Author(s): Wang Zhiyuan; Fan Niannian; Zhong Qiang; Liu Xingnian; Nie Ruihua
Linked Author(s): Xingnian Liu
Keywords: Very large-scale coherent structure; Acoustic Doppler current Profiler; Dongfeng Canal; Pre-multiplied spectr
Abstract: Turbulence is widely found in various natural flows such as rivers, lakes, estuaries and oceans. The study of coherent structures of open channel flow can help us further understand the turbulence phenomenon and solve related engineering problems. Since sediment movement is closely related to turbulence, the study of coherent structures of open channel flow also plays an important role in sediment regulation and management. Although researchers proposed the very large-scale coherent structure (at the scale of about 20 times of flow depth) could form from flume experiments, researchers doubt whether such very large-scale coherent structure exit in larger Reynolds number conditions. We used the Acoustic Doppler Current Profiler (ADCP) to carry out field measurements of the large-scale open channel in the Dongfeng Canal, Chengdu, China. The canal had a water surface width of 30 m and a flow depth of 3.0 m, the straight segment measurement site had a 550 m long straight section upstream, and the bend segment measurement site is located 120 m downstream of the straight segment measurement site. The velocities measured from the ADCP had a sample frequence of 1 Hz with spatial resolution of 0.2 m. By analyzing the pre-multiplied spectra of the collected data, we found that the peak of the pre-multiplied spectra in the straight segment shows at the scale close to 20 times of flow depth, and there is no peak of the pre-multiplied spectra in the bend segment at similar, indicating that the very large-scale coherent structures also exist in the straight segment of the large-scale open channel flow, meanwhile there is no the very large-scale coherent structures in the bend segment of the present measurement.
Year: 2024