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Piston-driven, unsteady separation at a sudden expansion in a tube: Flow visualization and LDA measurements (1989)

Durst, F. ; Maxworthy, T. ; Pereira, J. C. F.

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 1 (1989), S. 1249-1260

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: Flow visualization studies and laser-Doppler anemometry (LDA) measurements have been performed on the flow field generated at a sudden expansion in a cylindrical pipe during the intake stroke of a piston. The range of piston Reynolds numbers investigated, based on piston diameter and velocity, was 18–125 and covered a laminar and a transition-to-turbulence regime. A detailed study of the parameters influencing the structure of the flow, i.e., the clearance volume and the piston velocity, was carried out and is presented, and the mechanism for the creation of flow instabilities at low Reynolds numbers is outlined. One of the striking features of the flow relates to the formation of vortex structures during the intake flow. It is found that under some circumstances these structures become unstable, despite the relatively low Reynolds number of the flow.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.857348

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Measurement of the shear viscosity using a newly developed GRLDA-viscometer (1989)

Wunderlich, A. M. ; Brunn, P. O. ; Durst, F.

Springer

Rheologica acta 28 (1989), S. 473-481

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ISSN: 1435-1528

Keywords: Shearviscosity ; gradient laser Doppler anemometry ; polymersolutions ; surfactant solutions ; structuralturbulence

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Abstract A two-point laser-Doppler anemometer is used to determine velocity gradients. Measuring additionally the pressure drop in channel flow allows one to use this instrument as a viscometer. This is demonstrated by measuring two polymer solutions as well as water. Besides the velocity gradient, the system also furnishes the velocity as well as velocity fluctuations. For surfactant solutions the sudden increase in these fluctuations go hand-in-hand with the sudden shear thickening reported. This behavior thus seems to be caused by a change in type of flow field (structural turbulence) rather than a change in the rheology of the surfactant solutions.