山区峡谷桥址地形模型过渡段优化

针对山区峡谷桥址地形模型入口边界确定问题，以贵州省湘江特大桥桥址处地形为依托，选择维多辛斯基曲线作为地形模型过渡段的基本曲线形式，采用计算流体动力学方法对不同曲线参数进行计算，并结合关联度权重确定法确定最优过渡段曲线参数。在此基础上设计并制作了几何缩尺比为1：1 500的桥位地形模型，分别进行了有、无过渡段地形模型的风洞试验，对比了地形模型有、无过渡段对桥位桥面高度处横桥向风速、风攻角以及桥梁总长1/4跨、1/2跨、3/4跨风剖面的影响。过渡段曲线的二维数值模拟结果表明：采用最优过渡段可有效降低模型边界后方气流等效风攻角，并最大程度地保持入流风速，减小过渡段后湍流度；设置过渡段后风速场分布特性与入流参考风速场分布特性的一致性较好。地形模型风洞试验结果表明：曲线过渡段使风剖面逐渐抬升，气流过渡平缓，不存在明显的加速效应，剪切层发展较慢；设置过渡段后不同风剖面位置处平均风速较无过渡段时大，湍流强度较无过渡段时低；设置过渡段对桥梁主梁高度处风攻角存在一定的影响，但有、无过渡段时的风攻角变化趋势大致相同；采用优化后的过渡段使风剖面逐渐抬升，减小了"人为峭壁"对地形模型试验结果的影响，主梁高度处横桥向风速总体大于无过渡段时主梁高度处横桥向风速。

Optimization of Transition Sections Around Terrain Model at Mountain Canyon Bridge Site

To solve the problem of determining the entrance boundary conditions of a terrain model, the Xiangjiang Bridge, a proposed cable-stayed bridge in Guizhou, China was taken as an engineering example and the Witozinsky curve was chosen as the basic transition section form. Curve parameters were calculated by two-dimensional computational fluid dynamics (CFD) and the optimal combination form of the transition sections was determined by a weighted solution based on the correlation degree. On this basis, a terrain model with a geometric scale ratio of 1:1 500 was designed and fabricated; wind tunnel tests were carried out with and without the transition sections. The effects of the transition sections on transverse wind speed, wind attack angles at bridge deck level, and the wind profiles at 1/4, 1/2, and 3/4 of the total bridge length were compared. The two-dimensional numerical simulation results of the curve parameters show that the optimal transition section can effectively reduce the equivalent wind attack angle after the transition section, and maintain the inflow wind speed to a great extent while reducing the turbulence in the back of the transition section. Wind field characteristics of the terrain model with transition sections agree well with that of inflow reference wind field. The wind tunnel test results show that because the transition sections gradually uplift the wind speed profile, the speed-up effect is not obvious, and the shear layer develops slowly. When there are transition sections, the average wind speed at different wind profile locations is larger than that of the terrain model without any transition sections while the turbulence intensity is lower than that without the transition sections. Setting transition sections has a certain influence on the wind attack angles at the bridge deck level, but the variation trend of the wind attack angles with or without transition sections is roughly the same. The optimized transition sections are used to move up the wind speed profiles gradually, which reduces the influence of the "artificial cliff" on the terrain model test results. The transverse wind speeds at the bridge deck level are generally larger than those of the terrain model without transition sections.