PTV Measurement of Toms Effect in Micro Channel Turbulent Flow

Abstract

Drag-reducing turbulent flows of dilute polymer solution are measured using particle tracking velocimetry (PTV). The measurements are done in a micro channel 2 mm in wall-to-wall distance for the Reynolds numbers of about 300 and 10, 000. A double-pulsed Nd : YAG laser is used to illuminate 0.8μ-diameter acrylic tracer particles. It is confirmed that the turbulent drag reduction in polymer solution (i.e., Toms effect) becomes more pronounced in small conduits like the present micro channel than in other larger channels and pipes. The mean velocity profile in drag-reducing flows looks like the laminar velocity profile. The turbulence statistics measured in drag-reducing flows have shown that the streamwise and wall-normal velocity fluctuations, when normalized with the friction velocity, are approximately of the same magnitude as those in pure water flows but that the Reynolds stress almost vanishes. Separate PIV measurements indicate that the presence of elongated structures of streamwise velocity fluctuations contributing little to the generation of the Reynolds stress is the reason for the measured turbulence characteristics in the drag-reducing micro channel flows