Hub of an intermediate casing for an aircraft turbojet engine comprising doors with contoured geometry

1. A hub of an intermediate casing for an aircraft turbojet engine, comprising an internal ferrule configured to delimit both a primary flow space of a primary gas flow in a turbojet engine, and also at least one intermediate space, the internal ferrule being provided with at least one primary orifice as well as at least one moveable door forming a primary conduit for passage of air, said door being capable of sampling, from the primary orifice, air circulating in the primary gas space and sending back into the intermediate space sampled air in the direction of a secondary conduit for passage of air,

wherein the primary conduit has an internal surface comprising from upstream to downstream a convergent upstream part, then a non-convergent downstream part in which the downstream part comprises two portions of downstream lateral surfaces, and in which the upstream part further comprises two portions of upstream lateral surfaces, each portion of upstream lateral surface defining with a respective downstream lateral surface a lateral part of the internal surface, each portion of downstream lateral surface having a length according to an upstream-downstream direction representing between 30% and 50% of the curvilinear length from upstream to downstream of the corresponding lateral part.

2. The hub of an intermediate casing according to claim 1 , wherein each portion of downstream lateral surface is planar and forms an flaring angle from upstream to downstream of less than 5° with an average flow axis of the corresponding door.

3. The hub of an intermediate casing according to claim 1 , wherein each portion of lateral surface presents an S-shaped profile.

4. The hub of an intermediate casing according to claim 1 , wherein each door is movably mounted on the internal ferrule between a closing position and a maximum opening position of the primary orifice, and wherein the downstream part is contoured to direct airflow towards the entirety of the inlet orifice of the opposite secondary conduit when the door is in its maximum opening position.

5. The hub of an intermediate casing according to claim 1 , wherein the non-convergent downstream part tangentially extends the corresponding upstream part.

6. The hub of an intermediate casing according to claim 1 , wherein the downstream part is defined by two portions of downstream lateral surface and two radially internal and external surface portions relative to the axis of the hub, said radially internal and external portions being mutually non-convergent.

7. The hub of an intermediate casing according to claim 1 , wherein the downstream part is cylindrical.

8. The hub of an intermediate casing according to claim 1 , wherein each secondary conduit is extended from its inlet orifice by a deflector extending upstream into the corresponding intermediate space, each deflector forming an air guide conduit having an internal surface extending from said inlet orifice as far as a guide orifice arranged downstream of the outlet orifice of the corresponding door, and wherein the downstream part is contoured to confine an airflow towards the inside of the circumference of the guide orifice when the door is in a maximum opening position.

9. An intermediate casing for an aircraft turbojet engine, comprising the hub according to claim 1 .

10. An aircraft turbojet engine, comprising the intermediate casing according to claim 1 .