WO2014132001A1

WO2014132001A1 - Reduction of convective exchanges between the air and the rotor in a turbine

Info

Publication number: WO2014132001A1
Application number: PCT/FR2014/050432
Authority: WO
Inventors: Julien RENAUD; Carine BLOT; Franck Denece; Christelle JUBERT; Thierry Lequitte
Original assignee: Snecma
Priority date: 2013-02-28
Filing date: 2014-02-27
Publication date: 2014-09-04
Also published as: FR3002586A1; FR3002586B1

Abstract

The invention relates to a turbine, in particular a low-pressure turbine, comprising at least one stator (2) and a rotor (3), the stator (2) comprising a plurality of fixed vanes (24) extending radially with respect to a rotation axis (X) of the turbine (7) from an annular internal platform (21), the turbine (7) being characterized in that the stator (2) also comprises air slowing means (16) that are designed to reduce the relative speed of rotation of the air with respect to the rotor in a region adjacent to the annular internal platform (21).

Description

REDUCTION OF CONVECTIVE EXCHANGES BETWEEN AIR AND ROTOR IN A TURBINE

FIELD OF THE INVENTION

The invention relates generally to gas turbine engines, and more particularly to the reduction of convective exchanges in a turbine, for example a low-pressure turbine of a turbomachine. Fields of application of the invention are aircraft turbojet and turboprop engines and industrial gas turbines.

BACKGROUND

An example of a turbomachine has been illustrated in FIG.

A turbomachine 1 typically comprises a nacelle which forms an opening for the admission of a given flow of air to the engine itself. Generally, the turbomachine comprises one or more compression sections 4 of the air admitted into the engine (generally a low pressure section and a high pressure section). The air thus compressed is admitted into the combustion chamber 5 and mixed with fuel before being burned.

The hot combustion gases from this combustion are then expanded in different turbine stages. A first expansion is made in a high pressure stage 6 immediately downstream of the combustion chamber 5 and which receives the gases at the highest temperature. The gases are expanded again by being guided through so-called low pressure turbine stages 7.

A turbine, low pressure 7 or high pressure 6, conventionally comprises one or more stages, each consisting of a row of stationary turbine blades, also called distributor, followed by a row of turbine blades, which form the rotor. Dispenser 2 deflects the flow of gas drawn from the combustion chamber 5 to the turbine blades at a suitable angle and speed to drive these rotating blades and the rotor of the turbine in rotation. The distributor 2 comprises a plurality of blades spaced circumferentially about an axis of rotation X of the turbomachine 1 (said axis X corresponding to the axis of rotation of the turbine 7), and extending radially relative to this axis X in order to connect a radially inner annular element (or inner platform) and a radially outer annular element (or outer platform). The assembly forms an annular vein opposite the moving blades of the turbine.

The rotor itself comprises several discs, for example five discs, which generally comprise peripheral grooves such as cells in which the blades are nested, or are formed in one piece with the blades, which are then machined on the periphery of the discs. The different discs can be assembled coaxially by electron beam welding, rotary friction welding, or bolting.

The rotor of the turbine is subjected to a very hot thermal environment, well above the maximum permissible temperatures by the rotor parts. Specific ventilation for the rotor discs has therefore been put in place, during which a flow of pressurized air is introduced into the rotor in order to cool its parts, in particular its discs.

However, it is found that leaks F of hot air from the vein were introduced into the rotor, and caused convective heat exchange with the rotor discs. In particular, as illustrated in the appended FIG. 4, the leakage air F coming from the vein penetrates into the rotor, immediately downstream of the mobile wheels, passes under the internal platform of the distributors to reach the adjacent mobile wheel, disposed immediately downstream.

It has therefore been proposed to reduce the leakage air flow rate F introduced into the rotor by means of labyrinth seals, formed on the one hand by a winged rotating part (or wiper), and on the other hand by a static part having a bore 14 comprising an abradable material capable of withstanding high temperatures. The wipers generally consist of continuous or segmented annular blades arranged on the rotor at level of the junction between the movable wheels, while the bore of abradable material 14 is arranged facing, on a lower face of the internal platform of the distributor.

However, it turns out that the reduction in flow rate does not sufficiently reduce the convective exchanges with the rotor, since the exchange coefficients at the rotor discs remain too large for their temperature to be sufficiently reduced. The working temperature of the rotor discs therefore remains too high in view of the materials used, which tends to reduce their service life.

Document WO 2013/001240, in the name of the Applicant, describes a low pressure turbine comprising a distributor and a rotor. The dispenser comprises a plurality of fixed blades extending radially relative to an axis of rotation of the turbine from an inner annular platform. Moreover, to improve the sealing at the cavities between the distributor and the rotor, this document proposes to add an abradable material facing the downstream rotor, to form a labyrinth seal. Nevertheless, improved sealing does not reduce the convective exchanges with the rotor.

The document EP 2 574 724 itself only describes a high-pressure compressor, and is silent concerning the thermal problems experienced by the rotor of a turbine.

Finally, the document US 201 1/158797 describes a turbine distributor comprising a plurality of fixed blades extending radially with respect to an axis of rotation of the turbine from an inner annular platform, as well as means for tangential deflection of the flow of the turbine. air to reduce the pressure drop in the reintroduction of the leakage air in the main vein. However, in this document, the flow of air that is deflected flows from the downstream to the upstream of the turbine, and is deflected and / or accelerated by tangential deflection means to be reinjected upstream in the vein . These tangential deflection means therefore have no influence on the convective exchanges between the air flow and the rotor, and especially the flanges and the flange, since the flanges and the flange are arranged upstream tangential deflection means on the path of the air flow.

SUMMARY OF THE INVENTION

An object of the invention is therefore to overcome the aforementioned problems of the prior art, and in particular to provide a turbine comprising means for reducing more effectively the heat exchange between the hot air leakage from the vein with the rotor, and in particular the rotors disks, in order to increase their service life at a moderate cost and overall weight.

For this, the invention proposes a turbine, in particular a low-pressure turbine, comprising at least one distributor and a rotor, the distributor comprising a plurality of fixed blades extending radially with respect to an axis X of rotation of the turbine from an annular platform internal, the internal platform comprising:

an annular plate forming a support for said blades, and

a radial wall extending from the annular plate towards the axis of rotation of the turbine,

the turbine being characterized in that the distributor further comprises air braking means adapted to reduce the speed of rotation of the air said braking means (16) comprising protuberances which extend from an upstream face of the radial wall (22) of the inner annular platform and thus reduce the relative speed of rotation of the air relative to the rotor.

Some optional but non-limiting characteristics of this turbine are the following:

the inner annular platform further comprises an inner ring, extending from the radial wall, and protuberances extending between the annular plate of the inner annular platform and the inner ring, the protuberances extend from the inner ring / or the annular plate of the inner annular platform,

the protuberances are formed integrally and in one piece with the inner annular platform,

the protuberances and the inner annular platform are distinct pieces,

the protuberances comprise a series of fins extending from the inner annular platform,

the inner annular platform further comprises a radial annular wall extending from the inner ring towards the annular plate, and

the braking means extend between the radial annular wall and the inner ring.

The invention also proposes a distributor for such a turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention will appear better on reading the detailed description which follows, and with reference to the appended drawings given by way of non-limiting examples and in which:

FIG. 1 represents an example of a turbomachine to which the invention applies,

FIG. 2a is a perspective view of an exemplary embodiment of a distributor sector comprising a first embodiment of means for braking the leakage air F according to the invention,

FIG. 2b is a detailed perspective view of an internal platform of a distributor sector comprising a second embodiment of braking means according to the invention,

FIG. 3 is a sectional view in detail of a first embodiment of a turbine according to an exemplary embodiment of the invention, on which is visible the path traveled by the air coming from the vein at the level of a distributor blade, FIG. 4 is a detailed view of a section of a turbine according to the prior art, on which is visible the path traveled by the leakage air F at a distributor blade, and

FIG. 5 is a sectional view in detail of a second embodiment of a turbine according to an exemplary embodiment of the invention, on which is visible the path traveled by the air coming from the vein at the level of a distributor blade.

DETAILED DESCRIPTION OF AN EMBODIMENT

The invention will be described more particularly with reference to a low pressure turbine 7, comprising a series of alternating low pressure (or stator) distributors 2 along the axis X of rotation of the turbomachine 1 with a series of moving wheels (or rotor ). This is however not limiting, since the turbine 7 could comprise a different number of stages, and that the invention is also applicable in a high-pressure turbine 6, which can be single or multi-stage.

The turbine 7 conventionally comprises one or more stages, each consisting of a distributor 2 followed by a rotor 3 (or moving wheel).

The rotor 3 comprises a plurality of discs 30, for example five discs 30, which generally comprise peripheral grooves such as cells in which the blades 32 are interlocked, or are made in one piece with the blades 32, which are then machined on the periphery of the discs 30.

The various discs 30 can in particular be assembled coaxially by bolting. Each rotor disc 30 then comprises an annular flange 34a which extends upstream from the upstream radial face of the disc 30, around which an annular flange may be mounted, sealing the passage of the cooling air. discs 30, as well as a downstream annular flange 34b which extends from the downstream radial face of the disc 30, adapted to be connected with the upstream flange 34a of the adjacent downstream disc 30. Here, upstream and downstream are defined by the flow direction of the gases in the turbomachine.

Alternatively, the disks 30 may be coaxially assembled by electron beam or rotary friction welding.

The distributor 2 as for it comprises a plurality of fixed blades 24 arranged radially with respect to the axis of rotation X of the turbomachine 1, connecting a radially inner annular platform 20 and a radially outer annular platform 20. The platforms 20 and 25 distributor 2 form the annular vein opposite the blades 32 of the turbine.

The inner platform 20 comprises a plate 21, comprising an inner surface 21a and an outer surface 21b, the outer surface 21b forming a support for the blades 24, and a radial wall 22 extending from the inner surface 21a of said plate 21 towards the X axis of the turbomachine 1. The radial wall 22 of the inner platform 20 is also associated with an inner ring 23.

The distributor 2 and the rotor 3 of each stage are spaced so as to create a clearance and allow rotation and relative expansion of the rotor 3 relative to the distributor 2, which is a function in particular of the speed variations of the turbomachine 1. This game also forms a passage, through which leakage air F from the vein can be introduced into the rotor 3.

FIG. 3 shows a sectional view in detail of the platform 20 of a distributor 2, as well as the mobile wheels 32 immediately upstream and downstream of this distributor 2.

As indicated by the arrow, the leakage air F coming from the vein entering the rotor 3 enters between the disc 30 of the upstream movable wheel 3 and the distributor 2 (point 1), at the plate 21 of the platform 20, along the radial wall 22 and bypasses the inner ring 23 (point 2) of the inner platform 20, then passes under the distributor 2 (point 3), to finally reach the disk 30 of the downstream mobile wheel 3.

Optionally, the turbine may comprise labyrinth seals, including wipers 12 and the bore 14 of abradable material described above. The wipers 12 can then extend radially from the junction of the flanges 34 upstream and downstream of the discs 30, while the bore extends facing from the inner surface of the inner ring 23. The Applicant has found that the Exchange coefficients between the leakage air F from the vein and the rotor 3 were related to their relative speed of rotation. However, downstream of the moving wheels, the rotational speed of the leakage air F is generally equal in absolute value to the speed of rotation of the moving wheels, but rotates in the opposite direction about the axis X of rotation of the turbomachine the relative speed of rotation of the leakage air F with respect to the rotor 3 is therefore very high. As a result, the drag coefficient Kc of the leakage air F with respect to the rotor 3 (i.e., the ratio of the air velocity in the flow core to the rotational speed rotor disc 30) is negative in zone 1 of FIGS. 3 and 4, for example of the order of -1. During the passage of the leakage air F in the rotor 3 (zone 3), this coefficient Ke tends to increase to become positive, which implies a reduction of the exchange coefficients between the leakage air F and the rotor 3. However, this increase is not sufficient to avoid significant convective exchange, particularly at the flange 34s and flange 36 of the rotor 3, hence the high temperature of the discs 30 of the rotor 3 and ferrules.

The invention therefore proposes to slow down the speed of rotation of the air flow at the rotor 3 (zone 2), where the coefficient of entrainment is negative, in particular in the zone situated upstream of the labyrinth 12 (ie at internal platform level 20) in order to increase the entrainment coefficient Ke of the air and bring it closer to the value of 1, with the aid of braking means 16 of the leakage air flow F in the rotor 3. In fact, by reducing the speed of the leakage air flow F with respect to the rotational speed of the rotor 3, the convective exchanges are reduced, and therefore the capacity of the leakage air F to heat the discs 30 of the rotor 3.

For this, the braking means 16 comprise protuberances which preferably extend in the path of the leakage air flow F in the rotor 3, for example between the annular plate 21 of the inner annular platform 20 and the crown. internal 23 (zone 2).

For example, the protuberances 16 may extend from the inner ring 23 of the annular platform 20 and / or from an upstream face 22a of the radial wall 22 of the annular platform 20. Alternatively, the protrusions 16 may also extend from the plate 21, and possibly from an upstream face 22a of the radial wall 22 of the annular platform 20. The protuberances 16 may thus be formed integrally and in one piece with the platform internal 20, and more particularly the inner ring 23, the plate 21 and / or the radial wall 22, or alternatively be reported and fixed on the inner platform 20.

According to one embodiment, the protuberances 16 may in particular extend upstream from the inner platform 20, or in the direction of leakage air flow F. The protuberances 16 thus form an obstacle to the flow of leakage air F. in the rotor 3 and reduce its speed of rotation in the zone 2 relative to the rotor, which makes it possible to reduce the coefficient of exchange of the air with respect to the rotor 3 in the zone 3.

Thus, while the prior art was limited to simply reducing the leakage air flow F, in particular using labyrinths 12 arranged on the passage of air, the invention proposes to influence the level of convective exchanges by acting on the coefficient of entrainment of the leakage air F with respect to the rotor 3. It will of course be understood that the two technical solutions can be combined in order to further reduce the convective exchanges between the air and the disks The distributor 2 then comprises both protuberances 16 on the upstream side of the inner platform 20, in order to brake the leakage air F, and the bore 14 abradable material on the inner face 23a of the inner ring 23, to reduce the air flow, while the rotor 3 comprises the wipers 12 extending radially opposite the bore 14. In the exemplary embodiment illustrated in FIGS. 2a and 3, the protuberances 16 forming the braking means comprise a series of fins 16, each comprising a partition extending radially with respect to the axis X of the turbomachine between the inner ring 23 and the plate 21 of the inner platform 20 of the distributor 2. Here, the fins 16 extend in particular between the inner ring 23 and the radial wall 22 of the annular platform 20.

Alternatively, in the embodiment of Figure 5, the fins 16 extend between the annular plate 21 and the radial wall 22 of the annular platform.

In all cases, the implementation of such protuberances on the annular platform 20 locally stops the leakage air F which enters the rotor 3 in the zone 2, insofar as the protuberances 16 form an obstacle on its path to the discs 30. The exhaust air F thus slowed then bypasses the inner ring 23 (zone 3), before passing under the distributor 2 and reaching the rotor 30 downstream disc 3. The air flow therefore sees its drive coefficient Ke gradually increase between the zone 1, which corresponds to its point of entry into the rotor 3, where its value is negative, for example of the order of -1, to tend towards 0 after having was braked by the fins 16 in the zone 2, then to 1 at the zone 3 which is adjacent to the discs 30 of the rotor 3.

The convective exchanges can be further reduced thanks to the simultaneous (and optional) implementation of the labyrinth, comprising the wipers 12 and the abrasive material, which makes it possible to reduce the leakage air flow F between the two discs 30 of the rotor 3 .

The downstream disk 30 of the rotor 3 can then more rapidly put the leakage air F in rotation so that its drag coefficient tends more rapidly to the value 1 (which implies that the relative speed of rotation of the air relative to the rotor 3 tends to 0) than when the turbine 7 is devoid of braking means 16.

The convective exchanges between the leakage air F and the discs 30 are therefore significantly reduced, thus greatly reducing the temperature of the discs 30 of the rotor 3 (in particular in the region of the flanges 34 and the flange 36), which allows improve the service life of these parts.

The fins 16 preferably extend in a direction generally parallel to the axis X of the turbomachine. They can be straight, and extend radially with respect to the X axis, or have particular shapes to improve the slowing of the air flow, reduce material and manufacturing costs, and / or reduce the overall mass of the distributor 2. Thus, the fins 16 may have a curved surface, comprise a single continuous partition or alternatively several discontinuous partitions, include holes, etc. Thus, FIG. 2b illustrates an example of fins 16 extending between the inner ring 23 and the radial wall 22, and comprising a curved surface whose concavity is oriented towards the leakage air flow F. Here , the surface of the fins 16 substantially corresponds to the surface of a quarter cylinder whose axis of revolution is parallel to the axis X of the turbomachine. Alternatively (not shown in the figures), the fins 16 could also be shaped so that their axis of revolution extends radially relative to the axis X of the turbomachine, or that their surface is partially spherical. In this way, the direction of the air flow F is modified so that the air is deflected radially by the fins 16 relative to the axis X of the turbomachine.

The dimensions, the shape and the number of protuberances 16 as well as their position relative to the inner platform 20 determine their ability to slow down the speed of rotation of the air flow. This choice can however be limited by the cost and weight requirements of the turbine 7. For example, in the case of protuberances 16 comprising fins 16, the increase in the coefficient of drive depends in particular on the effective surface of the fins 16 (that is to say the surface of the fins 16 obstructing the air leakage F and to slow down its negative rotation speed and possibly deflect the leakage air flow F), and the number of fins 16, for example between 1 and 100 fins 16 per distributor 2. The number of fins 16 may in particular be determined according to the heat gain, the diameter of the distributor (and therefore the distributor stage) and the mass impact desired for the distributor sector.

In addition, their radial partition is dimensioned so as to withstand the thermal and mechanical stresses applied to it. For example, the fins 16 may be made of a material similar to the material constituting the inner platform 20 of the distributor 2. According to one embodiment, the annular platform may further comprise an annular radial wall 18 extending from the crown internal 23 towards the annular plate 21, adapted to limit the introduction of leakage air F from the vein in the rotor 3. The annular wall 18 may for example extend radially from the upstream end of the crown internal 23 towards the vein of air. The fins 16 can then extend to the annular wall 18, for example between the annular wall 18 and the upstream face 22a of the radial wall 22 of the inner platform 20.

Claims

1. Turbine (7), in particular low pressure, comprising at least one distributor (2) and a rotor (3), the distributor (2) comprising a plurality of fixed blades (24) extending radially with respect to an axis of rotation ( X) of the turbine (7) from an inner annular platform (20), the inner platform (20) comprising:

an annular plate (21) forming a support for said blades,

a radial wall (22) extending from the annular plate (21) in the direction of the axis of rotation (X) of the turbine,

the turbine (7) being characterized in that the distributor (2) further comprises air braking means (16) adapted to reduce the relative speed of rotation of the air relative to the rotor (3), said braking means (16) comprising protuberances which extend from an upstream face of the radial wall (22) of the inner annular platform (20).

The turbine (7) according to claim 1, wherein the inner annular platform (20) further comprises an inner ring (23) extending from the radial wall (22), and the protuberances extend between the plate annular (21) of the inner annular platform (21) and the inner ring (23).

3. Turbine (7) according to claim 2, wherein the protuberances (16) extend from the inner ring (23) and / or the annular plate (21) of the inner annular platform (20).

4. Turbine (7) according to one of claims 1 to 3, wherein the protuberances (16) are formed integrally and in one piece with the inner annular platform (20).

5. Turbine (7) according to one of claims 1 to 3, wherein the protuberances (16) and the inner annular platform (20) are separate parts.

6. Turbine (7) according to one of claims 1 to 5, wherein the protuberances (16) comprise a series of fins extending from the inner annular platform (20).

7. Turbine (7) according to one of claims 2 to 6, wherein the inner annular platform (20) further comprises a radial annular wall (18) extending from the inner ring (23) towards the annular plate (21).

8. Turbine (7) according to claim 7, wherein the braking means (16) extend between the radial annular wall (18) and the inner ring (23).

9. Distributor (2) of a turbine (7) according to one of claims 1 to 8, characterized in that it comprises air braking means (16) comprising protuberances which extend from a upstream face of the radial wall (22) of the inner annular platform (20) adapted to reduce the relative speed of rotation of the air with respect to the rotor (3).