Polymer Drag Reduction

Event Dates: 

Wednesday, November 11, 2015 - 4:00pm

CTQM Seminar Type: 

  • Related Seminar Series

Speaker Name(s): 

James Brasseur

Speaker Affiliation(s): 

Penn State

Abstract, Event Details: 

Fluid turbulence refers to a chaotic state of fluid motion that is dominated by strong nonlinearity among “eddies” spread over a broad range of length and time scales. It has been known since the 40’s that polymers injected at very low concentrations from the submerged surfaces of ships can dramatically reduce the drag on the ship hull by 40% or more, but that “polymer drag reduction” manifests only when the flow state is highly turbulent! The mechanical processes underlying the effect are so complicated that they are still under debate. Indeed, Pierre-Gilles DeGennes, who won the 1991 Nobel Prize in physics “for discovering that methods … can be generalized to more complex forms of matter, in particular to liquid crystals and polymers” wrote a paper on the topic that is still hotly debated by those who have researched the mechanisms. Why does the flow have to be turbulent and how do molecules orders of magnitude smaller than the smallest turbulent flow eddies cause such dramatic reductions in surface shear stress (i.e., drag)? I will address these questions using high-fidelity computer simulations of turbulent flow to argue that the essential mechanism is the suppression of momentum transport to the surface by strong interaction between polymer, turbulence and shear adjacent to the surface.