Drag reduction, turbulent systems

Drag reduction (DR), which was discovered more than 50 yr ago, is a turbulent flow phenomenon in which frictional energy losses can be significantly reduced by the addition of a small amount of a DR additive (DRA) to a turbulent flow system) Drag reduction in internal flows is calculated using the following equation ... 

Gasljevic, K., An experimental investigation of drag reduction by surfactant solutions and of its implementation in hydronic systems (turbulent flow, heat transfer), Ph.D. dissertation, Department of Mechanical Engineering. University of Cahfomia at Santa Barbara, 1995. 

The addition of polymers has been investigated also for twenty years. Polymers reduce the drag of the turbulent boundary layer, without avoiding transition. Since the layer remains turbulent, there is no stringent requirement for surface smoothness, as there is for many of the other techniques. Although much is not known about the detailed mechanism, practical success can be achieved more or less routinely. As there would be in the application of any drag reduction technique, there are practical problems that must be solved to make polymers operational these include such problems as how and with what and when to mix the polymer and how to eject it, and how to mate the propulsion system to the altered body characteristics. 

In Section 4.4 we list some more general systems which can show drag reduction on turbulent flow. Some of the systems are dominantly elastic while others are probably dominantly viscous. 

Mohsenipour, A. A. and R. Pal (2013). Drag reduction in turbulent pipeline flow of mixed nonionic polymer and cationic surfactant systems. Ihe Canadian Journal of Chemical Engineering 91(1) 190. 

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