Abstract:
An integrally bladed rotor is utilized in at least a stage of one of a compressor and turbine section. Airfoils extend radially outwardly from a platform, and there is an undercut inward from the platform at a downstream edge of the airfoil.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to an undercut rim used with a bladed rotor disk for a gas turbine engine section, wherein a plurality of rotor sections are held together by a tie shaft. 
         [0002]    Gas turbine engines are known, and typically include a compressor section that compresses air to be delivered into a combustion section. Air is mixed with fuel in the combustion section and ignited. Products of this combustion pass downstream over turbine rotors, driving the turbine rotors to rotate. 
         [0003]    Typically, the turbine rotors are arranged in several stages as are compressor rotors. It has typically been true that the rotor stages have been connected together by welded joints, bolted flanges, or other mechanical fasteners. This has required a good deal of additional weight and components. 
         [0004]    More recently, a tie shaft arrangement has been proposed wherein the rotors all abut each other, and a tie shaft applies an axial force to hold them together and transmit torque, thus eliminating the need for weld joints, bolts, etc. 
         [0005]    Some integrally bladed rotors have the abutment face in the proximity of the airfoil edge that will expose the airfoil to stresses generated by tie shaft preload and rotational forces. 
       SUMMARY OF THE INVENTION 
       [0006]    An integrally bladed rotor is utilized in at least a stage of one of a compressor and turbine section. The rotors feature and inner hub and an outer rim that includes the platform the airflow path (platform). Airfoils extend radially outwardly from a platform, and there is an undercut in the rotor rim under the platform between the airfoil and the abutting face at a downstream edge of the airfoil. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  schematically shows a typical compressor section. 
           [0009]      FIG. 2  shows a portion of the  FIG. 1  section with an undercut. 
           [0010]      FIG. 3  shows an enlarged portion of the  FIG. 2  section. 
           [0011]      FIG. 4  is a top view of an example rotor incorporated into the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]      FIG. 1  shows a compressor rotor  32  that utilizes a tie shaft connection. As known, a tie shaft  30  joins together a compressor section  32 , comprising of a plurality of rotor stages  40 ,  42 , and  44 . The sections  40 ,  42  and  44  may all be “integrally bladed rotors,” or may have removable blades. As illustrated, rotor  44  has removable blades, as an example. Rotor stage  40  is an integrally bladed rotor, with a rotor hub that rotates about an axis of the shaft  30 , and which carries a plurality of secured rotor blades  50 . 
         [0013]    As can be appreciated, an upstream end of the rotor  44  provides the stacking interface with a downstream end of the integrally bladed rotor  40 . Typically, these interfaces have been simply placed radially inward of the platform of the integrally bladed rotor, and abutting an end face of the neighboring rotor. As mentioned above, with such an arrangement, there has been a force or stress applied forcing the platform of the integrally bladed rotor radially outwardly. 
         [0014]    As shown, a rear hub  37  biases the stages together. A left side a front hub  100 , shown schematically, provides the reaction for the rotors stack being compressed by the tie shaft  30 . In practice, there may be something closer to the rear hub  37  extending radially away from the tie shaft  30  at the left side in place of the schematically shown hub  100 . A nut  34  directs a force through the hub  37  into the several stages, holding them together. A force vector along the axis of a portion  101  of a section  102 , directs the force into the rotor stages. 
         [0015]    As shown in  FIGS. 2 and 3 , the axial component F is delivered from the downstream stage  44  into the integrally bladed rotor stage  40 . The integrally bladed rotor stage  40  has an upstream ear  52  fitting within a recess  53  on the next most upstream rotor section  42 . The rotor stage  44  has a pocket  72  having an outer ear  74  and an inner ear  70 . A bottom portion  68  of a platform  52  of the rim of the integrally bladed rotor  40  has a forward edge  66  abutting the face  72 . Thus, the force F is passed into the face  66 . A curved undercut  64  is cut away from the rim under the platform  52 , such that a trailing edge  62  of the airfoil  50  is not exposed to the force F. Instead, the undercut  64  limits the upper surface  69  of the rim at the area of the connecting surfaces  66  and  72 . This ensures there are no forces transmitted from the force F into the airfoil  50 , which is undesirable. 
         [0016]    As can be appreciated from  FIG. 4 , the rim of the rotor stage  40  receives a plurality of airfoils  50  with trailing edges  62 , which is separated from the ear  74  such that the abutting contact is radially inward of the lowermost end of the airfoil  50 . 
         [0017]    With the disclosed embodiment, the forces are not transmitted into the airfoil, and the undercut ensures that the damage to the airfoil is limited or eliminated due to the force F. In addition, the stresses from the downstream rotor rim are also addressed with this arrangement. 
         [0018]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.