We report measurements of turbulent drag reduction of two different polyelectrolyte solutions: DNA and hydrolyzed Polyacrylamide. Changing the salt concentration in the solutions allows us to change the flexibility of the polymer chains. For both polymers the amount of drag reduction was found to increase with the flexibility. Rheological studies reveal that the elongational viscosity of the so...

Toms (1949) discovered that if a very small amount of drag reducing polymers (DRP) are added in the flow, approximately 10 ppm by weight or less, a substancial reduction in pressure drop at a given flow rate resulted. Then, since 1948, the phenomenon of drag reduction have been studied by many researchers with the objective of understand the drag reduction mechanism. In the last decades, the dr...

© Appl. Rheol. 15 (2005) 370–389 Abstract: We present a one-parameter model that fits quantitatively the mean velocity profiles from experiments and numerical simulations of drag-reduced wall-bounded flows of dilute solutions of polymers and non-Brownian fibers in the low and modest drag reduction regime. The model is based on a viscous mechanism of drag reduction, in which either extended poly...

The current study explores the use of an automated direct/iterative design method for the reduction of drag for transport con gurations, including con gurations with engine nacelles. The method requires the user to choose a proper target-pressure distribution and then develops a corresponding airfoil section. The method can be applied to two-dimensional airfoil sections or to three-dimensional ...

This paper presents a Computational Fluid Dynamics (CFD) investigation of the aerodynamic effects of drafting in cycling. In drafting, cyclists ride close behind each other to reduce aerodynamic drag. The CFD simulations for single cyclists and for a group of two cyclists are successfully compared with wind-tunnel measurements. Both CFD simulations and wind tunnel measurements show that also th...

Rocky intertidal organisms experience large hydrodynamic forces due to high water velocities created by breaking waves. Flexible organisms, like macroalgae, often experience lower drag than rigid organisms because their shape and size change as velocity increases. This phenomenon, known as reconfiguration, has been previously quantified as Vogel's E, a measure of the relationship between veloci...