Comparison of Methods for Bed Shear Stress Estimation in Complex Flow Field of Bend

Liyuan Zhang,Zhaoming Song,Shilin Tong,Ailing Cai,Faxing Zhang

doi:10.3390/w12102753

Abstract

Bed shear stress is closely related to sediment transport in rivers. Bed shear stress estimation is very difficult, especially for complex flow fields. In this study, complex flow field measurement experiments in a 60° bend with a groyne were performed. The feasibility and reliability of bed shear stress estimations using the log-law method in a complex flow field were analyzed and compared with those associated with the Reynolds, Turbulent Kinetic Energy (TKE), and TKE-w′ methods. The results show that the TKE, Reynolds, and log-law methods produced similar bed shear stress estimates, while the TKE-w′ method produced larger estimates than the other methods. The TKE-w′ method was found to be more suitable for bed shear stress estimation than the TKE method, but the value of its constant C2 needed to be re-estimated. In a complex, strong, three-dimensional flow field, the height of the measurement point (relative or absolute) should be re-estimated when a single point measurement is used to estimate the bed shear stress. The results of this study provide guidance for experimental measurement of bed shear stress in a complex flow field.

Highlights

Bed shear stress is a basic variable in the study of fluvial processes [1]
The bed shear stress obtained using the Reynolds method consisted of two parts: streamwise shear stress
The bed shear stress obtained by the log-law method consisted of the streamwise shear stress calculated from the time-averaged velocity in the streamwise direction (s) and the transverse shear stress calculated from the time-averaged velocity in the transverse direction (n)

Summary

Introduction

Bed shear stress is a basic variable in the study of fluvial processes [1]. It is very difficult to estimate bed shear stress via experimental methods, for complex, three-dimensional flow fields.The resistance balance method is the basic method used for calculating bed shear stress, but it is not suitable for local shear stress estimations. Bed shear stress is a basic variable in the study of fluvial processes [1]. It is very difficult to estimate bed shear stress via experimental methods, for complex, three-dimensional flow fields. The resistance balance method is the basic method used for calculating bed shear stress, but it is not suitable for local shear stress estimations. For a flume with limited length, measurements of the water surface profile often have large errors, which can greatly influence the calculated value of bed shear stress. The local mean bed shear stress can be measured by a shear plate sensor in small-scale and large-scale laboratory flumes [2]. With the development of advanced velocity measurement devices such as the Acoustic Doppler

Methods

Results

Conclusion