Effect Of Free Surface Flow On The Horseshoe Vortex System

The horseshoe vortex,which is three-dimensional and unsteady,is the main flow structure in the flow field around the wall-cylinder junction.It often interacts with the boundary layer and the structures in the junction are,poses threats to the safety of the structure of the angular region.In order to explore the characteristics of the horseshoe vortex in the junction area and study the effects of the water depth,velocity,the free surface of flow on the horseshoe vortex system,a wall-cylinder junction model is simulated using the computational fluid dynamics software Fluent and SST k-? IDDES method.In order to determine the optimal grid node distribution in the junction area,for the first condition,of which the depth h of water is 0.25m and the velocity is 0.673m/s,the single-phase flow fields model without free surface under three kinds of girds have been calculated.In addition,to verify the accuracy of this numerical method,the calculated results of three different kinds of grids are also compared.Based on the obtained optimal grid node distribution and grid quantity,the grid that can capture the free surface has been built.Besides,the feasibility of the calculation method is validated.For the single-phase flow without the free surface and the two-phase flow with the free surface,there are totally 16 conditions with the water depths of 0.1 m,0.175 m,0.25 m,and 0.325 m under Re=1.13×105 and 2.25 ×105 have been simulated.It is indicated that the oscillation of the turbulent horseshoe vortex system in the junction region is quasi-periodic under different flow conditions and its oscillation period is affected by water depth,Reynolds number,and the free surface.In the single-phase flow without the free surface,the water level has no obvious influence on the vortex system in the junction region under the same Reynolds number.Under the same water depth,the oscillation frequency of the vortex system increases with the increase of Reynolds number,besides,the increase of the Reynolds number makes the core of the main vortex move downstream,the vortex intensity of the system increases,but the skin friction coefficient decreases.With the increase of the height of the water level,the oscillation frequency of the vortex system in the junction region increases gradually.In addition,the core of the main vortex gradually moves to the downstream region which is close to the cylinder and the wall shear stress on the bed increases under the same Reynolds number in the two-phase flow considering the free surface.With the increase of the Reynolds number,the oscillation frequency of the vortex system decreases and the core of the main vortex moves away from the cylinder in the upstream direction,the vorticity intensity of the vortex increase,while the skin friction coefficient decreases under the same water depths.The influence of the Reynolds number on the vortex system in the junction region has decreased gradually with the increase of the water depth.In addition,the study found that,the influences of free surface on the oscillation frequency of the vortex system in the junction region,the position of the main vortex,the wall shear stress on the bed gradually decrease with the increase of the water depth when the Reynolds numbers are the same.