Interaction between open-channel turbulence and separation bubble in a cavity under a flow with a large water surface deformation

本文研究了具有非对称空腔的明渠水流。该流动也可以被认为是具有各种长宽比的空腔的后台阶流动。在研究的流动情况下，流动在空腔的入口处显示出临界深度，并且在空腔的下游处产生水跃。根据初步的视觉调查，水跃移上游的空腔的长宽比增加。当水跃的位置变得非常接近空腔时，水跃突然开始振荡。为了了解这些流动特征的形成机理，采用图像分析技术对空泡区纵向垂直截面上的二维速度场进行了测量。使用高速摄像机和高分辨率摄像机捕获通过激光光片可视化的示踪颗粒的连续流动图像。二维速度矢量可以通过使用粒子图像测速技术如PIV或PTV获得。在这项研究中，PTV用于稳定的流动和非定常振荡水跃的PIV。结果表明，当空腔长度大于来流的再附着长度时，能量耗散变大。此外，还绘制了振荡水跃情况下的流速演化图，揭示了水流的时变特性。

Open-channel flow with a non-symmetric cavity was investigated in this research. The flow can also be considered as a back-step flow with a cavity of various aspect rations. In the flow situation investigated, the flow shows a critical depth at the inlet of the cavity and a hydraulic jump is created downstream of the cavity. According to the preliminary visual investigation, the hydraulic jump shifts upstream towards the cavity as the aspect ratio of the cavity increases. When the location of the hydraulic jump becomes very close to the cavity, the hydraulic jump suddenly begins to oscillate. This phenomenon can be considered as a result of the interaction between separation vortices and water surface.In order to understand the mechanism of these flow features, image analysis techniques were introduced for measurements of two-dimensional velocity fields in a longitudinal vertical cross-section around a cavity area. A high-speed video camera and a high-resolution video camera were used to capture consecutive flow images of tracer particles visualized by a laser light sheet. Two-dimensional velocity vectors can be obtained by using particle image velocimetry techniques such as PIV or PTV. In this research, PTV was used for a steady flow and PIV for unsteady oscillating hydraulic jump. It was made clear that the energy dissipation becomes large when the length of the cavity is greater than the reattachment length of the inlet flow. In addition, the time-dependent flow characteristics were made clear by a velocity evolution diagram in the case of an oscillating hydraulic jump.