Porous Plate Method: Reduction in Local Scour around Pier-Type Structures in Multidirectional Flows

To reduce the local scour around pier-type structures, a “porous plate method” was proposed, aiming at effectiveness in multidirectional horizontal flows. The porous plates installed on the pier surface near the bed play two important roles in the reduction of the local scour. One is “breaking down or weakening” of the horseshoe vortex by a decline in vorticity. In the neighborhood (just upstream region), the local scour depth greatly decreases due to suppression of picking up sediment grains from the bed. Another is the resultant “flow regulation” in the boundary layer on the pier surface. In the downstream side, the wake separated from the pier surface behaves as “semi-homogeneous turbulence” without a Kármán vortex street, then the scour area drastically decreases.