Wave Breakdown and Turbulence

Some new ideas on the dynamics of shear flow turbulence are presented. Central to these is the phenomenon of wave breakdown. This is defined as the onset of a violent small-scale secondary instability developing on a large-scale primary disturbance of wave-like traveling type. It is suggested that breakdown together with the ensuing violent mixing process (a turbulent “burst”) constitutes the dominant nonlinear mechanism for the fluctuating velocity field in a turbulent boundary layer. A burst regeneration mechanism is proposed whereby one breakdown can excite large velocity defects in the shear flow which then may trigger a new breakdown, thus leading to self-maintenance of the turbulence.