Turbulent flow structure around submerged T-shape spur dike

Spur dikes are the training structures that may be used for river bank erosion protections. These structures may increase the navigation depth. The spur dike creates stable pool for aquatic habitat. Most of the previous researches focused on scour hole dimensions and the flowfield around the emerged spur dikes. As the spur dikes may be submerged during the floods، in this paper، the flowfield around a submerged T-shape spur dike was investigated using Vecterino apparatus. The experiment was conducted in a channel with 8m length، 60cm width and 80 cm depth at TarbiatModares University (Tehran- Iran). The parameters that were investigated in this paper includes، mean velocities، turbulence parameters and streamlines. The results of this study indicate that the high velocity region of the flow elongates to the far distance of downstream in the upper layers. There is a recirculating flow downstream of spur dike. Due to the effect of the spur dike overflow، the downstream recirculating flow، rotates in the opposite direction as compare to the emerged spur dike. The recirculating flow elongates to the far distance of downstream as compare to the submerged trapezoidal spur dike. Turbulence parameters analyzed in this research include normal Reynolds stress، bed shear stresses، the probability of each process and triple correlations. Maximum normal Reynolds stresses were observed at the upstream tip of the spur dike. In addition، the maximum shear stress was observed at the same region. The high stress region around the spur dikes showed a shear layer region around the spur dikes. Analysis of the probability of the turbulent bursting events in streamwise direction shows that ejection and sweep events are the most probable events in the upstream section of the spur dikes. In the streamwise direction، the interaction events are the most probable process near the upstream tip of the spur dike، while ejection and sweep events in the widthwise direction are the most probable events near the upstream tip of the spur dike. In the downstream recirculation zone of the spur dike، the probability of the events approximately are the same in the streamwise direction and interaction events are the most probable events in widthwise directions. Triple correlations presented useful information about the turbulent bursting process. The triple correlation analysis in widthwise direction showed that the ejection is the strongest event in shear layer region. Triple correlation analysis in the streamwise direction، showed that ejection was the strongest event in the upstream of the spur dike and in the region between near channel wall and spur dike wing. This causes sediment transport in streamwise direction as suspended load. The interaction events are the strongest events in the downstream recirculation zone، hence the sediments were deposited in this region.