PIVOT AT THE POLE FOOT WITH COOLING MEANS

Abstract

The main object of the invention is a pivot (52) for a blade root (58) of a propeller blade (48) of a turbomachine (1) (32), characterized in that it includes means for cooling (100) the blade root (58) by interaction with a ventilation airflow.

Description

TECHNICAL FIELD The present invention relates to the field of turbomachinery, particularly to that of unfaired turbomachine propellers, and more specifically to the cooling of the components of these propellers, in particular the blade roots. It thus relates to a blade root pivot, a turbomachine propeller comprising such a pivot, and also the turbomachine comprising such a propeller. The invention applies to all types of land-based or aeronautical turbomachinery, and in particular to aircraft turbomachinery such as turbojets and turboprops. More specifically, the invention finds a privileged application in the field of aircraft turbomachinery whose receiver comprises a pair of unfaired, counter-rotating propellers; this type of turbomachine is also known as an "open rotor" or "propfan" turbomachine. Such a turbomachine may, for example, have a fan mounted directly on the power turbine and outside the nacelle, or driven by a geared power turbine. PREVIOUS STATE OF THE ART Figure 1 schematically represents a turbomachine 1 with a doublet of unfaired contra-rotating propellers, known as an "open rotor", according to a classic embodiment of the prior art, as known from patent application FR 2 941 494. In Figure 1, direction A corresponds to the longitudinal or axial direction, parallel to the longitudinal axis 2 of the turbomachine 1. Direction B corresponds to the radial direction of the turbomachine 1. Furthermore, arrow 4 schematically represents the main direction of gas flow through the turbomachine 1. The terms "upstream" and "downstream" used in the following description should be considered in relation to this gas flow direction 4. In the front part, the turbomachine 1 has an air inlet 6 which continues towards the rear by a nacelle 8, the latter comprising overall an outer skin 10 and an inner skin 12, both centered on the axis 2 and radially offset from each other. The inner skin 12 forms an external radial casing for a gas generator 14, comprising, conventionally from front to rear, a low-pressure compressor 16, a high-pressure compressor 18, a combustion chamber 20, a high-pressure turbine 22, and an intermediate-pressure turbine 24. The compressor 16 and the turbine 24 are mechanically connected by a shaft 26, forming Thus, a low-pressure body, while the compressor 18 and the turbine 22 are mechanically connected by a shaft 28, forming a higher-pressure body. Consequently, the gas generator 14 preferably has a conventional, so-called twin-body design. Downstream of the intermediate pressure turbine 24 is a receiver 30 with a doublet of unshod, counter-rotating propellers, driven in this example by free-running power turbines. Alternatively, a geared power turbine can be used. More specifically, this receiver 30 is located downstream of a fixed housing 42, itself arranged in the rear extension of the external radial housing 12 of the gas generator 14. Moreover, the housings 12 and 42 can be made in one piece. The fixed housing 42 then extends rearward, narrowing in the radial direction, to form a fixed shaft 57 centered on the axis 2, forming the fixed housing of the receiver 30. The receiver 30 first comprises a first rotating assembly 32a equipped with a first propeller 32, a first free power turbine 34 driving this propeller, and a first rotating structural device 33 located in the axial extension of the free turbine 34 towards the front, interposed between the first stage of this turbine and the fixed housing 42. The rotating structural device 33 generally takes the form of a plurality of arms spaced circumferentially from each other and extending radially. These arms are connected to the The first propeller 32 carries the outer turbine housing 49, which is itself connected to the propeller 32 by means of a flange or a plurality of clips 44, allowing the propeller 32 to be radially offset outwards. The clips 44 have an internal radial end integral with the outer housing 49, and an external radial end integral with a polygonal ring (not shown in Figure 1) supporting the blades 48. These blades 48 project radially outwards from an outer propeller housing or cowling 46, one of the features of which is that it is located in the aerodynamic aft continuity of the outer skin 10 of the nacelle. Similarly, the receiver 30 comprises a second rotating assembly 36a equipped with a second propeller 36, a second free-running power turbine 38 driving this propeller, and a second rotating structural device 37 located in the axial extension of the free-running turbine 38 towards the rear, situated behind the last stage of this turbine 38. The rotating structural device 37, which extends essentially radially, supports the second propeller 36 by being connected to it, in particular, by a flange or a plurality of clips 51 allowing the propeller 36 to be radially offset outwards. Here too, the clips 51 have an internal radial end integral with the rotating structural housing 37, and an external radial end integral with a polygonal ring (not shown in Figure 1) supporting the blades 55. These blades 55 project radially outwards from a outer casing or hood 54, which is in the rear aerodynamic continuity of the outer hood 46 of the first propeller 32. Furthermore, the first and second free turbines 34, 38 are nested within each other to form a counter-rotating turbine pair. The stages of the first turbine 34 are thus arranged alternately with the stages of the second turbine 38, in direction A. This pair can therefore also be considered a turbine with two counter-rotating rotors. For illustrative purposes, the free turbines 34, 38 have no direct mechanical connection with the rotating components of the gas generator 14; that is, they neither drive nor are driven by elements 16, 18, 22, 24. Only the gases from the primary stream escaping from the intermediate pressure turbine 24 therefore ensure the rotation of these free turbines 34, 38 forming the counter-rotating turbine pair. With reference now more specifically to figures 2 to 4, the design of the first propeller 32 is shown in more detail, it being understood that the second propeller 36 has an identical or similar design, and will therefore not be described further. As mentioned previously, the propeller 32 has a polygonal ring 47 that supports the blades 48, this ring 47 forming a hub of the propeller. It has a plurality of housings 50 spaced circumferentially from each other, these housings 50 being called radial housings. Each of them receives a pivot 52, a bearing 80 being interposed between this pivot 52 and its associated housing 50 forming a bore, as shown in figure 3. Each pivot 52 has a lower portion 52a located inside its associated housing. This lower portion 52a is substantially cylindrical and hollow, presenting a cross-section generally shaped like a U open radially inwards. Furthermore, the pivot 52 extends radially outwards with an upper portion 52b situated above the ring 47. This upper portion 52b has a groove 56, schematically shown in Figure 4, whose function is to retain the root 58 of the associated blade 48. Thus, the pivot 52 supports the blade 48 and allows its angle of attack to be adjusted by controlling the rotation of this same pivot 52 within its housing 50 in the polygonal ring 47. The propeller 32 also includes the outer cowling 46, shown only in Figures 1 and 3. The outer surface of this cowling is open to the outside air. In this regard, it is noted that each blade 48 is equipped with a platform 59 from which its aerodynamic portion 60 projects radially outwards. Each circular platform 59 is positioned within an opening provided through the cowling 46, so as to obtain substantially flush aerodynamic junctions. As is most clearly visible in Figure 3, a blade cavity 64 is provided, associated with the blade 48. This cavity is intended to isolate the blade root from the rest of the turbomachine 1, by particular of the primary vein passing radially inwards. The cavity 64 has been schematically identified on figure 3 by the dashed line referenced 64. It is indeed closed radially outwards by the platform 59 and the outer cover 46 forming aerodynamic fairing, but also closed upstream by one or more covers 66, closed downstream by one or more covers 68, and closed radially outwards by one or more covers 70, here a single cover 70 fixed to the flange or the aforementioned clips 44. It is noted that a blade root cavity can be provided for each blade, as schematically shown in Figure 5, with an internal cover 70 provided for each blade, making the cavities independent of each other. Alternatively, a single blade root cavity can be shared by all 48 blades of the propeller 32, the single internal cover 70 then taking the form of a crown. As a ventilation option, each cavity 64 can, for example, be supplied with outside air by a scoop 72 or similar (e.g., a simple orifice), located on the outer cover 46. This scoop can, in particular, be placed downstream, and the air passing through cavity 64 can then, for example, be extracted by an outlet (not shown) located further upstream. As it passes through cavity 64, the fresh outside air surrounds and cools, by means of ventilation, the elements located within this cavity 64. in particular foot 58 of the blade as has been schematically represented by arrow 53. Ventilation and cooling of the propeller components 32, and in particular the blade roots 58, are difficult to achieve, especially due to the pressure conditions at low Mach number. However, such ventilation and cooling are particularly important when the blades 48 are made of composite materials, which have reduced resistance to high temperatures compared to metallic materials. In the configuration shown in Figure 1, known as the "pusher" configuration, in which the unfaired propellers are located at the rear, downstream of the combustion chamber, these propellers are positioned directly above the primary flow where the hot gases can reach 500°C. It is therefore essential to provide specific ventilation to prevent overheating of the blade roots of these unfaired propellers. However, the proposed solution described above relies solely on the pressure difference between the downstream dynamic air intake formed by scoop 72 and the upstream static air outlet. It is therefore highly dependent on aircraft speed, which proves detrimental during certain phases such as idle and takeoff, where the airflow at the blade root may be insufficient for adequate cooling. Furthermore, this solution, known from prior art, has the disadvantage of not achieving The cooling and ventilation of the blade roots 58 is achieved only through the exterior of the pivots 52. In other words, the blade roots 58 are not cooled by direct contact with the ventilation airflow, but solely by conduction and / or convection mechanisms due to contact with parts that are themselves cooled by the ventilation flow. Consequently, the cooling of the blade roots 58 is not optimal. DESCRIPTION OF THE INVENTION The invention is thus intended to remedy at least partially the needs mentioned above and the drawbacks relating to the achievements of the prior art. The invention aims in particular to provide a solution to enable efficient ventilation and cooling of blade roots, especially those made of composite materials. The invention thus relates, according to one of its aspects, to a pivot for a blade root of a turbomachine propeller blade, characterized in that it includes means for cooling the blade root by interaction with a ventilation airflow. The airflow is in particular an outside airflow, specifically a cold outside airflow to allow for ventilation. Thanks to the invention, it may be possible to ventilate and cool the blade roots by allowing the ventilation airflow to circulate directly over the blade roots. The presence Cooling methods within the pivot can increase the heat exchange surface area between the pivot and the ventilation airflow. The invention can increase the pivot's heat transfer capacity tenfold without significantly altering it, particularly without changing its external geometry or mechanical characteristics. The pivot according to the invention may further comprise one or more of the following characteristics taken individually or in any possible technical combinations. Cooling devices may include cooling fins. The pivot may include at least 4, or even at least 6, or even at least 8, or more, cooling fins. The cooling fins can be located inside the pivot. In particular, the cooling fins can be distributed symmetrically inside the pivot. The cooling fins can extend in planes containing the pivot's axis of rotation. The pivot may comprise a substantially cylindrical and hollow lower portion with a generally U-shaped cross-section, and an upper portion with a groove for retaining the blade root. The cooling means may be located inside the lower portion. The means of cooling the pivot can be achieved in different ways, for example by conventional machining or by electro-erosion machining (also called EDM for "Electre Discharge Machining" in English). The choice, number, and dimensions of the cooling elements, particularly the cooling fins, can be determined based on the desired heat exchange surface area. However, they may be limited by the available space inside the pivot. The invention also relates, according to another of its aspects, to a propeller for a turbomachine comprising a plurality of blades and a blade support ring provided with housings each receiving a pivot carrying the foot of one of said blades, characterized in that it comprises a pivot as defined above. The propeller can in particular be an unfaired propeller. The pivot may be equipped with at least one counterweight system, each containing at least one internal airflow channel designed to contact the cooling elements. This internal airflow channel may cool the blade root supported by the pivot. It may also cool any other component requiring specific ventilation. Similarly, it may also expel hot air from the area to be ventilated. The internal channel formed in the counterweight system can capture and guide the airflow to the precise location where ventilation is required, namely at the blade roots. The inner channel may have an inner end opening onto the pivot and at least one of an airflow inlet and one airflow outlet. In particular, the inner channel may have an airflow inlet end and an inner end opening onto the pivot to cool the pivot. Alternatively, the inner channel may have an inner end opening onto the pivot, through which hot air enters from the pivot into the inner channel, and an outlet end for expelling the hot air. The inlet and / or outlet end may include means for inlet and / or outlet in the form of an orifice or scoop. Preferably, the inlet and / or outlet end may include a dynamic scoop for the inlet and / or outlet of the airflow. The pivot may include at least one communicating internal channel, one end of which opens at the blade root and the other end at an internal channel of the counterweight system. The communicating internal channel may allow airflow from the inner end of the internal channel to be introduced at the blade root, or to eject the airflow from the blade root towards the inner end of the internal channel. Alternatively, the pivot may not have a communicating internal channel. The groove in the pivot that secures the blade root may, for example, have at least one opening opposite an inner end of an internal channel of a counterweight system. The counterweight system may include a counterweight arm and a counterweight. The internal channel may be located in the counterweight arm and / or the counterweight. Preferably, the counterweight arm may contain the internal channel. The pivot may be equipped with at least one first counterweight system, having at least one first internal channel with an airflow inlet end and an internal end, and a second counterweight system, having at least one second internal channel with an airflow outlet end and an internal end. The pivot may include a first communicating internal channel, one end of which opens at the blade root and the other end at the internal end of the first internal channel, and a second communicating internal channel, one end of which opens at the blade root and the other end at the internal end of the second internal channel. The blades, in particular the blade roots, and / or said at least one counterweight system and / or the cooling means and / or the pivot may be made of composite materials. The counterweight arm can be made of at least two parts, including metallic ones. The internal channel can be partially formed, for example by machining, in each of these two parts. Alternatively, the counterweight arm can be made in one piece. The counterweight arm, particularly if made of composite material such as woven or laminated, can incorporate the internal channel, especially during manufacturing. The invention also relates, according to another of its aspects, to a turbomachine characterized in that it comprises a pivot as defined above or a propeller as defined above. The propeller can, for example, be located upstream or downstream of a combustion chamber of the turbomachine. The turbomachine can preferably be of the "open rotor" type. In particular, the turbomachine can comprise a pair of unfaired, counter-rotating propellers, each of the two propellers being a propeller as defined previously. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood upon reading the detailed description that follows, along with non-limiting examples of its implementation. as well as to the examination of the schematic and partial figures of the attached drawing, on which: Figure 1 represents a schematic longitudinal half-sectional view of an aircraft turbomachine comprising a receiver with a doublet of contra-rotating propellers, according to a classical design of the prior art, - Figure 2 shows a partial perspective view of one of the counter-rotating propellers of the turbomachine shown in Figure 1, - Figure 3 shows a partial cross-sectional view in more detail of the propeller blade support ring and surrounding elements, - Figure 4 shows an exploded perspective view of a blade and its associated pivot, Figure 5 shows a perspective view of a prior art propeller, equipped with several blade root cavities, - Figure 6 shows, in perspective, an example of a pivot according to the invention, and Figure 7 illustrates, in cross-section and partially, another example of a pivot according to the invention comprising counterweight systems. Throughout these figures, identical references may designate identical or analogous elements. Furthermore, the different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible. DETAILED PRESENTATION SPECIAL METHODS OF IMPLEMENTATION Two examples of embodiments of the invention relating to an aircraft turbomachine with a doublet of unfaired contra-rotating propellers will be described below with reference to Figures 6 and 7, although these examples are not limiting. Figures 6 and 7 are schematic and partial, and reference should be made to Figures 1 to 5 described above for the visualization of elements not shown in Figures 6 and 7. With reference to figure 6, a first example of pivot 52 conforming to the invention has been shown. The pivot 52 has a lower part 52a substantially cylindrical and hollow having a cross-section generally U-shaped, and an upper part 52b having a groove 56 to retain the blade foot 58. According to the invention, the pivot 52 includes cooling means 100. More specifically, the cooling means 100 comprise cooling fins 101 distributed symmetrically inside the pivot 52 (in the bore of the pivot 52), in particular inside the lower part 52a. The pivot 52 comprises, for example, at least six cooling fins 101. Advantageously, the cooling fins 101 can interact with a ventilation airflow for cooling the blade root 58. The airflow, in contact with the fins of cooling 101, allows these to increase the air / metal heat exchange surface, thus improving heat exchange between the airflow and the pivot 52. Figure 7 shows another example of a pivot 52 according to the invention associated with counterweight systems 90 and 91 allowing the external airflow to be routed to the contact of the blade root 58 and the cooling fins 101. More specifically, the pivot 52 is equipped with a first counterweight system 90 and a second counterweight system 91. Each of the counterweight systems 90 and 91 is provided with an internal channel 93 and 96 for the flow of an air stream. The first counterweight system 90 comprises a counterweight arm 90a and a counterweight 90b at the end of the arm 90a opposite the pivot 52. Similarly, the second counterweight system 91 comprises a counterweight arm 91a and a counterweight 91b at the end of the arm 91a opposite the pivot 52. The counterweight arms 90a and 91a respectively comprise the internal channels 93 and 96. The inner channel 93 has an inner end 97a which opens onto the pivot 52 and an airflow inlet end 97b. Furthermore, the inner channel 96 has an inner end 98a which opens onto the pivot 52 and an ejection end 98b of the airflow. The inlet end 97b and the ejection end 98b each have a removable dynamic scoop for the passage of airflow. In addition, the pivot 52 has a first communicating internal channel 99a, one end of which opens at the blade root 58 and the other end opens at the internal channel 93 of the first counterweight system 90. Similarly, the pivot 52 has a second communicating internal channel 99b, one end of which opens at the blade root 58 and the other end opens at the internal channel 96 of the second counterweight system 91. Thus, the airflow is captured by the dynamic scoop at the inlet end 97b of the first counterweight arm 90a as indicated by arrow F1, and then flows inside the internal channel 93 and the communicating internal channel 99a to cool the blade root 58 as indicated by arrow F2. At this point, the airflow also communicates with the cooling fins 101 of the pivot 52 as indicated by arrow F4, which increases ventilation around the pivot 52 and allows fresh air to pass over almost the entire blade root 58 to cool it. The resulting hot flow can then flow into the communicating internal channel 99b and the internal channel 96 to be ejected at the discharge end 98b of the second counterweight arm 91b as indicated by arrow F3, either externally or towards the engine nacelle. In the above, the blades 48 and / or the counterweight systems 90 and 91 and / or the cooling fins 101 and / or the pivot 52 can be made of composite material. Of course, the invention is not limited to the examples of implementation that have just been described. Various modifications can be made to it by a person skilled in the art. 5 The phrase "containing a" must be understood as being synonymous with "containing at least one", unless otherwise specified.

Claims

DEMANDS 1. Pivot (52) of a propeller blade (48) (3; 5 characterized in that it cools (100) from interaction with a flux means of cooling (cooling (101) if 10 (52) . for a blade foot (58) ï) of turbomachine (1), includes means of blade root (58) by ventilation air, the 100) comprising fins sweating inside the pivot 2. Pivot (52) according to claim 1, characterized in that the cooling fins (101) are distributed symmetrically inside 15 of the pivot (52).

3. Pivot (52) according to any one of the preceding claims, characterized in that it comprises a lower part (52a) substantially cylindrical and hollow having a cross-section in the general shape of a U, and an upper part (52b) having a groove (56) for retaining the blade foot (58), the cooling means (100) being located inside the lower part (52a).

25.

4. Propeller (32) for turbomachinery. (1) comprising a plurality of blades (48) and a blade support ring (47) provided with housings (50) each receiving a pivot (52) carrying the foot (58) 30 of one of said blades (48), characterized in that it comprises a pivot (52) according to any one of the preceding claims.

5. Propeller according to claim 4, characterized in that the pivot (52) is equipped with at least one counterweight system (90, 91) provided with at least one internal channel (93, 96) for the flow of the air intended to come into contact with the cooling means (100).

6. Propeller according to claim 5, characterized in that said at least one internal channel (93, 96) has an internal end (97a, 98a) which opens onto the pivot (52) and at least one of an inlet end (97b) and an outlet end (98b) of the airflow, comprising in particular means for inlet and / or outlet in the form of an orifice or a scoop.

7. Propeller according to any one of claims 4 to 6, characterized in that the blades (48) and / or said at least one counterweight system (90, 91) and / or the cooling means (100) and / or the pivot (52) are made of composite material.

8. Turbomachine (1) characterized in that it comprises a pivot (52) according to any one of claims 1 to 3 or a propeller (32) according to any one of claims 4 to 7.

9. Turbomachine according to claim 8, characterized in that it comprises a propeller (32) according to any one of claims 4 to 7, and in that said propeller (32) is located downstream of a combustion chamber (20) of said turbomachine, said turbomachine preferably comprising a pair of unfaired, counter-rotating propellers, each of the two <x hélices (32, 36) étant une hélice selon l'une any of claims 4 to 7.

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