Patent Application
20150016950
This application claims priority to German Patent Application No. DE102013213520.3 filed on Jul. 10, 2013, the entirety of which is incorporated by reference herein.
This invention relates to a device and a method for discharging sealing air in a turbofan engine.
An aircraft engine at least includes a compressor, a combustion chamber and at least one turbine. A compressor and a turbine are connected here to one another via a shaft. Such a shaft is mounted in a bearing chamber with bearing elements that are lubricated and cooled with oil. The oil is usually drawn from an oil tank, supplied by means of an oil conveying pump to the bearing chamber and to the bearing elements, and returned to the oil tank via an oil suction pump.
To prevent any leakage of oil out of the bearing chambers, the latter are provided with seals and additionally subjected to sealing air from the outside. This sealing air forms an excess pressure (sealing pressure) around the bearing chambers and the seals, so that a positive pressure ratio is achieved at the bearing chamber seals. This means that the air pressure outside the bearing chamber, i.e. the sealing pressure, is greater than the air pressure inside the bearing chamber (so-called chamber pressure). With this positive pressure ratio, air flows into the bearing chamber via the seals and thus prevents oil leaking from the latter. The sealing air is drawn from the compressor of the turbomachine, usually as compressor bleed air, and supplied to the bearing chamber from the outside. It cannot be avoided here that excess sealing air escapes via a seal to a certain extent, and is guided into the airflow to the core engine.
Known sealing air systems are disadvantageous in that under certain conditions, in particular during transition between different operating states of the engine, the sealing air supply to the seals of the bearing chamber can be too low, such that the sealing pressure is insufficient to obtain a positive pressure ratio at the bearing chamber seals. This can result in oil leaking from the bearing chamber. An oil leakage may also be caused by wear on the bearing chamber seals. Such an oil leakage has the effect that oil is guided into the airflow to the core engine and from there into the bleed line for supplying fresh air to the aircraft, resulting in a contamination of the cabin air that is harmful to health.
An object underlying the present invention is to provide a device and a method for discharging sealing air in a turbofan engine that prevents the contamination of cabin air even in the event of lubricating oil exiting the bearing chambers.
The solution in accordance with the invention provides a device for discharging sealing air in a turbofan engine, said device forming a discharge path for escaping sealing air which extends up to the bypass duct of the turbofan engine. The discharge path thus extends from a point at which possibly oil-contaminated sealing air escapes, up to the bypass duct of the turbofan engine. This point can for example be a sealing air seal from which sealing air is escaping.
In the event that lubricating oil exits the bearing chamber via bearing chamber seals and mixes with the sealing air, it is ensured in this way that the sealing air contaminated with lubricating oil is not passed into the primary flow duct and through the core engine of the turbofan engine, but instead into the bypass duct of the turbofan engine.
The solution in accordance with the invention thus prevents, by discharging contaminated sealing air into the bypass duct of the turbofan engine, said contaminated sealing air from entering a compressor of the core engine and being tapped from there for fresh air supply and pressure control of the aircraft cabin.
According to an embodiment of the invention, the discharge path for escaping excess sealing air extends through at least one stator wheel of the primary flow duct. This is for example a stator wheel arranged at the start of the primary flow duct to remove from the airflow the swirl previously imparted to it in an area of the fan close to the hub. To provide an air passage for the sealing air, the stator wheel has for example at least one cavity forming an appropriate air passage.
By providing a section of the discharge path in a stator wheel of the primary flow duct, the sealing air can, using already existing structures and without interacting with the air flowing in the primary flow duct, pass said primary flow duct outwards in the radial direction. Adjoining it, the discharge path is provided up to the bypass duct of the turbofan engine.
The discharge path for the sealing air is for example formed by casing and/or wall elements that together form an air passage and thereby define the discharge path. It can be provided here that the discharge path extends along cavities already present in a casing.
According to an advantageous embodiment, it is provided that the discharge path has a seal to a rotating element of the engine, for example the fan or a rotor of a medium-pressure or high-pressure compressor, so that contaminated sealing air can escape into the primary flow duct either not at all or only to an insubstantial degree. Seals of this type are for example designed as labyrinth seals or brush seals.
It can for example be provided that the discharge path has at least one seal to a fan or a rotor of the engine so that a gap is closed between a casing delimiting the discharge path in this area and the fan or rotor, via which gap sealing air might otherwise escape into the primary flow duct.
The device in accordance with the invention is generally speaking suitable for sealing any bearing chambers of a turbofan engine that have oil-lubricated bearing elements. According to an embodiment, the bearing chamber is provided with bearing elements for mounting an engine shaft, for example an engine shaft coupling a low-pressure turbine to the fan of the turbofan engine. The bearing elements for mounting the engine shaft form for example an anti-friction bearing, however any other bearings can also be used.
It is pointed out that in embodiments of the invention, the bearing chamber, which is sealed using sealing air, is arranged in front of the tapping point for the bleed air relative to the axial direction of the engine. The tapping point is located for example at the high-pressure compressor of the engine. Since the bearing chambers supplied with sealing air are located in front of such a tapping point in the axial direction, the sealing air can be discharged into an axially front area of the bypass duct.
The precise section in which the discharge path ends in the bypass duct is generally speaking immaterial. It is only important in accordance with the invention that sealing air which is possibly contaminated with lubricating oil is guided into the bypass duct of the turbofan engine. It can be provided in design variants that the discharge path in the axial direction ends in the bypass duct in front of or behind a fan stator wheel arranged in said bypass duct.
In accordance with a further design variant, the device includes an axially front and an axially rear bearing chamber area. These two bearing chamber areas can be part of a single bearing chamber or alternatively provided by two separate bearing chambers. A discharge path section starts from each of the bearing chamber areas. The two discharge path sections combine to form the discharge path that then ends in the bypass duct. In an exemplary embodiment, this combination takes place before the exhaust path extends through a stator wheel in the primary flow duct.
According to an exemplary embodiment, the bearing chamber is supplied with sealing air when a sealing air seal associated with the bearing chamber is provided. The sealing air seal, which limits the escape of sealing air from a supply path, ensures that a defined sealing pressure prevails around the bearing chamber. However, excess sealing air escapes to a certain degree via the sealing air seal, since the latter cannot prevent a certain amount of leakage. The sealing air can here be contaminated with oil that has leaked from the bearing chamber. This escaping sealing air or leakage air is discharged via the discharge path to the bypass duct.
The present invention also relates to a turbofan engine provided with a primary flow duct, a bypass duct and a device. Here, the discharge path ends in the bypass duct and is designed to guide escaping sealing air, which is possibly contaminated with lubricating oil, into the bypass duct.
According to a further aspect of the invention, the invention relates to a method for discharging sealing air in a turbofan engine, which has the following process steps:
In particular, it can be provided that oil-contaminated sealing air exiting a sealing air seal, by which a certain sealing pressure is provided around the bearing chamber, is discharged into the bypass duct via the discharge path. The discharge path extends in this case from the sealing air seal up to the bypass duct.
The present invention is described in the following in more detail with reference to the figures of the accompanying drawings, showing several exemplary embodiments.
For a better understanding of the present invention, a turbofan engine that provides for supplying a bearing chamber with sealing air but does not yet implement the solution in accordance with the invention, is explained on the basis of
The section of a turbofan engine shown in
The primary flow duct 3 passes through the core engine that includes—in the case of a two-shaft engine—a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine. In the case of a three-shaft engine, a medium-pressure compressor and a medium-pressure turbine are additionally provided.
In the section shown, a stator wheel 5 and struts 6 are arranged in the primary flow duct 3. The stator wheel 5 is used to remove from the airflow the swirl imparted to it in the area of the fan 1 close to the hub. The primary flow duct 3 is surrounded by a casing structure 8 delimiting the primary flow duct 3 radially on the outside. The primary flow duct 3 is delimited radially on the inside by appropriate ring surfaces of the rotors and stators and by adjoining limiting structures.
The bypass duct 2 of the turbofan engine is delimited by an outer casing 9 radially on the outside and by the casing structure 8 radially on the inside. A fan stator wheel 71 is here located behind the fan 1 in the bypass duct 2, and performs the function of removing the swirl imparted to the flow by the fan 1 from that flow. Additionally, struts 72 can be located in the bypass duct 2 behind the fan stator wheel 71 which are designed to support structural loads. If the fan stator wheel 71 is itself designed to support structural loads, these struts 72 can be dispensed with.
The engine furthermore includes an engine shaft 11, which in the exemplary embodiment shown is intended to couple a low-pressure turbine of the engine to the fan 1. Bearings, for example anti-friction bearings, are provided for mounting the engine shaft 1.
The bearing chamber 12 is sealed using at least one bearing chamber seal 14. It is provided here that the bearing chamber seal 14 is additionally supplied with sealing air 10. Said sealing air 10 is tapped as bleed air from a compressor of the engine, for example from the high-pressure compressor. The bleed air 10 is supplied via a supply path 13 to the bearing chamber 12. The supply path 13 is formed for example by tubes and/or ducts. The sealing air 10 presses on the bearing chamber seal 14, and thereby prevents the exit of oil. The sealing air thus provides a sealing pressure on the outside of the bearing chamber 12 which is greater than the chamber pressure inside the bearing chamber 12.
The bearing chamber seal 14 is for example a labyrinth seal, a carbon seal or a brush seal.
To ensure that a sufficient sealing pressure is applied to the bearing chamber seal 14, a sealing air seal 15 is furthermore provided that largely prevents any escape of sealing air 10 from the supply path 13, hence ensuring a sufficient sealing pressure. It can be provided here that the sealing air seal 15 is provided on the circumference of a cavity surrounding the bearing chamber 12 and the bearing chamber seal 14 radially on the outside.
It is however the case that sealing air unavoidably escapes through the sealing air seal 15, i.e. leakage air flows through the sealing air seal 15. This air is guided as shown by the arrows 16, 17, 18 and past a gap between the fan 1 and the adjoining casing into the primary flow duct 3. This leads to problems in the event that lubricating oil exits the bearing chamber 12 and the bearing chamber seal 14 and mixes with sealing air. In this case, the return of oily sealing air into the primary flow duct 3 leads to the contaminated air being bled into a compressor of the core engine for supplying fresh air to the aircraft, possibly resulting in a contamination of the cabin air that is harmful to health and is an odour problem.
Reasons for the exit of lubricating oil can be wear on the bearing chamber seal 14 and/or certain operating states of the engine, in which the sealing air supply at the seal 14 of the bearing chamber 12 is too low to ensure a positive pressure ratio at the bearing chamber seal 14.
The inventive solution to remedy the problem described is explained in the following in light of two exemplary embodiments with reference to
According to the exemplary embodiment of
The discharge path 20 extends from the sealing air seal 15 up to the bypass duct 2, so that lubricating oil escaping from the sealing air seal 15 and mixed with sealing air can be supplied via the discharge path 20 to the bypass duct 2. Additionally, the section between the bearing chamber 12 and/or the bearing chamber seal 14 and the sealing air seal 15 can here be considered as part of the discharge path.
The discharge path 20 includes three sections 21, 22, 23, provided in the hub-side casing, in the area of the stator wheel 5 and in the area of the casing structure 8. The first section 21 of the discharge path 20 is formed by casing and/or wall elements of a non-rotating hub-side supporting structure 30 which extends in the axial direction behind the fan 1. An air passage for formation of the discharge path in this section 21 is here advantageously provided as far as is possible by already existing ducts and cavities connected to one another. To prevent sealing air from exiting at the transition between the rotating fan 1 and the supporting structure 30 and possibly entering the primary flow duct 3, a seal 24 is provided in this area, which can for example be a labyrinth seal. The proportion 25 of sealing air still leaving this seal 24 is so small as to be unproblematic.
The second section 22 of the discharge path 20 is provided by means of the stator wheel 5 arranged in the primary flow duct 3. In this connection, it is for example provided that the stator wheel 5 is designed hollow, thereby providing an air passage for the sealing air. In the area of the stator wheel 5, the sealing air possibly contaminated with lubricating oil passes the primary flow duct 3 without coming into contact with the air flowing in the primary flow duct 3.
The third section 23 of the discharge path 20 is provided in the casing structure 8, which extends in the radial direction between the primary flow duct 3 and the bypass duct 2 starting from the splitter 4. To do so, appropriate ducts and interconnected cavities are provided in the casing structure 8 by suitable casing and wall elements.
The discharge path 20 ends in the bypass duct 2, more precisely speaking in the area of the radially inner boundary surface of the bypass duct 2. In the exemplary embodiment shown, the discharge path 20 is designed such that it ends in the axial direction behind the fan stator wheel 71 in the bypass duct 2. This must however only be understood as an example. It can also be provided that the discharge path ends in front of the fan stator wheel 71 or at any other point in the bypass duct.
Like the bearing chamber 12, the bearing chamber 32 too has a bearing chamber seal 34 which is supplied with sealing air 10. To do so, the supply path for the sealing air 10 splits into two supply path sections 13, 13A which lead on the one hand to the bearing chamber 12 and on the other hand to the bearing chamber 32. The course as shown of the supply path sections 13, 13A must be understood only as an example here.
The second bearing chamber 32 is furthermore assigned a sealing air seal 35 which provides a sufficient sealing pressure around the bearing chamber 32 corresponding to the sealing air seal 15 of the supply path section 13.
As explained with reference to
Further discharge of the sealing air via the sections 22 and 23 of the discharge path 20 is as explained with reference to
It is pointed out that the discharge path section 26 too, at the transition to the rotor 40 of the medium-pressure or high-pressure compressor 40, forms a seal 27, with the remaining sealing air 28 exiting via the seal 27 being negligible. The seal 25 to the rotating fan 1 and the seal 27 to the rotating rotor 40 thus largely prevent any exit of sealing air from the discharge paths 21, 26 and ensure that the sealing air, possibly contaminated with lubricating oil, exiting the sealing air seals 15, 35 is passed via the discharge paths 21, 26, 22, 23 into the bypass duct 2. Hence the substantial proportion of the sealing air contaminated with lubricating oil is not passed into the airflow for the core engine, but into the bypass duct 2.
The present invention, in its design, is not restricted to the exemplary embodiments presented above, which are only to be understood as examples. It is thus possible in alternative embodiments to design the course and the structural embodiment of the discharge path 20 for sealing air in a different way. Also, the primary flow duct 3 and the secondary flow duct 2 can differ in their shape and in respect of the elements arranged inside them from the exemplary embodiments as described. Furthermore, the bearing chamber having oil-lubricated bearing elements for mounting a mechanical component of the turbofan engine can be a bearing chamber for mounting a different rotating part of the engine, instead of a bearing chamber for an engine shaft.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 213 520.3 | Jul 2013 | DE | national |
