Stochastic Fluctuations of Mass Transport through Turbulent Boundary Layers

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Abstract
The stochastic fluctuation of mass transport through turbulent boundary layers was investigated by measuring the fluctuation of local diffusion‐limited currents at microelectrodes (ϕ = 0.05 mm) which are inserted in macroelectrodes. The results allow to draw some conclusions concerning the fluctuations of the flow patterns in turbulent hydrodynamic boundary layers.—The model of Einstein and Li [1] and Hanratty [2] is not only confirmed but can be extended: the laminar sublayer is quasi‐stationary for relatively long times till the scarce event of eddy‐ejection destroys it nearly completely. The eddy‐ejection renews the boundary layer down to a wall distance which amounts from 30 to 50% of the diffusion boundary layer thickness which is less than three tenths of the extension of the laminar sublayer (in fluids with Sc ã 1000). The eddy ejection is so fast, that it cannot be resolved by the method used. It is followed by the relatively fast build‐up of the laminar sublayer and this ist followed by the relaxation of the diffusion layer which is the slowest process among the stochastic processes which gouvern the mass transport through turbulent boundary layers to a wall.