On Transition from Laminar to Turbulent Flow

Water-tank observations of the flow phenomena associated with boundary-layer transition have revealed that a two-dimensional discrete vortex line, which is considered to be the consequence of an amplified perturbation wave, has a strong tendency, in shear flows, to form three-dimensional vortex loops with a marked transverse wavelength. The formation and development of the vortex loop is found to be the essential feature preceding the creation of a turbulent spot which takes place near the top of the vortex loop and near the outer edge of the boundary layer. This formation and development provides the guiding principle of laminar-to-turbulent transition in wakes and jets as well as in the boundary layer.