基于PIV技术的透明黏性泥石流冲击桥墩模型试验

Physical Model Tests Evaluating Transparent Viscous Debris Flow Impact on Bridge Piers Using Particle Image Velocimetry

针对现有模型试验无法可视化泥石流与桥墩相互作用过程和泥石流内部流体运动特性,提出一种基于PIV技术的透明泥石流模型试验技术。采用2种具有不同表观黏度的透明矿物油(550USP白油与68#机油)配置而成2种具有不同表观黏度的透明泥石流,设计了一套透明泥石流冲击桥墩模型试验系统。在3种坡度条件下,分别针对表观黏度不同的2种透明泥石流对冲击方形、圆端形、圆形3种截面形状桥墩的情况开展了21组冲击试验。试验结果表明:量纲一冲高h/H会随着弗劳德数Fr的增大而逐渐增大,且透明泥石流对桥墩的冲击力与桥墩的截面形状、透明泥石流的雷诺数Re、弗劳德数Fr有关;当截面形状不变,冲击阻力系数Cd随雷诺数Re与弗劳德数Fr的增加而减小。透明泥石流表观黏度的改变对圆端形与圆形截面桥墩表面流速与流深的关系影响较小,对方形截面桥墩影响较大。透明泥石流的表面流速在经过桥墩后得到了显著提升,圆形截面桥墩的提升效果最为明显,圆端形截面桥墩提升幅度最少。在桥墩影响区域以外,透明泥石流垂直流向(y方向)表面速度呈现中间大、两侧小的“倒U形”分布;在桥墩范围内,表面流速呈“M形”分布。

Quantifying the impact force of debris flows on bridge piers is crucial to ensuring the safety of bridges in mountainous areas.A transparent debris flow modeling technology based on particle image velocimetry(PIV)was proposed to address the inability of existing modeling methods to visualize the interaction between a debris flow and bridge pier as well as the fluid movement characteristics inside the debris flow.A set of transparent debris flow models was designed using two transparent mineral oils(550 USP white oil and 68#engine oil)with different apparent viscosities to create two corresponding transparent debris flows.Twenty-one groups of impact tests were subsequently conducted using these two types of transparent debris flows under three slope conditions with three bridge pier cross sections(square,rounded end,and round).The results indicated that the dimensionless impulse height h/H gradually increased with the increase in the Froude number Fr,and the impact force was related to the cross-section of the bridge pier as well as the Reynolds number Re and the Fr of the transparent debris flow;when the section shape remained unchanged,the impact resistance coefficient Ca decreased with increasing Re and Fr.The change in the apparent viscosity of the transparent debris flow had less effect on the relationship between the surface flow velocity and flow depth for piers with rounded end and round sections,and greater effect on that for piers with square sections.The surface velocity of the transparent debris flow significantly increased after passing the piers,with the most significant increase occurring for round piers and the least significant increase occurring for the rounded end piers.Outside the pier-affected area,the surface velocity of the transparent debris flow in the vertical direction(y-direction)exhibited an"inverted U-shaped"distribution that was large in the middle and small on both sides;in the range of pier,the surface velocity exhibited an"M-shaped"distribution.