Patent Grant
12140043
This application claims priority to European Patent Application No(s). 23186279.8, filed on Jul. 19, 2023, the disclosure(s) of which is(are) incorporated herein by reference in its (their) entirety.
The present disclosure relates to a blade for a turbine, to a rotor assembly for a turbine, and to a turbine.
Blades of a turbine, e.g., of a steam or a gas turbine, typically, are mounted to a rotor disk rotating at high speed. A tip of the blade usually faces a turbine casing, wherein a small gap is present between the turbine casing and the blade. Due to the high velocity at which the blades rotate and due to the pressure difference between a suction side and a pressure side of the blade, a gas flow through the gap may occur which is referred to as over tip leakage. Over tip leakage flow forms a tip leakage vortex which causes aerodynamic losses decreasing the turbine's efficiency.
To reduce over tip leakage, various forms of squealer tips have been proposed that include a wall protruding from the tip of an airfoil of the blade, wherein the wall defines a tip cavity. Song Xue et al. in “Turbine Blade Tip External Cooling Technologies”, (Aerospace 2018, 5, 90) available under URL https://www.mdpi.com/2226-4310/5/3/90 discuss various aspects related to and measures reducing over tip leakage.
Documents U.S. Pat. No. 6,039,531 A and US 2002/0 197 159 A1 disclose a turbine blade comprising an airfoil that has a squealer tip extending along an entire circumference of the tip of the airfoil.
U.S. Pat. No. 3,635,585 A proposes a blade having a walled cavity at its tip, wherein cooling passages terminate at the bottom of the cavity. A portion of the wall is cut away on the low-pressure side of the blade adjacent its trailing edge such that the passages in the blade do not discharge into the main turbine gas stream but rather into a relatively constant pressure area within the cavity.
US 2008/0 044 289 A1 discloses a turbine blade comprising an airfoil which, at its tip, is provided with a wall protruding from the tip and extending along the entire circumference of the tip. The wall is formed by a pressure side rib and a suction side rib. A baffle protrudes from the tip and extends axially from a forward portion of the suction side rib near the leading edge to an aft portion of the same rib forward of the trailing edge. The baffle divides the tip of the airfoil into two cavities. A converging exit ramp is introduced at the aft ends of both cavities to provide a smooth transition for gas leaking into the respective cavity and discharging from the cavities.
It is one of the objects of the present disclosure to provide improved solutions for reducing an over tip leakage on a blade of a turbine.
To this end, the present disclosure provides a blade for a gas turbine, a rotor assembly and a turbine including the blade.
According to a first aspect of the present disclosure, a blade for a turbine comprises an airfoil extending between a platform end and a tip in a radial direction and extending between a leading edge and a trailing edge in an axial direction, wherein the tip comprises a tip surface. A pressure side surface and a suction side surface meet at the leading edge and at the trailing edge, wherein the pressure side surface defines a pressure side of the airfoil, and the suction side surface defines a suction side of the airfoil. The pressure side surface, for example, may comprise a concave curvature. The suction side surface, for example, may comprise a convex curvature. The tip surface defines a radial end of the airfoil and may, optionally, be a planar or substantially planar surface or comprise multiple planar or substantially planar surface areas.
The blade further includes a squealer tip wall protruding from the tip surface and defining a tip cavity. The squealer tip wall protrudes, at least partially, in the radial direction from the tip surface. For example, an outer surface of the squealer tip wall may extend continuously with the suction side surface and the pressure side surface, respectively. The squealer tip wall at least partially surrounds the tip surface or, in other words, extends along at least a part of the periphery of the radial end of the tip on both, the suction side and the pressure side. Thereby, the squealer tip defines a tip cavity having a bottom formed by the tip surface and which circumference is limited by the squealer tip wall. Hence, the tip cavity is open with regard to the radial direction. The tip cavity forms a volume into which working fluid streaming along the pressure side surface and the suction side surface of the airfoil may leak.
According to the present disclosure, the blade further comprises at least one separator wall protruding from the tip surface. The separator wall protrudes, at least partially, in the radial direction from the tip surface. The separator wall divides the tip cavity into at least a first tip cavity lying on a first side of the separator wall facing the pressure side, and a second tip cavity lying on a second side of the separator wall facing the suction side. Thus, the separator wall may, at least partially, extend along the axial direction. The separator wall separates the first tip cavity and the second tip cavity. Thereby, the tip cavity is divided into two volumes or sub-cavities, one of which being adjacent to the pressure side of the airfoil, the other one being adjacent to the suction side. Hence, working fluid leaking over the tip from the pressure side flows into the first tip cavity and, from there, may also flow into the second tip cavity. Further, it is not excluded that working fluid leaks over the tip from the suction side, e.g., in a region close to the leading edge, and flows into the second tip cavity.
The blade further includes a first exit opening formed in the squealer tip wall in the area of the trailing edge and a second exit opening formed in the squealer tip wall in the area of the trailing edge. The first exit opening defines a fluid passage between the first tip cavity and the pressure side. The second exit opening defines a fluid passage between the second tip cavity and the suction side. The exit openings allow fluid that leaks into the respective cavity to be discharged again from the respective cavity into the flow of working fluid in a region close to the trailing edge. In particular, the fluid being present in the first tip cavity, which lies on the side of the separator wall facing the pressure side, is discharged on the pressure side, and the fluid present in the second tip cavity, which lies on the side of the separator wall facing the suction side, is discharged on the suction side. Since the exit openings are positioned each in the region of the trailing edge, the fluid is discharged into an area of relatively low pressure which helps in preventing the working fluid to leak from the pressure side to the suction side of the airfoil. The exit openings each are formed in the squealer tip wall. For example, the squealer tip wall may be interrupted or cut or drilled through to form the respective opening therein.
According to a second aspect of the present disclosure, a rotor assembly comprises a rotor disk and a plurality of the blades according to the first aspect of the present disclosure, wherein the blades are coupled to the rotor disk.
According to a third aspect of the present disclosure, a turbine includes a blade according to the first aspect of the present disclosure. For example, the turbine may comprise a rotor assembly according to the second aspect of the present disclosure.
It is one of the ideas of the present disclosure to provide a squealer tip wall and separator wall on a tip of an airfoil to define a first, pressure side cavity and a second, suction side cavity on the tip, and to form exit or discharge openings in the squealer tip wall on the suction side and on the pressure side, close to the trailing edge through which fluid can be discharged from the respective cavity to the respective suction or pressure side.
The separator wall forms an additional barrier for working fluid leaking from the pressure side over the tip of the airfoil and redirects the leaked fluid towards the trailing edge as it extends along the axial surface. Thereby, the separator wall helps to prevent or reduce over tip leakage flow. The fluid leaking into the first and second cavities is again discharged into an area of relatively low pressure close to the trailing edge which further helps in preventing the working fluid to leak from the pressure side to the suction side of the airfoil. Additionally, by providing the exit openings within the squealer tip wall, the fluid from the respective cavity can be discharged directly into the respective flow on the pressure side and the suction side. Thereby, aerodynamic losses in the tip region can be reduced.
A further advantage of the separator wall is that it places additional mass on the tip of the airfoil without being directly exposed to the main flow of working fluid. Thereby, the mass of the separator wall may be used and adjusted to improve vibrational behavior of the blade, e.g., to tune a frequency of the vibrations of the blade. Moreover, the separator wall acts as a stiffener.
Further embodiments of the present disclosure are subject of the dependent claims and the following description, referring to the drawings.
According to some embodiments, the separator wall may extend from the region of the leading edge to the trailing edge of the airfoil. For example, the separator wall may be connected to the squealer tip wall in the region of the leading edge and, from there, extend towards the trailing edge. Optionally, the separator wall may end at the trailing edge. Thereby, the separator wall provides a barrier or obstacle for the leaked fluid between the pressure side and the suction side all the way to the trailing edge. This helps to further reduce the over tip leakage. In particular, as the separator wall extends all the way down to the trailing edge, the leaked fluid is efficiently redirected towards the trailing edge. Since the obstacle formed by the separator wall extends to the trailing edge, the flow of fluid leaking over the squealer tip wall at the suction side can be further reduced, whereby an amount of fluid provided to an over tip leakage vortex is reduced. As a result, aerodynamic losses caused by the over tip leakage are further reduced.
According to some embodiments, the separator wall may extend curved in an arc shape. For example, the separator wall may comprise a concave curved first surface facing the pressure side and a convex curved second surface facing the suction side. The arc shaped, curved course of the separator wall helps in defining the first and second cavities with a shape that narrows smoothly towards the trailing edge. In particular, the separator wall may extend curved such that a width of the respective first or second cavity with respect to a circumferential direction perpendicular to the radial direction and the axial direction, narrows towards the trailing edge. Thereby, leaked fluid flowing in the respective cavity is smoothly guided towards the trailing edge which reduces pressure loss and helps to further improve aerodynamic properties of the blade.
According to some embodiments, a wall thickness of the separator wall may lie in a range between ¼ to 1/32, in particular between 1/16 and 1/32, of a profile thickness of the airfoil. The profile thickness may be defined as a diameter of an incircle touching the suction side surface and the pressure side surface at an axial position of the blade where the diameter of the incircle is maximum. The profile thickness is measured at the tip of the airfoil. This range provides a good compromise for manufacturing and aerodynamic benefit. Optionally, the separator wall, over its length, has a substantially constant wall thickness.
According to some embodiments, the squealer tip wall may comprise a first wall portion that extends in a first peripheral area of the tip surface facing the pressure side, and a second wall portion of the squealer tip wall that extends in a second peripheral area of the tip surface facing the suction side, wherein the first exit opening is formed in the first side wall portion, and wherein the second exit opening is formed in the second side wall portion.
According to some embodiments, the separator wall may be connected to the second wall portion of the squealer tip wall and extend to the trailing edge of the airfoil. Connecting the separator wall to the second wall portion may help in forming the first cavity with a somewhat greater volume than the second cavity which is advantageous because leakage flow from the pressure side tends be greater than leakage flow from the suction side. Optionally, the separator wall may end at the trailing edge. Thereby, the separator wall separates the flow of leaked fluid on the first side, i.e., the pressure side, of the separator wall and the flow of leaked fluid on the second side, i.e., the suction side, of the separator wall all the way to the trailing edge. This helps to further reduce the over tip leakage and reduces aerodynamic losses caused by the over tip leakage.
According to some embodiments, the first wall portion of the squealer tip wall may end distanced to the trailing edge, and the first exit opening may be formed as a gap between an end region of the first wall portion facing the trailing edge and an end region of the separator wall facing the trailing edge. For example, the first wall portion of the squealer tip wall and the separator wall may approach each other towards the trailing edge so that a channel is defined therebetween, wherein the separator wall extends further towards the trailing edge than the first wall portion of the squealer tip wall, and the first exit opening is formed at the end of the channel defined by an end of the first wall portion of the squealer tip wall. Thereby, pressure losses of the leaked fluid being discharged through the first exit opening can be further reduced.
According to some embodiments, a groove may be formed in a transition between the tip surface and the pressure side surface adjacent to the trailing edge, and wherein the first exit opening opens into the groove. Since the trailing edge, typically, is a highly filigree structure, the groove eases forming the first exit opening. Optionally, cooling holes for discharging cooling fluid may be formed in the groove. Thereby, the leaked fluid can be discharged from the first cavity without compromising cooling of the region of the trailing edge.
According to some embodiments, the second wall portion of the squealer tip wall may end distanced to the trailing edge, and the second exit opening may be formed as a gap between an end region of the second wall portion facing the trailing edge and an end region of the separator wall facing the trailing edge. For example, the second wall portion of the squealer tip wall and the separator wall may approach each other towards the trailing edge so that a channel is defined therebetween, wherein the separator wall extends further towards the trailing edge than the second wall portion of the squealer tip wall, and the second exit opening is formed at the end of the channel defined by an end of the second wall portion of the squealer tip wall. Thereby, pressure losses of the leaked fluid being discharged through the first exit opening can be further reduced. Optionally, in the end region of the second wall portion, a wall thickness of the second wall portion may decrease towards the trailing edge. Thereby, the channel can be formed with a substantially constant width.
According to some embodiments, the separator wall may protrude further from the tip than the squealer tip wall. Thereby, the separator wall reduced the width of a gap between the blade and a turbine casing. Generally, over tip leakage can be further reduced thereby.
According to some embodiments, the airfoil, at the tip, may comprise a tip chord length, and a distance of the first exit opening to the trailing edge and/or a distance of the second exit opening to the trailing edge may lie in a range between 1/12 to ⅓, in particular between 1/9 and ¼ of the tip chord length. The tip cord length may be a distance, measured parallel to a tangent line touching the airfoil from the pressure side, between the trailing edge and a point on the suction side surface having a greatest distance to the trailing edge. Since the pressure side surface comprises a generally concave curvature, the tangent line touches the pressure side surface close to the leading edge and close to the trailing edge. The distance of the first exit opening and/or the second exit opening to the trailing edge may be measured parallel to the tangent line.
According to some embodiments, the second exit opening may lie further distanced from the trailing edge than the first exit opening. On the one hand, this configuration eases manufacturing the first and second exit openings. On the other hand, aerodynamic losses in connection with over tip leakage can be further reduced by this configuration.
According to some embodiments, the first tip cavity may comprise a first depth measured in the radial direction from the tip surface in the first tip cavity to a radial end of the first wall portion, and the second tip cavity may comprise a second depth measured in the radial direction from the tip surface in the second tip cavity to a radial end of the second wall portion, the second depth may be different from the first depth, e.g., smaller or larger than the first depth. Further optionally, it may be provided that at least one of the first and second depths varies along the axial direction.
According to some embodiments, a plurality of cooling holes may be formed in the tip surface in the first tip cavity and/or in the second tip cavity. Thereby, efficient tip cooling is achieved. Further, the cooling fluid being discharged from the cooling holes can be more efficiently mixed with the flow of working fluid as it is, at least in part, discharged through the respective first or second discharge opening.
According to some embodiments, the second exit opening may positioned closer to the trailing edge of the respective blade than a throat defined between the suction side surface of the respective blade and a pressure side surface of a further blade positioned adjacent to the respective blade. The throat may be defined as a position on the suction side surface of the airfoil having shortest distance to the pressure side surface of the adjacent blade. Discharging the fluid from the second cavity on the suction side downstream of the throat further reduces pressure loss and thereby improves the aerodynamic properties of the blade.
According to some embodiments, turbine may be a gas turbine comprising a compressor configured to compress a working fluid, a combustor receiving compressed working fluid from the compressor and configured to burn a fuel to heat the working fluid, and a turbine part comprising at least one rotor assembly as described above, the turbine part being configured to expand the working fluid causing the rotor assembly to rotate. Hence, the rotor assembly may form part of the turbine. As a working fluid, the compressor may suck air from the environment, and the compressed air may be used for combustion of the fuel in the combustor or burner. As a fuel, liquid fuel, such as kerosene, diesel, ethanol, or similar may be used. Alternatively, gaseous fuel such as natural gas, fermentation gas, hydrogen, or similar can be used.
The features and advantages described herein with respect to various aspects of the present disclosure are also disclosed for the other aspects and vice versa.
With respect to directions and axes, in particular, with respect to directions and axes concerning the extension or expanse of physical structures, within the scope of the present disclosure, an extent of an axis, a direction, or a structure “along” another axis, direction, or structure includes that said axes, directions, or structures, in particular tangents which result at a particular site of the respective structure, enclose an angle which is smaller than 45 degrees, preferably smaller than 30 degrees and in particular preferable extend parallel to each other.
With respect to directions and axes, in particular with respect to directions and axes concerning the extension or expanse of physical structures, within the scope of the present disclosure, an extent of an axis, a direction, or a structure “crossways”, “across”, “cross”, or “transversal” to another axis, direction, or structure includes in particular that said axes, directions, or structures, in particular tangents which result at a particular site of the respective structure, enclose an angle which is greater or equal than 45 degrees, preferably greater or equal than 60 degrees, and in particular preferable extend perpendicular to each other.
For a more complete understanding of the present disclosure and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. The present disclosure is explained in more detail below using exemplary embodiments, which are specified in the schematic figures of the drawings, in which:
In the figures, like reference signs denote like elements unless stated otherwise.
The compressor 310 of the gas turbine 300 may draw air as a working fluid from the environment and compress the drawn air. The compressor 310 may be realized as centrifugal compressor or an axial compressor.
The compressed air is supplied to the combustor 320 for combustion of a fuel, such as natural gas, hydrogen, diesel, kerosene, ethanol or similar. Further, a part of the compressed air is supplied as a gaseous cooling fluid to high-temperature regions of the gas turbine 300 for cooling purposes. The burner or combustor 320, by use of the compressed air, burns fuel to heat the compressed air.
As schematically shown in
The rotor disk 210, generally, may have the form of a ring and, at its outer circumference, includes multiple coupling interfaces 219 for coupling the blades 100 to the disk 210. As exemplarily shown in
As shown in
Generally, as shown schematically in
The airfoil 1 comprises a pressure side surface 1p and an opposite suction side surface 1s. The pressure side surface 1p defines a pressure side PS of the airfoil 1, and the suction side surface 1s defines a suction side SS of the airfoil 1. As only schematically shown in
As schematically shown in
The root 9 is connected to the platform 8, in particular, to a lower surface of the platform 8 and protrudes from the lower surface of the platform 8 along the radial direction R. Hence, the airfoil 1 and the root 9, with respect to the radial direction R, extend at opposite sides of the platform 8. As exemplarily shown in
Referring to
As visible best in
The squealer tip wall 2 protrudes from the tip surface 12a in the radial direction R. Generally, the squealer tip wall 2 may extend along at least a part of the periphery of the radially outer end of the airfoil 1. For example, the squealer tip wall 2 may extend substantially along the entire periphery of the radially outer end of the airfoil 1, as exemplarily shown in
An outer lateral surface 2a of the squealer tip wall 2 may form a continuous surface with the pressure side surface 1p and suction side surface 1s, respectively. As visible in
As further shown in
As visible in
As further visible in
The squealer tip wall 2 and separator wall 4 according to the present disclosure helps in preventing the over tip leakage flow, that is, a flow of working fluid from the pressure side PS to the suction side SS over the tip of the airfoil 1.
According to an embodiment, the first and second exit openings 5, 6 may be each formed in the squealer tip wall 2 in the area of the trailing edge 14. The first exit opening 5 defines a fluid passage between the first tip cavity 31 and the pressure side PS. As shown in
Generally, the exit openings 5, 6 are formed in the squealer tip wall 2. That is, portions of the squealer tip wall 2 are removed to form the respective opening 5, 6. As exemplarily shown in
As mentioned before, the first wall portion 21 of the squealer tip wall 2 and the separator wall 4 may approach each other towards the trailing edge 14. A channel may be defined between the downstream end region of the first wall portion 21 and the separator wall 4. Further, it may be provided that the separator wall 4 extends further towards the trailing edge 14 than the first wall portion 21 of the squealer tip wall 2, as shown in
The second exit opening 6 may also be formed at the downstream end of a channel defined between the separator wall 4 and a downstream end portion of the second wall portion 22 facing the trailing edge 14. As shown in
According to the present disclosure, the first and second exit openings 5, 6 allow discharging fluid leaked from the pressure side PS or the suction side SS into the respective first and second tip cavity 31, 32. Thereby, the leaked fluid can be efficiently conducted back into the main flow of working fluid flowing along the pressure side surface 1p and the suction side surface 1s. Consequently, over tip leakage as such and potential secondary effects caused by the over tip leakage, such as formation of vortices, are reduced. Since the exit openings 5, 6 are formed in the squealer tip side wall 2, the leaked flow is smoothly guided within the cavities 31, 32 and discharged from the cavities 31, 32.
A distance L5 between the downstream end of the first exit opening 5 and the trailing edge 14 and/or a distance L6 between the downstream end of the second exit opening 6 and the trailing edge 14 may lie in a range between 1/12 to ⅓, in particular between 1/9 and ¼ of a tip chord length tc1 of the airfoil 1 at the tip 12 when they are measured in a same direction. The tip chord length tc1 is measured at the tip 12 of the airfoil 1 in a direction which is parallel to a tangent line tL touching the airfoil 1 from the pressure side, as schematically shown in
When assembled in the rotor assembly 200, and when a throat O is defined between the suction side surface 1s of a respective blade 100 and a pressure side surface 1p of an adjacent blade 100 positioned next to the respective blade 100, the second exit opening 6 of the respective blade 100 is positioned closer to the trailing edge 14 of the respective blade 100 than the throat O. More specifically, the upstream end of the second exit opening 6 of the respective blade 100 may be positioned closer to the trailing edge 14 of the respective blade than the throat O. This situation is schematically shown in
Referring to
The wall thickness of the squealer tip wall 2 may lie substantially in the same range as the wall thickness t4 of the separator wall 4. For example, the wall thickness t21 of the first wall portion 21 and the wall thickness t22 of the second wall portion 22 each may lie in a range between ¼ to 1/16 of the profile thickness Pt of the airfoil 1, e.g., in a range between 1.5 mm and 6.5 mm.
The first cavity 31 may comprise a first depth h31 measured in the radial direction R from the tip surface 12a in the first tip cavity 31 to a radial end 21e of the first wall portion 21. Likewise, the second tip cavity 32 may comprise a second depth h2 measured in the radial direction R from the tip surface 12a in the second tip cavity 32 to a radial end 22e of the second wall portion 22. Generally, the first depth h31 and the second depth h32 may lie in a range between 1.5 mm to 5.5 mm. Optionally, as exemplarily shown in
The blade 100 may be manufactured, generally, in a casting process, such as conventional casting (CC), a directionally solidified (DS), or single crystal (SX) cast process. Nickel or Cobalt based high temperature alloys may be used for casting the blade 100.
The separator wall 4 may be formed by conventional manufacturing methods, e.g., by casting or machining. Alternatively, the separator wall 4 may be additively manufactured or may be formed by any combination of additive and subtractive methods. Nickel or Cobalt based high temperature alloys suitable for additive manufacturing may be used to form the separator wall 4 in an additive manufacturing process.
The surfaces on the tip 12 of the airfoil 1, i.e., the tip surface 12a, the surfaces of the squealer tip wall 2 and the surfaces of the separator wall 4 may be coated. For example, MCrAIY material or other suitable coating material may be used as bondcoat and applied, for example, by a low pressure plasma spray (LPPS), a vacuum plasma spray (VPS), or a high velocity oxy fuel (HVOF) process. Further optional, a topcoat may be applied. For example, a single or multi-layered ceramic, e.g., YSZ, may be applied by LPPS, an air plasma spray (APS), or similar.
Although only examples comprising one single separator wall 4 have been discussed above, the present disclosure is not limited thereto. Rather, two or more separator may be provided, e.g., to further divide the first or second tip cavity 31, 32 into sub cavities.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of at least ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Also, it is noted that any one feature of an embodiment of the present disclosure described in the specification may be applied to another embodiment of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23186279 | Jul 2023 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3635585 | Metzler, Jr. | Jan 1972 | A |
| 6039531 | Suenaga | Mar 2000 | A |
| 8398370 | Liang | Mar 2013 | B1 |
| 20020197159 | Roeloffs | Dec 2002 | A1 |
| 20080044289 | Klasing | Feb 2008 | A1 |
| 20090068021 | Liang | Mar 2009 | A1 |
| 20170226868 | Martinello | Aug 2017 | A1 |
| 20170226871 | Auzillon | Aug 2017 | A1 |
| Entry |
|---|
| Xue S, Ng WF. Turbine Blade Tip External Cooling Technologies. Aerospace. 2018; 5(3):90. https://doi.org/10.3390/aerospace5030090 (https://www.mdpi.com/2226-4310/5/3/90). |
| EP EESR Dated Dec. 10, 2023. |
