Airfoil and platform assembly for subsonic flow

1. An assembly comprising:

an airfoil for a turbine engine bladed wheel and a platform on which the airfoil is configured to be mounted;

a plurality of the airfoils configured to be fastened to the platform or to a plurality of the platforms assembled together so as to form a bladed wheel including a wheel axis and defining upstream and downstream directions along that axis, the airfoils being arranged radially in the wheel;

in the wheel, the platform or the assembled-together platforms present a platform surface between the airfoils and that radially defines an inside of gas-passing passages formed between the airfoils;

the platform surface presenting a circumferential depression extending axially substantially between a leading edge of an airfoil at its upstream end and up to no more than 60% of an axial extent of the airfoil at its downstream end;

wherein:

a skeleton curve is a curve representing variations of a skeleton angle of the airfoil in a section plane substantially parallel to the platform surface as a function of position along the axis of the wheel,

a linearized skeleton curve is a curve representing variations of an angle as a function of position along the axis of the wheel that connects together in a straight line points representing the skeleton angle respectively at 10% and at 90% of the axial extent of the airfoil from the leading edge,

in a vicinity of the platform, a lowered portion of the skeleton curve which lies under the linearized skeleton curve extends axially over at least half of the axial extent of the depression.

2. An assembly according to claim 1 , wherein the circumferential depression extends axially substantially between the leading edge at its upstream end and only 40% of the axial extent of the airfoil at its downstream end.

3. An assembly according to claim 1 , wherein a deepest section of the depression is situated axially in a range of 15% to 35% of the axial extent of the airfoil from the leading edge of the airfoil.

4. An assembly according to claim 1 , wherein the platform surface presents a circumferential bulging area situated axially in a downstream half of the airfoil.

5. An assembly according to claim 4 , wherein a most projecting section of the bulging area is situated axially in a range of 50% to 70% of axial extent of the airfoil from the leading edge of the airfoil.

6. An assembly according to claim 1 , wherein, in the vicinity, the skeleton curve presents a raised portion lying above the linearized skeleton angle curve and situated axially downstream from the lowered portion.

7. An assembly according to claim 6 , wherein the raised portion is located axially substantially at the level of a circumferential bulging area of the platform surface, the circumferential bulging area being situated axially in a downstream half of the airfoil.

8. An assembly according to claim 1 , wherein the skeleton curve presents a slope of absolute value that is less than that of the linearized skeleton curve in a range of 80% to 100%, or in a range of 60% to 100%, of the axial extent of the airfoil from its leading edge.

9. An assembly according to claim 1 , wherein an upstream skeleton angle is the skeleton angle at the leading edge of the airfoil; in a radially lower fourth of the airfoil, the upstream skeleton angle increases in absolute value on approaching the airfoil root.

10. A turbine engine blade comprising an assembly according to claim 1 and a platform formed integrally with at least one airfoil.

11. A turbine engine bladed wheel comprising blades according to claim 10 .

12. A turbine engine bladed wheel comprising at least one assembly according to claim 1 .

13. A turbine engine comprising at least one bladed wheel according to claim 11 .

14. A turbine engine comprising at least one bladed wheel according to claim 12 .