Nacelle inlet duct for a ducted fan engine

A ducted fan engine comprising:

• a fan assembly coupled to and driven by a drive mechanism;
• and
• a nacelle surrounding the drive mechanism and the fan assembly, the nacelle including an inlet duct arranged upstream of the fan assembly, the inlet duct having an inner circumferential surface extending in a circumferential direction about an inlet centerline axis and extending in an axial direction along the inlet centerline axis, and the inlet duct including:
• an inlet portion at an upstream end of the inlet duct, the inlet portion including an inlet lip and a hardwall portion, a highlight plane being defined at an upstream end of the inlet portion;
• an acoustic liner arranged downstream of the inlet portion, a hardwall-acoustic liner interface being defined at an interface of the hardwall portion and the acoustic liner;
• and
• a fan section arranged downstream of the acoustic liner,
• wherein (a) the inlet portion and the acoustic liner are coupled together at an inlet-acoustic liner interface extending circumferentially about the inner circumferential surface of the inlet duct, (b) the inlet lip varies circumferentially and axially with respect to the highlight plane and the inlet centerline axis, (c) the inlet lip includes a plurality of inlet lip crests arranged along the highlight plane, and a plurality of inlet lip troughs arranged downstream of the highlight plane, and (d) the hardwall-acoustic liner interface extends circumferentially about the inner circumferential surface and is arranged axially parallel to the highlight plane.