Abstract
The effect of dilute, long-chain, polymer solutions upon the spatial structure of the viscous sublayer in fully developed, turbulent, two-dimensional channel flows was determined. The longitudinal, low-speed streaks characteristic of the sublayer were made visible by seeping dye through a transverse slot in one wall. Motion pictures yielded a detailed description of the streak formation process and revealed two major differences in the sublayer structure when drag reduction occurs. At a given nondimensional distance from the wall, the average transverse spacing of the streaks increases as the amount of drag reduction increases. The average streak spacing within the viscous sublayer is not a function of the distance from the wall in water flows and flows at lower levels of drag reduction. At high levels of drag reduction, the average spacing varies within the sublayer increasing as the wall is approached.
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