Effects of permeable cylinders on wake region

Abstract

This paper investigates the effects of permeable cylinder on vortex shedding downstream of the permeable cylinder in deep water flow by PIV technique. In order to reveal the effect of porosity β on the vortex shedding, the permeable cylinder having four different porosities (β = 0.4, 0.5, 0.6 and 0.7) with a diameter of 45 mm have been used. During the experiments, the free-stream velocity is U∞= 156 mm/s, which corresponds to the Reynolds number of Re=5000 based on the solid cylinder diameter. The experiments show that the permeable cylinder is effective on the suppression of vortex shedding in the wake region for all porosities and in terms of the inner cylinder-outer permeable cylinder arrangement, it is understood that the inner-outer cylinder arrangement having the diameter ratio of D/d=1.5 is not effective on the attenuation of vortex shedding downstream of the inner cylinder-outer cylinder arrangement as expected. The inner and outer permeable cylinders behave like an impermeable cylinder having the diameter of D=45 mm for the porosities of β = 0.4, 0.5 and 0.6. The suppression of the large scale vortices is weak. On the other hand, for the porosity β = 0.7, the peak value of Reynolds shear stress drops to 0.0368 which is less than that of the bare cylinder. The reduction of is approximately 10%.