Device and method for letting off compressor air in an engine

0001The invention relates to an engine with a bypass channel and a device for blowing off compressor air and a method for blowing off compressor air in an engine.

0002It is known to take compressor air from a compressor of an engine in order to vary the mass flow through the compressor and to optimize it with regard to its aerodynamic stability. Blowing off compressor air serves, for example, to prevent unstable operating states of a low-pressure compressor.

0003From the<patcit id="pcit0001" dnum="US7594403B2"><text>US 7,594,403 B2</text></patcit> a device for removing compressor air from a low-pressure compressor is known, in which openings are formed in the wall of the low-pressure compressor, which can be released or closed by an external adjusting ring. The extracted compressor air is fed to a secondary flow channel via bypass channels. Such a device for the controllable blowing off of compressor air from a low-pressure compressor is also referred to as a BBV system (BBV = "Booster Bleed Valve").

0004From the<patcit id="pcit0002" dnum="US20020148216A1"><text>US 2002/0148216 A1</text></patcit> A turbofan engine is known in which openings are formed in the wall of the primary flow channel behind a low-pressure compressor, through which compressor air is directed into an annular cavity. A plurality of channels lead from the cavity to a secondary flow channel of the engine. Each of these channels is assigned a valve for opening or closing the respective channel.

0005In known BBV systems, for example, only the "open" and "closed" positions can be operated using valve rings or valve flaps, since the air swirls too much in the transition positions. This has the disadvantage that it is not possible to make a defined adjustment to the air flow that is passed through the bypass channel. If the openings are only partially opened, the known BBV systems create a high degree of turbulence, which leads to a loss of efficiency and an increase in noise.

0006From the<patcit id="pcit0003" dnum="US20080063515A1"><text>US 2008/0063515 A1</text></patcit> a device for blowing off compressor air in an engine is known, which comprises a closing element in the form of a displaceable valve. By means of the closing element, a bypass channel between a primary flow channel and a secondary flow channel of an engine can be closed. The closing element or The valve can assume a completely closed position in which the bypass channel is completely closed, can be partially open, or can be completely open. In the latter case, the gas from the bypass channel is led into the secondary flow channel via an opening, while the gas is passed into the secondary flow channel when the valve is in the closed position. Adjacent to the valve are air guide surfaces downstream, which are firmly connected to the movable valve.

0007The present invention is based on the object of providing an engine with a bypass duct and a device for blowing off compressor air and a method for blowing off compressor air in an engine, which enable a defined adjustment of the air flow through a bypass channel for compressor air to be blown off.

0008The solution according to the invention is then characterized by a closure element which is designed to be successively moved into the bypass channel. The air flow flowing through the bypass channel can be adjusted by the position of the closing element. Furthermore, an air guiding device coupled to the closing element is provided, which has air guiding surfaces which adjoin the closing element downstream, the spatial orientation of the air guiding surfaces being adjusted depending on the position of the closing element.

0009The solution according to the invention enables a defined adjustment of the air flow that is passed through the bypass channel and blown off. The air flow can be adjusted essentially continuously, with operating situations also being able to be implemented in which a defined mass flow is permanently blown out of the compressor in order to optimize the efficiency of the compressor.

0010At the same time, the provision of an air guide device with air guide surfaces in the bypass channel ensures that turbulence of the gas flow behind the closure element is prevented or reduced and instead the flow with high laminarity also flows behind the closure element in the bypass channel. For this purpose, the air guide surfaces adjoin, for example, a front edge of the closing element projecting into the bypass channel downstream.

0011Because the spatial alignment of the air guide surfaces depends on the position of the closing element, it can be ensured that at every position of the closing element, ie at every degree of opening of the bypass channel, the highest possible laminarity of the flow behind the bypass channel is partially closed Closing element is present.

0012It should be noted that the feature that the spatial orientation of the air control surfaces depends on the position of the closure element means that a normal vector that stands on an air control surface changes its orientation in space depending on the position of the closure element. In other words, such a normal vector is changed in terms of its spatial direction depending on the position of the closure element. For example, there is no change in the spatial orientation if an air guide surface is only moved parallel in one spatial direction. In this case, only the starting point of the normal vector is shifted without changing its direction in space.

0013According to the present invention, the closure element is formed by an axially displaceable ring or an axially displaceable ring segment. The bypass channel is designed to be rotationally symmetrical. By axially moving the ring or one or more ring segments, the bypass channel is successively closed.

0014One embodiment of the invention provides that the air guiding device is formed by a plurality of flaps. The flaps are each designed to be movable relative to the closing element, with each of the flaps forming an air guiding surface. Between the flaps there is a gap in the circumferential direction, which can be small. Providing a plurality of flaps ensures that they can change their spatial orientation depending on the position of the closing element. It is thus provided that the angle of inclination of the flaps depends on the position of the closing element.

0015According to one embodiment variant, in order to couple the flaps to the closing element, each of the flaps is connected to the closing element via at least one joint. As a result, when the position of the closing element changes, the spatial alignment of the flaps is automatically changed and adjusted. Furthermore, according to an embodiment variant, it is provided that each of the flaps is additionally connected to a stationary anchor point via a further joint. Such a stationary anchor point can be provided, for example, by an intermediate casing that absorbs structural loads (also referred to as IMC = "Intermediate Casing").

0016According to a preferred embodiment, the spatial orientation of the air guide surfaces changes depending on the position of the closing element in such a way that the increase in the laminarity of the flow provided by the air guide surfaces is maximum for each position of the closing element. For example, it is first calculated how the air guiding surfaces should be aligned at certain positions of the closing element in order to achieve the highest possible degree of laminarity of the flow, and the coupling between the air guiding device and the closing element is then designed in this way (e.g. by means of appropriately positioned joints). that an optimal spatial alignment of the air guide surfaces is achieved at every position of the closing element.

0017According to an alternative exemplary embodiment, the air guiding device is not formed by a plurality of flaps, but rather by a flexible, flat element. This forms two end regions, one end region being connected to the closure element in an edge region and the other end region being arranged in a stationary manner downstream of it on a boundary structure of the bypass channel. Such an arrangement of the element and due to its flexible properties also ensures in this embodiment variant that the spatial alignment of the air guide surfaces depends on the position of the closing element. The flat element is formed, for example, by a sheet of metal. It can be designed as a ring or as a ring segment.

0018The device according to the invention can, among other things, be designed to implement an operating state in which the closing element assumes a position such that 30% to 80%, in particular 40% to 70% of the maximum mass flow that can be blown off through the bypass channel is permanently flowed through the bypass channel stream. By providing a continuous mass flow, the efficiency of the compressor can be optimally adjusted in exemplary embodiments.

0019The realization of displaceability of the closing element can be done in a variety of ways. For example, the closing element (which, as mentioned, is designed, for example, as a ring or as a ring segment) can be coupled to an actuator via an eccentric. However, it can also be moved in another way, for example via a shaft system or using levers and joint rods.

0020The solution according to the invention is used, for example, in a low-pressure compressor of a turbofan engine. Compressor air is typically blown off at low speeds or during transient processes. However, the invention can in principle also be implemented with a different compressor of an engine, for example for blowing off compressor air from a high-pressure compressor of a core engine.

0021The invention also relates to a method for blowing off compressor air in an engine, wherein the compressor air to be released is directed from a compressor of the engine into a bypass channel. It is provided that air is released via the bypass channel during operation of the engine by pushing a displaceable closing element into the bypass channel in such a way that it is only partially closed. The compressor air flowing in the bypass channel is guided downstream of the closing element to increase the laminarity of the flow past air guiding surfaces of an air guiding device coupled to the closing element and the spatial orientation of the air guiding surfaces is adjusted depending on the position of the closing element.

0022The invention is explained in more detail below with reference to the figures of the drawing using several exemplary embodiments. Show it:<dl id="dl0001"><dt>Figure 1</dt><dd>Components of an exemplary embodiment of a turbofan engine, showing a fan, a primary flow duct, a secondary flow duct, a low-pressure compressor and a flexibly closable bypass duct through which air can be conducted from the low-pressure compressor into the secondary flow duct;</dd><dt>Figure 2</dt><dd>an enlarged view of the bypass channel<figref idref="f0001">Figure 1</figref>, wherein the bypass channel is assigned a device for blowing off compressor air with an axially displaceable closing element;</dd><dt>Figure 3</dt><dd>the bypass channel<figref idref="f0002">Figure 2</figref> showing a first position of the closure element;</dd><dt>Figure 4</dt><dd>the bypass channel<figref idref="f0002">Figure 2</figref> showing a second position of the closure element;</dd><dt>Figure 5</dt><dd>the bypass channel<figref idref="f0002">Figure 2</figref> showing a third position of the closure element; and</dd><dt>Figure 6</dt><dd>a second embodiment of a device for blowing off compressor air, which closes a bypass channel in a defined manner.</dd></dl>

0023Figure 7 shows components of a turbofan engine. The illustrated section of a turbofan engine includes a fan stage with a fan 1, from which the air mass sucked in by the fan 1 is directed into a secondary flow channel 2 and into a primary flow channel 3. The secondary flow channel 2 and the primary flow channel 3 are separated from each other behind the fan 1 by a splitter 4. The primary power channel 3 leads through the core engine. In the case of a twin-shaft engine, the core engine includes a low-pressure compressor 6, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine.

0024In the context of the present invention, blowing off compressor air from the low-pressure compressor 6 is important. However, it should be noted that the principles of the invention, which are explained below with reference to blowing off compressor air from a low-pressure compressor, can also be used in the same way for blowing off compressor air, for example from a high-pressure compressor or a medium-pressure compressor (in a three-shaft engine).

0025The low-pressure compressor 6 comprises several, in the exemplary embodiment shown two, compressor stages, which are also referred to as booster stages. In front of the low-pressure compressor 6, a stator 5 is arranged at the beginning of the primary flow channel 3, which serves to remove the swirl from the air flow that it has received in the area of ​​the fan 1 near the hub.

0026The low-pressure compressor 6 is surrounded by a peripheral housing 8, which delimits the primary flow channel 3 radially on the outside. Radially inside, the primary current channel 3 is formed by corresponding rim surfaces of the rotors and stators or by the hub or by elements of the corresponding drive shaft connected to the hub.

0027In the flow direction behind the low-pressure compressor 6, the peripheral housing 8 has an opening 9 which opens into a bypass channel 7. The bypass channel 7 is used to blow off compressor air from the low-pressure compressor 6. The bypass channel 6 blows the compressor air out into the secondary flow channel 2 and accordingly has an opening at its rear end 70 to the secondary flow channel 2 or alternatively to structures which in turn are connected to the Secondary current channel 2 is connected. The course of the bypass channel 7 is in the<figref idref="f0001">Figure 1</figref> only shown as an example.

0028The opening 9 in the primary flow channel 3 to the bypass channel 7 can be designed to be circumferential or consist of a plurality of openings evenly distributed over the circumference. The bypass channel 7 can be designed to be rotationally symmetrical, although it can be interrupted by structural elements, for example an intermediate housing (IMC) that accommodates structural loads.

0029A device 10 is assigned to the bypass channel 7 and sets the blowing off of compressor air through the bypass channel 7 in a defined manner. This device 10 is described below using the<figref idref="f0002 f0003 f0004 f0005">Figures 2 to 5</figref> explained in more detail.

0030According to the<figref idref="f0002">Figure 2</figref> The device 10 comprises an actuator 11, a closing element 12 and an air guide device 13. The actuator 11 is displaceable in the axial direction, as shown schematically by the double arrow. The closing element 12 is coupled to the actuator 10 in such a way that it can be successively moved into the bypass channel 7, the air flow flowing through the bypass channel 7 being adjustable by the position of the closing element 12. The air guiding device 13 is mechanically coupled to the closing element 12. It includes air guide surfaces which connect downstream in the bypass channel 7 to an edge of the closing element 12 which projects into the bypass channel.

0031The<figref idref="f0002">Figure 2</figref> shows a representation of three of the possible positions of the actuator 11, the closing element 12 and the air guiding device 13. The<figref idref="f0003">Figure 3</figref> corresponds to the first position<figref idref="f0004">Figure 4</figref> corresponds to the second position and the<figref idref="f0005">Figure 5</figref> corresponds to the third position. A detailed discussion of the structure of the closing element 12 and the air guiding device 13 is based on the<figref idref="f0003 f0004 f0005">Figures 3 to 5</figref>, as these are clearer due to the representation of only one position.

0032The closing element 12 comprises a closing surface 121 which rests against or forms the peripheral wall of the bypass channel 7 in the open position of the device, ie when the bypass channel 7 is completely open. The closing surface 121 forms an edge 122 at its rear end in the direction of flow, which projects furthest into the bypass channel 7 when the closing element 12 is axially displaced by means of the actuator 11, cf.<figref idref="f0004">Figure 4</figref>.

0033The closing element 12 further comprises a fastening arm 123, which is rigidly coupled to the actuator 11, so that the closing surface 121 is pushed in the axial direction into the bypass channel 7 by axially moving the actuator 11.

0034The axially displaceable closing surface 121 is designed as a ring or as a ring segment, so that when the closing surface 121 is moved into the bypass channel 7, which is designed to be rotationally symmetrical, its overall cross-section is reduced or completely closed.

0035The air guiding device 13 consists of a plurality of flaps 130 which are adjacent in the circumferential direction and which each form an air guiding surface 131 for the bypass channel 7. The flaps 139 are connected to a stationary joint 133 via an arm 134. On the other hand, they are connected via an arm 132 to a non-stationary double joint 14, which, in addition to the connection to the arm 132, has a connection to an arm 124 which protrudes from the fastening arm 123. This provides a coupling of the air guiding device 13 with the closing element 12 in such a way that the spatial alignment of the flaps 130 and the air guiding surfaces 131 provided by them is dependent on the axial position of the closing element 12.

0036Furthermore, it is provided that the closing surface 121 of the closing element 12 and the air guiding surface 131 of the flaps 130 are connected to one another at their mutually adjacent ends, ie, in the area of ​​the edge 122 of the closing element 12, on the side facing away from the bypass channel 7 by an element 15 are connected. This element 15 is, for example, a bendable sheet metal or the like. This bendable element 15 strengthens the structure of the device in the transition area between the closing surface 121 and the air guiding surface 131 and additionally prevents air from flowing through the gap between the closing surface 121 and the air guiding surface 131.

0037The<figref idref="f0004">Figure 4</figref> shows the device<figref idref="f0003">Figure 3</figref> in a state in which the closure element 12 compared to the state of<figref idref="f0003">Figure 3</figref> was moved axially into the bypass channel 7 without closing it. It can be seen that due to the coupling between the air guiding device 13 and the closing element 12 via the double joint 14, the axial position of the closing element 12 defines the spatial orientation of the air guiding surfaces 131 of the air guiding device 13. Due to this coupling, the spatial orientation of the air guide surfaces 131 changes smoothly depending on the axial position of the closing element 12.

0038An arched surface 17 is realized in structural components of the engine, which allows the end of the air guide surface 131 facing away from the closing element 12 to carry out a movement defined by the bearing 133. The type and dimensions of the double joint 14 and the spatial position of the stationary joint 133 can be used to define the spatial orientation of the air guide surface 131 when the closing element 12 is moved in the desired manner.

0039It is provided that the air guide surface 131 has a spatial orientation at every axial position of the closing element 12 such that the laminarity of the blow-off air flowing through the bypass channel 7 behind the closing element 12, in particular behind its front edge 122, is high or maximum, ie turbulence behind the closing element 12 in the bypass channel 7 is as small as possible. Such turbulence is disadvantageously associated with a loss of efficiency and an increase in noise.

0040Thus, by providing air guide surfaces 131 in the flow direction behind the closing element 12, and in particular behind the edge 122 of the closing element 12, it is achieved that the flow in the bypass channel 7 does not swirl behind the edge 122, but in particular in the in the<figref idref="f0004">Figure 4</figref> Area X shown is guided largely laminarly along the air guide surfaces 131. Starting from the narrowing of the bypass channel 7 provided by the closing element 12, the air guide surfaces 131 cause a continuous expansion of the bypass channel until a certain width is reached.

0041The<figref idref="f0005">Figure 5</figref> shows the device<figref idref="f0003">Figure 3</figref> with a position of the closing element in which it largely closes the bypass channel 7. The spatial alignment of the air guide surfaces 131 is automatically adapted to the new axial position of the closing element 2. The flexible element 15 provides a secure structural connection between the closing surface 121 and the air guiding surface 131.

0042The<figref idref="f0006">Figure 6</figref> shows an alternative embodiment of the invention. In this exemplary embodiment, the air guiding device is formed by a flexible, flat element 16, which is provided, for example, by a flexible sheet metal. The flexible element 16 forms two end regions 161, 162, one end region 161 being fixed in place in the region of the edge 122 of the closing element 12 and the other end region being fixed in place downstream to a boundary structure 71 of the bypass channel 7. The flexible element 16 forms air guide surfaces on its side facing the bypass channel 7, which prevent or reduce turbulence of the air flow behind the edge 122 of the closing element 12. At the same time, the flexible design of the element 16 ensures that the spatial alignment of the air guide surfaces provided by the element 16 is dependent on the position of the closing element 12, and accordingly there is an improved laminarity of the flow in the bypass channel 7 at every position of the closing element 12 .

0043The devices described in the figures enable air to be continuously released via the bypass channel 7 during operation of the engine, since the closing element 12 can be positioned in such a way that it only partially closes the bypass channel 7. In order to increase the laminarity of the flow, the compressor air flowing in the bypass channel 7 is guided past the air guide surfaces behind the closing element 12, which directly adjoin the closing element 12 downstream in the bypass channel 7.

0044The invention is not limited in its design to the exemplary embodiments presented above, which are only to be understood as examples. In particular, the structure and shape of the closing element and the air guide device are only to be understood as examples.