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Drag Reduction Effect Due to Polymer Coating in a Channel and a Boundary Layer Flow
Hiroshi Mizunuma and Hiroshi Nakashima

We developed an effective method of coating with polymers to produce a new drag reduction effect. The ends of polymer chains are anchored to the wall by an insoluble binder, and the other ends dissolve in water. The turbulent drag reduction induced by this polymer coating was investigated in a rectangular channel flow and in a boundary layer flow. The influence of molecular weight on the drag reduction was investigated in a channel flow, and it was shown that a polymer of molecular weight 3.6 million produced the highest drag reduction. The turbulent velocity profiles were measured in a channel flow using a LDV system. The drag reduction was caused by the increase in the intercept of the logarithmic velocity profile. For a boundary layer flow, the drag reduction was observed in the transitional region, but not in the turbulent region.

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