Author(s): Jiawei Lin; Sauyu Yuan; Yunqiang Zhu; Yuchen Zheng

Linked Author(s): Saiyu Yuan, Yuchen Zheng

Keywords: Channel confluence; Shear layer; Separation zone; Dissipation rate

Abstract: The gas exchange through water surface not only severs an important function in global carbon budget but is also significant to understand the distribution of dissolved oxygen, which is a crucial parameter for river water quality. Its velocity is largely controlled by the turbulence near water surface. Confluences are critical nodes in a river network and with complex hydraulics when the tributary f lows into mainstream, but the research of gas exchange in confluence is rare. Laboratory measurements in two different discharge ratios were conducted to observe the turbulence motion near water surface in a confluent flume with 60 degrees. Two -dimensional horizontal velocity fields were collected and turbulent dissipation was analyzed. The results showed that separation zone and shear layer are the dominant factors affecting the turbulent motion near water surface in stream confluence. The dissipation rate near water surface increases extremely in confluence, and higher dissipation rate is mainly distributed near the shear layer (10-5 W kg-1) as well as the separation zone boundary (10-4 W kg-1), with a wide range, contrast to that in ambient fluid (10-7 W kg-1-10-6 W kg-1). Shear layer plays a leading role in the area without separation zone and the magnitude of dissipation rates in shear layer under two different mixing mechanisms are in the same order. Behind the downstream junction, separation zone occurs and, together with the shear layer, affects the turbulent motion near water surface. Downstream, the strength of shear effect weakens and the separation zone gradually becomes the controlling factors.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0044-cd

Year: 2023