FLOW AROUND HORIZONTAL CIRCULAR-CYLINDER IN SHALLOW FLOWS

This paper describes changes to the flow pattern around a horizontal circular cylinder immersed in shallow open-channel flows, with different gap openings between the cylinder and the bed. Experiments show that the low flow depth causes backup of the upstream flow depth due to choking of the flow. This phenomenon causes the occurrence of a weir-flow condition at the cylinder, where a large drawdown forms. The net result is an increase of the drag force. When a gap is present between the underside of the cylinder and the bed, the oncoming flow divides itself into two components as it approaches the cylinder. The study presents a unique relationship describing the amount of gap flow as a function of the undisturbed flow depth and gap size. Changes to both the drag and lift forces exerted on the cylinder for different flow depth and gap size combinations were measured and reasons for these changes discussed.