Device for cooling a turbomachine rotor

A device cools a disk of a turbine extending along an axis. The disk includes on its circumference at least one recess surrounded by disk teeth each having an upstream face. The recess includes a bottom in fluid communication with an upstream cavity by way of at least one lunula. The lunula includes lateral surfaces that are inclined with respect to the radial plane which constitutes the plane of symmetry of the recess into which the lunula opens.

GENERAL TECHNICAL FIELD AND PRIOR ART

The invention relates to turbomachines in general, and more specifically the ventilation of the stages of a turbine. Some fields of application of the invention are turbojets and turboprops of aircraft and industrial gas turbines.

A turbomachine traditionally includes a nacelle, the opening of which admits a predetermined stream of air toward the engine strictly speaking. Conventionally, the gases flow from upstream to downstream through the turbomachine.

Generally, the turbomachine comprises one or more sections for compression 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 and mixed with fuel before being burned there.

The hot combustion gases resulting from this combustion are then decompressed in different turbine stages. A first decompression is done in a high-pressure stage immediately downstream of the combustion chamber and which receives the gases at the highest temperature. The gases are decompressed again, while being guided through the so-called low-pressure turbine stages.

A low-pressure or high-pressure turbine T with axis X, an example of which is illustrated inFIG. 1, conventionally includes one or more stages, each being constituted of a row of stationary blades1, also known as the distributor, followed by a row of movable blades2, which form the rotor3. The distributor1diverts the gas stream bled in the combustion chamber toward the movable turbine blades2at an appropriate angle and speed in order to rotationally drive these movable blades2and the rotor3of the turbine T.

The rotor generally comprises an assembly of several disks4, an example of which is represented inFIG. 1.

These disks4generally comprise, as in the embodiment represented inFIG. 2, peripheral grooves such as assembly indentations or recesses5in which the movable blades2are placed and held in position, particularly owing to the particular profile of the “teeth”6of the disk surrounding each indentation5(or recess) into which the blades2are inserted.

A disk tooth6has a profile including a first7and a second8span forming an assembly co-operating with complementary surfaces formed on the movable blade2. These spans7and8provide a radial and tangential stop at the blade root with respect to the disk. Other geometries can also provide these functions, such as for example a blade root having a dovetail section.

The axial stop of the movable blade2on the disk4can be provided by the rubbing between the blade2and the disk teeth6, or by upstream11and downstream12flanges represented inFIG. 3.

A specific ventilation circuit for the disks4of the rotor has been designed to limit the effects due to the extreme thermal environment to which the rotor3is exposed.

The ventilation circuit directs a charged stream F of charged air bled upstream of the turbine T, typically in one of the compressors, to introduce it into the rotor3with the aim of cooling its disks4, in particular its blades2.

For this purpose, the blade includes a series of inner channels allowing the cooling stream F to circulate inside them and to cool the blade2more effectively.

The blade2does not completely fill the recess5, forming a bottom10of the recess5extending substantially along the axis X, the bottom10of the recess5being located upstream (in the flow direction of the gases) of the inner channels allowing the circulation of the cooling stream F all the way to the latter.

This cooling stream F crosses several enclosures delimited by the rotor disks4and upstream11and downstream12flanges intended for this purpose, the different successive enclosures being put in fluid communication.

The axial and radial positioning necessary to the flanges11and12with respect to the rotor disks4to perform their role is conventionally produced by dog-clutches13located in the extension of the disk teeth6. In the illustrated example, these dog-clutches13form an extra thickness at the upstream surface of the disk4, this extra thickness forming an axial shoulder131allowing an axial positioning and a short centering132allowing a radial positioning of the sealing ring11on the rotor disk4.

The dog-clutches13surround lunules14, which are depressions extending substantially radially with respect to the axis X of the turbomachine and are usually machined directly on the upstream face of the rotor disk4.

These lunules14ensure the continuity of the ventilation circuit by forming a fluid communication between a cavity15located upstream in the flow direction of the fluids and the recess bottoms10located in the recesses5.

In the prior art illustrated inFIG. 4a(see patent FR 2 981 979), the lunules14have an offset as well as an inclination with respect to the upstream surfaces16of the disk teeth6. This embodiment has the disadvantage of forming an intermediate cavity17just upstream of the recesses5. The cooling stream F circulates from an upstream cavity15toward the intermediate cavity17by the lunules14.

In this intermediate cavity17, the cooling stream F has a tangential speed lower than that of the recesses5, this phenomenon being represented inFIG. 4b. This difference in tangential speed prevents the cooling stream F from circulating optimally toward the recesses5and reduces the performance of the cooling system.

With reference toFIG. 5a, a second embodiment has lunules14produced set back and not inclined with respect to the upstream surfaces16of the disk teeth6.

In this way, the stream F passing through a lunula14is more able to circulate in the recesses5, the effects of this embodiment being illustrated inFIG. 5b.

The disk teeth6can include keying pins18securing the assembly steps by avoiding the assembly of blades2axially back-to-front on the disks.

With reference toFIG. 6, the blade2is inserted into the recess of the disk, and has a geometry co-operating with the keying pin18to prevent the blade from being inserted in the incorrect direction.

The keying pins18can also serve to balance the disk.

The relative total pressure of the gases in the recess bottom10, represented inFIGS. 7aand 7b, emphasizes the effect of this modification on the distribution of the cooling stream F in the recesses5.

FIG. 7arepresents the distribution of the pressure of the gases in the recess bottom10in an embodiment where the lunules14have an angular offset and an offset of level in the upstream-ward direction with respect to the upstream surfaces16of the disk teeth6,FIG. 7brepresenting the same parameter in the embodiment where the lunula14is set back in the downstream-ward direction with respect to the upstream surfaces16of the disk teeth6.

The areas exhibiting lower relative total pressure levels25feed the cooling channels of the blading less effectively, which reduces the performance of the cooling system and therefore the lifetime of the blades2.

It can easily be seen that the location of the lunules14set back from the upstream surfaces16of the disk teeth6makes it possible to limit the disparities in the distribution of the charge and to obtain a more homogenous flow, and therefore better cooling.

If this modification provides a gain in performance for the cooling system, it does however provide a drawback for the lifetime of the rotor disk4. Specifically, the edge19between the lunula14and the recess5has areas of concentration of stresses, represented inFIG. 8.

These stress peaks greatly limit the lifetime of the disks4. The flow of the cooling stream further including several bends, the overall loss of charge of the circuit also accounts for a factor substantially lessening the performance of the cooling system of the blades2, and therefore limits the gain in lifetime of the blades2.

OVERVIEW OF THE INVENTION

An aim of the invention is to increase the lifetime of the rotor disks.

Another aim is to increase the lifetime of the blades.

Another aim is to increase the performance of the cooling system.

Another aim is to reduce the charge losses in the cooling system.

Another aim is to decrease the concentrations of stresses in the vicinity of the lunules.

Another aim of the invention is to reduce the flow rate of the stream bled upstream of the turbines to feed the cooling system.

According to an aspect, the invention proposes a device for cooling a disk of a turbine extending along an axis, the disk including on its circumference at least one recess surrounded by disk teeth each having an upstream face, the recess including a bottom in fluid communication with an upstream cavity by way of at least one lunula, the lunula including lateral surface portions, characterized in that the lateral surface portions are inclined with respect to the radial plane forming the plane of symmetry of the recess into which the lunula opens, the recess extending along an axis inclined by a broaching angle with respect to the axis of the turbomachine, the broaching angle being between 0 and 20°.

Such a device is advantageously completed by the following various features taken alone or in combination:the lunula includes a bottom located set back in the downstream-ward direction with respect to the upstream faces of the disk teeth;the boundary between the lunula bottom and the recess bottom has a broken edge;the broken edge includes an edge fillet which has:a first end, corresponding to an intersection between the fillet and a first tooth, and a second end, corresponding to an intersection between the fillet and a second tooth;a plurality of radial planes, each radial plane comprising the axis of the turbine and cutting the fillet between the first and the second end, anda plurality of radial sections, each radial section being defined by the intersection between an associated radial plane and the fillet, each radial section having a radius of curvature of the edge fillet, the radius of curvature of the edge fillet varying between the first and the second end, particularly according to the tangential position of the radius of curvature of the edge fillet;the ratio of the longest radius of curvature of the edge fillet to the shortest radius of curvature of said edge fillet can be between 2 and 20;the tangential position of the longest of the radii of curvature of the edge fillet is located at a stress peak of the edge fillet;the lunula includes a pressure side curved portion and a suction side curved portion joining the lateral surface portions and the bottom of said lunula, each curved portion containing a plurality of radii of curvature;the radii of curvature of the pressure side curved portion are different from the radii of curvature of the suction side curved portion;on the pressure side curved portion or the suction side curved portion, a ratio of a longer of the radii of curvature to a shorter of the radii of curvature is between 2 and 13;a ratio of each of the radii of curvature of the most charged of the pressure side and suction side curved portions to each of the radii of curvature of the least charged of the pressure side and suction side curved portions is between 1 and 20;an axis normal to the lunula bottom is defined as being perpendicular to a straight line passing through the ends of the bottom of the lunula, this normal axis being inclined by an angle of inclination with respect to the axis of the turbine in a first direction;the axis normal to the lunula bottom is inclined with respect to the axis of the turbine in a second direction;a ratio of the angle of inclination of the normal axis with respect to the axis of the turbine in the first direction, to the broaching angle, is between 0.2 and 1.4;the broaching angle ϕ) is between 3° and 16°, preferably between 6° and 12°;the lateral surface portions of the lunula are curved, and wherein at least one of the lateral surface portions has a radius of curvature between 20 mm and 200 mm;the lateral surface portions have, at the recess bottom, an inclination of less than 20° with respect to a plane passing through a median point of the lunula at the recess bottom;the lateral surface portions have a radially inner end, and wherein the lateral surface portions have, at the radially inner end, an inclination between 15° and 60° with respect to a plane passing through a median point of the lunula at the radially inner end of the lateral surface portions;the radius of curvature of a lateral surface portion has a maximum value at the recess and a minimum value at the radially inner end of the lateral surface portions.

According to another aspect, the invention proposes a rotor including such a device for cooling a disk.

According to another aspect, the invention proposes a turbomachine including such a device for cooling a disk.

DESCRIPTION OF ONE OR MORE METHODS OF IMPLEMENTATION AND EMBODIMENTS

The embodiments described below concern the case of a turbine T comprising a series of distributors (or stators) alternated along the axis X of rotation of the turbomachine with a series of movable disks4(or rotor). This is however non-limiting, insofar as the turbine T could comprise a different number of stages, and can be single- or multi-stages.

The disks4have lunules14, the geometry of which is optimized to facilitate the flow of the fluid in the cooling circuit and therefore the performance of the cooling system, while minimizing the concentrations of internal stresses in the part at the lunules14.

With reference toFIG. 9a, the bottom20of a lunula14extends substantially radially with respect to the axis X of the turbomachine and can be defined by a normal axis n.

As the bottom20of the lunula14can have a variety of geometries, the normal axis n can be defined as perpendicular to a straight line passing through the ends of the bottom20of the lunula14.

The normal axis n is inclined by an angle α with respect to the axis X of the turbomachine around a first radial axis Y of the rotor disk4.

In certain embodiments, the recesses extend along a broaching axis A which can be inclined by a broaching angle ϕ with respect to the axis X of the turbomachine T.

This broaching angle ϕ can be between 0 and 20° with respect to the axial direction X, preferably between 3° and 16°, in particular between 6° and 12°. This inclination can be oriented in all directions, such that the potential orientation of the broaching axis is contained in a cone with an axis parallel to the axis X of the turbomachine and an aperture of 20°.

The inclination of the broaching axis A generates an asymmetry of the stresses at the lunula14.

The wider the broaching angle ϕ, the more asymmetrical the distribution of the stresses.

In order to minimize the stresses in the lunules14, and particularly the stress maxima, the lunules14can have an asymmetrical geometry, making it possible to preserve the aerodynamic performance and the technical feasibility of the least charged part while promoting the mechanical performance in the most charged part.

The angle α of inclination of the normal n to the lunula14with respect to the axis X of the turbomachine thus makes it possible to reduce the effect of asymmetry of the stress distribution, particularly by reducing the stress peak in the most charged area.

The term “stress peak” is understood to mean a local maximum of stress.

The ratio of the angle α of inclination to the broaching angle ϕ can be between 0.2 and 1.4.

The closer the angle α of inclination to the broaching angle ϕ, the more the dissymmetry of the stresses is attenuated.

The normal n to the lunula14can be contained in a plane orthogonal to a radius issuing from the axis X of the turbomachine, the angle α of inclination being expressed in this plane.

The lunula14is also delimited by lateral surface portions21extending substantially radially, and two so-called pressure side22aand so-called suction side22bcurved surface portions joining the bottom20of the lunula14and the lateral surfaces21of the lunula14. The curved surface portions respectively pressure side22aand suction side22bcorrespond here to a surface portion arranged respectively on the pressure side and suction side of the vane of the blade2assembled in the corresponding recess5.

The pressure side22aand suction side22bcurved surface portions of the lunules14have radii of curvature R1, R1′ maximized to minimize the stress concentration coefficients.

Each curved portion22aand22bcan contain several different radii of curvature R1, R1′ according to the location of the point in question.

Due to the asymmetrical concentration of the stresses at the lunules14, a symmetrical geometry of the lunula14could fail to have any significant effect on the reduction of the maximum stress peak simulated in the disk4at the lunula14.

For this reason, each of the curved surface portions22aand22bhas a radius of curvature R1, R1′ that can be fixed or variable, the radius of curvature R1′ of the pressure side curved portion22abeing able to be identical to or different from the radius of curvature R1of the suction side curved portion22b.

As a function of the broaching angle ϕ, one among the pressure side curved portion22aand the suction side curved portion22bcan be more charged by stress than the other.

In the example illustrated inFIG. 9a, the inclination of the broaching axis A with respect to the axis X of the turbomachine generates a stress distribution in the lunula14in which the suction side curved portion22bis the most charged.

Obviously, for an opposite value of broaching angle ϕ, the stress distribution obtained would have higher stresses in the pressure side curved portion22athan in the suction side curved portion22b.

The greater the broaching angle ϕ, the greater the tangential distance of the stress peak from a median point of the lunula14and the more asymmetrical the stress distribution.

The term “median point of the lunula”14is understood to mean a point of the lunula14located equidistantly from the suction side curved portion22band the pressure side curved portion22a.

The term “tangentially” is understood to mean a tangential direction issuing from a radius, and which is orthogonal to said radius and to the axis X of the turbomachine.

For a zero broaching angle ϕ, the stress distribution would be symmetrical.

As a function of the configuration of the broaching angle D, and thus of the position of the stress peak, the most charged curved portion22a,22bhas greater radii of curvature than the least charged curved portion.

The ratio of a radius of curvature R1, R1′ of one of the most charged curved portions22a,22bto a radius of curvature of a lightly-charged curved portion can be between 1 and 20.

More particularly, the wider the broaching angle ϕ, the greater the ratio of the greatest radius of curvature R1, R1′ of the most charged curved portion22a,22bto the smallest radius of curvature of the least charged curved portion.

In the illustrated example, the ratio of the greatest radius of curvature of the suction side curved portion22bto the smallest radius of curvature of the pressure side curved portion22ais between 4 and 6, for example 5.

Such a configuration makes it possible to minimize the stress concentration coefficients and to decrease the intensity of the stress peak and the stresses in the lunula14.

A same curved portion22a,22bcan have different radii of curvature, distributed as a function of the position of the stress peak. The closest radius of curvature to the stress peak is the greatest, in such a way as to minimize the stress concentration coefficient at the most critical point.

The radius of curvature R1, R1′ over one and the same curved portion22a,22bcan vary from 1.5 mm in a lightly-charged area to 20 mm in a heavily-charged area.

Over one and the same curved portion22a,22b, the ratio of the shortest radius of curvature to the longest radius of curvature can thus be between 2 and 13.

This notably makes it possible to optimize the mechanical characteristics in the critical areas, and the manufacturing and the aerodynamic performance in the less charged areas of one and the same curved portion22a,22b.

In the illustrated example, the radius of curvature R1of the suction side curved portion22bcan vary between 1.65 mm and 10 mm, for a disk4having an outer diameter of 370 mm. The ratio of the longest radius of curvature R1to the shortest radius of curvature can be between 5 and 7.

The outer diameter of a disk4is expressed at the outer boundary of the teeth6. The different dimensions of the lunules14vary as a function of the diameter of the disk4.

With reference toFIG. 9b, the normal axis n is inclined by an angle β with respect to the axis X of the turbomachine around the second radial axis Z of the rotor disk4.

In an embodiment, the second radial axis Z is a tangential axis perpendicular to the first radial axis Y.

With reference toFIG. 9c, a critical factor for the concentration of stresses at the lunula14is the presence of a sharp edge19between the lunula14and the recess5.

This edge19can have a geometry designed to reduce the stress concentration factor in this area.

This geometry can comprise a chamfer, a fillet, a rounding, a boss, an extra thickness or any mechanical or thermal processing used to reduce the maximum stress peak measured in the area of the lunula or to locally improve the mechanical characteristics of the part.

In the case of an edge fillet, the fillet can have a radius of curvature r that varies with the point of the fillet. This embodiment makes it possible to significantly reduce the phenomenon of stress concentration in the area of the lunula14.

The fillet has:a first end, corresponding to an intersection between the fillet and a first tooth, and a second end, corresponding to an intersection between the fillet and a second tooth.a plurality of radial planes, each radial plane comprising the axis X and cutting the fillet between the first and the second end, anda plurality of radial sections, each radial section being defined by the intersection between an associated radial plane and the fillet.

Each radial section has a curvature. The curvature of said sections varies between the first and the second end. Notably, the radius of curvature r of the radial sections of the edge fillet varies according to the tangential position of the radius of curvature r of the edge fillet. For example,FIG. 12aillustrates two radial sections S1and S2defined by the intersection between two associated radial planes P1and P2and the fillet. As can be seen inFIG. 12b, the radii of curvature r1, r2of these radial sections S1, S2are different.

The area of the fillet the closest to the stress peak has the radius of curvature r of the longest edge fillet. More precisely, as a function of the broaching angle ϕ, the position of the stress peak can be closer to the first end of the edge fillet (or the second end, respectively). In this case, the radius of curvature of the edge fillet in the area adjacent to this first end must therefore be longer (or shorter, respectively) than that of the edge fillet in the area adjacent to the second end.

Consequently, the tangential position of the radius of curvature r of the longest edge fillet is a function of the broaching angle ϕ.

The more a point of the fillet is charged, the greater the radius of curvature r of the edge fillet at this point. The distribution of the radii of curvature r of the edge fillet depends on the distribution of the stresses on the edge19.

The ratio of the longest radius of curvature r of the edge fillet to the shortest radius of curvature of said edge fillet can be between 2 and 20, for example 5.

The shortest of the radii of curvature r of the edge fillet can be between 0.5 mm and 2.5 mm, for example between 0.8 and 1.5 mm for a disk4with an outer diameter of 370 mm having a recess bottom with a radius of curvature of 4 mm.

The longest of the radii of curvature r of the edge fillet can be between 2 mm and 10 mm, for example between 3.5 mm and 7 mm for a disk with an outer diameter of 370 mm having a recess bottom10with a radius of curvature of 4 mm.

The geometry of the edge19, and therefore of the fillet, varies as a function of the diameter of the disk4and the radius of curvature of the recess bottom10.

Such a configuration makes it possible to reduce the stress concentration coefficient in the most charged areas and therefore to decrease the stress levels, and the stress peak.

In addition to the stress concentration in the lunula14, this modification makes it possible to reduce the criticality of the part in a standard established by a consortium of engine manufacturers (Rotor Integrity Sub-Committee (RISC)).

This rating (RoMan) associates a degree of criticality to a part as a function of the geometrical elements it has, and is used to determine the manufacturing method that will be applied to produce this part.

The lower the criticality, the less stringent, and thus less expensive, the manufacturing methods.

The removal of a sharp edge19in favor of an edge19with a fillet makes it possible to reduce the criticality of the disk4. Reduction of the criticality of the disk4makes it possible to produce it by methods which are simpler to implement, and to reduce its manufacturing cost.

In an embodiment illustrated inFIG. 9d, the lateral surface portions21of the lunula14are inclined (angle δ) with respect to the radial plane which constitutes the plane of symmetry of the recess5into which the lunula14opens.

Specifically, despite the position of the lunules14set back from the upstream surfaces16of the disk teeth6, a difference in tangential speed remains between the cooling stream F and the recesses5. The cooling stream F first circulates axially to reach the upstream cavity15, then radially to reach the lunules14and finally axially to enter the recesses5despite the tangential speed of the latter due to the rotation of the disks4.

With reference toFIG. 10a, at the opening upstream of a lunula14, the coolant circulates at a tangential speed V1whereas the point of the disk4at this radius has a tangential speed V2greater than that of the fluid.

The fluid therefore has a relative speed V3with respect to the disk4, oriented inversely with respect to the speed V1of the disk4at this point.

The fluid therefore circulates with respect to the disk4in the reverse direction to the rotation of the disk4.

Consequently, to reduce the effect i of the bend in the stream of coolant, the lateral walls of the lunules14are inclined (angle δ) with respect to a radial plane Ps corresponding to a plane of symmetry of the recess5.

The inclination of the lateral surface portions21of the lunules14(angle δ) lessens the bend in the direction of the cooling stream F at the lunula14. It promotes its admission into the recess5by decreasing the singular charge loss in this area, thereby increasing the effectiveness of the cooling system.

The direction of inclination is chosen as a function of the desired direction of rotation for the disk4in operation in order to decrease the bend that the cooling stream F must cross.

With reference toFIG. 11, in order to limit the effect of the bends in the flow, the lateral surface portions21of the lunules14can have a curvature, thereby allowing the decrease of the singular charge losses in the ventilation circuit and thus increasing its performance.

This curvature can be a simple curvature or a more complex curvature (with a twist for example).

The curvature of the lateral surface portions21can be constant or have a variable radius of curvature configured to minimize the charge losses along the lunula14.

The curvature of the lateral surface portions21makes it possible to further reduce the effect i in the bend of the coolant stream.

Specifically, the inclination of the lateral surface portions21of the lunules14cannot exceed a certain limit due to the geometrical features of the disk4, its manufacturing process and the mechanical characteristics to be complied with.

A curvature makes it possible to reduce the effect of the bend in the coolant stream while also reducing the inclination of the lateral surface portions21for an equal effect.

The lateral surface portions21can have, at the bottom10of the recess, an inclination of less than 20° with respect to a radial plane P3, passing through a median point of the lunula14, preferably an inclination of less than 10°.

The term “radial plane” P3is understood to mean the plane passing through the median plane of the lunula14at the bottom10of the recess and containing the axis X of the turbomachine. The median point of the lunula14corresponds here to the point located at the bottom10of the recess and equidistant from the lateral surface portions21. Such a median point has been illustrated by way of example inFIG. 12.

The inclination of the lateral surface portions21at the recess bottom10promotes the entrance of the cooling stream into the recess5.

The lateral surface portions21have one end which is radially inner with respect to the axis of the turbomachine.

The lateral surface portions21can have, at their inner end, an inclination between 15° and 60° with respect to a radial plane P4, where the plane P4passes through a median point of the lunula14at the radially inner end of the lateral surface portions21and comprising the axis X, in such a way as to promote the entrance of the cooling stream into the lunula14.

The term “median point” is understood to mean the median point of the lunula14at the radially inner end of the lateral surface portions21, the point located at the inner end of the lateral surface portions21and equidistant from the lateral surface portions21.

In a plane normal to the axis X of the turbomachine and passing through a lateral surface portion21, the radius of curvature R of the lateral surface portion21can be between 20 mm and 200 mm. The radius of curvature R of the lateral surface portion21can be constant, and have for example a value of 50 mm.

In a variant, the radius of curvature R of the lateral surface portion21can vary and have a maximum value in the most stressed area, at the recess5, in such a way as to minimize the concentrations of stresses and a minimum value at the radially inner end of the lateral surface portions21, in such a way as to minimize the effect i of the bend of the cooling stream entering into the lunula14.

The decrease in charge losses in the cooling system makes it possible to improve its performance, thus increasing the lifetime of the disks4and the blades2.

This decrease in charge losses also makes it possible to reduce the flow rate of the stream bled upstream of the turbine to feed the cooling system, thus minimizing the effect of the cooling system on the performance of the turbomachine.