Flow patterns induced by a bubble screen in a sharply curved flume based on Acoustic Doppler Velocity Profiler measurements

Open-channel bends are characterized by a bed morphology where erosion occurs near the outer bank and a point bar develops at the inner bend. This morphology is induced by complex interactions between the streamwise flow, the curvature-induced secondary flow and the bed topography. Several techniques already exist to counteract the development of bend scour, which can endanger foundations of structures. However, existing techniques mostly imply substantial construction works in the river. Preliminary laboratory experiments have shown that a porous tube placed near the outer bank can generate a bubble screen that modifies the flow patterns and leads to a substantial reduction of the bend scour. A better understanding of the hydrodynamic mechanisms induced by the bubble screen and involved in the morphological development will allow determining the range of application of the bubble-screen technique. Experiments performed in a sharply curved open-channel bend under live-bed conditions show that the bubble screen is able to redistribute the velocity patterns in the bend. The bed morphology is then partially modified, specially at the bend exit. This paper illustrates Acoustic Doppler Velocity Profiler measurements of the bubble-induced secondary flow and its interaction with the channel base flow in the most influenced cross-section