Turbulence Generation in the Wind-Driven Subsurface Water Flow
The laminar-turbulent transition of the water surface boundary layer generated by a steady wind at the entrance of a wind-wave tank is investigated experimentally. Observations of the velocity field in water were made both by flow visualization techniques and laser Doppler velocimeter measurements. Two stages in the development of the perturbations have been clearly identified. First, the slow growth of streamwise longitudinal vortices embedded into the laminar flow is followed by a rapid development of secondary instabilities resulting in the pattern breakdown. The picture looks similar to the by-pass transition to turbulence in the boundary layers over rigid plate. At the second stage, peculiar to this free surface flow, an explosive deepening of the boundary layer and a fast development of inflexional instabilities occur inside localized areas. This phenomenon leads to an intense vertical mixing, which differs dramatically from the rigid plate scenario.
KeywordsBoundary Layer Wind Speed Particle Image Velocimetry Boundary Layer Thickness Laminar Boundary Layer
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