Speed dependence of integrated drag reduction in turbulent flow with polymer injection

Drag reduction is vitally important for marine applications, and a promising means of reducing the turbulent frictional drag in external flow is polymer injection. In this paper, the integrated drag reduction rate (DR) of polymer injection in turbulent flow is investigated using pressure measurements. As the inlet speed varies 1.0–3.5 m/s, the speed dependence of DR is derived, DR increases with speed at an equivalent normalized polymer flux, and a maximum value of 50.0% is obtained. It is postulated that the injected polymer interacts with the turbulence much more efficiently as the speed increases, which is similar to the drag-reducing behavior of homogeneous polymer flows. The DR performance in polymer-injected flows reported in this paper not only indicates the existence of speed dependence at moderate speeds, but also supplies the reported speed dependence in higher speed tests. Graphic abstract DR versus K for polymer injection in turbulent a rectangular channel flow and b circular pipe flow. In b , open symbols are magnified from the channel tests, filled symbols denote data obtained in pipe tests