Method for reducing the vibration levels of a propeller of a turbine engine

1. A method for reducing vibration levels capable of occurring, in a turbine engine including at least one propeller and one coupling structure, because of turbulence of aerodynamic origin generated by the coupling structure on the propeller, the coupling structure coupling the engine to an aircraft, said method comprising the following steps:

a step A of defining an initial configuration of aerodynamic profiles as a function of an expected performance of the turbine engine, with individual aerodynamic profiles of p sections (c 1 , c 2 , . . . cp) stacked radially between a root and a tip of airfoils of the propeller and of the coupling structure;

a step B of calculating, using a computer, a synchronous forced response y(ω) on the propeller as a function of a harmonic excitation pressure force f(ω) generated by the coupling structure based on a relation y(ω)=F( τ y υ *f(ω)), where F is a linear function of a generalized aerodynamic force τ y υ *f(ω) for a fundamental mode of vibration υ in question;

a step C of defining a coefficient (α<1) of reduction of the synchronous forced response y(ω);

a step D of determining, using the computer, a tangential geometric offset value θ of the individual aerodynamic profile for each of said p stacked sections (c 1 , c 2 , . . . cp) of one of the propeller or the coupling structure in order to reduce a term corresponding to the generalized aerodynamic force associated with the fundamental mode of vibration υ| τ y*f(ω)|, a temporal phase shift φ of the harmonic excitation pressure force f(ω) being linked to the tangential geometric offset by a relation θ=N excit *φ, where N excit is a number of exciter sources, such that a combination of the p sections with the tangential offsets defines a new configuration of the aerodynamic profile of said propeller or coupling structure;

a step E of calculating, using the computer, a synchronous forced response y′(ω) on the propeller;

a step F of repeating, if |y′(ω)|>α*|y(ω)|, the step D using new tangential geometric offset values;

a step G of applying, if |y′(ω)|<α*|y(ω)|, the new configuration to at least one portion of the aerodynamic profiles of said propeller or coupling structure.

2. The method as claimed in claim 1 , wherein

y

⁡

(

ω

)

=

F

⁡

(

y

υ

τ

*

f

⁡

(

ω

)

)

=

∑

υ

=

1

n

⁢

⁢

[

y

υ

*

y

υ

T

*

1

/

(

ω

υ

2

-

ω

2

+

j

*

ω

*

β

υ

)

]

*

f

⁡

(

ω

)

(

1

)

where

the symbol Σ means that the synchronous forced response y(ω) is a sum of forced responses of each fundamental mode of vibration υ to a pulsation ω,

y υ corresponds to modal deflection of a mode υ under a hypothesis of a unit norm of Eigen vectors relative to a weight,

T y υ corresponds to a transpose of a preceding vector,

ω υ corresponds to pulsation associated with the mode υ,

ω corresponds to the pulsation of excitation,

j 2 =−1,

β υ corresponds to a generalized modal damping for a mode, and

f(ω) is the harmonic excitation force in a form of f*cos(ω*t+φ),

where t is time and φ the temporal phase shift.

3. The method as claimed in claim 2 wherein the propeller is in a wake of the coupling structure.

4. The method as claimed in claim 2 wherein the propeller is upstream of the coupling structure.

5. The method as claimed in claim 2 wherein said propeller is any one of a set of two propellers forming a propfan, the propfan being corotating or contrarotating.

6. The method as claimed in claim 1 wherein the propeller is in a wake of the coupling structure.

7. The method as claimed in claim 1 wherein the propeller is upstream of the coupling structure.

8. The method as claimed in claim 1 wherein said propeller is any one of a set of two propellers forming a propfan, the propfan being corotating or contrarotating.

9. The method as claimed in claim 1 wherein the coupling structure is a mast.