Secondary flow in sharp open-channel bends: experiments and modelling

The dependence of curvature-induced secondary flow on the curvature ratio H/R and the Froude number Fr was systematically investigated in a series of 18 experiments in a sharply-curved laboratory flume. The investigated flow depths were 0.9 m, 0.13 m, 0.19 m and 0.26 m, resulting in H/R values of 0.053, 0.077, 0.112 and 0.153, and the Froude numbers were 0.1, 0.2, 0.3, 0.4 and 0.5. The normalized magnitude of the secondary flow did not increase with H/R, as predicted by commonly used parameterizations for secondary flow, but remained quasi-constant. This confirms observations by Blanckaert (2009), who called this phenomenon the saturation of the secondary flow. The experiments did not reveal any dependence of the secondary flow on Fr. Predictions of the magnitude of the secondary flow with the nonlinear model of Blanckaert and de Vriend ((2003, 2010) agreed very well with the experimental data.