Abstract: Although submerged vertical circular cylinders have been widely applied in engineering fields, there are no systematic study on the flow pattern and turbulence characteristics in the flow field around the submerged vertical circular cylinders.In view of this,we carried out indoor flume experiment with different slopes and accurately measured the instantaneous velocity field around the submerged vertical circular cylinders. According to the test result, we analyzed the impact of the submergence ratio on the vertical distribution of three-dimensional flow velocity and turbulence intensity along upstream and downstream vertical symmetry plane of the submerged vertical circular cylinders.On this basis, we researched the variations of scour strength of downstream flow, horseshoe vortex and tail flow vortex with submergence ratio, and revealed the mechanism of submergence ratio affecting local scour by clear water around the submerged vertical circular cylinders. Research results show that 1) increasing submergence ratio could reduce the effective length of vertical circular cylinder above water surface and weaken the resistant flow and disturbance of the cylinder on water; 2) the scour capacity of downward flow in the upstream of cylinder, horseshoe vortex around the cylinder, and tail flow vortex obviously decreases, which reduces the probability of sediment around vertical circular cylinder being eroded by vortex.

Key words: submerged vertical circular cylinder, flow pattern, turbulence characteristics, scour mechanism, submergence ratio