EXPERIMENTAL STUDY ON THE DRAG-REDUCING CHARACTERISTICS IN TWO-OSCILLATING GRID TURBULENCE WITH POLYMER ADDITIVES

摘要

In this paper, we carried out the experimental study to investigate the polymer effect on two-oscillating grid turbulence based on Particle Image Velocimetry. We chose five different concentrations (25, 50, 100, 150 and 200ppm) of polymer solution flow and the Newtonian fluid flow for comparison at three different grid oscillating frequencies (5, 7.5 and 10Hz). The results showed that comparison with the Newtonian fluid case, the turbulent kinetic energy is much smaller in polymer solution cases. A natural definition for drag reduction rate was proposed based on turbulent kinetic energy. It showed that the maximum drag reduction reaches around 80% and the drag-reducing effect increases as the concentration increases. Finally, proper orthogonal decomposition (POD) was used to extract coherent structures in grid turbulence.