The present invention generally relates to an engine inlet
system for a turbofan propulsion engine and, more particularly, to an engine inlet
system that is capable of separately diverting boundary layer air and free-stream
air into a turbofan propulsion engine
In conventional aircraft design, the wings of the aircraft
provide aerodynamic lift and further support the weight of the fuselage. Engines
are then coupled to the wings and/or the fuselage to provide thrust for propelling
However, recently there have been significant developments
into the design of "blended wing-body" aircraft. In a blended wing-body aircraft,
the fuselage and wings are joined to form a smooth curve along the exterior of the
aircraft with no discrete interface between the fuselage and the wing. In order
to maintain the aerodynamic efficiency and lift characteristics of a blended wing-body
aircraft, it has been determined that an aft-mounted engine configuration provides
the least disturbance of airflow over the wing-body surface, thereby maintaining
the aerodynamic efficiencies and advantages of the blended wing-body design.
Aerodynamic lift is the result of the movement of fluid
(e.g. air) over the surface of the wing. According to the laws of fluid dynamics,
such fluid movement produces a boundary layer between a region of low static pressure
and a region of high static pressure. According to current wing design technology,
it is preferable to keep this boundary layer attached along a wing surface in order
to delay or totally prevent flow separation. Such delay or prevention of the flow
separation improves the aerodynamic characteristics of the wing surface, thereby
providing a wing that produces less drag relative to a wing having a separated flow
During flight, the boundary layer air that typically forms
along the wing surfaces and fuselage is of low velocity and low static pressure.
Because low energy air causes poor engine performance, some aircraft have employed
some type of boundary layer diverter system to prevent the boundary layer air from
entering the engine inlet.
Present boundary layer diverters require various subsystems
or add on baffles to make them work properly. Such subsystems and/or baffles may
increase the weight, the cost of production, mechanical complexity, and the cost
of maintenance of the aircraft. Also, the engines would be mounted higher up, causing
nose-down moments and increased wetted area.
On the other hand, in the case of a blended wing-body aircraft,
when the engines are mounted generally flush with a trailing edge of the effective
wing, the mixture of boundary layer air and free stream air causes distortion in
a combined inlet. That is, simply aft mounting engines to a blended wing-body aircraft
may produce poor aerodynamic efficiency of the effective wing surface and may cause
poor engine efficiency due to the intake of low energy boundary layer air.
discloses an engine inlet assembly for a jet propulsion engine of an aircraft,
said engine inlet assembly comprising a first air inlet being positioned generally
within a boundary layer flowing around an exterior surface of the aircraft; a first
passage fluidly interconnecting said first air inlet and the jet propulsion engine;
a second air inlet being positioned generally outside of said boundary layer; and
a second passage fluidly interconnecting said second air inlet and the jet propulsion
Accordingly, there exists a need in the relevant art to
provide an engine inlet system for a turbofan propulsion engine that is capable
of separately diverting boundary layer air and free-stream air to a turbojet propulsion
engine. Furthermore, there exists a need in the relevant art to provide an engine
inlet system that is capable of maximizing the aerodynamic efficiency of the wing
surface and, simultaneously, maximizing the engine efficiency of the jet propulsion
engine. Still further, there exists a need in the relevant art to provide an engine
inlet system that overcomes the disadvantages of the prior art.
The present invention provides an engine inlet assembly
for a jet propulsion engine of a blended wing-body aircraft, said engine inlet assembly
being mountable upon a substantially uninterrupted lifting member of said blended-wing
aircraft, comprising a first air inlet being positioned generally within a boundary
layer flowing around said lifting member of the aircraft; a first passage fluidly
interconnecting said first air inlet and a bypass section the jet propulsion engine;
a second air inlet being positioned generally outside of said boundary layer; and
a second passage fluidly interconnecting said second air inlet and a turbine section
of the jet propulsion engine, wherein said first air inlet is generally rectangular,
said first air inlet being positionable generally flush on said exterior surface
of the aircraft; and said second air inlet is generally semi-circular, said second
air inlet being generally positioned in piggyback relationship with said first air
SUMMARY OF THE INVENTION
A dual boundary layer engine inlet for a turbofan propulsion
engine of an aircraft having an advantageous construction is provided. The engine
inlet includes a first air inlet positioned generally within the boundary layer
flowing around the exterior surface of the aircraft. A first passageway fluidly
interconnects the first air inlet and the jet propulsion engine to provide air from
the boundary layer to the bypass to reduce aerodynamic drag. A second air inlet
is positioned generally outside of the boundary layer. This second passageway fluidly
interconnecting the second air inlet and the turbofan propulsion engine to provide
free-stream air outside of the boundary layer to the core and compressor of the
turbofan engine to maintain engine efficiency.
Further areas of applicability of the present invention
will become apparent from the detailed description provided hereinafter. It should
be understood that the detailed description and specific examples, while indicating
the preferred embodiment of the invention, are intended for purposes of illustration
only and are not intended to limited the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood
from the detailed description and the accompanying drawings, wherein:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 FIG. 1 is a perspective view illustrating a blended wing-body aircraft
employing a dual boundary layer engine inlet system according to the principles
of the present invention;
 FIG. 2 is an enlarged side view, with portions in cross-section, illustrating
the dual boundary layer engine inlet system; and
 FIG. 3 is an enlarged perspective view of the inlets of the dual boundary
layer engine inlet system.
The following description of the preferred embodiment is
merely exemplary in nature and is in no way intended to limit the invention, its
application, or uses. For example, the dual boundary layer engine inlet system of
the present invention may find utility in a variety of different aircraft applications,
such as subsonic aircraft, supersonic aircraft, and conventional fuselage-wing aircraft.
The following disclosure simply relates to the preferred embodiment as illustrated
in the drawings, however, such description should not be interpreted as a limitation
of the scope of the present application.
Referring to FIG. 1, a blended wing-body aircraft 10 is
illustrated having a fuselage 12 and a pair of wings 14. Blended wing-body aircraft
10 of the preferred embodiment is characterized by the smooth shallow curve formed
by the exterior structural panels between fuselage 12 and wings 14. Unlike conventional
aircraft designs, blended wing-body aircraft 10 has no discrete interface between
fuselage 12 and wings 14. The exterior skin of fuselage 12 and wings 14 join together
to form a blended region 16. Fuselage 12, wings 14, and blended region 16 cooperate
to define a substantially uninterrupted wing member capable of providing aerodynamic
lift to blended wing-body aircraft 10 according to known aerodynamic principles.
Blended wing-body aircraft 10 further includes a plurality
of turbofan propulsion engines 18. As illustrated in the figures, the presently
preferred embodiment includes three turbofan propulsion engines 18 generally mounted
to an aft region 20 of blended wing-body aircraft 10. It should be appreciated,
however, that the principles of the present invention may be employed in aircraft
having any number of engines.
As best seen in FIG. 2, turbofan propulsion engine 18 served
by the presently preferred embodiment is a turbofan-type jet engine. For instance,
an "aft fan" arrangement was featured on the GENERAL ELECTRIC CF 700-1. Specifically,
turbofan propulsion engine 18 includes an aft-mounted bypass fan section 22 and
a turbine section 24. Turbine section 24 is disposed concentrically within bypass
fan section 22. Turbine section 24 generally includes a compressor casing 28 and
an exhaust nozzle 30. A turbine rotor 31 is operably mounted within compressor casing
28 and is mechanically linked to a compressor 32. Compressor 32 is disposed within
a compressor casing 28. Finally, a rear cone 34 is mounted within exhaust nozzle
30 so as to provide proper thrust flow from turbofan propulsion engine 18.
Bypass fan section 22 includes a plurality of fan blades
21 in a fan casing 38 so as to provide "cold" flow thrust from outlet 40 of bypass
fan section 22.
In operation, feed air is supplied to turbofan propulsion
engine 18 via a dual boundary layer engine inlet system 42. Engine inlet system
42 includes a compressor air inlet duct 44 and a bypass air duct 46.
Bypass air duct 46 includes an inlet end 48 and an outlet
end 50. In the presently preferred embodiment of FIGS. 1 and 3, inlet end 48 of
bypass air duct 46 is generally rectangular in shape such that it is positioned
and substantially follows the curvature of an upper surface 52 of blended wing-body
aircraft 10. It should be understood that upper surface 52 of blended wing-body
aircraft and, consequently, inlet end 48 of bypass air duct 46 may include any inlet
end profile that is conducive to the curvature shape of the aircraft or other aerodynamic
requirements. Outlet end 50 of bypass air duct 46 is generally circular in cross-section
so as to provide a proper fit with an inlet end 54 of bypass fan section 22 of turbofan
propulsion engine 18. Therefore, bypass air duct 46 includes a generally complex
three-dimensional transition from the generally rectangular inlet end 48 to the
generally circular outlet end 50.
Compressor air inlet duct 44 of engine inlet system 42
is generally S-shaped having an inlet end 56 and an outlet end 58. Inlet end 56
of compressor air inlet duct 44 is generally semi-circular in shape (FIG. 3) and
is positioned on top of or in a "piggy-back" position relative to bypass air duct
46. That is, a generally flat surface 60 of inlet end 56 of compressor air inlet
duct 44 is positioned upon a corresponding top surface 62 of bypass air duct 46.
Outlet end 58 of air inlet duct 44 is generally circular in shape and of sufficient
size so as to be coupled to an inlet end 64 of compressor casing 28. A grid 61 serves
as a trap for moisture and foreign objects, before the boundary layer air enters
the compressor air inlet duct.
According to the principles of the present invention, air
inlet duct 44 is positioned within a more high energy free-stream air. Accordingly,
during flight, boundary layer air, generally indicated at 66 (FIG. 2), flows over
upper surface 52 of blended wing-body aircraft 10. Inlet end 48 of bypass air duct
46 is generally disposed within this boundary layer air 66 so as to provide fluid
communication of boundary layer air 66 to bypass fan section 22 of turbofan propulsion
An advantage of this arrangement is that the operation
of bypass fan 21 in bypass fan section 22 produces a reduced pressure at inlet end
54 of bypass fan section 22. This reduced pressure condition further exists within
bypass air duct 46 and serves to scavenge the flow of boundary layer air 66 over
upper surface 52 of blended wing-body aircraft 10. That is, the reduced pressure
condition within bypass air duct 46 helps to enhance or promote the flow of boundary
layer air 66 over a larger longitudinal portion of upper surface 52 relative to
aircraft of conventional design not utilizing this reduced pressure condition.
In order to supply higher energy free-stream air to turbine
section 24 of turbofan propulsion engine 18, inlet end 56 of turbine air duct 44
is positioned substantially above boundary layer air 66 (FIG. 2) and, thus, is open
to free-stream air, generally indicated at 68. Such free-stream air 68 is supplied
to inlet end 56 of compressor inlet 58. As is well known in the art, free-stream
air serves to improve the engine efficiency of known jet propulsion engines.
As should be appreciated from the foregoing discussion,
the dual boundary layer engine inlet system according to the principles of the present
invention provides a number of aerodynamic and commercial advantages. For instance,
the dual boundary layer, engine inlet system of the present invention provides a
method of supplying high energy free-stream air to the engine's compressor inlet
while, simultaneously, supplying boundary layer air to a bypass fan inlet. The bypass
fan produces reduced pressure that scavenges and promotes the attached relationship
of the boundary layer air to the aircraft lift surfaces. Furthermore, the dual boundary
layer engine inlet system of the present invention enables the aft mounting of the
turbofan propulsion engines so as to facilitate simple and convenient repair and/or
maintenance in a commercial environment. Simple and convenient repair and maintenance
of the jet engines is a prerequisite to commercial viability within the passenger
and military transport arenas.
The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of the invention are
intended to be within the scope of the invention. Such variations are not to be
regarded as a departure from the scope of the invention.