Study Of The Unsteady Flow Around A Pier

In order to explore the mechanism of local scour around pier, to study vortex structure and unsteady characteristic around pier under different hydrological conditions, and free surface effects on flow field structure. A single cylindrical pier model is used to investigate in this paper, and using commercial CFD software (fluent) to solve the flow around pier under different water-level conditions at transcritical Reynolds number (Re=8.0×106).Firstly, this paper presents a Reynolds averaged Navier-Stokes (RANS) calculation as the grid independency test with 8 million,12 million,16 million test grids on the single phase flow under 5m water-level condition, finally, through combining the calculation analysis with the existing computing resources, the distribution of the 12 million node is confirmed as the node distribution of the other working conditions.Then, three different water-level conditions of 1m,2.5m,5m are calculated by a detached eddy simulation (DES) on the single phase flow, that is, the effect of free surface on the flow field is not considered; Through the analysis and comparison, it is concluded that the relative position of horseshoe vortices are basically the same under the condition of three different water-level without considering the effect of free surface on the flow field, in other words, which doesn’t vary with the water depth, and there is not exist significant coupling relation between wake vortex system and horseshoe vortex system. In addition, the formation mechanism and morphology of vortex structure around the pier are described in detail by analyzing the three time points in a "quasi period" of the RANS calculation results on the single phase flow under 5m water-level condition.Finally, consider the effect of the free surface which tracked by the volume of fluid (VOF) method in this paper, that concluded the horseshoe vortex system is basically the same on the two-phase and single phase flow; So, it can be concluded that free surface has no significant effect on horseshoe vortex system under 2.5m water-level condition, and there is also not exist significant coupling relation between wake vortex system and horseshoe vortex system in this condition.