| The bridge foundation in the river channel of mountain rivers changes the flow pattern of the river,leading to partial erosion of the bridge foundation,posing a threat to the safety of the bridge.At the same time,the sand in the mountain river bed is mostly gravel,pebbles and sand,and the bed sand has a wide range of grading,and the sediment is uneven.At present,there are few research results on the partial scouring of non-unifonn sandy riverbeds under double-row cylindrical piers.The actual practice of double-row cylindrical piers is more suitable for the local scouring test of double-row cylindrical piers under non-uniform sandy riverbeds.In this paper,the physical model test of the double-cylinder pier sink is carried out.The bed sand gradation in the bridge area of Heishidu Bridge is obtained as a typical gradation of non-uniform sand,and the test sand samples with the same median diameter and different non-uniformity coefficient are arranged to carry out the scour test.The distribution characteristics of turbulent flow field of double-column piers under the action of water-blocking of double-column piers are measured and analyzed.The sediment inhomogeneity and the local scour pits and dune distribution of double-column piers under the same flow velocity and different velocity are discussed.The relationship between the morphological characteristics of the crater under different non-uniform sand conditions is discussed.The results show that at the L4 line of the pier of the double-column bridge pier,the velocity distribution of the water in the advancing direction shows three peaks of flow velocity;the central axis of the double-column string,two measuring sections 10 cm behind the upstream and downstream piers,The three-direction turbulence intensity first increases and then decreases as the Z/H value decreases,reaching a maximum at a relative water depth of 0.45.The additional shear stress value of the turbulent flow in the previous section is larger than the latter;considering the flow velocity factor,the depth and radius of the local crater of the two piers tend to increase first and then change with the increase of bed sand non-uniformity;The sand dune behind the pier increases first and then decreases with the increase of sediment non-unifonnity.The double-row piers are independent of each other;with the increase of the flow velocity,the depth and radius of the double-pass piers increase and the radius of the front pier It is connected with the dune and the rear row of piers;regardless of the size of the sediment non-uniformity,the accumulation of dunes on both sides of the pier starts at an angle of about 450 to 600 from the direction of the water flow after the pier.In this paper,Flow-3d software is used to establish a three-dimensional water-sand two-phase flow model,and the non-uniform mixed sand parameters are set.Based on the RNG k-? turbulence model,the geometric model is discretized and partially encrypted by nested grid method.The flow characteristics of the flow field and the characteristics of local crater changes during sediment flow at high flow rates.The numerical simulation results are in good agreement with the experimental results,which proves the validity and rationality of numerical simulation,and provides a reference for the three-dimensional numerical simulation method of non-uniform sand. |
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