY OF THE INVENTION 
An exhaust nozzle for a gas turbine engine includes converging and 
diverging nozzles joined together at a throat and attached to a frame. An 
injection slot is disposed at the throat in flow communication with a 
transition duct for channeling injection air therethrough as controlled by 
an injection valve for fluidically varying throat area for exhaust gases 
discharged through the exhaust nozzle.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Illustrated schematically in FIG. 1 is a turbofan aircraft gas turbine 
engine 10 including a variable area converging-diverging (CD) exhaust 
nozzle 12 in accordance with an exemplary embodiment of the present 
invention. The engine 10 is axisymmetrical about a longitudinal or axial 
centerline axis 14 and includes in serial flow communication a fan 16, 
multi-stage axial compressor 18, annular combustor 20, high pressure 
turbine (HPT) 22, low pressure turbine (LPT) 24, and an afterburner or 
augmenter 26. The HPT 22 is suitably joined to the compressor 18 by one 
rotor shaft, and the LPT 24 is suitably joined to the fan 16 by another 
rotor shaft. An annular inner casing 28 surrounds the core engine 
downstream of the fan 16, and the augmenter 26 includes an annular 
combustion liner 26a. The inner casing 28 and augmenter liner 26a are 
spaced radially inwardly from an annular outer casing 30 to define an 
annular bypass duct 32 extending from the fan 16 to the exhaust nozzle 12. 
During operation, ambient air enters the engine 10 and is compressed in the 
compressor 18 for providing pressurized or compressed air 34a which is 
mixed with fuel in the combustor 20 and ignited for generating hot 
combustion gases 36 which flow through the HPT 22 and LPT 24 which extract 
energy therefrom and discharge the exhaust gases into the augmenter 26 for 
discharge from the engine through the exhaust nozzle 12. The HPT 22 powers 
the compressor 18, and the LPT 24 powers the fan 16. 
The fan 16 pressurizes a portion of the inlet air as compressed bypass air 
34b which bypasses the core engine and flows through the bypass duct 32 
around the augmenter liner 26a to the exhaust nozzle 12. 
But for the exhaust nozzle 12, the gas turbine engine 10 illustrated in 
FIG. 1 is conventional in configuration and operation, and is operable 
over varying output power settings including idle, cruise, and maximum 
afterburner. Accordingly, the exhaust nozzle 12 is variable in flow area 
in accordance with the present invention for enhancing efficiency of the 
engine 10 over its operating range. 
More specifically, and referring to FIGS. 2-4, the exhaust nozzle 12 is an 
assembly of components including a fixed, non-variable converging inlet 
channel or nozzle 38 disposed in flow communication with the augmenter 26 
for receiving the exhaust gases 36 therefrom. Disposed in flow 
communication coaxially with the converging nozzle 38 about the engine 
centerline axis 14 is a fixed, non-variable diverging outlet channel or 
nozzle 40 which joins the converging nozzle 38 at an annular throat 42 
having a minimum flow area designated A.sub.8. 
In the exemplary embodiment illustrated in FIG. 4, the converging nozzle 38 
has a circular or cylindrical forward end 38a defining an inlet for 
receiving the exhaust gases 36 from the augmenter 26 during operation. The 
cylindrical forward end 38a transitions to an elliptical aft end 38b at 
the throat 42. The converging nozzle 38 converges in area between the 
forward and aft ends 38a,b thereof in a fixed area ratio of suitable 
value. 
The diverging nozzle 40 is correspondingly elliptical from its forward end 
40a at the throat 42 to its aft end 40b, and diverges therebetween at a 
fixed diverging area ratio of suitable value. As shown in FIG. 2, the 
exhaust nozzle 12 transitions from the circular profile to the elliptical 
profile, with the major axis of the ellipse being in the horizontal plane, 
and the minor axis of the ellipse being in the vertical plane. However, 
the specific configuration or profile of the exhaust nozzle 12 may be 
otherwise selected as desired to include completely circular, rectangular, 
or other profiles, for example, for each specific nozzle configuration 
desired. 
However, in all embodiments the converging and diverging nozzles 38, 40 are 
fixed, non-variable flow ducts. In order to provide variable area 
capability of the otherwise fixed area CD exhaust nozzle 12, the nozzle 12 
further includes a circumferentially extending annular injection slot 44 
disposed coaxially at the throat 42 as initially shown in FIGS. 2-4. 
Cooperating with the injection slot 44 are suitable means for selectively 
injecting compressed air, such as the bypass air 34b in the engine 10, 
through the injection slot 44 for selectively and fluidically varying the 
effective flow area A.sub.8 for the exhaust gases 36 at the throat 42. By 
injecting the bypass air, designated injection air 34c, at the throat 42 
with suitable momentum, the available flow area for the exhaust gases 36 
may be reduced for effectively varying the throat area A.sub.8 fluidically 
instead of mechanically with a solid boundary. 
A portion of the injecting means in accordance with a preferred embodiment 
of the present invention is illustrated in more particularity in FIG. 5. 
The injecting means preferably includes a radially inwardly extending 
converging injection nozzle 46 which terminates at the injection slot 44 
defining an outlet therefor. The injection air 34c may therefore be 
injected with choked flow at a desired design point for maximizing fluidic 
area change. 
The injection nozzle 46 is preferably directed in part at its radially 
inner portion axially forward toward the injection slot 44 to define an 
upstream injection angle A which is preferably as close to 90.degree. as 
practical, with zero degrees (0.degree.) being radially inward, and has a 
value of about 60.degree., for example, from the radial axis for injecting 
the compressed injection air 34c in an initial upstream direction in the 
converging nozzle 38. 
The injection air 34c has suitable momentum to create a buffer or 
recirculation zone of primarily only the injection air 34c radially 
inwardly of the injection slot 44 to fluidically constrict the flow of 
exhaust gases 38 to a smaller effective area A.sub.8 at the physical 
throat 42. The physical throat 42 defines the maximum value of the throat 
area A.sub.8, whereas the maximum injection of the injection air 34c 
defines the minimum value of the effective throat area A.sub.8. 
The injection air 34c is preferably directed from the injection slot 44 
initially in the upstream direction relative to the exhaust gases 36 to 
maximize the reduction affect in throat flow area A.sub.8. Initially 
directing the injection air 34c in the downstream direction from the slot 
44 and into the diverging nozzle 40 is not desirable due to the inherent 
gas expansion therein which would entrain therewith the injection air 34c 
minimizing its affect for throat flow area control. 
The injection nozzle 46 may include a first or axially forward flow guide 
46a which is generally arcuate or convex in radial section for turning the 
injection air 34c from aft to forward directions. A second or axially aft 
flow guide 46b is spaced axially aft from the forward guide 46a, and is 
complementary therewith to converge in flow area radially inwardly from a 
guide inlet to the injection slot 44 which defines the guide outlet at the 
throat 42. The forward and aft flow guides 46a,b are preferably configured 
to effect the injection angle A of about 60.degree. in the preferred 
embodiment. 
As shown in FIGS. 4 and 6, the injecting means preferably also include an 
annular injection valve 48 disposed at the forward end of the exhaust 
nozzle 12 for controlling flow of the injection air 34c through the 
injection slot 44 for in turn fluidically varying the effective flow area 
(A.sub.8) available for the exhaust gases 36 at the physical throat 42. A 
significant objective of the present invention is to integrate fluidic 
area control and nozzle cooling into a lightweight production-type design 
which efficiently utilizes available space for maximizing aerodynamic and 
structural efficiency. 
More specifically, the exhaust nozzle 12 preferably includes an annular 
stationary frame 50 suitably joined coaxially with the outer casing 30 for 
providing structural integrity of the nozzle 12. The frame 50 may take any 
suitable form including a plurality of axially spaced apart, annular 
bulkheads or ribs having I-beam sections suitably attached to radially 
outer and inner walls. 
The converging nozzle 38 is preferably in the form of a thin liner suitably 
joined to the frame 50 at a forward end thereof in flow communication with 
the augmenter liner 26a for receiving the exhaust gases 36 from the 
engine. The diverging nozzle 40 is also preferably in the form of a thin 
liner suitably joined to the frame 50 at an aft end thereof in flow 
communication with the converging nozzle 38 at the throat 42. 
The frame 50 has a suitable configuration or profile for mounting the 
converging and diverging nozzles 38, 40 at a predetermined orientation for 
effecting desired amounts of converging flow area through the converging 
nozzle 38 and diverging flow area through the diverging nozzle 40 for each 
particular engine application. In this way, the converging and diverging 
nozzles 38, 40 are fixed to the frame 50 with a specific area ratio which 
may be selected for a specific operating point in the flight envelope of 
the engine 10. Variability of the CD nozzle 12 is provided by suitably 
adjusting the injection valve 48 for controlling flow of the injection air 
34c through the injection slot 44 as required for other operating points 
in the flight envelope. 
As shown in FIG. 3, the engine 10 may also include a conventional variable 
area bypass injector (VABI) valve 52 at the forward end of the augmenter 
liner 26a for use in conventionally controlling the variable cycle of the 
engine 10. The VABI valve 52 is in the exemplary form of a cylindrical 
sleeve which translates axially by a plurality of circumferentially spaced 
apart bellcranks which are suitably rotated from outside the casing 30 by 
conventional actuators. 
In the preferred embodiment illustrated in FIGS. 3 and 4, the injection 
valve 48 may be similar in configuration and operation to the VABI valve 
52, with the injection valve 48 being a cylindrical sleeve joined to a 
plurality of circumferentially spaced apart bellcranks 54 which extend 
through the outer casing 30 and are suitably pivotally joined thereto. The 
bellcranks 54 are suitably joined to an actuation link 56 which is 
illustrated in more particularity in FIG. 6. The actuation link 56 may be 
an arcuate or annular member suitably joined to one or more conventional 
actuators 58 which have extendable output rods suitably joined to the link 
56 for selectively rotating the link around the centerline axis of the 
engine. As the link 56 is rotated, the respective bellcranks 54 are 
rotated for in turn axially translating the injection valve 48 between 
open and closed position as illustrated in phantom line in FIG. 6. 
As shown in FIG. 3, both the injection valve 48 and VABI valve 52 may be 
moved to their "off" positions shown in solid line during operation of the 
augmenter 26, with the injection valve 48 closing off flow through the 
injection slot 44, and the VABI valve 52 allowing a portion of the bypass 
air 34b to enter the augmenter 26 radially inwardly of its liner 26a. In 
an opposite "on" position shown in phantom during dry engine operation, 
the injection valve 48 allows airflow through the injection slot 44, with 
the VABI valve 52 blocking bypass air flow inside the augmenter 26. 
However, the functions of the injection valve 48 and the VABI valve 52 may 
be combined if practical. 
In order to integrate air injection and nozzle cooling, the exhaust nozzle 
12 as illustrated in FIG. 4 preferably includes an annular transition duct 
60 disposed radially between the frame 50 and the converging nozzle 38 in 
flow communication with the injection slot 44. The transition duct 60 is 
defined by radially spaced apart inner and outer walls 60a,b. The 
transition duct 60 has an annular inlet at its forward end at which the 
injection valve 48 is disposed for controlling the area thereof and flow 
of the injection air 34c through the transition duct 60 and out the 
injection slot 44 defined at the outlet of the transition duct 60. In this 
way, the momentum of the injected air 34c may be used for fluidically 
varying the flow area of the exhaust gases 36 at the throat 42. 
As shown in FIGS. 4 and 5, the liner defining the converging nozzle 38 is 
spaced radially inwardly from the inner wall 60a of the transition duct 60 
to define a converging liner duct 62 for channeling therethrough cooling 
air 34d, shown in more particularity in FIG. 5. The converging liner duct 
62 is suitably disposed in flow communication with the bypass duct 32 for 
receiving a portion of the bypass air 34b therefrom. 
As shown in FIGS. 4 and 5, the liner of the diverging nozzle 40 is spaced 
radially inwardly from the inner wall of the frame 50 to define a 
diverging liner duct 64 for channeling therethrough cooling air 34e which 
is another portion of the bypass air 34b from the bypass duct 32. 
The transition duct 60 is also spaced radially inwardly from the inner wall 
of the frame 50 to define a feed duct 66 disposed in flow communication 
with the diverging liner duct 64 for channeling the cooling air 34e 
thereto and jumping or bypassing the injection slot 44. 
The transition duct 60, converging liner duct 62, diverging liner duct 64, 
and feed duct 66 are preferably annular channels which follow the 
respective configurations of the converging and diverging nozzles 38, 40 
as they transition from cylindrical to elliptical. The converging liner 
duct 62 has an annular inlet 62a, as shown in FIG. 4, disposed in flow 
communication with the bypass duct 32 for receiving a portion of the 
bypass air 34b. In the exemplary embodiment illustrated in FIG. 4, the 
afterburner liner 26 has a double wall construction through which a 
portion of the bypass air 34b is suitably channeled to the converging 
liner duct 62 throughout engine operation. 
The feed duct 66 has a cylindrical inlet 66a inside the outer casing 30 
disposed in flow communication with the bypass duct 32 for receiving the 
cooling air 34e therefrom independently of the cooling air 34d received by 
the converging liner duct 62. And, the transition duct 60 includes an 
annular inlet 60c in which the injection valve 48 is disposed, with the 
inlet 60c being disposed in flow communication with the bypass duct 32 for 
receiving a portion of the bypass air 34b for injection through the slot 
44. 
As shown in FIG. 5, the converging liner duct 62 has an annular outlet 62b 
disposed immediately upstream of the injection slot 44 for discharging the 
cooling air 34d into the exhaust gases 36. The feed duct 66 has an annular 
outlet 66b disposed downstream of the injection slot 44 in common with an 
inlet to the diverging liner duct 64 for channeling the cooling air 34e 
past the injection slot 44 for supplying cooling air to the diverging 
nozzle 40. As shown in FIG. 4, the diverging liner duct 64 has an annular 
outlet 64b at the aft end of the diverging nozzle 40 for suitably 
discharging the cooling air 34e therefrom. 
In this way, variable area of the exhaust nozzle 12 may be effected by 
positioning the injection valve 48 for controlling flow of the injection 
air 34c through the injection slot 44. The discrete auxiliary ducts 62, 
64, and 66 independently channel portions of the bypass air 34b for 
cooling both the converging and diverging nozzles 38, 40 irrespective of 
airflow through the transition duct 60. When the injection valve 48 is 
closed, airflow through the transition duct 60 is curtailed, yet cooling 
is still effected by the converging liner duct 62, and by the diverging 
liner duct 64 fed by the feed duct 66 while continuously receiving air 
from the bypass duct 32. 
As shown in FIG. 7 in more detail, the three ducts 60, 62, and 66 are 
configured in a unique structural assembly which integrates the several 
nozzle cooling and injection circuits in a lightweight and structurally 
efficient manner. More specifically, the inner wall 60a of the transition 
duct 60 is spaced radially outwardly from the converging nozzle liner 38 
to define the converging liner duct 62 using suitable support hangers 68. 
The outer wall 60b of the transition duct 60 is spaced radially inwardly 
from the inner wall of the frame 50 to define the feed duct 66, and is 
also spaced radially outwardly from the inner wall 60a to define the flow 
channel of the transition duct 60. 
A plurality of support ribs or trusses 70 extend radially between the inner 
and outer walls 60a,b and are suitably joined thereto by welding, brazing, 
or fasteners, for example. The support ribs 70 are spaced 
circumferentially apart from each other for channeling the injection air 
34c therebetween in a plurality of airflow passages which collectively 
feed the injection slot 44. 
Similarly, a plurality of support ribs or trusses 72 extend radially 
between the frame 50 and the transition duct outer wall 60b and are 
suitably joined thereto. The support ribs 72 are circumferentially spaced 
apart from each other to provide a plurality of airflow passages which 
collectively define the feed duct 66. The support ribs 70, 72 provide a 
lightweight, strong integrated assembly for accommodating the pressure and 
operating loads during operation while channeling airflow uniformly 
circumferentially around the nozzle. The diverging nozzle liner 40 may be 
similarly supported to the frame 50 by corresponding support ribs in a 
manner similar to that illustrated in FIG. 7 for the converging nozzle 
liner 38. 
The multiple radial and circumferential flow passages illustrated in FIG. 7 
provide enhanced cooling of the various components thereof during engine 
operation and reduce or eliminate thermal gradients. The use of dedicated 
or additional types or plenums is eliminated by using the internal 
passages defined by the various support ribs, which therefore eliminates 
components and reduces weight. 
Since the degree of variable area effected by the injection slot 44 is 
dependent upon momentum of the injection air 34c injected therethrough, 
the available pressure of the bypass air 34b therefore limits variability. 
In order to increase the degree of variability, the exhaust nozzle 12 may 
further include one or more injection ports 74, as illustrated in FIG. 8, 
suitably disposed in flow communication with the transition duct 60 and 
with the compressor 18 for channeling a portion of the compressor 
discharge air into the transition duct 60 to supplement the bypass air 34c 
being channeled through the injection slot 44. 
In this way, the highest available pressurized air from the compressor 18 
may be additionally used for increasing the momentum of the air injected 
through the injection slot 44 for enhancing throat area variability during 
operation. The injection port 74 may be in the form of a simple fitting 
extending through the outer wall 60b of the transition duct 60 joined to a 
suitable pipe or conduit routed through the inside of the frame 50 and 
along the outer casing 30 of the engine illustrated in FIG. 1 to the 
compressor 18 for receiving a portion of the discharge air therefrom. 
The improved variable area CD exhaust nozzle 12 disclosed above provides 
fluidic variable area control with otherwise fixed geometry converging and 
diverging nozzles 38, 40 mounted to a stationary frame 50. The nozzle 
assembly effectively utilizes the various support ribs and dividing walls 
for defining the various independent flow circuits required for fluidic 
area control and cooling of the nozzle 12 itself during operation. The 
advantages of a variable cycle engine may also be obtained for the 
relatively simple and lightweight nozzle 12. 
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. 
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: