TURBINE SHELL WITH OPTIMIZED COOLING AT THE OUTLET EDGE WITH UPWARD AND DOWNWARD CHANNELS AND INNER SIDE CAVES

Description

TECHNICAL FIELD

[0001] The invention relates to a turbine blade for an aircraft engine of the turbomachine type, such as for example a turbofan engine or a turbofan turboprop, and molding means for manufacturing such a blade. STATE OF PRIOR ART

[0002] In such an engine, outside air is admitted into an inlet sleeve to pass through a fan comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0003] The primary airflow is then compressed before entering a combustion chamber, after which it expands as it passes through a set of turbines before being expelled to the rear, generating thrust. The secondary airflow is then propelled directly to the rear by the fan to generate additional thrust.

[0004] The expansion in the turbines, which drives the compressor and blower, occurs at a high temperature because it takes place immediately after combustion. This turbine is therefore designed and sized to operate under severe conditions of temperature, pressure, and fluid flow.

[0005] Each turbine comprises a series of stages, each with a set of radially oriented blades regularly spaced around a central engine shaft. This central shaft carries the rotating elements of the turbine as well as the rotating elements of the compressor and blower.

[0006] In practical terms, the turbine blades that are subjected to the most severe conditions are those of the first expansion stages of this turbine, namely the stages closest to the combustion zone and which are commonly called high-pressure stages.

[0007] In general, increased performance requirements and evolving regulations are leading to the design of smaller engines operating in increasingly harsh environments. This implies increasing the durability and performance of high-pressure turbine blades, particularly with regard to their temperature resistance.

[0008] However, existing improvements in the materials and coatings of these blades are insufficient to allow them to withstand the high temperatures that can be reached by the flow downstream of the combustion chamber. This situation necessitates a reassessment of the blade cooling system to improve it so that they can withstand these new operating conditions.

[0009] This cooling is achieved by circulating fresh air inside the turbine blades. This air is drawn from the turbojet engine upstream of combustion, as described, for example, in US document 2008 / 0080979 A1. The air is admitted at the base of the blade, travels along an internal circuit to cool it, and is then expelled from the blade through perforations that pass through and are distributed across its surface. These perforations not only serve to expel the cooling air, but they also create a film of air on the outer surface of the blade that is cooler than the combustion air, thus further limiting the blade's temperature.

[0010] To increase cooling efficiency, the internal regions of the blade through which the cooling air circulates have artifices, that is to say internal reliefs which disturb the fluid flow of the cooling air to increase the heat transfer from the blade wall to this cooling air circulating in the internal ducts of the blade.

[0011] These cooling architectures are penalized by the fact that the length of the blade's internal circuit results in air being too strongly heated when it reaches the end of this circuit, so that its cooling efficiency is limited in the end-of-path regions, and in particular at the blade tip where, on the contrary, one seeks to obtain increased cooling efficiency.

[0012] The aim of the invention is to propose a blade structure that improves the cooling efficiency of this blade. SUMMARY OF THE INVENTION

[0013] For this purpose, the invention relates to a turbine blade as defined in claim 1.

[0014] With this arrangement, trailing edge cooling is significantly improved by the formation of a cooling film on the outer surface of the intrados wall upstream of the trailing edge. Thanks to the supply via the thermally insulated downstream duct, this air film also has a low temperature.

[0015] The invention also relates to a blade thus defined, in which each internal lateral cavity is provided with turbulence promoters and / or deflectors to increase heat exchange, and in which the upstream and downstream conduits have smooth walls to limit pressure losses.

[0016] The invention also relates to molding means configured for the manufacture of a blade thus defined, comprising cavities and a set of cores intended for the formation of internal channels and ramps, and internal cavities forming a screen.

[0017] The invention also relates to a turbomachine turbine comprising a blade as defined above.

[0018] The invention also relates to a turbomachine comprising a turbine as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] There figure 1 is a schematic view of a turbofan engine in longitudinal section; The figure 2 is a perspective view of a turbojet turbine blade shown on the figure 1 ; There figure 3 is a perspective view representing the hollow internal parts of a turbine blade according to a first embodiment not covered by the claims; The figure 4is a perspective view representing the hollow internal parts of a turbine blade according to a second embodiment not covered by the claims; The figure 5 is a perspective view representing the hollow internal parts of a turbine blade according to a third embodiment not covered by the claims; The figure 6 is a perspective view representing the hollow internal parts of a turbine blade according to a fourth embodiment which represents the invention. DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS

[0020] As seen on the figure 1 , a forward part of a turbofan engine 1 has an inlet sleeve 2 into which air is admitted before being sucked in by the blades of a fan 3. After passing through the fan region, the air splits into a central primary flow and a secondary flow which surrounds the primary flow.

[0021] The primary airflow then passes through a first compressor 4 located immediately after the blower 3 while the secondary flow is propelled backwards to directly generate additional thrust by being blown around the primary flow.

[0022] The primary flow then passes through a second compression stage 6, before reaching a chamber 7 where combustion takes place, after fuel injection and vaporization. After combustion, this primary flow expands in a high-pressure turbine 8 and then in a low-pressure turbine (not shown) to rotate the compression stages and the fan, before being expelled towards the rear of the engine to generate thrust.

[0023] Engine 1 and its components have a rotational shape around a longitudinal axis AX. In particular, it includes an external casing 9, also of a rotational shape, extending from the front of the engine, where it defines the air intake duct, to the rear, where it defines the duct through which the primary and secondary flows are discharged. The front and rear dimensions are considered relative to the direction of travel of the aircraft equipped with this turbojet engine. This casing 9 supports the rotating components located at the center of the engine, which include a rotating shaft carrying the fan blades, as well as the compressor stages and the turbine with its blades.

[0024] Such a dawn, which is marked by 11 on the figure 2 , comprises a foot P by which it is fixed to a rotating body (not shown), called a turbine disk, and a blade 12 carried by this foot P and constituting the aerodynamic part of this blade. As visible on the figure 2 , the blade 11 includes between the foot P and the blade 12 an intermediate region 13 called platform.

[0025] The assembly formed by the base P and the blade 12 is a single, hollow, cast piece with internal channels through which cooling air circulates. These internal channels are not visible in the figure 2 have intake openings on the underside 14 of the foot P through which these ducts are supplied with fresh air. The hollow wall of the blade 12 has through holes and slots through which the cooling air is expelled.

[0026] The blade 12 has a slightly twisted, left-handed shape with a roughly rectangular outline, resembling a parallelepiped. It comprises a base 16, by which it is connected to the foot P, and which extends approximately parallel to the axis of rotation AX. It also includes a leading edge 17 oriented radially with respect to the axis AX and located at the upstream AM of the blade, that is, the forward region of this blade, relative to the direction of travel of the engine it equips in operation. This blade also has a trailing edge 18 oriented approximately parallel to the leading edge 17, spaced from it along the axis AX, and located at the downstream AV or rear region of the blade. Finally, it includes a tip S, approximately parallel to the base 16 and spaced from it in a radial direction with respect to the axis AX.

[0027] The two main walls of this wing are its intrados wall 21, which is the wall visible in the figure 2, and its extrados wall, which is the opposite wall spaced from the intrados wall, and which is not visible in the figure 2 because it is masked by the lower surface wall 21. The lower and upper surfaces walls are joined at the leading edge 17, at the trailing edge 18, and also in the region of the apex S of this blade. These walls are spaced apart at the base 16 to allow the intake of cooling air into the internal region of the blade.

[0028] The leading edge 17 has a convex shape and is provided with a series of cooling holes 22 passing through the blade wall in this region. The trailing edge 18, on the other hand, has a tapered shape and includes a series of cooling slots 23. These slots 23 are short slots spaced apart and aligned along the end of the trailing edge 18.

[0029] Each slot 23 passes through the blade wall to draw cooling air from inside the blade and blow it onto the lower surface at the trailing edge. Additionally, the trailing edge is provided with external ribs oriented parallel to the AX axis to channel this cooling air.

[0030] During operation, the fluid in which this blade 11 is situated moves relative to it from the leading edge 17 to the trailing edge 18, along the lower surface 21 and the upper surface. The lower surface wall, which is subjected to significant heating during operation, has a series of holes 24 substantially parallel to the leading edge 17, located downstream of this leading edge, and another series of holes 26 substantially parallel to the trailing edge 18, located upstream of this trailing edge 18 and the slots 23 it contains. Both series of holes 24 and 26 thus extend along the span direction EV of the blade, which is the radial direction with respect to the axis AX.

[0031] The region of the summit S of the dawn 11 has, unlike the leading edge 17 and the trailing edge 18, a certain thickness, and this region of the summit also has a shape delimiting a hollow portion called bathtub-shaped.

[0032] More specifically, this vertex S has a closure wall that connects the intrados and extrados walls. This closure wall has an orientation that is generally perpendicular to the intrados and extrados walls and parallel to the AX axis, which corresponds to an orientation perpendicular to the wingspan direction EV. This closure wall, which is not visible on the figure 2 is located set back towards the AX axis relative to the free edge of the intrados wall and the free edge of the extrados wall, so that it constitutes, together with these edges, a hollow portion open in the opposite direction to the AX axis.

[0033] A series of additional holes 27 through the intrados wall is provided along the S-top to ensure significant cooling of this blade tip which is subject to significant stresses because it is the part with the highest velocity relative to the fluid.

[0034] The series of holes 27 extends parallel to the closing wall, and the blade also has holes not visible on the figure 2 which pass through the closing wall to open into the hollow portion called the bathtub which is at the top of the blade.

[0035] As mentioned above, such a blade is a hollow, one-piece component. It is manufactured by molding a metallic material such as titanium, using a set of cores to define the internal channels of its hollow portion, as well as rod sections to form its through holes. The cores, rods, and other components are removed once the molding operation is complete, typically using a chemical etching process capable of dissolving these elements without altering the molded material.

[0036] The following figures show internal regions of the blade according to the invention, represented therein by the shapes of the cores used to manufacture this blade. In other words, the shapes shown in relief in the following figures constitute representations of the hollow shapes of the blade according to the invention.

[0037] The idea behind the invention is to improve the cooling of the blade on the underside in the region of the trailing edge and its tip, this region being the first to deteriorate during the life of a blade.

[0038] This is achieved by means of a downstream duct which extends inside the blade while being thermally protected from the intrados wall, and by holes passing through the intrados wall towards this duct, upstream of the trailing edge, to form a cooling air film of the trailing edge on the side of the external face of the intrados.

[0039] This downstream conduit extends along the span direction from the base to the top of the blade to be supplied with air directly at the base and so that this air travels through the blade without being heated during its journey before being expelled through the cooling holes.

[0040] Dawn, according to a first embodiment which is identified by 31 in the figure 3 includes an upstream ramp 32 extending from the base of its blade to its apex S. This upstream ramp 32 cools the leading edge by means of through holes formed in the portion of wall corresponding to the leading edge.

[0041] This upstream ramp 32 is supplied in a calibrated manner by an upstream duct 33 which runs alongside this ramp 32, located downstream of it, and which collects cooling air at the base. The calibrated supply is ensured by regularly spaced calibrated passages 34 along the span direction EV of the blade, each connecting the upstream duct 33 to the upstream ramp 32.

[0042] Each passage 34 is calibrated to achieve approximately the desired airflow in the cooling holes located in the region of the ramp supplied by that passage. The desired airflow for a given hole or region is determined by the thermal stresses of the leading edge in the region cooled by that hole.

[0043] Another conduit, called the downstream conduit and identified by 36, runs alongside the upstream conduit, also extending in a substantially straight line from the base P of the blade to its top S. The intrados wall of the blade has a series of through holes 37 distributed in a straight line along the span direction, located at the level of the downstream region of the downstream conduit 36. Each through hole 37 thus connects the downstream conduit 36 ​​with the external face of the intrados wall upstream of the trailing edge to form a cooling film on the external face of this wall.

[0044] The intrados wall has in the trailing edge region a series of cooling slots 38, regularly spaced and extending in line with each other in the wingspan direction, to deliver cooling air to the trailing edge.

[0045] These slots are supplied by a downstream ramp 39 of the blade, which extends from the blade's base to the apex region S, situated between the downstream duct 36 and the blade's trailing edge. This downstream ramp 39 collects air through its lower end located in the blade's base and discharges this air to the cooling slots 38 that it supplies.

[0046] In addition, the blade according to the invention includes a thin internal lateral cavity 41 which runs along the intrados wall on the inner side of the blade to form a thermal screen protecting the upstream conduit 33 and the downstream conduit 36 ​​from the heat to which the intrados wall is subjected.

[0047] As seen on the figure 3, this internal cavity 41 has a thin thickness and a rectangular outline. It extends vertically, i.e. along the span direction, from the base of the blade to its top, and laterally it has a sufficient extent to form a screen covering the upstream and downstream conduits.

[0048] This lateral cavity, in which air circulation can be established, allows the upstream and downstream ducts to be thermally insulated from the intrados wall to reduce the heating of the air they carry.

[0049] Under these conditions, the cooling of the trailing edge of the blade, on the lower surface, is significantly improved by the presence of an external cooling air film which itself has a significant cooling efficiency because it is supplied with air by a thermally protected downstream duct and therefore has a low temperature.

[0050] According to a second embodiment corresponding to dawn 51 of the figure 4 The downstream duct, which is thermally protected to cool the intrados upstream of the trailing edge, also supplies fresh air to the trailing edge cooling slot that is closest to the top, so as to improve the cooling of this region.

[0051] In this second embodiment, the blade 51 also includes an upstream ramp 52 supplied in a calibrated manner by an upstream duct 53 through calibrated passages 54. It also includes a downstream duct 56, and its lower surface wall is provided with a series of through holes 57 distributed along the span direction EV in the downstream region of the duct 56 to connect this duct with the outer face of the lower surface wall upstream of the trailing edge. The air circulating in the downstream duct 56 is discharged through these holes 57, thus also forming a cooling film upstream of the trailing edge.

[0052] The intrados wall of this blade 51 also includes trailing edge cooling slots 58 supplied by a downstream ramp 59, which also extends from the foot P to a region below the apex S. It also includes a thin internal lateral cavity 61 which runs along the intrados wall to form a thermal screen protecting the upstream duct 53 and the downstream duct 56.

[0053] All these elements 52 to 61 are identical to the elements 32 to 41 of the blade 31 except that the downstream ramp 59 has a shorter length than the downstream ramp 39, and that the downstream conduit 56 feeds an upper cavity 63 which is located at the level of the apex S of the blade.

[0054] The upper cavity 63 is located in the extension of the end of the downstream ramp 59 and is supplied with air by the downstream duct so as to supply the trailing edge slot 64, which is closer to the top than the slots 58, with fresher air to further improve the cooling of the blade at the top of its trailing edge.

[0055] This upper cavity 63 extends along a vane closure wall that joins the lower and upper surfaces, oriented perpendicular to the wingspan direction EV. This upper cavity 63 is located downstream of the lower duct 56, bounded by the closure wall, the lower surface wall, and the upper surface wall, extending to the trailing edge. It is connected to the upper end of the lower duct 56 by an internal connecting channel 66.

[0056] Thanks to this upper cavity 63, the top of the trailing edge of the blade benefits from efficient cooling resulting from the supply in this area of ​​fresh air at a flow rate adjusted as needed.

[0057] According to a third embodiment which is represented on the figure 5 The upstream and downstream conduits, which are thermally insulated by the internal cavity along the intrados wall, are also thermally insulated by another internal cavity of the blade which runs along the extrados wall.

[0058] In this third embodiment which appears in the figure 5 , the auger 71 also includes an upstream ramp 72 supplied in a calibrated manner by an upstream conduit 73 by means of calibrated passages 74 each linking the upstream conduit to the upstream ramp.

[0059] It also includes a downstream duct 76 and through holes 77 in its lower surface wall, distributed along the wingspan direction EV in the downstream region of the duct 76 to connect this duct with the outer face of the lower surface wall upstream of the trailing edge. The air circulating in the downstream duct 76 is thus also evacuated through these holes 77, forming a cooling film upstream of the trailing edge which significantly improves the cooling of this trailing edge.

[0060] The lower surface wall also includes trailing edge cooling slots 78 supplied with air by a downstream ramp 79, this downstream ramp extending from the base P to the apex region S of the blade. The blade also includes a thin internal lateral cavity 81 that runs along the lower surface wall to form a thermal shield protecting the upstream duct 73 and the downstream duct 76 from the heat of the lower surface wall.

[0061] All these elements 72 to 81 are identical to elements 32 to 41 of blade 31 and to elements 52 to 61 of blade 51, except that the upstream duct 73 and the downstream duct 76 are thinner, and that in addition to the first lateral cavity 81 along the intrados, this blade 71 also has a second internal lateral cavity 82 along the extrados. The presence of two internal lateral cavities 81 and 82, which run along the intrados and extrados respectively, provides increased thermal insulation for the upstream duct 73 and the downstream duct 76.

[0062] The second internal lateral cavity 82 also has a small thickness, and it also extends from the foot P to the apex region S, presenting a generally rectangular outline, having a width sufficient to mask or cover the upstream conduit as well as the downstream conduit.

[0063] Thanks to these two internal lateral cavities, the air traveling through the upstream and downstream ducts is very slightly heated during its journey, which helps to further increase the efficiency of the cooling provided upstream of the trailing edge on the intrados side, and of the cooling provided at the leading edge.

[0064] According to a fourth embodiment representing the invention which is shown in the figure 6 The downstream duct, which is thermally protected to cool the intrados upstream of the trailing edge, also supplies fresh air to the trailing edge cooling slot that is closest to the top to improve the cooling of this region.

[0065] In this fourth embodiment which appears in the figure 6 , the dawn 91 also includes an upstream ramp 92 supplied in a calibrated manner by an upstream conduit 93 through calibrated passages 94.

[0066] It also includes a downstream duct 96, and its lower surface wall is provided with through holes 97 distributed along the wingspan direction EV in the downstream region of the duct 96 to connect this duct with the outer face of the lower surface wall upstream of the trailing edge. The air circulating in the downstream duct 96 is expelled through these holes 97, again to form a cooling film upstream of the trailing edge so as to significantly improve the cooling of this trailing edge.

[0067] The intrados wall also has trailing edge cooling slots 98 fed by a downstream ramp 99, which also extends from the foot P to the apex region S. This vane also has a thin internal lateral cavity 101 which runs along the intrados wall and another thin internal lateral cavity 102 which runs along the extrados wall, to form two thermal screens protecting the upstream duct 93 and the downstream duct 96.

[0068] All these elements 92 to 102 are identical to the elements 72 to 82 of the auger 71, except that the downstream ramp 99 has a shorter length than the downstream ramp 79, and that the downstream conduit 96 feeds an upper cavity 103 which is located at the level of the apex S of the auger.

[0069] The upper cavity 103 is located in the extension of the end of the downstream ramp 99 and is supplied with air by the downstream conduit 96 so as to supply the trailing edge slot 104 which is closest to the top with fresher air so as to increase the cooling of the blade at the top of its trailing edge.

[0070] This upper cavity 103 extends along a vane closure wall that joins the lower and upper surfaces, oriented perpendicular to the wingspan direction EV. This upper cavity 103 is located downstream of the lower duct 96, bounded by the closure wall, the lower surface wall, and the upper surface wall, extending to the trailing edge. It is connected to the upper end of the lower duct 96 by an internal connecting channel 106.

[0071] Thanks to this upper cavity 103, the top of the trailing edge of the blade benefits from efficient cooling resulting from the supply in this area of ​​fresh air at a flow rate adjusted as needed.

[0072] In general, the upper cavity of the second and fourth embodiments of the invention allows fresh cooling air to be supplied to the rear or downstream region of the blade tip to improve its cooling. This cavity thus supplies the trailing edge slot closest to the tip, and possibly the adjacent slots.

[0073] Additionally, holes through the lower surface wall at the level of the upper cavity, leading into this upper cavity, can be provided to improve the cooling of the outer face of the lower surface wall in the blade tip region. The upper cavity then supplies fresh air that passes through the lower surface wall to cool its outer face, in addition to supplying air to the slot closest to the tip, and also cooling the blade walls that define this upper cavity by thermal conduction.

[0074] Furthermore, holes through the blade walls, opening into internal lateral cavities that act as thermal shields, can be incorporated to ensure optimal airflow within these cavities. Each of these holes is advantageously positioned at a low-pressure area to promote air circulation. Each hole ensures that the air collected at the blade's base and channeled into a thermal shield cavity is then drawn out of the blade after passing through that cavity.

[0075] In the various embodiments, the cooling of the blade is further optimized by minimizing pressure losses in each internal duct to reduce heat exchange, and by providing turbulence promoters in each lateral cavity to increase heat exchange.

[0076] The lateral cavities thus have increased efficiency as a thermal screen because they absorb heat from the external walls they run alongside, and the air circulating in the internal ducts is subject to little pressure loss in order to circulate quickly and heat up as little as possible.

[0077] Internal ducts, such as the upstream and downstream ducts, have smooth inner walls to promote rapid circulation of cooling air while minimizing heat exchange between the air and the duct walls. Each lateral cavity is advantageously equipped with deflectors that promote airflow throughout the cavity. Furthermore, the internal surfaces of the cavity are fitted with baffles and / or bridges to create turbulence in the airflow, thereby promoting a high level of heat exchange between the air and the walls it passes along.

Claims

1. Blade (91) of a turbo engine turbine such as a turboprop or a turbo engine, with this blade (91) comprising a root (P), a vane borne by this root (P), with this vane comprising a leading edge and a trailing edge located downstream of the leading edge, with this vane comprising a pressure-side wall and a suction-side wall spaced laterally from one another and each one connecting the leading edge to the trailing edge, with this vane comprising: - at least one upstream duct (93) collecting cooling air at the root (P) in order to cool the leading edge by discharging this air by holes passing through the wall of the vane at its leading edge; - at least one downstream duct (96) separate from the upstream duct (93) and adjacent to the upstream duct (93) collecting cooling air at the root (P) in order to cool the trailing edge by discharging this air through holes (97) passing through the pressure-side wall upstream of the trailing edge; - an inner side cavity (102) running along the suction-side wall in order to form a heat shield that laterally has an extent that is sufficient to jointly insulate the upstream duct (93) and the downstream duct (96) from the suction-side wall; - cooling slots (98) spaced evenly and extending in line with each other and passing through its pressure-side wall along its trailing edge and a downstream ramp (99) for the supply of cooling air of these cooling slots (98) ; - an upper cavity (103) located at the tip (S) of the blade in order to supply the slot (104) of the trailing edge with air which is the closest to this tip (S), this upper cavity (63, 103) being separate from the downstream ramp (59, 99) and being supplied with air by the downstream duct (56, 96) ; - an upstream ramp (92) for supplying cooling holes of the leading edge, and the upstream duct (93) with a calibrated supply of the upstream ramp (92); characterized in that : - it comprises another inner side cavity running along the pressure-side wall in order to form a heat shield extending from the root to the tip (S) and that laterally has an extent that is sufficient to form a shield covering the upstream duct (93) and the downstream duct (96) from the pressure-side wall and to jointly insulate the adjacent upstream duct (93) and downstream duct (96) from the pressure side wall ; - and in that the upper cavity (103) is separate from the downstream ramp (99) and is supplied with air by the downstream duct (96).

2. Blade according to one of claims 1, in which each inner side cavity (101, 102) is provided with promoters of turbulence and / or deflectors in order to increase therein the heat exchanges, and in which the upstream duct (93) and the downstream duct (96) have smooth walls in order to limit load losses.

3. Means for moulding for the manufacture of a blade (91) according to one of claims 1 or 2, comprising imprints and a set of cores intended for the formation of inner ducts and ramps, and possibly inner cavities forming a shield.

4. Turbine de turbomachine comprising a blade (91) according to claim 1 or 2.

5. Turbomachine comprising a turbine as claimed in the preceding claim.