Development of Wake Vortices in a Shallow Water Layer

Development of wake vortices in a shallow water layer. Vortices are formed in the near-wake of a cylinder of diameter D in shallow water layer of depth hw. Three elevations h_L/h_w of the laser sheet are considered. The left column of images shows the time-averaged streamline topology. At elevations above the bed, the topology shows two foci and one saddle point. Close to the bed, additional saddle points and a nodal line appear. The right column exhibits the phase-averaged streamline topology, whereby the selected phase was based on the appearance of a defined saddle (critical) point in the near-wake. Near the free-surface, the pattern of swirling streamlines associated with the focus of the large-scale vortex is broadly distributed; as the bed is approached, this pattern becomes increasingly concentrated. These features are directly correlated with the near-wake vorticity patterns (not shown). D/h_w = 2, Re = UD/n = 10,052 and S = c_fD/h_w =0.06.