Turbine hollow blades

Abstract

A turbine hollow blade (11) comprises at least one blade (14) having lateral walls (15) intended to guide a flow in a flow path around the blade and fixed to a first platform (12) at a first longitudinal end of the blade (14), the blade (14) further comprising an internal cavity between the lateral walls (15) intended to allow a blade cooling fluid to pass through, wherein a fluid inlet opening (19) leads to the first platform (12), characterized in that a spiral surface network (18) fills at least a portion of the cavity, is arranged in the cavity to guide the cooling fluid, and is in contact with at least a portion of the lateral walls (15).

Description

Technical Field

[0001] The invention relates to turbine hollow blades, in particular turbine stator blades for high-pressure turbines, which are cooled by an air flow circulating in the inner cavity of these blades. Background Art

[0002] The prior art includes, inter alia, document US-A1-2014 / 0079540.

[0003] The high-pressure turbine stator of a turbine comprises, between an inner ring and an outer ring, an annular row of blades forming a duct through which the air leaving the combustion chamber passes. The structure of this annular row of blades is subjected to very high temperatures. Therefore, the blades of the turbine stator are usually hollow, and the walls of these blades bypassed by the air of the duct heated in the combustion chamber are cooled by the air flow circulating in the internal cavity. According to the prior art, an insert is placed in the cavity and is perforated to distribute cooling air towards the walls of the blades of the blades. The cooling air forms a jet through each hole of the insert, which jet makes it possible to cool the wall of the blade by impacting the internal face of the wall.

[0004] According to these methods, the turbine stator can be manufactured in a single piece or by assembling elements comprising one or more vanes, generally comprising blades having platforms forming segments of inner and outer rings that support these vanes. Generally, the manufacture of these elements is done by casting and machining. This manufacture becomes complicated and expensive, in particular due to the inserts.

[0005] Additive manufacturing offers an interesting alternative to produce the elements of turbine stators. Additive manufacturing of the parts is done in a known manner, for example by laser melting of successive layers of powder of the material forming the part. In particular, additive manufacturing makes it possible to consider more suitable shapes for the inserts to better distribute the cooling, or even to optimize the shape of the blades.

[0006] However, additive manufacturing does not allow the production of overhanging parts, in particular in the case of inserts. In order to produce overhanging parts, it is necessary to anticipate and provide supports capable of holding these overhanging parts when producing the layers that form the part that holds them. These supports must then be removed at the end of manufacturing.

[0007] More generally, for additive manufacturing, the parts referred to as overhangs are also the lower surfaces of the part relative to the direction of advance of the build layers, which make an angle of less than 30° with the plane of the build layers.

[0008] Both for inserts and for manufacturing blades with outer and inner ring segments supporting them, two types of configurations are commonly found, called suspended segments, which require the use of supports during machining. This makes additive manufacturing of turbine stators more complicated and may make it less applicable.

[0009] The object of the present invention is to propose a novel hollow blade which can be manufactured by additive manufacturing by overcoming the difficulty of supporting parts in the machining process.

[0010] A second object of the invention is to optimize the cooling of the blades by means of the air flow circulating in the cavity of the blades. Summary of the invention

[0011] To this end, the invention relates to a hollow turbine blade comprising at least one blade having lateral walls intended to guide a flow in a duct surrounding the blade and attached to a first platform at a first longitudinal end of the blade, the blade also comprising an internal cavity between the lateral walls intended to allow the passage of a fluid for cooling the blade, wherein an inlet opening for the fluid to enter leads to the first platform, characterized in that the array of spiral surfaces fills at least a portion of the cavity and is arranged to guide the cooling fluid in the cavity and in contact with at least a portion of the lateral walls.

[0012] A spiral surface array (a brief description of which is given below) is a surface that divides the space into two separate channels that allow fluid to pass through. Thus, the spiral surface array can be arranged to direct the fluid flowing inside towards the lateral walls of the blade, thereby promoting cooling.

[0013] In addition, the spiral surface maximizes the contact surface area with the fluid while forming a flow channel for the fluid without tightly closed bends. This has two complementary effects on the function of heat exchange with the cooling fluid. On the one hand, the spiral surface array made of conductive material can easily transfer the heat pumped by the spiral surface array to the fluid by conduction on the hot lateral walls in contact with it. On the other hand, the shape of the channel causes a low pressure drop, which minimizes the energy that must be used to circulate the cooling fluid through the exchanger.

[0014] Furthermore, due to its geometrical properties, the helical surface is self-supporting with respect to the manufacturing constraints of additive manufacturing. If some sections of the walls of the blade are in a "hanging" state at a given time during the manufacturing process, the fact that the array of helical surfaces is in contact with the walls of the blade at least in certain locations also makes it possible to support these walls during additive manufacturing.

[0015] Furthermore, the helical surface is formed by reproduction in three spatial dimensions of the basic cubic monomer unit. Advantageously, the cubic basic monomer unit may be oriented substantially parallel to the longitudinal direction.

[0016] Advantageously, the array of helical surfaces extends over the entire longitudinal extension of the blade and opens into an opening implemented in the first platform in order to direct the flow of the cooling fluid as soon as it reaches the blade.

[0017] Alternatively, the lateral walls of the blade may be attached to the second platform at the second longitudinal end, whereupon the array of helical surfaces may abut on the second platform between the lateral walls.

[0018] This is particularly advantageous for achieving support for arrays of blades and / or other elements during the manufacturing phase by additive methods.

[0019] Advantageously, since the helical surface array divides the space into two separate channels through which the cooling fluid can flow, the lateral wall of the blade forms part of the wall of said channel by intersecting the helical surface array.

[0020] This promotes heat exchange between the fluid and the walls of the blades.

[0021] The helical surface array may have a uniform structure across the cavity, but other alternative designs of the array are also contemplated.

[0022] For example, because the helical surface array is formed from substantially cubic monomeric units, the size of the monomeric units may vary with position in the cavity, such as decreasing from the center of the cavity toward the lateral walls.

[0023] Furthermore, the wall thickness of the helical surface may be variable, for example decreasing from the centre of the cavity towards the lateral walls.

[0024] These variants will depend on the choice of a person skilled in the art, for example in order to better direct the cooling fluid towards the hottest areas of the wall of the blade and / or in order to increase the mechanical strength of the array in the vane during operation.

[0025] The helical surface array may occupy all or nearly all of the cavity.

[0026] According to one embodiment, the bucket comprises an insert in the cavity, and the array of helical surfaces occupies the space between the insert and the lateral walls of the blade.

[0027] In this embodiment, the insert may be sized to cooperate with the spiral surface array to better distribute the cooling fluid toward the wall of the blade. Furthermore, the presence of the spiral acts as a support for the insert in a suspended position during the additive manufacturing process.

[0028] The vanes may comprise appendages such as bridges, spikes, fins, holes in contact with the helical surface array, in particular for reasons of mechanical strength of the array.

[0029] Advantageously, such a blade is formed from a single part obtained by additive manufacturing.

[0030] The present invention also relates to a bladed stator of a turbine, in particular a turbine stator of a high-pressure turbine, wherein the bladed stator comprises the blades as described above.

[0031] The present invention also relates to a turbine, comprising the above-mentioned bladed stator or wheel blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features and advantages of the present invention will become apparent from the following detailed description, for understanding of which reference is made to the accompanying drawings, in which:

[0033] Figure 1 is a schematic diagram of a cross section according to a plane perpendicular to the axis of symmetry of a segment of a turbine stator according to the prior art, in which no insert is present;

[0034] Figure 2 is with Figure 1 A schematic diagram of a section of a turbine stator according to the prior art corresponding to the schematic diagram of FIG. 1 , which shows the insert in a transparent manner in the axial direction;

[0035] Figure 3 is a schematic perspective view of a hollow blade according to the invention, showing in a transparent manner a gyroid surface arranged inside the blade;

[0036] Figure 4 and Figure 5 Two different views of the basic cubic monomer unit of the helix are shown;

[0037] Figure 6 schematically shows a cross section of a variant of a blade according to the invention; and

[0038] Figure 7 Another variant of a blade according to the invention is schematically shown, cut according to a transverse plane, without the presence of a helical surface to be arranged therein. DETAILED DESCRIPTION

[0039] Figure 1 and Figure 2An angular section of a conventionally manufactured turbine stator is shown. The blade comprises a hollow blade 1 made of a block having an outer ring 2 and an inner ring 3 defining a duct. At the connection with the outer ring 2, the wall of the blade of the blade extends into an air duct 4, which forms a passage for an internal cooling air flow. This air flow is discharged through vents 5 at the trailing edge. An insert 6 following the internal shape of the wall of the blade 1 guides the air arriving through the air duct 4 and distributes it towards the wall through holes 7 to ensure cooling. Here, the shape of the blade 1 is rather simple. Furthermore, an assembly of structures (studs 8, bridges 9 or strips 10) can be seen, which are arranged inside the wall to position and retain the insert 6.

[0040] Figure 3 A hollow turbine stator blade 11 according to the invention is shown, obtained by additive manufacturing, having an outer platform 12 and an inner platform 13 to which are connected walls 15 of blades 14. Depending on the method of manufacturing the turbine stator, the blade 11 may comprise one blade 14, the platforms 12 and 13 of which are intended to be assembled on the turbine stator, or one or more blades 14 connected by these platforms 12 and 13, which form segments of an outer ring element and an inner ring element.

[0041] Here, the longitudinal direction of the blade 14 corresponds substantially to the radial direction X relative to the symmetry axis Z of the turbine stator. The chord of the blade 14 follows a transverse direction lying in a plane defined by the axial direction Z and the tangential direction Y at the blade.

[0042] Here, the wall 15 of the blade 14 forms an inner cavity which opens into the outer platform and extends between the platform 12 and the platform 13 along the entire longitudinal extent of the blade 14. The profile of the blade 14 according to the cross-sectional plane has a curved shape. Furthermore, the blade 14 has an arcuate shape along the radial direction X. This shape is optimized for the aerodynamic performance of the turbine stator and in order to increase the efficiency of the high-pressure (HP) turbine to which it belongs.

[0043] The cross-sectional profile of the blade 14 is shaped so that the cavity widens near the leading edge 16 and narrows near the trailing edge 17. The helical surface 18 fills the internal cavity along the entire radial extent of the blade 14 between the platforms 12 and 13.

[0044] A spiral is a minimal surface without self-intersections, constructed by periodically reproducing in three dimensions the basic monomer units contained in a cube, such as Figure 4 and Figure 5The spiral is the only non-trivial integral part of the associated family of Schwarz P and D surfaces, with an associated angle of about 38.01°. A rigorous description of the spiral and Schwarz P and D surfaces can be found in the May 1974 document NASA TN D-5541 by scientist Alan Schoen. The spiral is drawn with high accuracy using the trigonometric approximation given by the following short equation Figure 4 and Figure 5 : The surface of the spiral is represented by :

[0045] [Formula 1]

[0046] sin x cos y + sin y cos z + sin z cos x = 0

[0047] The spiral divides the space into two opposing channels. Channels travel through the spiral maze in both directions, and when a channel crosses on one face of the cube, the channel emerges at an angle of 70.5 degrees relative to a given channel. Figure 3 and Figure 6 As can be more easily seen in FIG. 1 , the orifice of the channel along a cutting plane parallel to the sides of the basic monomer unit is very close to a circular shape.

[0048] The inclination of the walls of the spiral, at the intersection with the walls of the cube of the basic monomer unit, maintains an angle generally greater than 30°, which enables additive manufacturing by layer by layer starting from a plane parallel to the face of the cube of the basic monomer unit.

[0049] exist Figure 3 In the example of , the helical surface 18 is constructed by reproducing in a uniform manner a basic monolithic unit of the same size throughout the cavity of the blade 14. The helical surface 18 is in contact with the surface of the internal platform 13, which closes the cavity at its intersection with the wall 15 of the blade 14, and extends to the opening 19 of the cavity, situated in the external platform 12, for supplying cooling air.

[0050] Laterally, the helical surface 18 contacts the inner surface of the wall 15 of the blade 14 from the leading edge 16 to the area near the trailing edge 17. In practice, the helical surface 18 follows the chord of the blade 14 and ends at a point where the profile of the blade 14 becomes very thin. In the radial direction X, this defines a line 20 near the trailing edge 17.

[0051] In this region, substantially transversely oriented fins 21 connect the helical surface 18 to the wall 15 of the blade 14 .

[0052] exist Figure 3In the example of FIG. 1 , the helical surface 18 is dimensioned to perform multiple functions.

[0053] Firstly, the helical surface ensures the manufacturability of the blade manufactured by additive methods by making the blade 11 self-supporting during the manufacture of the successive layers. Firstly, as previously mentioned, the helical surface 18 itself can be additively manufactured due to its geometrical characteristics. Thus, this structure can be manufactured inside the blade 11 without requiring dedicated manufacturing supports that are difficult to remove when the blade is finished. In addition, if the blade is given a slightly complex shape, or if the blade 11 comprises a plurality of blades 14 distributed on a ring element, some parts of the wall 15 can have an inner surface in a suspended position with an excessive inclination relative to the plane of the successive manufacturing layers. The helical surface 18 then forms a support for such a wall section of the blades of the blade.

[0054] Secondly, the helical surface 18 forms a heat exchanger that guides the cooling fluid through the cavity. Figure 3 , the cooling fluid enters the cavity through an opening 19 implemented in the outer platform 12 and escapes through a vent (not shown) at the trailing edge 17. As briefly described, the spiral surface 18 divides the space of the cavity into two different slots. Each of these slots has an inlet at the opening 19 in the outer platform 12. The cooling air flow is thus divided into two parts and enters each slot through the inlet. This cooling air flow then follows a complex path in each slot along the entire longitudinal extension of the blade 14. As can be seen in Figure 3 As can be seen in FIG. 1 , the wall 15 of the blade 14 itself forms part of the wall of the channel by intersecting the helical surface 18. Since the helical surface 18 ends at a distance from the trailing edge 17, both channels have an outlet at the trailing edge 17. The cooling air is discharged through this outlet and is directed towards the vents of the trailing edge 17.

[0055] From the point of view of heat exchange performance, the spiral surface 18 has the first effect of directing the air flow towards the inner surface of the wall 15 of the blade 14. The air flow cools the wall by convection beside the wall 15. Secondly, the spiral surface 18 maximizes the exchange surface area with the cooling air flow. Preferably, the spiral surface 18 is made of a heat-conducting metal material similar to the material of the wall 15 of the blade 14. Therefore, the spiral surface 18 in contact with the wall 15 itself forms a heat sink, which pumps the heat from the wall 15 to discharge this heat into the cooling air flow.

[0056] From another point of view, the helical surface affects the performance in terms of pressure drop of the cooling air flow. To minimize the pressure drop, a person skilled in the art can exploit the ratio between the size of the basic monomer unit and the wall thickness of the helical surface 18 .

[0057] In addition, the design of the spiral surface 18 must take into account its mechanical strength in the blade 11 during operation. To this end, those skilled in the art will also adjust the ratio between the size of the basic monomer unit and the wall thickness of the spiral surface 18. Those skilled in the art will also define the connection fillet at the intersection with the wall 15 and design the processing shape for mechanical strength to ensure the durability of the spiral surface 18 installed in the blade 11. Figure 3 The fins 21 shown are part of these structures.

[0058] Variations of the embodiments may be considered in order to optimize the above mentioned properties or constraints.

[0059] Reference Figure 6 , the size of the monomer unit can expand along different directions of the space in the cavity. In this case, Figure 6 1 , the size of the single cells of the helical surface 18 'is larger in the center of the cavity and decreases as the wall 15 of the blade 14 is approached. The size of the single cells can be judged by the size of the nearly circular opening formed by the helical surface 18 'in the cross-sectional plane. In particular, this configuration makes it possible to define, for each of the two channels, a central channel of large diameter through which the cooling air flow can easily cross the blade in the radial direction X and then diffuse towards the wall 15 through the small single cells over the entire longitudinal extension of the blade. This makes it possible to better control the distribution of the cooling air along the longitudinal extension of the blade 14, so as to cool the areas exposed to the hottest air in the duct.

[0060] exist Figure 6 In the embodiment of the present invention, the wall thickness of the spiral surface also changes in a manner that decreases from the center toward the wall. Here, in the area 22 indicated by the dotted ring, the thickness around the large opening is the largest. The thickness of the spiral surface is adjusted taking into account the mechanical strength of the large monomer unit and the optimization of the heat exchange near the wall 15.

[0061] Reference Figure 7, the insert 23 is inserted into the cavity between the walls 15. In this case, a helical surface, not shown in the figures, fills the space defined between the inner surface of the wall 15 and the outer surface of the insert 23. Advantageously, the insert 23 is hollow and opens onto the outer platform 12. The insert is then equipped with openings (not shown) that pass through the wall of the insert along its longitudinal extension in the cavity. These openings open onto the channels of the helical surface. The insert 23 is then dimensioned so as to distribute an air flow over the longitudinal extension of the blades 14 that supplies the channels of the helix. The function of the insert 23 is then very similar to that of a monolithic unit of larger dimensions in the previous variant. It should also be noted that the presence of the helical surface enables the design of complex insert 23 shapes without adversely affecting the manufacturability by additive methods, since it will ensure support for the insert 23.

[0062] The examples shown are non-limiting. The invention encompasses other variations incorporating changes in the size and wall thickness of the monomer units of the helical surface and in the shape or function of any associated inserts.

Claims

1. A hollow turbine blade (11), comprising at least one blade (14), the blade having lateral walls (15) intended to guide a flow in a duct surrounding the blade, the lateral walls being attached to a first platform (12) at a first longitudinal end of the blade (14), the blade (14) further comprising an internal cavity between the lateral walls (15) intended to allow passage of a fluid for cooling the blade, wherein: an opening (19) for fluid entry leading to the first platform (12), characterized in that the array of helical surfaces fills at least a portion of the interior cavity and is arranged to guide cooling fluid in the interior cavity and in contact with at least a portion of the lateral wall (15), The spiral surface array divides the space into two separate channels through which cooling fluid can flow, and the lateral wall (15) of the blade (14) forms part of the wall of the channel by intersecting the spiral surface array. The helical surface array is formed from substantially cubic monomeric units whose dimensions vary with position within the interior cavity.

2. The hollow turbine blade (11) according to claim 1, characterized in that: The array of helical surfaces extends over the entire longitudinal extension of the blade (14) and leads to the opening (19) implemented in the first platform (12) to direct the flow of cooling fluid as soon as it reaches the blade (14).

3. The hollow turbine blade (11) according to claim 1 or 2, characterized in that: The lateral walls (15) of the blade (14) are attached to a second platform (13) at a second longitudinal end, and wherein the array of helical surfaces abuts against the second platform (13) between the lateral walls (15).

4. The hollow turbine blade (11) according to claim 1 or 2, characterized in that: The wall thickness of the helical surface array can vary.

5. The hollow turbine blade (11) according to claim 1 or 2, characterized in that: The turbine hollow bucket comprises an insert (23) in the internal cavity, and the helical surface array occupies the space between the insert (23) and the lateral wall (15) of the blade (14).

6. The hollow turbine blade (11) according to claim 4, characterized in that: The turbine hollow bucket is formed from a single component obtained by additive manufacturing.

7. The hollow turbine blade (11) according to claim 1 or 2, characterized in that: The turbine hollow blade (11) includes an appendage in contact with the spiral surface array.

8. The hollow turbine blade (11) according to claim 1 or 2, characterized in that: The hollow turbine blade (11) is formed from a single component obtained by additive manufacturing.

9. The hollow turbine blade (11) according to claim 1, characterized in that: The size of the monomer units decreases from the center of the internal cavity towards the lateral walls (15).

10. The hollow turbine blade (11) according to claim 4, characterized in that The wall thickness of the helical surface array decreases from the center of the internal cavity towards the lateral wall (15).

11. The hollow turbine blade (11) according to claim 7, characterized in that: The accessories are bridges, nails, fins, holes.

12. A bladed stator for a turbine, comprising the turbine hollow blade (11) according to any one of claims 1 to 11.

13. The bladed stator according to claim 12, characterized in that: The bladed stator is a high pressure turbine stator.

14. A turbine comprising a turbine hollow bucket (11) according to any one of claims 1 to 11 or comprising a bladed stator according to claim 12 or 13.

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