Time Resolved 3D3C Measurements of Shallow-water Island Wakes

The wakes behind islands subjected to strong oscillating tidal flows in shallow water are characterised by highly three-dimensional flow structures and significant cycle-to-cycle variability. As part of a broader study into the processes governing vertical and cross shelf mass exchanges in the topographically complex and strongly forced Kimberley coastal region, an experimental flume (the Shallow Oscillatory Flow Flume) has been designed and constructed to obtain time resolved, three-dimensional and three-component (3D3C) velocity field measurements of island wakes. The facility makes use of the Synthetic Aperture Particle Imaging Velocimetry (SAPIV) approach, a light field imaging technique that utilises multiple cameras to digitally reconstruct a three-dimensional particle intensity field. Three-dimensional particle image velocimetry techniques are then used to obtain the velocity field. A specific advantage of SAPIV over other 3D techniques includes its unique ability to deal with occlusions, higher particle seeding densities and volume reconstruction efficiency. This paper presents a description of the experimental facility and SAPIV system setup. The three velocity component SAPIV measurements are validated against co-located and synchronised ADV measurements.

Previous work by the authors has identified the importance of the Keulegan-Carpenter number and relative boundary layer thickness in governing the wake form of shallow islands subjected to tidal forcing. The new facility and SAPIV technique are utilised to investigate the wake form and evolution across a broad parameter range applicable to the Kimberley Region and provides a basis for quantitative model development of vertical and cross shelf mixing and exchange around islands.