2025 Volume 45 Issue 2 Pages 1-7
An experiment was carried out to examine the reduction in local scour around a cylinder in multidirectional horizontal flows, installing four porous plates on its surface with 90 degrees intervals, near the bed. The porous plates can break-down or weaken the two organized vortex structures around the cylinder: an upstream ‘horseshoe vortex’ and a downstream ‘Kármán vortex street’. Bed surface variations were intensively measured around the cylinder under the conditions of three approach flow directions. The scoured sediment volumes around the cylinder in the presence of the porous plates decreased by over 40 %, comparing that in the absence of them, for all approach flow directions. The decrease rates were especially conspicuous in the downstream side with disappearance of a Kármán vortex street. In addition, with respect to the scour depth, the porous plates completely extirpated the serious local scour area and effectively changed the medium scour area to the weak scour area.
