SHALLOW-WATER FLOW AROUND MODEL CONICAL ISLANDS OF SMALL SIDE SLOPE .2. SUBMERGED

Experiments have been conducted to study the unsteady wakes of submerg ed conical islands. The islands used in the tests have side slopes ran ging from 8.0 to 33.1 degrees. Experiments in a shallow-water channel with a steady, subcritical free stream showed vertex shedding to occur in the wake when the water depth above the island apex was relatively small, Flow separation from positions near the island apex was found to be important in producing this unsteady wake. As the water depth wa s increased the shedding was observed To become less vigorous and even tually stop. All islands tested produced similar results with the angl e of the island side slope exerting relatively little influence on the process. The results of wind tunnel visualization studies, which used a rigid top plate to produce the effect of fluid depth, support the r esults from the water channel, Pictures of the surface flow patterns p roduced on the islands by the wind action are presented. Two-dimension al (2D) and three-dimensional (3D) shallow-water numerical models with the hydrostatic pressure assumption have been run for comparison with the laboratory measurements. The complex 3D flow observed in the near wake provides a severe test for the models. Although both models were found to reproduce gross features of the submerged island wakes their mode of generation could be quite different in model and experiment.