Experimental study on design parameters of submerged vanes for sediment control at lateral intake in a 180 degree bend

Design of intakes as one of the flow diversion structures, always had been interested to hydraulics engineering. The important problem in design of intakes, is diversion of maximum discharge with minimum amount of sediment. Outer bank of the river bend is one of the best positions for lateral diversion. Since floodwater carries a large amount of sediment, the sediment enters to lateral intake situated even in outer bank of the bend. In these cases, submerged vanes can be useful as a sediment control method. Submerged vanes are frequently used devices that have several applications such as protection against bank erosion, exclusion of sediment from water intake structures. However there is not much information on the vanes application for sediment control to water intake located in a channel bends. In this research, an experimental study on the effective parameters of a 2 rows layout of vanes on sediment control at lateral intake in a U shape channel bend has been carried out. The intake was installed in position 115 degree of bend with 45 degree diversion angle according to previous research suggestion. The experiments were conducted in two phases. In the first phase, the sediment control experiments, was carried out with injection of sediment on rigid bed. The position of injection was upstream of bend and sediment injection rate was approximately equal to sediment transport capacity of straight channel upstream of the bend. In the second phase, in order to analyzing the results of first phase experiment and considering the effect of array vanes parameters on the flow field, the flow field measured by 3D Acoustic Doppler Velocimeter (Vectrino). At first, the effect of Frude Number and diversion discharge rate on mechanism of sediment entry to the intake was considered and the Fr=0.32 was selected as hydraulic conditions in the main experiments. In this Frude Number, the mechanism of sediment entry was consist of continues entrance from down stream edge of intake and periodic entrance from upstream of the intake. Then, the effects of design parameters of the 2 rows layout of vanes on the amount of sediment entry to lateral intake were considered for different discharge rate. The design parameters of array vanes consist of vane angle of attack with main flow (), distance from intake to vanes (b), vane spacing in streamwise and transverse direction (s and n, respectively), location of vanes with respect to upstream and downstream intake edges and position of first vanes upstream of the intake. The optimum value of design vanes parameters was obtained H=0.33y (y is water depth and H is vanes height), =20°, s=14H, n=1.5H, b=2H. Also zigzag arrangement of vanes cause reduction of strength of secondary vortex induced by vanes and therefore reduces the efficiency of vanes array. The results show that in arrangement of vanes array, one vane must be exist exactly before upstream edge of the intake an one vane must be exist exactly after down stream edge of the intake. The position of first vanes upstream of the intake was selected at section 70°, according to analyzing of flow field in bend. Finally, the optimum number of vanes upstream of bend was determined.