Accession Number : ADA112980

Title :   Wall Layer Structure and Drag Reduction: Role of Viscous Sublayer.

Descriptive Note : Technical rept. 2 Jan-31 Dec 81,


Personal Author(s) : Tiederman,William G ; Bogard,David G

PDF Url : ADA112980

Report Date : Dec 1981

Pagination or Media Count : 41

Abstract : The basic objective of this experimental study was to determine if the presence of a drag-reducing polymer solution in only the viscous sublayer of a turbulent channel flow of water can inhibit the formation of low-speed streaks, and thereby reduce both the production of turbulent kinetic energy and the wall shear stress. The experiments were performed in a long water channel with a 2.5 x 25 cm rectangular cross section. Drag-reducing polymer solutions, glycerin solutions (whose viscosity matched those of the polymer solutions) and water were seeped into the viscous sublayer of the fully developed, turbulent channel flow through thin slots in both of the 25 cm walls. Flow visualization conducted immediately downstream of the slot (before the injected fluid could migrate out of the sublayer) showed that the dimensionless spanwise spacing was the same for all injected fluids. Similarly pressure drop measurements showed that drag reduction occurred only after a portion of the polymer solutions had migrated out of the viscous sublayer. These results indicate that the drag-reducing molecules have a direct effect on the flow structures in the buffer region of turbulent wall flows. (Author)

Descriptors :   *Drag reduction, *Polymers, *Channel flow, *Turbulent flow, Water, Kinetic energy, Shear stresses, Walls, Buffers, Viscosity

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE