Development of structure within the turbulent wake of a porous body. Part 1. The initial formation region

This paper deals with the initial region (x/d = 1 to 20) of a turbulent wake generated by a mesh strip. The purpose of the study is to identify the formation mechanism of the large-scale vortices which have developed by the end of this zone. The region is characterized by the evolution and interaction of two parallel shear layers generated at the edges of the mesh. Multi-point hot-wire velocity measurements establish that the merging and interaction of the small-scale eddies account for the formation of the large-scale vortices. A numerical simulation based on a discrete vortex method was carried out to gain further insight into the interaction between the two shear layers. Both the experimental and numerical results suggest that low-frequency perturbation plays an important role in the communication between the two shear layers.