Direct numerical simulations of 2D channel flows in the presence of polymers

Direct numerical simulations of a two-dimensional channel flow in the presence of a polymeric fluid are presented. The flow is perturbed by an array of cylinders which generates a turbulent flow downstream and whose statistical properties are studied in detail. Several features emerge from this study such as the reduction of turbulent fluctuations at large scales, the reduction of the energy transfer rate, and the reduction of the fluctuations of the enstrophy and energy transfer rates. These features are in excellent agreement with previous experimental measurements and show that despite the possible limitations of the model used to describe the polymeric fluid (an Oldroyd-B model), the changes observed here and in experiments may be generic to two-dimensional turbulent flows. An examination of the stress and elongation fields shows that the stresses are important in strong elongation zones pointing out that the effects due to polymers may have their origin in the large elongation zones which develop between vortices