LASER ANEMOMETER MEASUREMENTS OF TURBULENCE IN NON-NEWTONIAN PIPE FLOWS.
MICHIGAN UNIV ANN ARBOR DEPT OF MECHANICAL ENGINEERING
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The structure of turbulence in non-Newtonian fluids flowing in a pipe is investigated by the use of a laser anemometer. The instrumentation of the optical system and signal processing to satisfy the optical requirements and the signal-to-noise ratio are presented. The spatial requirement of the beam signal is described with regard to the lens, aperture, wavelength, and the angular alignment of the scattered and reference beams. The Doppler-shifted frequency signal obtained in turbulent flows was converted to a corresponding instantaneous voltage and then analyzed electronically. A gravity-flow system was used instead of a pumped-flow system to minimize the degradation of polymer solutions. The measurements of flow rate vs shear stress indicate that the polymer additives used give a consistent delay of transition to turbulence, as compared with Newtonian fluids. This delay is believed to be due to the elastic property of the polymer solutions. The mean velocity distribution for fully turbulent flow of polymer solutions is more blunt and that near the transition region less blunt than profiles found for water. The axial turbulence intensities for polymer solutions are found to be substantially less than those found for water. This phenomenon of turbulence damping is believed also to be due to the elastic property of the polymer solutions. Author
- Fluid Mechanics