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On turbulent entrainment and dissipation in dilute polymer solutions

Liberzon, A. and Holzner, M. and Lüthi, B. and Guala, M. and Kinzelbach, W. (2009) On turbulent entrainment and dissipation in dilute polymer solutions. Physics of Fluids, 21 (3). 035107. ISSN 1070-6631.

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We present a comparative experimental study of a turbulent flow developing in clear water and dilute polymer solutions (25 and 50 wppm polyethylene oxide). The flow is forced by a planar grid that oscillates vertically with stroke S and frequency f in a square container of initially still fluid. Two-component velocity fields are measured in a vertical plane passing through the center of the tank by using time resolved particle image velocimetry. After the forcing is initiated, a turbulent layer develops that is separated from the initially irrotational fluid by a sharp interface, the so-called turbulent/nonturbulent interface (TNTI). The turbulent region grows in time through entrainment of surrounding fluid until the fluid in the whole container is in turbulent motion. From the comparison of the experiments in clear water and polymer solutions we conclude: (i) Polymer additives modify the large scale shape of the TNTI. (ii) Both, in water and in the polymer solution the mean depth of the turbulent layer, H(t), follows the theoretical prediction for Newtonian fluids H(t)∞√Kt, where K∞S^2f is the “grid action.” (iii) We find a larger grid action for dilute polymer solutions than for water. As a consequence, the turbulent kinetic energy of the flow increases and the rate of energy input becomes higher. (iv) The entrainment rate β=v_e/v_(rms) (where v_e=dH/dt is the interface propagation velocity and v_(rms) is the root mean square of the vertical velocity) is lower for polymers (β_p≈0.7) than for water (β_w≈0.8). The measured values for β are in good agreement with similarity arguments, from which we estimate that in our experiment about 28% of the input energy is dissipated by polymers.

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Additional Information:© 2009 American Institute of Physics. Received 28 April 2008; accepted 29 January 2009; published online 26 March 2009.
Subject Keywords:flow visualisation; fluid oscillations; polymer solutions; stratified flow; turbulence
Issue or Number:3
Record Number:CaltechAUTHORS:20090529-080508948
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14336
Deposited By: Tony Diaz
Deposited On:05 Aug 2009 17:21
Last Modified:03 Oct 2019 00:49

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