FR2910525A1 - METHOD FOR PREVENTING REFLUX AND FORMING A COOLING LAYER IN A PROFILE ELEMENT - Google Patents

Abstract

The present invention relates to a method for preventing reflux and forming a cooling layer in a shaped member (60) by creating release regions at an inlet (96) of a cooling slot and circulating the cooling fluid in the cooling slot (45).

Description

B 07-4246 EN Company called: GENERAL ELECTRIC COMPANY Process to prevent

  a reflux and form a cooling layer in a profiled element Invention of: ZAUSNER Jack Raul WALKER David James Manning Robert Francis Priority of a patent application filed in the United States of America December 21, 2006 under the number 11 / 643.415 2910525 BACKGROUND OF THE INVENTION The invention relates to a method for preventing reflux and forming a cooling layer in a shaped member. More specifically, the invention relates to a method for preventing reflux and forming a cooling layer in which release regions are formed at the inlet of a cooling slot. Gas turbine engines extract energy from a stream of hot combustion gases that follow a flow path defined by the turbine. A typical turbine engine comprises at least one stage of rotating turbine blades and a stage of fixed blades spaced from the turbine blades. Each stage of the turbine includes a plurality of circumferentially spaced, radially outwardly spaced blades or turbine members of a hub or disk so that a portion of each turbine blade is extends over the flow path and comes into contact with the flow of combustion gas along the flow path. In practice, turbine engines comprise multiple stages of blades and vanes. During engine operation, it is necessary to cool the turbine blades and blades to improve their ability to withstand prolonged exposure to hot flue gases. Cooling of the fins is frequently done by creating a cooling film along the fin. To develop the desired cooling film, the turbine blades comprise one or more rows of cooling air supply holes distributed along their span, called film forming holes, and these holes are positioned along the surface. of the fin. The film forming holes pass through the walls of the profiled member to establish fluid communication between a cooling fluid flowing in the fin and the hot combustion gases outside. In addition, the fin comprises a plurality of cooling slots spaced along the trailing edge of the fin. The slots are formed inside the fin and have exit ports spaced along the trailing edge of the fin. During engine operation, fluid or cooling air is typically supplied to the fin by a compressor upstream of the finned compressor. The cooling air circulates inside the fin, including the slots, and exits the fin through the film forming holes and outlets. The cooling air exits the holes and cooling slots in the form of a series of individual jets. The air escaping from the slots 5 and holes is intended to form the cooling film along the surface of the fin. A conventional shaped member illustrated in Figure 2 provides an example of a turbine blade 70 of the prior art. As shown in Fig. 2, the fin 70 includes a leading edge 71, a trailing edge 72, and a plurality of parallel cooling slots 75 at the trailing edge of the fin. In the prior art fin 70, each of the cooling slots is associated with an axially extending slot reference line 80. Each slot has an inlet 62 and an outlet 63. The outlet is at the trailing edge of the fin. The inlet and the outlet are substantially at the same radial position along the radial length of the fin.

For simplicity, the reference lines 80 are not shown for all the slots in FIG. 2, but the reference lines, however, apply to all the cooling slots 75. Each of the cooling slots is parallel to its cooling line. respective reference 80. Film cooling is an effective means of controlling the temperature of profiled surfaces, but in practice cooling films are difficult to effectively create. A disadvantage associated with the conventional parallel orientation of the cooling slots is that the fin is subject to reflux of the combustion gases into the cooling slots. Reflux occurs when the static pressure of the cooling air is not greater than the static pressure of the combustion gases flowing along the flow path. When reflux occurs, the flue gases pass through the cooling holes and enter the cooling slots. To overcome the sensitivity to reflux in conventional fins, the cooling air out of the slots and holes at a higher pressure. As a result of this relatively high pressure, the cooling air exits the cooling slots at a rate which prevents the cooling air from adhering effectively to the surface and edges of the shaped member. As a result, the desired cooling film does not form on the fin. On the contrary, the cooling air mixes directly with the combustion gases and is carried with them. As a result, a portion of the aerodynamic surface of the fin immediately downstream of each cooling hole or slot is exposed to the combustion gases and is not protected by a cooling film. In addition, each of the cooling air jets can locally shut off the flue gas flow and bifurcate it into a pair of tiny vortex swirling in opposite directions. The flue gas enters the exposed portion of the shaped member and can cause irreparable damage to the shaped member. The intense heat of the flowing gases can damage a shaped element quickly and irreparably. There is therefore a need to promote the efficient formation of a cooling film along the surface of a cooling slotted profile member.

According to the invention there is provided a method for preventing reflux and forming a cooling layer in a shaped member, said profiled member comprising a leading edge, a trailing edge, a fin tip at a first end. of the fin and a fin root at a second end of the fin, the tip and root being separated by a certain radial distance, a cooling duct extending between the leading and trailing edges and at least one cooling slot having an inlet end in fluid receiving communication with the cooling duct and an outlet end near the trailing edge. The inlet and the outlet of said slot are in different radial positions in the profiled element. According to the method, a cooling fluid is circulated in a first direction in said cooling duct to a cooling slot, the cooling fluid is circulated in a second direction in said cooling duct to the cooling slot, forms a release region near the inlet of the cooling slot and circulates the cooling fluid in said cooling slot and out of the slot to form a layer at the trailing edge of the shaped member .

The present invention makes it possible to obtain a better cooling of a profiled element. This improvement is achieved by metering the air flow rate into a plurality of inclined cooling slots. In addition, instead of drilling cooling slots in a shaped member, cooling slots 5 can be molded into a shaped member and thereby reduce manufacturing costs and increase the beneficial variability of the cooling slots upon their creation. The invention will be better understood on studying the following description, illustrated by the appended drawings in which the same numbers identify corresponding elements and in which: FIG. 1 is a schematic representation of a gas turbine; Fig. 2 is a sectional view of a prior art turbine blade comprising a conventional configuration of cooling slots; Fig. 3 is a sectional view of a turbine fin comprising an arrangement of cooling slots according to an embodiment of the present invention; Figure 4 is a sectional view of a turbine blade comprising another embodiment of the invention; and FIG. 5 is an enlarged detailed view of a portion of FIG. 3. FIG. 1 is a schematic representation of an example of a gas turbine engine 10. The engine 10 comprises a fan 12, a central engine 13, a high pressure compressor 14 and a combustion chamber 16. The engine 10 also comprises a high pressure turbine 18, a low pressure turbine 20 and a booster 22. The fan 12 comprises a set of fan blades 24 which extend radially outwardly from a rotor disk 26. The engine 10 has an inlet side 27 through which air enters the engine and an exhaust side 29 through which air exits the engine. In one embodiment, the gas turbine engine is a GE90-115B of the General Electric Company. The fan 12 and the turbine 20 are coupled by a shaft 31. The compressor 14 and the turbine 18 are coupled by a shaft 33. In use, air passes axially through the fan 12 in a direction which is substantially parallel to a central axis 34 extending through the engine 10. Compressed air is supplied primarily to the combustion chamber 16 by the high pressure compressor 14. Most of the highly compressed air is supplied to the chamber A flow of air (not shown in FIG. 1) from the combustion chamber 16 drives the turbines 18 and 20, and the turbine 20 drives the blower 12 through the shaft 31. The high pressure turbine 18 comprises a fin stage or profiled elements 60. FIG. 3 shows in more detail a fin or profiled element 60. The profiled element may also be a blade. The fin 60 includes a leading edge 74 and a trailing edge 76 opposite the leading edge. The fin also includes a radially opposed fin tip 81 and root 79. The tip and the root are separated by a certain radial distance. The fin is coupled to the rotor (not shown) at the root. The air circulating in the gas turbine engine along the flow path crosses the fin 60 in an axial direction from the leading edge 74 to the trailing edge 76. Compressed cooling air enters the vane through openings at the leading edge 74 of the vane and also through inlet ducts 77. The cooling air flowing in the ducts 77 flows radially outwardly in the direction of the vane. As the inlet ducts extend towards the end 81, they combine into a single cooling duct 91. The cooling duct extends in a serpentine inside the duct 81. fin. The fin 60 shown in FIG. 3 comprises two inlets, but it will be understood that the fin 60 may comprise any suitable number of inlet ducts 77. Arrows in FIG. 3 generally represent the direction of flow. cooling air within the fin 60. A plurality of blades 92 spaced from each other are positioned in the cooling duct 91 between the inlet ducts 77 and the end 81. The blades are oriented substantially parallel to each other. Each blade has a first end 94 and a second end 95. The first end 94 of each blade is positioned closer to the root 79 than the second end 95 of the same blade. For each blade, the second blade end 95 is positioned closer to the tip 81 than the first blade end 94. The vanes are attached to the wall defining a portion of the cooling duct 91 at the edge thereof. leakage of the fin. The blades are oriented at an angle with respect to an axis 99 extending substantially axially. Each blade is oriented relative to the axis 99 at an angle that is less than ninety degrees. By orienting the vanes in this manner, the first and second ends of each vane are in different radial positions and the cooling air is directed more efficiently to the cooling slots 45. As shown in FIG. The fin 60 comprises a plurality of cooling slots 45. The cooling slots are oriented substantially in parallel. In the illustrated embodiment of the invention, the fin 60 comprises seven slots, but it will be appreciated that the slots 45 may be provided in any suitable number. Each slot has an inlet 96 and an outlet 97. The outlets 97 are at the trailing edge 76 of the fin 60. The slots are formed in the fin near the trailing edge. The inlet is in fluid communication with the cooling duct 91, and the cooling air in the cooling duct 91 enters the cooling slot through the inlet 96. The slots 45 of the fin 60 have a dimension radial substantially constant, and the radial dimension may be a diameter, for example. For each cooling slot, the outlet 97 is positioned closer to the root 79 than the slot inlet 96. For each slot, the slot inlet 96 is positioned closer to the fin tip 81 than the outlet. Because of the positioning of the inlet and the outlet of each cooling slot at different radial positions along the fin, the profiled element creates a cooling film more efficiently along the fin. . More specifically, the shaped member 60 more effectively forms a cooling film 25 along the trailing edge 76 of the fin. FIG. 4 shows a fin 61 according to another embodiment, which comprises slots 48 similar to the slots 45. The slots 48 comprise an inlet 106 and an outlet 107. Like the slots 45, the inlet and the outlet of each Slot 48 is at different radial positions along the fin, with each inlet 106 positioned closer to the tip 81 than the outlet 107. The outlet 107 is positioned more near the root 79 than the inlet. 106. The radial dimensions of the inputs 106 and outputs 107 are not the same. As shown in Fig. 4, the input has a smaller radial dimension than the output. The radial dimension may be, for example, a diameter, the diameter of the inlet 106 then being smaller than the diameter of the outlet 107.

The fin 61 includes conduits 77, 91, a leading edge 74, a trailing edge 76, an end 81, a root 79 and vanes as described in the fin 60. Note that unless otherwise indicated, The following description of the slots 45 also applies to the slots 48. For simplicity, the description will relate to the slots 45. As shown in Figures 3 and 4, all the cooling slots 45, 48 can be oriented substantially. parallel, with the same angle alpha (_) as shown in detail in Figure 5. The angle alpha, marked 110, is measured between the reference line 35 and the central axis 120 of the slot 45. The reference line 35 is substantially horizontal. In another embodiment, the slots may not all be parallel. For example, only fifty percent of the slots may be arranged in parallel with the same angle 110. The angle 110 of the illustrated cooling slot 45 is less than 90 and greater than 0. In practice, the air flow in the cooling slot 45 of the present embodiment of the invention is different from the air flow in conventional slots in which the inlet and outlet of the slot is are at the same 20 radial positions along the length of the fin. The cooling slots 45 minimize the mass air flow rate in the slots 45, providing a controlled flow rate through the fin escaping through the slot outlet 97 at a greatly reduced speed relative to the cooling slots of the housing. prior art. This controlled or regulated air flow creates a partial restriction of the cooling air passing through the cooling slots 45. It will be understood that this restriction does not decrease the quality of the cooling layer formed on the fin 60. On the contrary, the regulated and dosed flow rate makes it possible to improve the formation of the cooling layer or film 130 and also to avoid both the cooling air leakage into the flow path of the combustion gases and the formation a reflux condition. By reducing the mass flow rate of cooling air through cooling slot 45, the rate of cooling air leaving the slots is reduced to form a cooler and slower moving boundary layer. As a result, as it exits the slot, the cooling air remains close to the surface and edges of the turbine blade 60, ensuring the formation of a suitable cooling layer.

Figure 5 is a more detailed view of the flow of cooling air entering and leaving the cooling slot 45. Although the flow of cooling air entering the cooling slot 45, passing through and out is only shown for a single slot 45, the flow is the same for all the slots 45 and 48. Of the Cooling air flows through line 91 to slot 45 in a first flow 126 to inlet 96 of the cooling slot. In contrast, cooling air flows in the duct 91 in a second flow 127 to the inlet 96 of the cooling slot. The cooling air of the first flow enters the fin through openings located at the leading edge 74 of the fin and passes through an upstream portion of the conduit 91 to the slots.

When the cooling air flows to the cooling slot 126, it can return substantially unobstructed into the cooling slot 45. When the air flows in the second flow 127, the flow can be obstructed by one or more release regions 136 created at or near the inlet 96 of the cooling slot. A peel region 136 appears in a region 20 adjacent to the inlet 96 of the cooling slot when the cooling air in the stream 127 approaches the slot 45, the cooling air of the stream 127 meeting sharply with the flow 126, and thereby creating one or more zones in which the air swirls or separates from its original flow, forming a detachment region 136.

In addition to the inclined orientation of the cooling slot 45, the detachment region 136 may assist in metering the flow of cooling air into the cooling slot 45 since it can, at least partially, prevent flow. The flow from the flow 127 enters the cooling slot 45. This prevents the formation of reflux and regulates the flow of cooling air into the slot. A cooling film 130 is formed by the cooling air exiting through the outlet of the cooling slot 45. The cooling film 130 is formed on the trailing edge 76 of the fin 60 and contributes to the cooling of the cooling rib. the surface of the turbine blade 60 protecting the fin against the damaging effects associated with the hot combustion gases.

The cooling slot 45 is oriented at an angle 110 which may range from about 1 degree (1) to about 88 degrees (88). In another embodiment, the angle 110 may range from about 10 degrees (10) to about 75 degrees (75). In yet another embodiment, the angle may range from about 20 degrees (20) to about 60 (60), or from about 30 degrees (30) to about 50 degrees (50).

The pressure ratio for each turbine fin 60 at the inlet 96 of each cooling slot 45 is from about 1.05 to about 2.0. The term "pressure ratio" refers to the quotient of the pressure inside the fin by the pressure in the outer flow path. It is desired to obtain a pressure ratio greater than 1.0 since a lower pressure ratio would create a reflux condition. It is also desired that the movement of air within the shaped member, in the cooling duct, slots and vanes, has a Mach number ranging from about 0.03 Mach to about 1 Mach. , 0. The Mach number is defined by the quotient of the speed of an object or flow by the speed of sound in the medium in which it moves. In the present invention, the Mach number falls within the desired range.

Other advantages associated with the fin of the present invention include the possibility of using more cooling slots 45 in engines having smaller turbine blades. The term "smaller turbine blades" refers to turbine blades applied to an aircraft engine in which the central engine flow is less than 13.61 kg / s, at the takeoff power. An example of an engine having smaller turbine blades of this type is a CT7 or T700 from General Electric Company. The fin of the present invention makes it possible to mold the cooling slots 45 instead of piercing them. The use of molded slots instead of drilled holes results in significant savings in manufacturing cost, resource utilization and material utilization. In one embodiment, at least a portion of the cooling slots 45 may be molded along the trailing edge 76 of the turbine blade 60. The cooling slots 45 of the invention also provide beneficial variability. The term "beneficial variability" means that one or more cooling slots 45 may have a variable diameter along their length and / or may, because of the molding, have diameters larger than pierced cooling slots 75. An example of beneficial variability is to use larger holes, i.e. the outlets of the cooling slots along the trailing edge of the turbine blades 60 (see Figure 4). Outlet holes larger than those obtained by drilling, for example laser drilling, make it possible to obtain a better coverage of the cooling film around the surface of the turbine blade 60. Moreover, since the outlets 107 can be larger than in current slot technology, fewer cooling slots 45 can be used than in fins using radial dimension or constant diameter slots.

2910525 12 COMPONENT LIST 10 Gas Turbine Engine 12 Blower 5 13 Central Engine 14 High Pressure Compressor 16 Combustion Chamber 18 High Pressure Turbine 20 Low Pressure Turbine 10 22 Blower 24 Fan Blade 26 Rotor Disc 27 Inlet Side 29 Exhaust Side 15 31 Shaft 33 Shaft 34 Center Shaft Reference line 45 Slot 20 48 Slot 60 Wing or profiled element 61 Wing 74 Leading edge 76 Trailing edge 25 77 Inlet duct 79 Locator 81 Tip 91 Cooling duct 92 Dawn 30 94 First end

Claims (4)

  A method of preventing reflux and forming a cooling layer (1:30) in a shaped member (60), said profiled member (60) comprising a leading edge (74), a trailing edge (76), a fin tip (81) at a first fin end and a fin root (79) at a second fin end, the end (81) and the root (79) being separated by a distance radial, a cooling duct (91) extending between the leading and trailing edges (74, 76), and at least one cooling slot (45) having an inlet end in fluid receiving communication with the cooling duct (91) and an outlet end near the trailing edge (76), the inlet (96) and the outlet (97) of said slot (45) are at different radial positions in the fin (60), characterized in that it comprises the steps of circulating a cooling fluid in a first direction. in said cooling duct (91) to a cooling slot (45), circulating the cooling fluid in a second direction in said cooling duct (91) to the cooling slot (45), forming a detachment region (136) near the inlet (96) of the cooling slot and circulating the cooling fluid in said cooling slot (45) and out of the slot (45) to form a layer (130) at the trailing edge (76) of the profiled element (60).   The method according to claim 1, wherein the cooling fluid circulates in the cooling slot (45) at a certain pressure, the pressure at the cooling slot (45) being different from the pressure of the fluid along the trailing edge (76) of the profiled element, the pressure ratio between the pressures in the slot (45) and at the trailing edge (76) being between 1.05 and 2.0.   The method of claim 1, wherein the cooling fluid is circulated within the profiled member (60) at a speed from Mach 0.03 to about Mach 1.0.   The method of claim 1, wherein the cooling fluid is circulated in the cooling slot (45) at an orientation angle of between about 1 degree and about 88 degrees relative to a reference straight line. (35) which is substantially parallel to an axis (34) extending axially.