风沙地区低净空桥梁下部流场结构及积沙特征分析

Analysis on Flow Field Structure and Sand Accumulation Characteristics under Low Clearance Bridges in Windblown Sand Area

为认识低净空桥梁下部积沙形成机理、分布特征及影响因素,利用计算流体力学软件,构建欧拉双流体非稳态模型,对桥梁周围风沙流的运动特征进行数值模拟,并与现场结果进行对比。结果表明:现场实测数据与模拟结果基本一致,所建数值模型能够较好地反映梁体周围的风沙流运动特征;T梁迎风侧和背风侧一定范围内位于风积区,而梁体正下方则位于风蚀区;T梁周围积沙主要集中在梁体迎风侧和背风侧,但在单一风向环境下前者积沙量大于后者,且积沙量随时间的推移呈递增趋势;气流速度的衰减是T梁迎风侧和背风侧积沙的主要原因,而腹板间气流的绕流是梁底形成少许积沙的可能原因;T梁周围的积沙量与梁底净空密切相关,且随着净空增大呈递减趋势,建议风沙地区的梁底净空不宜小于5.0 m;同等条件下,箱梁周围的积沙速率明显小于T梁,风沙危害严重地区的低净空桥梁考虑采用箱梁。

To understand the formation mechanism,distribution characteristics and influencing factors of sand accumulation under the bridge with low clearance,the Euler two-fluid unsteady state model is established by using the computational fluid dynamics software,and the movement characteristics of the wind-sand flow around the bridge are numerically simulated and compared with the field results.The results show that the field measured data is basically consistent with the simulation results,and this numerical model can better simulate the movement characteristics of wind-sand flow around the beam body.The windward and leeward sides of T beam are located in the wind accumulation area,while right below the beam body is located the wind erosion area.The sand accumulation around T beam is mainly distributed on the windward and leeward sides of the beam body,but the sand accumulation volume in the former is greater than that in the latter under a single wind direction environment,and the sand accumulation volume tends to increase over time.The attenuation of airflow velocity is the main reason for sand deposition on the windward and leeward sides of the T beam,while the around-flow between the webs is the possible reason for a little sand deposition at the bottom of the beam.The sand accumulation volume under the T beam decreases with increasing the clearance,and it is recommended that the bridge clearance should not be less than 5.0 m in the windblown sand areas.Under the same conditions,the sand accumulation rate around the box beam is significantly lower than that of the T beam,and the box beam should be used for the low clearance bridge in areas with serious windblown sand hazards.