Author(s): M. Bijankhan; S. Kouchakzadeh; G. Belaud
Linked Author(s): Gilles Belaud, Salah Kouchakzadeh
Keywords: Multiple gates; Parallel jets; Gate piers; Submergence threshold; Wide channels
Abstract: Due to construction, operation, and maintenance difficulties, usually installing very wide gates in open channels is not recommended. Instead, multiple parallel gates are used, which generate parallel jets. For maintenance and control reasons, when a low flow needs to be passed, it is frequent to see only some of the gates under operation. In such circumstances the jet width would be smaller than the downstream pool width, and consequently, a highly non-uniform velocity distribution with longitudinal vortices would be formed in the downstream pool. The flow structure and the submergence conditions may also be affected by the piers installed to support the gates. In this study, two gates were considered in parallel for which only one of them was under operation. Measurements were done for different openings and discharges, focusing on the distinguishing conditions and flow structure of the downstream jet. In the configuration without piers, it was shown that the submergence conditions were largely affected compared to the mostly studied configuration, basically two-dimensional, where the jet has the same width as the downstream pool. This was due to the interaction of the jet with the dead zone behind the closed gate, involving strongly three dimensional effects, increased head loss and friction forces. Then the effect of the separating piers was investigated experimentally. ADV measurements were done in the downstream pool to compare the velocity distribution with and without the separating piers. This suggests corrections of the momentum calculation in the downstream pool due to the asymmetrical jet configuration. The results of this study can be used to calculate the submergence threshold with and without the gate piers based on the momentum balance.
Year: 2015