Patent ID: 8066471

Claim:
An annular flow duct of a turbomachine a, comprising: a boundary wall of circular cross section arranged concentrically about a machine axis running in an axial direction of the turbomachine, where the boundary wall operatively guides a main flow, the boundary wall having a plurality of return flow passages distributed over the boundary wall circumference and through which in each case a partial flow is detached from the main flow at a bleed position and is returned to the main flow at a feed position situated upstream of the bleed position, and a plurality of aerofoils arranged radially in the flow duct of a blade collar where a tip of each aerofoil is arranged radially opposite the boundary wall and forming a gap in each case, wherein aerofoils of moving blades are movable in a predetermined direction of rotation along the circumference of the boundary wall or the boundary wall is movable in a predetermined direction of rotation relative to the aerofoils of stationary guide blades of the blade collar, wherein the bleed position of each return flow passage lies before of a corresponding feed position as viewed in the direction of rotation.