FR3066783A1 - SHIRT FOR OPTIMIZED COOLING TURBINE BLADE - Google Patents

Abstract

Cooling jacket (30) for cooling a hollow part in which it is intended to be inserted, comprising a longitudinal hollow body (32) surmounted by a flange (34) intended to be secured at its periphery in a sealed manner with this hollow part, the flange comprising a plurality of perforations (34A, 34B, 34C) for separating a main flow of cooling air Ft feeding the cooling jacket into two separate secondary flows, a first secondary cooling air flow Fc passing through the longitudinal hollow body at a central cavity (32A) to be discharged to the outside and a second secondary flow of cooling air F1, F2, F3 passing through the perforations and circulating around the longitudinal hollow body.

Description

Field of the invention

The present invention relates to the general field of turbomachine turbine blades, and more particularly to turbine blades provided with cooling jackets.

Prior art

In a manner known per se, a turbomachine comprises a combustion chamber in which air and fuel are mixed before being burned there. The gases from this combustion flow downstream of the combustion chamber and then supply a high pressure turbine and a low pressure turbine. Each turbine has one or more rows of fixed vanes (called distributors) forming a stator alternating with one or more rows of movable vanes (called movable wheels), circumferentially spaced around the rotor of the turbine. The fixed turbine blades are subjected to very high temperatures of the combustion gases, which reach values much higher than those which the blades which are in direct contact with these gases can withstand without damage, which has the consequence of limiting their duration of life.

Also, in order to reduce the temperature, it is known to provide these fixed blades with perforated cooling jackets.

FIGS. 2 and 3 represent a conventional distributor sector 10 of aeronautical engines comprising a plurality of fixed vanes 12 forming a grid straightening the air flow F passing through the engine gas stream delimited by a ferrule or external platform 14 and a ferrule or internal platform 16 supporting the fixed vanes 12. The hollow vane 12 comprises a cooling jacket 18 which defines an annular peripheral cavity 20 between the internal wall of the blade and the outside of the jacket (On the Figure 2 and for the sake of better understanding, the jacket 18 furthest to the left has been shown partially extracted from the cavity 20). At its upper part 18A in the form of a collar, the jacket is tightly fixed to the external platform of the blade by welding or brazing and its lower end part 18B is embedded in the internal platform of the blade at a guide zone 16A, leaving a certain clearance necessary for mounting and sliding the jacket under the effects of thermal expansion. Depending on the configuration envisaged, studs 22 secured to the internal wall or formed by bosses of the liner maintain a constant spacing between the liner and this internal wall.

The jacket 18 is of the multi-perforated type so that the flow of cooling air delivered by a source of pressurized air, in general the compressor of the turbomachine, enters the external platform 14 through an orifice inlet 24, arrives inside the liner 18 and partly escapes by the multi-perforation of the liner, forming in the peripheral cavity 20 air jets which cool by impact (or via fins 26 forming disturbers ) the inner wall of the blade 12, then are evacuated by calibrated bores made on the trailing edge or on the underside of this blade in order to form a protective air film (bridges not shown may be provided at the 'interior of the dawn to arrange the circulation of this cooling air). The remaining air flow leaves the jacket through the internal platform 16 which it crosses while cooling it to escape through an outlet orifice 28 outside the blade towards other organs of the engine. cool and in particular the turbine discs (high or low pressure purges).

However, this configuration has drawbacks related to the fact that this impact (or percussion) cooling in very specific areas of the blade, its trailing edge and its leading edge in particular, creates very large thermal gradients between the cold flow. and the impacted hot zone which have the effect of charging other zones and causing their premature wear. In addition, it is difficult to ensure a transfer of the cooling air to the turbine discs at the right pressure and at the right temperature.

Subject and summary of the invention

The present invention therefore aims to overcome the drawbacks associated with this inappropriate creation of thermal gradients by proposing a cooling jacket which avoids this premature wear of the dawn. The object of the invention is also to produce a blade whose geometry and therefore the manufacturing process is very little modified compared to the traditional manufacturing process in foundries, so as to avoid any deterioration in the general mechanical strength of this blade. Finally, it relates to any turbomachine turbine equipped with such blades with improved cooling jacket. To this end, a cooling jacket is provided for cooling a hollow part into which it is intended to be inserted, comprising a longitudinal hollow body terminated by a free end and surmounted by a flange intended to be secured to its periphery sealingly with said hollow part, characterized in that said flange comprises a plurality of perforations for separating a main flow of cooling air Ft supplying said cooling jacket in two separate secondary flows, a first secondary flow of cooling air Fc passing through said longitudinal hollow body at a main cavity to be evacuated through said free end and a second secondary flow of cooling air F1, F2, F3 passing through said perforations and circulating around said longitudinal hollow body.

In this way, by simple convection, good ventilation of the hollow part into which the jacket is inserted is ensured and by the passage of air in the central cavity, the conditions of temperature, pressure and flow rate desired for cooling elements are met. external to this hollow part, for example turbine disks in the case where this hollow part is a blade of a turbomachine distributor. The structure of the shirt is thereby simplified by eliminating its multi-perforation without modifying the manufacturing process of the hollow part in which the shirt is inserted.

Preferably, said main cavity is a central cavity of substantially oblong shape and arranged in a centered position.

According to the embodiment envisaged, said flange comprises two perforations arranged at two ends of said central cavity and preferably at least one lateral perforation disposed on a side of said central cavity.

Advantageously, said first secondary flow of cooling air Fc represents 55 to 65% of said main flow of cooling air Ft and preferably 60%. The invention also relates to a hollow part comprising a cooling jacket as mentioned above defining an annular cavity between an external wall of said cooling jacket and an internal wall of said hollow part, said main flow of cooling air Ft being introduced into said hollow part for the one hand, by crossing said perforations, ensuring its internal cooling and for the other hand, by crossing said main cavity, evacuating part of this cooling air outside of said hollow part.

Said hollow part advantageously forms a fixed blade of a turbomachine distributor, the cooling air passing through said main cavity being intended to cool a disc carrying said fixed blade. Finally, the invention relates to any turbomachine turbine fitted with a plurality of fixed blades as mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting nature and in which: - Figure 1 is a perspective view of a jacket of a turbine distributor blade according to the invention, - Figure IA is a sectional view of a blade provided with the jacket of Figure 1, - Figure 2 is a view in perspective of part of a turbine distributor of the prior art, and - Figure 3 is a sectional view of the distributor of Figure 2.

Detailed description of an embodiment

It will be noted first of all that if the invention as described is applied to the fixed blades of low pressure distributors, it can of course be easily adapted to any other part requiring internal cooling (more generally any hollow part to be vented).

According to the invention, it is proposed to change the way of distributing the cooling air in this hollow room by promoting convection to cool the hot walls of the room while keeping a central cavity naturally away from these hot walls to direct cooler air in the direction of zones external to this part, in this case, the low-pressure turbine discs when this hollow part is a fixed blade of a turbomachine distributor.

Thus, if we consider the total cooling flow available, the present invention allows, by the innovative configuration of the cooling jacket, to separate this main flow into two secondary flows: one passing through the cooling jacket, and going directly to the outside towards the turbine discs and the other circulating inside the blade, around the cooling jacket, before being expelled by the trailing edge and / or the leading edge for the or cool them by forming a protective air film. This configuration makes it possible to meet the criteria for purging, cooling the disks and cooling the leading edge and / or the trailing edge, while avoiding favoring a particular type of thermal degradation as in the devices of the prior art. .

It has been recalled in the preamble to the present application that a fixed turbine distributor blade is mounted between an external platform and an internal platform, the external platform defining an external wall for the gas flow stream combustion through the turbine and the internal platform an internal wall for this same flow stream. Such a fixed blade of hollow structure is subjected to the very high temperatures of the combustion gases and therefore needs to be cooled. To this end and as illustrated in FIGS. 1 and 1A, the blade 12 comprises a cooling jacket 30 comprising on the one hand a longitudinal hollow body 32 terminated by a free end 33, supplied with cooling air by a first flow of secondary air Fc entering at a first end into a main cavity 32A of this body and leaving through this free end, and which defines an annular peripheral cavity 20 between the internal wall of the blade and the external wall of the jacket and other share a perforated flange 34 surmounting this hollow body and arranged to fix this jacket in a sealed manner on the external platform 14 of the blade by welding or brazing and supplied with cooling air by a second secondary air flow F1, F2, F3 crossing its perforations 34A, 34B, 34C, all of these secondary air flows forming the main air flow Ft. The first secondary air flow Fc represents 55 to 65% of the main air flow F t and preferably 60%. The main cavity is advantageously of substantially oblong shape and arranged in a centered position.

The collar is preferably obtained by forming the sheet forming the jacket but it could also be attached to the body of this jacket and it has the various perforations allowing the passage of the second secondary air flow. More particularly, a first perforation 34A made in the extension of a first end of the main cavity 32A forming the internal part of the jacket allows the passage of a first flow F1 of cooling air proportional to the section of this opening. Similarly, a second perforation 34B made in the extension of another end of the main cavity allows the passage of a second flow F2 of cooling air proportional to the section of this opening and possibly a third perforation 34C (shown in dotted on the figure) formed on one of the two sides of the main cavity allows the passage of a third flow F3 of cooling air proportional also to the section of this opening. More generally, these perforations, the number of which is not limited, are made in the available spaces of the flange around the main cavity 32A, with the exception of course of the periphery 34D of the flange necessary for its sealing sealing external platform. The cooling air introduced into the main cavity 32A of the jacket, for its part, comes out directly at its lower part to purge the turbine discs.

Thus, by separating the cooling of the blade from that of the turbine disks, account can be taken of the specific temperature, pressure and flow requirements both of the blade and of the disks, thus allowing optimized cooling.

With the invention, it can be noted that the process of manufacturing the blade does not have to be modified, only the configuration of the jacket being changed in a minor way, its manufacturing process by stamping and stirring not being not more modified. In addition, this makes it possible to supply the turbine disks with a temperature and a flow allowing their lifespan to be extended relative to a blade without a jacket without changing the flow of cooling air (no variation of the purge). . It also increases the lifespan of dawn by reducing cracks and burns. The invention therefore makes it possible to combine the benefits of the two solutions (with and without jacket) usually used for such ventilated hollow parts without adding manufacturing complexity and without changing the design of parts having a strong industrial impact and remaining interchangeable with the parts. already implemented (this "retrofit" can for example be carried out during a maintenance operation). In addition, in the case of turbomachine distributors, the liner manufacturing cycle is reduced due to the absence of multi-perforation on this liner.

Claims (9)

1. Cooling jacket (30) for cooling a hollow part (12) into which it is intended to be inserted, comprising a longitudinal hollow body (32) terminated by a free end (33) and surmounted by a flange ( 34) intended to be secured at its periphery in a sealed manner with said hollow part, characterized in that said flange comprises a plurality of perforations (34A, 34B, 34C) to separate a main flow of cooling air Ft supplying said jacket cooling in two separate secondary flows, a first secondary flow of cooling air Fc passing through said longitudinal hollow body at a main cavity (32A) to be discharged through said free end and a second secondary flow of air from cooling F1, F2, F3 passing through said perforations and circulating around said longitudinal hollow body. 2. Cooling jacket according to claim 1, characterized in that said main cavity is a central cavity of substantially oblong shape and arranged in a centered position. 3. Cooling jacket according to claim 2, characterized in that said collar comprises two perforations (34A, 34B) disposed at two ends of said central cavity. 4. Cooling jacket according to claim 2, characterized in that said collar further comprises at least one lateral perforation (34C) disposed on a side of said central cavity. 5. Cooling jacket according to any one of claims 1 to 4, characterized in that said first secondary flow of cooling air Fc represents 55 to 65% of said main flow of cooling air Ft and preferably 60%. 6. Hollow part (12) comprising a cooling jacket according to any one of claims 1 to 5 defining an annular cavity (20) between an outer wall of said cooling jacket and an inner wall of said hollow part, said main flow of cooling air Ft being introduced into said hollow part, on the one hand, by passing through said perforations, ensuring its internal cooling and, on the other hand, passing through said main cavity, evacuating part of this cooling air at l outside said hollow part. 7. Hollow part according to claim 6 forming a fixed blade of a turbomachine distributor, the cooling air passing through said main cavity being intended to cool a disc carrying said fixed blade. 8. A turbomachine distributor comprising a plurality of fixed vanes according to claim 7. 9. Turbomachine comprising a turbomachine distributor according to claim 8.