Experimental Investigation On The Characteristics Of Main Flow In An Open Channel Bend

Flows in river bend present complex patterns that play an important role for riverregulation and control. Experiments were conducted to investigate the evolution of the main flow in a U-shape flume (both of the inflow and outflow segments are 11m long). A Particle Image Velocity system (PIV) was used to measure the streamwise-vertical velocity fields at seven sections along the flume. Three cases (flow depth=4, 5, and 6 cm respectively) have been studied. Three major features of the flow have been revealed. Firstly, the maximum velocity occurs near the inner-side of the entrance of the bend, and it turns to the external side later and remains so all the way to the bend end. The exact position of the deflecting position is logarithmically related to the flume width B, centerline radius Rc and water depth H. Secondly, the flow shows dramatic change at around the 1/5 of the bend, where the deflecting position and the maximum velocity occur near the inner bank. Thirdly, with the combined effect of water surface slope, gravity and centrifugal force, the axis of the maximum velocity goes down along the bend and this trend becomes stronger with the increase of H. Results in this study provide real data for verifying mathematical models and for reference in practical engineering.