Experiments on turbulence and near bank vorticities in an open channel sharp bend

Alireza Farhadi,Michael Tritthart,Helmut Habersack,Christine Sindelar,A Paquier,N Rivière

doi:10.1051/e3sconf/20184005069

Alireza Farhadi, Michael Tritthart + Show 4 more

Open Access

https://doi.org/10.1051/e3sconf/20184005069

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Abstract

Turbulence has a significant influence on fluvial processes. Especially in the sharp bends of geometrically complex natural streams, the interaction of turbulence and flow three-dimensionalities is considerable. Here, generation and evolution of streamwise vorticity in an open channel bend is assessed by means of term-by-term experimental investigations. As a result, corresponding mechanisms are shown and analysed. In addition, based on the homogeneity term of vorticity equation, the applicability of a widely used simplified equation of streamwise vorticity is discussed. The presented comparison reaffirms the inadequacy of the equation in order to estimate near bank vorticities.

Highlights

Cross-stream circulations, known as secondary flows, characterize open-channel flow in bends
We already presented the simplified downstream vorticity equation, which is widely applied in linear models [7]
Linear models do not consider nonlinear feedback between downstream velocity profiles and cells of secondary flow; this often leads to misestimation of vorticty and three-dimensionality in bends [5]

Summary

Introduction

Cross-stream circulations, known as secondary flows, characterize open-channel flow in bends. The outer-bank cells (OBC) are of utter importance in bank erosion research Their role in bank erosions is already discussed [4, 5]; due to the scarcity of detailed experimental investigations, this issue is still an open discussion. The main-cell of secondary flow is defined based on the local centrifugal force and the cross-stream pressure gradient in cross-stream momentum equation as explained in [5], which gives the following simplified downstream vorticity equation. Equation 1 shows the balanced between vorticity generator (i.e. centrifugal force) and dissipator (i.e. turbulent shear stress) components. This equation is widely applied in classical hydraulic and engineering practices. Based on a term-by-term approach, the range of discrepancies between the simplified equation (i.e. equation 1) and full equation terms, concerning OBCs zone, is investigated and discussed

Experimental setup and results

Discussion and Conclusion