US Patent 8667773 Counter-rotating turbomachinery

A turbomachine comprises a flow duct with coaxially arranged radially inner and outer endwalls, first and second sets of axially spaced rotor stages arranged between the inner and outer endwalls, and a plurality of variable endwall segments arranged along the inner endwall. The first set of rotor stages rotates in a first direction, and the second set rotates in a second direction. The first and second sets alternate in axial series along the flow duct, such that axially adjacent rotor stages rotate in different directions. The variable endwall segments are radially positionable, in order to regulate loading on the first and second sets of rotor stages by changing a cross-sectional flow area between the inner and outer endwalls.