Propulsion unit for an aircraft

An aeronautical propulsion unit along which a gas flow can circulate from upstream to downstream, the propulsion unit having a central longitudinal axis (X), and comprising:

• a) a first series of blades (9),
• b) a second series of blades (6) positioned downstream of the first series of blades (9),
• drive means (3,18,21,23,40,94,104,920) for rotating the blades of at least one among the first series of blades (9) and the second series of blades (6), about the central longitudinal axis,
• c) a nacelle (5) which has an aerodynamic external surface (50) relative to which the first series of blades (9) and the second series of blades (6) project radially to the central longitudinal axis (X), each blade of the first series of blades and second series of blades having:
• a free end (51) opposite to a connection end (53) forming a blade root close to the nacelle (5),
• a pressure side face (55) and a suction side face (57),
• a chord line C, at a radius centered on the central longitudinal axis (X),
• a radius (Ri) between the central longitudinal axis (X) and a location, on the blade or a pitch arm (39,36) of the blade, which is level with the external surface (50) of the nacelle (5),
• a radius (Re) between the central longitudinal axis (X) and a location, on the free end (51) of the blade, that is farthest from the central longitudinal axis (X), in a direction transverse to the central longitudinal axis (X), and
• a span (L), defined, radially to the central longitudinal axis (X), between the free end (51) and the connection end (53), in said transverse direction,
• at least some of the blades of the first series of blades (9) having variable pitch, such that each of them can pivot around a pitch arm (39) to which said blade is fixed, about a pitch axis (390) which passes through the blade (90), and/or
• at least some of the blades of the second series of blades (6) having variable pitch, such that each of them can pivot around a pitch arm (36) to which said blade is fixed, about a pitch axis (360) which passes through the blade (60),
• wherein in said propulsion unit:
• at least one of the blades of the first series of blades (9) has a trailing edge (91) having serrations (93), and/or at least one of the blades of the second series of blades (6) has a leading edge (61) having serrations (63), said serrations having tooth tips (635) and tooth troughs (634) which successively alternate,
• at least some of said blades of the first series of blades (9) and/or of the second series of blades (6) each have, along the span (L) of the blade (90, 60) or radially to the central longitudinal axis (X), a pitch angle variation (Δγ) that is less than 45°, between:
• a first straight line connecting the leading edge and the trailing edge, at a first radius where one of said tooth tips (635) is located, and
• a second straight line connecting the leading edge and the trailing edge, at a second radius where one of said tooth troughs (634) is located, adjacent to said one of the tooth tips (635),
• wherein the drive means comprise a gas turbine (21,23,24,96,102) for driving said rotation of the blades of the at least one of the first series of blades (9) and second series of blades (6), about the central longitudinal axis (X),
• wherein the gas turbine (21,23,24,96,102) is part of an engine (3) for driving the rotation of blades around the central longitudinal axis (X), and the first series of blades (9) and the second series of blades (6) are located towards an upstream end of the engine (3), and
• the nacelle (5) has an air inlet (35),
• on the nacelle (5), the air inlet (35) is located axially between pitch axes (390,360) of the blades of the first series of blades (9) and of the second series of blades (6),
• on the nacelle (5), the air inlet (35) has a lip (37) located at a radius Rb from the central longitudinal axis (X), and
• the trailing edge (91) of the first series of blades (9) has serrations located at said radius Rb.

An aeronautical propulsion unit along which a gas flow can circulate from upstream to downstream, the propulsion unit having a central longitudinal axis (X), and comprising:

• a) a first series of blades (9),
• b) a second series of blades (6) positioned downstream of the first series of blades (9),
• drive means (3,18,21,23,40,94,104,920) for rotating the blades of at least one among the first series of blades (9) and the second series of blades (6), about the central longitudinal axis,
• c) a nacelle (5) which has an aerodynamic external surface (50) relative to which the first series of blades (9) and the second series of blades (6) project radially to the central longitudinal axis (X), each blade of the first series of blades and second series of blades having:
• a free end (51) opposite to a connection end (53) forming a blade root close to the nacelle (5),
• a pressure side face (55) and a suction side face (57),
• a chord line C, at a radius centered on the central longitudinal axis (X),
• a radius (Ri) between the central longitudinal axis (X) and a location, on the blade or a pitch arm (39,36) of the blade, which is level with the external surface (50) of the nacelle (5),
• a radius (Re) between the central longitudinal axis (X) and a location, on the free end (51) of the blade, that is farthest from the central longitudinal axis (X), in a direction transverse to the central longitudinal axis (X), and
• a span (L), defined, radially to the central longitudinal axis (X), between the free end (51) and the connection end (53), in said transverse direction,
• at least some of the blades of the first series of blades (9) having variable pitch, such that each of them can pivot around a pitch arm (39) to which said blade is fixed, about a pitch axis (390) which passes through the blade (90), and/or
• at least some of the blades of the second series of blades (6) having variable pitch, such that each of them can pivot around a pitch arm (36) to which said blade is fixed, about a pitch axis (360) which passes through the blade (60),
• wherein in said propulsion unit:
• at least one of the blades of the first series of blades (9) has a trailing edge (91) having serrations (93), and/or at least one of the blades of the second series of blades (6) has a leading edge (61) having serrations (63), said serrations having tooth tips (635) and tooth troughs (634) which successively alternate,
• at least some of said blades of the first series of blades (9) and/or of the second series of blades (6) each have, along the span (L) of the blade (90, 60) or radially to the central longitudinal axis (X), a pitch angle variation (Δγ) that is less than 45°, between:
• a first straight line connecting the leading edge and the trailing edge, at a first radius where one of said tooth tips (635) is located, and
• a second straight line connecting the leading edge and the trailing edge, at a second radius where one of said tooth troughs (634) is located, adjacent to said one of the tooth tips (635),
• wherein the drive means comprise a gas turbine (21,23,24,96,102) for driving said rotation of the blades of the at least one of the first series of blades (9) and second series of blades (6), about the central longitudinal axis (X), and
• wherein the turbine (21,23,96,102) is connected to the first series of blades (9) so as to drive the rotation, around the central longitudinal axis (X), of only the blades (90) of the first series of blades (9), the blades of the second series of blades (6) defining swirl recovery vanes (60).

An aeronautical propulsion unit along which a gas flow can circulate from upstream to downstream, the propulsion unit having a central longitudinal axis (X), and comprising:

• a) a first series of blades (9),
• b) a second series of blades (6) positioned downstream of the first series of blades (9),
• drive means (3,18,21,23,40,94,104,920) for rotating the blades of at least one among the first series of blades (9) and the second series of blades (6), about the central longitudinal axis,
• c) a nacelle (5) which has an aerodynamic external surface (50) relative to which the first series of blades (9) and the second series of blades (6) project radially to the central longitudinal axis (X), each blade of the first series of blades and second series of blades having:
• a free end (51) opposite to a connection end (53) forming a blade root close to the nacelle (5),
• a pressure side face (55) and a suction side face (57),
• a chord line C, at a radius centered on the central longitudinal axis (X),
• a radius (Ri) between the central longitudinal axis (X) and a location, on the blade or a pitch arm (39,36) of the blade, which is level with the external surface (50) of the nacelle (5),
• a radius (Re) between the central longitudinal axis (X) and a location, on the free end (51) of the blade, that is farthest from the central longitudinal axis (X), in a direction transverse to the central longitudinal axis (X), and
• a span (L), defined, radially to the central longitudinal axis (X), between the free end (51) and the connection end (53), in said transverse direction,
• at least some of the blades of the first series of blades (9) having variable pitch, such that each of them can pivot around a pitch arm (39) to which said blade is fixed, about a pitch axis (390) which passes through the blade (90), and/or
• at least some of the blades of the second series of blades (6) having variable pitch, such that each of them can pivot around a pitch arm (36) to which said blade is fixed, about a pitch axis (360) which passes through the blade (60),
• wherein in said propulsion unit:
• at least one of the blades of the first series of blades (9) has a trailing edge (91) having serrations (93), and/or at least one of the blades of the second series of blades (6) has a leading edge (61) having serrations (63), said serrations having tooth tips (635) and tooth troughs (634) which successively alternate, and,
• at least some of said blades of the first series of blades (9) and/or of the second series of blades (6) each have, along the span (L) of the blade (90, 60) or radially to the central longitudinal axis (X), a pitch angle variation (Δγ) that is less than 45°, between:
• a first straight line connecting the leading edge and the trailing edge, at a first radius where one of said tooth tips (635) is located, and
• a second straight line connecting the leading edge and the trailing edge, at a second radius where one of said tooth troughs (634) is located, adjacent to said one of the tooth tips (635), and
• wherein at least one of the blades (90,60) of one of the series of blades (9,6) has the greatest deflection at a radial position located over a radial length of 0.4×(Re-Ri) from the free end (51).