ASSEMBLY OF TURBINE BLADES AND CORRESPONDING ARTICLE OF MANUFACTURE

An assembly of turbine blades or vanes includes a first and a second airfoil extending span-wise from a first and a second platform respectively. The first and the second platform respectively have a first and a second mate face that interface along a platform splitline. The first mate face is proximal to a suction side of the first airfoil the second mate face is proximal to a pressure side of the second airfoil. The first mate face is chamfered or filleted along an aft portion thereof. The chamfered or filleted portion of the first mate face lies in a region in a flow path between the first and second airfoils where a mean velocity of the working medium is directed from the second platform to the first platform.

BACKGROUND

The present invention relates to rotating turbine blades or stationary turbine vanes for gas turbine engines, and in particular to platforms of turbine blades or vanes.

2. Description of the Related Art

In a turbomachine, such as a gas turbine engine, air is pressurized in a compressor section and then mixed with fuel and burned in a combustor section to generate hot combustion gases. The working medium, comprising hot combustion gases is expanded within a turbine section of the engine where energy is extracted to power the compressor section and to produce useful work, such as turning a generator to produce electricity. The working medium travels through a series of turbine stages within the turbine section. A turbine stage may include a row of stationary vanes, followed by a row of rotating blades, where the blades extract energy from the hot combustion gases for providing output.

A turbine blade or vane unit typically comprises at least one airfoil extending span-wise from a platform. In some cases, for example, in stationary vanes, the airfoil(s) may extend between two platforms, namely an outer diameter platform and an inner diameter platform. Each platform has a pair of mate faces on laterally opposite ends, which extend from a platform leading edge to a platform trailing edge. Each mate face of the platform engages with an opposite mate face of a circumferentially adjacent blade or vane unit, to form an assembly of a row of turbine blades or vanes. The platforms define an endwall for a flow path of the working medium between circumferentially adjacent airfoils.

A turbine blade or a vane unit may be manufactured, for example, by casting, which may be optionally followed by a post-machining process. Manufacturing variation and machining tolerances may lead to a step in the flow path at the interface of the mate faces of the platforms of two circumferentially adjacent airfoils, which may potentially affect engine performance.

SUMMARY

Briefly, aspects of the present invention provide a chambered mate face for turbine blades and vanes. The embodiments described may minimize impact of manufacturing variation on engine performance.

According to a first aspect of the invention, an assembly of turbine blades or vanes is provided. The assembly comprises a first airfoil extending span-wise from a first platform and a second airfoil extending span-wise from a second platform. Each of the first and second airfoils comprises a respective outer wall formed of a pressure side and a suction side joined at a respective airfoil leading edge and at a respective airfoil trailing edge. Each of the first and second platforms extends from a respective platform leading edge to a respective platform trailing edge. The first platform comprises a first mate face proximal to the suction side of the first airfoil and the second platform comprises a second mate face proximal to the pressure side of the second airfoil. The first mate face faces the second mate face along a platform splitline extending between the platform leading and trailing edges of the first and second platforms. A flow path for a working medium is defined between the suction side of the first airfoil and the pressure side of the second airfoil. The first mate face is chamfered or filleted along an aft portion thereof. The chamfered or filleted portion of the first mate face lies in a region in the flow path where a mean velocity of the working medium is directed from the second platform to the first platform.

According to a second aspect of the invention, an article of manufacture is provided. The article of manufacture comprises at least one platform with one or more airfoils extending span-wise from the platform. Each of said one or more airfoils comprises an outer wall formed of a pressure side and a suction side joined at an airfoil leading edge and at an airfoil trailing edge. The platform extends from a platform leading edge to a platform trailing edge. The platform comprises a first mate face and a second mate face spaced along a pitch-wise direction. The first mate face is proximal to the suction side of one of the airfoils and the second mate face being proximal to the pressure side of the same airfoil or a different airfoil of said one or more airfoils. The first and second mate faces extend between the platform leading edge and the platform trailing edge. The first mate face is chamfered or filleted along an aft portion thereof. The chamfered or filleted portion of the first mate face extends from the platform trailing edge to a first intermediate point on the first mate face located between the platform leading edge and the platform trailing edge.

DETAILED DESCRIPTION

In the description and drawings, the directional axes A, R and C respectively denote an axial direction, a radial direction and a circumferential direction of a gas turbine engine.

Referring now toFIG. 1, a turbine blade10is illustrated, wherein an embodiment of the present invention may be implemented. The turbine blade10comprises an airfoil12extending span-wise radially outward from a platform14in relation to a rotation axis A. The blade10further comprises a root portion16extending radially inward from the platform14, and being configured to attach the blade10to a rotor disk (not shown). The airfoil12is formed of an outer wall18that delimits a generally hollow airfoil interior. The outer wall18includes a generally concave pressure side20and a generally convex suction side22, which are joined at an airfoil leading edge24and at an airfoil trailing edge26. The platform14comprises a radially outer surface15defining a radially inner boundary for a flow path of a working medium. The platform14thereby defines inner diameter endwall for the flow path. The platform14extends from a platform leading edge28to a platform trailing edge30. The platform14also includes a first mate face32and a second mate face34spaced in a circumferential or pitch-wise direction C. Each of the mate faces32and34extends from the platform leading edge28to the platform trailing edge30, with the first mate face32being proximal to the suction side22of the airfoil12and the second mate face34being proximal to the pressure side20of the airfoil12. The mate faces32and34extend radially inward from the radially outer surface15of the platform14and interface with correspondingly opposite mate faces of circumferentially adjacent platforms to form an assembly of a row of turbine blades.

FIG. 2schematically illustrates a portion of an assembly100of a row of turbine blades10. The assembly100includes a first blade10ahaving a first airfoil12aextending from a first platform14a, and a circumferentially adjacent second blade10bhaving a second airfoil12bextending from a second platform14b. The first platform14ahas a first mate face32proximal to the suction side22of the first airfoil12a. The second platform has a second mate face34proximal to the pressure side20of the second airfoil12b. The first and second mate faces32and34face each other and are separated by a mate face gap G. In the shown example, the radial thickness taof the first mate face32is greater than a design mate thickness t within a manufacturing tolerance, while, the radial thickness tbof the second mate face34is lesser than the design mate thickness t within the manufacturing tolerance. Such a manufacturing variation may lead to a step in the flow path at the interface of the mate faces of the platforms of two circumferentially adjacent blades.

It has been observed that at least in some regions of the flow path between circumferentially adjacent blades, the mean velocity of the working medium is not purely axial but also has a pitch-wise component, i.e., directed from one platform to the circumferentially adjacent platform. In the example shown inFIG. 2, the mean velocity F of the working medium at the given section has a component which is directed from the second platform14bto the first platform14a, whereby a forward facing step is defined at the interface of the mate faces32,34. In general, a forward facing step may be said to formed when the mate face of the downstream platform (in relation to the direction of the mean velocity F) extends further into the flow path than the mate face of the upstream platform. The present inventors have recognized that especially a forward facing step, as shown in the example ofFIG. 2, may cause aerodynamic losses and heat transfer problems due to flow separation and vortex formation at the platform mate faces. Embodiments of the present invention address at least the above described technical problem. In particular, the embodiments illustrated inFIG. 3-5are directed to providing a chamfer and/or fillet along a portion of the mate face of one of the platforms, which is at a downstream position with respect to a circumferentially adjacent platform, in relation to the direction of the mean velocity of the working medium.

FIG. 3illustrates portion of an assembly100of turbine blades10according to one embodiment of the present invention. Each blade10may include one or more airfoils12extending from a platform14. In the example shown, a first airfoil12aextends span-wise from a first platform14aand a second airfoil12bextends span-wise from a second platform14bcircumferentially adjacent to the first platform14a. Each of the airfoils12a,12bcomprises a respective outer wall18formed of a pressure side20and a suction side22joined at a respective airfoil leading edge24and at a respective airfoil trailing edge26. Each of the first and second platforms14aand14bextends from a respective platform leading edge28to a respective platform trailing edge30. Each of the platforms14aand14bfurther includes a pair of mate faces32,34spaced in a circumferential or pitch-wise direction C. The pair of mate faces include a first mate face32proximal to the suction side22of the respective airfoil12aor12b, and a second mate face34proximal to the pressure side20of the respective airfoil12aor12b. The first mate face32of the first platform14ais parallel to and faces the second mate face34of the second platform14balong a platform splitline80extending between the platform leading and trailing edges28,30. A flow path for a working medium is defined between the suction side22of the first airfoil12aand the pressure side20of the second airfoil12b. The working medium flows in a generally axial direction from the platform leading edge28to the platform trailing edge30, with the mean velocity varying in direction, as may be represented by the directional arrow F for the purpose of illustration.

It has been observed that especially toward the aft end of the interface between the mate faces32,34, the mean velocity F is typically directed from the second platform14bto the first platform14a, with the flow Mach numbers being highest near the platform trailing edge30. In the present embodiment, as shown inFIG. 4with continued reference toFIG. 3, the first mate face32of the first platform14amay be chamfered or filleted along an aft portion36thereof. In particular, the first mate face32may be chamfered or filleted to an extent such that the chamfered or filleted portion36lies in a region in the flow path where a mean velocity F of the working medium is directed from the second platform14bto the first platform14a. The second mate face34of the second platform14bmay be unchamfered and unfilleted along the extent thereof that lies directly opposite to the chamfered or filleted portion36of the first mate face32of the first platform14a.

In particular, as shown inFIG. 3, the chamfered or filleted portion36of the first mate face32of the first platform14aextends from the platform trailing edge30of the first platform14ato a first intermediate point42on the first mate face32of the first platform14a. The first intermediate point42is located between the platform leading edge28and the platform trailing edge30of the first platform14a. The location of the first intermediate point42may be based, for example, on the determination of a point of inflection82on the first mate face32. In an exemplary embodiment, such a point82may be determined by first determining a point90of tangency of a line32′ parallel to the first mate face32to the mean camber line40of one of the airfoils, and projecting said point90on the first mate face32along the circumferential direction C to locate the point82on the first mate face32, as shown inFIG. 3. The first intermediate point42on the first mate face32may lie at or aft of the point82. In other embodiments, the extent of the chamfered or filleted portion36on the first mate face32may be determined by other means, including, for example, consideration of flow velocities during engine operation.

As shown inFIG. 4, in one embodiment, the chamfered portion of the first mate face32of the first platform14acomprises a chamfered surface50extending radially from a first chamfer edge52to a second chamfer edge54at a chamfer angle α1, which may be, for example and without limitation, 30 to 70 degrees, particularly about 40 to 50 degrees, with respect to the radial direction R. In an alternate embodiment, a similar technical effect may be realized by providing a fillet comprising a rounded surface50′ (shown with dashed lines) with predefined radius r1extending between the edges52,54. The radial height t1of the chamfered or filleted surface50,50′ may dependent on the manufacturing process tolerances. In some embodiments, the chamfer height t1may range from 0.5% to 2% pitch distance of the blade/vane assembly. The chamfered or filleted surface50,50′ on the mate face32of the downstream platform14amay reduce flow separation and vortex formation at the interface of the mate faces32,34, thereby minimizing aerodynamic losses and heat transfer issues that may be potentially caused by a forward facing step due to manufacturing variation. Referring toFIG. 3, the first mate face32of the second platform14bmay be provided with a similarly chamfered or filleted portion36at an aft portion, while the second mate face34of the first platform14amay be provided with a corresponding unchamfered and unfilleted portion along an extent of the second mate face34that lies pitch-wise directly opposite to the chamfered or filleted portion36of the first mate face32.

In a further embodiment, as shown inFIGS. 3 and 5, the second mate face34of the second platform14bmay be chamfered or filleted along a forward portion38thereof. This embodiment may be applicable to configurations in which the mean velocity F of the working medium has a pitch-wise component directed from the first platform14ato the second platform14bat a forward portion of the interface of the mate faces32,34. Accordingly, the second mate face34of the second platform14bmay be chamfered or filleted to an extent such that that the chamfered or filleted portion38lies in a region in the flow path where a mean velocity F of the working medium is directed from the first platform14ato the second platform14b. The first mate face32of the first platform14amay be unchamfered and unfilleted along the extent thereof that lies directly opposite to the chamfered or filleted portion38of the second mate face34of the second platform14b. The choice of having the chamfered (or filleted) portion38on the second mate face34may depend, for example, on a combination of blade geometry and engine flow parameters. For example, in some configurations, the mean velocity in the flow path may be substantially axial in the forward portion, whereby the need for chamfering or filleting a forward portion of the second mate face34may be obviated.

In the illustrated embodiment as shown inFIG. 3, the chamfered or filleted portion38of the second mate face34of the second platform14bextends between the platform leading edge28of the second platform14band a second intermediate point44on the second mate face38of the second platform14b. The second intermediate point44is located between the platform leading edge28and the platform trailing edge30of the second platform14b. The chamfered or filleted portion38of the second mate face34may extend all the way up to the platform leading edge28of the second platform14bor may stop short at a distance therefrom. The location of the second intermediate point44may be based, for example, on the determination of a point of inflection84on the second mate face34. In an exemplary embodiment, such a point84may be determined by first determining a point90of tangency of a line34′ parallel to the second mate face34to the mean camber line40of one of the airfoils12, and projecting the point90on the second mate face34along the circumferential direction C to locate the point84on the second mate face34, as shown inFIG. 3. The second intermediate point44on the second mate face34may lie at or forward of the point84. In other embodiments, the extent of the chamfered or filleted portion38on the second mate face34may be determined by other means, including, for example, consideration of flow velocities during engine operation.

As shown inFIG. 5, in one embodiment, the chamfered portion of the second mate face34of the second platform14bcomprises a chamfered surface60extending radially from a first chamfer edge62to a second chamfer edge64at a chamfer angle α2, which may be, for example and without limitation, 30 to 70 degrees, particularly about 40 to 50 degrees, with respect to the radial direction R. In an alternate embodiment, a similar technical effect may be realized by providing a fillet comprising a rounded surface60′ (shown with dashed lines) with predefined radius r2extending between the edges62,64. The radial height t2of the chamfered or filleted surface60,60′ may dependent on the manufacturing process tolerances. In some embodiments, the chamfer height t2may range from 0.5% to 2% pitch distance of the blade/vane assembly. The chamfered or filleted surface60,60′ on the mate face34of the downstream platform14bmay reduce flow separation and vortex formation at the interface of the mate faces32,34, thereby minimizing aerodynamic losses and heat transfer issues that may be potentially caused by a forward facing step due to manufacturing variation. Referring toFIG. 3, the second mate face34of the first platform14amay be provided with a similarly chamfered or filleted portion38at a forward portion, while the first mate face32of the second platform14bmay be provided with a corresponding unchamfered and unfilleted portion along an extent of the first mate face32that lies pitch-wise directly opposite to the chamfered or filleted portion38of the second mate face34.

In a still further embodiment, the platforms14a,14bmay define a contoured endwall facing the flow path, which is non-axisymmetric about the engine axis. In particular, a non-axisymmetric endwall may comprise one or more hills48and/or troughs46formed on the endwall, as shown by dashed lines inFIG. 3. A hill be may be defined as a contour wherein the endwall extends into the flow path in relation to a nominal radius of the endwall, whereas a trough may be defined as a contour wherein the endwall extends away from the flow path in relation to the nominal radius of the end wall. In one embodiment, at least one hill48and/or trough46may extend across the platform splitline80, as shown inFIG. 3. In such a case, manufacturing variations caused by standard tolerances may lead to a steeper forward facing step than in a configuration without endwall contouring. The provision of a chamfer at the downstream platform is especially advantageous for contoured endwalls, to maximize the aerodynamic benefits provided by the contouring of the endwall. As shown inFIG. 6, on account of the non-axisymmetric endwall contouring, the first mate face32and/or the second mate face34may have a wavy contour70, in a direction from the platform leading edge28to the platform trailing edge30. In accordance with one embodiment, the chamfered or filleted portions36,38respectively of the first and second mate faces32,34may have a respective chamfer surface50/50′,60/60′ that follows said wavy contour70, that is, the first chamfer/fillet edge52,62is parallel to the respective second chamfer/fillet edge54,64, as shown inFIG. 6.

The above-described embodiments relate to inner diameter platforms of rotating turbine blades, wherein the first and second platforms14aand14bdefine an inner diameter endwall for the flow path of the working medium. In alternate embodiments, aspects of the present invention may be applied to inner or outer diameter platforms of stationary turbine vanes, wherein the platforms may define an inner or an outer diameter endwall for the flow path of the working medium.

While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.