Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland
Beamer Rock, a 50-m-wide island in the Firth of Forth, produces a distinctive von Kármán vortex street wake, the characteristics of which depend on the speed and direction of the tidal flow. ADCP (acoustic Doppler current profiler), CTD (conductivity–temperature–depth) and aerial photograph data were collected from the region during flood and ebb tidal flow under neap and spring conditions. Good agreement was found between the observations and the results from a fixed-grid depth-averaged numerical tidal model. The island wake parameter correctly predicted the unsteady nature of the wake, and the Strouhal number (defined in terms of flow past a circular cylinder) was found to give excellent predictions of the wake wavelength when scaled on the island width. Contrary to published results, the study shows that it is possible to accurately simulate an unsteady island wake using a relatively coarse fixed-grid numerical model.
KeywordsIsland wake Firth of Forth ADCP observations Tidal model Island wake parameter Strouhal number
Unable to display preview. Download preview PDF.
This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) as part of project GR/M88020. Thanks to Gwynne Parry Jones and Ben Powell, who assisted with the collection of the in situ data. Thanks also to Scott Couch at Oregon State University for providing the numerical code and Graham Copeland at Strathclyde University for providing bathymetry data.