Study On Water Blocking Performance Of Cylindrical Bridge Piers In Mountain Rivers

The bridge pier is the primary factor of bridge influencing the current of water, and the objective aspect performance of pier water blocking is the backwater in river course. Because of the bridge opening restricting flow, the water velocity under the bridge increases, the upstream water surface rises, and the downstream water surface falls, leaving a discrepancy in elevation between the upper and lower stream, which would pose a threat to the security of both sides embankments and the bridge structure in flood season. As for the mountain river, the backwater height of upper stream and the creep height of coming water would perform a crucial influence on the clear opening under the bridge and the built height of river embankment.Numerical simulation method is adopted to calculate the backwater and the creep height of coming water in this paper. Calculating the river water under the non-bridge condition, and calculating the river water under different skew bridge conditions, then the backwater height is the difference value between the water levels under different skew bridge conditions and under non-bridge condition. So using FLUENT software to establish three-dimensional numerical model of water flume, in which a k-εturbulent model is used to simulate close Reynolds equations and volume of fluid (VOF) method is used to track the free water surface, the disturbed flow field of a single cylinder pier, right bridge and skew bridge can be achieved, then the laws and conclusions of which can be obtained as follows:(1) Using k-εturbulent model and volume of fluid (VOF) method is effective to simulate the disturbed flow field and get the water surface profile.(2) With the increase of flow rate, the included angle between oblique shock wave and flow direction reduces gradually, the included angleθ( that is the angle between normal direction of oblique shock wave and flow direction) increases with the Fr, and theθis situated between 21°～55°. As for medium and large sized flood, theθis situated between 48°～55°, that is the most unfavorable angle range. When designing the skew bridge, we should avoid adopting this angle range as far as possible.(3) With the increase of skew angle, the creep height of coming water augments first and then falls. Whenαis between 50°～60°, the creep height obtains the maximum value. The backwater height in front of the first pier increases with the increase of skew angle, but from the second pier on, with the increase of skew angle, the backwater height increases at first then decreases, and the minimum value is between 45°～55°.(4) With the increase of skew angle, flow deflection angle augments first and then falls. Whenαis around 50°, the flow deflection angle usually obtains the maximum value. At this time, the flow direction deflects most, and the conveyance capacity under the bridge increase obviously, so the backwater height drops evidently.