Characteristics of Flow around Open Channel 90° Bends with Vanes

Abstract

Sharp open-channel bends are commonly encountered in hydraulic engineering design. Disturbances such as secondary flows and flow separation caused by the bend may persist for considerable distances in the downstream channel. A simple way of reducing these disturbances is through the insertion of vertical vanes in the bend section. A laser Doppler anemometry (LDA) unit was used to measure the three-dimensional mean and turbulent velocity components of flow in an experimental rectangular open-channel bend. Flow characteristics of the bend with no vanes are compared with those of bends having one or three vertical vanes. The size of the flow separation zone at the inner wall of the bend was determined from dye visualization data and confirmed with mean streamwise velocity data. Results show that the vertical vanes are effective in considerably reducing flow separation, intensity of secondary flows, and turbulence energy in the downstream channel. Furthermore, energy loss for bends with vanes is slightly less than for the no-vane case.