3D Numerical Simulation Of Turbulent Flow And Local Scour Around Spur Dikes

Spur dikes play an important rule in regulating river channel and protecting river bank. The flow around a spur dike has obvious 3-D turbulent characteristics, so it should be computed by using 3-D turbulent mathematical model. Utill now, however, 3D numerical computation of turbulent flow around spur dikes is not too much. Local scour around a spur dike is very important to the stability of spur dike. So it is significant in both theory and practice to research 3-D turbulent flow and local scour around spur dikes.Previous numerical simulations were realized under low resolution grids or under small domain model. In this paper, standard k-ε model and two-fluid k-ε model with high resolution grids for 3-D turbulent flow are successfully used to numerically simulate turbulent flow around a spur dike of real scale.Numerical simulation of turbulent flow around a spur dike in different conditions by using standard k - ε model indicates that there are two small vortices in the head of spur dike, and many secondary-eddies except a large circulating flow behind a spur dike in high speed condition. Previous numerical simulations only catch circulating flow behind spur dike and a small vortex in front of spur dike, and cannot catch another small vortex in front of spur dike. Numerical simulation in this paper successfully catches two small vortices in front of spur dike, which indeed exist in physical model.Numerical simulation also finds that descent (or submerged) flow and ascent flow occur in the zones of two small vortices in front of spur dike. This provides a theoretical evidence reasonablly to explain the mechanism of local scour around spur dikes. In other words, the descent flow and ascent flow are the most main causes of local scour around spur dikes except increase in velocity due to shrinkage of streamline.The depth , size and shape of local scour around spur dikes are calculated from 3-D turbulent flow, and the plot of local scour is also drawn. Maximumdepth of scour around a spur dike is about 15m.