Method and device for reducing the noise of turbo-machines

A turbo-machine which comprises:

• at least one ring of circumferentially spaced, radially oriented rotor blades, the inner edges of which are attached to a rotor shaft;
• a rotatable cylindrical screen positioned around said rotor blades and integrally connected to their outer edges;
• and
• means for reducing the noise produced by the rotor blades during rotation with said cylindrical screen, said means comprising
• means forming a plurality of perforations in said cylindrical screen near the peripheral edges of said rotor blades,
• means for injecting pressurized fluid in the form of a jet through each of said perforations in said cylindrical screen,
• means capable of modulating the flow of said fluid jets at a frequency which is a whole number multiple of the rotational frequency of said rotor shaft,
• means for regulating the phase of said modulated injected fluid such that the acoustic waves generated by said fluid flows are substantially in opposition with respect to phase to those of the noise created by said rotating blades,
• said means capable of modulating the flow of said fluid jets comprising a stationary pierced ring which is configured to be coaxial with said cylindrical screen and positioned in slidable engagement with the outer periphery thereof, said ring being located between said means forming perforations in said cylindrical screen and said means for injecting pressurized fluid through each perforation such that said fluid must pass therethrough.