Streaklines in a shear layer perturbed by two waves

Streaklines are computed for a shear flow, which is perturbed by two waves in the form of a fundamental and a subharmonic, with various combinations of the two. It is shown that the streakline gives an erroneous impression of wave amplification and presence of discrete vortices. Under certain circumstances, moreover, the streakline development could be misinterpreted as evidence of vortex merging that never exists in the assumed flow field.