Blade with non-axisymmetric platform: recess and boss on the extrados

1. A blade for a turbomachine impeller, comprising:

an airfoil including a pressure surface, a suction surface, a trailing edge, and a leading edge;

a platform extending at one of the ends of the airfoil in a direction globally perpendicular to a longitudinal direction of the airfoil;

the blade being adapted to be arranged with a plurality of substantially identical blades to form a ring around a ring axis and define therealong upstream and downstream directions, with the ring having the airfoils arranged substantially radially therein;

wherein a suction surface profile at the surface of the platform and along the suction surface has a first recessed part located axially in an upstream half of the airfoil, and a first boss-like part located axially downstream of the first recessed part.

2. The blade according to claim 1 , wherein

sections of the platform surfaces of the blades assembled into a ring, respectively close to the upstream and downstream of the airfoils, with the sections being perpendicular to the ring axis, define an upstream median circle and a downstream median circle, with these two circles defining a cone coaxial with the ring axis,

the first recessed part is depressed with respect to the cone, and

the first boss-like part is protruding with respect to the cone.

3. The blade according to claim 1 , wherein a pressure surface profile at the surface of the platform along the pressure surface includes a second boss-like part, located axially mainly in the upstream half of the airfoil.

4. The blade according to claim 3 , wherein the second boss-like part is axially extending over more than three quarters of the airfoil.

5. The blade according to claim 3 , wherein the second boss-like part is located axially between 0 and 50% of the airfoil.

6. A turbomachine comprising at least one impeller comprising at least one blade according to claim 3 .

7. The blade according to claim 1 , wherein the first recessed part is located axially between 0 and 40% of the airfoil.

8. The blade according to claim 1 , wherein a bottom point of the first recessed part is located between 12% and 35% of the airfoil.

9. The blade according to claim 1 , wherein the first boss-like part is located axially between 40 and 80% of the airfoil.

10. The blade according to claim 1 , wherein a pressure surface profile of the platform surface along the pressure surface further includes a second recessed part situated axially between 60% and 100% of the airfoil.

11. The blade according to claim 1 , wherein the platform surface further comprises an area of revolution on the side of the pressure surface of the airfoil located axially at about 75% of the airfoil.

12. The blade according to claim 11 , wherein the area of revolution extends from an inter-blade edge of the platform to the pressure surface of the airfoil.

13. The blade according to claim 1 , wherein the platform surface includes an area of revolution with respect to the ring axis close to the trailing edge of the airfoil.

14. The blade according to claim 1 , wherein portions adjacent to the platform surfaces of two adjacent blades located between their respective airfoils define an inter-airfoil surface, most of the inter-airfoil surface being generated by moving a line segment based on the suction surface and pressure surface profiles.

15. A turbomachine comprising at least one impeller comprising at least one blade according to claim 1 .