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Modifying turbulent structure with drag-reducing polymer additives in turbulent channel flows

Published online by Cambridge University Press:  26 April 2006

T. Wei  and
W. W. Willmarth
T. Wei
Affiliation:
Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, NJ 08855-0909, USA
W. W. Willmarth
Affiliation:
Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109-2140, USA
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Abstract

New power spectra computed from LDA measurements of the fluctuating u- and v-velocity signals in a turbulent channel flow with and without drag-reducing polymer (polyethylene oxide) injection are presented. LDA data rates were sufficiently high to reconstruct the simultaneous time-dependent u- and v-velocity signals along with the time-dependent Reynolds stress signal. Time-averaged statistics of the turbulent flow are presented in conjunction with the power spectral measurements which show a dramatic reduction in both the v-velocity fluctuations and Reynolds stress fluctuations throughout the channel over all frequencies. There is also a redistribution of energy in the u-velocity fluctuations from high frequencies to low frequencies throughout the channel. Different injection conditions were examined: different polymer concentrations were injected at different flow rates such that the total amount of polymer in the channel remained constant. For certain polymer concentrations, ‘large’ negative Reynolds stress, -〈uv〉/uτ2 ≈ − 0.2, was measured in the near-wall region. In addition, there is a marked difference in the u-velocity spectra and the Reynolds stress spectra close to the wall for the different injection conditions.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 245 , December 1992 , pp. 619 - 641
Copyright
© 1992 Cambridge University Press

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