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ISSN オンライン: 2642-0554

THE VISCOELASTIC REACTION OF POLYMERS AND THE ALTERATION OF WALL TURBULENCE

Elisabetta De Angelis
Dipartmento di Meccanica e Aeronautica, Universita di Roma "La Sapienza" - Via Eudossiana, 18 - 00184 Roma; DIN University of Bologna Via Fontanelle, 40, 47121 Forli, Italy

Carlo M. Casciola
Department of Mechanics and Aeronautics, 'Sapienza' University of Rome, Via Eudossiana 18, 00184 Rome, Italy

Renzo Piva
Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy,

要約

The exchange between the kinetic energy of turbulent flow and free energy of the polymer molecules is here argued to be the key issue in understanding the drag reducing mechanism in dilute polymer solutions. At the moment, direct numerical simulation gives the best approach to face the problem, due to the extremely small scales of the relevant phenomena which hampers experimental investigations. However, in all the current simulations, different sorts of artificial dissipation have been introduced to follow the evolution of the polymers quantities. This alters the thermodynamic balance between the rate of change of free energy and the extra-dissipation caused by the molecules. To avoid this inconvenience, the correct balance is evaluated along sample Lagrangian trajectories obtained by the available coupled solution for the fluid dynamic field. The latter can be in fact considered a good first order approximation of the exact solution.
The Lagrangian analysis shows that the free energy acts as an intermediate energy absorber. Overall the interference mechanism provided by the polymers is found to be dissipative in nature but the role of viscoelasticity is substantial, since a considerable delay between the accumulation and dissipation is observed.