An Experimental Study of Turbulence Production Near a Smooth Wall in a Turbulent Boundary Layer with Zero Pressure-gradient

Detailed study of the structure of a turbulent boundary layer near a smooth wall is presented including instantaneous values of: velocity profiles, fluctuation data, and turbulence production rates. It is shown that essentially all the turbulence production occurs during 'bursting times.' The details of the bursting process are described in three stages: low-speed streak lifting, oscillatory growth, and breakup. It is shown that the streak-lifting creates an unstable (inflexional) region in the instantaneous velocity profile. This unstable region is followed, in the downstream flow, by oscillatory growth and breakup. Short duration energy spectra, auto-correlation data, fluctuation data in mean value and for bursting and non-bursting times, detailed photos of the flow processes, and comparison of measured frequencies with calculated unstable frequencies all suggest that the process of turbulence production near smooth walls is due to the formation of a local instability of the Kelvin-Helmholz type arising from the interaction of the wall model with the outer flow, that is from low-speed streak lifting. (Author).