Mohammad Bijankhan, Salah Kouchakzadeh, Gilles Belaud
Tuesday 30 june 2015
12:48 - 12:51h at Africa (level 0)
Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation, Poster pitches
Parallel session: Poster pitches: 5F. Engineering - Instrument
Due to construction, operation, and maintenance difficulties, usually installing very wide gates in open channels is not recommended. Instead, multiple parallel gates have been used, which generate parallel jets. They can also be observed downstream the hydro-plants. Due to the maintenance reasons and sometimes in drought seasons it would be probable 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. Practically the piers between the jets are constructed to install the gates. The length and the geometry of the piers may affect the flow conditions and the threshold between free and submerged flow. In this study two gates were considered in parallel for which only one of them was under operation. Measurements were done for different openings, discharges and submergence conditions, 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 headloss 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. Finally, based on the momentum balance suitable relationships were developed to calculate the submergence threshold with and without the gate piers.