Turbojet compressor

1. A turbojet compressor comprising:

a shroud rotatable about a longitudinal axis of the compressor; and

a plurality of blades, each fastened via a root to the shroud and circumferentially spaced apart from one another so as to define between them flow passages for a gas stream passing through the compressor;

each blade having a pressure-side surface and a suction-side surface circumferentially opposite from its pressure-side surface, the pressure-side and suction-side surfaces extending axially between a leading edge and a trailing edge of the blade;

wherein the shroud presents, level with each blade root:

a suction-side ramp adjoining the suction-side surface of the blade and extending axially from the trailing edge of the blade to beyond its leading edge;

a pressure-side ramp adjoining the pressure-side surface of the blade and extending axially from the trailing edge of the blade to beyond its leading edge;

the pressure-side and suction-side ramps joining together upstream from the leading edge of the blade to form a projection, said projection presenting a profile that is twisted about an axis of the shroud so as to force the gas stream flowing in each flow passage to go around the blade root essentially via the suction-side thereof;

the suction-side ramp presenting, between the leading edge and the trailing edge of the blade, a profile that is inclined relative to the outside surface of the shroud so as to deflect the gas stream flowing in the corresponding flow passage from the suction-side surface of the blade towards the pressure-side surface of an adjacent blade; and

the suction-side ramp extending circumferentially over a distance that increases progressively from the leading edge to the trailing edge of the corresponding blade.

2. A compressor according to claim 1 , wherein the inclination of the profile of each suction-side ramp decreases progressively from the leading edge to the trailing edge of each corresponding blade.

3. A compressor according to claim 2 , wherein the inclination of the profile of each suction-side ramp decreases progressively from an angle close to 90° near the leading edge to an angle close to 0° near the trailing edge of each corresponding blade.

4. A compressor according to claim 1 , wherein the profile of the projection associated with a blade is twisted about the longitudinal axis of the compressor in the direction of rotation of the shroud.

5. A compressor according to claim 1 , wherein the upstream end of the projection associated with a blade is substantially in axial alignment with the leading edge of an adjacent blade.

6. A compressor according to claim 1 , wherein each pressure-side ramp presents, between the leading edge and the trailing edge of the corresponding blade, a profile that is inclined relative to the outside surface of the shroud.

7. A compressor according to claim 6 , wherein the inclination of the profile of each pressure-side ramp increases progressively from the leading edge to the trailing edge of the corresponding blade.

8. A compressor according to claim 7 , wherein the inclination of the profile of each pressure-side ramp increases progressively from an angle close to 0° near the leading edge to an angle close to 90° near the trailing edge of the corresponding blade.

9. A compressor according to claim 6 , wherein each pressure-side ramp extends circumferentially over a distance that decreases progressively from the leading edge to the trailing edge of the corresponding blade.

10. A compressor according to claim 1 , constituting a turbojet fan.

11. A turbojet, including a compressor according to claim 1 .

12. A compressor according to claim 1 , wherein the thickness of the projection decreases progressively from the leading edge of the blade and disappears level with an upstream end of the shroud.

13. A compressor according to claim 1 , wherein the pressure-side and suction-side ramps raise above the level of the outside surface of the shroud.