Experiment

Unsteady free surface waves generated in a shallow water flume over a bump are investigated with different measurement systems. Conventional wave gauges and standard particle image velocimetry systems are used to determine the wave profiles and flow velocity distributions around the bump. An imaging technique is developed to measure the duration, displacement, and size of the bulge-scar pattern of free surface deformation from the bump top to the primary wave crest, and a unique configuration of particle image velocimetry is used to measure the velocity distribution related to the free surface bulge-scar pattern, i.e. visualized free surface bulge is captured together with seeding particles in the stereo PIV recording. Test results indicate that a bulge-scar pattern of free surface deformation is related to a stream-wise vortex pair possibly resulting from the Görtler type centrifugal instability of flow over the convex bump surface or the Taylor-Dean instability of curved flow at the wave trough.