Aircraft engine exhaust mixer having stiffened portions for attenuating vibration

An aircraft engine comprising:

• an engine casing housing a core of the aircraft engine, the engine casing extending circumferentially about an axis of the aircraft engine and defining a core flow passage therewithin;
• a nacelle located radially outward from and circumferentially around the engine casing, a bypass flow passage radially defined between the nacelle and the engine casing;
• and
• a mixer mounted to the engine casing, the mixer including a peripheral wall having a leading edge attached to the engine casing and a trailing edge axially spaced from the leading edge and extending around the axis, the peripheral wall including a lobed portion defining lobes that are circumferentially spaced apart and that terminate at the trailing edge, the peripheral wall including a lobeless annular portion upstream of the lobed portion and, wherein a first mixer portion and a second mixer portion are circumferentially spaced apart and respectively extend away from the leading edge from a first axial location to a second axial location, the first mixer portion at least partially including a first lobe of the lobes and the second mixer portion at least partially including a second lobe of the lobes;
• wherein the peripheral wall of the first lobe includes a stiffener at a location of line nodes of the mixer, the stiffener being a discrete feature configured to attenuate resonant vibration of the mixer, the stiffener imparting a localized increase in stiffness relative to the second lobe that is free of the stiffener and has a lower stiffness than the first lobe, wherein the mixer is rotationally asymmetrical about the axis and has an asymmetrical mass distribution about the axis for attenuating the resonant vibration of the mixer;
• and
• wherein the stiffener has a thickness that is greater than a wall thickness of the lobeless annular portion of the mixer upstream of the stiffener, the stiffener having an axial length extending from the first axial location to the second axial location downstream of the first axial location, the thickness of the stiffener being less than the axial length thereof, and the stiffener comprises one or more additional layers of the peripheral wall to define the thickness that is greater than a wall thickness of the lobeless annular portion of the mixer upstream of the stiffener.