Sound propagation in uniformly lined straight ducts with uniform mean flow is well established by its analytically exact description in duct modes [1, 2, 3]. In cross-wise nonuniform flow there are still modes, although the (Pridmore-Brown) equation that describes them is in general not solvable in terms of standard functions [4, 5, 6, 7, 8, 9] and has to be solved numerically. These modal solu...