LMFA, CNRS-Université de Lyon, INSA de Lyon, Bat. Joseph Jacquard, 20 Av. A. Einstein, 69621 Villeurbanne, France.
The recirculations are essential in river engineering because they form silting zones and favour the development of speciﬁc fauna and ﬂora. This paper deals with the behaviour of the recirculation zones occurring downstream the sudden expansion of an open channel. An Acoustic Doppler Velocimeter is used to measure the ﬂow details. The mean ﬂow property such as the length of the recirculation, the average velocity ﬁeld and velocity gradient are obtained. Then the self-similarity of the velocity proﬁle is retrieved . The numerical simulation for the similar conditions are preformed with the CFD software STAR CCM+. When compared with the experiments, the two approaches correspond well in terms of length of recirculation zone and also regarding details such as the velocity gradient proﬁles. Finally, the eddy viscosity concept is tested and the turbulent viscosity coefﬁcient are obtained along the streamwise axis for all ﬂows.