Apparatus for re-energizing boundary layer air

Air is blown into an air boundary layer to re-energize the boundary layer prior to its ingestion by an engine inlet (12) of a supersonic aircraft (10).

DESCRIPTION 
1. Technical Field 
This invention relates to engine inlets for supersonic aircraft. More 
particularly, the invention relates to a supersonic inlet mounted to an 
aircraft in a position such that the inlet may ingest or receive boundary 
layer air during supersonic flight. 
2. Background Art 
The presence of boundary layer air on the fuselage of an aircraft during 
flight is a well-known phenomenon. In supersonic aircraft, it is desirable 
that little or no boundary layer air be received or ingested by an engine 
inlet because inlet ingestion of the boundary layer can cause pressure 
recovery and airflow distortion problems in the inlet. 
Several different forms of boundary layer diverters have been used in those 
types of supersonic aircraft wherein inlets are positioned nearby surfaces 
upon which a boundary layer develops. One common type of diverter 
displaces the inlet a sufficient distance away from the surface so that 
the entire boundary layer is positioned between the inlet and the surface. 
This is schematically illustrated in FIG. 1, wherein a supersonic aircraft 
10 is shown having an inlet 12 mounted a certain distance away from the 
bottom surface 14 of the aircraft fuselage. 
Another type of diverter, not shown in the drawings, employs a scoop ahead 
of the inlet. When this type of diverter is used the inlet is typically 
mounted directly to the aircraft fuselage and the diverter scoop is 
mounted to the fuselage forwardly of the inlet. The scoop captures the 
boundary layer and diverts it through a passageway to a location aft of 
the inlet where it is dumped into the ambient atmosphere. 
A person skilled in the art would realize that both of the above-described 
diverters cause increased aircraft drag which is undesirable. These 
diverters also increase aircraft cross-sectional area and increase 
aircraft weight, both of which are also undesirable. 
The purpose of this invention is to eliminate the use of conventional 
diverters and to permit the mounting of a supersonic inlet directly 
adjacent an exterior surface of a supersonic aircraft. This arrangement is 
schematically illustrated in FIG. 2 and would alleviate the 
above-mentioned drawbacks associated with conventional diverter designs. 
3. Disclosure of the Invention 
The present invention is meant for use in supersonic aircraft having at 
least one jet engine inlet mounted adjacent a surface of the aircraft upon 
which boundary layer air is present. Currently, many supersonic aircraft 
have engine inlets mounted adjacent the bottom side of the aircraft 
fuselage, as in the manner schematically shown in FIGS. 1 and 2. Boundary 
layer air develops along the bottom of the fuselage and at least a portion 
thereof is likely to be received or ingested by the inlet unless adequate 
preventive measures are taken. 
Boundary layer air has a certain pressure profile which, by way of 
illustrative example only, typically has the shape shown by the solid line 
16 in FIG. 3. As a person skilled in the art would know, boundary layer 
air develops between an aircraft exterior surface and the ambient 
environment, which will be referred to herein as free stream air. Free 
stream air has a pressure profile that looks like the dashed line 18 in 
FIG. 3. 
The invention provides a means for blowing air into the boundary layer, for 
re-energizing the boundary layer, so that it will have a total pressure 
profile that substantially matches the total pressure profile of free 
stream air. By accomplishing this, any pressure recovery or airflow 
distortion problems caused by inlet ingestion of the boundary layer will 
be alleviated or eliminated. 
The air blowing means is positioned forwardly of the inlet. It may include 
at least one port in the exterior surface of the aircraft, a means for 
providing a source of high pressure air, and a nozzle connecting the high 
pressure air source means to the port. The air pressure provided by the 
air source means must be higher than the pressure of the air in the 
boundary layer. It also must be high enough to re-energize the boundary 
layer so that its profile will match the free stream profile. The nozzle 
and port cooperate to direct a flow of high pressure air from the air 
source means into the boundary layer, whereby the flow is directed from 
the port toward the aircraft inlet. 
Engine bleed air, in combination with a high pressure plenum, may be 
utilized as the high pressure air source means. Present calculations have 
shown that the boundary layer can be re-energized by bleeding and blowing 
approximately 1% of total engine airflow. Aircraft designers generally 
acknowledge that it is a disadvantage to utilize engine bleed air since it 
adversely affects engine performance. The disadvantage in this case, 
however, is offset by the advantage of a reduction in drag due to the 
elimination of conventional diverters, and the further advantage of 
reducing aircraft cross-sectional area and weight.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to FIG. 6, therein is shown a central portion 20 of the 
fuselage of the aircraft 10, the aircraft also being shown throughout 
FIGS. 1, 2, 4 and 5. This portion 20 includes a high pressure air plenum 
22. Connected to the plenum 22 is a nozzle 24 which blows high pressure 
air from the plenum 22 out through a port 26. 
The port 26 of the nozzle is located in the bottom fuselage surface 14 
forwardly of a leading edge 38 of the inlet 12. The nozzle 24 and port 26 
may take a variety of suitable forms but will preferably occupy a region 
such as region 40 shown in FIG. 4. 
The high pressure air is blown into an air boundary layer 28 that is 
located adjacent the bottom surface 14 of the fuselage, between the 
surface 14 and ambient or free stream air 30. The boundary layer 
(forwardly of the port 26) and free stream air 28, 30 together have a 
pressure profile that is substantially the same as the profile indicated 
by the dashed line 32 in FIG. 6. 
The nozzle and port 24, 26 cooperate to direct or blow the high pressure 
air into the boundary layer 28 in the manner indicated by arrow 34. This 
high pressure air 34 re-energizes the boundary layer 28 so that its 
pressure profile substantially matches the pressure profile of the free 
stream air 30, before the boundary layer is ingested by the inlet 12. The 
resultant effect of such re-energization is schematically illustrated by 
the dashed line 36 in FIG. 6. 
An air source or means for providing high pressure air to the plenum 22 may 
be provided by bleeding high pressure air from an engine 42 located 
onboard the aircraft 10. An air delivery conduit 44 could be provided by 
communicating engine bleed air from the engine 42 to the plenum 22. The 
technology for providing this type of conduit would be well-known to a 
person skilled in the art. 
In one embodiment of the invention, the nozzle and port 24, 26 may be in 
the form of a full width slot positioned in the region 40 forwardly of the 
inlet 12. This embodiment is illustrated in FIG. 7. The nozzle 24 has a 
first sidewall 46 having a straight portion that extends in an elongated 
manner transversely and forwardly of the inlet leading edge 38. This is 
illustrated by the top Fig. in FIG. 7. A second sidewall portion 48 of 
this nozzle includes a rounded portion 50 and a straight portion 52. The 
rounded and straight portions 50, 52 of the second sidewall 48 cooperate 
with the straight portion 46 of the first sidewall 46 to form a nozzle 
throat region. 
The full width slot configuration shown in FIG. 7 could be replaced by a 
plurality of high aspect 2-D C-D nozzles having the same general cross 
section as the nozzle shown in the bottom part of FIG. 7. This 
configuration is not shown in the drawings, however. 
In another embodiment of the invention, shown in FIG. 8, the nozzle 24 is 
in the form of a plurality of nozzles which occupy the region 40. In this 
embodiment, each nozzle 24 includes a first sidewall 54 having an inwardly 
curving portion 56, an outwardly curving portion 58, and a straight 
portion 60. This nozzle also has a second sidewall 62 which includes both 
a rounded portion 64 and a straight portion 66. The curving and straight 
portions 56, 58, 60 of the first nozzle sidewall 54 cooperate with the 
rounded and straight portions 64, 66 of the second nozzle sidewall 62 to 
form a nozzle throat region leading into the port 26. 
The nozzle configuration shown in FIG. 8 is commonly known in the art as a 
discrete 2-D C-D nozzle or jet. Each nozzle in this configuration has a 
pair of straight outer sidewalls 68, 70 which are oriented generally 
perpendicular to the bottom surface 14 of the fuselage. Each nozzle also 
has a straight but sloping sidewall 72 which generally faces outwardly 
relative to the aircraft 10. 
Still another embodiment of the invention is shown in FIG. 9. In this 
embodiment, a plurality of nozzles 24 may be positioned in the region 40 
having the cross section generally shown in the lower part of FIG. 9. Each 
nozzle 24 has a first sidewall 74 that includes an inwardly curving 
portion 76 and a straight portion 78. Each nozzle also has a second 
sidewall portion 80 having a rounded portion 82 and a straight portion 84. 
The curving and straight portions 76, 78 of the first sidewall 74 
cooperate with the rounded and straight portions 82, 84 of the second 
sidewall 80 to form still another configuration of a nozzle throat region. 
The outer portion 86 of each nozzle in FIG. 9 has a half-rounded surface 
as shown in the top part of FIG. 9. 
All of the nozzle configurations described and illustrated in FIGS. 7-9 
were tested in a wind tunnel test section much like that shown in FIG. 10. 
Each nozzle configuration was constructed as part of an insert 88 that was 
placed in a surface 90 in a wind tunnel. An airflow 92 was generated 
adjacent the surface 90 to simulate aircraft flight. A plurality of 
pressure transducers 94 were positioned in a vertical surface of a wedge 
96 mounted to the surface 90. The pressure transducers 94 were positioned 
away from the surface 90 at different vertical positions so that they 
could measure the pressure profile of the airflow 92 after it was 
re-energized by the nozzle 24. 
FIGS. 11 and 12 show the test results for each nozzle shown in FIGS. 7-9 
and for the configuration wherein the full width slot nozzle in FIG. 7 is 
in the form of a plurality of discrete nozzles. As can be seen in FIGS. 11 
and 12, utilizing the discrete 2-D C-D nozzles shown in FIG. 8 will 
provide sufficient re-energization of the boundary layer so that its 
profile substantially matches the free stream profile. Future tests may 
show that other nozzle configurations may provide even better results. 
The description provided above is to be used for exemplary purposes only. 
It is not meant to limit the spirit and scope of the invention in any way. 
It is to be understood that still other embodiments of the invention, and 
specifically, different nozzle configurations may be provided without 
departing from the conceptual teachings of the invention. The invention is 
to be limited only by the appended claims which follow.