Investigation of bed shear stresses subject to external turbulence

Abstract

The fluctuating bed shear stress has largely been investigated only for uniform channel flows and boundary layers. In practical

engineering, the flow conditions are often modified due to the presence of various hydraulic structures. To what extent the modification

affects the known characteristics of the bed shear stress is not clear. This study presents experimental results of the bed shear

stress fluctuations, which are obviously subjected to external turbulence generated by superimposing artificial structures in the open

channel flows. The statistical analysis of the measurements shows that the probability density function of the bed shear stress can be

described by the lognormal function. Some associated relations concerning higher-order moments, skewness and kurtosis, which are

derived from the lognormal function, are further compared with the experimental data. Physical implication of the skewed probability

density distribution is finally discussed.