Turbofan engine inlet duct modes (M = 0.5 )

kb = 3, m = 1, soft wall

kb = 16, m = 10, hard wall

kb = 20, m = 10, soft wall

kb = 30, m = 10, hard wall

(see Journal of Fluid Mechanics 380, 1999, p.279-296;  437, 2001, p.366-383;  495, 2003, p.157-173)