Power turbine vane airfoil profile

A power turbine includes a first stage vane having an airfoil with a cold un-coated nominal profile substantially in accordance with at least an intermediate portion of the Cartesian coordinate values of X, Y and Z set forth in Table 2. The X and Y values are distances, which when smoothly connected by an appropriate continuing curve, define airfoil profile sections at each distance Z. The profile sections at each distance Z are joined smoothly to one another to form a complete airfoil shape.

TECHNICAL FIELD

The application relates generally to a vane airfoil and, more particularly, to an airfoil profile suited for use in a power turbine stage of a gas turbine engine.

BACKGROUND OF THE ART

Every stage of a gas turbine engine must meet a plurality of design criteria to assure the best possible overall engine efficiency. The design goals dictate specific thermal and mechanical requirements that must be met pertaining to heat loading, parts life and manufacturing, use of combustion gases, throat area, vectoring, the interaction between stages to name a few. The design criteria for each stage is constantly being re-evaluated and improved upon. Each airfoil is subject to flow regimes which lend themselves easily to flow separation, which tend to limit the amount of work transferred to the compressor, and hence the total thrust or power capability of the engine. The vanes of a power turbine are also subject to harsh temperatures and pressures, which require a solid balance between aerodynamic and structural optimization. Therefore, improvements in airfoil design are sought.

SUMMARY

In one aspect, the present application provides a turbine vane for a gas turbine engine having a gaspath, the vane comprising an airfoil having an intermediate portion contained within the gaspath and defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 2 to 8 set forth in Table 2, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the turbine vane, the Z values are radial distances measured along the stacking line, the X and Y are coordinate values defining the profile at each distance Z.

In another aspect, the present application provides a turbine vane for a gas turbine engine having a gaspath, the turbine vane having a cold uncoated intermediate airfoil portion contained within the gaspath and defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 2 to 8 set forth in Table 2, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the turbine vane, the Z values are radial distances measured along the stacking line, the X and Y are coordinate values defining the profile at each distance Z.

In another aspect, the present application provides a turbine stator assembly for a gas turbine engine having a gaspath, the assembly comprising a plurality of vanes, each vane including an airfoil having an intermediate portion contained with the gaspath of the engine and defined by an un-coated nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 2 to 8 set forth in Table 2, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the turbine vane, the Z values are radial distances measured along the stacking line, the X and Y are coordinate values defining the profile at each distance Z.

In a still further aspect of the present application, there is provided a first stage power turbine vane comprising: at least one airfoil having a surface lying substantially on the points of Table 2, the airfoil extending between platforms defined generally by at least some of the coordinate values given in Table 1, wherein a fillet radius is applied around the airfoil between the airfoil and platforms.

Further details of these and other aspects of the present application will be apparent from the detailed description and figures included below.

DETAILED DESCRIPTION

FIG. 1illustrates a turboshaft gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a multi-stage compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. According to the illustrated example, the turbine section18comprises a two-stage power turbine18aand a single-stage compressor turbine18b. The power turbine18adrives a rotatable load12(e.g. a helicopter rotor) via a low pressure shaft19. Each power turbine stage comprises a set of circumferentially spaced-apart blades radiating from a disk mounted for rotation about a central axis of the engine10.

FIG. 2illustrates a portion of an annular hot gaspath of the power turbine18a. Arrows27illustrate the flow of hot combustion gases through the power turbine18a. The gaspath is defined by annular inner and outer walls28and30respectively, for directing the stream of hot combustion gases axially in an annular flow through the power turbine18a. The profile of the inner and outer walls28and30of the cold coated annular gaspath is defined by Cartesian coordinate values such as the ones given in Table 1 below. More particularly, the inner and outer gaspath walls28and30are defined with respect to mutually orthogonal x and z axes, as shown inFIG. 2. The x axis corresponds to the engine first power turbine vane centerline29. The radial distance of the inner and outer walls28and30from the engine turbine rotor centerline and, thus, from the x-axis at specific axial locations is measured along the z axis. The z values provide the inner and outer radius of the gas path at various axial locations therealong. The x and z coordinate values in Table 1 are distances given in inches from the point of origin O (seeFIG. 2). It is understood that other units of dimensions may be used. The x and z values have in average a manufacturing tolerance of about ±0.030″. The tolerance may account for such things as casting, coating, ceramic coating and/or other tolerances. It is understood that the manufacturing tolerances of the gas path may vary along the length thereof.

The power turbine section18ahas two stages located in the gaspath downstream of the combustor16and the compressor turbine18b. Referring toFIG. 2, the power turbine stages each comprise a stator assembly32,34and a rotor assembly36,38having a plurality of circumferentially arranged vane40a,40band blades42a,42brespectively. The vanes40a,40band blades42a,42bare mounted in position along respective stacking lines44-50, as identified inFIG. 2. The stacking lines44-50extend in the radial direction along the z axis at different axial locations. The stacking lines44-50define the axial location where the blades and vanes of each stage are mounted in the engine10. More specifically, stacking line44located at x=0 corresponds to the first stage of vanes40aof the power turbine18a.

More specifically, the stator assemblies32,34each include a plurality of circumferentially distributed vanes40aand40brespectively which extend radially across the hot gaspath27.FIG. 3shows an example of a vane40aof the first stage of the power turbine18a. It can be seen that each vane40ahas an airfoil54having a leading edge56and a trailing edge58, extending between an inner platform60and an outer platform62.

The novel airfoil shape of each first stage power turbine vane40ais defined by a set of X-Y-Z points in space. This set of points represents a novel and unique solution to the target design criteria discussed above, and are well-adapted for use in a two-stage power turbine design. The set of points are defined in a Cartesian coordinate system which has mutually orthogonal X, Y and Z axes. The X axis extends axially along the turbine rotor centerline29, i.e., the rotary axis. The positive X direction is axially towards the aft of the turbine engine10. The Z axis extends along the vane stacking line44of each respective vane40ain a generally radial direction and intersects the X axis. The positive Z direction is radially outwardly toward the outer shroud62of the vane. The Y axis extends tangentially with the positive Y direction being in the direction of rotation of the rotor assembly36. Therefore, the origin of the X, Y and Z axes is defined at the point of intersection of all three orthogonally-related axes: that is the point (0,0,0) at the intersection of the center of rotation of the turbine engine10and the stacking line44.

In a particular embodiment of the first stage power turbine vane, the set of points which define the vane airfoil profile relative to the axis of rotation of the turbine engine10and stacking line44thereof are set out in Table 2 below as X, Y and Z Cartesian coordinate values. Particularly, the vane airfoil profile is defined by profile sections66at various locations along its height, the locations represented by Z values. For example, if the vanes40aare mounted at an angle with respect to the radial direction, then the Z values are not a true representation of the height of the airfoils of the vanes40a. Furthermore, it is to be appreciated that, with respect to Table 2, Z values are not actually radial heights, per se, from the centerline but rather a height from a plane through the centerline—i.e. the sections in Table 2 are planar. The coordinate values are set forth in inches in Table 2 although other units of dimensions may be used when the values are appropriately converted.

Thus, at each Z distance, the X and Y coordinate values of the desired profile section66are defined at selected locations in a Z direction normal to the X, Y plane. The X and Y coordinates are given in distance dimensions, e.g., units of inches, and are joined smoothly, using appropriate curve-fitting techniques, at each Z location to form a smooth continuous airfoil cross-section. The vane airfoil profiles of the various surface locations between the distances Z are determined by smoothly connecting the adjacent profile sections66to one another to form the airfoil profile.

The coordinate values listed in Table 2 below represent the desired airfoil profiles in a “cold” non-operating un-coated condition (and at nominal restagger). However, the manufactured airfoil surface profile will be slightly different, as a result of manufacturing and applied coating tolerances. According to an embodiment of the present invention, the finished vane is coated with a thermal protecting layer.

The Table 2 values are generated and shown to three decimal places for determining the profile of the first stage power turbine vane airfoil. However, as mentioned above, there are manufacturing tolerance issues to be addressed and, accordingly, the values for the profile given in Table 2 are for a theoretical airfoil. A profile tolerance of ±0.009 inches, measured perpendicularly to the airfoil surface is additive to the nominal values given in Table 2 below. The vane airfoil design functions well within these ranges of variation. The cold or room temperature profile is given by the X, Y and Z coordinates for manufacturing purposes. It is understood that the airfoil may deform, within acceptable limits, once entering service.

The coordinate values given in Table 2 below provide the preferred nominal first stage power turbine vane airfoil profile.

It should be understood that the finished first stage power turbine vane40adoes not necessarily include all the sections defined in Table 2. The portion of the airfoil54proximal to the platforms60and62may not be defined by a profile section66. It should be considered that the vane40aairfoil profile proximal to the platforms60,62may vary due to several imposed constraints. However, the vane40ahas an intermediate airfoil portion64defined between platforms60,62thereof and which has a profile defined on the basis of at least the intermediate sections of the various vane profile sections66defined in Table 2.

It should be appreciated that the intermediate airfoil portion64of the vane40ais defined between the inner and outer gaspath walls28and30and that the platforms60,62forms part of the gaspath walls28,30. The airfoil profile physically appearing on vane40aand fully contained in the gaspath includes Sections 2 to 8 of Table 2. The remaining sections are at least partly located outside of the gaspath27, but are provided, in part, to fully define the airfoil surface and/or, in part, to improve curve-fitting of the airfoil at its radially distal portions. The skilled reader will appreciate that a suitable fillet radius is to be applied between the platforms60,62and the airfoil portion of the vane. The vane inner diameter endwall fillet is in the range of about 0.070″ to about 0.090″. The vane outer diameter endwall fillet is about 0.150″. The local ID/OD endwall profile tolerance is +/−0.0125″.

FIG. 4illustrates the tolerances on twist angles. The twist “N” is an angular variation at each vane section, whereas restagger is the angular reposition of the entire airfoil. Both the twist and the restagger angles are about the stacking line44. The section twist “N” (section restagger) tolerance with respect to the stacking line is +/−0.60 degrees (casting tolerance). The global restagger capability for the airfoil with respect to the stacking line is full stager capabililty (airfoil can be fully closed or open).