Windmill powerplant

The present invention relates to a method for converting air-flow energy, which comprises using the energy of free air flows (Vo) around a device and subsequently expanding the air flows in order to obtain a speed of the air flow on the working blades of a turbine which is close to the speed of sound and with a constant rotational frequency of the generator. The air flows (Vo, V1, V2) circulating around the device generate a depression at the outlet section of an annular gap between the inner surface of the external envelope and the surface of the central body. This device comprises an external envelope as well as a central body which is mounted on the symmetry axis of said device and has an electrical generator fitted inside. The generator has a turbine mounted on its shaft with a convergent tube in front of it. Annular gaps are provided between the central body and the fairing, between the inner surface of the external envelope and the outer surface of the fairing, and between the inner surface of the external envelope and the surface of the central body, wherein said annular gaps increase the kinetic energy of the flow using its internal energy and the pressure energy.