Abstract
The present study investigates the effects of strip roughness on surface velocity divergence (SD) to develop physical modelling of gas transfer mechanisms in natural rivers. Particularly, turbulence measurements were conducted by PIV in a computer-controlled laboratory flume with varying water discharge and roughness spacing systematically, in order to obtain the space and time distributions of surface velocity divergence, turbulent kinetic energy and dissipation rate on the horizontal plane. Finally, a new empirical model for the surface velocity divergence was proposed considering turbulence microscales.
Highlights
McCready et al [3] report that the surface velocity divergence (SD) is relevant to gas transfer processes at the air-water boundary
Point out that turbulence structure depends significantly on a ratio of roughness spacing to roughness height, many uncertainties remain about the relation between the SD and the coherent turbulence induced by the rough bed
Turbulence measurements were conducted by PIV in a computer-controlled laboratory flume with varying water discharge, flow depth and roughness spacing systematically, in order to obtain the space and time distributions of SD, turbulent kinetic energy and dissipation rate
Summary
McCready et al [3] report that the surface velocity divergence (SD) is relevant to gas transfer processes at the air-water boundary. The present study focuses on two-dimensional rough-bed flows, in which strip roughness elements are placed with constant spacing. Point out that turbulence structure depends significantly on a ratio of roughness spacing to roughness height, many uncertainties remain about the relation between the SD and the coherent turbulence induced by the rough bed. In this study we investigated hydrodynamic effects of strip roughness on the SD to develop physical modelling of gas transfer mechanisms in natural rivers. Turbulence measurements were conducted by PIV in a computer-controlled laboratory flume with varying water discharge, flow depth and roughness spacing systematically, in order to obtain the space and time distributions of SD, turbulent kinetic energy and dissipation rate. A new empirical model for the SD in natural rivers was proposed considering turbulence structure
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