Hole diameter effect on flow characteristics of wake behind porous fences having the same porosity

The hole diameter effect on the flow characteristics of wake behind porous fences has been investigated experimentally in a circulating water channel having a test section of 300(w) x 200(h) x 1200(l) (mm). Three porous fence s having different hole diameters of d = 1.4, 2.1,2.8 mm were tested in thi s study, but they have the same epsilon = 38.5% geometric porosity. One tho usand instantaneous velocity fields for each fence were measured consecutiv ely by the hybrid PTV system employing a high-speed CCD camera. Free stream velocity was fixed at 10 cm/sec and the corresponding Reynolds number base d on the fence height was Re = 2,985. Consequently, the fence with the smal lest hole diameter d = 1.4 mm (d(1.4)) decreases the streamwise velocity co mponent and increases the vertical velocity component. Among the three hole diameters tested in this study, the d(1.4) fence has the largest turbulenc e intensity in the shear layer developed from the fence top. Regardless of the hole diameter, however, all three fences having the same porosity reduc e the reduction of turbulent intensity in the lower region below the fence height (y/H < 1). (C) 2001 Published by The: Japan Society of Fluid Mechani cs and Elsevier Science B.V. All rights reserved.