Bleed flow duct for a turbomachine comprising a passively actuated variable cross section VBV grating

An intermediate casing hub for a bypass turbine engine, said hub comprising:

• an inner shroud configured to delimit a primary flow space of the primary gas flow of the turbine engine,
• an outer shroud configured to delimit a secondary flow space of the secondary gas flow of said turbine engine,
• a discharge stream duct extending between the inner shroud and the outer shroud, said discharge stream duct leading on the one hand into the primary flow space through an inlet opening formed in the inner shroud, and on the other hand into the secondary flow space through an outlet opening formed in the outer shroud,
• a door that is movable between a closed position, in which the door closes a passage cross-section of the inlet opening, and an open position, in which the door opens a passage cross-section of the inlet opening, and
• discharge fins comprising a leading edge and a trailing edge opposite the leading edge,
• said discharge fins being rotatably mounted around a pivot in the discharge stream duct at the outlet opening between an open configuration, in which an air flow from the inlet opening is able to pass between the discharge fins, and a closed configuration, in which the discharge fins block a passage cross-section of the outlet opening,
• the intermediate casing hub wherein the pivot of each discharge fin is closer to its leading edge than to its trailing edge and in that the discharge fins comprise a downstream portion extending between the pivot and the trailing edge and an upstream portion extending between the pivot and the leading edge, the downstream portion and the upstream portion of the discharge fins having a different density.