Abstract:
A retaining ring presenting, on its periphery, a plurality of radial bores, each of the bores being able to receive a blade root. The retaining ring also includes at least one first radial opening traversed by a compression tube and at least one second radial opening, the at least first radial opening and the at least second radial opening being separated from each other by at least one of the bores of the plurality of radial bores. The ventilation device finds a particularly interesting application in the field of turbine engines including a pusher open rotor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to French Patent Application No. 1056021, filed Jul. 22, 2010, the entire content of which is incorporated herein by reference in its entirety. 
     FIELD 
     The invention relates to a retaining ring with at least one blade root. The invention more particularly applies to a retaining ring comprising a ventilation system for at least one of the blade roots of a pusher open rotor equipping a turbine engine. 
     BACKGROUND 
     Conventionally, a pusher open rotor is especially constituted of two propellers, each comprising a retaining ring equipped with a plurality of blades. As represented in  FIG. 1 , a propeller  1  is generally formed by a retaining ring  2  (typically in titanium or composite material) comprising a plurality of radial bores  3  uniformly distributed at its periphery. Each radial bore  3  is adapted to receive a root  4  of a blade  5  equipped with a pivot  6  (also called blade root pivot). 
     However, a configuration such as described above is likely to present some disadvantages. In fact, propeller  1  constitutes a disk with a relatively high mass that must resist the centrifugal forces applied to it when the propeller shaft rotates. Furthermore, such mass is increased by the metal blade roots  4 . In addition, this high mass generates, for the airplane, high fuel consumption. 
     To reduce this high mass, it is possible to use blades  5  in which the root  4  is in a composite material. In fact, the utilization of such material enables the mass of the assembly formed by the retaining ring  2  and blades  5  to be reduced. 
     However, airplanes equipped with a pusher open rotor  7  whose propellers  1  are situated at the rear present a primary stream  9  in which gases that may exceed 500 degrees circulate, this primary stream  9  being situated below and near the blade  5  roots  4  (see  FIG. 2 ). Consequently, roots  4  of blade  5  are subjected to high temperatures. 
     A disadvantage resides in the fact that composite materials don&#39;t resist high temperatures very well and deteriorate rapidly. Therefore, the lifetime of a blade comprising a root in a composite material is limited. 
     SUMMARY 
     More particularly, an aspect of the invention is to remedy the disadvantages of the aforementioned devices. In this context, an embodiment of the invention aims to propose a device reducing the weight of a propeller while ensuring a long lifetime for the blades that the propeller comprises. In general, an embodiment of the invention aims to cool the lower part of the blade roots of a propeller. 
     An aspect of the invention applies to a retaining ring comprising at least one blade root presenting, on its periphery, a plurality of radial bores, each of said bores being able to receive a blade root. 
     In addition, said retaining ring comprises at least one first radial opening traversed by a compression tube and at least one second radial opening, said at least first radial opening and said at least second radial opening being separated from each other by at least one of the bores of said plurality of radial bores. 
     For the rest of the description, radial opening is understood to refer to an opening whose axis of revolution is substantially coaxial with one of the radius of the retaining ring. 
     For the rest of the description, tube is understood to refer to a hollow cylinder of linear section, the inner diameter of the tube may be constant. 
     For the rest of the description, compression vortex is understood to refer to a rotation movement of the air situated in the tube around the axis of revolution of the tube. This movement enables the air situated below the compression tube to be aspirated. 
     Thanks to this feature, the air may circulate through the second opening to pass from the outside of the ring to the inside of the ring and then through the first opening to pass from the inside of the ring to the outside of the ring. 
     When the retaining ring is equipped with a plurality of blades, each blade root forms an integral part with a pivot and is positioned in one of said radial bores. When the propulsion assembly rotates, each blade compresses and expels the air at its root. This compressed air circulates in the region of the upper part of the blade root and then part of this compressed air passes, via the second opening, in the region of the lower part of the blade root. Thanks to this air system, the upper part and the lower part of the blade root are cooled. 
     Preferably, in an embodiment, said first radial opening is positioned upstream from said retaining ring and said second radial opening is positioned downstream from said retaining ring. 
     According to an advantageous embodiment of the retaining ring, the retaining ring comprises a mask covering at least one blade root, said mask presenting a cavity to allow a flow to circulate under said retaining ring. 
     Thanks to this mask, when the retaining ring is rotating, a compression vortex is created in the radial tube that traverses the first upstream radial opening. This compression vortex aspirates the air found in the lower cavity, formed by the mask and the inner surface of the retaining ring, to then expel it to the outside. The vortex also enables the exterior air to be aspirated via said at least one second downstream radial opening. In other words, the compression vortex enables the air from the outside to circulate under the blade root. 
     In addition to the principal characteristics that have just been mentioned in the previous paragraph, the retaining ring equipped with at least one blade root according to an embodiment of the invention may present one or more of the additional characteristics below, considered individually or according to all technically feasible combinations:
         said mask forms an internal ring with a U-shaped section, the upper part of said U-shaped section being covered by said retaining ring;   each blade root is covered by a mask;   for each radial bore, a first opening and a second opening are placed opposite each other, said first opening and said second opening are separated from each other by said radial bore;   said second opening of said retaining ring comprises a diameter greater than the diameter of said first opening, this characteristic limiting the pressure drops through said first opening;   said tube comprises a length greater than the length of said second opening, this difference in length being necessary for creating said compression vortex.       

     Another aspect of the invention is a turbine engine comprising a pusher open rotor, this turbine engine comprising a retaining ring according to at least one of the aforementioned embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will clearly emerge from the description given below, for indicative and in no way limiting purposes, with reference to the attached figures, among which: 
         FIG. 1  represents a propeller comprising a retaining ring equipped with blades according to the prior art; 
         FIG. 2  represents part of a pusher open rotor comprising two propellers similar to that represented in  FIG. 1 ; 
         FIG. 3  represents a partial view of a propeller equipped with a retaining ring according to an embodiment of the invention; 
         FIG. 4  represents a possible assembly between a blade root and a blade root pivot; 
         FIG. 5  represents an enlargement of part of the retaining ring according to an embodiment of the invention represented in  FIG. 3 ; 
         FIGS. 6A and 6B  illustrate two possible embodiments of masks enabling ventilation of the lower part of the blade roots. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     For reasons of clarity, only the elements useful for understanding the invention have been represented, without respecting the scale and schematic manner. In addition, the same elements found on different figures bear identical references. 
       FIGS. 1 and 2  were described previously with reference to the prior art. 
       FIG. 3  schematically illustrates a partial view of a propeller  10  comprising a retaining ring  14  equipped with at least one blade  13  root  12 . Propeller  10  is suitable for being rotated via a propeller shaft (not represented) at a high-speed, for example on a pusher open rotor turbine engine of an airplane. Propeller  10  comprises a retaining ring  14  equipped with a plurality of radial bores  15 , each comprising a blade  13  root  12 . 
     In a non-limiting manner, a blade  13  may present a dovetail type root  12  (see  FIG. 4 ), in this embodiment the blade  13  root  12  is mounted in a groove R that comprises a blade  13  root  12  pivot  16 . 
     In the example represented in  FIGS. 3 and 5 , each blade  13  root  12  is integral with a pivot  16 , each assembly (pivot  16  and root  12 ) being inserted in a radial bore  15 . More particularly,  FIG. 5  represents an enlargement of part of the partial view illustrated in  FIG. 3 . 
     The retaining ring  14  according to an embodiment of the invention represented in  FIG. 5  comprises:
         a radial bore  15 ,   a first upstream radial opening  17 ,   a second downstream radial opening  18 ,   a mask  19 ,   A tube  20 .       

     For the rest of the description:
         upstream UP is understood to refer to the end of the retaining ring  14  situated in the region of the leading edge of blades  13 ;   downstream DO is understood to refer to the end of the retaining ring  14  situated in the region of the trailing edge of blades  13 .       

     When blade  13  is subjected to a rotation movement, it compresses the air and expels part of this air at its root  12 . 
     At the same time, when retaining ring  14  is rotated, a compression vortex is created within tube  20  situated in the region of the first opening  17 . This compression vortex enables the air found below the blade  13  root  12  to be aspirated, and then forces the exterior air (i.e., at the periphery of the retaining ring  14 ) situated at the region of blade  13  root  12 , through the second opening  18  to be found between mask  19  and retaining ring  14 . This air is then expelled to the outside via compression tube  20 . 
     In other words, the first opening  17  traversed by the compression tube  20 , the second opening  18  and the mask  19  enable a ventilation system to be created to cool blade  13  root  12  and pivot  16 . More particularly, the ventilation system thus created enables the lower part of blade  13  root  12  to be cooled. 
     In a particularly interesting manner, tube  20  situated in the region of the first upstream opening  17  presents a length (or height) greater than the length (or height) of the second downstream opening  18 , the length (or height) of the second opening  18  being formed by the thickness of retaining ring  14 . This feature ensures that the compression of the compression vortex, generated by tube  20 , is greater than the pressure release generated by the second opening  18 . 
     Tube  20  may, for example, present a length on the order of 14 cm and an inner diameter on the order of 1 cm. 
     In summary, thanks to an embodiment of the invention, an upper air system As and a lower air system Ai is generated to cool blade  13  root  12 . 
     The upper air system As is generated by blade  13  itself that compresses part of the downstream air to direct it to its root  12 . 
     Lower air system Ai is generated by tube  20  in the region of the first opening  17  that, when retaining ring  14  is subjected to a rotation movement, creates a compression vortex enabling, on the one hand, the air situated in the lower cavity formed by mask  19  to be aspirated and, on the other hand, to force, via the second opening  18 , part of the air found at blade  13  root  12  to penetrate into mask  19 . 
     In an embodiment represented in  FIG. 6A , a mask  19  is placed under each blade  13  root  12 . Each mask  19  may be made secured with the retaining ring  14  by any means such as, for example, screwing or welding. 
     In another embodiment represented in  FIG. 6B , a single mask  19  is used to protect the blade  13  roots  12  assembly. In this embodiment, mask  19  is formed by a ring presenting a U-shaped section whose top is covered by the retaining ring  14 . It is therefore possible to use a single first opening  17  and a single second opening  18  to create a ventilation system enabling the blade  13  roots  12  assembly to be ventilated. 
     In a particularly interesting manner, each radial bore  15  is surrounded by a first opening  17  comprising a tube  20  and a second opening  18 . This embodiment generates a ventilation system for each root  12  that is inserted in a radial bore  15 . It follows that each root  12  is efficiently cooled. 
     According to a non-illustrated embodiment, mask  19  has a U-shaped section as represented in  FIG. 6B , mask  19  being divided into several cavities so as to create a cavity for each blade  13  root  12 . Each part of retaining ring  14  covering a cavity comprises a radial bore  15 , a first opening  17  and a second opening  18 . This modality enables a single mask  19  to be used for the blade  13  root  12  assembly mounted on the retaining ring  14  and promotes an optimal air flow under each blade  13  root  12 . 
     Embodiments of the invention were more particularly described in the context of turbine engines comprising a pusher open rotor. However, it is understood that the retaining ring according to embodiments of the invention applies to any type of propeller that airplanes comprise or, more generally, any type of propeller operating in a high-temperature environment. 
     The person skilled in the art is capable of carrying out different variations of the retaining ring  14  according to embodiments of the invention, particularly as relates to the shape of the mask  19  and the number of first openings  17  and/or second openings  18 , without necessarily departing from the scope of the abovementioned invention.