Wall layer structure and drag reduction: Bursting rates

The basic objective of this experimental study was to determine how the presence of a drag-reducing polymer solution in various portions of the wall region effects the bursting rate of the coherent wall layer structure and the wall shear stress. This was accomplished by injecting drag-reducing polymer solutions, glycerin solutions (whose viscosity matched those of the polymer solutions) and water into the viscous sublayer of fully developed, two-dimensional channel flows of water. Two injection flow rates and two set of slots were used. With thin slots and injection flow rates of 1/10 the sublayer flow rate, results were obtained when the injected solutions were confined almost entirely within the sublayer. With large slots and injection flow rates equal to the sublayer flow rate, results were obtained for situations where the injected fluid had mixed into the buffer region of the channel flow. Bursting rates were deduced from flow visualization dyed fluid while wall pressure measurements were used to determine the wall shear stress.