Bypass transition

It occurs when a laminar boundary layer transitions to a turbulent one through some secondary instability mode, bypassing some of the pre-transitional events that typically occur in a natural laminar–turbulent transition.

[a] The bypass transition scenario was first observed experimentally by P. S. Klebanoff, during his experiments in elevated free-stream turbulence flow.

In an experiment using hot wires, he studied flow over a flat plate that was subjected to a 0.3% free-stream turbulence level.

He also observed fluctuations in boundary layer thickness, which does not occur in low-turbulence free-stream flow.

Through various laboratory experiments and computational studies, it has been observed that low frequency streaky flow structures are present in the laminar boundary layers.