Patent Application
20080124221
The invention relates generally to a vane airfoil for a gas turbine engine and, more particularly, to an airfoil profile suited for a low pressure turbine (LPT) stage vane of an auxiliary power unit (APU).
Where a vane airfoil is part of a single stage turbine driving a fan or other output shaft (i.e. is part of a single stage LP turbine), as opposed to being part of multiple stage turbine, the requirements for such a vane airfoil design are significantly more stringent, as the fan/output shaft relies solely on this single stage LP turbine to deliver work, as opposed to work being spread over several turbine stages. Over and above this, the airfoil is subject to flow regimes which lend themselves easily to flow separation. Such a situation would limit the amount of work transferred to the fan/output shaft, and hence the total thrust (or power) capability of the engine. Further complicating the aerodynamic situation in a single stage LP turbine occurs where the LP vane follows a transonic high pressure turbine stage (HPT), and where a significant gaspath flare angle away from the engine center line, which is provided to improve work output of the turbine, but which then must be re-directed by the LP vane into being more parallel to the engine center line prior to entering the following LP blade passage. Therefore, improvements in airfoil design are sought.
It is therefore an object of this invention to provide an improved vane airfoil design for use in a single stage low pressure turbine of an APU.
In one aspect, the present invention provides a turbine vane for a gas turbine engine comprising an airfoil having an intermediate portion defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 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 invention provides a turbine vane for a gas turbine engine having an intermediate airfoil portion at least partly defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 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, and wherein the X and Y values are scalable as a function of the same constant or number.
In another aspect, the present invention provides a turbine stator assembly for a gas turbine engine comprising a plurality of vanes, each vanes including an airfoil having an intermediate portion defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 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 invention provides a low pressure 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 Table 1, wherein a fillet radius is applied around the airfoil between the airfoil and platforms, and wherein the values of Table 2 are subject to relevant tolerance.
The design profile of the present invention improves performance of a single stage LPT of a large auxiliary power unit. In accordance with a general aspect, the radial distribution of aerofoil sectional throats is optimized for providing optimum work on the downstream power turbine blades. The vane profile is also designed to reduce static pressure gradients and, thus, minimize secondary losses.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
The gas turbine engine 10 further includes a turbine exhaust duct 20 which is exemplified as including an annular core portion 22 and an annular outer portion 24 and a plurality of struts 26 circumferentially spaced apart, and radially extending between the inner and outer portions 22, 24.
A plurality of turbine stages of the turbine section 18 are shown in the gaspath 27, and more particularly a high pressure turbine (HPT) stage located downstream of the combustor 16 and a low pressure turbine (LPT) stage further downstream are exemplified. The turbine exhaust duct 20 is shown downstream from the LPT stage. The LP turbine has a single stage.
Referring to
More specifically, the stator assemblies 32, 34 each include the plurality of circumferentially distributed vanes 40a and 40b respectively which extend radially across the hot gaspath 27. The LPT stator assembly 32 comprises 38 vanes 40b that are uniformly circumferentially distributed.
The novel airfoil shape of each LPT stage vane 40b is 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 is well-adapted for use in a single-stage LPT 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 centerline 29, i.e., the rotary axis. The positive X direction is axially towards the aft of the turbine engine 10. The Z axis extends along the LPT vane stacking line 48 of each respective vane 40 in a generally radial direction and intersects the X axis. The positive Z direction is radially outwardly toward the outer vane platform 62. The Y axis extends tangentially with the positive Y direction being in the direction of rotation of the rotor assembly 38. 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 engine 10 and the staking line 48.
In a particular embodiment of the LPT stage, the set of points which define the LPT stage vane airfoil profile relative to the axis of rotation of the turbine engine 10 and the stacking line 48 thereof are set out in Table 2 below as X, Y and Z Cartesian coordinate values. Particularly, the vane airfoil profile is defined by profile sections 66 at various locations along its height, the locations represented by Z values. It should be understood that the Z values do not represent an actual radial height along the airfoil 54 but are defined with respect to the engine centerline. For example, if the vanes 40b are mounted about the stator assembly 34 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 vanes 40b. 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 section 66 are 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 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 sections 66 to one another to form the airfoil profile.
The coordinate values listed in Table 2 below represent the desired airfoil profiles in a cold (i.e. “non-operating”) condition. However, the manufactured airfoil surface profile will be slightly different as a result of manufacturing tolerances. The coordinate values listed in Table 2 below are for an uncoated airfoil. It is noted that according to an embodiment of the present invention, the vanes are not coated subsequent to being cast.
The Table 2 values are generated and shown to three decimal places for determining the profile of the LPT stage vane airfoil. However, as mentioned above, there are manufacturing tolerance issue to be addressed and, accordingly, the values for the profile given in Table 2 are for a theoretical airfoil to which a ±0.003 inch manufacturing tolerance is additive to the X and Y values given in Table 2 below. The LPT stage vane airfoil design functions well within this preferred range. 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 uncoated nominal LPT stage vane airfoil profile.
It should be understood that the finished LPT vane 40b does not necessarily include all the sections defined in Table 2. The portion of the airfoil 54 proximal to the platforms 60 and 62 may not be defined by a profile section 66. It should be considered that the vane 40b airfoil profile proximal to the platforms 60 and 62 may vary due to several imposed. However the LPT vane 40b has an intermediate airfoil portion 64 defined between the inner and outer vane platforms 60 and 62 thereof and which has a profile defined on the basis of at least the intermediate Sections of the various vane profile sections 66 defined in Table 2.
It should be appreciated that the intermediate airfoil portion 64 of the LPT stage vane 40b is defined between the inner and outer gaspath walls 28 and 30 which are partially defined by the inner and outer vane platforms 60 and 62. Therefore, the airfoil profile physically appearing on LPT vane 40b includes, Sections 3 to 8 of Table 2. Sections 2 and 9 are partly included within the gaspath. Sections 1 and 10 are located outside of the boundaries set by the inner and annular outer gaspath walls 28 and 30, but is provided, in part, to fully define the airfoil surface and, in part, to improve curve-fitting of the airfoil at its radially inner distal portion. The skilled reader will appreciate that a suitable fillet radius is to be applied between the platforms 60 and 62 and the airfoil portion of the vane.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. For example, the airfoil and/or gaspath definitions of Tables 1 and 2 may be scaled geometrically, while maintaining the same proportional relationship and airfoil shape, for application to gas turbine engine of other sizes. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
