Effects of Submerged Vegetation Density on Turbulent Flow Characteristics in an Open Channel

• Main Authors: Hanqing Zhao, Jing Yan, Saiyu Yuan, Jiefu Liu, Jinyu Zheng
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Water
• Subjects: open channel; submerged vegetation density; turbulent flow type; turbulent statistics; turbulence spectra
• Online Access: https://www.mdpi.com/2073-4441/11/10/2154

The vegetation density <i>&#955;</i> affects turbulent flow type in the submerged vegetated river. This laboratory study investigates different types of vegetated turbulent flow, especially the flow at 0.04 &lt; <i>&#955;</i> &lt; 0.1 and <i>&#955;</i> = 1.44 by setting the experimental <i>&#955;</i> within a large range. Vertical distributions of turbulent statistics (velocity, shear stress and skewness coefficients), turbulence kinetic generation rate and turbulence spectra in different <i>&#955;</i> conditions have been presented and compared. Results indicate that for flow at 0.04 &lt; <i>&#955;</i> &lt; 0.1, the profiles of turbulent statistics manifest characteristics that are similar to those of both the bed-shear flow and the free-shear flow, and the turbulence spectral curves are characterized with some slight humps within the low-frequency range. For <i>&#955;</i> = 1.44, the turbulent statistics above the vegetation top demonstrate the characteristics of boundary-shear flow. The spectral curves fluctuate intensely within the low-frequency range, and the spectra of low-frequency eddies above vegetation top are significantly larger than the values below. The change of turbulent flow type induced by an increase of <i>&#955;</i> would increase the maximum value of turbulence kinetic generation rate <i>G</i>_S and change the point where <i>G</i>_S is vertically maximum upwards to the vegetation top.