新型开孔桥墩水动力特性的PIV试验

基于粒子图像测速技术（Particle Image Velocimetry，PIV）对新型开孔桥墩周围的水流结构进行试验研究。通过分析开孔桥墩中轴面（y/b=0）处的立面流场和桥墩周围不同水深位置处的平面流场，探究开孔桥墩周围水流动力结构。试验结果表明，矩形开孔桥墩周围水流呈明显的三维结构特点。在桥墩上设置方孔，能有效地抑制墩前部分下降流的形成、降低墩前壅水的高度和改善墩侧水流流态，同时明显改变墩后尾流结构。方孔所在水深位置处（z/h=0.45），墩侧低速区最大相对宽度以及墩后尾流区最大相对宽度与相对孔宽比（w/b）呈二次曲线关系，且相关关系密切。近水面处（z/h=0.75），w/b=0.5条件下墩后旋涡对的相对长度为无孔时的70%；相反，近床面处（z/h=0.15）旋涡对的相对长度略有增加，但旋涡对的相对宽度一直保持在1左右。

PIV measurement of hydrodynamic characteristics of pier with a slot

This paper investigates flow structures around a bridge pier with a slot by experimental data obtained with PIV (Particle Image Velocimetry). Dynamic structures of the flows are examined on the central vertical flow plane and horizontal planes at different heights. It is found that the presence of the slot reduces the rise of water surface in front of the pier and subcutaneously changes wake vortex structures behind the pier. The flows around the pier with a slot exhibit strongly three dimensional characteristics. The maximum relative width of the low velocity region beside the pier and that at the wake region located at z／h=0.45 vary approximately linearly with the value of w／b, w being width of the slot and b being width of pier. On the horizontal plane at z／h=0.75, the relative length of vortex pair behind the pier with a slot(w／b=0.5)is 70% of that in case of the traditional pier, whereas, on the plane z／h=0.15, it increases slightly. In addition, the relative width of the vortex pair remains as 1 all the time.