Turbomachine with active tip clearance control

A turbomachine comprising:

• a case means having a longitudinal centerline,
• an annular shroud rigidly attached to said case means having an inner wall defining a side of an annular gas flow path of said turbomachine around said longitudinal centerline flaring radially outward in the downstream direction of said gas flow path,
• a rotor having a plurality of rotor blades thereon,
• means mounting said rotor on said case means with said rotor blades in said gas flow path for rotation about said longitudinal centerline and for bodily shiftable movement in the direction of said longitudinal centerline in a first direction toward said shroud and in an opposite second direction away from said shroud including,
• a bearing assembly having
• an inner race rigidly attached to said rotor,
• an outer race, and
• a plurality of antifriction elements between said inner and said outer races permitting relative rotation between said inner and said outer races and preventing relative bodily shiftable movement between said inner and said outer races in the direction of said longitudinal centerline
• said rotor being subjected to a net dynamic force in said first direction during operation of said turbomachine,
• means on each of said rotor blades defining a blade tip flaring radially outward in the downstream direction of said gas flow path and cooperating with said inner wall of said shroud in defining a clearance gap therebetween decreasing in response to bodily shiftable movement of said rotor in said first direction and increasing in response to bodily shiftable movement of said rotor in said second direction,
• a ferromagnetic thrust plate rigidly connected to said rotor,
• an electromagnet means on said case means having a magnetic flux field when said electromagnet means is turned on which intercepts said thrust plate and magnetically attracts said rotor in said second direction,
• a spring means between said case means and said outer race of said bearing assembly biasing said bearing assembly and said rotor in said second direction and maintaining the direction of the net force on said bearing assembly in said second direction regardless of the magnetic attraction of said electromagnet means on said thrust plate,
• position sensing means on said case means operative to generate an electrical signal during operation of said turbomachine corresponding to the instantaneous magnitude of said clearance gap between said rotor blade tips and said inner wall of said shroud, and
• control means connected to said electromagnet means and to said position sensing means operative to modulate the magnetic attraction of said electromagnet means in response to said signals from said position sensing means to maintain a substantially constant clearance gap between said rotor blade tips and said inner wall of said shroud.