Turbulent Duct Flow with Polymers

Abstract: Direct numerical simulation of the turbulent flow in a square duct with polymers has been performed and the results have been compared with the laboratory experiments done at KTH Mechanical engineering department. The polymer suspension is simulated with the FENE-P model, and the numerical results are used to elucidate the mechanism that provides drag reduction and the effect of polymers on the secondary motion which is typical of the turbulent flow in ducts. Experiments are used to support and validate the numerical data, and to discuss the Reynolds number dependency of the obtained drag reduction. The study shows that the Prandtl's secondary flow is modified by the polymers: the classical 8 regions, in the cross section with high vorticity, are bigger in the polymer flow than those in the Newtonian case, and their centers are displaced towards the center of the duct away from the wall. In plane fluctuations are reduced and streamwise coherence of the flow enhanced in the presence of polymers.