Optimization of Geometric Parameters of Submerged Vane in Straight Alluvial Channel With Taguchi Method and GRA

Submerged vanes are plane structures mounted vertically on river bed with an angle to the approach flow. These structures are usually used in group. The operation of the submerged vanes is production of secondary flow around their length axis that changes the flow pattern and bed topography. The performance of a submerged vane is related to its geometric parameters such as length، height and the angle of attack of the approach flow. In this study the optimization of geometric parameters of a submerged vane in a straight alluvial flume is done numerically to achieve the best condition for increasing the scour depth of channel in front of lateral intake and deviation of sediment from lateral intakes. The SSIIM software is applied for simulating the flow and sediment pattern around a submerged vane. Verification of numerical model with experimental results is done. The effect of geometric parameters of the vane on the performance of the submerged vane is studied. Length، height and the angle of a vane are investigated in four levels and four responses including minimum scour depth near the leading edge of the vane، minimum scour depth near the trailing edge of the vane، maximum scour volume at the downstream of the vane and maximum sedimentation depth at the downstream of the vane are calculated numerically. In previous studies the scour depth at the leading and the trailing edges of the vane were not included in optimization and this is one of the innovation of this paper. The other two last responses are normalized with appropriate parameters. The maximum scour volume at the downstream of the vane is normalized with the volume of the vane and the maximum sedimentation depth at the downstream of the vane is normalized with the length of the vane. Taguchi method is used to design studies in order to minimize the number of cases without affecting the results. 16 tests are investigated instead of 64 tests. Grey Relational Analysis is used for analyzing the responses. The results of this study show that the angle of a vane has more effect on the performance of the vane than the height and the height is more effective than the length. The ratio of 0. 25 for the height of the vane to the depth of flow and 15 degree for the angle of attack are proposed to obtain the optimum performance of the submerged vane. Changing the ratio of the length to the height of the vane has a little effect on the responses. So the smaller length of the submerged vanes (in this paper the ratio of 1. 25 among 1. 25 to 3 for the length to the height of the vane) is economical.