Turbomachine comprising a trap for foreign objects circulating in an air flow

A turbomachine of the «open rotor» type or a turboprop engine comprises a nacelle defining an air inlet, a central hub and an annular air intake section surrounding the central hub and opening into a air supply main section, with the central hub comprising a central trap having an aperture for trapping the foreign objects in an air flow entering the turbomachine, and an air recovery channel having a discharge end, through which said air recovery channel opens into the main section, is provided on the central hub.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of International Application No. PCT/FR2016/053104, filed on Nov. 25, 2016, which claims the benefit of French Patent Application No. 1561517, Nov. 27, 2015, the contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a turbomachine of the «open rotor» type or a turboprop engine and more specifically a trap for foreign objects for such a turbomachine.

BACKGROUND

Turbomachines, and specifically turbomachines for aircrafts include an air main circuit which makes it possible to guide air, captured by an air inlet, through a gas generator, so as to generate the thrust required for the movement of the aircraft.

Air entering the turbomachines may contain foreign objects, also called FODs («Foreign Object Damage»), i.e. objects which may damage internal elements of the turbomachine.

Among such objects, sand, small size birds, or water, which quickly turns into ice, at a high altitude, can be mentioned.

To prevent such risks, limiting the number of FODs entering the gas generator, or at least reducing the speed thereof, and thus the shock loads thereof when FODs hit internal elements of the turbomachine, is necessary.

For this purpose, the international patent application WO 2011/045373 in the name of the Applicant, disclosed, as shown inFIG. 1, a turbomachine10comprising a nacelle12which defines an air intake14, a central hub16and an annular air intake section18surrounding the central hub16, and opening into an air supply main section20of a gas generator (not shown). Furthermore, such machine comprises a FOD ejection channel22which rejects the FODs out of the nacelle12, with such ejection channel22being connected to the air intake section18in way of the junction between the air intake section18and the air supply main section20. This figure shows an axis of symmetry DD of the turbomachine10, with such axis coinciding with the air flowing direction, i.e. from the upstream portion, or air inlet14, to the downstream portion of the turbomachine10.

Although such machine makes it possible to eject the FODs out of the nacelle, it sustains an important ingestion of FODs in the air supply main section20and thus remains perfectible.

As a matter of fact, too high an ingestion of FODs in the section20may, in the long term, make the machine dangerous, or even useless.

Besides, in order to evacuate the FODs out of the turbomachine10, it is typically necessary to create an annular duct going through the nacelle of the turbomachine10and opening to the outside of the nacelle10. As the nacelle plays a significant structural role for the turbomachine10, the structure of the turbomachine10has to be reinforced at the expense of the weight, and also and above all, at the expense of the architectural simplicity of the turbomachine10.

Document U.S. Pat. No. 3,368,332 discloses a turbomachine comprising a nacelle defining an air inlet, a central hub provided with a FOD trap and an annular air intake section surrounding the central hub and opening into an air supply main section of a gas generator. The trap comprises a tubular air recovery channel which goes through the annular air intake section to reach the nacelle, wherein a filter is accommodated, and then opens into the air supply main section, from the nacelle.

The air recovery channel thus generates interferences in the flow of air circulating in the annular air intake section. Such interferences may for instance create a circumferential unbalance of the air flow in the air section.

The air recovery channel being gone through by the air section creates an obstacle which may require modifying and specifically reducing the section of the air recovery channel. Fairing can further be required.

SUMMARY

One specific aim of the invention is to bring a simple, efficient and cost-saving solution to such technical problems, including a simplified architecture of the turbomachine.

For this purpose, it provides for a turbomachine for an aircraft, said turbomachine comprising at least one unenclosed propeller and comprising a nacelle defining an air inlet, a central hub positioned downstream of the air inlet and an air intake section surrounding the central hub and opening into an air supply main section, with the hub comprising a central trap having an aperture for trapping foreign objects contained in an air flow entering the turbomachine, and the air intake section being totally annular about the aperture of the central trap, with the central trap comprising an annular air recovery channel or at least a tubular air recovery channel, with said air recovery channel including a filter for filtering the foreign objects in the recovered air, characterized in that one discharge end of said air recovery channel, through which said air recovery channel opens into the main section, provided on the central hub.

Recovered air can thus be reinjected into the air flow which may supply said gas generator so as to limit the efficiency loss of the turbomachine without said recovery creating any interference in said air flow with a channel going through the section.

In the case of an annular air recovery channel, a better air flow will be guaranteed. Pressure distortions in the air supply main section of said gas generator will thus be avoided.

Such trap makes it possible to separate the FODs from the air flow which can actually be used by the turbomachine, so that it is not damaged by the FODs. The air flow is directed into the annular air intake section and the FODs are directed to the trap, because of their inertia.

According to the invention, the air inlet has an inner diameter having a first extremum, the hub has an outer diameter having a second extremum and the main section has an outer diameter having a third extremum. Such diameters are so selected that the second extremum is out of the parallelogram formed by the first extremum, the third extremum and an axis of symmetry of the turbomachine, in a plane radial to the axis of symmetry.

Then, when the FODs enter the annular air intake section, they will thus bounce against the walls of the annular section, i.e. against the nacelle and the central hub so that they lose speed and energy, before entering the air supply main section, and are thus less dangerous for the internal elements of the turbomachine.

The trap may include an accommodation wherein the foreign objects are retained. Foreign objects can thus be recovered through the front of the nacelle, and neither the air section nor the structure of the nacelle are impacted.

The trap may include two tubular air recovery channels, each one including one said filter. The two tubular air recovery channels are advantageously mutually diametrically opposed. The pressure circumferential distortion at the gas generator inlet will thus be limited.

The filter of the air recovery channel is positioned at the air recovery channel inlet, substantially as an extension of an inner bottom wall of the trap, so as to filter the air circulating from the trap to the air supply main section.

DETAILED DESCRIPTION

FIG. 2shows the upstream portion AM, according to the invention, of a turbomachine24for an aircraft. Such turbomachine24comprises, in the downstream portion AV thereof, which is common with the prior art, and shown inFIG. 1, at least one unenclosed propeller14a,and here two such propellers14a.Such turbomachine24also comprises a nacelle26defining one air inlet28, a central hub30and an annular air intake section32surrounding the central hub30and opening into an air supply main section34which supplies a gas generator (not shown).

As can be seen inFIG. 2, the central hub30is provided with a trap36, here a recess forming an aperture38in the central hub30, which can retain foreign objects or FODs.

Such FODs may damage the turbomachine24when they impact, at full speed, internal elements such as the compressor blades, for instance.

InFIG. 2, the path followed by FODs is shown by the central arrow40and the path followed by air to supply the gas generator is shown by the external arrows42.

However, some FODs which travel along a not rectilinear path or along a specific angle can directly enter the annular air intake section32.

To remedy such possible event, and prevent FODs from having too high a speed upon their impacting the mobile or fragile elements, FODs must rebound, so as to be slowed down.

For this purpose, the air inlet28has an inner diameter d1having a first extremum A, the central hub30has an outer diameter d2having a second extremum B and the main section34has an outer diameter d3having a third extremum C.

The respective diameters d1, d2, d3of the air inlet28, the central hub30and the main section34are advantageously so selected that the second extremum B is out of the parallelogram formed by the first extremum A, the third extremum C and an axis DD of symmetry of the turbomachine24, in a plane radial to the axis DD, as shown inFIG. 2. Advantageously, the radial plane is a vertical plane when the machine24is mounted on an aircraft.

The FODs which will directly enter the annular air intake section32will thus bounce at least against the walls of said section32, then against the central hub30or reversely, first against the central hub30and then against the section32, with such rebounds resulting in the FODs being slowed down and losing energy, which makes same less dangerous for the internal elements of the turbomachine24.

FODs rebounds are shown inFIG. 3by broken lines. Such paths are shown as examples and do not aim at limiting the possible paths of FODs. Similarly, some FODs may bounce several times against the annular air intake section32and against the central hub30, as shown inFIG. 3.

FIG. 3shows a first alternative embodiment (also illustrated byFIGS. 2 and 4) of the trap36of the turbomachine24.

The trap36comprises a closed inner bottom wall44which forms an accommodation46. FODs are then caught in said accommodation46when the turbomachine24is operating. A maintenance technician can then empty the trapped FODs from the accommodation46, using some tools, at regular intervals or upon each stoppage of the turbomachine24.

As shown inFIG. 4, the inner bottom wall44is provided with at least one aperture forming at least one tubular air recovery channel48through which a part of the air flowing together with the FODs in the trap36can be reused and injected into the air supply main section34. The tubular air recovery channel48has a discharge end48awhich is positioned on the central hub30and through which the tubular air recovery channel48opens into the main section34. The inner bottom wall44comprises at least one filter50, preferably a mesh or a sieve, which makes it possible to retain the FODs in the accommodation46and to let air through, from the trap36to the air supply main section34.

The discharge end48aprovided on the central hub30makes it possible to simplify the architecture of the turbomachine24since no duct is required through the section34and the nacelle26for the disposal of FODs. The air flow in the main section34is thus no longer affected since there is no through duct.

According to a second embodiment shown inFIGS. 5 and 7, the inner bottom wall44is provided with two apertures forming two tubular air recovery channels48. Of course, the tubular air recovery channel48has a discharge end48awhich is positioned on the central hub30and through which the tubular air recovery channel48opens into the main section34. The two tubular air recovery channels48are mutually diametrically opposed so as to limit the pressure circumferential distortion generated by the partial recovery of the trapped air and the reinjection thereof into the air supply main section34, with such distortion being particularly significant when the turbomachine24is provided with one single tubular air recovery channel48. The inner bottom wall44further comprises, for each tubular air recovery channel48, one filter50, preferably a mesh or a sieve, which makes it possible to retain the FODs in the accommodation46and to let air through, from the trap46to the air supply main section34. The inner bottom wall44can include a larger number of tubular air recovery channels48, preferably an even number thereof, so as to limit the pressure circumferential distortion.

As disclosed above, a maintenance technician can empty the trapped FODs from the accommodation46and clean the filter50of the stuck FODs, using some tools, at regular intervals or upon each stoppage of the turbomachine24.

According to another alternative embodiment shown inFIG. 6, the inner bottom wall44is provided with an annular aperture forming one annular air recovery channel48′ through which a part of the air flowing together with the FODs in the trap36can be reused and injected into the air supply main section34. The annular air recovery channel48′ thus has a discharge end (here an annular one48a′) which is positioned on the central hub30and through which the annular air recovery channel48′ opens into the main section34.

The inner bottom wall44further comprises at least one annular filter50′, preferably a mesh or a sieve, which makes it possible to retain the FODs in the accommodation46and to let air through, from the trap36to the air supply main section34.

Each filter50,50′ is advantageously positioned at the air recovery channel48,48′ inlet, substantially as an extension of an inner bottom wall44.

The turbomachine24for aircrafts which has just been disclosed has numerous advantages, among which:increased service life of the turbomachine24as well as reduced frequency of maintenance of the internal elements of the turbomachine24;increased efficiency of the turbomachine24;reduced mass and overall dimensions of the air inlet28, andsimplified architecture of the turbomachine24.

The increased service life of the turbomachine24is provided by adding the trap36to the central hub30. As a matter of fact, most FODs are caught in the trap36of the central hub30. The amount of FODs which can directly enter the annular air intake section32loses energy and speed when bouncing, which results in limiting the damage impacts on the internal elements of the turbomachine24.

This is the reason why maintenance can be reduced, since the internal elements are less damaged. This results in savings in the operation of the turbomachine24.

The efficiency of the turbomachine24is increased by the at least partial recovery of the air trapped with the FODs. The thus recovered air can then be reinjected into the air supply main section34to supply the gas generator with a higher air flow rate.

The reduced mass of the turbomachine24is obtained by using a portion of the central hub30which was not used in the prior art. A smaller quantity of material is thus required for manufacturing the central hub30, while providing the central hub30with a correct rigidity.

Such gain in mass further makes it possible to reduce the fuel consumption of the turbomachine24and thus to limit the impact on the environment of the turbomachine24, specifically as regards the emission into the atmosphere of polluting particles.

Eventually, the simplified architecture of the turbomachine24results from the absence of external channels through the nacelle26for the disposal of FODs. These channels thus reduce the mechanical strength of the nacelle26and increase the complexity of the design to provide a good rigidity of the nacelle26while limiting the increase in the mass of the turbomachine24.