Drag reduction in two phase and polymer flows

The basic dynamics of turbulent boundary layers of several media is described qualitatively: suspensions of several types and polymer solutions. Despite the considerable differences in these media, it is argued that a number of the flows are affected only in the buffer layer, and drag reduction can result if behavior in the sublayer and buffer layer differ. In polymer solutions, it is argued that molecular expansion is responsible for the difference, and experimental evidence of this expansion is presented, and compared with calculations.