Power plants – Reaction motor – Interrelated reaction motors
Reexamination Certificate
1999-02-25
2001-01-30
Freay, Charles G. (Department: 3746)
Power plants
Reaction motor
Interrelated reaction motors
C239S265190
Reexamination Certificate
active
06178740
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a turbo fan engine nacelle exhaust system having a concave primary nozzle plug for reduced shock associated noise.
2. Background Information
Referring to
FIGS. 1
,
2
and
3
, a prior art turbo fan engine nacelle
10
is shown. In
FIG. 1
, the prior art turbo fan engine nacelle
10
is shown attached to a wing
12
of an aircraft. As shown in
FIG. 2
, the turbo fan engine nacelle
10
houses an engine
11
including a fan
14
which draws air through inlet
15
, and forces the air to be exhausted through a primary nozzle
16
and fan nozzle
18
. The primary nozzle
16
is bordered interiorly by the primary nozzle plug
20
, and bordered exteriorly by the primary nozzle sleeve
23
. The fan nozzle
18
is bordered interiorly by a core cowl
22
, and bordered exteriorly by a fan nozzle sleeve
24
. Accordingly, the engine
11
forces exhaust through the primary nozzle
16
and fan nozzle
18
, and as shown in
FIG. 1
, the imperfectly expanding supersonic flow
26
exhausted from the turbo fan engine
11
interacts with turbulent air structures from the jet and creates a dominant “shock cell” noise producing region
28
which radiates sound waves
29
to the cabin, thereby producing undesirable aircraft cabin noise.
Referring to
FIG. 3
, the shock cell structure in the exhaust plume of an engine is the result of two flow features: (1) a compression of the secondary (fan) flow
30
on the aft section of core cowl
22
and the resulting expansion off the secondary-ambient flow shear layer
34
; and (2) compression waves necessary to turn the radially contracting secondary flow
30
and primary flow
32
in the axial direction. The compression wave near the core cowl trailing edge reflects alternately off the secondary and ambient flow shear layer
34
as an expansion wave and the primary-secondary shear layer
36
as a compression wave. This initial wave reflection pattern is reinforced in the flow turning region
38
above and immediately aft of the primary nozzle plug
20
, thereby resulting in higher (shock cell) strength for the compression and expansion waves between the shear layers
34
,
36
.
The common solution to the cabin noise problem is to add insulation to the aircraft. However, additional insulation adds significant weight which reduces fuel economy of the aircraft and also reduces passenger carrying capacity of the aircraft.
Accordingly, it is desirable to provide a turbo fan engine nacelle exhaust system which produces lower shock cell noise to the cabin without requiring additional sound insulation in the aircraft.
SUMMARY OF THE INVENTION
The present invention reduces shock cell noise produced by a turbo fan engine nacelle exhaust system by reducing shock strength of the engine exhaust. This is achieved primarily by providing the primary nozzle plug with a concave conical shape and by optimally designing the primary nozzle and fan nozzle aerodynamic lines.
More specifically, the present invention provides a turbo fan engine nacelle exhaust system including a contoured primary nozzle and a fan nozzle specifically positioned along a common central axis. The primary nozzle is bordered interiorly by a primary nozzle plug and bordered exteriorly by a primary nozzle sleeve. The fan nozzle is bordered interiorly by the core cowl and bordered exteriorly by a fan nozzle sleeve. The primary nozzle plug includes a generally cone shaped outer surface which is concave when viewed in side elevation. The concave outer surface has a radius of curvature R
c
. The radius of curvature R
c
may be constant or variable, but it is continuous. The core cowl has a distal end which is radially spaced from the outer surface of the primary plug by a distance &Dgr;H in a direction perpendicular to the central axis. The primary nozzle plug and core cowl define a ratio R
c
/&Dgr;H between approximately 14 and 18, thereby reducing shock associated noise of the turbo fan engine.
Preferably, the distal end of the core cowl has a core cowl radius R
p
with respect to the central axis, and a discharge end of the fan nozzle sleeve has a fan nozzle sleeve radius R
f
, wherein a ratio R
p
/R
f
is between approximately 0.4 and 0.6. Additionally, the outer surface of the primary plug nozzle is sloped at an angle &phgr;
p
between approximately 13° and 19° at the primary nozzle exit.
Objects, features and advantages of the invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
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Gally Thomas A.
Newsum Sean A.
Podleski Steve D.
Su Michael W.
Brooks & Kushman P.C.
Evora Robert Z.
Freay Charles G.
The Boeing Company
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