Ventilation device including a turbine mounted inside a radially volute-shaped casing, the peripheral wall of the casing moving progressively away from the periphery of the turbine from a volute tongue to a distal end (E2) of the volute, the radial expansion of the volute being defined by an angle of expansion (ai), characterised by the fact that the initial angle of expansion (a1) in the vicinity of the volute tongue is 1.5 times to 3 times greater than the final angle of expansion (a2) in the vicinity of the distal end (E2) of the volute, so that the peripheral wall of the casing moves away from the blades more rapidly at the start of the volute minimising the turbulences generated at the volute tongue.
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