WO2008017567A1

WO2008017567A1 - Air inlet for a jet engine

Info

Publication number: WO2008017567A1
Application number: PCT/EP2007/057137
Authority: WO
Inventors: Konrad Schafroth; Hans Pflugshaupt
Original assignee: Team Smartfish Gmbh
Priority date: 2006-08-11
Filing date: 2007-07-12
Publication date: 2008-02-14

Abstract

An air inlet (2, 3) for a jet engine (1) is disclosed. The air inlet (2, 3) has a housing (5) with an inlet lip (51) which is mounted on the surface (6) of the aircraft. The flow upstream of the air inlet (2, 3) has a boundary layer (9). The air inlet comprises two mutually separate inlets (2, 3), with the incident flow to the first air inlet (2) comprising air essentially outside the boundary layer (9), and with the incident flow to the second air inlet (3) comprising air essentially in the boundary layer. The first air inlet (2) is guided into the jet engine (1), and the second air inlet (3) is guided in an annular shape around the first air inlet (2), which both open into the jet engine (1). A method for operation of a jet engine (1) is also disclosed.

Description

Air intake of a jet engine

Technical area

The invention relates to an air intake of a jet engine of an aircraft and a method for operating a jet engine of an aircraft having the features of the independent claims.

State of the art

Modern aircraft are powered by jet engines. A jet engine draws in the ambient air and compresses it to increase the pressure in a compressor. In the combustion chamber following the compressor, the fuel is injected and the resulting fuel-air mixture is then burned. The combustion associated with expansion increases the temperature and flow rate, with the static pressure of the gas falling slightly. The flow energy supplied to the gas is then discharged in the turbine behind it and converted into rotary motion, with the gas partially expanding further. The turbine serves as the drive of the compressor, the fan and other aggregates such as e.g. of the generator and hydraulic pumps. The gas expands almost to ambient pressure into the exhaust nozzle located behind the turbine, further increasing the flow rate. In the exhaust nozzle, the actual propulsion force (thrust) is generated by the outflowing gas.

Virtually all aircraft produced today with jet turbines are equipped with turbofans. Turbofan engines are characterized by at least two coaxial shafts and an enlarged first compressor stage, which is driven by its own turbine part. Behind her, the air flow divides into an inner air flow, which enters the actual gas turbine, and an outer air flow, which is passed outside of the turbine on. Outstanding technical feature of a turbofan is the bypass ratio, so the ratio the amount of air flowing outside through the fan to the amount of air flowing through the gas turbine.

A turbofan offers several advantages over a turbojet:

• Better efficiency of the engine due to the lower average speed of the drive air jet and thus lower fuel consumption.

• Reduction of noise by dampening the hot, fast and therefore loud turbine gases by the surrounding cool and quieter gas flow of the first stage.

Through an inlet air is supplied to the engine. Actually, the inlet is "only" a pipe, through which the air required by the engine is supplied to the compressor.The geometrical design of the inlet is to be achieved in particular that the flow of the compressor is stable, as evenly as possible over the cross section and with a for the compressor optimum speed (about Mach 0.4 to 0.5) takes place - and at the lowest possible pressure losses and in all attitudes and power settings.

Especially the last requirement leads to compromises: If the aircraft is at the start and requires full thrust, the flow velocity is of course zero - the air flow must be accelerated in the inlet. The air is drawn in from all directions: directly from the front, radially or behind the inlet lip. At low airspeeds, the flow tube, which approaches the inlet lip, has a larger diameter than the inlet cross section of the inlet lip.

In cruising flight of a commercial aircraft with Mach Mach 0.8, on the other hand, the flow velocity is too high - it has to be reduced in the inlet. In order to achieve a uniform and stable flow, the contour must be as smooth as possible, with a rounded inlet leading edge flow separation should be prevented at Unterschalleinläufen. The cross section of the power tube is in this case smaller than the cross-section of the inlet, and the inlet overflows, so to speak, and the excess air flows around the air inlet. This overflow of the air inlet can lead to a significant increase in resistance.

When flying at the ideal speed for the intake, both the flow tube and the inlet have the same cross-sectional area. Figure 1 shows the known from the prior art flow conditions of a flow tube at different speeds.

If the entrances are attached to the fuselage, as is usually the case with fighter jets, it is also necessary to prevent the lower-energy fuselage boundary layer from flowing into the intake. This happens regardless of whether there is a supersonic or supersonic flow, for example by a splitter plate.

Ideal would therefore be an air intake with the largest possible cross-section for take-off and climb and a small cross-section for cruising.

When starting, a lot of air is needed because the engine is running at full load, and the forward speed of the aircraft is typically rather small. Accordingly, the engine may not receive enough air through the flow tube directly in front of the inlet and therefore must draw in additional air from the sides of the inlet and around the inlet lip. If the inlet lip is too sharp, the flow at the inlet lip can break off, and this can lead to disturbances in the speed and pressure distribution in the compressor. Also, no suction force can build up on the inlet lip, which leads to significant thrust losses.

Another problem is the speed and pressure distribution. In order for a modern turbofan to function properly, it is imperative that the speed and pressure distribution at the engine entrance be as uniform as possible. This on the one hand the efficiency is as high as possible, and thus On the other hand, the mechanical load on the engine blades is not too large. If the velocity distribution is irregular then for a turbine blade the angle of attack changes over one revolution. This leads to high mechanical loads, vibrations and fatigue, and not least also causes noise.

One factor contributing to non-uniformity of the air entering the engine is the presence of the fuselage or wing interface in the air intake. When an air stream flows along a surface, a thin layer of air is affected by friction and decelerated. This so-called boundary layer becomes thicker, the longer the air flows along a wall, the larger the distance traveled on the wall. One way to reduce the boundary layer thickness is now to make the surface in front of the air inlet as small as possible. This is one reason why jetliners are used in gondolas, at sufficiently great distance from the wings and fuselage, and thus outside the wing and fuselage boundary layer. US6634595B2 discloses an embodiment for separately receiving the air of the boundary layer in a duct and returning it to the main flow before the engine.

In some cases, however, it may be advantageous to arrange the air inlet in the immediate vicinity of the fuselage or wings. In these cases, the boundary layer formed by the flow of the surfaces in front of the air inlet is removed, for example, by the boundary layer is sucked through a porous surface, or by the energy is supplied to the boundary layer by blowing air at high speed, or by the boundary layer is led away from the engine inlet through a separating plate. All these systems work, but have disadvantages such as additional resistance, or are very complex to implement.

The dividers are according to the prior art sharp-edged and mounted with the edge perpendicular to the flow direction. With every mismatch, a small detachment thus occurs at the leading edge of the separating plate. Since the leading edge is unswept, In addition, there is still a local shock, which increases the losses even further.

One way to reduce the noise pollution for the residents of an airfield is to place the engine on the fuselage or the wing surface of an aircraft. As a result, the noise generated by the fan is radiated upward and thus reduces the noise. Another advantage of this arrangement is that fewer FOD (Foreign Object Damage) damage occurs because the engine is largely protected by the hull or wings from sucking small rocks or debris from the roadway. Disadvantages of this arrangement, however, are that then the engine is arranged in the region of a thick boundary layer and outside of it in a flow region with increased speed.

Presentation of the invention

It is an object of the present invention to design the air intake so that the engine is always supplied with the optimum amount of air and at the same time the external resistance is minimized.

The aim of the invention is also to be able to arrange the air inlet of an engine where there is a boundary layer, for example on the fuselage / wing top of a blended wing body aircraft and at the same time to have a uniform velocity and pressure distribution at the engine entrance.

These objects are achieved according to the invention by an air inlet of a jet engine of an aircraft according to independent claim 1, wherein the housing is mounted on the surface of the aircraft, so that the flow located in front of the air inlet has a surface layer facing the surface, the air inlet of two separate inputs, wherein the second air inlet is located near the surface and substantially receives the near-surface boundary layer air and the first air inlet is disposed above the second air inlet and receives substantially air outside the boundary layer, wherein the first air inlet is guided directly into the jet engine, wherein the second air inlet annularly around the first air inlet is guided and opens, if necessary, in front of the jet engine together with the first air inlet into the jet engine.

These objects are achieved according to the invention also by a method according to the method according to the independent method claim 17.

This object is achieved according to the invention in that the air inlet is combined from two inlets. The first air inlet receives air outside the boundary layer, the second air inlet receives the air of the boundary layer. The second air inlet is annularly guided around the first air inlet and, if necessary, the air of the second air inlet is supplied to the jet engine.

In a first embodiment, the second air inlet can be guided annularly around the first air inlet, the air of the second air inlet is supplied to the jet engine both in the start and in the cruise case. In this case, baffles may be present in the second air inlet to achieve a desired velocity and pressure distribution. This embodiment applies in particular to a blended wing body aircraft in which a large boundary layer exists on the aircraft surface.

In a second embodiment, in cruising flight the engine can advantageously be fed only with the first air inlet and the boundary layer entering the second air inlet can be guided so that it can not get into the engine. The air is used, for example, to cool structures in the engine area and to power the air conditioning; the excess air that is not for the Engine flow and the internal systems of the aircraft is used, is blown out at a point on the aircraft again, where as little air resistance is generated. Ideally, the first air inlet is chosen so that the area of the air inlet at the entrance has the same cross-section as the corresponding power tube in cruising flight.

Instead of a loss-generating separating plate, the boundary layer has to be removed with a dividing element which is rounded everywhere and swept everywhere. Thus, the flow changing conditions can adapt to low loss and local bumps are avoided. The separating element takes the form of a protruding, "gothic" or pointed arched arrowhead.

Further advantageous embodiments are specified in the subclaims.

Brief description of the figures

The invention will be explained in more detail with reference to the accompanying figures, wherein

Fig. 1 shows the flow conditions of a flow tube known from the prior art at different speeds;

Fig. 2 shows a view of an air inlet according to the invention, which consists of two separate inlets, each having the cross-sectional area A1 and A2;

3 shows an overall view of a jet engine according to the invention with the flow conditions in the air inlet during starting;

4 shows an overall view of a jet engine according to the invention with the flow conditions in the air inlet in cruising flight;

Fig. 5 shows a front and a side view of the cross-sectional areas A1 and A2 of the two air inlets in front of the jet engine; FIG. 6 illustrates a first embodiment of an air inlet according to the invention with a separating plate; FIG.

Fig. 7 shows a first embodiment of an inventive air inlet with a separating plate;

Fig. 8 shows an embodiment of a tapered air inlet and

9 shows an example of an aircraft (blended wing body) with an inventive air intake on the surface.

Ways to carry out the invention

Figure 2 shows a front and a side view of an inventive air intake 2, 3 of a jet engine 1. The air inlet 2, 3 is surrounded by a semi-circular housing 5, which is mounted on the surface 6 of the aircraft. In principle, the surface 6 could be the fuselage or the wings of the aircraft. The housing 5 has on the front side an inlet lip 51, which is acted upon directly by the incoming flow. The inventive air inlet consists of two separate inlets 2, 3, each having the cross-sectional area A1 and A2. The second air inlet 3 is arranged directly on the surface 6 and has a substantially square inlet cross-section, while the first air inlet 2 is arranged above the second air inlet 3 and has a substantially semicircular inlet.

FIG. 2 also shows the velocity distribution which the flow has directly in front of the air inlet. In the vicinity of the surface 6, the flow has a boundary layer 9 directed towards the surface 6, which has a variable speed, while a substantially uniform speed is established thereabove. The air inlet according to the invention is now constructed in such a way that the first air inlet 2 with the cross-sectional area A1 receives substantially air outside the boundary layer 9, while the second air inlet 3 is provided with the transverse air flow. Section A2 is essentially only the near-surface boundary layer air is supplied. However, since the boundary layer thickness can vary depending on the flow conditions and velocities, it is conceivable within certain limits that the second air inlet 3 also receives additional air outside the boundary layer. On the other hand, if a very large boundary layer 9 is present on the surface 6, it could happen that the boundary layer 9 grows beyond the second air inlet 3 into the first inlet 2.

Between both air inlets 2, 3 is a partition wall, for example, a separating plate 7 (engl, splitter plate) arranged. The separating plate 7 also has a flow-in inlet lip 71 at the front side.

FIG. 3 shows a section through a jet engine 1 according to the invention with the flow conditions in the air inlet 2, 3 when starting the aircraft. When starting, a lot of air is needed because the engine 1 is running at full load, and the forward speed of the aircraft is typically rather small. According to the invention, the engine 1 is additionally supplied with air from the second inlet 3 (boundary layer inlet). For this purpose, the air from the boundary layer inlet 3 is annularly mixed with the air from the inlet 2. This annular admixture is shown very well in FIG. 5. Figure 5 shows a front and a side view of the cross-sectional areas A1 and A2 of the two air inlets 2, 3 in front of the engine inlet 11 of the jet engine 1. In this way, the engine 1 receives sufficient air, and the velocity and pressure distribution on entering the engine. 1 is OK. With increasing airspeed but less and less air from the boundary layer inlet is needed so that the engine 1 works optimally.

From a certain speed, the engine 1 is then no longer supplied with air from the second inlet 3. FIG. 4 shows an overall view of a jet engine 1 according to the invention with the flow conditions in the air inlet 2, 3 in cruising flight. In cruising the engine 1 is fed only with the air inlet 2. The area A1 is smaller than the cross section of the engine inlet 11, ie the air inlet 2 at the same time has the function of a diffuser. The air inlet 3 with the cross-sectional area A2 plays the role of the boundary layer diverters. In cruise, the boundary layer 9, which enters the air inlet 3, guided so that they can not get into the engine 1. For example, the air may be used to cool structures in the engine compartment and / or to power the aircraft's air conditioning system; the excess air, which is not used for the engine cooling and internal systems of the aircraft, is blown out again at a point on the aircraft where it produces low air resistance. Advantageously, the air inlet 2 is selected so that the surface A1 has the same cross-section as the corresponding flow tube in cruising flight.

In the channel of the second air inlet 3, a device is provided which makes it possible to vary the ratio of the air flows of the two air inlets 2 and 3. A conceivable configuration is shown in Figure 4: The air from the second air inlet 3, which is not required by the engine in cruise, since the engine 1 is supplied by the first air inlet 2 with sufficient air, serves to cool the engine 1 , For this purpose, the air from the second air inlet 3 is guided around the engine 1 and then admixed with the flow of the outlet 4, which exits the engine 1. The geometry can even be designed so that the engine jet at least sucks in the air from the second air inlet 3, which is roughly comparable to a water jet pump. In cruising flight, therefore, the engine 1 is essentially supplied with air outside the boundary layer 9 from the first air inlet 2, and the air of the boundary layer 9 is taken up by the inlet 3, guided by the engine 1 and blown out at the back.

In the starting case (FIG. 3), however, the pressure conditions at the air inlet 2 are such that without countermeasures, the air inlet 2 would suck air from the engine compartment, since the air inlet 2 is also connected to the engine compartment and the outlet 4. As can be seen in Figures 3 and 4, it is possible to have the behavior with only one However, this must then be a controlled flap 8.

However, a system of controlled flaps may also be installed, which are controlled manually or with a computer depending on the operating condition of the aircraft and the engine, so that the efficiency of the engine is optimal and the external air resistance is minimized by the engine installation.

Advantageously, however, two flaps can be installed. One flap controls the air flow of the boundary layer inlet 3 to the engine inlet 11, the second flap controls the air flow from the boundary layer inlet to the engine end 12 or to the outlet 4 and / or the other structures of the engine. The flaps must be controlled in any case so that they allow the air from the boundary layer inlet 3 only in one direction, the first flap from the boundary layer inlet 3 towards engine inlet 11, the second flap from the boundary layer inlet 3 towards engine outlet 12. It must be prevented that warm Retract air from engine exit 12 and enter engine entrance 11. Likewise, it must be prevented that air from the main inlet 2 can enter the boundary layer inlet 3 in front of the engine inlet 11.

The flaps may be simple check valves 8 or flaps 8 with a check valve, which are preferably equipped with a damping device, so that the system is not susceptible to vibration. A check valve is in fluid technology, a directional valve, which automatically blocks the passage of the medium (hydraulic fluid, compressed air) in a flow direction. Constructively, the lock is released by a spring which presses a flap or a membrane into the respective seat. If there is a pressure in the direction of the passage that can overcome the force of the return spring, the sealing element is lifted off the seat and the flow is released.

In a further embodiment, when in cruise a very large boundary layer 9 is present on the surface 6, it is it is possible to design the cross-sectional areas A1 and A2 or the first inlet 2 and the second inlet 3 such that the entire flying area can be designed without flaps. In this embodiment, the air from the second inlet 3 is only annularly guided around the first air inlet 3 and the air of the second air inlet 3 is supplied to the jet engine 1. Since in cruising the boundary layer is large, the amount of air that is supplied via the boundary layer inlet, low. In this case, guide baffles may be present in the second air inlet 3 in order to achieve a desired velocity and pressure distribution there. It may be necessary in this case that the turbine blades are shaped differently for this design case.

The first and the second air inlet 2, 3 can be separate inlets, but can also only be separated by a separating plate 7, as can be seen in FIG. An embodiment with a separating plate 7 is shown in FIGS. 6 and 7. The shown separating plate 7 of the two figures 6 and 7 protrudes from the air inlet 2, 3 against the flow direction.

However, the flow conditions are almost never ideal, and therefore sharp edges must be avoided so that detachment can be avoided. In the case of detachments, first of all, additional resistance arises, and secondly, it can then not be ensured that the engine 1 is provided with sufficient air, which, thirdly, can lead to a loss of efficiency and / or loss of thrust. This can be achieved by providing the separating plate 7 with a round, thick inlet lip 71 (compare FIGS. 3, 4, 7). The thickness of the inlet lip 71 of the separating plate 7 should be at least one fifth of the thickness of the inlet lip 51 of the housing 5. The baffle 7 is fixed laterally to the housing 5 of the air inlet 2, 3 and has a substantially round or ellipsoidal shape, which extends with a counter to the flow radius of the housing 5 in a plane of the incoming flow. An imaginary center of the circle or the ellipse lies on the separating plate 7 in the middle of the housing 5. In order to further reduce the resistance and to avoid delamination, it is advantageous if the separating plate 7 receives a rounded and sharply swept inlet lip 71, as is visible in FIG. This can be avoided that at high Mach numbers and because of the thick inlet lip 71 problems caused by bumps. The separator has the shape of a protruding, "gothic" or pointed arched pointed tip.

This has the further advantage that then the second air inlet 3 is further away from the first air inlet 2, and the engine outlet 12 with the channel arranged around it acts like a water jet pump with sufficient suction force, which sucks the boundary layer air from the second air inlet 3 and so generates a unique flow direction. So that as much air with little resistance can be sucked in at the second air inlet 3, it is advantageous if the second air inlet 3 is designed as a separate air inlet with round shapes as possible.

In order for the flow when entering the engine 1 to have the most uniform possible velocity distribution, the inlet can also be specially designed. One possibility for this is, as visible in FIG. 8, for example, to bevel the housing 5 of the inlet 2 and to pull it forward in the direction of flow. As a result, the flow from the forwardly projecting part of the air inlet 2 is partially displaced, which thus results in a concentration of the flow at the cut-off point. This effect can now be exploited to influence the speed and pressure distribution at the engine inlet 11.

In the embodiment of Figure 8, no baffle 7 is shown, but it is conceivable to use this embodiment also with a separating plate 7, as described above. FIG. 8 shows a chamfer against the direction of flow, but within the scope of the present invention it is also conceivable to reset the housing 5. When the air inlet 2 is in the immediate vicinity of the surface 6 or the wing of the aircraft, on the one hand the As described above, the boundary layer 9 is prevented from entering the inlet 2 or, with the boundary layer inlet, the boundary layer 9 is annularly supplied to the engine as needed. Due to the chamfering of the air inlet 2 but it can now come through the swept inlet lips 51 to a vortex formation in the air inlet 2. This is most easily prevented by designing the air inlet 2 so that the inlet lip 51 is fixed perpendicular to the surface 6.

In principle, it is possible for the bevel (in or against the flow direction) mentioned at an air inlet of an aircraft in connection with FIG. 8 to be mounted vertically on the surface, also independently of the described air inlet, which consists of two inlets 2, 3 to use to reach the mentioned concentration of the flow.

In another embodiment, not shown, one air inlet 2, 3 is arranged on the left and right of the surfaces 6 of an aircraft. The air inlet 2, 3, which consists of two separate parts, each has two separate inlets 2, 3, wherein both parts are brought together before the jet engine 1. The second air inlet 3 is in each case guided in a semicircular manner around the first air inlet 2, so that the second air inlet 3 is guided overall annularly around the first air inlet 2. Before the jet engine 1, the two partial flows of the air of the first air inlet 2 are brought together and passed together with the air of the second inlet 3 into the jet engine 1. This happens depending on the case of execution as already described if necessary or only in the starting case. At the point where the two air inlets 2 are brought together, there is a blade similar to a chevron nozzle or designed like a chevron nozzle. This has advantages for the speed and pressure distribution, but also in terms of noise and vibration behavior. The air channel of the first air inlet 2 between the air inlet 2 and the engine inlet 11 has at least one point at least one at least at one point kidney-shaped cross-section. The embodiment of an air inlet, which consists of two parts, wherein both parts are merged, is independent of the described embodiment. In front of the jet engine 1, the two partial flows of the air of the first air inlet are brought together and passed together in the jet engine. At the point where the two air inlets are brought together, there is a blade similar to a chevron nozzle or a chevron nozzle. This embodiment can also be used on its own to positively influence the velocity and pressure distribution, but also in terms of noise and vibration behavior. The air channel of the first air inlet between the air inlet and the engine inlet can have a kidney-shaped cross section at at least one point.

FIG. 9 shows by way of example an aircraft with an air inlet according to the invention. This aircraft is a so-called blended wing body.

LIST OF REFERENCE NUMBERS

1 jet engine

1 1 Engine entrance

12 engine exit

2 first air intake, main inlet

3 second air inlet, boundary layer inlet

4 outlet

5 housing

51 inlet lip of the housing 5

6 surface

7 separating plate

71 inlet lip of the separating plate. 7

8 flap

9 boundary layer

A1 Cross section of the first air inlet A2 Cross section of the second air inlet

Claims

claims

1. An air inlet (2, 3) of a jet engine (1) of an aircraft, wherein the air inlet (2, 3) has a housing (5) with an inlet lip (51), wherein the housing (5) on the surface (6) is attached to the aircraft so that the flow located in front of the air inlet (2, 3) has an interface (10) directed towards the surface (6),

Wherein the air inlet consists of two separate inlets (2, 3),

Wherein the second air inlet (3) is arranged close to the surface and essentially receives the near-surface boundary layer air and the first air inlet (2) is arranged above the second air inlet (3) and receives substantially air outside the boundary layer (10),

Wherein the first air inlet (2) is guided directly into the jet engine (1),

• wherein the second air inlet (3) is annularly guided around the first air inlet (2) and, if necessary, in front of the jet engine (1) opens together with the first air inlet (2) in the jet engine (1).

2. The air inlet (2, 3) according to claim 1, characterized in that the second air inlet (3) is annularly guided around the first air inlet (2) and the air in the start case in front of the jet engine (1) together with the air of the first Air inlet (2) opens into the jet engine (1).

3. The air inlet (2, 3) according to claim 1 or 2, characterized in that the second air inlet (3) is guided in cruising for cooling purposes to the structures of the jet engine (1) and in the second air inlet (3) a check valve (8 ) is present, so that it can come in this channel to no backflow of air from the structures of the jet engine (1) to the engine inlet (1 1) and / or the inlet of the second air inlet (3).

4. The air inlet (2, 3) according to claim 1 or 2, characterized in that the second air inlet (3) is annular around the first Air inlet (2) is guided and the air in the start and Reisefall before the jet engine (1) opens together with the air of the first air inlet (2) in the jet engine (1).

5. The air inlet (2, 3) according to claim 4, characterized in that baffles in the second air inlet (3) are present in order to achieve a desired velocity and pressure distribution.

6. The air inlet (2, 3) according to one of claims 1 to 5, characterized in that between the first and the second air inlet (2, 3) a separating plate (7) is present.

7. The air inlet (2, 3) according to claim 6, characterized in that the separating plate (7) has an inlet lip (71) and the thickness of the inlet lip (71) of the separating plate (7) at least one fifth of the thickness of the inlet lip (51 ) of the housing (5).

8. The air inlet (2, 3) according to claim 6 or 7, characterized in that the separating plate (7) protrudes from the housing (51) of the air inlet (2, 3) against the flow direction.

9. The air inlet (2, 3) according to any one of claims 6 to 8, characterized in that the separating plate (7) is laterally attached to the housing (5) of the air inlet (2, 3) and substantially a round shape with a Having the flow opposite radius.

10. The air inlet (2, 3) according to one of claims 1 to 9, characterized in that the housing (5) of the air inlet (2, 3) has a substantially round shape and directly at the front edge of the inlet (2, 3 ) is tapered in the direction or against the flow.

1 1. The air inlet (2, 3) according to any one of claims 1 to 10, characterized in that the housing of the air inlet (2, 3) is designed so that the part of the inlet lip (51) substantially perpendicular to the surface ( 6) is attached.

12. The air inlet (2, 3) according to any one of claims 1 to 1 1, characterized in that the area (A1) of the first air inlet (2) at the inlet of the air inlet (2) smaller than the cross section of the engine inlet (1 1) is.

13. The air inlet (2, 3) according to one of claims 1 to 12, characterized in that in cruise the surface (A1) of the first air inlet (2) at the inlet of the air inlet (2) has substantially the same cross-section as the corresponding flow tube ,

14. The air inlet (2, 3) according to one of claims 1 to 13, characterized in that the air inlet (2, 3) consists of two separate parts, each having two separate inlets, a first and a second air inlet (2 , 3), wherein both parts are brought together in front of the jet engine (1), wherein in each case the second air inlet (3) is guided in a semicircle around the first air inlet (2), so that the second air inlet (3) is annular overall around the first air inlet (3) Air inlet (2) is guided and if necessary in front of the jet engine (1) opens together with the merged air of the two parts of the first air inlet (2) in the jet engine (1).

15. The air inlet (2, 3) according to claim 14, characterized in that the cutting edge, which is located at the junction of the two parts of the first air inlets (2), is designed substantially like a chevron nozzle.

16. The air inlet (2, 3) according to one of claims 1 to 15, characterized in that the channel of the first air inlet (2) between the air inlet (2) and the engine inlet (1 1) at least one point has a kidney-shaped cross-section ,

17. A method for operating a jet engine (1) of an aircraft with an air inlet (2, 3), wherein the air inlet (2, 3) has a housing (5) with an inlet lip (51) which is located on the surface (6). is attached to the aircraft so that the flow located in front of the air inlet (2, 3) has a boundary layer (10) directed towards the surface (6). wherein the air inlet consists of two separate inlets (2, 3), the method comprising the following method steps

The air inlet (2, 3) is supplied with the flow,

• wherein the first air inlet (2) is substantially supplied with air outside the boundary layer (10) and the second air inlet (3) is substantially flown with the near-surface boundary layer air and

• wherein the air of the first air inlet (2) is fed directly into the jet engine (1) and

• wherein the air of the second air inlet (3) is guided annularly around the first air inlet (3) and, if necessary, the jet engine (1) is supplied.

18. The method according to claim 17, characterized in that the second air inlet (3) is guided annularly around the first air inlet (3) and in the start case, the air of the second air inlet (3) is supplied to the jet engine (1).

19. The method according to claim 17 or 18, characterized in that in cruise the air of the second air inlet (3) is used to cool structures of the jet engine (1) and / or to feed an air conditioner.

20. The method according to any one of claims 17 to 19, characterized in that in cruise the air of the second air inlet (3) for cooling the structures of the jet engine (1) is guided and / or to feed an air conditioner and in the channel of the second air inlet (3) a check valve (8) is present, so that there is no backflow of the air to the engine inlet (11) and / or to the second air inlet (3) in this channel.

21. A method according to any one of claims 17 to 20, characterized in that, in cruising flight, excess air of the second air inlet (3), which is not used for the engine cooling and the internal systems of the aircraft, is blown out again at a location on the aircraft, where a low air resistance is generated.

22. The method according to any one of claims 17 to 21, characterized in that the air inlet (2, 3) consists of two separate parts, each having two separate inlets (2, 3), a first and a second air inlet, wherein both parts are brought together in front of the jet engine (1), the second air inlet (3) being guided in a semicircle around the first air inlet (2), so that the second air inlet (3) is guided in a ring around the first air inlet (2) and the air in the specified case of need before the jet engine (1) is guided together with the merged air of the two parts of the first air inlet (2) in the jet engine (1).

23. The method according to claim 18, characterized in that the second air inlet (3) is annularly guided around the first air inlet (3) and in the start and in the Reisefall the air of the second air inlet (3) the jet engine (1) is supplied ,

24. The method according to claim 23, characterized in that by baffles in the second air inlet (3) a desired speed and pressure distribution is achieved.

25. A method for operating a jet engine (1) of a blended wing body aircraft with an air inlet (2, 3), wherein the air inlet (2, 3) has a housing (5) with an inlet lip (51) on the Surface (6) of the aircraft is attached, so that in front of the air inlet (2, 3) located flow to the surface (6) directed boundary layer (10), wherein the air inlet consists of two separate inlets (2, 3) , the method comprising the following method steps

The air inlet (2, 3) is supplied with the flow,

• wherein the air of the first air inlet (2) is fed directly into the jet engine (1) and wherein the air of the second air inlet (3) is guided annularly around the first air inlet (3) and is supplied to the jet engine (1) in the start and in the cruise case.