Numerical Study On Hydrodynamic Characteristics Around The Pier And New Flow Resistance Formula

During the interaction between the water flow and the pier,the water flow is strongly turbulent,causing serious damage to the building,leading to collapse of the bridge and collision of the bridge.There are many factors in the collapse of the bridge and the collision of the bridge.A considerable part of the reason is that the pier is designed for the pier.It is of great engineering practical significance that the flow resistance in the river and the influence of the bridge pier on the water flow area do not accurately grasp the hydrodynamic characteristics around the pier and the flow resistance.In this study,numerical simulation method is used to carry out three-dimensional numerical simulation research on water flow and different cross-section piers.Based on open-ended OpenFOAM package interFoam solver,large eddy simulation is selected to analyze the variation law of flow velocity around square piers.The distribution of time-averaged vorticity is analyzed.The frequency of tail-vortex shedding is analyzed.The three-dimensional eddy structure is analyzed.The time-average characteristics of flow resistance and wake vortex area are discussed.The length L of the straight section of the pier and the length of the circle end are discussed.The relationship between the ratio a/b and the vortex region behind the pier.The results show:The flow field and flow velocity changes around the piers of different cross-sections have been regular.In the upstream of the pier,there is a horseshoe vortex;the low velocity zone appears on the two side walls of the pier column,and a pair of large eddy currents with substantially symmetrical and opposite directions of rotation appear in the downstream of the pier.When the Reynolds number Re is 7500?20000,the distribution of the uniform vorticity with the Reynolds number increases with the water depth of the characteristic section(z/h=0.5).The frequency of the vortex shedding at the back of the pier has no obvious change.The square,the front semicircle,the rear semicircle and the round end are respectively 0.139,0.212,0.185 and 0.275.The water body after the pier has strong turbulence and obvious tail vortex.The shedding phenomenon,the larger the Reynolds number,the more obvious the tail vortex shedding.It was found that the maximum cross flow around the pier was about 42%of the inflow velocity.The square pier is 10mm away from the separation point,the flow velocity is reduced by 18.98%;the front semicircular pier is increased by 10mm from the separation point,and the flow velocity is reduced by 21.91%;the front semicircular pier is increased by 10mm from the separation point,and the flow velocity is reduced by about 12.88.%;the round-end pier is increased by 10 mm from the separation point,and the flow rate is reduced by about 19.12%.The coefficient of flow resistance is analyzed.It is found that the coefficient of flow resistance is 1.5 times when the flow surface is semicircular.When combined with theoretical analysis,theoretical derivation is established to establish a new formula for flow resistance.There is a good linear relationship between the time-averaged relative area,the dimensionless mean flow resistance and the dimensionless new flow resistance formula and the Reynolds number in the vortex region of the elliptical pier.The round-end pier column changes the length of the straight line segment L.It is found that the area of the vortex area behind the pier has a strong linear relationship with the straight line segment L/B of the pier;changing the ratio of the length of the circle end to the short axis a/b,the tail of the pier is found.There is no obvious linear law between the area of the vortex area and the length-to-minor axis ratio a/b of the round end of the pier.