抄録
Little amount of flexible polymer induces drag reduction (DR) to suppress turbulent flow. While this phenomenon is well known and has been studied for long years, the mechanism is not understood so far. We assume that the origin of the DR is related extensional viscosity due to the elongation of polymer under extensional strain in the turbulence flow. It is possible that the steep increase of the extensional viscosity in the high rate region of the strain effectively suppress the growth of turbulence. Here we study whether the DR is induced by the addition of a rigid polymer, hydroxypropyl cellulose (HPC), in comparison with a flexible polymer, polyethylene oxide (PEO). We use our original visualization method of 2-dimentional turbulent flow, named Film Interference Flow Imaging (FIFI), to analyze the difference between the cases of the HPC and PEO. The FIFI succeeds to observe that while the PEO obviously induces the DR, the HPC hardly induces the DR. We discuss the different behaviors of the extensional vi scosity toward the strain rate in the cases of flexible and rigid polymers and their different effects on the DR.
