ROTATABLY DRIVEN EXHAUST MIXER

A turbofan engine (10) has a bypass passage for channelling a bypass flow and a core passage for channelling a core flow around a central axis (30). An exhaust mixer arrangement (32; 32') comprises a mixer body (33) mounted for rotation about the central axis (30) and having an annular wall extending around the central axis (30). The annular wall defines a plurality of circumferentially distributed alternating inner and outer lobes (42, 44), with each inner lobe (42) protruding into the core passage, and each outer lobe (44) protruding into the annular bypass passage (24). A driving unit (50) is operatively connected to the mixer body (33) for selectively driving the mixer body (33) in rotation about the central axis (30). A controller (62) is operatively connected to the driving unit (50) for controlling a rotational speed of the mixer body (33) as a function of a flight operating condition.