High-order moments of velocity fluctuations around a cylinder in a dredged channel

Abstract

The effect of a channel pit on the turbulence structure around an embedded cylinder was explored based on the behaviour of high-order moments of streamwise velocity fluctuations. Instantaneous velocities across the flow depth were recorded upstream and downstream of a circular cylinder in a sand bed flume with and without channel dredging. The variance of streamwise velocity fluctuations and higher-order velocity moments around the cylinder were studied for both cases. Logarithmic scaling of was observed in the down-flow upstream of the cylinder and in the wake zone downstream of the cylinder. Higher-order velocity moments up to 2p = 4 and 2p = 6 were also evaluated to validate the logarithmic scaling. The mean flow structure developed due to the fluid–solid interactions around the cylinder was found to govern the scaling characteristics of velocity fluctuations. The experimental data showed that channel dredging increased the near-bed values of at the cylinder front and also increased the peak of turbulence production downstream of the cylinder. These alterations may be linked to excess scour and undermining of bridges due to channel dredging.