Applied Physics

Shaking Up Viscous Fluids

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Science  19 May 2006:
Vol. 312, Issue 5776, pp. 974
DOI: 10.1126/science.312.5776.974d

The transition from smooth laminar flow to chaotic turbulent flow is a problem of fundamental interest and is also of practical relevance in areas ranging from manufacturing to weather pattern formation. In Newtonian fluids such as pure water, the transition arises as a consequence of an increase in the flow rate, which in turn causes bifurcations in the flow that lead to localized flow rolls and then to chaotic or turbulent flows; in viscous fluids, these inertial instabilities are suppressed, but turbulent-like transitions have nonetheless been observed.

Schiamberg et al. used a parallel plate rheometer to study a series of polymer solutions in which instabilities arise from the elastic motions of individual polymer chains as they stretch and contract within a less viscous solvent. On slowly increasing the flow stress, the authors observed secondary flows: first, axially symmetric rings that formed near the outer edge of the sample; then, with rising shear stress, competing nonsymmetric rings that led to chaotic multispirals and eventually to elastic turbulence, with an accompanying factor of 13 rise in the apparent viscosity (or resistance to flow). Changing the polymer concentration induced additional flow modes, offering a rich library for theoretical development and comparison with the inertial transitions seen in Newtonian fluids. — MSL

J. Fluid Mech. 554, 191 (2006).

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