Drag-reducing flow owing to polymer additives in wall turbulence is investigated by means of numerical simulations. A spring-damper chain element model is employed to express a spatial concentration and flexible motion of the polymer in a turbulent flow. The model consists of some beads linked by springs and dampers. The influence of the model's length upon the turbulent flow is mainly focused. As lengthening the model, the skin-friction drag decreases since the turbulent contribution to the skin-friction coefficient decreases while the body force term due to the model increases. The behavior of the model and the energy transport process in the drag-reducing flow due to the model are discussed to clarify the mechanism of the drag reduction.
