Abstract:
Gas turbine engines and related systems involving variable vanes are provided. In this regard, a representative vane assembly for a gas turbine engine includes: a first inner diameter platform; a first outer diameter platform spaced from the first inner diameter platform; and a variable vane airfoil rotatably attached to and extending between the first inner diameter platform and the first outer diameter platform such that at least a portion of the vane airfoil extends beyond a periphery of at least one of the first inner diameter platform and the first outer diameter platform.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to gas turbine engines. 
     2. Description of the Related Art 
     Many gas turbine engines incorporate variable stator vanes, the angle of attack of which can be adjusted. Conventionally, implementation of variable vanes involves providing an annular array of vane airfoils, with each of the vane airfoils being attached to a spindle. The spindles extend radially outward through holes formed in the engine casing in which the vane airfoils are mounted. Each of the spindles is connected to a lever arm that engages a unison ring located outside the engine casing. In operation, movement of the unison ring pivots the lever arms, thereby rotating the spindles and vane airfoils. 
     SUMMARY 
     Gas turbine engines and related systems involving variable vanes are provided. In this regard, an exemplary embodiment of a vane assembly for a gas turbine engine comprises: a first inner diameter platform; a first outer diameter platform spaced from the first inner diameter platform; and a variable vane airfoil rotatably attached to and extending between the first inner diameter platform and the first outer diameter platform such that at least a portion of the vane airfoil extends beyond a periphery of at least one of the first inner diameter platform and the first outer diameter platform. 
     An exemplary embodiment of a variable vane for a gas turbine engine comprises: a shaft having a first end and a second end; a vane airfoil attached to the shaft between the first end and the second end; a tapered spline located between the airfoil and the second end, the spline being configured such that a narrow portion of the spline is located toward the second end. 
     An exemplary embodiment of a gas turbine engine comprises: a compressor; a combustion section operative to receive compressed air from the compressor; a turbine operative to drive the compressor, the turbine having a vane assembly; the vane assembly comprising: a first inner diameter platform; a first outer diameter platform spaced from the first inner diameter platform; and a variable vane airfoil rotatably attached to and extending between the first inner diameter platform and the first outer diameter platform such that at least a portion of the vane airfoil extends beyond a periphery of at least one of the first inner diameter platform and the first outer diameter platform. 
     Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine. 
         FIG. 2  is a partially cut-away, schematic diagram depicting a portion of the vane assembly of the embodiment of  FIG. 1 . 
         FIG. 3  is a schematic diagram depicting an exemplary embodiment of a vane assembly. 
         FIG. 4  is a schematic diagram depicting assembly detail of the embodiment of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Gas turbine engines and related systems involving variable vanes are provided, several exemplary embodiments of which will be described in detail. In this regard, some embodiments involve the use of a variable vane airfoil that spans at least a portion of a gap formed between adjacent vane platforms. By positioning the vane airfoil in such a manner, the vane tends to block radial gas leakage through the platform gap. 
       FIG. 1  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine. As shown in  FIG. 1 , engine  100  incorporates a fan  102 , a compressor section  104 , a combustion section  106  and a turbine section  108 . Engine  100  also incorporates a variable vane assembly  110 . Although depicted in  FIG. 1  as being positioned between a low-pressure turbine and a high-pressure turbine, various other locations of a variable vane assembly can be used in other embodiments. Additionally, although depicted in  FIG. 1  as a turbofan gas turbine engine, there is no intention to limit the concepts described herein to use with turbofans as other types of gas turbine engines can be used. 
     With reference to the partially cut-away, schematic diagram of  FIG. 2 , vane assembly  110  includes an annular arrangement of vanes positioned about a longitudinal axis  112 . Inner and outer diameter platforms of the vanes mount vane airfoils. By way of example, vanes  120  and  130  include inner diameter platforms  122 ,  132 , respectively, and outer diameter platforms  124 ,  134 , respectively. Vane airfoils (e.g., airfoil  136 ) extend radially across the annulus located between the inner and outer platforms. Notably, in contrast to being positioned entirely within the periphery defined by the platforms of a single vane, airfoil  136  extends beyond the periphery of platforms  132 ,  134 . 
     In the embodiment of  FIG. 2 , an inner platform gap  126  is located between adjacent inner platforms  122 ,  132 , and an outer platform gap  128  is located between adjacent outer platforms  124 ,  134 . Airfoil  136  obstructs at least a portion of each of the gaps. In some embodiments, the length of the gap spanned can be as much as a chord length of the airfoil. In those embodiments in which the airfoil obstructing the gap is a variable vane, the vane length of the gaps being spanned can vary depending upon the rotational positioning of the airfoil. Notably, the gap can be oriented in various manners relative to the longitudinal axis of the engine. For instance, in the embodiment of  FIG. 2 , the gap is not parallel with longitudinal axis  112 . 
     An exemplary embodiment of a vane is depicted in  FIG. 3 . As shown in  FIG. 3 , vane  150  is configured as a doublet incorporating two vane airfoils. Specifically, airfoil  152  is a stationary airfoil, whereas airfoil  154  is a variable airfoil. In other embodiments, various other numbers and configurations of airfoils can be used. 
     The vane airfoils  152 ,  154  extend between an inner diameter platform  156  and an outer diameter platform  158 . Platform  156  includes an inner diameter surface  160 , an outer diameter surface  161 , a forward edge  162 , an aft edge  164 , and side edges  166 ,  168  that extend between the forward and aft edges. Platform  158  includes an inner diameter surface  170 , an outer diameter surface  171 , a forward edge  172 , an aft edge  174 , and side edges  176 ,  178  that extend between the forward and aft edges. 
     Outer diameter surface  161  of the inner platform and inner diameter surface  170  of the outer platform incorporate recesses that are configured to receive corresponding ends of variable airfoils. In particular, surface  161  of the inner platform includes a suction-side root recess  180  that intersects side edge  168 , and a pressure-side root recess  182  that intersects side edge  166 . Suction-side root recess  180  is sized and shaped to receive the root  184  of airfoil  154 , whereas pressure-side root recess  182  is sized and shaped to receive the root of an adjacent variable airfoil (not shown). Surface  170  of the outer platform includes a suction-side root recess  186  that intersects side edge  178 , and a pressure-side root recess  188  that intersects side edge  176 . Suction-side root recess  186  is sized and shaped to receive the tip  190  of airfoil  154 , whereas pressure-side root recess  188  is sized and shaped to receive the tip of an adjacent variable airfoil (not shown). 
     By placing the airfoil  154  on the suction side of airfoil  152 , the sweep of the trailing edge  191  of the variable vane can be contained within the vane  150 . Such a configuration tends to ensure that vane-to-vane variations do not affect the leak path located between adjacent vanes. 
     Vane airfoil  154  is a portion of a variable vane  200  that includes a shaft  202  and a bearing  204 . In the embodiment of  FIG. 3 , the shaft is a hollow shaft that extends through the airfoil from an outer diameter portion of the shaft (located near the tip of the airfoil) to an inner diameter portion of the shaft (located near the root of the airfoil). The hollow shaft receives a flow of cooling air for cooling the vane airfoil. In some embodiments, cooling air is directed from the outer diameter portion of the shaft through to the inner diameter portion of the shaft. 
     In other embodiments, cooling air can be provided through stationary airfoil  152 , such as from the outer diameter to the inner diameter. From the inner diameter of the stationary vane, the cooling air can be routed to the inner diameter portion of the shaft and then outwardly to the outer diameter portion. Such a configuration can reduce the size requirements of the hollow portion of the shaft at the outer diameter, thereby permitting the use of a narrower shaft and associated components. Additional cooling can be provided by the platform gaps formed between adjacent platforms of adjacent vanes. 
     Shaft  202  includes a tapered spline  206 , with bearing  204  being located between the airfoil and the spline. The spline is operative to receive torque for positioning the variable vane. That is, rotation of the shaft via the spline pivots the airfoil. Notably, use of a tapered spline may promote engagement of spline teeth of the shaft with those of an actuation arm (not shown), thereby eliminating a source of hysteresis. 
     Bearing  204  is configured as a pillow block in the embodiment of  FIG. 3 . Bearing  204  incorporates flanges  210 ,  212  that engage corresponding flanges  214 ,  216  located on the outer diameter surface of the outer platform  158 . So engaged, the shaft is received by a split aperture  220  formed in side edge  178  of the outer diameter platform. A corresponding split aperture  222  is formed in side edge  176  that receives a portion of a shaft of a variable vane of an adjacent vane (not shown). The inner diameter platform incorporates a bearing  224  that receives distal end  226  of the shaft  202 . 
     In some embodiments, bearing  224  can be configured as a cartridge bearing and/or contain a spherical bearing. It should be noted that by providing a spherical surface, misalignment of the inner diameter and outer diameter platforms should not induce a bending moment on the on airfoil  154 . 
     As mentioned before, multiple vanes typically are configured in an annular arrangement of vanes to form a vane assembly. The vane assembly defines an annular gas flow path between the vanes and platforms. Multiple vanes similar in construction to vane  150  can be provided in such an assembly. As such, the annular arrangement includes alternating stationary and variable airfoils. 
     Assembly detail of the embodiment of  FIG. 3  is shown in the schematic diagram of  FIG. 4 . As shown in  FIG. 4 , stationary portions of the vane are provided as an assembly  230  that is adapted to receive variable vane  200 . Locating the variable vane at the side edges of the platforms enables the distal end  226  of the shaft to be received by the bearing. The free end  240  of the shaft then can be pivoted about the distal end so that flanges of the pillow block engage corresponding flanges of the outer diameter platform. This also enables the root and tip of the airfoil  154  to be received within corresponding recesses of the platforms. 
     Since the variable vane is configured as a removable portion of the vane assembly, the variable vane can be separately formed from the assembly. This can result in relative ease of manufacture. Notably, various materials can be used to form a variable vane and/or associated vane airfoil such as ceramic, Ceramic Matrix Composite (CMC), metals and/or metal alloys, e.g., nickel-based superalloy. 
     It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.