Author(s): Zhonghua Yang; Zhaoyang Hu; Kaichun Gao; Xiaoyuan Xiong; Shuran Yin
Linked Author(s): Zhonghua Yang
Keywords: Tetrahedron penetrating frame; Turbulence intensity; Reynolds stresses; Velocity profiles; PIV
Abstract: The tetrahedron penetrating frame, which is made by six square cross-section columns, has been widely used in river engineering as a new effective scour countermeasure in China. In this paper, experiments were conducted to investigate flow characteristics over a single tetrahedron penetrating frame. The experiments were carried out in a straight open channel with a smooth fixed bed and transparent Plexiglas walls. It’s 8m long, 0. 3m wide and 0. 5m high. The frame model comprises six identical columns, each with a square cross-section (5mm×5mm), and length L=50mm. A 2-Dimensional Particle Image Velocimetry (PIV) was used to measure the flow under various flow conditions (Re=10400~23466) and two typical frame arrangements, where the frame vertex are pointing upstream and downstream respectively. The mean longitudinal velocity, vorticity, turbulence intensity, and Reynolds stress are calculated from 240 instantaneous flow velocity fields. The results show that the flow field is strongly affected by the presence of the tetrahedron penetrating frame and there exists a notable decelerating area behind the tetrahedron penetrating frame. For vertex pointing upstream frame, there is an ‘S’ type mean longitudinal velocity profile and the maximum velocity locates at the height of 0. 3L. The turbulence intensity and vorticity are noticeably enhanced near the frame head. The total shear stresses are decreased at the bottom height near the frame, which may induce sediment deposition in a sediment laden flow. However, the bed shear stresses are larger than those for the undisturbed approach flow further away from the frame (x/L>0. 15). This indicates that group of tetrahedron penetrating frames will be effective in protecting bank from erosion and inducing sediment deposition, where the distance between each frame is short enough to avoid the large shear stress caused by each frame. In addition, it works better in retarding flow for the vertex pointing downstream arrangement than the ones pointing upstream.
Year: 2013