An axial turbine (1) has a plurality of expansion stages (2) each defined by stator blades (13) and rotor blades. The expansion stages (2) are followed by an exhaust diffuser (4) for collecting the flow passing through the expansion stages (2) and discharging it to the outside. The expansion stages (2) and/or the diffuser (4) have at least a non-axial symmetric portion. The stator blades (13) define different openings (17) along the circumference of the turbine.