Abstract
Jet flow can occur by gate opening at downstream of a hydraulic structure such as weir of drainage gate. If the stream bed is not hard or the bed protection is not sufficient, vortex erosion occurs and a resulting scour hole will be formed due to the high shear stress of the jet flow. Once the scour hole is formed, a vortex occurs in ti and this vortex causes additional erosion. If this erosion continues and reaches to the hydraulic structure, it can undermine the bottom of the hydraulic structure and this will lead to failure of the structure itself. Thus, it is necessary to define the physical features of the vortex structure in the scour hole for the design of the bed protection. This study presents the turbulent vortex structure in the scour hole by the gate opening of the hydraulic structure. Characteristics of vortex motion, circulation, vortex scale and vortex were analyzed through experiments. Experimental results of the vortex velocity were compared with theoretical ones. From these, circulation and vortex scale were obtained with known values of inflow depth, inflow velocity and scale of scour hole