Disc firtree slot with truncation for blade attachment

Abstract

A turbine rotor disc includes a plurality of attachment slots for receiving firtree-profiled blade roots. Each attachment slot is formed in an undulating profile having substantially smoothly curved and laterally, alternately recessed and projecting portions. At least one pair of substantially smoothly curved projecting portions being truncated at a tip thereof, respectively.

1 . A disc of a gas turbine rotor adapted to support a plurality of blades attached thereto, the disc comprising a plurality of attachment slots for receiving a root of the respective blades, the attachment slots being circumferentially spaced apart one from another and axially extending through a periphery of the disc, each slot including a pair of opposed side walls, each side wall being in an undulating profile having substantially smoothly curved and laterally, alternately recessed and projecting portions extending along a length of the respective slots, the recessed and projecting portions of one side wall substantially and circumferentially aligning with the respective recessed and projecting portions of the other side wall to thereby provide a profiled space defined between the opposed side walls, at least one pair of the circumferentially aligning and substantially smoothly curved projecting portions being truncated at a tip thereof, respectively. 
   
   
       2 . The disc as defined in  claim 1  wherein the truncated pair of projecting portions each define a flat surface at the tip thereof extending along an entire width of the respective projecting portions. 
   
   
       3 . The disc as defined in  claim 2  wherein the flat surface is smoothly connected to an adjacent surface of each truncated projecting portion through a curved transitional surface at each side of the flat surface. 
   
   
       4 . The disc as defined in  claim 1  wherein each pair of the circumferentially aligning and substantially smoothly curved projecting portions are truncated at a tip thereof, respectively. 
   
   
       5 . A rotor assembly of a gas turbine engine, comprising:
 a rotor disc defining a plurality of attachment slots circumferentially spaced apart one from another and extending axially through a periphery thereof;   an array of rotor blades extending radially outwardly from the periphery of the rotor disc, each of the rotor blades including an airfoil section, a blade root and platform segments extending laterally from sides of the airfoil section into opposing relationship with corresponding platform segments of adjacent blades, each of the blade roots including a series of smoothly curved lateral projections in pairs on opposite sides thereof extending along an axial length of the blade root to form a firtree profile; and   wherein each slot of the rotor disc includes a pair of opposed side walls having substantially smoothly curved and laterally, alternately recessed and projecting portions extending along a length of the respective slots, the recessed and projecting portions of one side wall substantially and circumferentially aligning with the recessed and projecting portions of the other side wall to thereby provide a profiled space defined between the opposed side walls substantially in accordance with the firtree profile of the respective blade roots, at least one pair of the circumferentially aligning and substantially smoothly curved projecting portions being truncated at a tip thereof, respectively, thereby creating a small clearance between the truncated tip of the respective projecting portions of the attachment slot and the blade root of a rotor blade attached thereto.   
   
   
       6 . The rotor assembly as defined in  claim 5  wherein the firtree-profiled blade roots and attachment slots are sized so as to provide a desired radial play therebetween. 
   
   
       7 . The rotor assembly as defined in  claim 5  wherein the truncated pair of projecting portions define a flat surface at the tip thereof extending along an entire width of the respective projecting portion. 
   
   
       8 . The rotor assembly as defined in  claim 7  wherein the flat surface is smoothly connected to an adjacent surface of the truncated projecting portion through a curved transitional surface at each side of the small flat surface. 
   
   
       9 . The rotor assembly as defined in  claim 5  wherein each pair of the circumferentially aligning and substantially smoothly curved projecting portions are truncated at a tip thereof, respectively. 
   
   
       10 . A disc for a gas turbine engine comprising a plurality of firtree slots provided through the disc around a periphery of the disc, the slots defined by a plurality of opposed lobes pairs extending through the disc to define sidewalls of the slot, at least one opposed lobe pair each having opposed rounded apexes, and at least one opposed lobe pair each having opposed truncated apexes.