Experimental study on drag reduction characteristics through PIV visualization

Abstract

The fluid force reduction characteristics with respect to changes in the diameter and gap ratios between two cylinders in a flow field were experimentally investigated by installing two cylinders in a circulating tank in which the Reynolds number was maintained at 10,000. The velocity vector fields were examined through flow visualization with particle image velocimetry (PIV). The temporal drag and lift variation measurement results showed that the magnitude of the drag and the amplitude of the lift were reduced when a smaller cylinder was present, as compared to the reference case without the smaller cylinder. The optimum gap ratio for which the drag reduction was the greatest differed with the diameter ratio of the two cylinders. The mean drag coefficient was the smallest when the diameter ratio was 0.4 and the gap ratio was 0.5. The mean absolute values of lift coefficient decreased near the optimum gap ratio in all cases, but this tendency was not observed as the gap ratio increased. PIV visualization showed the correlation between the velocity distribution and drag reduction characteristics of the stagnant region between the two cylinders.