Interact: Interesting Assorted Problems Involving Geophysical Flows

The flow through porous structures is relevant to a wide range of situations of ecological relevance, such as vegetation patches or logjams. Many studies on aquatic vegetation have focused on arrays of vertical cylinders and investigated the effect of solid volume fraction and submergence level, while the effect of the internal arrangements is yet to be explored.

Experiments in an open channel were conducted to investigate emergent porous structures with different internal arrangements: (1) regular with cylinders oriented vertically to mimic a rigid vegetation patch, (2) regular with grid-like oriented cylinders to model an engineered logjam, and (3) randomly arranged cylinders to model a natural logjam. Particle image velocimetry and particle tracking velocimetry were used to investigate the near-wake characteristics below and along the surface, respectively.

The random arrangement led to one low velocity region at the centerline. The regular arrangements showed two low velocity regions starting at the downstream edges of the structures, converging to the centerline going further downstream. This implies that the internal arrangement is mainly affecting the flow in the near field. Moreover, the imaging allows us to capture flow differences within the structures and the drag exerted by them.