Development of structure within the turbulent wake of a porous body. Part 2. Evolution of the three-dimensional features

The present investigation deals with the development stage (x/d = 20–100) of the porous-body wake, generated by a mesh strip. Pattern-recognition analysis was applied to the velocity signals from hot-wire measurements in the vertical centreplane and various horizontal planes in the flow field. Spanwise coherent structures (with ωz) and lateral coherent structures (ωy) have been identified. An examination of the fine-scale turbulence is used to show that the two kinds of structures are indeed connected. In the near region of the wake, the lateral structures are ‘ribs’ attached to the spanwise vortices. In the intermediate region, the interaction of the two structures changes the original spanwise vortices into three-dimensional structures. Beyond this zone, in the far region, the’ legs’ of the original spanwise structure merge with the’ ribs’, and it can be inferred that the coherent structures within the flow are essentially randomly distributed hairpin-like vortices.