263 / 2024-02-28 19:05:21

Study of Very Large-Scale Coherent Structures in large-scale Open Channel Flows

very large-scale coherent structure; acoustic Doppler current Profiler; Dongfeng Canal; multiplied spectra.

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 water depth of 3.0 m, and the measurement site had a 550 m long straight section upstream. 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 appears near 20 times of the water depth, indicating that the very large-scale coherent structures also exist in the large-scale open channel flow.