FR3040439A1 - DOUBLE FLOW TURBOREACTOR WITH CONFLUENCE WALL - Google Patents

Abstract

A turbofan engine (1) comprising a low-pressure compressor (3) capable of taking a stream of air intended to be divided into a distinct primary air flow (F1) and a secondary air flow (F2), a primary channel (10) capable of conveying the primary air flow (F1) from the low pressure compressor (3) to a confluence zone (12) of the primary and secondary air flows (F1 and F2) allowing the dilution of the secondary air flow (F2) in the primary air flow (Fi), a secondary channel (11) capable of conveying the secondary air flow from the low pressure compressor (3) to the zone confluence (12). The turbojet engine (1) comprises an annular confluence wall (13) pierced with a plurality of through orifices (14).

Description

BACKGROUND OF THE INVENTION The invention relates to double-flow turbojet engines, in particular for aircraft, and more particularly to the dilution of primary air with secondary air in a confluence.

In "turbojet" type turbofan engines, the flow of air sucked by the low pressure compressor is divided into two parts. A first part, the primary flow or hot flow through a gas generator comprising a high-pressure compressor, a combustion chamber and a high pressure turbine, then a low pressure turbine. A second part, the secondary flow or cold flow, flows at the periphery of the turbojet engine and is used in particular for the cooling of certain organs. The secondary flow, formed of the air precompressed by the low pressure compressor which does not pass through the gas generator, flows around the gas generator to a confluence zone in which the primary flow and the secondary flow are mixed. after combustion of the primary flow air.

The proportion of air constituting the cold flow which is variable according to the engines is expressed by the ratio between the mass flow rate of the secondary flow and the mass flow rate of the primary flow. This report is called the "By-Pass Ratio" and is called BPR.

Military engines optimized for supersonic flight generally have dilution rates of less than 1, while civil or military engines optimized for cruises around Mach 0.8 generally have dilution ratios between 5 and 10. Double engines flow and high dilution rate, in English "turbofans", derive most of their thrust from the cold flow, the hot flow representing 20% of the thrust, and are close to the turboprop engines.

In a turbojet engine with a non-ducted fan, or Open rotor in English, which is a turbojet engine whose fan is fixed directly on the power turbine and outside the nacelle, the turbine may also comprise a primary stream delivering a flow primary hot and a secondary vein carrying a cold secondary flow for cooling some organs around the gas generator. The primary flow and the secondary flow are intended to be mixed between the outlet of the primary stream and the inlet of a power turbine mounted downstream of the gas generator. Whatever the type of turbojet having a double flow on one of the stages, the confluence zone is generally located at the junction of the exits of the primary channel and the secondary channel, before the exit of the gasses of the nacelle, just as well. before the output of the nacelle upstream of a turbine, for example a power turbine, mounted upstream of the outlet of the gasses of the nacelle. From an aerodynamic point of view, in a turbojet engine with an unducted fan, the confluence is intended to mix the primary and secondary flows to provide acceptable flow to the power turbine.

In an unducted fan turbojet engine, there is little point in feeding the power turbine with a large low pressure flow. This is why a "turbojet" type architecture is used upstream of the power turbine, rather than a "turbofan" type architecture. The arrangement and the dimensions of the secondary vein and the primary vein are such that the dimensions of the secondary vein are smaller than in turbofan-type turbofan turbofan engines.

In addition, in a non-ducted fan turbojet engine, the desired dilution rate in the confluence zone is very low for the sizing points of the thermodynamic cycle of a non-ducted fan. Indeed, at the output of the gas generator of a non-ducted fan, one operates generally at very low dilution rates, of the order of 0.23 to 0.25.

However, in all turbofan engines, the dilution ratio is set by the desired performance for the engine. It depends on the chosen cycle and varies according to the altitude, the Mach number and the engine speed. The proper sizing of the confluence is therefore important in turbofan engines because the confluence makes it possible to regulate the secondary and primary flows and thus the dilution ratio.

In jet engines having small dimensions for the secondary channel, or secondary vein, and a low dilution ratio, such as for example at the output of the gas generator in the form of a "turbojet" of turbojet turbofan engines not ducted, it It is very difficult to set up a specifically calibrated confluence, robust to manufacturing tolerances and having good resistance to the different thermomechanical conditions that this zone may experience when the turbojet engine is running.

The geometric section of the confluence is difficult to master. Firstly, because of manufacturing tolerances of the primary vein casing, also called confluence sheet, and the casing including the confluence sheet and forming with it the secondary vein. Secondly, due to the differential thermal expansion between the very hot primary stream and the colder secondary stream. And, thirdly, because of displacements at the trailing edge of the confluence which follows the movements in operation of the entire high pressure body while the casing follows those of the low pressure structure.

OBJECT AND SUMMARY OF THE INVENTION The aim of the invention is to propose a turbofan engine whose mixture of primary and secondary flows takes place before the exit of the nacelle and which has a robust confluence with manufacturing tolerances and makes it possible to accurately calibrate the engine. dilution rate especially for low dilution rates and small secondary vein dimensions. The subject of the invention is a turbofan engine comprising a low-pressure compressor capable of taking off a stream of air intended to be divided into a distinct primary air stream and a secondary air stream, a primary channel capable of conveying the primary air flow from the low pressure compressor to a confluence zone of the primary and secondary air flows allowing dilution of the secondary air flow in the first primary air flow at the outlet of the primary channel, and a secondary channel capable of conveying the secondary air flow from the low pressure compressor to the confluence zone at the outlet of the secondary channel.

According to a general characteristic of the invention, the turbojet engine comprises an annular confluence wall pierced with a plurality of through orifices.

The annular confluence wall is arranged, as indicated, in the confluence zone, and more particularly at the inlet of the confluence zone, so as to control, upon entry into the confluence zone, the flow rate of the secondary flow injected into the primary flow and thus control the dilution ratio of the mixture.

The through orifices provided in the confluence wall are configured to allow an air portion of the secondary flow delivered by the secondary channel to escape through the confluence wall into the confluence zone. The orifices make it possible to better control the flow rate of the secondary flow delivered by the secondary channel, and consequently the rate of dilution of the gas generator, whatever the thermal conditions of the medium. The through orifices have a diameter of the order of a few millimeters to a few tens of millimeters, the diameter varying as a function of the turbomachine and the number of orifices.

The thermal and mechanical expansion of the through-orifices provided in the wall is less important than the expansion undergone by the primary channel or a confluence device extending between the primary channel and the secondary channel, such as for example a confluence nozzle which is used in the state of the art. Indeed, the temperatures of the outer casing and the inner casing are clearly different from the difference between the temperatures of the primary and secondary flows. As a result, the expansion differential between the primary channel and the secondary channel can be significant, thus resulting in a significant variation in the mouth of the secondary canal, that is to say the confluence nozzle, and therefore the rate of resulting dilution.

According to a first aspect of the turbojet, the end of the secondary channel opening onto the confluence zone is at least partially closed by said confluence wall. The closure of the secondary channel by the confluence wall extending between an inner ferrule delimiting the primary channel and an outer ferrule delimiting with the inner ferrule the secondary channel makes it possible to limit leaks and to control the flow rate of the secondary flow, in particular by virtue of the size and number of through-holes provided in the confluence wall. The closure of the secondary canal by the confluence wall makes it possible to dispose the confluence wall exactly at the interface between the outlet of the secondary channel and the entrance of the confluence zone, and thus to optimize the control of the dilution ratio .

According to a second aspect of the turbojet, the orifices of the confluence wall are distributed over at least two circles of the same axis of rotation and of different radii. The axis of rotation of the circles preferably corresponds, in the case of a non-ducted fan or a turboprop, to the axis of rotation of the power turbine and therefore to the axis of revolution of the inner shell forming the primary channel and the axis of revolution of the outer shell forming with the inner ferrule the secondary channel.

The distribution of the orifices passing through a plurality of different circles provides a first possibility of optimizing the temperature profile in the confluence zone. Indeed, the trajectories of the different flows delivered by each of the through orifices will penetrate the primary flow at different locations of the latter, and, depending on the circles on which the through holes from which they emanate, at different distances from the exit of the channel primary in the direction of the axis of rotation of the turbine. These different paths thus make it possible to distribute the secondary cold flow over a wide spatial range and thus to optimize the mixing and to improve the homogeneity of the mixed air flow obtained.

According to a third aspect of the turbojet engine, the orifices of the confluence wall distributed on the same circle are equidistributed in the azimuthal direction on the annular wall, that is to say distributed at equidistant angle on the same circumference. The equidirectional distribution of orifices passing through the same circle offers a second possibility of optimizing the temperature profile in the confluence zone, in particular making it possible to homogenize and accelerate the mixing of the two flows. The orifices arranged on the same circumference are separated from the two adjacent orifices of the same angular distance with respect to the center of the circle.

According to a fourth aspect of the turbojet, it comprises at least one through orifice having a first diameter and at least one second through orifice having a second diameter different from the first diameter.

The variation in the dimensions of the through orifices offers a third possibility of optimizing the temperature profile in the confluence zone. This configuration makes it possible to create an inhomogeneous flow at the outlet of the confluence wall by favoring certain parts of the confluence zone for mixing.

According to a fifth aspect of the turbojet, it comprises a first ferrule adapted to form said primary channel and a second ferrule extending around the first ferrule and adapted to form with the first ferrule said secondary channel, the annular wall of confluence projecting from the end of the first ferrule opening on the confluence zone and toward the second ferrule.

The confluence wall is thus integral at one of its ends with the first ferrule and free at its opposite end opposite the second ferrule. The confluence wall can thus be deformed with the first shell and prevent any leakage between the first shell and the confluence wall.

According to a sixth aspect of the turbojet engine, the latter comprises a movable seal, for example a flap seal, disposed on the free end of the annular confluence wall and configured to form a tight junction between the annular confluence wall and the second ferrule.

The mobile joint makes it possible to reduce or even eliminate parallel leakage of secondary flow, in particular between the confluence wall and the second ferrule, and thus to improve control of the dilution ratio.

The movable seal may be sectored slats distributed over the entire circumference of the annular confluence wall.

According to a seventh aspect of the turbojet, the latter comprises a gas generating part comprising a high pressure compressor, a combustion chamber and a high pressure turbine mounted in the primary channel downstream of the low pressure compressor, and a separate power turbine. the gas generating portion by said confluence zone which allows dilution of the secondary air flow in the primary air flow upstream of the power turbine.

According to an eighth aspect of the turbojet engine, it comprises an external rotor blade. The invention also relates to an aircraft comprising at least one turbojet engine as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood on reading the following, by way of indication but not limitation, with reference to the accompanying drawings, in which: FIGS. 1a and 1b show schematically two structural examples of a turbojet according to FIG. invention; - Figure 2 is a schematic sectional view of a portion of a turbojet according to the invention; and FIG. 3 shows a partial perspective view of the confluence zone of the turbojet engine of FIG. 1.

Detailed description of embodiments

FIGS. 1a and 1b show very schematically two structural examples of a turbojet engine 1 according to the invention.

In the example illustrated in FIG. 1a, the turbojet engine 1 comprises an outer shell 2 extending along an axis of rotation X and forming a casing inside which are mounted a low pressure compressor 3, an HP compressor 42, a low-pressure turbine 5 mechanically coupled to the low-pressure compressor 3, and a power turbine 6 mechanically coupled to an external non-faired fan 7 which extends partially out of the outer shell 2.

The turbojet engine 1 further comprises an inner shell 8 inserted in the outer shell 2 along the same axis of rotation X and extending over a portion of the length of the outer shell 2 so as to comprise the gas generator 4 and the turbine low pressure 5.

The gas generator 4 comprises a high-pressure compressor 42, a combustion chamber 44 and a high-pressure turbine 36 mechanically coupled to the high-pressure compressor 42.

The turbojet engine 1 further comprises a central shell 9 not shown in Figures la to but visible in Figure 2, inserted along the same axis of rotation X in the inner shell 8 and extending over the entire length of the outer shell 2.

The three rings 2, 8 and 9 thus form a primary vein 10, or primary channel, and a secondary vein 11, or secondary channel. The primary vein 10 extends between the central ferrule 9 and the inner ferrule 8, and the secondary vein 11 extends between the inner ferrule 8 and the outer ferrule 2.

Thus the flow of air F, sucked by the low pressure compressor 3 is divided into a primary flow Fi through the primary vein 10 and a secondary flow F2 through the secondary vein 11, to a confluence zone 12 in which the flow primary Fi and the secondary flow F2 are mixed to form an optimal air flow F at the input of the power turbine 6.

In the example illustrated in FIG. 1b, the turbojet engine 1 differs from the example illustrated in FIG. 1a in that it does not have a low-pressure turbine, and in that the low-pressure compressor 3, the power turbine 6 and non-faired external fan 7 are mechanically coupled together by the same shaft for example.

FIG. 2 shows a sectional view of a portion of a turbojet engine 1 according to the invention having a structure corresponding to that in FIG.

The view presented in FIG. 2 is centered on the confluence zone 12 of the turbojet engine 1, so that the primary and secondary veins 10 and 11 are partially represented, their respective end facing the low-pressure compressor 3, the low-pressure compressor 3 and the gas generator 4 not being illustrated.

The primary vein 10 extends, in an axial direction, between a first end of the primary vein 10 arranged facing the low-pressure compressor 3 and formed by a first end of the inner shell 8, and a second end 102 of the vein primary 10, opposite to the first end of the primary vein 10, and formed by the second end 82, free, of the inner shell 8.

The secondary vein 11 extends in an axial direction between the outer surface of the wall of the inner ferrule 8 and the inner surface of the outer ferrule 2. The secondary vein 11 extends, in a radial direction, between a first end secondary vein 11 arranged facing the low-pressure compressor 3 and a second end 112 of the secondary vein 11, opposite the first end of the secondary vein 11, and formed by the second end 82 of the inner shell 8 and the part 22 of the outer shell 2 opposite the second end 82 of the inner shell 8, that is to say coplanar with the second end 82 of the inner shell 8.

Throughout the text, the terms "internal" and "external" are used with reference to the position or orientation relative to the axis of rotation X of the primary vein 10.

Throughout the text, the terms "upstream" and "downstream" are used with reference to the flow direction of gas flow indicated by the arrows in Figures 1 and 2.

The primary vein 10 and the secondary vein 11 thus both open, via their respective second end 102 and 112, to the confluence zone 12 in which the secondary gas stream F2 mixes with the primary gas stream Fi in order to increase the quantity of gas. heated gas and thus increase the thrust factor upstream of the power turbine 6. At the second end 112 of the secondary vein 11 facing the confluence zone 12, the secondary vein 11 is closed by a confluence wall 13 pierced through orifices 14, configured in the form of circular holes passing the gas of the secondary flow F2.

As is illustrated in Figure 3 which shows a partial perspective view of the confluence zone 12 of the turbojet engine 1, the confluence wall 13 has an annular shape so as to close the secondary channel 11 over its entire surface.

The confluence wall 13 comprises a first circular end 131 and a second circular end 132 opposite the first circular end 131. The first circular end 131 of the confluence wall 13 is integral with the second end 82 of the inner shell 8 opening on the confluence zone 12. The confluence wall 13 extends in projecting internal shell 8, in a plane substantially orthogonal to the cylindrical surface of the inner shell 8, in the direction of the part 22 of the outer shell 2 forming, with the second end 82 of the inner ferrule 8, the second end 112 of the secondary vein 11.

The second circular end 132 of the confluence wall 13 which is arranged facing the outer shell 2, and more particularly opposite the part 22 forming the second end 112 of the secondary stream 11, comprises a seam seal 15. The joined with lamellae 15 makes it possible to form a tight junction between the confluence wall 13 and the outer shell 2 at the level of the part 22 and thus to ensure that the secondary flow F2 admitted into the confluence zone 12 is delivered only through the orifices through 14 of the confluence wall 13. This allows to better control the dilution rate of the confluence.

As illustrated in FIG. 3, the orifices 14 of the confluence wall 13 are distributed, in this embodiment, on two distinct circles and uniformly on each of the two circles, that is to say that on the same circle the distance separating two adjacent holes 14 is always the same. In other words, the arc between two adjacent orifices 14 is always the same throughout the circle.

The holes 14 may be provided with different diameters depending on the desired configuration, or with a non-uniform distribution.

The turbojet turbine according to the invention thus has a robust confluence with manufacturing tolerances and makes it possible to precisely calibrate the dilution ratio, in particular for low dilution rates and low secondary vein dimensions.

Claims (10)

1. A turbofan engine (1) comprising a low-pressure compressor (3) able to take a stream of air intended to be divided into a distinct primary air flow (Fi) and a secondary air flow (F2). a primary channel (10) capable of conveying the primary air flow (Fi) from the low pressure compressor (3) to a confluence zone (12) of the primary and secondary air streams (Fi and F2) allowing the dilution of the secondary air flow (F2) in the primary air flow (Fi), and a secondary channel (11) capable of conveying the secondary air flow (F2) from the low pressure compressor (3) to the confluence zone (12), characterized in that it comprises an annular wall of confluence (13) pierced with a plurality of through orifices (14). 2. Turbojet engine (1) according to claim 1, wherein the end of the secondary channel (112) opening on the confluence zone (12) is at least partially closed by said confluence wall (13). 3. turbojet engine (1) according to one of claims 1 or 2, wherein the orifices (14) of the confluence wall (13) are distributed over at least two circles of the same axis of rotation (X) and different radii . 4. Turbojet engine (1) according to one of claims 1 to 3, wherein the orifices (14) of the confluence wall (13) distributed on the same circle are equidistributed in the azimuthal direction on the annular wall of confluence (13). ). 5. Turbojet engine (1) according to one of claims 1 to 4, comprising at least one through hole (14) having a first diameter and at least a second through hole having a second diameter different from the first diameter. 6. turbojet engine (1) according to one of claims 1 to 5, comprising a first ferrule (8) adapted to form said primary channel (10) and a second ferrule (2) extending around the first ferrule (8). and adapted to form with said first ferrule (8) said secondary channel (11), the annular confluence wall (13) projecting from the end of the first ferrule (8) opening onto the confluence zone (12). ) and towards the second ferrule (2). 7. Turbeactor (1) according to claim 6, comprising a movable seal (15) disposed on the free end (132) of the annular confluence wall (13) and configured to make a tight junction between the annular wall of confluence ( 13) and the second ferrule (2). 8. Turbojet engine (1) according to one of claims 1 to 7, comprising a gas generating portion (4) comprising a high pressure compressor (42), a combustion chamber (44) and a high pressure turbine (46) mounted in the primary channel (10) downstream of the low pressure compressor (3), and a power turbine (6) separated from the gas generating part (3) by said confluence zone (12) which allows the dilution of the flow of secondary air (F2) in the primary air flow (Fi) upstream of the power turbine (6). 9. Turbojet engine (1) according to one of claims 1 to 8, comprising an outer rotor blade (7). 10. Aircraft comprising at least one turbojet engine (1) according to one of claims 1 to 9.