Applied Scientific Research 59: 331–352, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands. 331 DNS of the Turbulent Channel Flow of a Dilute Polymer Solution A. BARON and S. SIBILLA Dipartimento di Ingegneria Aerospaziale, Politecnico di Milano, via Golgi, 40, 20133 Milano, Italy Abstract. A direct numerical simulation of the turbulent channel flow of a dilute polymer solution has been performed in order to compare its turbulence statistics with those obtained in a Newtonian channel flow. The viscoelastic flow has been simulated by solving the whole set of continuity, mo- mentum and constitutive equations for the six independent components of the extra-stress tensor induced by polymer addition. The Finitely Extensible Nonlinear Elastic dumbbell model was adopted in order to simulate a non-linear modulus of elasticity and a finite extendibility of the polymer macromolecules. Simulations were carried out under the “narrow channel” assumption at a Reynolds number of 169 based on the channel half height and on the friction velocity; they showed a significant reduction in drag, dependent on the influence of the elastic properties of the chains. A qualitative comparison with experiments at a higher Reynolds number has shown that the model here adopted is capable of reproducing all the main features of the polymer solution flow. Analysis of the turbulence statistics suggests that a dilute polymer solution can affect the intensity of the streamwise vortices, leading to an increase in the spacing between low speed streaks and eventually to a turbulent shear stress reduction. Key words: turbulent flow, viscoelastic fluid, drag reduction, DNS, FENE. Abbreviations: DNS – Direct Numerical Simulation; FENE – Finitely Extensible Nonlinear Elastic; LSS – Low Speed Streaks 1. Introduction The drag reducing properties of a small amount of soluble long-chain polymer molecules added to a turbulent flow of a Newtonian solvent have been extensively studied since the first experiments done by Toms [18]. Experiments carried out in channel flows [11], pipe flows [6] and turbulent boundary layers [9] highlighted several features concerning the modification of the turbulent structures due to the addition of the dilute polymer solution. However, the physical mechanism through which turbulent drag reduction is obtained is still far from fully understood. Only recently direct numerical simulations of the resulting non-Newtonian tur- bulent flow have been attempted [6, 15] because of the high computational costs involved as well as the complexity of the constitutive equations. However, even when the numerical results show a qualitative agreement with the data obtained by experimental measurements, the latter are usually performed at Re numbers higher