Experimental Study on Flow Around Circular Cylinders With Low Aspect Ratio

Experiments were carried out in a recirculating water channel regarding the flow around stationary circular cylinders with low aspect ratio piercing the water free surface. Eight different aspect ratios were tested, namely L/D = 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0; this range corresponds to aspect ratio related to circular offshore systems, such as spar and monocolumn platforms. Force was measured using a six degree-of-freedom load cell and Strouhal number is inferred through the transverse force fluctuation frequency. The range of Reynolds number covers 10,000 < Re < 50,000. PIV measurements were performed in some aspect ratio cases, namely 0.3, 0.5, 1.0 and 2.0 for Reynolds number equal to 43,000. The results showed a decrease in drag force coefficients with decreasing aspect ratio, as well as a decrease in Strouhal number with decreasing aspect ratio. The PIV showed the existence of an arch-type vortex originated in the cylinder free end.