Patent Publication Number: US-2023160319-A1

Title: Turbine housing cooling device

Description:
FIELD OF THE INVENTION 
     This invention relates to a turbine casing of a turbomachine, in particular of a turbojet engine or of an airplane turbo-propeller engine. 
     PRIOR ART 
     The casing of a low-pressure turbine is a master part for carrying the low-pressure turbine and guaranteeing the correct transmission of the expansion energy to the low-pressure turbine, to the low-pressure compressor and to the fan. This casing mainly supports the ring segments which surround each wheel and the nozzle guide vane using casing hooks. These hooks are subjected to high temperatures and steep thermal gradients. Specifically, outside the casing, the air has a temperature level in the order of a few hundred degrees, while the flow path air, which can reach over 1000° C., circulates inside the casing. It is therefore advantageous to cool the casing hooks. 
     In addition, to guarantee high efficiency of the turbomachine, it is advisable to limit the air flow not passing through the wheels of the different stages, i.e. to limit the leaks between the radially outer ends of the blades and the abradable material ring. To do this, it is advisable to control the clearance at the level of this interface, this clearance being dependent on the temperature of the casing, and particularly of the areas of said casing including the hooks or flanges supporting the ring. 
     In order to control the aforementioned clearance and avoid any premature degradation of the different fixed and movable parts of the turbine, it is thus necessary to make provision for effective cooling means which can easily be incorporated into the environment of the turbomachine. 
     The attached  FIG.  1    shows a cooling device of a casing according to the patent application FR3021700, in the name of the Applicant. This figure shows a cooling device  21  of a casing  18  of a low-pressure turbine  7 , this turbine  7  being itself visible only in  FIGS.  3  and  4   . This cooling device includes collector boxes  22 , each collector box  22  forming a channel extending axially. The device  21  also includes tubes  23  extending circumferentially on either side of the collector boxes  22 . Said tubes  23 , also known as manifolds, are formed by curved lines of circular section, each tube  23  extending circumferentially around the casing, for example around an angle of approximately 90 degrees. Each tube  23  includes an air inlet opening into the channel of the corresponding collector box  22  and a closed distal end. Each tube  23  further includes a cylindrical wall provided with air exhaust holes turned toward the casing  18 , such that the cooling air can enter into the collector boxes  22  then in the tubes  23 , before opening via the exhaust holes facing the casing  18 , in such a way as to cool it. This is in particular known as impingement cooling since air impinges on the casing  18 . 
     Furthermore, although this is not visible in  FIG.  1   , the casing  18  comprises on its radially inner face, at least one annular hook which makes it possible to attach fixed vanes or sealing ring segments. The aforementioned airjet impingement cooling technique does not however make it possible to cool correctly these hooks. It would therefore be desirable to improve the cooling of the casing skin in such a way as to improve the cooling of the hooks over their whole length and thus improve the thermal resistance at the hook tip. 
     Also known is the document EP1847687, which makes provision for a device for cooling a turbine casing of a turbomachine. The attached  FIGS.  2 ,  2   a  and  2   b    show such a cooling device. The latter uses a part of the air intended for the cooling of the nozzle guide vane upstream of the turbine to cool the hooks  70 ,  72  and a lock  74  allowing the attachment of the ring segments  34 . Thus, in this document, a supply chamber  48  supplies air to the inner cavities  46  of the vanes of the nozzle guide vane using cylindrical tubes  54 . Openings  80 ,  82 ,  90  are made in such a way as to connect the inner cavities  46  of the vanes to the annular housing space  76  in which the attaching hooks  70 ,  72  are located. More precisely, openings are made
     either in the plates  64  enclosing the inner cavity of each vane and in the downstream outer rim  42  of the outer wall  38  of the nozzle guide vane as shown in  FIGS.  2  and  2   a   ;   or in the outer annular rim  42  of the nozzle guide vane and in the annular tab  44  of this outer rim  42  of the nozzle guide vane, as is shown in  FIG.  2   b   .   

     However, in both cases, the air used to cool the hooks is relatively warm due to the convective exchanges with the radially outer platform  38  of the nozzle guide vane. Furthermore, the ducts that bring the cooling air from the inside of the vanes to the hooks are relatively long, which means that the air undergoes additional heat exchanges in these ducts. 
     Finally, from the documents EP 0 892 153, GB 2 103 718, EP 1 205 637 and US 2014/030066 devices are known for cooling a casing equipped on its radially inner face with ring segment attaching hooks. However, all these devices comprise a collector duct intended to convey the cooling air, which is separate from the casing bearing the hooks. The cooling is done via air exhaust holes, drilled through the collector duct and oriented in the direction of said casing. Such impingement cooling is not enough to effectively cool the hooks. 
     There is therefore a need to improve the cooling techniques of the prior art. 
     SUMMARY OF THE INVENTION 
     One aim of the invention is to make provision for better cooling of the turbomachine casing hooks than the solutions of the prior art described above. 
     Provision is hence made according to a first aspect of the invention, for a turbomachine turbine casing, said casing extending around an axis, comprising an annular wall and a cooling device, the wall being provided with at least one casing hook which extends in radial protrusion from the inside of the wall, each hook being configured to allow the mounting, on the casing, of ring segments disposed circumferentially end to end around the axis, and wherein the cooling device comprises at least one collector duct intended to convey the cooling air which extends circumferentially around the wall, each collector duct having a cooling air inlet and outlet. 
     In accordance with the invention each collector duct and the wall have a common portion which delimits said collector duct and from which a corresponding hook extends. 
     In other words, the wall from which the hook extends constitutes a portion of the wall of the collector duct intended for conveying the cooling air. 
     This configuration makes it possible to cool a greater part of the outer surface of said casing than that which can be cooled with the devices of the prior art, and thus to increase the lifetime of the casing. 
     Advantageously, the turbine casing also comprises one or more of the following features:
     the cooling device comprises two axially adjacent collector ducts separated by a separating wall.   each collector duct is in fluid communication with a ventilation circuit which extends in the corresponding hook.   each ventilation circuit extends in the greater axial part of the axial extent of the corresponding hook.   each ventilation circuit extends circumferentially in the corresponding hook.   the inlet of each collector duct is connected to a supply tube for conveying air into the collector duct.   each ventilation circuit opens mainly radially into the corresponding collector duct via an inlet channel.   each ventilation circuit opens onto an outer surface of the cooling device via an outlet channel.   the inlet channel and/or the outlet channel extends plumb with the corresponding hook.   the inlet channel and the outlet channel extend at a first and second circumferential position of the corresponding hook, the first and second circumferential position of said corresponding hook being intended to coincide with the circumferentially opposite ends of a ring segment intended to be suspended on the corresponding hook.   

     The proposed cooling device allows a better cooling of the casing hook over its entire length, an increase in the lifetime of the hook by limiting thermal gradients over the length of the hook, and by limiting tangential thermal gradients. 
     In addition, the circulation of air over sectors which extend circumferentially makes it possible to cool the hook ends better and to reduce angular thermal distortion. 
     Furthermore, the casing collector system makes it possible to homogenize the inlet cooling temperature of the casing. 
     In addition, by comparison with the prior art, the proposed cooling device makes it possible to draw off a lower bleed flow rate to provide the same function of thermal protection of the casing. 
     Also, the proposed cooling device can be easily incorporated into models of engine composed of a casing with hooks. 
     According to a second aspect, the invention makes provision for a turbomachine including a turbine, and a turbine casing according to one of the preceding features. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       Other features, aims and advantages of the invention will become apparent from the following description, which is purely illustrative and non-limiting, and which must be read facing the appended drawings wherein: 
         FIG.  1    described previously is a perspective view of a cooling device of the prior art; 
         FIG.  2    described previously is a section view of a cooling device of the prior art; 
         FIG.  2   a    described previously is a magnified section view of the device of  FIG.  2   ; 
         FIG.  2   b    described previously is a magnified section view of another cooling device of the prior art; 
         FIG.  3    is an axial section view of a bypass turbojet engine of the prior art. 
         FIG.  4    is an axial section view of a part of the turbojet engine of the prior art, in particular illustrating the low-pressure turbine, 
         FIG.  5    is a perspective view of a turbomachine casing cooling device according to an embodiment of the invention; and 
         FIG.  6    is a detail view of the turbomachine casing cooling device of  FIG.  5   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  3    shows a twin spool bypass turbomachine 1. The axis of the turbomachine bears the reference X and corresponds to the axis of rotation of the rotating parts. In the following text, the terms axial and radial are defined with respect to the axis X. 
     The turbomachine  1  includes, from upstream to downstream in the direction of flow of the gas, a fan  2 , a low-pressure compressor  3 , a high-pressure compressor  4 , a combustion chamber  5 , a high-pressure turbine  6  and a low-pressure turbine  7 . 
     The air coming from the fan  2  is divided into a primary flow  8  flowing in a primary annular flow path  9 , and a secondary flow  10  flowing through a secondary annular flow path  11  surrounding the first annular flow path  9 . The low-pressure compressor  3 , the high-pressure compressor4, the combustion chambers, the high-pressure turbine  6  and the low-pressure turbine  7  are fashioned in the primary flow path  9 . 
     The rotor of the high-pressure turbine  6  and the rotor of the high-pressure compressor  4  are rotationally coupled by way of a first shaft  12  in such a way as to form a high-pressure spool. 
     The rotor of the low-pressure turbine  7  and the rotor of the low-pressure compressor  3  are rotationally coupled by way of a second shaft  13 , in such a way as to form a low-pressure spool, the fan  2  being able to be connected directly to the rotor of the low-pressure compressor  3  or by way of an epicyclic gear train for example. 
     As can be seen more clearly in  FIG.  4   , the low-pressure turbine  7  in particular includes different successive stages including wheels  14  and fixed parts. The wheel includes a disc  15 , at the level of which vanes  16  are mounted. The ends of the vanes  16  are surrounded by a fixed ring  17  made of abradable material, said ring  17  being attached to the casing  18  of the turbine. Nozzle guide vanes  19  are located upstream of the wheels  14 . The nozzle guide vanes  19  and the rings  17  are mounted on the casing by way of flanges or hooks  20  extending from the radially inner surface of the casing  18 . This casing  18  mainly supports the ring segments which surround each wheel  14  and the nozzle guide vane  19 , using circumferential hooks  20  attached to the casing. 
     With reference to  FIGS.  5  and  6   , the illustration shows a cooling device  100  of a turbine casing  130 , such as a low-pressure turbine for a turbomachine  1 , according to an embodiment of the invention. 
     This cooling device  100  is incorporated into the casing  130 . 
     The casing  130  extends around the longitudinal axis X of the turbomachine, which is also that of the turbine. 
     The casing  130  comprises, over a radial wall, an outer surface  131  and an inner surface  132 . 
     The casing  130  further comprises a plurality of hooks  120  radially protruding inward with respect to its inner surface  132 , the hooks  120  allowing, as previously described, the attachment of vanes of stator blading (nozzle guide vane) of the low-pressure turbine and sealing ring segments comprising an abradable element which is intended to be arranged radially facing the blades of the rotor. 
     Advantageously, the hooks  120  extend continuously over the circumference of the inner surface  132  in such a way as to form an annular manifold, in several positions axially offset from the casing  130 . 
     It is necessary to protect the casing  130  from excessive heating to preserve the integrity of the elements of the casing  130  but also for another role, which is that of the control of the radial clearance between the blades of the turbine and the casing  130  surrounding it. Specifically, the changes in the temperature of the casing  130  cause a variation in the clearance between the blades and the casing because of the thermal expansion of the casing  130 . 
     The reduction of the clearance between the tips of the blades and the casing  130  is a determining element for the performance of the turbomachine since the lower the radial clearances, the lower the flow rate bypassing the blades and the better the efficiency of the turbine. 
     Controlling the clearances thus avoids the turbine losing performance. In the engine, it is of prime importance to control the clearances between the blade tips and a peripheral envelope. The radial displacement of this annular envelope being dependent on the expansion of the casing  130 , the control of the temperature of at least a part of this casing  130  with fresh air is therefore essential. 
     As these hooks  120  are the portions of the casing  130  which directly determine the clearances at the blade ends, it is useful for the cooling device  100  to make provision for means for cooling these hooks  120 . 
     With this aim, the device  100  includes a plurality of collector ducts  110  extending circumferentially all around the casing  130  substantially over the entire periphery, i.e. substantially at 360°. In the exemplary embodiment shown in  FIGS.  5  and  6   , these collector ducts  110  are two in number. 
     Each collector duct  110  surrounds the casing on respective circumference parts of the casing  130 . As indicated the hooks  120  are disposed on the circumference of the inner surface  132  of the casing  130 , over several axially separate stages. Advantageously, each collector  110  is disposed in such a way as to extend over a circumferential segment including a stage of hooks  120 . 
     Typically for a low-pressure turbine, the cooling device  100  includes a plurality of collector ducts  110  disposed on as many stages of hooks  120  of the casing  130 . 
     Each collector duct  110  is connected to a supply duct  140 . Said supply duct  140  is mainly radial and opens onto the outer surface of the cooling device  100 . The supply duct  140  is configured to draw off cool air from a bleed point; it is usually from a point of the secondary flow path of the gas of the machine, of which a part of the flow is drawn off, in a manner known to the prior art. Each collector duct  110  is thus connected to a pressurized air supply source for conveying air into said duct  110 . 
     In the illustrated embodiment, a collector duct  110  includes an outer wall  111  (radially outer) and an inner wall  112  (radially inner), and two side walls  113  disposed on either side of the outer  111  and inner walls  112 . Two axially adjacent collector ducts  110  can be separated by a separating wall consisting of one of the side walls  113  common to the two adjacent collector ducts  110 . 
     The outer wall  111  includes a hole for connecting the collector duct  110  to the supply duct  140 . Provision could be made for the connection to the pressurized air supply source on any wall of the collector  110  except for the inner wall  112 . 
     The outer  111  and inner  112  walls are concentric, the collector duct  110  being able to have a trapezoidal cross section. 
     Advantageously, the inner wall  112  is configured to fit the shape of a circumferential segment of the casing  130 , such that the inner wall  112  constitutes a part of the outer surface (skin) of the casing  130 . In other words, each collector duct  110  and the wall  112  equipped with at least one hook  120  have a common portion  150 , as can be seen in  FIG.  5   . This configuration makes it possible to cool a greater part of the outer surface of said casing  130  than that which can be cooled with the devices of the prior art and thus to increase the lifetime of the casing  130 . 
     Advantageously, the collector duct  110  is made of a single part and can be obtained by an additive manufacturing process, such as laser melting. 
     As illustrated in more detail on  FIG.  6   , unlike the prior art, at least one hook  120  is not of solid section but includes at least one ventilation circuit  121  including an inlet channel  122 , an outlet channel  124 , and an inner longitudinal channel  123  extending over the circumferential length of the hook  120  between the inlet channel  122  and the outlet channel  124 . 
     The inlet channel  122  is used to connect the longitudinal channel  123  with the inside of the collector duct  110 . Preferably, the inlet channel  122  is plumb with the hook  120 . 
     The outlet channel  124  makes it possible to connect the longitudinal channel  123  with the outside of the casing  130  and of the collector duct  110 , by a passage  115  passing through the collector duct  110  and opening onto the surface of the outer wall  111 . Preferably, the outlet channel  124  is plumb with the hook  120 . 
     Advantageously, the outlet channel  124  is used to connect the longitudinal channel  123  to a point of the turbomachine  1 , where the pressure is lower than the pressure of the bleed point. Preferably, the discharge point is in the core. 
     As described previously, the hooks  120  are configured to support ring segments. Preferably, the hooks  120  comprise one inlet channel  122  and one outlet channel  124  per ring segment. The inlet channel  122  and the outlet channel  124  being advantageously disposed at a first and a second circumferential position of the hook  120  corresponding to the circumferentially opposite ends of a ring segment positioned in the hook  120 . Thus, the circumferential length of the longitudinal channel  123  is equivalent to approximately the circumferential length of one ring segment. 
     Typically for a low-pressure turbine, a casing  130  hook  120  is configured to support  20  to  30  ring segments. Thus for one circumferential segment of the casing  130  including one stage of hooks  120 , the cooling device  100  will include a corresponding number of ventilation circuits  121 , i.e.  20  to  30  following one another circumferentially. 
     Preferably, within one and the same hook  120 , for two successive ventilation circuits  121 , the outlet channel  124  of a first ventilation circuit  121  is joined to the inlet channel  122  of a second ventilation circuit  121 . 
     Advantageously, unlike the prior art in which the hooks are cooled by impingement jet devices, the cooling device  100  makes it possible to use a pressurized air source and to make it circulate inside the casing  130  hooks  120  in such a way as to increase the cooling capacity by pumping cooling air. 
     In addition, the circulation of air over sections extending circumferentially makes it possible to better cool the hook ends and to reduce angular thermal distortion. 
     The cooling device  100  therefore allows a better cooling of the casing  130  hook  120  over its whole length, an increase in the lifetime of the hook by limiting the thermal gradients over the length of the hook  120 , and by limiting the tangential thermal gradients. 
     Furthermore, the system of collector ducts  110  of the casing  130  makes it possible to homogenize the cooling inlet temperature of the casing  130 . 
     In addition, by comparison with the prior art, the cooling device  100  makes it possible to draw off less bleed flow to perform the same function of thermal protection of the casing. 
     Also, the cooling device  100  can be easily incorporated into models of engines comprising a casing with hooks. 
     Naturally the invention is not limited to the embodiments described with reference to the figures and variants could be envisioned without departing from the scope of the invention. The collector duct could thus have other geometries.