Soliton/like coherent structures: a key to opening the door to turbulence

This review summarizes recent advances in the origin of turbulence. The soliton/like coherent structure (SCS) has been identified not only as a common structure in natural transition and K-type transition, but also as a fundamental structure in N-type, O-type, and bypass-type transitions which dominates the turbulence generation. It has also been confirmed as an essential structure in turbulent boundary layers. Notably, the SCS has been successively observed in pipe flows, stratified flows, mixing layers, jet flows, falling films, and wakes. These findings collectively indicate that the SCS serves as a fundamental structure in shear flows, providing significant insights into the origin of shear turbulence.