FR3106617A1 - STATORIC BLADE SECTOR WITH IMPROVED PERFORMANCE - Google Patents

Abstract

The invention relates to a one-piece turbomachine stator bladed sector (23) comprising a first and a second platform (24; 26) extending in a circumferential direction (AY) and each intended to delimit a portion of a flow stream. fluid (Vp), and blades (22) which each connect the first platform (24) to the second platform (26) by being spaced from each other in the circumferential direction, in which at least two blades (22) have different thicknesses. Figure for the abstract: Figure 3

Description

STATOR BLADED SECTOR WITH IMPROVED PERFORMANCES

The present invention relates to the field of turbomachine stator blades, in particular to distributors within low pressure turbines.

PRIOR ART

Referring to Figure 1, there is shown a turbine engine 1 turbofan type aircraft and double body. The turbomachine 1 has a central axis AX, defining a longitudinal direction, and around which its various components extend. It comprises, from upstream AM to downstream AV in a main direction of gas flow 2, a fan 3, a low pressure compressor 4, a high pressure compressor 6, a combustion chamber 7, a high pressure turbine 8 and a low pressure turbine 9.

The turbomachine 1 is delimited by an engine casing 10 extending from its upstream part to delimit an inlet sleeve 11, to its downstream part to delimit a gas ejection nozzle 12. Conventionally, the air is introduced into the turbomachine 1 through the inlet sleeve 11 to meet the fan 3. After having passed through this fan, the air is divided into a central primary flow Fp and a secondary flow Fs which surrounds the primary stream.

The primary flow Fp flows in a primary stream Vp for the circulation of gases passing through the compressors 4 and 6, the combustion chamber 7 and the turbines 8 and 9, before being evacuated towards the rear through the nozzle 12. In particular, the thermal and kinetic energy of the primary flow Fp at the outlet of the combustion chamber is transformed into mechanical energy when passing through the low and high pressure turbines by causing them to move. The secondary flow Fs circulates in a space called secondary vein Vs which surrounds the primary vein Vp, being separated from each other by an inter-vein casing 13.

In practice, the increased performance requirements of turbomachines require reducing the size and weight, so as to reduce specific consumption, as well as optimizing the work done by the blades of compressors and turbines in order to improve their efficiency. overall.

These compressors and turbines can be seen as a succession of stages, each stage of which is composed of a bladed rotor part, namely a rotating part around the central axis of the turbomachine, and a bladed stator part which is fixed and whose function is to straighten the air flow downstream of the rotor part of the stage directly upstream in order to compensate for the gyration of the flow.

In this dynamic, the object of the invention is to propose an optimized design of stator blading, in particular in an application for a low pressure turbine nozzle.

To this end, the subject of the invention is a one-piece stator bladed sector of a turbomachine comprising a first and a second platform extending in a circumferential direction and each intended to delimit a portion of a fluid flow path, and blades which each connect the first platform to the second platform while being spaced from each other in the circumferential direction, the blades each comprising a lower surface wall and a lower surface wall extending halfway from a camber surface respective, wherein the camber surfaces of the blades are identical, and wherein at least two blades have different thicknesses.

With this solution, the general mechanical status of the bladed stator sector is improved: the thickness of the blades and the overall mass of the bladed sector is limited to iso-strength to the forces. This results in a gain in performance of the turbomachine which is equipped with it.

The invention also relates to a bladed sector thus defined, comprising two blades whose maximum thicknesses differ.

The invention also relates to a bladed sector thus defined, comprising two blades having different average thicknesses.

The invention also relates to a bladed sector thus defined, comprising two blades having local thicknesses at the trailing edge which differ.

The invention also relates to a bladed sector thus defined, in which the two blades each located at a circumferential end of the sector are thicker than at least one of the other blades.

The invention also relates to a bladed sector thus defined, in which the blades are arranged symmetrically with respect to a median plane of the distributor sector and have the same thicknesses.

The invention also relates to a turbine nozzle comprising at least one bladed sector thus defined.

The invention also relates to a turbomachine turbine comprising a distributor thus defined.

The invention also relates to a turbomachine comprising a turbine thus defined.

already described is a block diagram of a turbofan engine in longitudinal section;

illustrates a portion of a turbomachine low-pressure turbine according to the invention;

represents a distributor sector according to the invention;

represents a distributor sector blade profile according to the invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

FIG. 2 represents a portion of the low pressure turbine 9 of the turbomachine 1 as described above.

This low pressure turbine 9 is formed of a succession of stages along the axial direction of the turbomachine and the number of which is established according to the energy requirements of the low pressure compressor and of the fan which it rotates. In the example of the figure, there are four stages identified by 16a, 16b, 16c and 16d. Each stage includes a distributor 17a, 17b, 17c, 17d upstream and a bladed wheel 18a, 18b, 18c and 18d downstream. The bladed wheel is a rotating part extracting energy from the flow traversing it to move, while the distributor 17a, 17b, 17c, 17d is a fixed part whose purpose is to accelerate and guide the flow coming from the impeller of the stage upstream by redirecting it to the impeller directly downstream.

The bladed wheels 18a, 18b, 18c, 18d each comprise a rotating disc 19, centered on the central axis AX of the turbomachine, which carries a cascade of rotating blades 21 distributed at regular intervals in a circumferential direction indicated by AY. These rotating vanes 21 each extend radially, that is to say along the direction AZ orthogonal to the longitudinal direction of the turbomachine. The discs 19 are in particular connected to each other by clamping.

The distributors 17a, 17b, 17c, 17d each comprise an annular row of fixed blades, denoted 22, of radial orientation AZ, or having at least one radial component.

In the context of the invention, all of the distributors 17a, 17b, 17c, 17d are formed from an assembly of independent one-piece sectors and arranged circumferentially end-to-end.

As visible in more detail in Figure 3, a distributor sector, marked by 23, comprises two coaxial annular platforms 24 and 26, inner and outer respectively, extending one inside the other and interconnected by blades 22 spaced from each other in the circumferential direction AY.

In the example of Figure 3, the sector has six blades, but it is understood that the invention is not limited to this count, the number of blades being a function of the angular extent of the sector 23 and the spaces between -blades 22 which can vary according to the turbine stage considered.

The outer platform 26 further comprises an outer base 27 forming a junction interface with the blades 22. In the same way, the inner platform 24 comprises an inner base 28 forming a junction interface with the blades 22, and delimiting a portion of the vein primary Vp of the turbomachine, together with the outer base 27. In particular, the outer base 27 is extended radially by bulbs 29 ensuring the attachment of the sector 23 to an outer turbine casing. The inner base is itself extended radially by a core 30, having the shape of the inverted letter T, provided to ensure the fixing of the sector 23 to a corresponding portion of the fixed ferrule carrying elements made of abradable material.

In general, each blade 22 comprises an intrados wall 31 and an extrados wall 32 which are spaced from each other on either side of a median plane of the profile of the blade , identified by 33 in Figure 4. This median plane, extending halfway between the extrados and intrados walls, is also called the skeleton or camber surface, identified by 33 in Figure 4. These walls of intrados 31 and extrados 32 are joined at a first end of the skeleton 33 located in an upstream region AM of the blade by a leading edge 34 and at a second end of the skeleton 33 located in a downstream region AV of the blade by a trailing edge 36. The leading edge and the trailing edge are in particular curved walls.

Different geometric parameters of the nozzle blades influence the performance of the turbine. Among these parameters, we distinguish in particular the angle of incidence, the setting, the surface condition, or the aerodynamic profile used, the latter being defined as the contour of the blade in orthogonal section. Designed according to the direction of arrival of the primary flow Fp at the leading edge 34 and the desired direction of drawdown at the trailing edge 36, each blade 22 of the distributor sector extends between the two platforms 24, 26 in twisting. In particular, the blades 22 each have an aerodynamic profile which is hollow to ensure the redirection of the flow. This nature of profile is marked by a concave intrados wall 32 and a convex extrados wall 32, seen from the flow in which the blade 22 bathes.

The aerodynamic profile is in practice established on the basis of a compromise to ensure a level of efficiency sufficient for an admissible mechanical resistance, that is to say making it possible to guard against any failure. Usually, the blades of all the sectors forming a distributor have identical geometric parameters and adapted to the flow parameters at the stage considered, in particular according to the pressure of the flow which drops at each crossing of a stage extracting a amount of energy given.

Distributor sectoring is a design feature adopted by engine manufacturers because it limits manufacturing costs and extends the service life of distributors, the reuse of a defective distributor being made possible by replacing advantageously the sectors damaged in maintenance.

Nevertheless, it has been observed that this sectoring has the consequence of breaking the cyclic symmetry of the forces as observed in the case of a distributor formed in one piece over 360°, even if it is considered that each distributor comes from the assembly of identical and perfectly tuned sectors successively. In other words, the study of the stress maps shows a heterogeneity of the forces within each distributor sector: according to their location along the circumferential direction AY, the blades are not subjected to the same loads although identical to each other. others.

In this respect, the particularity of the invention lies in an optimization of the aerodynamic profile of the blades 22 of the distributor sectors 23 by defining the thickness of each just as needed, the thickness being defined as a distance measured between the walls of intrados and extrados 31 and 32 orthogonally to the skeleton 33. In other words, a distributor sector according to the invention comprises blades having an identical skeleton 33 and differing from one another by the quantity of material with which they are formed.

As understood, the sector 23 according to the invention redirects the primary flow from upstream to downstream in the same direction, the blades retaining an identical skeleton 33, but has an optimized mass.

Concretely, the thickness which differentiates at least two blades of a distributor sector according to the invention can also designate the relative thickness, defined as the ratio of the maximum thickness to the chord length, the average thickness, or even a local thickness measured at identical points of the skeleton of the two blades. Among all the local thickness values, we distinguish in particular the maximum thickness noted Em or a trailing edge thickness Ef, defined at the junction between the trailing edge and the intrados and extrados walls.

In particular, by comparing the mechanical behavior between a usual distributor with identical blades and formed in one piece, with its usual equivalent formed by an assembly of several sectors with identical blades, it appears that only the blades located at the circumferential ends of the sectors are stressed in tension-compression of a magnitude reaching that of the stresses observed for all the blades of the one-piece distributor. In other words, the so-called inner blades, this term designating the blades other than those at the circumferential end of the distributor sector, appear to be oversized according to this scenario with respect to the mechanical stresses to which they are subjected.

With regard to this comparison, the invention provides, according to one embodiment, to form the inner blades, identified by 22i in FIG. 3, comprising a thickness which is less than that of the blades at the circumferential end of the sector, denoted 22e. These blades at the circumferential end, called outer blades as opposed to the inner blades, have a thickness corresponding to that measured in the state of the art for the same turbine stage 16a, 16b, 16c, 16d. Advantageously, the thickness of the inner blades 22i results from a reduction of the order of two to five times the thickness of the outer blades 22e. By way of non-limiting example, the maximum thickness of the inner blades 22i has a value of 1mm when the maximum thickness of the outer blades 22e has a value of 3mm.

More precisely, in the case where the transiting force values are symmetrical with respect to a median plane of the distributor sector, the invention advantageously provides that the blades arranged symmetrically with respect to the median plane have the same thicknesses.

It should be noted that the invention is not limited to the described embodiment of the distributor sector, namely with the inner blades 22i having a thickness less than those at the end of the sector 22e. Concretely, the invention allows different morphologies as soon as the thickness of the blades is optimized to the exact need. This condition according to the invention results in the formation of a distributor sector of which at least two blades have different thicknesses, it being understood that the blades constituting the sector are stressed differently according to their relative position.

In general, the replacement of usual distributors by distributors formed from an assembly of sectors according to the invention ensures a gain in performance, it being understood that a reduction in the mass of the low pressure turbine 9 leads to a reduction in the specific consumption of the turbomachine. Also, it should be noted that a reduction in the thickness of the blades, in particular at the level of the trailing edge 36, tends to limit the drag as well as the phenomena of wakes which dissipate the energy of the primary flow Fp. The mobile wheels 18 downstream of the distributors 17 can thus extract a greater quantity of energy from the flow, which amounts to inflating the efficiency of the low pressure turbine 9.

The optimization of the thickness of each of the blades 22 has been explained as taking place with regard to the stresses of mechanical origin to which they are subject. In general, the thickness is one of the parameters also influencing the behavior of the distributor under stresses of different origins, such as for example the vibration damping of aeroelastic phenomena, the deformations under temperature gradient, or even the fatigue resistance. . In this respect, it must be understood that these different load cases, and in particular their interactions, must be considered in addition to the resistance under mechanical stresses when optimizing the thickness. In other words, after having identified, at the stage 16a, 16b, 16c, 16d considered, that certain blades of a usual sector with identical blades, are weakly constrained and therefore eligible for a reduction in thickness to achieve an optimized sector according to the invention, the new thickness should be fixed with regard to other dimensioning criteria in order to ensure the non-existence of a perverse effect leading a posteriori to additional re-design costs. In this respect, the invention advantageously provides for the thickness of the optimized blades to be fixed at least at 0.2 mm as regards the local thickness at the trailing edge Ef, and at least at 0.7 mm as regards the so-called maximum local thickness.

The invention makes it possible to increase the performance of the turbomachine equipped with such one-piece sectors with blades of optimized thickness, while maintaining control of manufacturing costs. Indeed, the foundry process, usually used, remains compatible by using keys to obtain the different desired shapes. Also, the use of additive manufacturing is also possible, and moreover advantageous for the case where the different stages 16a, 16b, 16c and 16d each have a distributor comprising sectors 23 with a single morphology, this process being particularly well suited for production in small series.

Finally, the sector with performance optimized by blade thickness differentiation has been described for an application of a distributor 17a, 17b, 17c, 17d of a low pressure turbine 9. However, it should be noted that the invention also remains applicable for the high pressure turbine 8, or else for the low and high pressure compressors 4, 6 whose bladed stator parts, designated as rectifiers, perform the same flow guiding function as the distributors of the low pressure turbine. Concretely, the invention relates to a bladed stator sector with improved performance.

Claims (9)

One-piece stator bladed sector (23) of a turbomachine (1) comprising first and second platforms (24; 26) extending in a circumferential direction (AY) and each intended to delimit a portion of a fluid flow path ( Vp), and blades (22) which each connect the first platform (24) to the second platform (26) while being spaced from each other in the circumferential direction (AY), the blades each comprising an intrados wall ( 31) and an extrados wall (32) extending halfway from a respective camber surface (33),
characterized in that the camber surfaces (33) of the blades (22) are identical, and in that at least two blades (22) have different thicknesses. Bladed sector according to Claim 1, comprising two blades (22) whose maximum thicknesses (Em) differ. Bladed sector according to Claim 1, comprising two blades having local thicknesses at the trailing edge (Ef) which differ. Bladed sector according to claim 1, comprising two blades having different average thicknesses. Bladed sector according to one of the preceding claims, in which the two blades (22e) each located at a circumferential end of the sector are thicker than at least one of the other blades (22i). Bladed sector according to Claim 5, in which the blades (22) arranged symmetrically with respect to a median plane of the distributor sector have the same thicknesses. Distributor (17) of turbine (9) including at least one bladed sector according to one of the preceding claims. Turbomachine turbine (9) comprising a distributor (17) according to claim 7. Turbomachine (1) comprising a turbine (9) according to claim 8.