Turbulence Structure and Momentum Exchange in Compound Channel Flows With Shore Ice Covered on the Floodplains

• Published in: Water resources research 2021-04, Vol.57 (4), p.n/a
• Main Authors: Wang, Feifei, Huai, Wenxin, Guo, Yakun, Liu, Mengyang
• Format: Article
• Language: English
• Subjects: Channel flow; Compound channel; Compound channels; Computational fluid dynamics; Constants; Eddy viscosity; Exchanging; Floodplains; Fluid flow; Ice; Ice cover; Interface stability; Kelvin-helmholtz instability; Laboratory experiments; Mixed layer; Momentum; momentum exchange; Oscillations; River beds; Rivers; Shear; Shear layers; shore ice; Spectral analysis; Spectrum analysis; Transverse momentum; Turbulence; turbulence structure; Turbulent flow; Velocity; Vortices; Water flow
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2020WR028621

Ice cover formed on a river surface is a common natural phenomenon during the winter season in cold high latitude northern regions. For the ice‐covered river with compound cross‐section, the interaction of the turbulence caused by the ice cover and the channel bed bottom affects the transverse mass and momentum exchange between the main channel and floodplains. In this study, laboratory experiments are performed to investigate the turbulent flow of a compound channel with shore ice covered on the floodplains. Results show that the shore ice resistance restricts the development of the water flow and creates a relatively strong shear layer near the edge of the ice‐covered floodplain. The mean streamwise velocity in the main channel and on the ice‐covered floodplains shows an opposite variation pattern along with the longitudinal distance and finally reaches the longitudinal uniformity. The mixing layer bounded by the velocity inflection point consists of two layers that evolve downstream to their respective fully developed states. The velocity inflection point and strong transverse shear near the interface in the fully developed profile generate the Kelvin‐Helmholtz instability and horizontal coherent vortices. These coherent vortices induce quasi‐periodic velocity oscillations, while the dominant frequency of the vortical energy is determined through the power spectral analysis. Subsequently, quadrant analysis is used in ascertaining the mechanism for the lateral momentum exchange, which exhibits the governing contributions of sweeps and ejections within the vortex center. Finally, an eddy viscosity model is presented to investigate the transverse momentum exchange. The presented model is well validated through comparison with measurements, whereas the constants α and β appeared in the model need to be further investigated. Key Points The longitudinal evolution of the streamwise velocity in a compound channel with shore ice is presented using laboratory experiments The shore ice induced resistance restricts the flow development and affects the width and momentum thickness of the mixing layer Whether the floodplain is covered by the shore ice, the transverse momentum exchange mechanism is similar